基于等效阻抗的VSG电压支撑影响因素分析与改进控制策略研究

doi:10.19595/j.cnki.1000-6753.tces.241876

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摘要

虚拟同步机（VSG）控制因其主动支撑特性而受到广泛关注,但其电压支撑能力的影响因素尚不明确,兼顾电压支撑能力与短路电流限制的VSG控制策略需要进一步研究。针对上述问题,首先,基于变流器电压源特性分析稳态时各控制环节等效阻抗,并建立系统等效电路模型;其次,基于等效电路推导机端电压表达式,并进行影响因素分析;然后,兼顾限流要求与电压支撑能力,提出虚拟阻抗与电压补偿系数自适应控制策略;最后,通过Matlab/Simulink仿真平台进行验证。结果表明：通过减小虚拟阻抗、无功电压下垂系数或增大电压补偿系数,能够提高VSG电压支撑能力;该文所提出的虚拟阻抗与电压补偿系数自适应控制,在短路电流不越限的情况下能够最大限度的实现电压支撑。

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关键词 ：虚拟同步机, 等效阻抗, 电压支撑, 自适应

Abstract：

Under the impetus of "dual carbon" targets, new energy sources are increasingly integrated into the power grid through power electronic converters, leading to a gradual decline in the proportion of synchronous machines. To enhance the stability of "highly renewable and highly flexible" systems, the flexible controllability of converters can be leveraged by employing grid-forming control to provide reliable voltage and frequency support to the system. Virtual synchronous generator (VSG) control emulates the operating characteristics of synchronous generators to achieve voltage and frequency regulation, providing active frequency and voltage support capabilities while effectively increasing the inertia level of new energy units. VSG control has garnered significant attention due to its active support features; however, the factors influencing its voltage support capability are not yet fully understood, necessitating further research on VSG control strategies that balance voltage support with short-circuit current limitations.
To address these issues, this paper first analyzes the equivalent impedance of each control stage of grid-forming converters based on VSG control during steady-state operation and establishes an equivalent circuit model of the system. Secondly, based on the system's equivalent circuit, the expression for terminal voltage is derived, quantifying the relationship between terminal voltage, internal electromotive force, and system impedance, and analyzing the factors affecting the voltage support capability of VSG. Subsequently, improvements to VSG control are made considering both current limitation requirements and voltage support capability, proposing adaptive control strategies for virtual impedance and voltage compensation coefficients. Finally, the accuracy of the theoretical analysis and the effectiveness of the proposed strategy are verified using the MATLAB/Simulink electromagnetic simulation platform.
The analysis results show that reducing virtual impedance, reactive power voltage droop coefficient, or increasing the voltage compensation coefficient can enhance the voltage support capability of VSG. However, decreasing virtual impedance and reactive power voltage droop coefficient reduces the system's equivalent impedance, while increasing the voltage compensation coefficient increases the system's internal electromotive force, thus imposing higher demands on the system's current-limiting capacity. By adopting the proposed adaptive control strategy for virtual impedance and voltage compensation coefficients, virtual impedance can be self-adaptively configured according to the system state, ensuring voltage support capability under the premise of meeting current-limiting requirements.
Through theoretical analysis and simulation experiments, the following conclusions can be drawn: (1) When the grid-forming converter system based on VSG control enters a steady state, its various control stages can be represented by equivalent impedance, which characterizes the relationship between terminal voltage, internal electromotive force, and system impedance. (2) The voltage support capability of VSG is related to virtual impedance, reactive power voltage droop coefficient, and voltage compensation coefficient. Reducing the reactive power voltage droop coefficient, decreasing virtual impedance, and adding voltage compensation control to the reactive power loop can all improve voltage support capability. (3) Voltage support capability and short-circuit current limitation of VSG interact. Through adaptive control of virtual impedance and voltage compensation coefficients, short-circuit currents can be fully utilized, maximizing the voltage support capability of VSG without exceeding the short-circuit current limit.

Key words： Virtual synchronous generator equivalent impedance voltage support adaptive

收稿日期: 2024-10-21

PACS:

TM341

基金资助:

国网冀北电力有限公司科技项目资助（520101240005）

通讯作者: 高本锋男,1981年生,副教授,研究方向为高压直流输电和电力系统次同步振荡。E-mail：gaobenfeng@126.com

作者简介: 刘思佳女,2000年生,硕士,研究方向为新能源电力系统分析与控制。E-mail：1264993435@qq.com

引用本文:

刘思佳, 刘海涛, 张隽, 于思奇, 孙大卫, 邢晶, 高本锋. 基于等效阻抗的VSG电压支撑影响因素分析与改进控制策略研究[J]. 电工技术学报, 0, (): 1876-. Liu Sijia, Liu Haitao, Zhangjun, Yu Siqi, Sun Dawei, Xingjing, Gao Benfeng. Research on the Analysis of VSG Voltage Support Influence Factors and Improvement Control Strategies Based on Equivalent Impedance. Transactions of China Electrotechnical Society, 0, (): 1876-.

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