一起风电场高频振荡事故的原因和解决方法分析

基于广西木格风电场高频振荡时的电气参数以及风机网侧变频器的控制原理,建立了风机网侧变频器的传递函数模型。通过网侧变频器传递函数模型和其诺顿等效电路的对比分析,求出了网侧变频器等效阻抗的频域表达式。通过伯德图对网侧变频器等效阻抗和电网阻抗的幅频特性、相频特性进行分析,得出了高频振荡事故的原因是在特定频率下网侧变频器等效阻抗和电网阻抗形成了谐振。然后提出了通过修改前馈电压系数来改变网侧变频器等效阻抗的幅频、相频特性,从而解决高频振荡问题的方案。对修改前馈电压系数后的风机并网系统传递函数模型进行分析,求出了其开环传递函数。用伯德图进行分析证明了修改后系统的稳定裕度明显增加。木格风电场采取此措施后在各种工况下验证,均能够正常运行,证明了所提解决方案的有效性。

Analysis of causes and solutions of a high-frequency oscillation accident in a wind farm

Based on the high frequency oscillation characteristics of Guangxi Muge wind power plant and the control principle of the grid-side frequency converter of a wind turbine, a transfer function model of the wind turbine grid-side frequency converter is established. By comparative analysis of the transfer function model of the grid-side frequency converter and its Norton equivalent circuit, the frequency domain expression of the grid-side equivalent inverter impedance is obtained. Bode diagram analysis of amplitude-frequency and phase-frequency characteristics of the grid-side frequency converter equivalent impedance show that the incidence of high frequency oscillation is caused by resonance from the grid and converter impedances at a certain frequency. To overcome the problem of high-frequency oscillation, the method of modifying the feedforward voltage coefficient then changing the amplitude and frequency of the equivalent impedance and converter phase-frequency characteristics is proposed. The open-loop transfer function can be obtained by modifying the feedforward voltage coefficient of the grid connected system transfer function. Bode diagram analysis shows that the margin stability of the system is increased significantly after modification. It has been verified that a Muge wind power plant can operate normally under various working conditions after taking this measure. This demonstrates that the proposed solution is effective. This work is supported by the National Natural Science Foundation of China (No. 61803219).