A Novel Sliding Mode Control Strategy of the Grid-Connected Inverter Under Unbalanced Grid Voltage

Abstract

As the actual grid voltage is not always balanced, the control strategy of the photovoltaic grid-connected inverter significantly affects the quality of the current injected into the grid. The double closed-loop control strategy based on the traditional proportional–integral controller cannot effectively suppress the second-order harmonic fluctuation of inverter output power and grid current distortion under unbalanced grid voltage. According to the mathematical model of a grid-connected inverter under unbalanced grid voltage, this paper proposes a novel sliding mode control strategy to eliminate negative sequence current. The strategy eliminates the necessity for separating positive- and negative-sequence currents or implementing decoupling control, thereby simplifying the controller design and parameter adjustment. The designed sliding mode controller with an integral sliding surface and an improved exponential approaching law mitigates chattering while enhancing the system response speed. Simulation and experimental studies of the proposed control strategy are conducted under unbalanced grid voltage conditions to verify its feasibility and effectiveness.