To see the other types of publications on this topic, follow the link: Voltage source converter.
Dissertations / Theses on the topic 'Voltage source converter'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Voltage source converter.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Borisov, Konstantin A. "Multifunctional voltage source converter for shipboard power systems." Diss., Mississippi State : Mississippi State University, 2007. http://library.msstate.edu/etd/show.asp?etd=etd-06042007-142951.
Full text
2
Kazerani, Mehrdad. "Dyadic matrix converter theory : development, and application to voltage-source-converter type matrix converter." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28794.
Full textAbstract:
For the past twenty years, the theoretical advance of the matrix converters has been impeded by the complexity arising from the time-varying trigonometric functions in their transformation matrix. In addition, the switching difficulties associated with the bidirectional switches have complicated the practical implementation of this class of converters.In this thesis, the dyadic matrix structure and the a-b-c to d-q-0 transformation have been melded together to develop the dyadic matrix converter theory which is a generalized theory for the three-phase to three-phase matrix converters.
The thesis addresses the zero-sequence interaction in the matrix converters and the role of the zero-sequence elements in the Displacement Power Factor (DPF) correction on the utility-side, based on the Static VAR Controller (SVC) principle. Also, it is proved that using all the control degrees of freedom available, the dual condition of Unity Displacement Power Factor (UDPF) on side-1 and Field Vector Control (FVC) on side-2 can be established.
In this thesis, a new matrix converter topology, based on the three-phase voltage-source converters, has been proposed in which the switching difficulties reported in the conventional nine-bidirectional-switch topology have been bypassed. The theoretical expectations have been verified by the simulation as well as experimental tests on a laboratory prototype of the new matrix converter topology composed of three units of voltage-source converters each rated at 1 kVA.
3
Lu, Bin. "A feedback control algorithm for voltage-source matrix converter." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ37268.pdf.
Full text
4
Lu, Bin 1969. "A feedback control algorithm for voltage-source matrix converter /." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28001.
Full textAbstract:
One application of the voltage-source, matrix converter is as an asynchronous link, joining two AC power systems with different frequencies (50Hz/60Hz), or at the same frequency (60Hz/60Hz) but at different phase angles. This thesis work shows that for this kind of link, there exists an automatic closed-loop feedback strategy to control the real and reactive powers quickly and independently.In this thesis, the new matrix converter topology, based on the three-phase voltage-source converters, has been used.
The thesis mixes the dyadic matrix structure the a-b-c to d-q-o transformation and feedback control theory together to get the results.
Digital simulations are presented.
5
Martin, Fregelius. "Power electronics and controller interface for a Voltage Source Converter." Thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-322903.
Full textAbstract:
The purpose of the thesis is to develop a system for a split-rotor drive and evaluatecontrollers and their internal components such as processors, communicationprotocols and execution speed for controlling magnetization currents in a hydropower station.The first part of the thesis builds the theory review and provides an introduction tothe most common processors and controllers available. The processors which wasevaluated were microprocessor, DSP and FPGA which have a high capacity andvariety of implementation possibilities. Two controllers, PLC and PAC whereevaluated, which contain some or several of the processors and have a wide variety ofinputs and outputs and support as well several communication protocols.Three different communication protocols; WLAN 802.11, Ethernet 802.3 andBluetooth 802.15.1. Evaluation was made by comparing BER, throughput, speed and implementationcomplexity. The second part of the thesis was to develop and order an interface card forconnecting power-electronics and measurements circuits for the system, based on thetheory and evaluation of the controller and communication protocols.
6
Ormrod, James Ernest. "Harmonic state space modelling of voltage source converters." Thesis, University of Canterbury. Electrical and Computer Engineering, 2013. http://hdl.handle.net/10092/8081.
Full textAbstract:
The thesis describes the development of a model of the three-phase Voltage Source Converter (VSC) in the Harmonic State Space (HSS) domain, a Linear Time Periodic (LTP) extension to the Linear Time Invariant (LTI) state space. The HSS model of the VSC directly captures harmonic coupling effects using harmonic domain modelling concepts, generalised to dynami- cally varying signals. Constructing the model using a reduced-order three-phase harmonic signal representation achieves conceptual simplification, reduced computational load, and direct inte- gration with a synchronous frame vector control scheme.
The numerical switching model of the VSC is linearised to gain a small-signal controlled model, which is validated against time-domain PSCAD/EMTDC simulations. The controlled model is evaluated as a STATCOM-type system, exercising closed-loop control over the reactive power flow and dc-side capacitor voltage using a simple linear control scheme. The resulting state- space model is analysed using conventional LTI techniques, giving pole-zero and root-locus analyses which predict the dynamic behaviour of the converter system. Through the ability to independently vary the highest simulated harmonic order, the dependence on the closed-loop response to dynamic harmonic coupling is demonstrated, distinguishing the HSS model from fundamental-only Dynamic Phasor models by its ability to accurately model these dynamics.
7
You, Keping Electrical Engineering & Telecommunications Faculty of Engineering UNSW. "A new bidirectional AC-DC converter using matrix converter and Z-source converter topologies." Awarded by:University of New South Wales, 2007. http://handle.unsw.edu.au/1959.4/37450.
Full textAbstract:
This thesis proposes a new bidirectional three-phase AC-DC power converter using matrix converter and Z-source inverter topologies. Advantages of the AC-DC matrix converter are the inherently controllable power factor, the tight DC voltage regulation, the wide bandwidth with quick response to load variation, the single-stage buck-voltage AC-to-DC power conversion; advantages of the z-source inverter are the increased reliability by allowing the shoot-through between upper and lower power switches of one inverter leg, insensitivity to DC bus voltage due to the extra freedom of controlling DC-link voltage. The proposed Matrix-Z-source converter (MZC) marries up both advantages of AC-DC matrix converter and Z-source inverter. It can achieve voltage-boost DC-AC inversion capable of variable voltage variable frequency (VVVF) AC output; it can achieve voltage-buck AC-DC rectification capable of inherent control over AC current phase angle and DC output regulation with a (VVVF) AC source supply. Both foresaid performance in DC-AC inversion and AC-DC rectification can be implemented in a simple open-loop control manner. Three constraints of VSI, in the bidirectional AC-DC power conversion, are the peak AC voltages are always less than DC-link voltage, closed-loop control has to be employed when DC regulation and/or AC current phase angle control are required, and AC voltage is sensitive to the variation of the DC-link voltage in DC-AC inversion. The voltage-boost inversion and/or voltage-buck rectification of MZC overcomes the first constraint; thus MZC enables the AC machine voltage increased higher than DC-link voltage hence advantages of running AC machine at relatively high voltages are enabled. The direct DC voltage regulation and inherent AC-current-phase-angle control of MZC overcomes the second constraint in an open-loop manner; hence a simplified system design is obtained with sufficient room for the further improvement by closed-loop control schemes. The extra freedom in controlling DC-link voltage of MZC overcomes the third constraint hence a DC source voltage adaptable inverter is obtained. This thesis focuses on the study of the feasibility of the proposed MZC through theoretical analysis and experimental verification. At first, the proposed MZC is conceptually constructed by examining the quadrant operation of AC-DC matrix converter and Z-source inverter. After the examination of the operating principles of both AC-DC matrix converter and Z-source inverter, the configuration of MZC is then proposed. The MZC has two operating modes: DC-AC inversion and AC-DC rectification. Circuit analysis for both operating modes shows that the new topology does not impose critical conflict in circuit design or extra restriction in parameterization. On the contrary, one version of the proposed MZC can make full advantage of Z-source network components in both operating modes, i.e. a pair of Z-source inductor and capacitor can be used as low-pass filter in AC-DC rectification. The modulation strategy, average modeling of system, and features of critical variables for circuit design of the proposed MZC were examined for each operating mode. Simulations of the proposed MZC and its experimental verification have been presented. Analytical models of conduction and switching losses of the power-switch network in different operating mode have shown that the losses in the MZC compare favorably with conventional VSI for a range of power factor and modulation indices.
8
Xie, Hailian. "Voltage Source Converters with Energy Storage Capability." Licentiate thesis, Stockholm : Division of electrical machines and power electronics, Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4191.
Full text
9
Lamont, Lisa Ann. "Modelling and control of a VSC (voltage source converter) tranmission system." Thesis, University of Ulster, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414074.
Full text
10
Zhao, Xiaodong. "Advanced control of voltage source converter based multi-terminal HVDC systems." Thesis, Queen's University Belfast, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.676499.
Full textAbstract:
This thesis focuses on the advanced control methods for multi-terminal High Voltage Direct Current (HVDC) systems integrating offshore wind farms. Several key issues are investigated in this thesis, including controller design to improve the system dynamic performance, power loss reduction with controller optimization, system stability and dynamics assessment. A DC voltage backstepping control method is designed considering the cable dynamics and controller delay effects. DC cable and converter current loop dynamics are included in the voltage controller design. This control method is applied to a point-to-point and a 4-terminal HVDC system with a conjunction point. Simulation results show that the controller performance can be improved in terms of the disturbance rejection., The relation between Voltage Source Converter (VSC) control action and power losses in the multi-terminal HVDC systems is investigated. For a 4-terminal system, it is shown that the transmission loss can be reduced by properly setting the droop gain ratio between different terminals. For each converter, it is demonstrated by simulation that through a proper controller design, the power loss can be significantly reduced while controller performance can be maintained. A new droop setting design method is proposed. It is shown that due to the existence of droop control, DC voltage deviation will affect the power flow accuracy when the steady state is changed. The impact of DC voltage deviation on the power flow accuracy is studied to tackle this problem, and the DC voltage deviation can be kept unchanged, without affecting the steady state power flow. A droop gain selection procedure is proposed to satisfy the system stability requirement. A state feedback enhanced droop controller is proposed to improve the dynamic performance and stability requirement. With the proposed method, it is shown that the system stability can be guaranteed under both small and large droop gains.
11
Ayachit, Agasthya. "Steady-State and Small-Signal Modeling of A-Source Converter." Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1534187954423628.
Full text
12
Meier, Stephan. "Novel voltage source converter based HVDC transmission system for offshore wind farms." Licentiate thesis, KTH, School of Electrical Engineering (EES), 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-568.
Full textAbstract:
Offshore wind farms have recently emerged as promising renewable energy sources. For increasing distances between offshore generation and onshore distribution grid, HVDC transmission systems based on voltage source converters can be a feasible and competitive solution. This thesis presents a comprehensive evaluation of a novel integrated wind farm topology that includes the generator drive system, the turbine interconnection and the HVDC transmission.
In the proposed concept, every wind turbine is connected to a single-phase medium-frequency collection grid via a distribution transformer and a cycloconverter, which allows the wind turbines to operate at variable speed. The collection grid is connected to an HVDC cable via a transmission transformer and a single-phase voltage source converter. This thesis evaluates in detail the principle of operation, which is also verified with system simulations in PSCAD.
The proposed concept promises several potential benefits. Converter switching losses and stress on the semiconductors for example can be considerably reduced by applying a soft-switched commutation scheme in all points of operation. Single-phase medium-frequency transformers have comparably low losses and their compact size and low weight implies an important benefit in an offshore environment. In addition, the voltage source converter is considerably simplified by the reduction to one phase leg, which implies a substantial cost saving.
