Sliding-Mode and Proportional-Resonant Based Control Strategy for Three-Phase Grid-Connected LCL-Filtered VSI

Abstract

A sliding-mode and proportional-resonant based control strategy for three-phase grid-connected LCL-filtered voltage source inverter (VSI) is proposed. The generation of three-phase capacitor voltage references is essential in the proposed control strategy. Although the reference capacitor voltage for a specific phase can be generated by adding the measured grid voltage for that phase with the voltage drop on the grid-side inductor caused by the reference grid current, the computation of the voltage drop on the inductor requires a derivative operation which is not preferred in a control algorithm. Therefore, a proportional-resonant (PR) controller is employed to generate the three-phase reference capacitor voltages. The consequence of using PR controller is that the need for using the derivative operation is eliminated. The PR controller offers another advantage regarding the ability to track ac quantities with zero steady-state error. In addition, the equation for the optimum sliding coefficient is derived analytically. Computer simulation results are presented and reported to validate the proposed control approach.