Modular parallel three-phase inverter system

This paper develops three-phase inverter modules that have the following functions: (1) inverters for stand-alone operation; (2) inverters in parallel; and (3) inverters in parallel with the utility system. For obtaining parallel operation, the parallel technique for a voltage-controlled PWM inverter and (N-1) current-controlled PWM inverters is proposed in this paper. Through the current control, the current-controlled PWM inverter can be operated in synchronism with the voltage-controlled PWM inverter. By a load-sharing center, the load is shared to each inverter in parallel, and accurately limits the output current of each inverter to its maximum rating. In this paper, system operations are described in detail and experimental results are developed. From the experiment results, this proposed scheme is adequate.