电工技术学报  2024, Vol. 39 Issue (9): 2682-2695    DOI: 10.19595/j.cnki.1000-6753.tces.231765
“规模化分布式源荷接入下交直流混合配电网优化运行与稳定控制技术”专题(特约主编:贾宏杰 唐 巍 肖 迁 冀浩然) |
弱电网下并网逆变器恒定带宽及稳定裕度的自适应控制策略
曾祥辰, 刘青, 王嘉晨, 辛振
省部共建电工装备可靠性与智能化国家重点实验室(河北工业大学) 天津 300401
Adaptive Control Strategy of Grid-Connected Inverters with Constant Bandwidth and Stability Margin in Weak Grids
Zeng Xiangchen, Liu Qing, Wang Jiachen, Xin Zhen
State Key Laboratory for Reliability and Intelligence of Electrical Equipment Hebei University of Technology Tianjin 300401 China
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摘要 随着可再生能源在电网中的占比不断提高,电网逐渐呈现出弱电网特性,即电网阻抗不可忽略且频繁波动。电网阻抗的存在会改变逆变器控制环路的增益,导致控制环路的稳定裕度减小,因而引发稳定性问题,同时,控制环路的截止频率也因电网阻抗的存在而减小,环路带宽也随之减小,使得逆变器动态性能变差。针对弱电网下电网阻抗变化引发的相关问题,现有的控制策略往往侧重于提升逆变器的并网稳定性,而对其动态性能下降的问题缺乏关注。鉴于此,为同时解决以上问题,该文提出一种基于环路增益测量的自适应控制策略以保障逆变器优越且恒定的控制性能,首先通过环路增益的在线测量实现对逆变器控制性能的实时监测;然后依据实时监测的控制性能指标参数自适应地调整控制器的参数,以提升逆变器对弱电网的适应性;最后以单相并网逆变器为例进行实验验证,实验结果证明了所提方案的有效性。
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曾祥辰
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关键词 稳定性自适应控制弱电网并网逆变器    
Abstract:Driven by the large-scale adoption of electronic power converters for widespread renewable generation, power grids gradually present weak grid characteristics, i.e., the grid impedance can’t be ignored and fluctuates frequently. The grid impedance directly affects the control loop gain of inverters, which can decrease the stability margin and lead to poor dynamic performance. To solve these issues jointly, an adaptive control strategy based on loop gain measurement technique is proposed in this work to improve the adaptability of inverters to pre-unknown weak grid conditions.
The proposed adaptive control strategy includes two important steps: (1) The monitoring of control performance indexes and (2) Auto-tuning of controller parameters. Firstly, a control performance monitor is proposed for online monitoring of control performance indexes (crossover frequency fc, phase margin φM) of inverter systems. These indexes can be used to characterize, in real time, the dynamic performance and stability, respectively. The proposed control performance monitor is designed based on Middlebrook’s loop gain measurement technique with small signal injection. The corresponding signal extraction structure is realized by a high-pass second order generalized integrator (HPSOGI), which can enhance the attenuation ability of low-frequency harmonics. With the measured performance indexes (fc, φM), an auto-tuner is then designed to adjust controller parameters of inverters accordingly. The sensitivity analysis method is adopted to decouple the controller parameters (Kp, Kr) and control performance indexes (fc, φM). A general adaptive law is therefore designed as following: the crossover frequency fc is designed to adjust the proportional gain Kp until the desired crossover frequency fREFc is achieved; the phase margin φM is designed to adjust the resonance gain Kr until the desired phase margin φREFM is achieved. In this way, high dynamic performance and sufficient stability margin can be guaranteed simultaneously by the proposed auto-tuner. Additionally, the relevant parameters selection and design of regulators are discussed.
The experimental results show that the monitoring process can be completed within 60ms with an accuracy of 96%, which is sufficient for the subsequent auto-tuning process. Both the measurement time and the accuracy can be further improved by refining the auto-tuner coefficients. With the proposed adaptive control strategy, the crossover frequency and phase margin can be maintained at expected value (fc=1 kHz, φM=45°) under grid impedance variations and low-voltage ride through conditions. With the increased loop gain, total harmonic distortion (THD) of the injected grid current is also decreased.
The following conclusions are drawn from this paper: (1) The HPSOGI structure adopted in control performance monitor can improve accuracy and speed of the monitoring process. (2) Sensitivity analysis method can be used to design adaptive law to improve the adaptability of adaptive control strategy to various regulators such as PI and PR regulator. (3) The proposed adaptive control strategy can maintain high dynamic performance and sufficient stability margin of inverter system under grid impedance variation and fault conditions such as low-voltage ride through.
Key wordsStability    adaptive control    weak grids    grid-connected inverters   
收稿日期: 2023-10-24     
PACS: TM464  
基金资助:国家自然科学基金青年项目(62003126)、河北省自然科学基金绿色通道项目(E2021202157)和河北省留学人员资助项目(C20220318)资助
通讯作者: 刘 青 女,1990年生,副教授,研究方向为电力电子系统建模、控制与稳定性分析。E-mail:qing.liu@hebut.edu.cn   
作者简介: 曾祥辰 男,1999年生,硕士研究生,研究方向为并网逆变器控制及稳定性分析。E-mail:202121401093@stu.hebut.edu.cn
引用本文:   
曾祥辰, 刘青, 王嘉晨, 辛振. 弱电网下并网逆变器恒定带宽及稳定裕度的自适应控制策略[J]. 电工技术学报, 2024, 39(9): 2682-2695. Zeng Xiangchen, Liu Qing, Wang Jiachen, Xin Zhen. Adaptive Control Strategy of Grid-Connected Inverters with Constant Bandwidth and Stability Margin in Weak Grids. Transactions of China Electrotechnical Society, 2024, 39(9): 2682-2695.
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