基于HSS的三相VSC频率耦合导纳建模与谐波特性分析

Three-phase VSC frequency coupling admittance modeling and harmonic characteristics analysis based on HSS

针对非线性并网变流器系统中,因频率耦合现象产生的不期望谐波给电力系统带来的不可预测的稳定性问题。由于传统的LTI模型难以分析频率耦合现象,因此文章采用基于线性时间周期理论的谐波状态空间建模方法对三相电压源型变流器建模。所提模型考虑了输入信号的多频率响应特性,可深入分析各频次谐波间的交互关系。推导了三相VSC系统的谐波传递函数矩阵,结果表明随着分析频率的升高,谐波传递函数矩阵呈现为非主对角占优。这说明耦合导纳的确不容忽视,因此利用忽略耦合效应的LTI模型进行全频段的谐波响应分析,会使得结果不准确。HSS模型在分析VSC谐波特性时,由于其能揭示系统的多输入多输出特性及交直流侧谐波间的频率耦合现象,因此具备更高精确度。最后,利用时域仿真结果验证了HSS模型的准确性。

In nonlinear grid-connected converter systems, the undesired harmonics generated by the frequency coupling phenomenon bring unpredictable stability problems to the power system. In the traditional LTI model, it is difficult to analyze the frequency coupling phenomenon. A harmonic state space modeling method based on linear time period theory was adopted to represent a three-phase voltage source converter. The proposed HSS model considers the multi-frequency response of the input signal, and can deeply analyze the interaction relationship among different harmonics. The harmonic transfer function matrix of the three-phase VSC system was deduced, and the results show that as the analysis frequency increases, the harmonic transfer function matrix appears to be non-dominant diagonally dominant. This shows that the coupling admittance cannot be ignored. Therefore, using the LTI model that ignores the coupling effect to analyze the harmonic response of the whole frequency band will make the result inaccurate. When in the HSS model, the harmonic characteristics of the VSC is analyzed, it has higher accuracy because it can reveal the multiple-input multiple-output characteristics of the system and the frequency coupling phenomenon between the AC and DC side harmonics. Finally, accuracy of the HSS model is verified by the results of time domain simulation.