Unbalanced Control of Grid-connected Inverters Based on Proportion Integraland Reduced Order Resonant Controllers

The effective control of grid-connected inverters(GCI) under unbalanced grid voltages is very important to improve the grid-connected operation of the inverters.This paper proposes a novel controller,proportion integral plus reduced order resonant(PI-ROR) controller,which can achieve zero error output adjustment to the AC signals,and can easily be digitally realized.The PI-ROR controller,which does not require any decomposition of positive-and negative-sequence currents,can achieve zero current error control in the positive synchronous rotating reference frame directly.The feasibility of adopting the PI-ROR controller to control the unbalanced current,and the control performances of the PI-ROR and PI controller are verified by the simulations and experiments.Results show that the PI-ROR control scheme is capable of realizing the unbalance control targets with excellent transient performances.Therefore,the fault operation capability of GCI under unbalanced grid voltages is enhanced.