Several technical challenges are identified and critically evaluated in order to guarantee the feasibility of the proposed concept. Especially the design of the medium-frequency collection grid is crucial as unwanted system resonances can cause dangerous overvoltages. Most of the technical challenges concern the specific characteristics of the proposed concept. The insulation of the single-phase medium-frequency transformers for example needs to withstand the high voltage derivatives. This thesis contains also considerations regarding the dimensioning and optimization of different system components.
A survey of different transmission systems for the grid connection of wind farms shows the potential of the proposed concept, which addresses several problems associated with electrical systems of wind farms. Both the requirements for variable-speed operation of the wind turbines and an interface for HVDC transmission are fulfilled in a cost-effective way. Compared to conventional voltage source converter based HVDC transmission systems, the initial costs are reduced and the expected annual energy production is increased. In addition, the proposed voltage source converter based HVDC transmission system can fully comply with recent requirements regarding the grid connection of wind farms.
13
Lu, Weixing 1966. "Control and application of multi-terminal HVDC based on voltage-source converter." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82921.
Full textAbstract:
A Multi-Terminal Direct Current (MTDC) system consists of several Voltage-Source Converters (VSCs) whose dc terminals are connected in shunt across the buses of a dc network. The dc voltages are determined by the electric charges stored across the dc capacitor of every Voltage-Source Converter (VSC). As dc over-voltage leads to failure in the solid-state switches and dc under-voltage leads to waveform distortion, the target of safe, economic design is a narrow voltage margin of about 5% around a nominal dc voltage rating. The worst case scenario consists of an accidental loss of a Voltage-Source Converter because the sudden large change in dc power causes the dc capacitors to charge up or down, exceeding the voltage margin before power balance can be re-established by local feedbacks of the Voltage-Source Converters (VSCs).Part I of the thesis shows how the target can be achieved by: (1) planning the dc voltage reference setting and the power reference settings of the Voltage-Source Converters (VSCs) which satisfy the voltage margins in steady-state for both the pre-fault and post-fault conditions; (2) incorporating an Advanced DC Voltage Control (ADCVC) which enables the dc voltage margins to be satisfied during the transient periods.
Part II of the thesis is concerned with finding innovative applications for Multi-Terminal Direct Current (MTDC) systems. It shows that the high degree of controllability of the Multi-Terminal Direct Current (MTDC) system can be exploited in: (1) optimal acquistion of wind power in offshore wind-farms; (2) providing premium quality power in underground cable in-feeds of city centers; (3) providing simultaneous inter-area decoupling and local area damping in interconnections.
14
AL, Jowder Fawzi A. Rahman. "Embedded SSSC in series capacitor compensation and in voltage source converter station." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84869.
Full textAbstract:
This thesis shows that series capacitive compensation of transmission lines by a combination of Static Synchronous Series Compensator (SSSC) and dielectric capacitors lowers the cost of series compensation. The SSSC has two functions: (1) to provide some series capacitive reactance compensation; (2) to damp out incipient unstable Subsynchronous Resonance (SSR) modes. Digital simulation using HYPERSIM shows that for an overall capacitive depth of compensation of 0.7 pu, the SSSC component is only about 1/3 of the capacitive Mvar. Based on the transient stability limit, the transmissibility of the line is increased by a factor of 2.23 for a depth of compensation of 0.7.A second objective of this thesis is to extend the application of the SSSC concept. This application is found in HVDC, where there is no synchronizing power. In the family of Voltage-Source Converter (VSC) HVDC, it is possible to embed the control of the SSSC in the converter station so that there is enhanced synchronizing power. The effectiveness of the synchronizing power (together with damping power) is demonstrated through digital simulations of a turbine-generator system which is connected to a VSC-HVDC Station.
The thesis shows that the SSSC has two modes of operation: (1) the constant reactance mode, in which the SSSC voltage is proportional to the line current, and (2) the constant quadrature voltage mode, in which the SSSC voltage is a constant quadrature voltage independent of the line current. A comparison between the two modes shows that the constant reactance mode provides higher synchronizing power and has a higher transient stability limit.
Eigenvalue analysis and digital simulations are the methodologies used.
15
Xu, Ling. "Modeling, Analysis and Control of Voltage-Source Converter in Microgrids and HVDC." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4967.
Full textAbstract:
The objective of this dissertation is to carry out dynamic modeling, analysis and control for Voltage-Source Converters (VSC). Two major applications of VSC will be investigated in this dissertation: microgrid application and High Voltage Direct Current (HVDC) application.
In microgrid applications, VSC is used to integrate distributed energy sources such as battery and provide system functions: such as real and reactive power regulation, voltage and frequency support during islanding condition, and abnormal system condition mitigation. In HVDC applications, VSC is used to interconnect dc systems with ac systems. The functions supplied by VSC are similar to that in microgrids. However, the transfer capability and stability in such kind of system are of major interests.
Therefore, Part I of this dissertation focuses on VSC's applications in microgrids. A battery's inverter can be operated in both grid-connected PQ regulation mode and voltage and frequency support mode during islanding condition. Transition scheme between these two control modes is firstly investigated to guarantee a smooth dynamic performance. Secondly, a coordinated control strategy between battery's and PV station's VSCs is developed to improve microgrid's power flow. Thirdly, power quality improvement through the battery's inverter is investigated. VSC's control and capability for microgrid operation at normal, transient, and abnormal conditions will be modeled and analyzed.
Part II of this dissertation focuses on VSC's applications in HVDC. The following topics are investigated in this dissertation: (i) how to design VSC-HVDC's controller using system identification method? (ii) How to coordinate VSCs in multi-terminal HVDC scenarios? And (iii) how to determine VSC-HVDC system's transfer capability based on stability limits? High-fidelity simulation technology is employed to tackle control validation while frequency domain impedance modeling technique is employed to develop analytical models for the systems. With linear system analysis tools such as Nyquist plots and Bode plots, stability limits and impacting factors of VSC-HVDC systems can be identified.
This dissertation led to four journal papers (two accepted, one request of revision, one to submit) and five conference papers. The major contributions of this dissertation include:
1) Developed VSC and microgrid models in high-fidelity simulation environment. Developed and validated VSC control schemes for variety of microgrid operations: normal, abnormal, and transient. The developed technologies can facilitate a battery to make up solar power, improve system dynamic performance during transients, and improve power quality.
2) Developed VSC-HVDC simulation models, including two-terminal HVDC and multi-terminal HVDC. Developed VSC-HVDC control schemes for two-terminal and multi-terminal systems. Developed analytical impedance models for VSC-HVDC systems and successfully carried out stability limit identification.
16
Sen, Gokhan. "Voltage and Current Programmed Modes in Control of the Z-Source Converter." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1226508637.
Full text
17
Ucak, Onur. "Design And Implementation Of A Voltage Source Converter Based Hybrid Active Power Filter." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12611095/index.pdf.
Full textAbstract:
This research work is devoted to the analysis, design and implementation of a shunt connected Hybrid Active Power Filter by the use of a lower rated voltage source PWM converter, and a series connected LC passive filter. In recent years, voltage and current harmonics have become a serious problem both in transmission and distribution systems, due to the widespread usage of non-linear loads such as diode/thyristor rectifiers, electric arc furnaces and motor drives. In order to obtain a better performance than those of the conventional passive filter solutions, active power filters (APF) have been worked on and developed. Among various
configurations listed in the literature, conventional shunt connected voltage source active power filter is widely used in industrial applications. Unfortunately, for large power applications, the losses and the rating of the APF increase considerably. As a result, various hybrid filter topologies have been developed which combine the advantages of both passive and active filters.
In this thesis, a shunt connected hybrid active power filter is developed by combining a 4.7 kVA voltage source converter and a 30kVAR 7th harmonic passive filter. The developed system has been implemented to eliminate the most dominant 5th, 7th and 11th current harmonic components existing at 400V low voltage bus of TUBITAK SPACE Technologies Institute. The theoretical and experimental results have shown
that the DC link voltage of the converter and the rating of APF are minimized while keeping the filtering performance satisfactory.
18
Bicer, Nazan. "A Current Source Converter Based Statcom For Reactive Power Compensation At Low Voltage." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/2/12612007/index.pdf.
Full textAbstract:
This research work is devoted to the analysis, design and development of the Current-Source Converter (CSC) based distribution-type Static Synchronous Compensator (D-STATCOM) for low-voltage applications in reactive-power control in order to achieve i) faster transient response in reactive-power control, ii) lower current harmonic distortion, iii) lower power losses and iv) minimum storage elements in comparison with conventional solutions. The developed CSC-D-STATCOM includes a low-pass input filter and a three phase forced-commutated CSC which is composed of six insulated gate bipolar transistors (IGBT) with built-in series diodes. The analysis and the control of the CSC-D-STATCOM are carried out in dq-synchronous reference frame in order to obtain the reference current waveform which is to be generated by switching the IGBTs at 3kHz with the use of space vector modulation.
19
Hamad, Mostafa Saad Abdallah. "Performance improvement of a medium-voltage series-connected twelve-pulse current source converter." Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607443.
Full textAbstract:
This thesis investigates the performance of a medium-voltage (MV) 12-pulse controlled rectifier in conjunction with a tapped front-end transformer used with a shunt active power filter (APF) for ac-side compensation. A series APF based on a magnetic amplifier is used for dc-side compensation. The series APF is coupled with the shunt APF to a common controlled dc-bus. forming an ac/dc unified power controller. An operating power locus is introduced that combines symmetrical and asymmetrical firing of the two constituent 6-pulse converters. It provides the ' lowest' total harmonic distortion (THO) with a maximum reactive power of 0.5 pu. Even with the proposed power locus, a harmonic compensation technique is mandatory. Hence a shunt APF is connected to the secondary taps of the front-end, star/star/delta, transformer to improve the input current THD and power factor. The APF with predictive current control and synchronous d-q frame base control arc used. To avoid time delay effects, the actual APF inverter transfer function is u.sed to formulate an open loop control strategy, used to achieve better harmonic cancellation than previously investigated techniques. To reduce the active filter current, a fixed shunt capacitor bank is connected to the transformer secondary taps to offset the proposed power locus and consequently, to minimize VAr compensation required of the APF. A series APF with a magnetic amplifier is used as a voltage harmonic compensator on the deside. It improves the output voltage ripple factor (RF) and reduces the de-link smoothing inductance requirement. Coupling both compensation techniques improves the supply current TI-ID, produces a near unity power factor, and the output voltage RF is reduced. An auxiliary dc-voltage source for the series APF is avoided by coupling the two compensators back-to-back. MATLAi3 simulation results for the MY system are experimental1y verified with a scaled low-voltage prototype system.
20
Hawley, Joshua Christiaan. "Modeling and Simulation of a Cascaded Three-Level Converter-Based SSSC." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/10109.
