Adaptive virtual impedance control based on second-order generalized integral for circulating current suppression
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ORIGINAL ARTICLE
Adaptive virtual impedance control based on second‑order generalized integral for circulating current suppression Baifu Zhang1 · Xiaoqing Han1 · Runquan Meng1 · Chunguang Ren1 · Lei Wang1 · Tianhao Song1 · Yizhao Liu2 Received: 23 June 2020 / Revised: 8 October 2020 / Accepted: 13 October 2020 © The Korean Institute of Power Electronics 2020
Abstract The redundant design of multi-paralleled bidirectional power converters (BPCs) provides technical support for hybrid microgrid systems to consume more distributed generations (DGs) and DC loads. However, the multi-BPCs also provide paths for circulating current. In addition, the AC sub-grid may operate under unbalanced conditions due to the consumption of single-phase loads and power electronic devices. In addition, unbalanced three-phase voltage deteriorates the generation of circulating current. In this paper, an adaptive virtual impedance control method based on second-order generalized integration (SOGI) is proposed to suppress circulating current on the basic analysis of circulating current generation mechanism, the equivalent model establishment, and the suppression principle. The virtual impedance is dynamically adjusted in realtime based on the power oscillation caused by unbalanced voltage. Moreover, an integral term is added to the reactive power droop control to realize the tracking of voltage without static error. Finally, the effectiveness and feasibility of the proposed control algorithm are verified by experiments. The research results show that the proposed control method can optimize the damping characteristics, reduce the voltage difference between the BPCs, and improve the current sharing effect. Keywords Hybrid microgrid · Bidirectional power converters (BPCs) · Unbalance conditions · Circulating current · Adaptive virtual impedance
1 Introduction The development and utilization of renewable energy, such as wind and solar, have attracted increasing attention from scholars and researchers. The concept of AC/DC hybrid microgrids has emerged to integrate distributed generations (DGs) and various DC/AC loads [1–5]. In a hybrid microgrid, unnecessary DC/AC or AC/DC conversions can be reduced, and the energy conversion efficiency can be improved [6]. Multi-BPCs are always connected between common DC and AC buses to improve the power capacity and reliability of hybrid AC/DC microgrids. Nevertheless, one of the crucial problems is the circulating current among multi-BPCs.
* Baifu Zhang [email protected] 1
College of Electrical and Power Engineering, Taiyuan University of Technology, Taiyuan, China
Electric Power Research Institute, State Grid Shanxi Electric Power Company, Taiyuan, China
2
Many efforts have been made to suppress ZSCC under symmetrical operation. For example, hardware was adopted to cut off circulating current paths [7–9], virtual impedance was adopted to cover the mismatch of external feeder impedance [10, 11] and a modified space vector pulse width modulation (SVPWM) control was proposed to regulate the
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