基于电流源模型的中性点不接地系统铁磁谐振频域解析方法

Frequency-domain Resolution Method for Ferro Resonance in Neutral Ungrounded System Based on Current Source Model

在中性点不接地配电系统中,由于PT饱和后励磁电感的非线性特征,在一定条件下容易发生铁磁谐振现象,对系统的安全稳定产生严重的影响。基于中性点不接地系统等效电流源并联模型,列写关于非线性电感电流和磁链的微分方程,在复频域下进行拉普拉斯变换,从而间接构建各次谐波的频域约束方程。利用描述函数法计算出发生铁磁谐振时的线路参数状态,同时利用增量描述函数,根据稳定性理论判断谐振状态条件下状态值的稳定性,从而得到发生n次谐波谐振的必要条件。为深入认识和研究配电系统的铁磁谐振状态规律提供了一种解析方法,并通过仿真分析验证了方法的正确性。

In the neutral ungrounded distribution system,ferro resonance is likely to occur under certain conditions due to non-linear characteristics of excitation inductance after PT saturation,thus producing serious impact on system safety and stability.Based on a parallel model of equivalent current source of the neutral ungrounded system,a differential equation of non-linear inductance current and flux linkage was formulated,and Laplace transformation was carried out in the complex frequency domain so that frequency domain constraint equations were constructed indirectly for each harmonic.Line parameter state in the case of ferro resonance was calculated in the descriptive function method.In the meanwhile,the stability of the state value under the condition of the resonance state was judged according to the theory of stability by using incremental describing function,so that necessary conditions for the occurrence of n-th harmonic resonance might be obtained.Thus,an analytical method was provided for better understanding and research of the laws of ferro resonance state of the distribution system.Furthermore,the correctness of the presented method was verified through simulation analysis.