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.