Full textAbstract:
This thesis is dedicated to a comprehensive study of static series synchronous compensator (SSSC) systems utilizing cascaded-multilevel converters (CMCs). Among flexible AC transmission system (FACTS) controllers, the SSSC has shown feasibility in terms of cost-effectiveness in a wide range of problem-solving abilities from transmission to distribution levels. Referring to the literature reviews, the CMC with separated DC capacitors is clearly the most feasible topology for use as a power converter in the SSSC applications. The control for the CMC-Based SSSC is complicated. The design of the complicated control strategy was begun with well-defined system transfer functions. The stability of the system was achieved by trial and error processes, which were time-consuming and ineffective.
The goal of this thesis is to achieve a reliable controller design for the CMC-based SSSC. Major contributions are addressed as follows: 1) accurate models of the CMC for reactive power compensations in both ABC and DQ0 coordinates, and 2) an effective decoupling power control technique.
To simplify the control system design, well-defined models of the CMC-Based SSSC in both ABC and DQ0 coordinates are proposed. The proposed models are for the CMC-Based SSSC focus on only three voltage levels but can be expanded for any number of voltage levels. The key system transfer functions are derived and used in the controller design process. To achieve independent power control capability, the control technique, called the decoupling power control used in the design for the CMC-Based STATCOM is applied. This control technique allows both the real and reactive power components to be independently controlled.
With the combination of the decoupling power control and the cascaded PWM, a CMC with any number of voltage levels can be simply modeled as a three-level cascaded converter, which is the simplest topology to deal with. This thesis focuses on the detailed design process needed for a CMC-Based SSSC.Master of Science
21
Sirisukprasert, Siriroj. "The Modeling and Control of a Cascaded-Multilevel Converter-Based STATCOM." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11142.
Full textAbstract:
This dissertation is dedicated to a comprehensive study of static synchronous compensator (STATCOM) systems utilizing cascaded-multilevel converters (CMCs). Among flexible AC transmission system (FACTS) controllers, the STATCOM has shown feasibility in terms of cost-effectiveness in a wide range of problem-solving abilities from transmission to distribution levels. Referring to the literature reviews, the CMC with separated DC capacitors is clearly the most feasible topology for use as a power converter in the STATCOM applications. The controls for the CMC-based STATCOM were, however, very complicated. The intricate control design was begun without well-defined system transfer functions. The control compensators were, therefore, randomly selected. The stability of the system was achieved by trial and error processes, which were time-consuming and ineffective. To be able to operate in a high-voltage application, a large number of DC capacitors are utilized in a CMC-based STATCOM. All DC capacitor voltages must be balanced in order to avoid over-voltages on any particular link. Not only do these uneven DC voltages introduce voltage stress on the semiconductor switches, but they also lower the quality of the synthesized output waveforms of the converter. Previous researches into DC capacitor voltage-balancing techniques were very straightforward, in that individual voltage compensators were added into the main control loop. However, the compensator design for these individual loops is very problematic because of the complexity of the voltage-loop transfer functions. Basically, the trial and error technique again provides the simplest way to achieve acceptable compensators. Moreover, the greater number of voltage levels, the more complex the control design, and the main controller must perform all of the feedback control procedures. As a result, this approach potentially reduces the reliability of the controller.
The goal of this dissertation is to achieve high-performance, reliable, flexible, cost-effective power stages and controllers for the CMC-based STATCOM. Major contributions are addressed as follows: 1) optimized design for the CMC-based STATCOM power stages and passive components, 2) accurate models of the CMC for reactive power compensations in both ABC and DQ0 coordinates, 3) an effective decoupling power control technique, 4) DC-link balancing strategies; and 5) improvements in the CMC topology.
To enhance the modularity and output voltage of the CMC, the high-switching-frequency, high-power H-bridge building block (HBBB) and the optimized design for its power stage and snubber circuits are first proposed. The high-switching-frequency feature is achieved by utilizing the Virginia Tech-patented emitter turn-off (ETO) thyristor. Three high-power HBBB prototypes were implemented, and their performance was experimentally verified.
To simplify the control system design, well-defined models of the CMC in both ABC and DQ0 coordinates are proposed. The proposed models are for the CMC with any number of voltage levels. The key system transfer functions are achieved and used in the control design processes. To achieve independent power control capability, the control technique, called the decoupling power control, is proposed. By applying this control technique, real and reactive power components can be controlled separately.
In order to balance the DC capacitor voltages, a new, effective pulse width modulation (PWM) technique, which is suitable for any number of H-bridge converters, is proposed. The proposed cascaded PWM algorithm can be practically realized into the field programmable gate arrays (FPGA), and its complexity is not affected by the number of voltage levels. In addition, the complexity of the main controller, which is essentially based on the digital signal processor (DSP), is no longer a function of the number of the output voltage levels. The basic structure of the cascaded PWM is modular, which, in general, enhances the modularity of the CMC power stages.
With the combination of the decoupling power control and the cascaded PWM, a CMC with any number of voltage levels can be simply modeled as a three-level cascaded converter, which is the simplest topology to deal with. This significantly simplifies and optimizes the control design process. To verify the accuracy of the proposed models and the performance of the control system for the CMC-based STATCOM, a low-power, seven-level cascaded-based STATCOM hardware prototype is implemented. The key control procedures are performed by a main controller, which consists of a DSP and an FPGA. The simulation and experimental results indicate the superior performance of the proposed control system, as well as the precision of the proposed models.Ph. D.
22
Spahić, Ervin. "Voltage source converter HVDC connection of offshore wind farms and the application of batteries." Aachen Shaker, 2008. http://d-nb.info/992480779/04.
Full text
23
Efika, Ikenna Bruce. "A multi-level multi-modular flying capacitor voltage source converter for high power applications." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/12154/.
Full textAbstract:
Two vital and dynamically changing issues are arising in the electric grid - an increase in electrical power demand, and subsequent reduction in power quality. Power electronics based solutions such as the Static Synchronous Compensator are increasingly deployed to mitigate power quality issues while High Voltage DC Transmission converters are currently installed to support the existing grid transmission capacity. Both applications require high power and high voltage power converters using switching devices with limited voltage ratings. The advent of Modular Multilevel Converters (MMC) is one of the recent responses to this need. These use half or full H-bridge circuits stacked up to form a chain, and hence can withstand high voltages using lower-rated switching devices. This thesis introduces a new member into the MMC family, i.e the Modular Multi-level Flying Capacitor Converter (MMFCC). This uses a three-level flying capacitor full-bridge circuit as a sub-module and offers features of modularity, scalability and fault tolerance. The choice of FC topology in place of the simple H-bridge stems from the FC’s ability to offer two extra voltage levels in the sub-module output and hence more degrees of freedom per module in controlling the voltage waveform. A three-level full-bridge FC sub-module uses three capacitors - an outer one for supporting the sub-module voltage, and two inner floating ones with half of the outer one’s capacitance and voltage rating. This use of slightly more complex FC sub-modules gives the benefits of a modular structure but without using twice as many sub-modules with their associated capacitors for the same total voltage. The thesis presents the principles of this topology, switching states redundancies and a method for capacitor voltage balancing. Also discussed are: the configuration of MMCC including the MMFCC in Single-Star Bridge-Cell (SSBC) or Single-Delta Bridge-Cell (SDBC) for FACTS and Battery Energy Storage System (BESS) applications; and Double-Star Chopper-Cell (DSCC) or Double-Star Bridge-Cell (DSBC) for HVDC systems. A novel overlapping hexagon pulse width modulation scheme is introduced and discussed for switching control of the MMFCC. This uses multiple hexagons all centred on one point, the same in number as the cascaded FC sub-modules, which are phase displaced relative to each other. The approach simplifies the modulation algorithm and brings flexibility in shaping the output voltage waveforms for different applications. An MMFCC experimental rig was designed and built in-house to validate some of the simulation results obtained for the modulation of this new topology. Details of the rig as well as results captured are discussed.
24
Terciyanli, Alper. "Design And Implementation Of A Current Source Converter Based Active Power Filter For Medium Voltage Applications." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611767/index.pdf.
Full textAbstract:
This research work is devoted to the design, development and implementation of a Current Source Converter (CSC) based Active Power Filter (APF) for Medium Voltage (MV) applications. A new approach has been proposed to the design of the CSC based APF for reducing the converter kVA rating considerably. This design approach is called the Selective Harmonic Amplification Method (SHAM), and is based on the amplification of some selected harmoniccurrent components of the CSC by the input filter, and the CSC control system, which is specifically designed for this purpose. The proposed SHAM has been implemented on the first industrial CSC based APF for the elimination of 11th and 13th current harmonics of 12-pulse rectifiers fed from Medium Voltage (MV) underground cables in order to comply with IEEE Std. 519-1992. 450 kVA rated APF with only 205 kVA CSC rating has been connected to the MV bus via a coupling transformer of 600kVA, 34.5/1.1 kV. The power stage of the CSC based APF is composed of water-cooled high voltage IGBT and diode modules. Reference currents to be generated by the CSC are obtained by the use of a selective harmonic extraction method, by mploying synchronously rotating reference frames for each selected harmonic component. An Active damping method is also used to suppress the oscillations around the natural frequency of the input filter, excluding the harmonic components to be eliminated by APF. Simulation and field test results have shown that SHAM can successfully be applied to a CSC based APF for reduction of converter kVA rating, thus making it a cost- competitive alternative to voltage source converter based APFs traditionally used in industry applications.
25
Spahić, Ervin [Verfasser]. "Voltage Source Converter HVDC Connection of Offshore Wind Farms and the Application of Batteries / Ervin Spahic." Aachen : Shaker, 2009. http://d-nb.info/1161309888/34.
Full text
26
Lee, Dong-Ho. "A Power Conditioning System for Superconductive Magnetic Energy Storage based on Multi-Level Voltage Source Converter." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/11042.
Full textAbstract:
A new power conditioning system (PCS) for superconductive magnetic energy storage (SMES) is developed and its prototype test system is built and tested. The PCS uses IGBTs for high-speed PWM operation and has a multi-level chopper-VSC structure. The prototype test system has three-level that can handle up to 250-kVA with a 1800-V DC link, a 200-A maximum load current , and a switching frequency reaching 20-kHz with the help of zero-current-transition (ZCT) soft-switching. This PCS has a great number of advantages over conventional ones in terms of size, speed, and cost.
Conventional PCSs use thyristors, due to the power capacity of the SMES system. The speed limit of the thyristor uses a six-pulse operation that generates a high harmonic. To reduce the harmonic, multiple PCSs are connected together with phase-matching transformers that need to be precise to be effective in reducing the harmonics. So, the system becomes large and expensive. In addition, the dynamic range of the PCSs are also limited by the six-pulse operation, because it limits the useful area of the PCS applications.
By employing a high-speed PWM, the new PCS can reduce the harmonics without using the transformers reducing size and cost, and has wide dynamic range. However, the speed of a switching device is generally inversely proportional to its power handling capacity. Therefore, employing a multi-level structure is one method of extending the power-handling capability of the high-speed device. Switching loss is another factor that limits the speed of the switch, but it can be reduced by soft-switching techniques. The 20-kHz switching frequency can be obtained with the help of the ZCT soft-switching technique, which can reduce about 90% of switching losses from the IGBT during both turn-on and turn-off transients. There are two different topologies of the PCS; the current source converter (CSC) type and the chopper and voltage source converter (VSC) type. In terms of the SMES system efficiency, the chopper-VSC type shows a less volt-ampere requirement of the power device. Therefore, the new PCS system has a chopper-VSC structure.
