Observer-Based Second-Order Sliding Mode Current Controller for Thyristor-Controlled LC-Coupling Hybrid Active Power Filter

In this article, a second-order sliding mode observer (SOSMO)-based second-order sliding mode controller (SOSMC) for the thyristor-controlled LC-coupling hybrid active power filter (TCLC-HAPF) is proposed. The proposed SOSMO-based SOSMC ensures the TCLC-HAPF low steady-state error, fast dynamic response, fixed switching frequency, and good system robustness under parameter variation and nonideal grid conditions. First, the SOSMO for the TCLC-HAPF system model is proposed, and its parameter design is provided. Based on the SOSMO model, the SOSMC for the TCLC-HAPF is proposed and designed accordingly. Then, simulation studies and experiments on a three-phase TCLC-HAPF are carried out to verify the steady-state and dynamic performance of the proposed SOSMO-based SOSMC compared with the other existing current controllers: proportional-integral controller, hysteresis current controller, and multi-quasi-proportional-resonant controller. Finally, the system robustness, unbalance compensation capability, and dc-link voltage control performance of the proposed SOSMO-based SOSMC under different nonideal grid conditions are also verified by simulation and experimental results.