DESIGN, DEVELOPMENT AND CONTROL OF VOLTAGE SOURCE CONVERTERS FOR GRID INTEGRATION OF GRID INTEGRATION OF SOLAR PV

Abstract

The PV based generation is recognized as one of the most promising RES technology and large scale implementation projects in various countries demonstrate this trend. Due to such large scale PV integration, power systems are growing in size and getting complex. Moreover, the use of other renewable energy sources such as wind has also seen an upswing and further trends also show significant increase in power electronic based loads thereby affecting the nature and performance of power systems. Moreover, today‟s power distribution system face greater challenges like power quality (PQ), efficiency and reliability to maintain grid stability and reliability because of high penetration of PV. It is a major challenge to supply reliable and good quality power round the clock. Voltage fluctuations, voltage imbalance, voltage sag, harmonics and transients are all well-known PQ issues that impair power system performance even in the wake of contemporary technological advancements. Traditional cost effective solutions include passive filters; however fast and accurate control within 1-2 cycles and transition from lagging to leading vars is possible only using shunt compensators. Voltage source converter (VSC) can be used as shunt compensators to enhance the system's power quality and minimize issues including harmonics, reactive power burden, low power factor, and load unbalancing. New grid code requirements stipulate that the DG system including PV, vehicle to grid and wind turbine system shall contribute to grid stability and services as well as deliver active power to grid. The proposed work‟s objective is to develop and design techniques for improving the quality of power supplied to non-linear loads by single-phase and three-phase systems during normal and abnormal grid conditions including low voltage ride through operation. To achieve these objectives, several control algorithms have been developed for improving power quality and LVRT operation. The control methods require the feed forward term, DC-link voltage controllers, synchronization techniques, estimation of the basic component of load current and reference active and reactive power based on magnitude of voltage sag during LVRT operation. Extensive simulation and experimental investigations have been conducted to assess the effectiveness of the system and the vi control algorithms. Conventional control techniques viz Synchronous Reference frame Theory (SRFT) and Second Order generalized Integrator (SOGI) have been initially tested on the prototype system developed in the laboratory. Two new control algorithms for single phase and three phase single stage grid connected PV system which includes self-adaptive Batmen Polynomial (BP) and Radial Basis Function Neural Network (RBFNN) algorithm for active power injection and reactive power compensation. The H-bridge inverters are employed as a SAPF to mitigate many power quality issues and achieve load compensation in single-phase and three-phase systems feeding a range of linear and non-linear loads. Detailed simulation results are recorded and verification of these results on the experimental setup is performed. Simulation has been performed in MATLAB/SIMULINK environment. PQ problems in three phase distribution system under distorted grid condition have been studied. The control algorithms developed for this system are Levenberg Marquardt (LM) trained SOGI filter with unit template synchronization method and conductance-based control algorithm with D-SOGI based synchronization method. Detailed simulation results are recorded and verification of these results on the experimental setup is performed. Simulation has been performed in MATLAB/SIMULINK environment. Next, the operation and grid requirement of single phase system during LVRT mode of operation. The designed controllers include adaptive Laguerre polynomial (LP) and Sliding Window Recursive Discrete Fourier Transform (SWRDFT) based controller. The experimental setup has been controlled using dSPACE 1104. Experimental results of all techniques have been analyzed in details. The operation and grid requirement of three-phase system during LVRT mode of operation includes the design and development of a (Gagenbuer Polynomial) GP function-based and Load power based controller for LVRT and UPF mode of operation. The developed controllers have been equipped with enhanced LVRT capabilities and respond quickly and correctly to changing system conditions. Simulation and experimental results of all techniques have been analyzed in details.