A variable-band hysteresis modulated multi-resonant sliding-mode controller for three-phase grid-connected VSI with an LCL-filter

The control schemes of the VSI system have been studied worldwide for many years. However, most of the linear control methods can only achieve parts of the performance requirements. This paper presents a novel control strategy that combines a multiple-resonant sliding-mode controller (MRSMC) with a variable-band hysteretic modulator for a three-phase grid-connected voltage source inverter (VSI) with an LCL-filter. This strategy has a fast dynamic response, good steady-state performance and strong robustness. The mathematical model of the VSI is obtained and a third-order sliding-mode controller is designed to regulate the grid current. In addition, to fully eliminate the grid current tracking error and suppress its THD effectively, multiple resonant terms of grid current error are added to the sliding function. Because the finite switching frequency will cause chattering in sliding mode control, which may excite series current harmonics, a hysteretic modulator is introduced to solve the problem. However, variable switching frequency caused by a fix-band hysteretic modulator will spread the ripple current all over the bandwidth. A solution to this limitation is proposed by means of a hysteretic modulator with a variable band. Furthermore, the analysis and simulation results of dynamic response and rejection of current harmonics are shown.