Since the chopper-VSC structure consists of multiple legs that can be modularized, a power electronics building block (PEBB) leg is a good choice; all of the system problems caused by the high frequency can be solved within the PEBB leg. The VSC is built with three of the PEBB legs. Three-phase AC is implemented with a three-level space vector modulation (SVM) that can reduce the number of switching and harmonic contents from the output current. A closed-loop control system is also implemented for the VSC, and shows 600-Hz control bandwidth.
The multi-level structure used requires too many high-speed switches. However, not all of them are used at the same time during normal multi-level operation. A new multi-level topology is suggested that requires only two high-speed switches, regardless of the number of levels. Other switches can be replaced with slow-speed switches that can allow additional cost savings.Ph. D.
27
Brinsfield, Jason. "Modeling and Simulation of Parallel D-STATCOMs with Full-Wave Rectifiers." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1209.
Full textAbstract:
In recent years, both a significant increase in electrical demand and a large influx of intermittent renewable energy sources have put a considerable stress on the nation’s electrical grid. Conventional power flow control techniques such as capacitor banks and tap-changing transformers are incapable of adequately handling the rapid fluctuations in power supply and demand that today’s grid experiences. Flexible AC Transmission System (FACTS) controllers are a practical way to compensate for such rapid power fluctuations. One type of shunt FACTS controller is the Static Synchronous Compensator (STATCOM), which uses fully controllable switches to source or sink reactive power to a point on the grid, thus reducing voltage fluctuations due to load changes. The purpose of this thesis is to model and simulate the operation of two Distribution STATCOMs (D-STATCOMs) operating on the same point on the grid. These D-STATCOMs also utilize parallel full-wave rectifiers that directly connect the ac grid to the dc capacitor of the D-STATCOMs. Parameters such as power loss, reaction time, stability, and THD are measured for several test scenarios. Results from this thesis show that two D-STATCOMs operating on the same point can be stable and effective under a wide range of conditions. This thesis also concludes that the inclusion of parallel rectifiers with the D-STATCOMs results in no performance improvement of the D-STATCOMs.
28
Cetin, Alper. "Design And Implementation Of A Voltage Source Converter Based Statcom For Reactive Power Compensation And Harmonic Filtering." Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608307/index.pdf.
Full textAbstract:
In this thesis, design and implementation of a distribution-type, voltage source converter (VSC) based static synchronous compensator (D-STATCOM) having the
simplest converter and coupling transformer topologies have been carried out. The VSC STATCOM is composed of a +/- 750 kVAr full-bridge VSC employing selective harmonic elimination technique, a low-pass input filter, and a ∆
/Y connected coupling transformer for connection to medium voltage bus. The power stage of VSC based STATCOM is composed of water-cooled high voltage IGBT modules switched at 850 Hz for the elimination of 5th, 7th, 11th, 13th, 17th, 19th, 23rd,and 25th voltage harmonics. Special care has been taken in the laminated busbar design to minimize stray inductances between power semiconductors and dc link capacitor. Reactive power control is achieved by applying the phase angle control technique. The effect of input filter on total demand distortion has been investigated theoretically by mathematical derivations. The proposed VSC STATCOM has been implemented for reactive power compensation of Coal Preparation System in Kemerkö
y Thermal Power Plant. The field test results have shown the success of the implemented system in view of fast response in reactive power compensation, and minimum input current harmonic content, and compliance with the IEEE Std. 519-1992 even for the weakest power systems. The application of selective harmonic elimination technique and phase angle control to VSC STATCOM has led to optimum switching frequency and device utilization for high voltage IGBTs at the expense of slower response as compared to other PWM techniques.
29
Perera, Lasantha Bernard. "Multi Level Reinjection ac/dc Converters for HVDC." Thesis, University of Canterbury. Electrical and Computer Engineering, 2006. http://hdl.handle.net/10092/1085.
Full textAbstract:
A new concept, the multi level voltage/current reinjection ac/dc conversion, is described in this thesis. Novel voltage and current source converter configurations, based on voltage and current reinjection concepts are proposed. These converter configurations are thoroughly analyzed in their ac and dc system sides. The fundamentals of the reinjection concept is discussed briefly, which lead to the derivation of the ideal reinjection waveform for complete harmonic cancellation and approximations for practical implementation. The concept of multi level voltage reinjection VSC is demonstrated through two types of configurations, based on standard 12-pulse parallel and series connected VSC modified with reinjection bridges and transformers. Firing control strategies and steady state waveform analysis are presented and verified by EMTDC simulations. The multi level current reinjection CSC is also described using two configurations based on standard 12-pulse parallel and series connected CSC modified with associated reinjection circuitry. Firing control strategies and steady state waveform analysis are presented and verified by EMTDC simulations. Taking the advantage of zero current switching in the main bridge valves, achieved through multi level current reinjection, an advanced multi level current reinjection scheme, consisting thyristor main bridges and self-commutated reinjection circuitry is proposed. This hybrid scheme effectively incorporates self-commutated capability into a conventional thyristor converter. The ability of the main bridge valves to commutate without the assistance of a turn-off pulse or line commutating voltage under the zero current condition is explained and verified by EMTDC simulations. Finally, the applications of the MLCR-CSC are discussed in terms of a back to back HVDC link and a long distance HVDC transmission system. The power and control structures and closed loop control strategies are presented. Dynamic simulation is carried out on PSCAD/EMTDC to demonstrate the two systems ability to respond to varying active and reactive power operating conditions.
30
Vormedal, Pål Kristian Myhrer. "Voltage Source Converter Technology for Offshore Grids : Interconnection of Offshore Installations in a Multiterminal HVDC Grid using VSC." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11243.
Full textAbstract:
This master thesis has investigated the possible application of voltage source converters (VSC) for the interconnection of offshore installations, i.e. wind farms and petroleum platforms, in a multiterminal DC (MTDC) grid. The master thesis is written at the Norwegian University of Science and Technology, Department of Electric Power Engineering and is a continuation of the project written during the autumn of 2009. The work has been carried out in cooperation with Statnett SF, the Norwegian TSO, as a contribution to an ongoing research and development program on offshore electrification. The motivation behind this thesis is the possibilities the VSC technology bring about for the realization of renewable wind energy far from shore and supplying petroleum installations from the main onshore grid, thus reducing emissions. A theoretical study has been conducted, describing the VSC technology from basic operation to topics related to the implementation of a high power rated offshore MTDC grid. A suggested model of a small power system was established in the simulation program PSS®E. The model consisted of a four converter MTDC connecting three separate AC systems. One of the AC systems was a simplified representation of a main onshore grid, and the other two were small offshore AC grids made up of a wind farm and a petroleum platform. The MTDC was modeled using ABBs HVDC Light Open model v 1.1.9-2, developed for use in PSS®E. A series of dynamic simulations have been performed using the model to demonstrate and analyze the principles of operation for a MTDC and the interaction between the AC systems and the MTDC. The dynamic simulations demonstrate the basic operation of a MTDC with a master-slave control scheme for the active power control, as implemented in the HVDC Light model. The simulation results confirm the functionality of a MTDC as described in the theoretical analysis of the technology.The analysis based on both the literature and simulations conclude that VSC technology is a realistic solution for an offshore grid with the objective of supporting passive network installations far from shore. Simulation results conclude that an advanced control system for the active power control operation (Poption) of all the converters in a MTDC may greatly improve the performance of the system following a disturbance. Both theoretically and through simulations it has been demonstrated that the VSC MTDC provides stability improvements to the connected AC grid, by actively controlling the injected active and reactive power to the grid. The possibility to use the MTDC as an alternative path for transferring large amounts of power has been investigated, and this was found to be beneficial for the system. The difficulties related to fault protection in a MTDC have been highlighted, and a theoretical analysis concluded that the protection scheme using IGBT circuit breakers is the preferred solution with present available technology.
31
Cvetkovic, Igor. "Modeling and Control of Voltage-Controlling Converters for Enhanced Operation of Multi-Source Power Systems." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/85850.
Full textAbstract:
The unconventional improvements in the power electronics field have been the primary reason for massive deployment of renewable energy sources in the electrical power grid over the past several decades. This needed trend, together with the increasing penetration of micro-, and nano- grids, is bringing significant improvements in system controllability, performance, and energy availability, but is fundamentally changing the nature of electronically-interfaced sources and loads, altering their conventionally mild aggregate dynamics, and inflicting low- and high- frequency dynamic interactions that never before existed at this magnitude. This problem is not restricted only to the grid; modern electronic power distribution systems built for airplanes, ships, electric vehicles, data-centers, and homes, comprise dozens, even hundreds of power electronics converters, produced by different manufacturers, who provide very limited details on converters' dynamic behavior - distinctiveness that has the highest impact on how two converters, or converter and a system interact. Consequently, substantial dispersion of power electronics into the future grid will significantly depend on engineers' capability to understand how to model and dynamically control power flow and subsystem interactions. It is therefore essential to continue developing innovative methods that allow easier system-level modeling, continuous monitoring of dynamic interactions, and advanced control concepts of power electronics converters and systems.
The dissertation will start with a "black box" approach to modeling of three-phase power electronics converters, introducing a method to remove source and load dynamics from in-situ measured terminated frequency responses. It will be then shown how converter, itself, can perform an online stability assessment knowing its own unterminated dynamics, and being able to measure all terminal immittances. The dissertation will further advance into an approach to control power electronics converters based on the electro-mechanical duality with synchronous machines, and end with selected examples of system-level operation, where small-signal instability in multi-source power systems can be mitigated using this concept.Ph. D.
32
Johansson, Frank. "Implementation of a SM drive in a voltage-source converter control system with a PCSad/EMTDC simulation software interface." Thesis, University West, Department of Technology, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-391.
Full text
33
Gongora, Vicente de Lima. "Sistema de fornecimento de potência a partir de célula a combustível utilizando conversor estático com modulação delta modificada." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/18/18153/tde-13122018-134202/.
