Research on Composite Control Strategy of Energy Storage Unified Power Quality Conditioner for Voltage Sag

Abstract

Traditional unified power quality conditioner (UPQC) only relies on DC-side capacitors for energy storage, which leads to severe DC bus voltage fluctuation, steady-state AC tracking error of series-side voltage compensation, and insufficient energy supply for long-duration compensation under deep voltage sag conditions. To address these issues, a photovoltaic-battery energy storage unified power quality conditioner (PV-BESS-UPQC) topology is proposed in this paper. A proportional-integral quasi-resonant (QPIR) composite dual-loop control strategy is adopted to realize error-free tracking of distorted voltage. A fuzzy PI dual-channel voltage regulation strategy driven by the square of DC voltage deviation is constructed on the DC bus to suppress instantaneous power shocks induced by voltage sags. MATLAB/Simulink simulation results demonstrate that under voltage sag conditions, the proposed scheme significantly suppresses the fluctuation amplitude of the DC bus voltage. Compared with the traditional single PI control, it achieves stable mitigation of long-duration deep voltage sags, and is suitable for comprehensive voltage quality governance of distribution networks with high penetration of new energy.