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

Study on the Influence Factors of Harmonic Distribution and Amplitude of Common-Mode Current of Permanent Magnet Synchronous Wind Turbines

永磁同步发电机由于能量密度大、结构简单、运行效率高等优点,成为风力发电系统广泛使用的机型之一。永磁同步发电机在通过变流器向电网供电时,变流器产生的高频共模电流会带来严重的电磁干扰和轴承电腐蚀问题。定量研究共模电流频谱分布以及幅值的影响因素,就可以根据需要人为地改变共模电流的谐波分布,将共模电流的幅值控制在合理的范围内,从而降低共模电流对系统的负面效应。该文从一台MW级风力永磁同步发电机的共模电流测试实验出发,提出一种变流器-电缆-电机的建模及实验提取参数的方法,从时域和频域两个方面验证了模型的准确性。在此模型基础上,针对谐振和上升时间两个因素,对共模电流的谐波分布和幅值的影响进行定量分析和仿真研究,结果表明,共模回路阻抗决定共模电流的谐波分布,共模电流上升时间与共模电流的幅值成反比。

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 t_(r),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.