Dissertations / Theses on the topic 'Four leg three phase inverter'

Three-phase four-leg voltage source inverters (VSIs) are widely used in distributed power generation applications, three-phase UPS systems and fault-mode operation of a balanced three-phase system where the balanced three-phase voltage output is required when the loads are unbalanced. A three-dimensional space vector modulation (3-D SVM) switching scheme, which is proved to be compatible with modern DSP implementation for a four-leg VSI, has the advantage of higher DC link utilization, less harmonic contents and less switching losses compared with sinusoidal PWM. Therefore it is the first choice of switching schemes for a four-leg inverter. Electromagnetic interference (EMI) which is associated with common-mode switching for a high voltage level power system can degrade the equipment performance and cause communication problems. The conventional 3-D SVM switching scheme exhibits high common-mode voltage (CMV) characteristics which may result in problems in high power applications. The 3-D SVM has the drawback of being complex which could become a software burden in computationally intense real-time control applications. Attempts to reduce the complexity of the 3-D SVM have been made by many researchers and new switching schemes such as carrier-based PWM proved to have the same performance. This thesis presents a switching scheme called near-state 3-D SVM that can reduce the CMV voltage level of a four-leg inverter by avoiding the use of the two zero switching states of the inverter. A laboratory test bench has been built to validate the proposed switching scheme. An in-depth analysis has been carried out for a four-leg inverter in terms of total harmonic distortion (THD) factor, current harmonic distortion factor, conduction losses and switching losses. The proposed switching scheme is analyzed and compared with the conventional 3-D SVM using the analysis method. Additionally, a simplified switching scheme which is still based on space vector theory is proposed. This simplified switching scheme remains compatible with vector control. Experimental results show that the simplified switching scheme has the same performance as 3-D SVM, with reduced program execution time. Abstract iii An output voltage control loop with current feed-forward term in d-q-0 coordinate, which is designed in the discrete-time domain, proves to be most compatible with a DSP-based control system. Experimental results demonstrate the performance of the control loop in both steady state and transient operation.

A method for high performance output voltage control of a four-leg inverter based three-phase transformerless UPS is proposed. Voltage control loop is employed and the method employs stationary frame resonant filter controllers for the fundamental and harmonic frequency components. A capacitor current feedback loop provides active damping and enhances the output voltage dynamic performance. The controller design and implementation details are given. Linear and nonlinear loads for balanced and unbalanced load operating conditions are considered. The steadystate and dynamic performance of the UPS are investigated in detail. A scalar PWM method with implementation simplicity and high performance is proposed and implemented. The control and PWM methods are proven by means of theory, simulations, and experiments.

