A novel seamless transfer control strategy for wide range load

This paper proposes a novel seamless transfer control strategy of three-phase grid-connected inverter between grid-connected (GC) and stand-alone (SA) modes which can cover from no load to full load, even in non linear (NL) loads. The three-phase grid-connected inverter which uses in distributed generation (DG) system can be operated in both GC and SA control modes, especially for energy storage systems. The current and the voltage is controlled by the inverter in GC and SA mode respectively. In other words, the control methods are differently applied to each mode. When the grid outage, the inverter changes its operation mode. During the mode transition from GC to SA, undesired phenomena such as a voltage spike and a current spike are occurred. With the proposed method, the seamless transfer can be achieved. In addition, proposed algorithm is considered the non detection zone (NDZ) condition which the inverter cannot recognize changes such as magnitude and frequency variation of critical load. The proposed control method is verified by the experimental results.