Full textAbstract:
Este trabalho, constitui-se em uma contribuição para o estudo das estratégias de mo-dulação direta baseadas em histerese e que funcionam em frequência fixa de comutação. Tem como objetivo principal propor a estratégia delta modificada, que diferencia-se na forma de ajuste da largura de banda de histerese, alterando-se seus limites e em como executa o comando de bloqueio das chaves de potência, para que a corrente de saída se mantenha em frequência fixa de operação e apresente rápida resposta dinâmica no sistema controlado. Para tanto, não necessita da utilização de derivadas, nem de uma corrente média de referência, tão pouco, se utiliza dos tempos de comutação. A estratégia proposta, comprova que é possível produzir os adequados pulsos de comando para o processamento da energia proveniente de célula combustível, através do conversor estático de potência, utilizando-se, principalmente, dos valores de ultrapassagem nos limites estabelecidos de histerese. Como objetivo secundário desta pesquisa, desenvolve-se um conversor CC/CC auxiliar para adaptar e estabilizar a energia proveniente da CAC, compondo-se um sistema útil que serve de base para fornecer energia, aos mais diversos tipos de cargas em CC. Além disso, apresenta-se uma revisão das estratégias de modulação em modo direto para o controle da corrente de saída no conversor estático, tendo como base a tensão nos terminais de um indutor. Contudo, outras estratégias são naturalmente citadas, no transcorrer deste trabalho, devido haver combinações entre as diferentes estratégias moduladoras e controladoras comentadas.This work, is a contribution to the study of direct modulation strategies based on hysteresis and that operate at fixed switching frequency. Its main objective is to propose the modified delta strategy, which differentiates from the others strategies in the form of adjustment of hysteresis bandwidth, changing its limits and in executing the locking command of the power keys, so that the output current is maintain at fixed frequency of operation and a rapid dynamic response in the controlled system. In order to do so, it does not require the use of derivatives or a reference average current and also the switching times are not used. This strategy shows that it is possible to produce the appropriate command pulses for the processing of fuel cell energy by the static power converter using mainly the exceedance limit values. As a secondary objective of this research, an auxiliary DC/DC converter is developed to adapt and stabilize the energy coming from the fuel cell, forming a useful system that serves as a base to supply power to the most diverse types of DC loads. In addition, we present a review of the direct-mode modulation strategies for the control of the output current in the static converter, updating data, and based on the voltage at the terminals of an inductor; how-ever, others strategies are naturally cited because there are combinations between the different modulating strategies and controllers commented on in the course of this work.
34
Nord, Thomas. "Voltage Stability in an Electric Propulsion System for Ships." Thesis, KTH, Elektriska energisystem, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118932.
Full textAbstract:
This Master of Science thesis was written based on the shipbuilder Kockums AB feasibility study regarding the development of an All- Electric Ship for the Swedish Navy. The thesis was aiming at addressing voltage stability issues in a dc system fed by PWM rectifiers operating in parallel when supplying constant power loads. A basic computer model was developed for investigating the influence from various parameters on the system. It was shown that the voltage stability is dependent upon the ability to store energy in large capacitors. It was also shown that a voltage droop must be implemented maintaining load sharing within acceptable limits. Different cases of operation were modelled, faults were discussed, and the principal behaviour of the system during a short-circuit was investigated. It was shown that the short-circuit current is much more limited in this type of system in comparison to an ac system. It was concluded that more research and development regarding the components of the system must be performed.
35
Ridenour, Daniel Keith. "Examination of Power Systems Solutions Considering High Voltage Direct Current Transmission." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/63927.
Full textAbstract:
Since the end of the Current Wars in the 19th Century, alternating current (AC) has dominated the production, transmission, and use of electrical energy. The chief reason for this dominance was (and continues to be) that AC offers a way minimize transmission losses yet transmit large power from generation to load. With the Digital Revolution and the entrance of most of the post-industrialized world into the Information Age, energy usage levels have increased due to the proliferation of electrical and electronic devices in nearly all sectors of life. A stable electrical grid has become synonymous with a stable nation-state and a healthy populace.
Large-scale blackouts around the world in the 20th and the early 21st Centuries highlighted the heavy reliance on power systems and because of that, governments and utilities have strived to improve reliability. Simultaneously occurring with the rise in energy usage is the mandate to cut the pollution by generation facilities and to mitigate the impact grid expansion has on environment as a whole. The traditional methods of transmission expansion are beginning to show their limits as utilities move generation facilities farther from load centers, which reduces geographic diversity, and the integration of nondispatchable, renewable energy sources upsets the current operating regime. A challenge faces engineers - how to expand generation, expand transmission capacity, and integrate renewable energy sources while maintaining maximum system efficiency and reliability.
A technology that may prove beneficial to the operation of power system is high voltage direct current transmission. The technology brings its own set of advantages and disadvantages, which are in many ways the complement of AC. It is important to update transmission planning processes to account for the new possibilities that HVDC offers. This thesis submits a discussion of high voltage direct current transmission technology itself and an examination of how HVDC can be considered in the planning process.Master of Science
36
Björklund, Erik. "Control Strategies for VSC-HVDC links in Weak AC Systems." Thesis, Uppsala universitet, Avdelningen för systemteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-373650.
Full textAbstract:
In this master thesis control systems for a voltage-source converter HVDC connected to weak ac networks are investigated. HVDC stands for high voltage direct current and is a way to transfer power in the electrical power system. A HVDC uses direct current (dc) instead of alternate current (ac) to transfer power, which requires transformation between ac and dc since most power grids are ac networks. The HVDC uses converters to transform ac to dc and dc to ac and the converter requires a control system. A complete control system of a voltage source converter HVDC contains many different parts. The part investigated in this thesis is the active power control. Different structures containing PID controllers have been tested and evaluated with respect to stability and performance using control theory. The impact of weak ac networks has been evaluated in regards to the different control structures. The investigations have been conducted using mainly steady-state simulations. Based on the simulation and analyzes of the simulation results a promising control structure has been obtained and suggested for further investigation.
37
Wahid, Ferdus. "Analysis Of A Wave Power System With Passive And Active Rectification." Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-425722.
Full textAbstract:
Wave energy converter (WEC) harnesses energy from the ocean to produce electrical power. The electrical power produced by the WEC is fluctuating and is not maximized as well, due to the varying ocean conditions. As a consequence, without any intermediate power conversion stage, the output power from the WEC can not be fed into the grid. To feed WEC output power into the grid, a two-stage power conversion topology is used, where the WEC output power is first converted into DCpower through rectification, and then a DC-AC converter (inverter) is used to supply AC power into the grid. The main motive of this research is to extract maximum electrical power from the WEC by active rectification and smoothing the power fluctuation of the wave energy converter through a hybrid energy storage system consisting of battery and flywheel. This research also illustrates active and reactive power injection to the grid according to load demand through a voltage source inverter.
38
Lobato, Salatiel de Castro. "Fonte de corrente para aplicação em magnetos de aceleradores de partículas." Universidade Federal de Juiz de Fora (UFJF), 2016. https://repositorio.ufjf.br/jspui/handle/ufjf/3646.
Full textAbstract:
Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-03-13T15:20:14Z
No. of bitstreams: 1
salatieldecastrolobato.pdf: 51678452 bytes, checksum: 022776c88833a1e47901180ebd1f826b (MD5)Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-03-13T19:33:17Z (GMT) No. of bitstreams: 1 salatieldecastrolobato.pdf: 51678452 bytes, checksum: 022776c88833a1e47901180ebd1f826b (MD5)
Made available in DSpace on 2017-03-13T19:33:17Z (GMT). No. of bitstreams: 1 salatieldecastrolobato.pdf: 51678452 bytes, checksum: 022776c88833a1e47901180ebd1f826b (MD5) Previous issue date: 2016-11-07
O objetivo geral desta dissertação é o aperfeiçoamento do projeto de uma nova fonte de corrente em desenvolvimento para o acelerador de partículas Sirius. A corrente da fonte é aplicada em magnetos de elevada indutância e são programadas para apresentar forma de onda com significativa componente senoidal em corrente contínua e em baixa frequência, de acordo com as características operacionais necessárias do Sirius. Para efeitos de estudo, a metodologia empregada consiste essencialmente em desacoplar a análise e o projeto do controle em um estágio regulador de tensão seguido de um estágio de síntese da corrente. Foram realizados ensaios em uma fonte em construção no Laboratório Nacional de Luz Síncroton e em um protótipo desenvolvido na UFJF. As principais contribuições descritas nesta dissertação são: i) atenuação da propagação de distúrbios de baixa frequência para a rede elétrica; ii) emprego de retificador de tensão controlado para regulação da tensão do barramento CC, melhoria do fator de potência e redução de componentes harmônicas. Os resultados experimentais evidenciam que as alterações de projeto propostas nesta dissertação apresentam grande potencial para melhorar o desempenho da fonte de corrente em termos da qualidade de energia elétrica e da sintetização de corrente senoidal no magneto do acelerador de partículas.
This work consists in the evaluation and improvement of a current source for a particle accelerator. The output current presents a DC sinusoidal waveform in low frequecy which flows through the windings of high inductance electromagnets. The methodology consists in separating the analysis and project of the control into two parts: a voltage regulator stage,followedbyacurrentsynthesisstage. Testswereperformedonacurrentsourceunder construction at the Brazilian Synchrotron Light Laboratory (LNLS) and on a prototype developed at UFJF. The work main contributions are: i) Attenuation of the low frequency disturbances on the electrical grid; ii) Use of a controlled rectifier to regulate the voltage of the DC bus, improvement in power factor and reduction of harmonic components. The experimental results show that the proposed changes have potential in improving the performace of the current source in terms of its electric power quality and synthesis of sinusoidal current in the particule accelerator.
39
Zhang, Bin. "Development of the Advanced Emitter Turn-Off (ETO) Thyristor." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/26095.
Full textAbstract:
Advancements in the power electronics systems have been directly related to the availability of improved power semiconductor devices. The device performance greatly determines the efficiency, reliability, volume, and cost of the power electronics system. This dissertation is dedicated to develop an advanced high power semiconductor device, the emitter turn-off (ETO) thyristor, which is targeted to improve the limitations of the present high power devices.
Major improvements in electrical and mechanical designs of the ETO for high power and high frequency operation are proposed which result in improved snubberless turn-off capability, low conduction loss, and low gate drive power consumption of the new generation ETO.
A revolutionary self-power generation method of the ETO is proposed. Different from the conventional high power devices which require the external power input for their gate drivers, ETO achieves complete optically controlled turn-on and turn-off and all the internal power required is self-generated. This advancement will have a major impact to high power converter designs.
A novel integrated method to eliminate the dead-time requirement is proposed for ETO. This method not only improves the output waveform quality but also increases the reliability and reduces the cost of the high power PWM voltage source converters. With this unique function, the upper and the lower ETO's within a converter phase leg can receive the ideal complementary (without dead-time) PWM signals and solve shoot-through problems.
Method to measure the ETO current and transfer the current information to a PWM signal is proposed. Based on the ETO's built-in current sensor, the over-current protection function of the ETO is designed as well. The experimental results show that the built-in current sensor has a very high precision, and the over-current protection function can effectively protect the ETO during the short circuit faults.
In order to improve ETO's turn-off capability, a comprehensive investigation of the turn-off failure mechanism of the ETO was performed. A series of simulations and experiments are carried out to study the ETO turn-off operation. The detail turn-off failure mechanisms are presented. The conditions to cause the ETO failure are addressed. The approaches to improve the ETO's turn-off capability are discussed.Ph. D.
40
Chaour, Issam. "Efficiency Improvement of RF Energy Transfer by a Modified Voltage Multiplier RF DC Converter." Universitätsverlag Chemnitz, 2018. https://monarch.qucosa.de/id/qucosa%3A33143.
Full textAbstract:
Radio Frequency (RF) energy transfer is getting increasingly importance in new generations of wireless sensor networks and this trend is tremendously supported by the modern trends to Internet of things (IoT). This promising technology enables proactive energy replenishment for wireless devices. With RF energy, transmission long distances between the energy source and the receiver can be overbridged. The main challenge thereby is the power conversion efficiency from a low level RF input power to a Direct Current (DC) voltage which is able to supply the mobile system.
