A seamless control strategy of distributed generation inverter for critical load safety under strict grid disturbance

This paper is to introduce a seamless grid interconnection control strategy for the renewable energy distributed generations such as photovoltaic, wind generator, and fuel cell systems. The proposed control method consists of a voltage controller in stand alone mode, a current controller in grid connected mode, and a hybrid voltage controller in a transition mode, which is to minimize the grid overvoltage. The hybrid voltage controller is added to the Q-axis current control loop in order to improve the response time under light load condition or to protect the critical load in SA operation during the grid fault conditions. The proposed control strategy reduces the impact of the renewable energy and the critical load under the grid fault or disturbance conditions. In addition, the smooth operation of the inverter will also enhance the stability and reliability of the utility grid. Real time digital simulator based hardware in the loop tests and simulation results show that distributed generation inverter can achieve seamless mode change under grid fault conditions.