Dissertations / Theses: 'Three Phase Load Unbalance'

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Ye, Zhihong. "Modeling and Control of Parallel Three-Phase PWM Converters." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/29476.

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This dissertation studies modeling and control issues of parallel three-phase pulse-width modulated (PWM) converters. The converters include three-phase boost rectifiers, voltage source inverters, buck rectifiers and current source inverters. The averaging of the parallel converters is performed based on a generic functional switching unit, which is called a phase leg in boost rectifiers and voltage source inverters, and a rail arm in buck rectifiers and current source inverters. Based on phase-leg and rail-arm averaging, the developed models are not only equivalent to the conventional three-phase converter models that are based on phase-to-phase averaging, but they also preserve common-mode information, which is critical in the analysis of the parallel converters. The models reveal such parallel dynamics as reactive power circulation and small-signal interaction. A unique feature of the parallel three-phase converters is a zero-sequence circulating current. This work proposes a novel zero-sequence control concept that uses variable zero-vectors in the space-vector modulation (SVM) of the converters. The control can be implemented within an individual converter and is independent from the other control loops for the converter. Therefore, it greatly facilitates the design and expansion of a parallel system. Proper operation of the parallel converters requires an explicit load-sharing mechanism. In order to have a modular design, a droop method is recommended. Traditionally, however, a droop method has to compromise between voltage regulation and load sharing. After parametric analysis, a novel droop method using a gain-scheduling technique is proposed. The numeric analysis shows that the proposed droop method can achieve both good voltage regulation and good load sharing. An interleaving technique is often used in parallel converter systems in order to reduce current ripples. Because of its symmetrical circuit structure, the parallel three-phase converter system can reduce both differential-mode and common-mode noise with a center-aligned symmetrical SVM. Based on the concept that a symmetrical circuit can reduce common-mode dv/dt noise, a conventional three-phase, four-leg inverter is modified so that its fourth leg is symmetrical to the other three legs. The common-mode dv/dt noise can be practically eliminated with a new modulation strategy. Meanwhile, with a modified control design, the new four-leg inverter still can handle low-frequency common-mode components that occur due to unbalanced and nonlinear load. Ph. D.

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Li, Yun. "Voltage balancing on three-phase low voltage feeder." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/voltage-balancing-on-threephase-low-voltage-feeder(4320ec9a-f287-4e83-86fd-c8e29e8d49f4).html.

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Voltage imbalance in low voltage (LV) networks is expected to deteriorate as low carbon technologies, e.g. electric vehicles (EVs) and heat pumps (HPs) are increasingly deployed. The new electrical demand attributable to EVs and HPs would increase the voltage magnitude variation, increasing the possibility of voltages moving outside the statutory LV magnitude limits. Moreover, the single-phase nature of EVs and HPs, which will be connected via a single-phase 'line & neutral' cable to a 3-phase four-wire LV mains cable buried beneath the street, further entangles this voltage management problem; the non-balanced voltage variations in the three phases boost the levels of voltage imbalance. Excessive voltage imbalance and magnitude variation need to be mitigated to limit their adverse effects on the electric network and connected plant. The voltage imbalance in LV networks is conventionally reduced by reinforcing the network, generally at a high cost. Some modern methods for voltage imbalance mitigation have been introduced in recent years. The power electronic converter based methods are inadequate due to the generation of harmonics, significant power losses and short lifetime. Besides, automatic supply phase selection and smart EV charging rely on an advanced smart communication system, which currently is not available. This project aims to develop alternative solutions that mitigate the voltage imbalance seen in LV networks. A voltage balancing method based on Scott transformer (ST) is proposed. This method does not generate harmonics and is independent of the smart communication system. Computer simulations demonstrated the proposed method is able to convert a non-balanced 3-phase voltage into a balanced 3-phase voltage at either a point on the LV feeder or a 3-phase load supply point with the predefined voltage magnitude. Besides, a physical voltage balancing system was created based on the proposed method and it was tested in an LV network in the laboratory. The test results show the balancing system is capable of maintaining a low level of voltage imbalance on the LV feeder by rapidly compensating for the voltage rises and sags caused by single-phase load variations. This voltage balancing method is a potential solution for the network utilities to accommodate the significant penetration of low carbon technologies without breaching the network voltage limits. The impact of EVs and HPs on the LV network voltages is investigated based on a Monte Carlo (MC) simulation platform, which comprises a statistical model of EV charging demand, profiles generators of residential and HP electrical demand, and a distribution network model. The MC simulation indicates the impact of EVs and HPs is related to their distribution; when more than 21EVs and 13HPs are non-evenly distributed on a 96-customer LV feeder, the voltage limits are likely to be violated. Moreover, the effectiveness of the ST based voltage balancing method and the demand response based TOU tariff, implemented either alone or together, in mitigating the impact of EVs and HPs is investigated based on the established MC simulation platform. The results indicate the ST based balancing method alone is able to completely mitigate the voltage limit violations regardless of the penetration levels of EVs and HPs. Moreover, using both of the two investigated methods further enhances the balancing effectiveness of the ST based voltage balancing method.

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Singh, Bhanu Pratap. "Real-time detection of stator resistance unbalances in three phase drives." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-286813.

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An estimated 30% of the faults in Induction Machine (IM) are related to its stator. These faults are mostly in the form of an Inter-Turn Short Circuit (ITSC) fault i.e., when two winding inside the stator of IM are shorted due to insulation failure. However, ITSC fault can be avoided by detecting them in advance and then scheduling the maintenance of the IM. This thesis studies two methods for detecting this incipient ITSC fault in a three-phase IM and then estimating the stator resistance unbalance due to the ITSC fault. The first method is based on the asymmetry caused in the IM by the ITSC fault. As a result of this asymmetry, the negative sequence components of the stator voltages and the stator currents are generated inside the IM. A healthy IM also have these negative sequence components due to the manufacturing process and the supply voltage unbalances. The characteristics and the compensation methods of these negative sequence components in a healthy IM are discussed. The results show that after compensating the negative sequence components in a healthy machine, they can be used for detecting an ITSC fault and then to calculate the fault quantities as well as the stator resistance unbalances. The second method for detecting an ITSC fault is based on analysing the stator resistance unbalances. A three-phase drive is used to inject DC voltage in the stationary reference frame. The DC current generated by this DC voltage is measured and then by applying Ohm’s law stator phase resistances are calculated. In a healthy IM, the phase resistances are balanced. However, in case of ITSC fault in any of the phases, the phase resistance of that phase deviates from those of the other two phases which can be utilized for detecting ITSC fault. Uppskattningsvis 30% av alla fel i induktionsmaskiner (IM) är kopplad till dess stator. Dessa fel är i huvudsak Inter-Turn Short Circuit (ITSC)-fel, dvs. två lindningar inom IM:ens stator blir kortsluta pga. ett isoleringsfel. Emellertid kan man undvika ITSC-fel genom att detektera dem i förhand och planera underhåll. Det här examensarbetet undersöker två metoder för att detektera ett förestående ITSC-fel i en tre-fas IM. Den första metoden är baserad på asymmetrin i IM:er pga. ITSC-felet. Resultatet av den här asymmetrin är att en negativ sekvens genereras i IM:ens statorspänning och statorström. En oskadad IM kan också visa dessa negativa sekvenser pga. tillverksprocessen och statorspänningsobalanser. Egenskaperna och kompensationsmetoderna för dessa negativa sekvenser i en oskadad IM kommer att diskuteras. Resultaten visar att efter kompenseringen av de negativa sekvenserna i en oskadad IM, kan de användas för att detektera ITSC-fel och efteråt för att beräkna felstorheter och även statormotståndobalanser. Den andra metoden för att detektera ITSC-fel är baserad på en undersökning av statormotståndobalanser. Ett tre-fas-drivsystem används för att injektera likspänning i den stationära referensramen. Likströmmen som följer av denna likspänning mäts och statorfasmotstånden beräkna efteråt med Ohms lag. I en oskadad IM är fasmotstånden balanserade. Däremot, när ett ITSC-fel uppstår i en fas, avviker fasmotståndet i den felaktiga fasen från de andra två fasernas, vilket kan användas för att detektera ITSC-fel.

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Yao, Xiao Guang. "Investigation of the no-load performance of a model three-phase three-limb laminated transformer core operating under sinusoidal and PWM voltage excitation." Thesis, Cardiff University, 2010. http://orca.cf.ac.uk/54939/.

