A Unified Framework for Adaptive and Flexible Phase Angle Regulation in Single-Phase UPQC

The unified power quality conditioner (UPQC) is an effective solution for addressing power quality issues in modern power systems, with its ability to regulate both voltage and current. However, existing UPQC operational strategies lack sufficient adaptability and flexibility in managing load-side phase, especially when dealing with complex grid disturbances. This article proposes a unified framework for adaptive and flexible phase angle regulation, primarily based on two novel algorithms: the practical optimized-VA-loading operational strategy (POOS) and the universal flexible control method (UFCM). First, the proposed POOS method, utilizing phase angle control, enables online VA loading optimization within the UPQC's safe operating range according to real-time grid conditions. A comprehensive discussion of the method is presented, including the working principles, operational boundaries, and iterative computation process. Second, the proposed UFCM ensures smooth phase control of the load voltage throughout complex grid events. A dual-speed phase-locked loop is introduced to decouple the target and real-time phase, with parameter design guidelines and a discretization process provided. Furthermore, the unified framework is thoroughly explained, which balances the steady-state optimization requirements of the UPQC with the dynamic load-side power quality. Finally, experimental results validate the effectiveness of the unified framework under complex grid disturbance scenarios.