基于矩阵的迹的弱电网下永磁直驱风电场直流电压时间尺度小扰动振荡稳定性分析

Small disturbance oscillation stability analysis of permanent magnet synchronous generator wind farm under weak grid in DC voltage timescale based on matrix trace

弱电网下锁相环与直流电压环强交互作用给并网永磁直驱风电场稳定运行带来了安全隐患,以往研究主要采用基于具体仿真算例的模式分析法研究弱电网下风电场系统的锁相环或直流电压环稳定性规律,无法揭示所得稳定规律的内在机理。为此,建立考虑直流电压环和锁相环动态的并网永磁直驱风电场降阶模型,推导出系统状态矩阵的迹的数学表达式,从理论分析的角度揭示了弱电网下永磁直驱风电场的直流电压时间尺度小扰动稳定性规律。分析结果表明在风机控制参数固定不变的条件下,当系统运行参数如线路电抗、风电场无功出力或风机数量增大时矩阵的迹向正方向移动,这表明考虑锁相环动态影响时由直流电压动态主导的永磁直驱风电场系统至少有一个模式的阻尼变弱。

The strong interaction between PLL(Phase-Locked Loop) and DC voltage loop brings safety hazard to the stable operation of grid-connected permanent magnet synchronous generator wind farm under weak grid. In previous researches,the modal analysis method based on detailed simulation cases is mainly used to study the stability law of the wind farm system induced by PLL or DC voltage loop under weak grid,while the internal mechanism of stability law obtained by this method cannot be revealed. For that,the reduced order model considering the dynamics of DC voltage loop and PLL is built,and the mathematic expression of matrix trace is deduced. The small disturbance stability law of the permanent magnet synchronous generator wind farm under weak grid in DC voltage time scale is revealed theoretically. Analysis results show that under the condition of the control parameters for wind turbine are fixed,when the system operating parameters such as the line reactance,the reactive power output of wind farm or the number of wind turbine increase,the matrix trace moves toward the positive direction,which shows that when considering the dynamic influence of PLL,the damping of at least one mode for the permanent magnet synchronous generator wind farm system dominated by DC voltage loop dynamic is weakened.