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Transformers subjected to PWM voltage excitation are becoming more and more common in industrial applications and renewable energy supply systems. Therefore, the assessment and improvement in the performance of transformer cores under PWM voltage excitation have become prominent. This project intends to characterise the no-load performance, total power loss and acoustic noise level, of a model three-phase, three-limb laminated transformer core, operating under sinusoidal and PWM voltage excitation. Measurements of total power losses and localised flux density in the joint regions of the core under sinusoidal and PWM voltage excitation for assigned modulation index ma with switching frequency fs varied from 1 kHz to 3 kHz, has been carried out. The analysis highlights the form factor Kf of the secondary induced voltage as a key parameter in controlling the performance of eddy-current component loss in the core. The estimate localised rotational losses due to rotating flux and planar eddy-current losses due to normal flux density in the joints have been analysed, also the analysis of measurement results contributes towards a better understanding of the influence of ma and fs. Moreover, the acoustic noise level of the core and the corresponding vibration at investigated points on the core surface has been measured under sinusoidal and PWM voltage excitation. Measurement results show that the values of acoustic noise and core vibration under PWM voltage excitation were much higher than under corresponding sinusoidal voltage condition. Also, the magneto-mechanical resonant phenomenon of the core under PWM voltage excitation has been observed, which was due to switching frequency fs close to the resonance vibration frequency of the core laminations that is a possible cause of increasing acoustic noise. The measurement results inferred that the resonant phenomenon could possibly occur in cores with different length laminations leading to variability of noise output according to how close the magnetising frequency or predominant harmonics are to the resonant frequency.

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Zhong, Shan. "Measurement calibration/tuning & topology processing in power system state estimation." Texas A&M University, 2003. http://hdl.handle.net/1969.1/1595.

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State estimation plays an important role in modern power systems. The errors in the telemetered measurements and the connectivity information of the network will greatly contaminate the estimated system state. This dissertation provides solutions to suppress the influences of these errors. A two-stage state estimation algorithm has been utilized in topology error identification in the past decade. Chapter II discusses the implementation of this algorithm. A concise substation model is defined for this purpose. A friendly user interface that incorporates the two-stage algorithm into the conventional state estimator is developed. The performances of the two-stage state estimation algorithms rely on accurate determination of suspect substations. A comprehensive identification procedure is described in chapter III. In order to evaluate the proposed procedure, a topology error library is created. Several identification methods are comparatively tested using this library. A remote measurement calibration method is presented in chapter IV. The un-calibrated quantities can be related to the true values by the characteristic functions. The conventional state estimation algorithm is modified to include the parameters of these functions. Hence they can be estimated along with the system state variables and used to calibrate the measurements. The measurements taken at different time instants are utilized to minimize the influence of the random errors. A method for auto tuning of measurement weights in state estimation is described in chapter V. Two alternative ways to estimate the measurement random error variances are discussed. They are both tested on simulation data generated based on IEEE systems. Their performances are compared. A comprehensive solution, which contains an initialization process and a recursively updating process, is presented. Chapter VI investigates the errors introduced in the positive sequence state estimation due to the usual assumptions of having fully balanced bus loads/generations and continuously transposed transmission lines. Several tests are conducted using different assumptions regarding the availability of single and multi-phase measurements. It is demonstrated that incomplete metering of three-phase system quantities may lead to significant errors in the positive sequence state estimates for certain cases. A novel sequence domain three-phase state estimation algorithm is proposed to solve this problem.

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Zadeh, Ramin Agha. "Performance control of distributed generation using digital estimation of signal parameters." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/47011/1/Ramin_Agha_Zadeh_Thesis.pdf.

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The Queensland University of Technology (QUT) allows the presentation of a thesis for the Degree of Doctor of Philosophy in the format of published or submitted papers, where such papers have been published, accepted or submitted during the period of candidature. This thesis is composed of seven published/submitted papers, of which one has been published, three accepted for publication and the other three are under review. This project is financially supported by an Australian Research Council (ARC) Discovery Grant with the aim of proposing strategies for the performance control of Distributed Generation (DG) system with digital estimation of power system signal parameters. Distributed Generation (DG) has been recently introduced as a new concept for the generation of power and the enhancement of conventionally produced electricity. Global warming issue calls for renewable energy resources in electricity production. Distributed generation based on solar energy (photovoltaic and solar thermal), wind, biomass, mini-hydro along with use of fuel cell and micro turbine will gain substantial momentum in the near future. Technically, DG can be a viable solution for the issue of the integration of renewable or non-conventional energy resources. Basically, DG sources can be connected to local power system through power electronic devices, i.e. inverters or ac-ac converters. The interconnection of DG systems to power system as a compensator or a power source with high quality performance is the main aim of this study. Source and load unbalance, load non-linearity, interharmonic distortion, supply voltage distortion, distortion at the point of common coupling in weak source cases, source current power factor, and synchronism of generated currents or voltages are the issues of concern. The interconnection of DG sources shall be carried out by using power electronics switching devices that inject high frequency components rather than the desired current. Also, noise and harmonic distortions can impact the performance of the control strategies. To be able to mitigate the negative effect of high frequency and harmonic as well as noise distortion to achieve satisfactory performance of DG systems, new methods of signal parameter estimation have been proposed in this thesis. These methods are based on processing the digital samples of power system signals. Thus, proposing advanced techniques for the digital estimation of signal parameters and methods for the generation of DG reference currents using the estimates provided is the targeted scope of this thesis. An introduction to this research – including a description of the research problem, the literature review and an account of the research progress linking the research papers – is presented in Chapter 1. One of the main parameters of a power system signal is its frequency. Phasor Measurement (PM) technique is one of the renowned and advanced techniques used for the estimation of power system frequency. Chapter 2 focuses on an in-depth analysis conducted on the PM technique to reveal its strengths and drawbacks. The analysis will be followed by a new technique proposed to enhance the speed of the PM technique while the input signal is free of even-order harmonics. The other techniques proposed in this thesis as the novel ones will be compared with the PM technique comprehensively studied in Chapter 2. An algorithm based on the concept of Kalman filtering is proposed in Chapter 3. The algorithm is intended to estimate signal parameters like amplitude, frequency and phase angle in the online mode. The Kalman filter is modified to operate on the output signal of a Finite Impulse Response (FIR) filter designed by a plain summation. The frequency estimation unit is independent from the Kalman filter and uses the samples refined by the FIR filter. The frequency estimated is given to the Kalman filter to be used in building the transition matrices. The initial settings for the modified Kalman filter are obtained through a trial and error exercise. Another algorithm again based on the concept of Kalman filtering is proposed in Chapter 4 for the estimation of signal parameters. The Kalman filter is also modified to operate on the output signal of the same FIR filter explained above. Nevertheless, the frequency estimation unit, unlike the one proposed in Chapter 3, is not segregated and it interacts with the Kalman filter. The frequency estimated is given to the Kalman filter and other parameters such as the amplitudes and phase angles estimated by the Kalman filter is taken to the frequency estimation unit. Chapter 5 proposes another algorithm based on the concept of Kalman filtering. This time, the state parameters are obtained through matrix arrangements where the noise level is reduced on the sample vector. The purified state vector is used to obtain a new measurement vector for a basic Kalman filter applied. The Kalman filter used has similar structure to a basic Kalman filter except the initial settings are computed through an extensive math-work with regards to the matrix arrangement utilized. Chapter 6 proposes another algorithm based on the concept of Kalman filtering similar to that of Chapter 3. However, this time the initial settings required for the better performance of the modified Kalman filter are calculated instead of being guessed by trial and error exercises. The simulations results for the parameters of signal estimated are enhanced due to the correct settings applied. Moreover, an enhanced Least Error Square (LES) technique is proposed to take on the estimation when a critical transient is detected in the input signal. In fact, some large, sudden changes in the parameters of the signal at these critical transients are not very well tracked by Kalman filtering. However, the proposed LES technique is found to be much faster in tracking these changes. Therefore, an appropriate combination of the LES and modified Kalman filtering is proposed in Chapter 6. Also, this time the ability of the proposed algorithm is verified on the real data obtained from a prototype test object. Chapter 7 proposes the other algorithm based on the concept of Kalman filtering similar to those of Chapter 3 and 6. However, this time an optimal digital filter is designed instead of the simple summation FIR filter. New initial settings for the modified Kalman filter are calculated based on the coefficients of the digital filter applied. Also, the ability of the proposed algorithm is verified on the real data obtained from a prototype test object. Chapter 8 uses the estimation algorithm proposed in Chapter 7 for the interconnection scheme of a DG to power network. Robust estimates of the signal amplitudes and phase angles obtained by the estimation approach are used in the reference generation of the compensation scheme. Several simulation tests provided in this chapter show that the proposed scheme can very well handle the source and load unbalance, load non-linearity, interharmonic distortion, supply voltage distortion, and synchronism of generated currents or voltages. The purposed compensation scheme also prevents distortion in voltage at the point of common coupling in weak source cases, balances the source currents, and makes the supply side power factor a desired value.

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Galdino, Francisco Clebson Sousa. "Análise de de sistemas de distribuição com modelagem de geradores eólio-elétricos dos tipos I, II e IV." Universidade Federal Rural do Semi-Árido, 2015. http://bdtd.ufersa.edu.br:80/tede/handle/tede/531.

