Abstract：Due to the instantaneous power imbalance between AC and DC sides, DC secondary ripple voltage is generated in the single-phase half-bridge transformer-less UPQC during grid-connected and islanded modes. In grid-connected mode, the DC secondary ripple voltage would degrade the compensation performance of UPQC. This paper introduces a trap filter to the parallel-side converter's voltage loop and improves the sub-harmonic control in the current loop. For the series-side converter, a third harmonic voltage control is added to the current loop for voltage compensation. In islanded mode, this paper proposes a novel method that utilizes the idle series-side converter and reused split DC capacitors to build an active power decoupling circuit. It can effectively suppress secondary ripple voltage without additional power decoupling circuit components. Moreover, with the proposed compensation and suppression strategies for secondary ripple, the design of DC capacitor parameters can be optimized to further reduce the volume of the UPQC equipment. Firstly, by analyzing the impact of DC voltage ripple on UPQC, different control strategies are developed for different sides of converters. Secondly, a notch filter is added to the voltage outer loop of the parallel side converter, and a sub-harmonic control is added to the current inner loop, which suppresses the impact from the DC voltage ripple. On the series side, a third harmonic voltage control is introduced to the current inner loop of the converter, significantly reducing the THD of the grid side current and load voltage. Thirdly, the generation of the secondary ripple voltage of a two-stage single-phase DC-AC converter in islanded mode is analyzed. Composed of UPQC idle series converter and DC side shunt capacitor, a symmetrical half-bridge active power decoupling circuit is proposed to reduce the voltage ripple. Simulation and experimental results show that UPQC with proposed control in grid-connected mode can achieve 30% voltage compensation for grid under voltage and overvoltage, and the grid current THD is less than 3%. In islanded mode, the DC secondary ripple voltage of a single-phase inverter can be effectively reduced by the proposed active power decoupling circuit under different loading conditions, and the maximum reduction in DC secondary ripple voltage is 75%. Moreover, 64% of the DC capacitance can be reduced compared to the traditional passive power decoupling method. The following conclusions can be drawn: (1) In grid-connected mode, compared with the transient current control, the voltage-current double-loop control based on single-phase dq decoupling with trap filters and sub-harmonic compensation can effectively reduce the grid current THD. (2) In islanded mode, the proposed active power decoupling method significantly reduces the THD of the load voltage with the increase of load power. (3) Compared with the DC capacitance increment, the proposed active power decoupling method has better performance in reducing the total DC secondary voltage ripple. Thus, the proposed compensation and suppression strategies can reduce DC bus capacitance, further improving the power density of UPQC.
马兰, 曹晓琦, 张影, 向诗彪, 舒泽亮. 单相统一电能质量调节器二次纹波补偿及抑制策略[J]. 电工技术学报, 2024, 39(22): 7197-7212.
Ma Lan, Cao Xiaoqi, Zhang Ying, Xiang Shibiao, Shu Zeliang. Secondary Ripple Compensation and Suppression Strategy for Single-Phase Unified Power Quality Conditioner. Transactions of China Electrotechnical Society, 2024, 39(22): 7197-7212.
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2024, Vol. 39 
