Control of Distributed Power Inverter with Unbalanced and Nonlinear Loads

Inverters in a distributed power system are used to supply high quality power for all kinds of loads. For unbalanced and nonlinear loads, a PID controller of three-phase four-leg inverter based on the pole assignment is proposed. Firstly, the switch-cycle average method and rotating coordinates transformation are used to establish a continuous constants system model. Then the transfer function of the controller, expected pole distribution and performance indices are obtained. Based on which, a PID controller with appropriate parameters is designed. By analyzing output voltages under unbalanced loading conditions and harmonics components with nonlinear loads, it is indicated that the four-leg inverter system combined with the optimal PID controller can achieve excellent steady-state and dynamic performances. Moreover, the method is simple in theory, easy to implement and flexible. Detail simulation and experimental results validate the proposed method.