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Made available in DSpace on 2016-08-31T13:33:43Z (GMT). No. of bitstreams: 1 FranciscoCSG_DISSERT.pdf: 1707836 bytes, checksum: f3a5558058650f68e08a82541000dc7b (MD5) Previous issue date: 2015-06-05 In power distribution systems are the major causes of voltage imbalances, variations in single-phase loads cause the currents in the conductors of the three phases is different, resulting in different voltage drops, causing imbalance. The study of voltage imbalances in the distribution of energy is very important, since the proper functioning of equipment connected to the system is directly related to the mains imbalance factor. When it comes to stress profiles, has become one of the biggest challenges of electric utilities, which is to serve consumers and customers with adequate voltage levels to those required in current legislation in Brazil has the 2001 resolution no. 505 ANEEL (National Electric Energy Agency) stating that the voltage to be contracted with the utility or the ONS should be between 95% (0.95 pu) and 105% (1.05 pu) of the nominal operating voltage system at the delivery point. In relation to electrical losses, although not established limits by law, these are an important economic factor for electric utilities, seeking to reduce them to maximize their profits. When it comes to connecting wind turbines to the distribution systems is not aware of scholarly conducting parallel operating conditions of the various components that operate in this plan when they are working together with the different configurations of wind generators. The objective of this study is to analyze the imbalances problem, tensions profiles and electrical losses in distribution systems by various operating situations, especially with the inclusion of wind turbines type I, II and IV, based on the system 13 bars IEEE. Also, are proposed and simulated some ways to reduce imbalances and losses through the use of engineering techniques: as promoting the balancing system loads, connecting wind farms to the distribution feeder, installing banks of single-phase voltage regulators at substations and correcting the power factor of the generator turbines. Technical proposals to reduce the levels of network imbalance are effective and also influenced the reduction of overall system losses and improve the levels of stress profiles and are therefore measures that may contribute to the proper functioning of a power system Nos sistemas de distribuição de energia elétrica se encontram as maiores causas dos desequilíbrios de tensão, variações nas cargas monofásicas fazem com que as correntes nos condutores das três fases sejam diferentes, o que resulta em quedas de tensões diferentes, provocando desequilíbrio. O estudo de desequilíbrios de tensão na distribuição de energia é muito importante, uma vez que o bom funcionamento de equipamentos ligados ao sistema está diretamente relacionado ao fator de desequilíbrio da rede elétrica. Quando se trata de perfis de tensões, tem-se um dos maiores desafios das concessionárias de energia elétrica, que é atender os consumidores e clientes com níveis de tensão adequados aos exigidos na legislação vigente, no Brasil tem-se a resolução de 2001 nº 505 da ANEEL (Agência Nacional de Energia Elétrica) estabelecendo que a tensão a ser contratada com a concessionária ou com o ONS deve situar-se entre 95% (0,95 p.u) e 105% (1,05 p.u) da tensão nominal de operação do sistema no ponto de entrega. Já com relação às perdas elétricas, apesar de não serem estabelecidos limites pela legislação vigente, estas são um importante fator econômico para as concessionárias de energia elétrica, que buscam diminuí-las para maximizar seus lucros. Quando se trata de conexão de turbinas eólicas nos sistemas de distribuição não se tem conhecimento de trabalhos acadêmicos que realizam um paralelo das condições de operação dos diversos componentes que atuam nesse plano quando os mesmos estão atuando juntamente com as diferentes configurações de geradores eólicos. O objetivo deste trabalho é analisar o problema de desequilíbrios, perfis de tensões e das perdas elétricas em sistemas de distribuição mediante diversas situações de operação, principalmente com a inserção de turbinas eólicas tipo I, II e IV, tomando como base o sistema 13 barras do orgão IEEE. Além disso, são propostas e simuladas algumas maneiras de reduzir os desequilíbrios e perdas através do uso de técnicas de engenharia: como promovendo o balanceamento de cargas do sistema, conectando parques eólicos ao alimentador de distribuição, instalando bancos de reguladores de tensão monofásicos em subestações e corrigindo o fator de potência dos geradores das turbinas. As técnicas propostas para reduzir os graus de desequilíbrio da rede se mostraram eficazes e influenciaram também na redução das perdas globais do sistema e melhora dos níveis de perfis de tensões, sendo portanto medidas que podem contribuir para o bom funcionamento de um sistema de energia elétrica

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Carvalho, Hamilton Dias de. "Avaliação de desempenho do gerador de indução trifásico assimétrico conectado a uma rede monofásica - aplicações rurais." Universidade Federal de Uberlândia, 2006. https://repositorio.ufu.br/handle/123456789/14635.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior This work has for motive to obtain the project and build of an assymmetrical three-phase induction generator connected to single-phase supply system, in order to be used in rural areas. This equipment has been presented as a better alternative in relation the others proposed more commercialized at the moment, due to its robustness, low cost, less maintenance requirements and excellent performance. Firstly, in the theoric part concerned to the system it is presented a mathematical representation, frequency domain mathematical model, whose equations are performed in function of an unbalance factor in order to obtain balance three-phase voltages in the system. Then, some simulations are performed in the simulator that was developed in the Microsoft Excel program. From these implements, it is carried out study cases to prove the assymmetrical three-phase induction generator use potentialities. A prototype is projected and built, which experimental results are compared to the computer result. O objetivo deste trabalho é obter o projeto e a construção de um gerador de indução trifásico assimétrico conectado a um sistema de distribuição de energia elétrica monofásica; visando aplicá-lo em áreas rurais. Este dispositivo, em face de sua robustez, baixo custo, menores requisitos de manutenção e bom desempenho, consiste numa alternativa bastante atrativa em relação às outras propostas existentes atualmente. O estudo teórico inicia-se através da elaboração de uma modelagem matemática para o sistema, no domínio da freqüência, cujas equações são colocadas em função de um fator indicativo do nível de desbalanceamento, visando à obtenção de tensões balanceadas na carga. Para tanto, a modelagem matemática elaborada é implementada num simulador desenvolvido no programa Microsoft Excel. A partir desta implementação, são efetuados estudos de casos no sentido de evidenciar as potencialidades do gerador assimétrico conectado a cargas rurais. Os trabalhos computacionais são devidamente validados à luz de resultados experimentais extraídos de um protótipo de equipamento concebido, projetado e construído para fins deste trabalho. Mestre em Ciências

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Carrander, Claes. "Magnetizing Currents in Power Transformers : Measurements, Simulations, and Diagnostic Methods." Doctoral thesis, KTH, Elektroteknisk teori och konstruktion, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-208422.

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This thesis demonstrates a method for transformer core diagnostics. The method uses the no-load current of the transformer as an indicator, and gives different characteristic signatures for different types of faults or defects. Using the no-load current for the diagnostic gives high sensitivity. The method is therefore able to detect defects that are too small to have an impact on the losses. In addition to different types of fault, the method can in some cases also distinguish between faults in different locations within the core. Both single-phase and three-phase transformers can be diagnosed using this method, and the measurements can be easily performed at any facility capable of measuring the no-load loss. There are, however, some phenomena that occur in large transformers, and in transformers with high rated voltages. Examples include capacitive resonance and magnetic remanence. This thesis proposes and demonstrates techniques for compensating for these phenomena. With these compensating techniques, the repeatability of the measurements is high. It is shown that units with the same core steel tend to have very similar no-load behavior. The diagnostics can then be performed either by comparing the transformer to another unit, or to simulations. The thesis presents one possible simulation method, and demonstrates the agreement with measurements. This topological simulation method includes both the electric circuit and an accurate model of the magnetic hysteresis. It is therefore also suitable for other, related, studies in addition to core diagnostics. Possible subjects include ferroresonance, inrush, DC magnetization of transformers, and transformer core optimization. The thesis also demonstrates that, for three-phase transformers, it is possible to compare the phases to each other. This technique makes it possible to diagnose a transformer even without a previous measurement to compare to, and without the data required to make a simulation. QC 20170607

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Louganski, Konstantin P. "Modeling and Analysis of a Dc Power Distribution System in 21st Century Airlifters." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/35514.

