Performance Enhancement for Unified Power Quality Conditioner Using Passivity Fractional-Order Sliding Mode Control

Unified power quality conditioner (UPQC) can comprehensively address power quality issues related to voltages and currents, but its control system is usually dominated by proportional-integral (PI) controllers, which may affect the system’s operation performance in the face of uncertain interferences. Therefore, in this paper, a control strategy based on passivity fractional-order sliding mode control (PFOSMC) is proposed to enhance the performance and robustness of UPQC. The passivity of system is demonstrated by establishing the Euler-Lagrange model, and then the passivity-based control (PBC) is designed to accelerate the convergence speed of system to errors. In practice, changes in the stable equilibrium points may cause disturbances to the passive control law, so a SMC is employed to optimize PBC by utilizing the advantages of SMC in resisting internal and external disturbances. To suppress the chattering, a fractional-order term is introduced into SMC, which promotes the system to approach the sliding surface more smoothly. After that, the control law of PFOSMC is designed, and the overall control strategy of UPQC is given based on this control law. To verify the superiority of the proposed PFOSMC in operation performance, the comparative experiments on PI, PBC, SMC and PFOSMC are tested under various working conditions from the aspects of overshoot, dynamic response and total harmonic distortion. Experimental results indicate that the proposed PFOSMC-based control strategy can more effectively enhance the UPQC’s operation performance.