This thesis deals with control of three phase inverter as three phase sinusoidal voltage source for UPS application. Thesis is split to two parts, teoretical and practical. Teoretical part deals with three phase inverter topology analysis according requirement of neutral line wire and possibilities of generating sinusoidal PWM in depend of topology. There are also analysed properties of contorled system and designed 3 regulation methods with simulations. Second part of thesis deals with realisation of sinusoidal power source with inverter borrowed by Elcom company. To inverter control is used digital signal controler TMS320F28335 with implemented control algorithms. There are also presented the measurement results of the prototype of power source. In conclusion, simulation results are compared with measurements and achieved results are summarized.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2017-10-06T12:04:38Z No. of bitstreams: 2 Dissertação - Lázaro Rubens Araújo Pinto - 2017.pdf: 16272237 bytes, checksum: 9f3d1693d0282cbf28a35702c1a9cf17 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)<br>Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-10-06T12:04:51Z (GMT) No. of bitstreams: 2 Dissertação - Lázaro Rubens Araújo Pinto - 2017.pdf: 16272237 bytes, checksum: 9f3d1693d0282cbf28a35702c1a9cf17 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)<br>Made available in DSpace on 2017-10-06T12:04:52Z (GMT). No. of bitstreams: 2 Dissertação - Lázaro Rubens Araújo Pinto - 2017.pdf: 16272237 bytes, checksum: 9f3d1693d0282cbf28a35702c1a9cf17 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-08-07<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES<br>This work proposes an analysis of the closed-loop operation of a distributed generation system connected to a three-phase four-wire AC power system by a three-phase four-leg inverter. The modulation strategy adopted for this inverter is determined by the Model Predictive Control (MPC) method. Reasons for the use of this topology and the control method are discussed. The chosen structure for the MPC predictive control aims to supply of active and reactive power by the inverter in order to maximize the power factor measured by the four-wire AC source (Y-n). Four possible cases of operation are reported for the analysis of the proposal in the three-phase four-leg inverter and other two cases for a three-phase full-bridge inverter (3F) for comparison purposes. Based on the monitoring of the active powers involved and the other variables of interest, it was possible to exemplify the achievement of the proposed objectives and validate the adopted method, at least under modeling and software simulation level.<br>Este trabalho propõe uma análise da operação em malha fechada de um sistema de geração distribuída para conexão em um sistema trifásico a quatro fios, a partir do controle de um inversor trifásico a quatro braços. A estratégia de modulação adotada para este inversor é determinada pelo método de controle preditivo baseado em modelo (MPC - Model Predictive Control). Justificativas para a utilização dessa topologia e do método de controle são discutidas. A estrutura escolhida para o controle preditivo MPC objetiva o fornecimento de potência ativa e reativa pelo inversor tendo em vista a maximização do fator de potência medido a partir da fonte pela fonte CA a quatro fios (Y-n). Quatro casos são abordados para análise da proposta no inversor trifásico a quatro braços e dois casos para um inversor trifásico em ponte completa (3F) para efeito de comparação. Baseando-se no monitoramento das potências elétricas envolvidas e nas demais grandezas de interesse, foi possível concluir que os resultados de simulações exemplificam o alcance dos objetivos propostos e validam o método adotado, pelo menos em relação à modelagem matemática empregada e à simulação do sistema de geração proposto em ambiente computacional.

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.<br>Ph. D.

碩士<br>中華大學<br>電機工程學系<br>106<br>Three-phase three-leg inverter has an inherent common mode voltage (CMV) problem.Therefore, three-phase four-leg inverter is proposed to mitigate the CMV. This study discusses the characteristics of multicarrier pulse width modulation (PWM) for three-phase four-leg inverter. The analysis of sinusoidal PWM and space vector PWM with multicarrier is presented. The simulation results are utilized to validate the performances of the proposed multicarrier PWM scheme.

碩士<br>中華大學<br>電機工程學系<br>106<br>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.

碩士<br>清雲科技大學<br>電機工程研究所<br>96<br>Generally,the traditional three-phase three-leg DC-to-AC power inverter are used widely with three phase balanced loads. But, when the three-phase loads are unbalanced, that three phase voltage outputs can not be symmetrical. In this paper presents a three-phase four-leg DC-to-AC power inverter can be supply a midpoint to three phase unbalanced loads.So the three-phase four-leg DC-to-AC power inverter outputs three phase symmetrical voltages. Using symmetrical model analysises three-phase four-leg DC-to-AC power inverter how it suppresses the unbalanced loads. The mathematic model of three-phase four-leg DC-to-AC power inverter is established in different coordinates. Paper accomplishes the decoupling of the three-phase four-leg DC-to-AC power inverter. PI double loop controller based on synchronous frame is applied. The control circuit cosists of digital processor(DSP TMS320F2808PZA),which programmed in C language. The performance of system is simulated MATLAB SIMULINK. Experiments the three-phase four-leg DC-to-AC power inverter can output three-phase balanced AC voltage under the unbalanced loads conditions.