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A DC power distribution system (PDS) of a transport aircraft was modeled and analyzed using MATLAB/Simulink software. The multi-level modeling concept was used as a modeling approach, which assumes modeling subsystem of the PDS at three different levels of complexity. The subsystem models were implemented in Simulink and combined into the whole PDS model according to certain interconnection rules. Effective modeling of different scenarios of operation was achieved by mixing subsystem models of different levels in one PDS model. Linearized models were obtained from the nonlinear PDS model for stability analysis and control design. The PDS model was used to examine the system stability and the DC bus power quality under bidirectional power flow conditions. Small-signal analysis techniques were employed to study stability issues resulting from subsystem interactions. The DC bus stability diagram was proposed for predicting stability of the PDS with different types of loads without performing an actual stability test based on regular stability analysis tools. Certain PDS configurations and operational scenarios leading to instability were identified. An analysis of energy transfer in the PDS showed that a large energy storage capacitor in the input filter of a flight control actuator is effective for reduction of the DC bus voltage disturbances produced by regenerative action of the actuator. However, energy storage capacitors do not provide energy savings in the PDS and do not increase its overall efficiency. Master of Science

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Avelino, Luana Locatelli. "Estimação de demanda trifásica em tempo real para sistemas de distribuição radiais." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18154/tde-03082018-095459/.

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Os estimadores de estado são ferramentas primordiais para monitoramento em tempo real dos sistemas elétricos de potência, principalmente por permitir a execução de funções básicas relacionadas à segurança destes sistemas. No entanto, nos sistemas de distribuição, por possuírem uma série de particularidades e pelo reduzido número de medidas disponíveis em tempo real, os estimadores de estado convencionais desenvolvidos para sistemas de transmissão não são capazes de oferecer boas estimativas para determinação do estado da rede. Neste contexto, o Estimador de Demanda Trifásico em Tempo Real (EDTTR) desenvolvido neste trabalho, fundamentado nos métodos de estimação de demanda, tem como foco principal proporcionar maior precisão ao monitoramento da rede primária de alimentadores de distribuição radiais, ao contemplar as características intrínsecas do modelo da rede. O EDTTR consiste em dois estágios principais: o primeiro é caracterizado pela estimação off-line das demandas dos transformadores de distribuição por meio do processo de agregação de cargas, considerando informações dos consumidores. O segundo estágio é realizado em tempo real, utiliza um algoritmo eficiente de Varredura Direta Inversa para a solução do fluxo de carga, auxiliado da estrutura de dados chamada Representação Nó-Profundidade para armazenar a topologia da rede. Neste estágio também ocorre o ajuste recursivo das estimativas obtidas no Estágio 1 com base nas poucas medidas disponíveis em tempo real. No intuito de melhorar a representação da rede primária, o EDTTR desenvolvido possibilita o tratamento dos transformadores de distribuição conectados em Delta-Yn. Esta proposição permite uma caracterização do modelo das cargas mais fiel, sendo capaz de superar problemas de convergência, além de contribuir para a qualidade do processo de estimação. Desenvolveu-se, também, uma plataforma de testes que permite a análise do impacto de fatores que deterioram o processo de estimação de demandas, como: a má classificação dos consumidores, o comportamento dos mesmos, que na prática não é exatamente igual ao da classe de carga a ele atribuída, a possibilidade de perdas não técnicas, erros grosseiros e falhas de comunicação nos medidores do alimentador. O EDTTR foi validado em simulações utilizando um alimentador real da cidade de Ribeirão Preto com base em dados fornecidos pela distribuidora CPFL Paulista. The state estimators are primordial tools for electric power systems real time monitoring. These tools allow the execution of basic functions related to systems security. However, conventional state estimators, developed for transmission systems, can not provide good estimates to the state of distribution systems. This is due to two main factors, the few real time measures available in distribution systems, and the intrinsic complexity of them. In this context, the developed Real Time Three-Phase Load Estimator (EDTTR), based on load estimation methods, aims to provide better estimates to the monitoring of the primary network of radial distribution feeders, considering all the intrinsic sets of the system model. The EDTTR consists of two main stages: the first is characterized by the off-line load estimation of the distribution transformers by a load aggregation process, which uses consumers information as input data. In the second stage the off-line estimates obtained in Stage 1 are recursively refined in real-time basing on the available measurements. This procedure is executed by a computationally efficient backward/forward sweep load flow algorithm based on the data structure called Node-depth Encoding. The developed EDTTR allows the treatment of distribution transformers connected in Delta-Yn improving the primary network representation. A test platform is also developed that enables the analysis of the impact of factors that deteriorate the demand estimation process, such as the poor classification of consumers, the poor representativeness of the load class for certain consumers, the possibility of non-technical losses, and of gross errors and communication faults in the feeder meters. The developed EDTTR performance was tested in simulations that uses a real feeder from Ribeirão Preto city, based on system data provided by CPFL Paulista utility.

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Fantin, Camila dos Anjos. "Metodologia para estimação de estado trifásica em sistemas de distribuição incorporando medidas SCADA, virtuais, pseudo-medidas e medidas fasoriais sincronizadas." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18154/tde-01022017-150726/.

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Este trabalho propõe o desenvolvimento e implantação, em computador, de uma metodologia para tratamento de diversas etapas do processo de estimação de estado em Sistemas de Distribuição (SDs), que possibilite um tratamento adequado para as particularidades dos SDs no contexto atual (com poucas medidas disponíveis) e futuro (contando com mais medidas SCADA, com as Medidas Fasoriais Sincronizadas (MFSs) e com as avançadas infra-estruturas de medição), ou seja, que possibilite: análise de sistemas desbalanceados e desequilibrados, com ramais monofásicos, bifásicos e trifásicos; o tratamento de sistemas radiais e malhados sem perda de precisão; uma modelagem adequada dos componentes dos SDs, considerando as várias possibilidades de conexão dos transformadores e dos reguladores de tensão; o tratamento de diversos tipos de medidas (medidas convencionais obtidas pelo sistema SCADA, medidas virtuais, pseudo-medidas de carga e de dados históricos e MFSs), ponderando-as de acordo com as respectivas precisões. A metodologia proposta baseia-se no método dos mínimos quadrados ponderados, trabalha no nível dos alimentadores e compreende os seguintes quatro estágios: Estágio 1 geração de pseudo-medidas de carga; Estágio 2 - análise e restauração de observabilidade e identificação de medidas críticas; Estágio 3 - estimação de estado propriamente dita; e Estágio 4 - processamento de erros grosseiros. Tendo em vista as respostas coerentes das diversas simulações realizadas com os alimentadores de teste trifásicos de 4 e 34 barras do IEEE, demonstra-se satisfatoriamente a performance da metodologia proposta. This thesis proposes a multi-phase unbalanced distribution system (DS) state estimation methodology based on the weighted least squares technique, which allows: load pseudo-measurement modeling; observability analysis and restoration by selecting the required pseudo-measurements (load pseudo-measurements and/or historical measurement data); identication of critical measurements; state estimation; and, nally, gross errors processing. The proposed methodology intends to be a practical tool able to be applied to a variety of DSs, considering latest and future realities. Therefore, the proposed methodology has the following features: (i) includes all realistic DS modeling details, such as, various types of transformer and voltage regulator connections, the presence of single, two and three-phase circuits, as well as the possibility of both the mutual coupling between phases and the shunt susceptance; (ii) treat three-phase networks with high resistance/reactance ratios in a unied framework; and (iii) process measurements with very distinct qualities, some of them are real-time measurements provided by Supervisory Control Data Acquisition (SCADA) systems, Advanced Metering Infrastructure (AMI), Phasor Measurement Units (PMUs), other are virtual measurements (information provided by the buses of zero power injection) and also the pseudo-measurements (load pseudo-measurements, load proles and historical measurement data). Several simulations results (with IEEE 34 and 4 node test feeders) have demonstrated satisfactory performance of the proposed methodology.

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Guo, Wu-Yi, and 郭武義. "Transformer Load Regulation Strategy For Distribution Feeders Three Phase Unbalance." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/03059815618748867523.

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碩士 國立高雄應用科技大學 電機工程系碩士班 95 With the development of economic, the distribution system becomes more complex followed by the rapid load growth. Therefore the demand on high power quality and reliability have been concerned by customers. Providing stable power supply and better customer service are the main goal of Taipower company. Hence, the distribution engineer evolves a new methodology and technique to efficiently solve the problems related to power quality and operation performance. This paper proposes an artificial immune algorithm (AIA) based distribution transformer optimum phase connecting scheme to relief the feeder three-phase unbalance such that the more robust power supply can be achieved. In this thesis, an entire feeder load balance is defined as antibody as well as the objective function and the optimum distribution transformer phasing connection is defined as an antigen. In the AIA procedure, the affinity relationship among antigen group is applied to increase the diversity among antibody and the intimacy between antibody and antigen is used to avoid the local optimum solution such that the quick convergent speed and the global optimum solution can be achieved. Besides, in this thesis, the outage operation mapping system (OMS) and customer information system (CIS) are applied to evaluate hourly distribution transformers’ phase P/Q loading for three-phase load flow by considering the customer daily load patterns. Finally, a feeder located at kaohsiung district with the mixture of residential and commercial load customers is selected as a testing case for computer simulations. Results show that the proposed AIA can efficiently solve the feeder three-phase unbalance by deriving an optimum solution and the effectiveness and the practicality of the proposed method can be justified.