For this purpose, a novel approach for RF DC conversion is proposed. It consists of a modified voltage multiplier RF DC converter circuit by incorporating an inductor at the input of the circuit, which generates an induced voltage able to boost the output circuit and improve the conversion efficiency. Analytical analysis of the novel approach has been carried out to determine the optimal value of the inductor to maximize the output power. The experimental investigations show that the proposed solution is able to improve significantly both the output voltage and the power conversion efficiency, compared to the state of the art, and this especially at low input power ranges, which are often the case. At -10 dBm input power, the modified voltage multiplier RF DC converter circuit can reach 1.71 V output voltage and 49.21 % power conversion efficiency for, respectively, 500 kΩ and 10 kΩ resistive loads.
In order to validate the new proposal for the RF transfer system experimentally, microstrip meander line antennas and microstrip patch antenna arrays are designed for different ISM bands, where relevant requirements for RF energy transfer are respected. For each antenna a modified voltage multiplier RF DC converter circuit has been applied and the system is tuned to the corresponding resonant frequency to avoid mismatching. In this investigation several scenarios have been addressed, such as RF transmission energy, RF energy harvesting in Global System for Mobile (GSM) bands and Wireless Local Area Networks (WLAN) band are developed. Field test results show high performances of experimental results in comparison to the state of the art.:1 Introduction
2 Theoretical Background
3 State of the Art of RF Energy Transfer
4 Novel Approach for a RF DC Converter Circuit
5 Antennas Design
6 Experimental Verification at Specific Scenarios
7 ConclusionDie RF-Energieübertragung (RF) gewinnt in neuen Generationen von drahtlosen Sensornetzen zunehmend an Bedeutung. Dieser Trend wird durch das Internet der Dinge (IoT) weiter unterstützt. Diese vielversprechende Technologie ermöglicht eine proaktive Energieversorgung für drahtlose Geräte. Mit RF-Energie können große Entfernungen zwischen der Energiequelle und dem Empfänger überbrückt werden. Die größte Herausforderung dabei ist der Wirkungsgrad, mit dem von einer niedrigen HF-Eingangsleistung in eine Gleichspannung (DC), mit welcher das mobile System versorgt wird, gewandelt wird. Zu diesem Zweck wird ein neuer Ansatz für einen RF-DC-Wandler vorgeschlagen. Er besteht aus einer modifizierten Spannungsvervielfacher-RF-DC-Wandlerschaltung, die eine Spule am Eingang der Schaltung integriert. Diese erzeugt eine induzierte Spannung, die in der Lage ist die Ausgangsschaltung zu verstärken und den Umwandlungswirkungsgrad zu verbessern. Analytische Untersuchungen zu diesem neuartigen Ansatz wurden durchgeführt, um den optimalen Wert der Spule zu bestimmen und die Ausgangsleistung zu maximieren. Die experimentellen Untersuchungen zeigen, dass die vorgeschlagene Lösung in der Lage ist, sowohl die Ausgangsspannung als auch den Wirkungsgrad der Leistungsumwandlung im Vergleich zum Stand der Technik deutlich zu verbessern. Dies gilt besonders für niedrige Eingangsleistungsbereiche, welche häufig vorkommen. Bei -10 dBm Eingangsleistung kann die modifizierte Spannungsvervielfacher-RF-DC-Wandlerschaltung 1.71 V Ausgangsspannung und 49.21 % Leistungswandlungswirkungsgrad für jeweils 500 kΩ und 10 kΩ ohmsche Last erreichen. Um das neue RF-Übertragungssystem experimentell zu validieren, werden Mikrostreifenmäanderlinienantennen und Mikrostreifen-Patch-Antennenarrays für verschiedene ISM-Bänder ausgelegt, wobei die relevanten Anforderungen an die RF-Energieübertragung eingehalten werden. Für jede Antenne wurde eine modifizierte Spannungsvervielfacher-HF-DC-Wandlerschaltung verwendet und das System auf die entsprechende Resonanzfrequenz abgestimmt, um Fehlanpassungen zu vermeiden. Dabei wurden mehrere Szenarien untersucht, wie z.B. RF-Energieübertragung, RF-Energiegewinnung aus GSM-Bändern und WLAN-Netzwerken. Die Feldtests zeigen eine hohe Leistungsfähigkeit der experimentellen Ergebnisse im Vergleich zum Stand der Technik.:1 Introduction 2 Theoretical Background 3 State of the Art of RF Energy Transfer 4 Novel Approach for a RF DC Converter Circuit 5 Antennas Design 6 Experimental Verification at Specific Scenarios 7 Conclusion
41
Zare, Firuz. "Multilevel converter structure and control." Thesis, Queensland University of Technology, 2001. https://eprints.qut.edu.au/36142/7/36142_Digitsed%20Thesis.pdf.
Full textAbstract:
In recent years, multilevel converters are becoming more popular and attractive than traditional converters in high voltage and high power applications. Multilevel converters are particularly suitable for harmonic reduction in high power applications where semiconductor devices are not able to operate at high switching frequencies or in high voltage applications where multilevel converters reduce the need to connect devices in series to achieve high switch voltage ratings. This thesis investigated two aspects of multilevel converters: structure and control.
The first part of this thesis focuses on inductance between a DC supply and inverter components in order to minimise loop inductance, which causes overvoltages and stored energy losses during switching. Three dimensional finite element simulations and experimental tests have been carried out for all sections to verify theoretical developments. The major contributions of this section of the thesis are as follows:
The use of a large area thin conductor sheet with a rectangular cross section separated by dielectric sheets (planar busbar) instead of circular cross section wires, contributes to a reduction of the stray inductance. A number of approximate equations exist for calculating the inductance of a rectangular conductor but an assumption was made that the current density was uniform throughout the conductors. This assumption is not valid for an inverter with a point injection of current. A mathematical analysis of a planar bus bar has been performed at low and high frequencies and the inductance and the resistance values between the two points of the planar busbar have been determined.
A new physical structure for a voltage source inverter with symmetrical planar bus bar structure called Reduced Layer Planar Bus bar, is proposed in this thesis based on the current point injection theory. This new type of planar busbar minimises the variation in stray inductance for different switching states. The reduced layer planar busbar is a new innovation in planar busbars for high power inverters with minimum separation between busbars, optimum stray inductance and improved thermal performances. This type of the planar busbar is suitable for high power inverters, where the voltage source is supported by several capacitors in parallel in order to provide a low ripple DC voltage during operation.
A two layer planar busbar with different materials has been analysed theoretically in order to determine the resistance of bus bars during switching. Increasing the resistance of the planar busbar can gain a damping ratio between stray inductance and capacitance and affects the performance of current loop during switching. The aim of this section is to increase the resistance of the planar bus bar at high frequencies (during switching) and without significantly increasing the planar busbar resistance at low frequency (50 Hz) using the skin effect. This contribution shows a novel structure of busbar suitable for high power applications where high resistance is required at switching times.
In multilevel converters there are different loop inductances between busbars and power switches associated with different switching states. The aim of this research is to consider all combinations of the switching states for each multilevel converter topology and identify the loop inductance for each switching state. Results show that the physical layout of the busbars is very important for minimisation of the loop inductance at each switch state. Novel symmetrical busbar structures are proposed for multilevel converters with diode-clamp and flying-capacitor topologies which minimise the worst case in stray inductance for different switching states. Overshoot voltages and thermal problems are considered for each topology to optimise the planar busbar structure.
In the second part of the thesis, closed loop current techniques have been investigated for single and three phase multilevel converters. The aims of this section are to investigate and propose suitable current controllers such as hysteresis and predictive techniques for multilevel converters with low harmonic distortion and switching losses. This section of the thesis can be classified into three parts as follows:
An optimum space vector modulation technique for a three-phase voltage source inverter based on a minimum-loss strategy is proposed. One of the degrees of freedom for optimisation of the space vector modulation is the selection of the zero vectors in the switching sequence. This new method improves switching transitions per cycle for a given level of distortion as the zero vector does not alternate between each sector. The harmonic spectrum and weighted total harmonic distortion for these strategies are compared and results show up to 7% weighted total harmonic distortion improvement over the previous minimum-loss strategy. The concept of SVM technique is a very convenient representation of a set of three-phase voltages or currents used for current control techniques.
A new hysteresis current control technique for a single-phase multilevel converter with flying-capacitor topology is developed. This technique is based on magnitude and time errors to optimise the level change of converter output voltage. This method also considers how to improve unbalanced voltages of capacitors using voltage vectors in order to minimise switching losses. Logic controls require handling a large number of switches and a Programmable Logic Device (PLD) is a natural implementation for state transition description. The simulation and experimental results describe and verify the current control technique for the converter.
A novel predictive current control technique is proposed for a three-phase multilevel converter, which controls the capacitors' voltage and load current with minimum current ripple and switching losses. The advantage of this contribution is that the technique can be applied to more voltage levels without significantly changing the control circuit. The three-phase five-level inverter with a pure inductive load has been implemented to track three-phase reference currents using analogue circuits and a programmable logic device.
42
Tazay, Ahmad F. "Smart Inverter Control and Operation for Distributed Energy Resources." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/7097.
Full textAbstract:
The motivation of this research is to carry out the control and operation of smart inverters and voltage source converters (VSC) for distributed energy resources (DERs) such as photovoltaic (PV), battery, and plug-in hybrid electric vehicles (PHEV). The main contribution of the research includes solving a couple of issues for smart grids by controlling and implementing multifunctions of VSC and smart inverter as well as improving the operational scheme of the microgrid. The work is mainly focused on controlling and operating of smart inverter since it promises a new technology for the future microgrid. Two major applications of the smart inverter will be investigated in this work based on the connection modes: microgrid at grid-tied mode and autonomous mode.
\indent In grid-tied connection, the smart inverter and VSC are used to integrate DER such as Photovoltaic (PV) and battery to provide suitable power to the system by controlling the supplied real and reactive power. The role of a smart inverter at autonomous mode includes supplying a sufficient voltage and frequency, mitigate abnormal condition of the load as well as equally sharing the total load's power. However, the operational control of the microgrid still has a major issue on the operation of the microgrid. The dissertation is divided into two main sections which are:
1- Low-level control of a single smart Inverter.
2- High-level control of the microgrid.
The first part investigates a comprehensive research for a smart inverter and VSC technology at the two major connections of the microgrid. This involves controlling and modeling single smart inverter and VSC to solve specific issues of microgrid as well as improve the operation of the system. The research provides developed features for smart inverter comparing with a conventional voltage sourced converter (VSC). The two main connections for a microgrid have been deeply investigated to analyze a better way to develop and improve the operational procedure of the microgrid as well as solve specific issues of connecting the microgrid to the system.
A detailed procedure for controlling VSC and designing an optimal operation of the controller is also covered in the first part of the dissertation. This section provides an optimal operation for controlling motor drive and demonstrates issues when motor load exists at an autonomous microgrid. It also provides a solution for specific issues at operating a microgrid at autonomous mode as well as improving the structural design for the grid-tied microgrid. The solution for autonomous microgrid includes changing the operational state of the switching pattern of the smart inverter to solve the issue of a common mode voltage (CMV) that appears across the motor load. It also solves the issue of power supplying to large loads, such as induction motors. The last section of the low-level section involves an improvement of the performance and operation of the PV charging station for a plug-in hybrid electric vehicle (PHEV) at grid-tied mode. This section provides a novel structure and smart controller for PV charging station using three-phase hybrid boost converter topology. It also provides a form of applications of a multifunction smart inverter using PV charging station.