碩士<br>國立臺灣科技大學<br>電機工程系<br>97<br>The thesis is concerned with the analysis and development of six-leg three-phase inverter for permanent-magnet synchronous motor(PMSM) drives. The power circuit uses six-leg three-phase inverter. Connecting each winding to two separately controlling legs yields three phase dc-ac converter. The inverter control strategy uses unipolar voltage switching method to raise the utilization factor of dc-link voltage. When a winding of three-phase PMSM breaks down, the associated load may have to be reduced to retain continuous running and increase the reliability of the system. In the fault tolerance control strategy, the current of PMSM is used to determine which winding is broken, so that the other two winding currents can be corrected to result in a 60-degree angle difference, thereby reducing torque pulsation. In the proposed system, six Hall-effect sensors are used to measure the position and speed of the rotor to facilitate the coordinate transformation of feedback current to achieve d-q currents and speed closed-loop control. In this thesis, Matlab/Simulink is used to simulated the proposed PMSM system including six-leg three-phase inverter with unipolar voltage switching method control strategy, d-q current closed-loop control, speed closed-loop control and fault tolerance control strategy. The digital signal processor TMS320F2808 is adopted as the control core. A prototype of 100W six-leg three-phase inverter for PMSM drives is built. The speed is 170 rpm and the load is 4 N-m. When under the normal operation of the system, the total harmonic distortion of each phase-current is 14.67 %. While for two-winding operations of three different cases, the total harmonic distortions of three phase-currents for each case measured are 17.90%, 16.48% and 17.37%, respectively. The proposed system performance is thus verified experimentally.

碩士<br>國立臺灣海洋大學<br>電機工程學系<br>107<br>This thesis proposes a novel type of modulated model-free predictive current control for three-phase four-arm two-level inverters. Compared to traditional techniques, the proposed method effectively improves current response at high frequencies by incorporating the optimal selection of two switching states based on simple calculation and then combines to the next switching state. This selection method effectively detects the optimal two modulated switching states in each sampling period. In addition, the improved control response at high frequency effect is introduced using an enhanced updating mechanism of the current difference. This is to enable the switching states of alike phase voltage to update current difference amount at the same time. In order to verify the proposed method, the simulation is conducted using MATLAB/Simulink software, and implemented using the TMS320F28379D dual-core digital signal controller by Texas Instruments. The simulation and experimental results show that the proposed method can significantly improve the current tracking performance compared with the existing methods.

碩士<br>國立宜蘭大學<br>電機工程學系碩士班<br>96<br>A novel four-switch three-phase inverter is designed and implemented. A low cost four main switches and four auxiliary switches power converter configuration of the three-phase inverter is proposed. All main switches in the three-phase inverter operate at zero voltage switching (ZVS) turn on and turn off. Also, the auxiliary switches operate at zero current switching (ZCS) turn on and turn off. Moreover, the reduction in the number of main switches can also increase the reliability, since the control circuits and the auxiliary circuits are there by reduced to two sets. Therefore, the proposed power converter configuration achieves the low cost and high efficiency inverter without changing devices rate. The principle of operation, computer simulation and experimental results of the four-switch three-phase inverter, rated 200W and operated at 40kHz are provided to demonstrate the performance. Keywords: Zero-Voltage Switching (ZVS), Zero-Current Switching (ZCS), Four-Switch Three-Phase Inverter (FSTPI)