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Chu, Ching-Chung, and 朱進忠. "The justification of three phase load flow and the system unbalance reduction." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/36422642383034832959.

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碩士 大同工學院 電機工程研究所 81 The unbalance problem is getting more and more important, but at present there are not many three phase load flow programs used for analyzing the unbalanced system, and the assumptions and the models of those programs are not the same. In this thesis, the accuracy of the three load flow is verified by comparing with the field test data of ITRI (Industrial Technology Research Institute), and the system unbalance of ITRI is examined under some kinds of load combination. A process of deriving the model of the three phase induction motor adopted for the three phase load flow program is presented, and the unbalance effects of the different step down transformers connected with the motor are analyzed. By using this model, the analysis of distribution system can be more exact. Several methods which may alleviate the unbalance of the system is examined in this thesis by using the simulation results and mathematical derivation. It will provide information for the demand side customers while they are working on the system planning or plant operation.

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Che-WeiChang and 張哲瑋. "Study on Three-Phase Stand-Alone Power Inverter for Unbalance and Nonlinear Loads." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/73908575655025667537.

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碩士 國立成功大學 電機工程學系 102 To supply the modern electrical equipment, it is needed to develop an inverter that can compensate current harmonics with fast voltage response. However, due to the limited capability of the proportional and integral Controller (PI Controller) to deal with unbalance and nonlinear loading problems, this thesis introduces the proportional and resonant controller (PR Controller) for dealing with similar loading conditions. First, by analyzing the loading behavior and designing a cascaded PR controller, it improves the power quality of unbalance and nonlinear loadings. The contents of this thesis include modeling of a three-phase stand-alone inverter, derivation of the predictive current controller, and design procedure of the PR Controller. Tests of three different controllers (PI Controller, dual PR Controller, and Proportional and Resonant controller with Predictive Current Controller) are applied to the three-phase stand-alone system to show that the PR with PCC controller presents the best power quality performance compared with those of the counterparts.

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Lai, Yu-Kai, and 賴煜凱. "Intelligent Photovoltaic Power System with Three-Phase Unbalanced Load Current Compensation." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/uff69k.

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碩士 國立中央大學 電機工程學系 106 A improved method is proposed to compensate the three-phase unbalanced currents of power grid under three-phase unbalanced load for a two-stage photovoltaic (PV) power system without the augmentation of active power filter (APF). The PV power system is composed of an interleaved DC/DC converter and a three-level neutral-point clamped (NPC) inverter. Moreover, the PV power system possesses the smart inverter function, in which the output active and reactive powers of the PV inverter are predetermined by a power factor according to grid codes of the utilities. In the proposed method, -axis compensation currents are obtained through low pass filters (LPFs) to compensate the three-phase unbalanced currents of power grid. Furthermore, in order to improve the control performance of the DC bus voltage of the PV power system under unbalanced load variation condition, an online trained compensatory neural fuzzy network with an asymmetric membership function (CFNN-AMF) is proposed to replace the traditional proportional-integral (PI) controller for the DC bus voltage control. In the proposed CFNN-AMF, the compensatory parameter to integrate pessimistic and optimistic operations of fuzzy systems is embedded in the CFNN. In addition, the dimensions of the Gaussian membership functions are directly extended to AMFs. Additionally, the proposed controllers of the PV power system are implemented by two control platforms using floating-point digital signal processor (DSP). Finally, excellent compensation performance for the three-phase currents of power grid under three-phase unbalanced load can be achieved from the experimental results.

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Cheng, Kuang-Hsiung, and 鄭光雄. "Analyses of Three-Phase Self-Excited Induction Generator under unbalanced load conditions." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/b85w3y.

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碩士 崑山科技大學 電機工程研究所 92 This thesis analyses the steady-state and dynamic characteristics of a three-phase self excited induction generator (SEIG) under static loading conditions. This thesis employs eigenvalue and eigenvalue sensitivity to determine minimum values of excitation capacitance of the studied induction generator under different operating conditions. Since the examined induction generator is under either balanced or unbalanced three-phase conditions, five different operating modes, i.e., three phase load perturbation, three phase short circuit and fault clearing, line-to-line short circuit, single phase capacitor opening and load rejection, single-line opening at capacitor bank, are respectively investigated, the three-phase induction machine model based on q-d-0 variables in a stationary reference frame is employed. Finally, experimental results obtained from a laboratory 1-hp induction machine set is compared with the simulated results to validate the effectiveness and feasibility of the proposed schemes.

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Xiu-HuaGuo and 郭修華. "Automatic Voltage Compensation Technique for Three-Phase Stand-Alone Inverter with Unbalanced / Nonlinear Load." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/88587974821323491727.

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碩士 國立成功大學 電機工程學系 103 In this thesis, a three-phase inverter providing automatic voltage compensation for unbalanced or nonlinear load under stand-alone operation is presented. An ideal load-side inverter should provide constant amplitude, frequency, and sinusoidal voltage at point of common coupling (PCC). Without the stiff sinusoidal voltage support by grid, voltage quality at PCC is heavily affected by the type of loads. The nonlinear loads could produce voltage harmonics that degrade voltage quality. To maintain voltage quality at certain level, a proportional-resonant (PR) controller embedded with automatic harmonic compensation scheme is proposed. Harmonic components of voltage can be neutralized by resonant controllers that are tuned at harmonic frequencies. This method requires that the voltage harmonics need to be identified before resonant controllers are applied. Using the fast Fourier transform (FFT), dominant harmonic components could be identified for the PR controller to compensate harmonics at some resonant frequencies. The effectiveness of proposed voltage compensation strategy is verified through experiments on a testbed of the three-phase stand-alone system.

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Santosh, Kumar A. "Voltage Stability Analysis of Unbalanced Power Systems." Thesis, 2016. http://etd.iisc.ac.in/handle/2005/3065.

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The modern day power system is witnessing a tremendous change. There has been a rapid rise in the distributed generation, along with this the deregulation has resulted in a more complex system. The power demand is on a rise, the generation and trans-mission infrastructure hasn't yet adapted to this growing demand. The economic and operational constraints have forced the system to be operated close to its design limits, making the system vulnerable to disturbances and possible grid failure. This makes the study of voltage stability of the system important more than ever. Generally, voltage stability studies are carried on a single phase equivalent system assuming that the system is perfectly balanced. However, the three phase power system is not always in balanced state. There are a number of untransposed lines, single phase and double phase lines. This thesis deals with three phase voltage stability analysis, in particular the voltage stability index known as L-Index. The equivalent single phase analysis for voltage stability fails to work in case of any unbalance in the system or in presence of asymmetrical contingency. Moreover, as the system operators are giving importance to synchrophasor measurements, PMUs are being installed throughout the system. Hence, the three phase voltages can be obtained, making three phase analysis easier. To study the effect of unbalanced system on voltage stability a three phase L-Index based on traditional L-Index has been proposed. The proposed index takes into consideration the unbalance resulting due to untransposed transmission lines and unbalanced loads in the system. This index can handle any unbalance in the system and is much more realistic. To obtain bus voltages during unbalanced operation of the system a three phase decoupled Newton Raphson load ow was used. Reactive power distribution in a system can be altered using generators voltage set-ting, transformers OLTC settings and SVC settings. All these settings are usually in balanced mode i.e. all the phases have the same setting. Based on this reactive power optimization using LP technique on an equivalent single phase system is proposed. This method takes into account generator voltage settings, OLTC settings of transformers and SVC settings. The optimal settings so obtained are applied to corresponding three phase system. The effectiveness of the optimal settings during unbalanced scenario is studied. This method ensures better voltage pro les and decrease in power loss. Case studies of the proposed methods are carried on 12 bus and 24 bus EHV systems of southern Indian grid and a modified IEEE 30 bus system. Both balanced and unbalanced systems are studied and the results are compared.

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Santosh, Kumar A. "Voltage Stability Analysis of Unbalanced Power Systems." Thesis, 2016. http://hdl.handle.net/2005/3065.

