基于阻抗法的光储逆变器交直流建模及耦合分析

doi:10.19595/j.cnki.1000-6753.tces.230286

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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 words： Solar-storage system DC and grid side coupling combined impedance ratio stability

Received: 24 May 2023 Published: 07 June 2024

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Li Da,Zhang Tao. Modeling and Coupling Analysis of DC and Grid Side of Solar-Storage Inverter Based on Impedance Method[J]. Transactions of China Electrotechnical Society, 2024, 39(10): 3038-3048.

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https://dgjsxb.ces-transaction.com/EN/10.19595/j.cnki.1000-6753.tces.230286 OR https://dgjsxb.ces-transaction.com/EN/Y2024/V39/I10/3038

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