In this paper, a second-order sliding mode observer (SOSMO) based second-order sliding mode controller (SOSMC) for the 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 non-ideal 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 non-ideal grid conditions are also verified by simulation and experimental results.