电工技术学报  2024, Vol. 39 Issue (10): 3038-3048    DOI: 10.19595/j.cnki.1000-6753.tces.230286
电力电子 |
基于阻抗法的光储逆变器交直流建模及耦合分析
李达, 张涛
三峡大学电气与新能源学院 宜昌 443000
Modeling and Coupling Analysis of DC and Grid Side of Solar-Storage Inverter Based on Impedance Method
Li Da, Zhang Tao
College of Electrical and New Energy Three Gorges University Yichang 443000 China
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摘要 在共母线式光储逆变器中,交直流单元通过直流母线电容连接。传统的逆变器建模方法将母线电容视为无穷大,认为交直流侧运行相互解耦。然而,当直流母线电容较小时,光储逆变器的交直流侧将产生交互影响,引起电流谐振。该文以单个单元稳定运行为前提,推导出直流共母线系统稳定性的合阻抗比(CIR)判据。该判据的数学形式便于利用Bode图对并联系统的谐振源进行分析与定位。首先,对光储逆变器交直流各单元进行阻抗建模,利用合阻抗比判据分析直流侧储能单元相对于光伏单元更易与网侧发生谐振。然后,通过在电流环路加入陷波器改善储能单元的阻抗特性。最后,仿真及实验结果证实了所提合阻抗比稳定性判据的正确性。
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关键词 光储系统交直流耦合合阻抗比稳定性    
Abstract:In solar-storage inverters, the photovoltaic unit, the energy storage unit on the DC side, and the inverter unit on the AC side are interconnected through a DC bus. Typically, the DC bus serves to isolate the operation of each module. However, as the bus capacity reduces, the inter-module coupling effect emerges, leading to oscillations in the bus voltage and current. Assessing the stability of the multi-module interconnected coupling system, identifying the resonance source, and eliminating oscillations have become major concerns.
The DC bus stability issue in solar-storage inverters can be equated to the stability problem of a multi-module parallel model. In previous studies, the “impedance ratio” method was commonly used to assess the stability of multi-module interactive systems. However, the impedance ratio method can only assess the stability of interactions between two-port sources. When dealing with multi-module interactions, the system is usually divided into “source” and “load” components. This approach should be more conducive to identifying and attributing resonance causes within specific units. Therefore, this paper proposes a combined impedance ratio stability criterion based on the stable operation of single modules. It deduces that the number of poles in the right half-plane of the parallel impedance of each module impedance in the system determines the stability of the DC parallel system. Accordingly, the system stability criterion is transformed into the sum of the impedance ratios of each unit. This mathematical form is beneficial for assessing system stability using the traditional Bode diagram stability method. The source of system resonance is determined by comparing the contribution of the amplitude-frequency gain of each unit's impedance ratio Bode diagram to the system's combined impedance ratio at the resonance frequency.
By impedance modeling for each unit of the solar-storage inverter and analyzing the impedance ratio Bode diagram, it is concluded that the energy storage unit and its rapid change of the impedance characteristics in high frequency can cause system resonance. In contrast, the photovoltaic unit has an equivalent input internal resistance that suppresses the change in its impedance characteristics, remaining resistive and inductive at all times. Subsequently, a notch filter is incorporated into the energy storage unit's controller to reduce the resonance peak of the open-loop transfer function in high frequency and enhance the output impedance characteristics.
Finally, the developed model is validated through simulation and experimentation. The cause of system resonance can be accurately analyzed and identified through comparative analysis and applying the combined impedance ratio criterion. The control delay of the energy storage unit indeed causes the mutual resonance problem of the photovoltaic storage inverter. The photovoltaic unit has a natural equivalent internal resistance that contributes very little to the resonance peak and is not responsible for the system resonance. Simulation and experimental results demonstrate the correctness of the model and the effectiveness of the proposed strategy.
Key wordsSolar-storage system    DC and grid side coupling    combined impedance ratio    stability   
收稿日期: 2023-05-24      出版日期: 2024-06-07
PACS: TM615  
基金资助:国网浙江省电力有限公司科技资助项目(5211JX1900CX)
通讯作者: 李达 男,1995年生,硕士研究生,光伏控制软件高级工程师,研究方向为并网逆变器稳定性分析及控制。E-mail: l1d2moan@126.com   
作者简介: 张涛 男,1981年生,教授,博士生导师,研究方向为新能源发电与并网技术、电力系统优化运行、高电压绝缘及测试。E-mail: unifzhang@foxmail.com
引用本文:   
李达, 张涛. 基于阻抗法的光储逆变器交直流建模及耦合分析[J]. 电工技术学报, 2024, 39(10): 3038-3048. Li Da, Zhang Tao. Modeling and Coupling Analysis of DC and Grid Side of Solar-Storage Inverter Based on Impedance Method. Transactions of China Electrotechnical Society, 2024, 39(10): 3038-3048.
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https://dgjsxb.ces-transaction.com/CN/10.19595/j.cnki.1000-6753.tces.230286          https://dgjsxb.ces-transaction.com/CN/Y2024/V39/I10/3038