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The modern day power system is witnessing a tremendous change. There has been a rapid rise in the distributed generation, along with this the deregulation has resulted in a more complex system. The power demand is on a rise, the generation and trans-mission infrastructure hasn't yet adapted to this growing demand. The economic and operational constraints have forced the system to be operated close to its design limits, making the system vulnerable to disturbances and possible grid failure. This makes the study of voltage stability of the system important more than ever. Generally, voltage stability studies are carried on a single phase equivalent system assuming that the system is perfectly balanced. However, the three phase power system is not always in balanced state. There are a number of untransposed lines, single phase and double phase lines. This thesis deals with three phase voltage stability analysis, in particular the voltage stability index known as L-Index. The equivalent single phase analysis for voltage stability fails to work in case of any unbalance in the system or in presence of asymmetrical contingency. Moreover, as the system operators are giving importance to synchrophasor measurements, PMUs are being installed throughout the system. Hence, the three phase voltages can be obtained, making three phase analysis easier. To study the effect of unbalanced system on voltage stability a three phase L-Index based on traditional L-Index has been proposed. The proposed index takes into consideration the unbalance resulting due to untransposed transmission lines and unbalanced loads in the system. This index can handle any unbalance in the system and is much more realistic. To obtain bus voltages during unbalanced operation of the system a three phase decoupled Newton Raphson load ow was used. Reactive power distribution in a system can be altered using generators voltage set-ting, transformers OLTC settings and SVC settings. All these settings are usually in balanced mode i.e. all the phases have the same setting. Based on this reactive power optimization using LP technique on an equivalent single phase system is proposed. This method takes into account generator voltage settings, OLTC settings of transformers and SVC settings. The optimal settings so obtained are applied to corresponding three phase system. The effectiveness of the optimal settings during unbalanced scenario is studied. This method ensures better voltage pro les and decrease in power loss. Case studies of the proposed methods are carried on 12 bus and 24 bus EHV systems of southern Indian grid and a modified IEEE 30 bus system. Both balanced and unbalanced systems are studied and the results are compared.

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張鴻鈞. "Development of three-phase uninterruptible power supplies for unbalanced loads." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/05799623218573729296.

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碩士 國立臺灣科技大學 電機工程系 90 Abstract This thesis is concerned with the analysis and implementation of three-phase uninterruptible power supply for unbalanced and nonlinear loads. In the AC-to-DC power converter, a current controller under rotating frame is adopted to maintain the balance of the utility source and make the input power factor close to unity with low current harmonics. While in the DC-to-AC power inverter, a four-leg power transistor scheme is introduced to get 3-phase 4-wire output. Transformation of inverter performance equations to synchronous rotating frame is exercised to facilitate the independent control of voltage and current for blanced, unbalanced as well as nonlinear loads. A 16-bit digital signal processor (DSP TMS320F240) is used to implement the whole proposed system. The performance of the system is simulated by MATLAB SIMULINK. Experiments are then given to justify the analysis.

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Rodrigues, Ana Maria da Cunha. "Desenvolvimento do conversor CC-CA trifásico de um sistema de advanced load-shift." Master's thesis, 2019. http://hdl.handle.net/1822/64778.

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Dissertação de mestrado em Engenharia Eletrónica e de Computadores Devido à previsível escassez e às desvantagens inerentes ao uso de combustíveis fósseis na produção de energia elétrica, tem-se vindo a apostar em fontes de energia renovável, nomeadamente a eólica e a solar fotovoltaica. Contudo, estes tipos de fontes apresentam como principais desvantagens a intermitência na produção de energia, bem como a necessidade de um equipamento de interface com a rede elétrica, que tipicamente introduz problemas de qualidade de energia elétrica (QEE). Assim, de forma a possibilitar a integração de fontes de energia renovável na rede elétrica e explorar os incentivos referentes aos períodos de menor procura de energia, surgem novas oportunidades relativamente aos sistemas de armazenamento e gestão de energia, nomeadamente, o conceito de load shifting. Neste sentido, a presente dissertação de mestrado encontra-se inserida no desenvolvimento de um sistema de load-shift com características avançadas. Este dispositivo permite a interface de um sistema de armazenamento de energia com a rede elétrica, simultaneamente com a compensação de problemas de qualidade de energia elétrica relacionados com a corrente, nomeadamente, harmónicos, desequilíbrios e potência reativa. Nesta dissertação é abordado o desenvolvimento do conversor CC-CA trifásico, responsável pela interface com a rede elétrica, absorvendo ou injetando energia elétrica, dependendo do modo de operação do sistema de armazenamento. Além disso, este conversor CC-CA permite a operação como filtro ativo paralelo (FAP) trifásico, sendo esta uma das principais contribuições para a operação do sistema. Ao longo do desenvolvimento desta dissertação, foi possível validar a topologia de conversor CC-CA trifásico com quatro braços a operar em diferentes modos, bem como o seu sistema de controlo. Estes modos envolveram um estudo teórico necessário à execução dos testes de simulação e validação experimental do desempenho do sistema implementado. Recently, there has been a focus on renewable energy sources, namely wind and solar photovoltaic, due to the predictable scarcity and inherent drawbacks of the use of fossil fuels in the production of electric energy. However, these types of energy sources have their own shortcomings: the intermittence of energy production as well as the need for an electrical network interface device that typically introduces power quality (PQ) problems. Thus, to allow the integration of renewable energy sources in the grid and to explore the incentives for periods of lower energy demand, new opportunities arise regarding energy storage and management systems, namely the load shifting concept. In this context, the present master dissertation is focused on developing a system of load-shift with advanced characteristics. This device allows the interface of a system of energy storage with the electric network, while fixing the electrical power quality problems related to current harmonics, unbalances and reactive power. This investigation discusses the development of three-phase DC-AC converter, which is responsible for interfacing with the grid, absorbing or injecting electrical energy, depending on the mode of operation of the storage system. Additionally, one of the main contributions to the system operation is that the DC-AC converter allows operation as a three-phase shunt active filter (APF). Throughout the development of this dissertation, it was possible to validate the topology of the three-phase DC-AC converter with four legs operating in different modes, as well as its control system. These modes involved a theoretical study, which is necessary to perform the simulation tests and experimental validation of the performance of the implemented system. Este trabalho de mestrado está enquadrado no projeto de IC&DT “Quality4Power - Enhancing the Power Quality for Industry 4.0 in the era of Microgrids”, financiado pela Fundação para a Ciência e Tecnologia, com a referência PTDC/EEI-EEE/28813/2017. Este trabalho de mestrado está enquadrado no projeto de IC&DT “newERA4GRIDs – New Generation of Unified Power Conditioner with Advanced Control, Integrating Electric Mobility, Renewables, and Active Filtering Capabilities for the Power Grid Improvement”, financiado pela Fundação para a Ciência e Tecnologia, com a referência POCI-01-0145-FEDER-030283.

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Li, Bo-Ying, and 李柏穎. "Development of On-Line Three-Phase Uninterruptible Power Supplies for Unbalanced Loads." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/60955883292684358738.

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碩士 國立臺灣科技大學 電機工程系 102 This thesis is concerned with the implementation of on-line three-phase uninterruptible power supply systems. When the AC mains is normal, the three-phase power factor corrector converts the mains voltages into a constant DC and also provides boost/buck converter standalone charge to the battery bank. Then, a three-phase three-leg power inverter creates balanced three-phase sinusoidal voltages with low harmonic distortion across the load terminals. If the AC mains fails, the system will supply the battery power to the load under the discharge mode. In the three-phase power factor corrector, a DC voltage closed-loop control which stabilizes the DC voltage is adopted to maintain the balance of the utility source and make the input power factor close to unity with low current harmonics. As to the management of battery bank, the charging/discharging schemes are fulfilled by the boost/buck converter. While in the three-phase power inverter, a AC voltage closed-loop control is adopted to facilitate the independent control of voltage for balanced, unbalanced as well as nonlinear loads. The control scheme of the system is implemented by a 32-bit digital signal processor(DSP, TMS320F28335) to reduce the hardware components. The experimental results for 3 kW balanced liner resistive load, 2 kW unbalanced resistive load and 2 kW nonlinear load show that the total harmonic distortions of output are 0.82%, 1.55% and 4.41%, respectively. It is seen that the efficiency of UPS is 84.3% and 87.4% can be achieved for AC normal and AC off operation modes respectively. In conclusion, the experimental results demonstrate that the controller successfully achieves the steady-state RMS voltage regulation specification as well as the total harmonic distortion and the dynamic response requirements of major UPS standards.

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Zhuo, Yi Kai, and 卓怡愷. "Methods to reduce the three-phase unbalance in power system." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/92732273620886498804.

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Chang, Chen-Wei, and 張陳維. "A multicarrier PWM for unbalance three-phase four-leg inverter." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/p2a73t.

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碩士 中華大學 電機工程學系 106 The three-phase four-leg inverter is a system for mitigating common-mode voltages better than three-phase three-arm inverters. Therefore, for the common mode voltage (CMV), two techniques for three-phase four-arm inverters with multi-carrier pulse width modulation (PWM), sinusoidal PWM (SPWM) and space vector PWM (SVPWM) are proposed. To lower the CMV. This method is used to explore the impact on the system under load imbalance. Finally, the experimental and simulation software PSIM platform is used to analyze its system to verify the correctness of the proposed method.

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Dong, Yao-Qi, and 董曜齊. "Applications of static var compensators for improving three-phase unbalanced loads and power factor correction." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/xzde3g.

