Seamless transfer algorithm of AC microgrid inverter compensating load current for weak grid

Abstract

In this paper, we propose a voltage control technique for the seamless transfer algorithm of a microgrid inverter. When the microgrid inverter is switched from grid-connected mode to standalone operation mode, an output voltage transient may occur, and adversely affect the load. To solve this, seamless transfer algorithms that complete mode switching within 4 ms have been studied. However, previous control techniques have very complex structures. In this study, we find the cause of the voltage transient occurring in the mode conversion, through state average modeling of the inverter. Subsequently, we propose a feed-forward compensator for seamless transfer. The cause of the voltage transient is removed by the compensation, and smooth mode switching is achieved. The proposed controller is verified by Powersim (PSIM) simulations.