Abstract：When the permanent magnet synchronous wind turbine supplies power to the power grid through the converter, the high-frequency common-mode current generated by the converter will bring serious electromagnetic interference and bearing electrical corrosion problems. By studying the spectrum distribution of common-mode current and the influencing factors of its amplitude, the harmonic distribution of common-mode current can be artificially changed according to the needs, and the amplitude of common-mode current can be controlled within a reasonable range, thus reducing the negative effects of common-mode current on the system. In this paper, the 5.5 MW permanent magnet synchronous wind turbine system is taken as the object to carry out measurement and simulation analysis, and a common-mode loop model modeling method and parameter determination method of converter-cable-motor are put forward, and the decisive factors of common-mode current resonance frequency and influencing factors of amplitude are quantitatively analyzed and simulated. Firstly, the common-mode test platform of wind-driven permanent magnet synchronous motor is built to collect common-mode voltage, common-mode current and bearing voltage waveforms. Through the port impedance test method, the stray capacitances, common-mode inductance, eddy current resistance and cable parameters in the motor are extracted. The common-mode equivalent circuit model of permanent magnet synchronous wind turbine system is established. The model is simulated and analyzed, and compared with the measured results in time domain and frequency domain, which proves the effectiveness of the simulation circuit and parameter extraction method. Then, based on the above circuit model, the determinants of common-mode current amplitude and harmonic distribution are studied, and the frequency determinants of common-mode current harmonic concentration are deduced and verified by simulation. The common-mode voltage is simplified as a trapezoidal wave with rise time of tr, and the common-mode circuit is simplified as a RLC series circuit. The relationship between the rise time of inverter switch and the amplitude of common-mode current is deduced analytically and verified in the original cable-motor simulation model. The results show that the three key parameters that affect the harmonic distribution of common-mode current are equivalent inductance of cable, common-mode inductance of motor and capacitance between motor winding and casing, which determine the distribution of resonance frequency of common-mode current. The simulation results of common-mode current amplitude and switching rise time show that the low-frequency component of common-mode current has nothing to do with the rise time, and the high-frequency component of common-mode current is approximately inversely proportional to the rise time. Because the common-mode current is mainly composed of high-frequency components, the simulation results show that the curve of the amplitude and rise time of common-mode current has a good fitting relationship with the inverse proportional function, which verifies the above inference. Through the above analysis, we can draw the following conclusions: the frequency of harmonic concentration of common-mode current in permanent magnet synchronous wind turbine system is determined by the common-mode impedance of motor and cable; The peak-to-peak value of common-mode current is approximately inversely proportional to the switching rise time. By adjusting the parameters of the cable or installing a filter device, the resonance point of the system can be shifted to low frequency, thus effectively reducing the high frequency component of the common-mode current. At the same time, on the basis of satisfying the switching frequency and other properties, the amplitude of common-mode current can be effectively reduced by choosing a switching tube with a long rise time.
贾磊, 刘瑞芳, 李知浩, 李术林, 黄鑫, 彭亮. 永磁同步风力发电机高频共模电流谐波分布及幅值影响因素研究[J]. 电工技术学报, 2023, 38(zk1): 101-113.
Jia Lei, Liu Ruifang, Li Zhihao, Li Shulin, Huang Xin, Peng Liang. Study on the Influence Factors of Harmonic Distribution and Amplitude of Common-Mode Current of Permanent Magnet Synchronous Wind Turbines. Transactions of China Electrotechnical Society, 2023, 38(zk1): 101-113.
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2023, Vol. 38 