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碩士 國立雲林科技大學 電機工程系 107 Unbalanced loads and low power factor are the most commonly encountered power quality issues in power distribution systems. In addition to increasing the loss of the line, they also affect normal operation of transformers and motors. In order to improve problems mentioned above, a -connected Static Var Compensator is set up and is calculated based on a new theoretical method of power analysis. The PID controller is used to control its firing angles so that it can balance the unsymmetrical load as well as correct the power factor at the delivery point. The theoretical method does not require information on the type and the connection method of the load. It can be processed merely by identifying both active and reactive power consumption. Therefore, any load connected to a three-phase three-wire (or four-wire) system or a single-phase load can be converted into a balanced load with unity power factor. Finally, simulation is performed by ATP-EMTP software to evaluate the system performance. Results show that the design is able to reach either one or both goals, namely correcting power factor and balancing loads. Consequently, it can reduce the power loss, cut down the current unbalance rate, improve the power quality without the need of active power filter, and lower the cost.

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Zeng, Zu You, and 曾祖佑. "A study on three-phase voltage unbalance in electrical distribution systems." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/32015554709544642417.

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Woinowsky-Krieger, Alexis. "Adaptive phase synchronization techniques for unbalanced and distorted three-phase voltage system." Phd thesis, 2010. http://hdl.handle.net/10048/1564.

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Interfacing and operating AC power electronic systems requires rapid and accurate estimation of the phase angle of the power source, and specifically of the positive sequence of the three-phase utility grid voltage. This is needed to ensure reliable operation of the power control devices and of the resulting power flow. However, the quality of this information is undermined by various distortions and unbalanced conditions of the three-phase grid voltage. Phase estimation and power control can both be performed in real time by a DSP, but a DSP typically has limited computational resources, especially in regards to speed and memory, which motivates the search for computationally efficient algorithms to accomplish these tasks. In contrast to conventional PLL techniques, recent approaches have used adaptive amplitude estimation to enhance the acquisition of the phase information, resulting in faster response and improved performance. This thesis presents a novel technique to estimate the phase of the positive sequence of a three-phase voltage in the presence of frequency variations and unbalanced conditions, referred to as hybrid negative sequence adaptive synchronous amplitude estimation with PLL, or H-NSASAE-PLL. The key feature consists of a feedback structure which embeds a positive sequence PLL and an adaptive synchronous negative sequence estimator to enhance the performance of the PLL. The resulting benefits include faster estimation of the phase of the positive sequence under unbalanced conditions with zero steady state error, simplified tuning of PLL parameters to address a wide range of application requirements, robust performance with respect to distortions and PLL parameters, a structure of minimal dynamical order (fifth) to estimate the main signal parameters of interest, simplified discretization, and reduced computational costs, making the proposed technique suitable for real time execution on a DSP. The H-NSASAE-PLL is developed in the Matlab/Simulink environment, and a specialized test signal generator is developed to evaluate its performance. The overall system is executed, and experimental results are produced, in real time, on a dSPACE DS1104 controller board. Power Engineering and Power electronics

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Tang, Jong-Heng, and 唐仲亨. "Analysis and Simulation of the Characteristics of a Three-phase Self-excited Induction Generator with Unbalanced Loads." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/52069245087849950237.

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碩士 國立雲林科技大學 電機工程系碩士班 94 This thesis compares two analytical methods, i.e., the two-port network method and the loop impedance method, for analyzing the characteristics of a self-excited induction generator supplying unbalanced loads. The two methods have been found to give the same results. However, not only does the former give better physical interpretation than the later, but it is also computationally more efficient. This is followed by a simulation study using the EMTP, and an experimental study using a 375-W induction machine, to validate the results obtained from the analytical methods. In comparison with the simulation and the experimental studies, the analytical methods give satisfactory results in most situations.

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Eren, Suzan. "Modifying the Three-Phase Synchronous Reference Frame Phase-Locked Loop to Remove Unbalance and Harmonic Errors." Thesis, 2008. http://hdl.handle.net/1974/1635.

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As an increasing number of distributed power generation systems (DPGS) are being connected to the utility grid, there is a growing requirement for the DPGS to be able to ride through short grid disturbances. This requires improvements to be made to the grid-side control scheme of the DPGS. An important part of the grid-side control scheme is the grid synchronization method, which is responsible for tracking the phase angle of the grid voltage vector. The state-of-the-art grid synchronization methods being used today are phase-locked loops. This thesis presents a modified phase-locked loop which is more robust towards grid disturbances. It consists of a multi-block adaptive notch filter (ANF) integrated into a conventional three-phase synchronous reference frame phase-locked loop (SRF-PLL). The addition of the multi-block ANF to the system allows it to become frequency adaptive. Also, since the multi-block ANF consists of multiple ANF blocks in parallel with one another, the system is able to remove multiple input signal distortions. Thus, the proposed system is able to eliminate the double frequency ripple that is caused in the conventional three-phase SRF-PLL by input unbalance, as well as harmonic errors, despite the presence of frequency variations in the input signal. Simulation results found using Matlab/Simulink, and experimental results found using the dSPACE DS1103 DSP board, demonstrate the feasibility of the modified SRF-PLL. Also, the modified SRF-PLL is compared to a conventional three-phase SRF-PLL, as well as to a conventional three-phase SRF-PLL with a simple notch filter, and the advantages of the modified SRF-PLL are discussed. Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2008-12-17 12:38:02.589

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(9833834), Steven Senini. "The application of hybrid active filter technology to unbalanced traction loads." Thesis, 1999. https://figshare.com/articles/thesis/The_application_of_hybrid_active_filter_technology_to_unbalanced_traction_loads/13424726.

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This thesis examines the application of hybrid active filter technology to large unbalanced loads such as those presented by electric railway traction systems. The thesis provides a systematic overview of possible hybrid topologies which will provide improvement over existing topologies. Several new topologies are identified in this process. The topologies are analysed to demonstrate the potential reduction in ratings of the active element achieved by the use of the hybrid topologies. A weakness is identified in the areas of signal detection and control system modelling. These areas are also addressed in the thesis and the modelling approach presented is believed to be new in this area. The modelling approach is demonstrated using one topology identified as having the lowest active element ratings. The analysis, operation and control algorithms are demonstrated using both simulation studies and experimental studies. The theoretical, simulated and experimental results show good correlation. The concept of duality is used to analyse and explain the operation of several new topologies identified as useful for harmonic isolation between two distorted buses. The use of hybrid topologies for harmonic isolation has not been seen before in the literature. These topologies are demonstrated using simulation studies.

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JIN, YUAN-JIE, and 金原傑. "Three-phase load modeling studies based on microcomputer." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/19260239990101212298.

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Yang, Ming-Jer, and 楊明哲. "A Study into the Probabilistic Characteristics of Three-phase Voltage Unbalance in Distribution Systems." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/86902601201609606533.

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碩士 國立雲林科技大學 電機工程技術研究所 87 Three-phase voltage unbalance is a commonly encountered phenomenon that deteriorates the quality of power supply in electric distribution systems. This paper aims to the study and modeling of random variation of voltage unbalance through field measurement and Monte Carlo simulation. This paper is composed of three parts which include: (1) development of a novel Monte Carlo simulation technique capable of simulating statistically correlated multivariates, (2) comparison of measured data and simulation results for validating the proposed probabilistic model, and (3) a proposal for setting the limit of voltage unbalance based on the cumulative distribution function of voltage unbalance.

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Tung, Shuo-Hsuan, and 董碩軒. "Effects of Three-phase Voltage Unbalance on Harmonic Currents of a Static Var Compensator." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/hu86dh.

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碩士 國立雲林科技大學 電機工程系 104 This thesis analyzes harmonic currents produced by a three-phase delta-connected static var compensator (SVC) under voltage unbalance. Three-phase voltage unbalance is a commonly encountered disturbance but voltage unbalance factor (UBF) is in general lower than 5%. In this thesis, the effects of voltage unbalance on harmonic currents of a three-phase thyristor-controlled reactor (TCR) are made salient by considering a high value of voltage UBF of 25%. The analytical model of TCR current waveform is analyzed by Fourier analysis. The total harmonic distortion and UBF of harmonic currents can then be obtained. To validate the harmonic analysis, time domain dynamic simulation using the ATP (Alternative Transients Program) has been carried out. Simulation results show that harmonic currents of the TCR under voltage unbalance can be accurately predicted by the proposed analytical model.

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Wu, Yi-Tsung, and 吳宜宗. "Analyses on Third Nuclear Generation Plant Affected by Three-Phase Unbalance of Taipower 345kV System." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/59238739309058408549.

