A fixed switching frequency integral resonant sliding mode controller for three-phase grid-connected photovoltaic inverter with LCL-filter

Sliding mode control (SMC) is recognized as robust controller with a high stability in a wide range of operating conditions, however it suffers from chattering problem. Damping the chattering effect is to smooth the discontinuity of SMC. Nevertheless it also limits the performance of SMC. Moreover in the real implementation of SMC, the sliding surface that is a linear combination of the system state variables and the generated references would drift while the system parameters change or external disturbance exists, which affects the tracking error and THD of system output seriously. In this paper, a fixed switching frequency integral resonant SMC (IRSMC) based on pulse width modulation (PWM) under d-q rotate frame is proposed for three-phase grid-connected inverter with LCL-filter. The chattering problem of SMC is eliminated by adopting Gao´s reaching law. In order to obtain an optimal trade-off between the elimination of chattering and the guarantee of performance of SMC, the parameters of SMC are optimized according to the ripple of the system output based on PWM. Moreover, an extra integral term of grid current error is introduced in sliding surface to eliminate the fundamental component of the tracking error. In order to suppress the grid current THD effectively, multiple resonant terms of the grid current error are added to the sliding function. Experimental results on a 30-kVA three-phase grid-connected inverter prototype show the effectiveness of the proposed control strategy.