Power Quality Compensation Strategy of MMC-UPQC Based on Passive Sliding Mode Control

While the unified power quality conditioner based on modular multilevel converter (MMC-UPQC) can be used for recovering power quality of voltage and current in high voltage grids, it is difficult to manage the power quality when the grid voltage imbalance is large. In this paper, a passivity-based control (PBC) combined with sliding mode control (SMC) is proposed for MMC-UPQC to improve the power quality under the unbalance of grid voltage in power systems. First, according to the structure of MMC-UPQC, the equivalent mathematical model is presented for unbalanced power grids. Second, the detection quantity is separated without phase-locked loop using a method of positive and negative sequence separation. Furthermore, a passive sliding mode control (PSMC) strategy is designed and applied to a multi-level and high voltage power quality compensation system. The proposed controller can improve the control accuracy of system parameters, response speed, and compensation effectiveness. Finally, the MATLAB/Simulink simulation and the real time laboratory (RT-LAB) based hardware-in-the-loop (HIL) experimental results show that the proposed PSMC strategy can compensate voltage and current rapidly and accurately, and the controller has strong robustness against system parameter changes.