The second part of the research is focusing on improving the performance of the microgrid by integrating several smart inverters to form a microgrid. It investigates the issue of connecting DER units with the microgrid at real applications. One of the common issues of the microgrid is the circulating current which is caused by poor reactive power sharing accuracy. When more than two DER units are connected in parallel, a microgrid is forming be generating required power for the load. When the microgrid is operated at autonomous mode, all DER units participate in generating voltage and frequency as well as share the load's power. This section provides a smart and novel controlling technique to solve the issue of unequal power sharing. The feature of the smart inverter is realized by the communication link between smart inverters and the main operator. The analysis and derivation of the problem are presented in this section.
The dissertation has led to two accepted conference papers, one accepted transaction IEEE manuscript, and one submitted IET transaction manuscript. The future work aims to improve the current work by investigating the performance of the smart inverter at real applications.
43
Hernandez, Michael. "Applications of modern control in power electronics." Paris 11, 2010. http://www.theses.fr/2010PA112161.
Full textAbstract:
Dans la première partie, cette dissertation continue le cadre pour l'analyse et la conception (probablement des compensateurs de facteur) de puissance (PF) non linéaire pour les systèmes électriques fonctionnant dans des régimes nonsinusoïdaux (mais périodiques) avec les charges non linéaires. En particulier, dans la prétention standard que le générateur est une source de tension sans l'impédance, nous avons caractérisé toutes les charges non linéaires dont le pf est amélioré avec un compensateur non linéaire indiqué. Et ce cadre est employé pour étudier le problème de lacompensation passive de pf d'un redresseur commandé par pont classique. Est donné le fonctionnement "à l'avance de phase" du redresseur qu'on s'attend à ce que la compensation capacitive améliore le pf. Il est cependant moins évident que ceci puisse également être réalisé (dans quelques conditions appropriées) avec des inducteurs. Dans la deuxième partie, on a proposé la méthodologie d’A pour concevoir les contrôleurs (PI) proportionnel-intégraux linéaires utilisés des applications de convertisseur de puissance et en assurant la stabilité asymptotique. La technique s’est fondée sur le fait de base que si un système d’affinage peut être rendu passif avec une commande constante, alors il est stabilisable avec pi. Un état structural a été imposé alors au convertisseur de puissance pour satisfaire l’ancienne propriété avec un résultat passif produit comme combinaison linéaire des états. Cette condition est technique et n’a aucune interprétation physique claire. Ce résultat est prolongé dans trois directions : d’abord, la condition mentionnée ci-dessus est enlevée ; en second lieu, une plus grande classe des convertisseurs (avec des sources extérieures de commutation) est considérée ; troisièmement, la résistance de charge est assumée qu’on propose l’inconnu et un contrôleur adaptatif de pi (avec trois estimateurs différents). La méthodologie est appliquée au problème de la compensation de facteur de puissance d’un redresseur triphasé de source de tension, avec des résultats de simulation proposés. En outre, pi adaptatif stable est conçu pour la régulation de tension de rendement d’un convertisseur quadratique de poussée montrant l’exécution au moyen de résultat expérimental. Dans la troisième partie quelques contrôleurs basés sur le concept de la commande de charge pour un convertisseur utilisé dans une mise sous tension la correction de facteur sont montrés. Le convertisseur se compose par le raccordement intercalé de deux convertisseurs ou plus de poussée reliée à la grille à l’aide d’un redresseur de diode non commandé. La commande de charge représente une solution bon marché pour garantir la mise en commun courante entre les différents convertisseurs impliqués, et est normalement employée en combination avec d’autres contrôleurs. Les deux contrôleurs sont d’abord conçus pour garantir le facteur de puissance de près d’un avec la tension CC Réglée, à laquelle la commande de charge est ajoutée pour distribuer le courant égal parmi les convertisseurs. En conclusion, on présente une simplification avec l’exécution semblable qui élimine l’utilisation des sondes courantes, excepté les transformateurs de courant exigés pour mettre en application la commande de charge, des résultats expérimentaux accomplissent cette cloison. La quatrième partie, présente l’exécution et la programmation d’une méthode pour dépister le point de puissance maximum (MPP) dans des applications (PV) photovoltaïques. Ce point de fonctionnement est d’intérêt spécial pendant qu’on l’exige pour extraire la puissance maximum disponible à partir des rangées photovoltaïquesIn the first part, this dissertation continues with the framework for analysis and design of (possibly nonlinear) power factor (PF) compensators for electrical systems operating in non-sinusoidal (but periodic) regimes with nonlinear loads. In particular, under the standard assumption that the generator is a voltage source with no impedance, we characterized all nonlinear loads whose PF is improved with a given nonlinear compensator. And this framework is used to study the problem of passive PF compensation of a classical half-bridge controlled rectifier. Given the “phase advance” operation of the rectifier it is expected that capacitive compensation improves PF, it is however less obvious that this can also be achieved (under some suitable conditions) with inductors. In the second part, A methodology to design linear proportional-integral (PI) controllers used in power converter applications and ensuring asymptotic stability was proposed. The technique relied on the basic fact that if an affine system can be rendered passive with a constant control, then it is stabilizable with a PL A structural condition was imposed then on the power converter to satisfy the former property with a passive output generated as a linear combination of the states. This condition is technical and has no clear physical interpretation. This result is extended in three directions : first, the aforementioned condition is removed ; second, a larger class of converters (with switching external sources) is considered ; third, the load resistance is assumed unknown and an adaptive PI controller (with three different estimators) is proposed. The methodology is applied to the problem of power factor compensation of a 3-phase. Voltage source rectifier, with simulation results proposed. Also, a stable adaptive PI is designed for the output voltage regulation of a quadratic boost converter showing the performance by means of experimental result. In the third part some controllers based on the concept of charge control for a converter used in an application of power factor correction are shown. The converter is composed by the interleaved connection of two or more boost converters connected to the grid by means of a non controlled diode rectifier. Charge control represents a cheap solution to guarantee current sharing among the different converters involved, and is normally used in combination with other controllers. The two controllers are first designed to guarantee the power factor close to one with regulated DC voltage, to which charge control is added to distribute equal current among the converters. Finally, a simplification with similar performance is presented that eliminates the use of current sensors, except for the current transformers required to implement the charge control, experimental results complete this part. The fourth part presents the implementation and programming of a method to track the maximum power point (MPP) in photovoltaic (PV) applications. This operation point is of special interest as it is required to extract the maximum power available from the photovoltaic arrays
44
Giraneza, Martial. "High voltage direct current (HVDC) in applications for distributed independent power providers (IPP)." Thesis, Cape Peninsula University of Technology, 2013. http://hdl.handle.net/20.500.11838/1077.
Full textAbstract:
Thesis submitted in fulfillment of the requirements for the degree
Master of Technology: Electrical Engineering
in the Faculty of Engineering
at the Cape Peninsula University of Technology
2013The development of power electronics did remove most of technical limitations that high voltage direct current (HVDC) used to have. HVDC, now, is mostly used for the transmission of bulk power over long distances and for the interconnection of asynchronous grid. Along with the development of the HVDC, the growth of power demand also increased beyond the utilities capacities. Besides the on-going increasing of power demand, the reforms in electricity market have led to the liberalization and the incorporation of Independent power providers in power system operation. Regulations and rules have been established by regulating authority for grid integration of Independent power providers. With the expected increase of penetration level of those new independent power providers, result of economic reason and actual green energy trend, best method of integration of those new power plants are required. In this research HVDC technology, namely VSC-HVDC is used as interface for connecting independent power providers units to the grid. VSC-HVDC has various advantages such as short-circuit contribution and independent control of active and reactive power. VSC-HVDC advantages are used for a safe integration of IPPs and make them participate to grid stabilization. MATLAB/Simulink simulations of different grid connected, through VSC-HVDC system, IPPs technologies models are performed. For each IPP technology model, system model performances are studied and dynamics responses during the disturbance are analyzed in MATLAB/ Simulink program. The simulation results show that the model satisfy the standard imposed by the regulating authority in terms of power quality and grid support. Also the results show the effect of the VSC-HVDC in preventing faults propagation from grid to integrated IPPs units.
45
Ghasemi, Negareh. "Improving ultrasound excitation systems using a flexible power supply with adjustable voltage and frequency to drive piezoelectric transducers." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/61091/1/Negareh_Ghasemi_Thesis.pdf.
Full textAbstract:
The ability of a piezoelectric transducer in energy conversion is rapidly expanding in several applications. Some of the industrial applications for which a high power ultrasound transducer can be used are surface cleaning, water treatment, plastic welding and food sterilization. Also, a high power ultrasound transducer plays a great role in biomedical applications such as diagnostic and therapeutic applications. An ultrasound transducer is usually applied to convert electrical energy to mechanical energy and vice versa. In some high power ultrasound system, ultrasound transducers are applied as a transmitter, as a receiver or both. As a transmitter, it converts electrical energy to mechanical energy while a receiver converts mechanical energy to electrical energy as a sensor for control system. Once a piezoelectric transducer is excited by electrical signal, piezoelectric material starts to vibrate and generates ultrasound waves. A portion of the ultrasound waves which passes through the medium will be sensed by the receiver and converted to electrical energy. To drive an ultrasound transducer, an excitation signal should be properly designed otherwise undesired signal (low quality) can deteriorate the performance of the transducer (energy conversion) and increase power consumption in the system. For instance, some portion of generated power may be delivered in unwanted frequency which is not acceptable for some applications especially for biomedical applications.
To achieve better performance of the transducer, along with the quality of the excitation signal, the characteristics of the high power ultrasound transducer should be taken into consideration as well. In this regard, several simulation and experimental tests are carried out in this research to model high power ultrasound transducers and systems. During these experiments, high power ultrasound transducers are excited by several excitation signals with different amplitudes and frequencies, using a network analyser, a signal generator, a high power amplifier and a multilevel converter. Also, to analyse the behaviour of the ultrasound system, the voltage ratio of the system is measured in different tests. The voltage across transmitter is measured as an input voltage then divided by the output voltage which is measured across receiver. The results of the transducer characteristics and the ultrasound system behaviour are discussed in chapter 4 and 5 of this thesis.
Each piezoelectric transducer has several resonance frequencies in which its impedance has lower magnitude as compared to non-resonance frequencies. Among these resonance frequencies, just at one of those frequencies, the magnitude of the impedance is minimum. This resonance frequency is known as the main resonance frequency of the transducer. To attain higher efficiency and deliver more power to the ultrasound system, the transducer is usually excited at the main resonance frequency. Therefore, it is important to find out this frequency and other resonance frequencies. Hereof, a frequency detection method is proposed in this research which is discussed in chapter 2.
