A control method for 3-phase inverters enabling smooth transferring of the operation modes of distributed generation system

Distributed generation (DG) systems should be able to transfer from grid-tied mode to islanding mode to back up critical load when utility is outage. A new control method for three phase inverter is proposed to realize transferring operation mode in DG systems. Compared to conventional hybrid voltage and current control, good dynamic performance is reserved, and load voltage quality during the transition is improved with the proposed control method. In the grid-tied mode, the inverter is controlled as a current source to inject given active and reactive current to the utility. As soon as islanding happened, the power mismatch between the inverter output and critical load demand leads the drift of voltage magnitude and frequency. And when the drift reach given value, the current reference of inverter is regulated to adjust the generated power to match the load demand. As a result, the drift can be controlled in the given range, and the load voltage quality during the transition can be improved. Besides, the whole system is analyzed and parameters are designed in the paper. Finally, the proposed control method is verified by simulation and experimental results.