A Low-Loss Grid Decoupling Mechanism in a Three-Phase Grid-Connected Inverter

Abstract

Due to the existence of unknown grid impedance, the grid-connected inverter interacts with the grid and other distributed multiple paralleled inverters at the point-of-common-coupling (PCC). Such interaction challenges the system stability and the power quality especially when the inverter is with an LCL filter. A low-loss grid decoupling mechanism is proposed to counteract the effects of grid impedance in a three-phase grid connected inverter. It is composed of dual PCC voltage feedforward mechanisms, in which one is inserted at the inverter controller and the other is involved in the voltage regulation of an additional bidirectional dc/ac voltage source converter (B-VSC). The outputs of the B-VSC are connected in series with the ac filter capacitors while its inputs are provided with dc capacitors at the inverter dc bus. Because of small volt-ampere (VA) rating, the system efficiency is not sacrificed by the B-VSC. To validate its effectiveness, a three-phase inverter prototype with the proposed grid decoupling mechanism is verified successfully in the simulation.