Control strategy for com-leg in single-phase transformerless three-leg Unified Power Quality Conditioner

Single-phase three-leg Unified Power Quality Conditioner (UPQC) is relatively a good choice for power quality compensation in low-power applications as it can achieve high performance with low cost. In this paper, a decoupling control method is proposed to eliminate the interaction between the series and shunt converters of the three-leg UPQC. In the proposed method, output voltage of the common leg is controlled proportional to the grid voltage and the proportional coefficient is optimized to ensure the compensation of both the series and shunt converter with lower DC-link voltage. Additionally, theoretical analysis and certain design criterions are provided in the paper. Simulation and experimental results are also presented to verify the feasibility and effectiveness of the proposed decoupling control method.