博士<br>國立中正大學<br>電機工程研究所<br>103<br>This dissertation presents a division-summation (D-Σ) digital control for three-phase four-wire bi-directional inverters with wide inductance variation. The bi-directional inverters can fulfill grid connection, rectification and uninterrupted power supply (UPS). When AC grid is operated normally and the inverter system is connected to the grid, the system will be operated in grid-connection (GC) mode, which includes four functions: unity power factor (PF), rectification with pow-er-factor correction (PFC), PF leading and PF lagging. On the contrary, when the in-verter system is disconnected from AC grid due to grid fault, the system will be operated in UPS mode, supplying stable power continually for loads. The proposed D-Σ control summarizes the inductor-current variations over one switching cycle to derive control laws directly, which can overcome limitations of a-b-c to d-q transformation (Park transformation). With the proposed control, the inverter can track its sinusoidal reference currents or voltages, and it is allowed to have wide inductance variation, reducing core size significantly. In the literature, the D-Σ digital control for three-phase three-wire grid-connected inverters has been presented. However, the inverter with the previous control approach requires four control laws and four vector combinations, increasing the complexity of firmware programming. Since its region division is determined based on the zero-crossing point of line currents, the inverter is required to select different vector combinations corresponding to the phase shift between line currents and line voltages. To improve the limitations, the dissertation presents the improvement of the control-law derivation and region selection for the D-Σ digital control. By selecting the zero crossing points of phase voltages as region transitions, the control laws and the related parameter tables for the four modes can be unified to a general form. The switching sequences of the four modes are also unified to the switching pattern of the GC mode. Additionally, a D-Σ transformation matrix is identified to simplify the derivation procedure of the division (D) and summation (Σ), which can obtain the control law directly. To improve current distortion under low current levels, this dissertation presents three attempts, including mid-point current sampling, smooth region transition, current interleaving, and duty splitting. In the design and implementation, the inductances corresponding to various inductor currents are measured and tabulated into a single-chip microcontroller for tuning loop gain cycle by cycle, ensuring system stability. For extending of the application of D-Σ digital control, this dissertation presents the D-Σ digital control based three-phase four-wire inverter which is adopted for uninterruptible power supply. The D-Σ digital control cannot be directly applied to voltage tracking inverter since the above control is a current tracking control. Thus, this dissertation proposes an impedance estimation to estimate the load current variation, and the D-Σ digital control based voltage tracking can be achieved. Moreover, a repetitive control is also included in the D-Σ control to reduce harmonic distortion. The repetitive control not only records the voltage error of the last line cycle, but uses the error to modify the next switching-cycle voltage control which can fine tune the voltage tracking more sinusoidally. For a micro-grid application, this study combines the D-Σ current tracking and voltage tracking controls into the inverter operation, and the control strategies for mode transitions from GC mode to UPS mode and vice versa are presented. When connecting or disconnecting the grid, the two types of inverter operations can transit smoothly based on the proposed control strategies. Experimental results have con-firmed the discussions The above controls are all based on an LC filter. However, high frequency ripple current injection to the grid cannot be avoided. Actually, there are grid impedance and grid-voltage harmonics, which result in harmonic current injection to the grid. To reduce grid current harmonics, this dissertation presents an improvement of LCL-filter design and control method based on the D-Σ digital control. Its feasibility has been verified from the measurement of a single-phase inverter and the simulation results of a three-phase four-wire inverter. Keywords: Division-summation (D-Σ), digital control, three-phase inverter, induct-ance variation, impedance estimation, repetitive control, LCL-filter.

碩士<br>國立中正大學<br>電機工程研究所<br>100<br>This thesis presents design and implementation of a three-phase four-wire inverter with load impedance estimation. The inverter can fulfill both grid-connected and stand-alone mode operations. In the stand-alone mode, the inverter with a neutral leg can generate sinusoidal output voltage for unbalanced load and nonlinear load. With the load impedance estimation, the controller can track the sinusoidal reference voltage accurately, and the inverter is allowed to have a wide inductance variation, reducing core loss and size significantly. The control law is derived based on the two-phase modulation (TPM) scheme with a dead-beat control and on-line load impedance estimation, in which the repetitive control concept is adopted to reduce the estimation tolerance. Computer simulation and experimental results from a 10 kVA three-phase four-wire inverter have been presented to confirm the feasibility of the inverter.

碩士<br>國立聯合大學<br>電機工程學系碩士班<br>99<br>This thesis is focused on the design of low-cost high-performance power system controllers, in which static synchronous compensators (STATCOM) and static series synchronous compensators (SSSC) are two major design targets. The development of the proposed power flow controllers is mainly based on the hardware configuration of a 2-leg 4-switch (2L4S) three-phase inverter and issues regarding advantages and possible limitations in performing power flow regulation and voltage control functions are the main concerns. In this thesis, a number of switching techniques, e.g. voltage hysteresis, sinusoidal pulse width modulation and space vector pulse width modulation techniques are investigated. The concepts of P-Q axis control scheme and the conventional PI controllers are utilized in the proposed power flow controllers. The main control functions designed for the proposed hardware simplified compensators include the dynamic voltage control and P-Q regulations of power networks. To demonstrate the feasibility of the proposed controllers and verify their performances, a set of simulation cases on simplified power systems are constructed in the MATLAB/SIMULINK software environment and comprehensive simulation studies are carried out. Results obtained from various case studies verify the feasibility and effectiveness of the proposed 2L4S based power flow controllers. Keywords: power system control, power flow controller, power converter, static synchronous compensator, static series synchronous compensators

