Repetitive Controller for VSIs in Droop-Based AC-Microgrid

A major requirement of ac-microgrid is to keep on feeding its connected load at regulated voltage and frequency, which is difficult to achieve especially in inverter-based microgrid. In modern distribution system, most of the loads are nonlinear in nature and draw harmonic current. The variable load with the nonlinear characteristics may distort the output voltage and degrade the power quality. In order to mitigate the negative impact of these disturbances on the output voltage, a novel repetitive controller (RC) has been proposed. A mixed-sensitivity-based approach is used here to design the RC and the comparison of performance with nonlinear load is shown with a conventional proportional plus integral regulator. The overall microgrid system is designed and simulated with the help of various toolboxes available in MATLAB/SIMULINK. Furthermore, a scaled hardware prototype of microgrid consisting of two voltage source inverter is developed and controlled using RC in real time with the help of field programmable gate array (FPGA).