Voltage unbalance and harmonics compensation in AC microgrid using add-on repetitive controller

Voltage unbalance and harmonics are the major power quality issues in inverter-based low voltage microgrids (MGs). In the presence of nonlinear load, the interconnecting inverters in the MG may not be able to compute the amount of reactive power and harmonics to be compensated independently without violating their respective ratings. This may result in disproportionate sharing of power by the individual inverters, and consequently resulting in the overloading of some of the inverters. Therefore, in the proposed work, a repetitive controller (RC) in addition to an existing controller has been developed and added in the outer most. This RC can control the individual inverters to compensate voltage unbalance and nonlinear loading through proportionate effort sharing by individual inverters in the MG. This technique has been successfully implemented on three-phase voltage source inverter which is controlled to maintain perfect three-phase balanced set of voltages under unbalance nonlinear loading conditions. The proposed strategy has shown an effective compensation even under highest degree of unbalance and nonlinear loading in MG. The proposed controller is designed and simulated with MATLAB/Simpower system. Field programmable gate array-based hardware prototype has been developed to validate the control approach experimentally.