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碩士 國立清華大學 電機工程學系 90 On March 18, 2001, a 3A-level emergency accident occurred at Taipower’s ThirdNuclear Generation Plant, or 3rd Nuke Plant in brief. The investigation team organizedby Taiwan’s National Science Council pointed out that it is necessary to analyze the effect of three-phase unbalance of Taipower 345kV system on the 3rd Nuke Plant. Moreover, an accident on February 13, 1996, at the 3rd Nuke Plant triggered by negative sequence relay resulted in the tripping of a main generator of the plant. This research intends to ascertain whether the negative sequence current is the cause of theMarch 18 accident at the 3rd Nuke Plant. First, this thesis focuses on the negative sequence current due to the three-phase unbalance of Taipower 345kV system only, and calculates the ampere value of the negative sequence current flowing into each rotating machine and the voltage unbalance ratio of each bus at the 3rd Nuke Plant. For this purpose, the thesis proposes a methodology for quick evaluation of negative sequence current distribution within the plant network. Then the author utilizes a simple methodology to establish a whole negative sequence network model including submodels for Taipower 345kV system, 345kV transmission lines, and the 3rd Nuke Plant network. Comparing the simulation result with the record of the negative sequence voltage during the March 18 accident, the correction of model was then verified. The negative sequence voltage level was further compared with the IEC standard, to ascertain whether the negative sequence current was the cause of the March 18 accident at the 3rd Nuke Plant. Last, the research evaluates the improvement on phase-balance current relay setting to avoid the Reactor Cooling Pump (RCP) Motor caused by the insulator fault of 345kV transmission lines, and reviews whether the relay setting had kept enough margin for the unbalance phase current during the March 18 accident. Moreover, according to the voltage unbalance international standard, this thesis studies whether there are still some defects in the protection for the RCP Motor after changing the relay setting.

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Xiu-YuLu and 盧修宇. "Improvement of Three-phase Voltage Unbalance in Distribution Systems Using a Multilevel Static Synchronous Compensator." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/7g4fas.

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Liao, Jyh-Yih, and 廖智毅. "Numerical Evaluation on the Main Substation Three –phase Voltage Unbalance of Taiwan High Speed Rail." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/m448p5.

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碩士 國立臺北科技大學 電機工程系所 93 Seven bulk supply stations erected along the 345 km long HSR. In principle, the stations are designed to be operative even if any one of then fails. To meet the requirement of dual-circuit and three-phase input, each circuit adopts one set of transformers with the primary connected to Scott wire. Each bulk supply station uses 4 sets of autotransformers. The traction power required for trains is supplied by feeding a 2x30kV voltage from these seven stations to the overhead catenary system, the traction car then picks up with its pantograph the 30kV power between the catenary and tracks for use in train. Two sets of same phased power on the secondary end of transformer be fed to the overhead catenary in parallel. The feeder adopts the type of 2x30 kV +AT that is more consistent with the trend of application at this time. With increase of speed, high-speed trains requires more current, and with the development of electronic control circuits, their advantage is that the problem of the phase unbalance coming from power stations. This paper presents methodologies and results of numerical evaluation on the three-phase voltage unbalance, which accounts for unbalanced load from 7 main substations of Taiwan High Speed Railway.

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Hsiao, Ming-Tsung, and 蕭明宗. "A study into the effects of voltage unbalance on the three-phase induction motor using three different simulation tools." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/88702241485694761946.

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碩士 國立雲林科技大學 電機工程系碩士班 101 Operation of a three-phase induction motor under several conditions of voltage unbalance is studied in this thesis using three simulation tools: the Type-56 three-phase induction machine (IM) module and the universal machine(UM) module of the Alternative Transients Program(ATP), and the three-phase induction motor module of Matlab/Simulink. Since the Type-56 IM module is a newly released program, it will be described in more details, and its simulation results are compared and verified by those obtained from the UM and Matlab/Simulink modules. The voltage unbalance conditions studied in this thesis include (1)simple three-phase voltage unbalance; (2) steinmetz connection; (3)single-line disconnect; (4)one-line grounding fault. In addition to verifying the results obtained from the UM and Matlab/Simulink modules, calculation results given by an analytical method are also provided for comparisons.

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Yu, Y. M., and 余耀明. "Analysis and Improvement of Feeders Three-Phase unbalance in a Distribution System Using Artificial Immune Algorithm." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/99769501350033978293.

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碩士 國立高雄應用科技大學 電機工程系碩士班 95 With the development of economic, the distribution system becomes more complex followed by the rapid load growth. Therefore the demand on high power quality and reliability have been concerned by customers. Providing stable power supply and better customer service are the main goal of Taipower company. Hence, the distribution engineer evolves a new methodology and technique to efficiently solve the problems related to power quality and operation performance. This paper proposes an artificial immune algorithm (AIA) based distribution transformer optimum phase connecting scheme to relief the feeder three-phase unbalance such that the more robust power supply can be achieved. In this thesis, an entire feeder load balance is defined as antibody as well as the objective function and the optimum distribution transformer phasing connection is defined as an antigen. In the AIA procedure, the affinity relationship among antigen group is applied to increase the diversity among antibody and the intimacy between antibody and antigen is used to avoid the local optimum solution such that the quick convergent speed and the global optimum solution can be achieved. Besides, in this thesis, the outage operation mapping system (OMS) and customer information system (CIS) are applied to evaluate hourly distribution transformers’ phase P/Q loading for three-phase load flow by considering the customer daily load patterns. Finally, a feeder with the mixture of residential and commercial load customers is selected as a testing case for computer simulations. Results show that the proposed AIA can efficiently solve the feeder three-phase unbalance by derived an optimum solution and the effectiveness and the practicality of the proposed method can be justified.

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Wang, Fuh Min, and 王富民. "Develop a Three-phase Newton Optimal Power Flow Method for Analysis of Unbalance in Power System." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/30877982011090359638.

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Yu, Shang-Wei, and 尤上瑋. "Development of Bidirectional Three-phase Inverters with Load Power Compensation." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/20628436691617966944.

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碩士 國立臺灣科技大學 電機工程系 102 This thesis is concerned with the analysis and implementation of bidirectional power flow three-phase inverters for three-phase grid-connected power systems. The digital phase-lock loop (PLL) technique is used to calculate the phase-angle for grid-connected system. In the three-phase inverter, the dc voltage and ac current closed-loop control strategy is adopted to maintain the dc voltage stable under the power supply or load variation, and make the current in phase with the grid voltage in ac side. The advantages of this strategy are better input-output power balance and faster dc voltage response, reducing the current harmonics and improving power factor. The direct and quadratic axis current closed-loop control strategy with synchronous frame and the design of current controller are used for the three-phase inverters to improve the current response speed. In this thesis, a 32-bits digital controller is used as the control core to implement the bidirectional three-phase inverters, and all strategies are accomplished by software. The integration of two inverters with bidirectional power flow conversion is completed by CAN-bus that serves as an interface between two inverters. One of the three-phase inverters transmits power to the dc side while the other three-phase inverter converts power from the dc side to the grid, and vice versa. A prototype of 3kW power conversion system is developed under grid-connection. The dc voltage is 380V and the grid voltage is 220V, 60Hz. Experimental results show that the efficiency of the system reaches 89% with current harmonic distortion of 6.19% and power factor of 0.996.

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Kao, Fu-Chien, and 高富建. "Impact of the Specification of Minimum Short-Circuit current on Harmonics, Flicker, and Three-phase Unbalance Limitation." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/91454855805334773813.

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YU, CHIH-CHUN, and 余智淳. "Light Load Efficiency Improvement of Three Level Phase-Shift Controlled Converter." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/ru5qx2.

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碩士 國立臺北科技大學 電機工程系 107 The objective of this thesis is to improve the light load efficiency of three level phase-shift controlled converter. The basic idea is to increase the resonant inductance to achieve zero voltage switching even under light load. In the thesis, a three level phase-shift controlled converter has been designed and implemented using UCC3895. The specifications of this converter are as follow: input voltage 400 V/DC, output voltage 48 V/DC, output current 10 A, output power 480 W, and switching frequency 120 kHz. The experimental result show that the peak efficiency is 90.71% at maximum load when resonant inductance is 35 H, and the efficiency is 78.34% under 1A load condition. These results fully support and confirm the design and experimental work.

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Cheng, Chang-Min, and 鄭健閔. "Analysis of a Three-Phase Isolated Self-Excited Induction Generator Feeding a Single-Phase Load." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/81043427425363658840.

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碩士 國立成功大學 電機工程學系 87 This thesis analyzes the steady-state and dynamic characteristics of a three-phase isolated self-excited induction generator supplying a static single-phase load. The eigenvalue sensitivity scheme is employed to find the critical value of the studied machine under different operating conditions. Since the research area in this thesis focuses on the unbalanced loading characteristics, the three-phase induction machine model is utilized to derive mathematical equations of the studied machine. The obtained dynamic simulated results is employed to examine the steady-state characteristics of the studied machine. Finally, experimental results obtained from a laboratory 1.1kW induction machine confirm the feasibility and effectiveness of the proposed method.

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Dissertations / Theses on the topic 'Three Phase Load Unbalance'

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