A seamless transfer algorithm based on feed-forward control method for bi-modal grid-connected PCS

This paper proposes a seamless transfer control strategy for bi-modal grid-connected (GC) power conditioning system (PCS). The load can be supplied the power continuously, regardless of the grid states. The PCS should be operated in two modes. One is the GC mode and the other is stand-alone (SA) mode. A current control loop and a feed-forward voltage control loop are used to control the grid current and load voltage respectively. A current controller with a feedforward voltage control loop helps the load voltage regulation fast in transient time (i.e., operation mode change time). In order to detect the grid abnormal condition and to reduce the fault detection time, the load frequency is employed. Proposed control algorithm is confirmed by the experimental results.