碩士<br>國立雲林科技大學<br>電機工程系<br>105<br>Due to the demand of power consumption is increasing, renewable energy technology is developed in every country. A three phase bidirectional structure is developed in this paper, which includes three modes: one is a grid connected inverter, another is a power factor corrector converter, and the last is an uninterruptible power system. Moreover, the paper also considers the situation when this system operates in grid connected mode but the sudden grid fault, the passive island detection method is developed to detect the island phenomenon. This method is able to discover grid fault and turn off the grid-connected output immediately. The paper use bidirectional structure to reduce the circuit size and cost, and adopted Renesas Electronics' microcontroller RX62T for digital control. The MCU is used to detector the zero crossing point of grid and sense the voltage and current, then calculate and output the suitable switching control signals. Grid connected and power factor corrections are performed by the division-summation control method; Uninterruptible power system is implemented with sinusoidal pulse width modulation and a PI controller. The operating principle of circuit, algorithm derivation, hardware and software are detailed in this paper. And, a 10kW three-phase four-wire half-bridge bidirectional inverter is implemented, the experimental results show the hardware and software design of this paper is workable.

碩士<br>國立清華大學<br>電機工程學系<br>104<br>This thesis presents design and implementation of a three-phase four-wire inverter with LLCL output filter. To achieve higher applicability in the emerging development of dc micro-grid and renewable energy systems, the inverter is equipped with multiple functions, including grid-connection, rectification, dc-link voltage regulation and active power filtering (APF). In general, control strategies used in most multi-function systems tend to be complex, where each operation mode requires its own way of control. However, the division-summation (D-∑) digital control adopted in this thesis is able to overcome the above problem. With one common duty-ratio expression, various operations can be realized with different current commands, which greatly reduces the control complexity. Furthermore, with system parameters such as grid voltage, dc-link voltage, filter inductance and switching period included in the duty-ratio expression, the inverter is capable of operating normally despite of parameter variation. Being the first to apply the D-∑ digital control to the inverter with an LLCL filter, this thesis also proposes several solutions on problems that could occur in hardware implementation; besides, parameter design procedure is also addressed and can be adapted to applications with different specifications. Finally, each operation mode has been tested with a prototype built in lab. Measured results show consistency with simulation, and most importantly, output current can comply with the total harmonic distortion requirement stated in “IEEE Std 519™-2014”.

碩士<br>國立中正大學<br>電機工程研究所<br>101<br>This thesis presents design and implementation of a three-phase four-wire inverter with load impedance estimation and iterative-learning control. The inverter can operate at the grid-connected and stand-alone mode conditions. In the stand-alone mode, the inverter with a neutral leg can generate sinusoidal output voltage for unbalanced load and nonlinear load. With the load impedance estimation, the controller can track the sinusoidal reference voltage accurately, and the inverter has considered a wide inductance variation, reducing core size significantly. The control law is based on a two-phase modulation (TPM) scheme with a D-∑ digital control and on-line load impedance estimation. Additionally, the iterative-learning control concept is adopted to reduce total voltage harmonic distortions. Finally, the computer simulation and experimental results measurements are performed for a 10 kVA three-phase four-wire inverter to verify the feasibility of the inverter.

