Modeling and Parameter Identification of Converter Transformer for High-Frequency Resonance Problem of Flexible DC Converter Station
Hu Yinghong1, Li Yu1, Li Yang2, Chen Jikai2, Zhang Yang3
1. Electric Power Research Institute of State Grid Jibei ElectricPower Co. Ltd Beijing 100045 China; 2. Key Laboratory of Modern Power System Simulation and Control & Renewable Energy Technology Ministry of Education Northeast Electric Power University Jilin 132012 China; 3. School of Electrical Engineering Nanchang Institute of Technology Nanchang 330099 China
Abstract：In December 2020, a high-frequency resonance of around 3 200 Hz occurred during the no-load starting process of Kangbao station, triggering high-frequency component protection, which resulted in the converter station blockage and system trip. When the resonance occurred, the converter station charged the converter transformer. However, the bus was not connected to any AC overhead line, which means that the converter transformer participated in the high-frequency resonance of a modular multilevel converter (MMC) with the no-load bus. The modeling method that the converter transformer is equivalent to the leakage reactance can not reflect the high-frequency characteristics of the converter transformer, failing to analyze this high-frequency resonance accurately. For the high-frequency resonance problem in Zhangbei Kangbao MMC with the no-load bus, the research focuses on the physical characteristics of the converter transformer and the modeling method in the high-frequency range. Firstly, the high-frequency equivalent model is established considering the interturn capacitance, the coupling capacitance, and the capacitance to ground. The high-frequency model of the converter transformer is simplified by neglecting the capacitance to ground. Then, based on the measured frequency response data of the Kangbao converter transformer, the improved Powell algorithm is used to calculate the high-frequency equivalent model parameters. The critical parameters are checked, and the application scope of the model is determined. Moreover, the effects of equivalent capacitance parameters on the high-frequency impedance of the converter transformer are analyzed. Finally, based on the high-frequency equivalent model, the high-frequency resonance phenomenon is reproduced in Kangbao MMC with the no-load bus. The simulation results verify the accuracy of the equivalent model. Different from the power frequency model, interturn and coupling capacitances should be considered in converter transformer modeling at the high-frequency band. The capacitance effect makes the equivalent impedance characteristics of the converter transformer appear capacitive in the frequency band of 1~5 kHz. Compared with the measured frequency response data of the Kangbao converter transformer, the proposed method can easily obtain accurate high-frequency model parameters within 5 kHz, such as the interturn capacitance, the coupling capacitance, and the leakage induction. The simplified high-frequency model of the converter transformer meets the accuracy requirements of the high-frequency resonance analysis of MMC with the no-load bus. The grid side winding's interturn capacitance of the converter transformer has the most obvious influence on its high-frequency impedance, and the high-frequency resonance frequency of MMC with the no-load bus decreases with the increase of its capacity. During the no-load starting process, the high-frequency characteristic of the converter transformer is an essential factor in determining whether the high-frequency resonance risk exists at a converter station. If the high-frequency characteristic of the converter transformer is addressed, the high-frequency resonance problem of MMC with the no-load bus can be accurately analyzed.
胡应宏, 李雨, 李阳, 陈继开, 张扬. 面向柔直换流站高频谐振问题的换流变压器建模与参数辨识[J]. 电工技术学报, 2024, 39(22): 7154-7166.
Hu Yinghong, Li Yu, Li Yang, Chen Jikai, Zhang Yang. Modeling and Parameter Identification of Converter Transformer for High-Frequency Resonance Problem of Flexible DC Converter Station. Transactions of China Electrotechnical Society, 2024, 39(22): 7154-7166.
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2024, Vol. 39 
