Baoge Zhang, Xiong LvThis email address is being protected from spambots. You need JavaScript enabled to view it., Hao Tian, Yongquan Ren, and Fuhong Cui
School of Automation and Electrical Engineering, Lanzhou Jiaotong University, Lanzhou,730070, China
Received: July 22, 2023 Accepted: December 18, 2023 Publication Date: March 8, 2024
Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.
Distributed power sources are generally connected to the microgrid through inverters. However, due to the output line impedance mismatch, it will result in the traditional droop control not being able to achieve accurate reactive power sharing. To address this problem, this paper proposes an improved droop control strategy based on virtual impedance. The output reactive power mismatch term is introduced into the droop control as a feedback signal to achieve the adaptive adjustment of virtual impedance and improve the accuracy of reactive power sharing. Meanwhile, the adaptive regulation strategy of secondary frequency and voltage recovery is proposed. The frequency offset and voltage offset during the stable operation of the system are compensated. Finally, the three inverters parallel system of isolated microgrid is built in matlab/Simulink for simulation study. The reactive power output of the parallel system without adaptive virtual impedance is compared to the reactive power output of the parallel system without adaptive virtual impedance (Q1 = 3000var, Q2 = 2000var, Q3 = 1000var ) in 0 − 2 s. The output reactive power of the parallel system with the addition of the adaptive virtual impedance is Q1 = Q2 = Q3 = 2000 var. the addition of the virtual impedance achieves good power equalization. At the same time, the secondary voltage and frequency strategies are added so that the output voltage and frequency of the parallel system after adding the adaptive virtual impedance are restored to 311 V and 50 Hz from the original 310 V and 49.7 Hz. The frequency and voltage offsets are compensated. The simulation results verify the effectiveness and feasibility of the proposed control strategy.
Keywords: droop control, virtual impedance, frequency offset, voltage offset
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