Continuous Higher Order Sliding Mode Controller for LCL-Type Grid-Connected Shunt Active Filters

A LCL grid connected three-phase and three-wire shunt active filter (SAF) is studied and controlled. It is known that SAFs generate distortive components caused by a high switching frequency of a voltage source inverter (VSI). In order to prevent spreading these distortive components to the grid, the LCL filter (usually controlled by a linear control feedback) is used; while a parasitic phase shift/lag between the reference and injected currents emerges and severely deteriorates the filtration quality. On the other hand, the use of a sliding mode controller (SMC) reduces phase shift effects and consequently ensures good filtration quality of the SAF while improving robustness to system's disturbances. A side effect of SMC is in generating discontinuous very high switching frequency control command that can severely hurt the switching elements of the VSI. In this work, the robust continuous higher order sliding mode controller (C-HOSM), whose output is processed by pulse-width modulators (PWM), is studied for controlling the SAF. The proposed robust control set up provides a fixed given frequency of control switching, required for the VSI safe operation. The proposed approach was validated on industrial nonlinear load via simulations carried out using Matlab, Simulink, and Simscap-Sim_Power_System code.