An extended electrical model of the ultrasound transducer with multiple resonance frequencies consists of several RLC legs in parallel with a capacitor. Each RLC leg represents one of the resonance frequencies of the ultrasound transducer. At resonance frequency the inductor reactance and capacitor reactance cancel out each other and the resistor of this leg represents power conversion of the system at that frequency. This concept is shown in simulation and test results presented in chapter 4.
To excite a high power ultrasound transducer, a high power signal is required. Multilevel converters are usually applied to generate a high power signal but the drawback of this signal is low quality in comparison with a sinusoidal signal. In some applications like ultrasound, it is extensively important to generate a high quality signal. Several control and modulation techniques are introduced in different papers to control the output voltage of the multilevel converters. One of those techniques is harmonic elimination technique. In this technique, switching angles are chosen in such way to reduce harmonic contents in the output side. It is undeniable that increasing the number of the switching angles results in more harmonic reduction. But to have more switching angles, more output voltage levels are required which increase the number of components and cost of the converter. To improve the quality of the output voltage signal with no more components, a new harmonic elimination technique is proposed in this research. Based on this new technique, more variables (DC voltage levels and switching angles) are chosen to eliminate more low order harmonics compared to conventional harmonic elimination techniques. In conventional harmonic elimination method, DC voltage levels are same and only switching angles are calculated to eliminate harmonics. Therefore, the number of eliminated harmonic is limited by the number of switching cycles. In the proposed modulation technique, the switching angles and the DC voltage levels are calculated off-line to eliminate more harmonics. Therefore, the DC voltage levels are not equal and should be regulated. To achieve this aim, a DC/DC converter is applied to adjust the DC link voltages with several capacitors. The effect of the new harmonic elimination technique on the output quality of several single phase multilevel converters is explained in chapter 3 and 6 of this thesis.
According to the electrical model of high power ultrasound transducer, this device can be modelled as parallel combinations of RLC legs with a main capacitor. The impedance diagram of the transducer in frequency domain shows it has capacitive characteristics in almost all frequencies. Therefore, using a voltage source converter to drive a high power ultrasound transducer can create significant leakage current through the transducer. It happens due to significant voltage stress (dv/dt) across the transducer. To remedy this problem, LC filters are applied in some applications. For some applications such as ultrasound, using a LC filter can deteriorate the performance of the transducer by changing its characteristics and displacing the resonance frequency of the transducer. For such a case a current source converter could be a suitable choice to overcome this problem. In this regard, a current source converter is implemented and applied to excite the high power ultrasound transducer. To control the output current and voltage, a hysteresis control and unipolar modulation are used respectively. The results of this test are explained in chapter 7.
46
Tan, Jiak-San. "Flexibility in MLVR-VSC back-to-back link." Thesis, University of Canterbury. Electrical and Computer Engineering, 2006. http://hdl.handle.net/10092/1119.
Full textAbstract:
This thesis describes the flexible voltage control of a multi-level-voltage-reinjection voltage source converter. The main purposes are to achieve reactive power generation flexibility when applied for HVdc transmission systems, reduce dynamic voltage balancing for direct series connected switches and an improvement of high power converter efficiency and reliability. Waveform shapes and the impact on ac harmonics caused by the modulation process are studied in detail. A configuration is proposed embracing concepts of multi level, soft-switching and harmonic cancellation. For the configuration, the firing sequence, waveform analysis, steady-state and dynamic performances and close-loop control strategies are presented. In order not to severely compromise the original advantages of the converter, the modulated waveforms are proposed based on the restrictions imposed mathematically by the harmonic cancellation concept and practically by the synthesis circuit complexity and high switching losses. The harmonic impact on the ac power system prompted by the modulation process is studied from idealistic and practical aspects. The circuit topology being proposed in this thesis is developed from a 12-pulse bridge and a converter used classically for inverting power from separated dc sources. Switching functions are deduced and current paths through the converter are analysed. Safe and steady-state operating regions of the converter are studied in phasor diagrams to facilitate the design of simple controllers for active power transfer and reactive power generations. An investigation into the application of this topology to the back-to-back VSC HVdc interconnection is preformed via EMTDC simulations.
47
Jimenez, Saldana Cristhian Carim. "Large Scale Analysis of Massive Deployment of Converter-based Generation equipped with Grid- forming Strategies." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-292690.
Full textAbstract:
To mitigate the carbon footprint and the need to fulfil the energy goals in terms of sustainability, it is required to deploy a large integration of green energies. Therefore, in the previous and the coming years, there will be a high research and technological interest in the high penetration of converter-based generation. With the replacement and integration of power converters into the bulk power grid, new challenges and issues must be faced to maintain the system´s stability and reliability in terms of procedures for the transmission system operators. The main objective of this thesis project is to analyze and to implement the current- limiting techniques implemented in voltage source converters, which are equipped with grid-forming functionalities so that these electronic devices are safeguarded during a severe transient event as three-phase short-circuit and remain connected to the grid during the fault scenario. The model of the voltage source converter with grid-forming strategies is described as well as the grid-forming strategies (droop control, virtual synchronous machine (VSM) and dispatchable virtual oscillator control (dVOC)) utilized in the outer loop. The low-inertia and zero-inertia system in the IEEE 9-Bus test system were exhibited to be resilient towards 3-phase fault events, and their behavior shows neither significant oscillations during and after the incident of the fault nor noticeable difference in their performance regarding the location. In this test system model, the current-limiting techniques were validated and analyzed results display good effectiveness for the current and frequency. The Hydro-Québec network model was employed to have a more practical approach in the behavior of the current limitation strategies in the power converters in a real power system. The fault location and the percentage of participation of the voltage source converters in the energy generation were the two main scenarios, in which the proposed control strategies for restricting the current work but simultaneously, it is required an appropriate control to keep the system´s stability.För att minska koldioxidutsläppet och uppnå energimålen med avseende på hållbarhet krävs integrering av hållbara energikällor. Därmed, under de föregående och kommande åren kommer stort fokus riktas mot forskning kring ökad penetration av kraftelektronikomriktare i kraftsystemet. När kraftelektronikomriktare ersätter traditionella generationsenheter uppkommer nya utmaningar och problem som behöver lösas för att upprätthålla systemets stabilitet och pålitlighet med avseende på tillvägagångssätt för systemansvariga för överföringssystemet. Avhandlingens huvudmål är att analysera och implementera strömbegränsande metoder för kraftelektronikomriktare av typen voltage source converters med en nätformande (”grid- forming”) funktionalitet. Strömbegränsaren ska säkerställa att kraftelektronikomriktaren skyddas under allvarliga transienta händelser och att kraftelektronikomriktaren förblir ansluten till nätet under händelsen. Modellen av kraftelektronikomriktaren med nätformande egenskaper är beskrivna tillsammans med nätformande kontrollstrategier, virtuella synkronmaskniner (VSM) och användande av avsändande virtuell oscillerande kontroll i den yttre slingan. Den låga trögheten och noll-tröghetssystemet i IEEE 9-Bus test-system visade sig vara motståndskraftig mot trefasfel eftersom testsystemets beteende visade varken signifikanta oscillationer under och efter felet eller märkbar förändring i dess prestanda beroende på var felet inträffade. I denna testsystemsmodell var strömbegränsande tekniker validerade och de analyserande resultaten visade på god effektivitet för strömmen och för frekvensen. Hydro-Québec nätverks-modellen användes för att få en mer praktisk inriktning med hänsyn till beteendet hos strömbegränsarna där olika strategier har använts. Felpositionen och andelen av kraftelektronikomriktare i energigenereringen var två huvudsakliga scenarion, där de föreslagna kontrollstrategierna för att begränsa strömmen fungerade men kräver samtidigt att en lämplig kontroll för att behålla systemets stabilitet.
48
Macík, Tomáš. "Model trojfázové umělé sítě." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2020. http://www.nusl.cz/ntk/nusl-413220.
Full textAbstract:
The Diploma thesis deals with control of three-phase active rectifier and a three-phase DC/AC converter. It also explains phase-locked loop principle. The theoretical part including first three chapters lists several control approaches to three phase active rectifier and three phase DC/AC converter. Described control approaches to the active rectifier are control in dq frame and control in dq UVW frame. Listed control approaches to the DC/AC converter include cascaded control structure and a full state feedback control. The practical part is divided into last three chapters and includes mathematical description of phase-locked loop principle, model of active rectifier controlled in dq frame and a model of DC/AC converter controlled both by a cascaded control and a full¬ state feedback. The models are created in Matlab Simulink.
49
Boulanger, Isabelle. "Lillgrund Wind Farm Modelling and Reactive Power Control." Thesis, KTH, Elektriska energisystem, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-119256.
Full textAbstract:
The installation of wind power plant has significantly increased since several years due to the recent necessity of creating renewable and clean energy sources. Before the accomplishment of a wind power project many pre-studies are required in order to verify the possibility of integrating a wind power plant in the electrical network. The creation of models in different software and their simulation can bring the insurance of a secure operation that meets the numerous requirements imposed by the electrical system. Hence, this Master thesis work consists in the creation of a wind turbine model. This model represents the turbines installed at Lillgrund wind farm, the biggest wind power plant in Sweden. The objectives of this project are to first develop an accurate model of the wind turbines installed at Lillgrund wind farm and further to use it in different kinds of simulations. Those simulations test the wind turbine operating according to different control modes. Also, a power quality analysis is carried out studying in particular two power quality phenomena, namely, the response to voltage sags and the harmonic distortion. The model is created in the software PSCAD that enables the dynamic and static simulations of electromagnetic and electromechanical systems. The model of the wind turbine contains the electrical machine, the power electronics (converters), and the controls of the wind turbine. Especially, three different control modes, e.g., voltage control, reactive power control and power factor control, are implemented, tested and compared. The model is tested according to different cases of voltage sag and the study verifies the fault-ride through capability of the turbine. Moreover, a harmonics analysis is done. Eventually the work concludes about two power quality parameters.
50
Ahmadi, Seyedhesam, and Mehrdad Bahmani. "Reglering av effektflöde i HVDC-system genom centraliserad och distribuerad spänningskontroll i realtid." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-254267.
Full textAbstract:
“High voltage direct current” (HVDC) teknologi har blivit allt viktigare teknik för att integrera förnybara energikällor i elnätet. För att styra ett sådant elsystem på bästa möjliga sätt krävs optimala kontrollstatergier både för omvandlarna och nätet. Så syftet med detta projekt är att undersöka hur olika regleringsmetoder, såsom centraliseradoch distribuerad spänningskontroll, kan påverka driften i ett 4-terminal HVDC-system. Ett optimalt effektflöde uppstår i systemet endast när likspänningen inte avviker från sitt börvärde och det uppnås genom att ha aktiv effekt regulator i varje nod i nätet. Olika scenarier som ändring av effektens börvärde och omvandlaravbrott har simulerats med hjälp av HIL-processen i realtid. Simuleringarna hjälper till att analysera hur väl dem implementerade regleringsmetoder i nodernas regulatorer hantera dessa förändringar. Resultatet ger bevis på att både centraliseradoch distruebued metoden har positiva och negativa aspekter. Fördelen med centraliserade metoden är att den ger en väldefinierad operationspunkt men den hanterar den inte svåra transienter (tex. avbrott) vilket distribuerade metoden gör.