A discrete-time integral sliding-mode controller with nonlinearity compensation for three-phase grid-connected photovoltaic inverter

This paper presents a novel control strategy that combines a discrete-time integral sliding-mode controller (DISMC) with nonlinearity compensation under d-q rotating frame for three-phase grid-connected photovoltaic inverter to suppress the current harmonics as well as improve the dynamic response and robustness. Because of the nonlinearity introduced by dead time and turn on/off delay of three-phase grid-connected inverter, the output voltage of inverter is distorted seriously. This distortion increases the THD of the grid current. In this paper, the nonlinearity of inverter output voltage is analyzed and the model of inverter with the nonlinearity effect is established accordingly. In addition, a discrete-time integral sliding-mode controller is designed according to the new model to regulate the grid current. The novel control strategy achieves both exact nonlinearity compensation and strong robustness control of the whole system. Finally the control scheme is verified in a 100 kW three-phase grid-connected photovoltaic inverter prototype. The simulation and experimental results show that the proposed control strategy has fast dynamic response, strong robustness and good current harmonics rejection.