碩士<br>國立清華大學<br>電機工程學系<br>103<br>This thesis presents design and implementation of a 20 kVA division-summation (D-Σ) digital controlled three-phase four-wire multi-function inverter system. The in-verter can be operated in grid-connected or stand-alone mode to act as a renewa-ble-energy ac power-supply system. In the stand-alone mode, the control of this in-verter uses the D-Σ digital control law for voltage tracking which includes load im-pedance estimation and repetitive control, causing the inverter can stabilize sinusoidal output voltage for unbalanced load and nonlinear load. For the grid-connected mode, in order to achieve a specific PF and stabilize grid voltage and frequency, the control is the D-Σ digital control law for current tracking which supplemented by a droop control based linear P-Q compensation. Moreover, the D-Σ digital control law in this research is based on Two-Phase Modulation (TPM) scheme and associated with the switching sequence transformed from space vector pulse width modulation (SVPWM) scheme, and thus, the inductance variation can be taken into account, reducing core size significantly. Finally, the control laws are verified with measured results from a 20 kVA three-phase four-wire inverter system.

碩士<br>國立臺灣海洋大學<br>電機工程學系<br>103<br>This thesis presents a novel predictive current control for four-switch three-phase inverter-fed synchronous reluctance motor drive systems. We not only develop a new strategy for four-switch three-phase inverter-fed synchronous reluctance motor drive systems, but also discuss the feasibility and correctness of this method so as to improve the ability of the current control of the motor drive system. Furthermore, we expect to meet the industrial requirements of low-cost drive system equipped with high-performance current control. Compared to the six-switch drive system, the four-switch three-phase drive system can effectively reduce the development costs in both hardware and software. For a four-switch three-phase synchronous reluctance motor drive system, its switch strategies that we can choose are few. Generally speaking, the drawback of hysteresis current control is that it has large ripples in the output currents of the inverter. In order to improve the current-tracking performance, the development of the new switching strategy for low-cost drive system is urgently needed. As a result, the proposed method is based on the stator current measurement and the current variation so as to predict the future stator current. A digital signal processor, TMS320F2809, made by Texas Instruments Company, is used to execute the algorithms of the proposed predictive current control and hysteresis current control. Experimental results can be used as a reference for developing a new switching strategy of a four-switch three-phase drive system in the future.

The necessity to incorporate renewable energy systems into existing electric power grid and need of efficient utilization of electrical energy are growing every day. A shunt connected Voltage Source Inverter(VSI) capable of bidirectional power flow and fast control has become one of the building block to address such requirements. However with growing number of grid connected VSI, new requirements related to harmonic injection, higher overall efficiency and better performances during short term grid disturbances have emerged as challenges. For this purpose a grid connected three phase four wire VSI with LCL filter can be considered as a general module to study different control approaches and system behavior under ideal and non-ideal grid conditions. This work focuses on achieving enhanced performance by analyzing effect of non-ideal conditions on system level and relating it to individual control blocks. In this work a phase locked loop structure has been proposed which is capable of extracting positive sequence fundamental phase information under non-ideal grid conditions. It can also be used in a single phase system without any structural modification. The current control for the three phase four wire VSI system has been implemented using Proportional Resonant (PR) controller in a per phase basis in stationary reference frame. A simplified controller design procedure based on asymptotic representation of the system transfer function is proposed. Using this method expressions for controller gains can be derived. A common mode model of the inverter system has been derived for low frequencies. Using this model a controller is designed to mitigate DC bus imbalance caused by sensor and ADC channel offsets. A multi-rate approach for digital implementation of PR controller with low resource consumption, that is suitable for an FPGA like digital controller ,is proposed. This multi-rate method can maintain resonance frequency accuracy even at low sampling frequency and can easily be frequency adaptive. Anti-wind up methods for PI controller have been studied to find suitable anti-wind up methods for PR controller. The tracking anti-wind up method is shown to be suitable for use with a PR controller. The effectiveness of this method under sudden disconnection and reconnection of VSI from grid is experimentally verified. A resonant integrator based second order filter is shown to be useful for active damping of LCL filter resonance with a wide range of grid inductance variation. The proposed method utilizes the LCL filter capacitor voltage to estimate resonance frequency current. Suitability of fundamental current PR controller for active damping alone, and with the proposed method show the superiority of the proposed method especially for low switching frequencies. Design oriented analysis of the above topics are included in the thesis. The theoretical understandings developed have been verified through experiments in the laboratory and can be readily implemented in industrial power electronic systems.