感性电网阻抗下三相光伏逆变器稳定性分析

Stability Analysis of Three-phase PV Inverter Under Inductive Grid Impedance Condition

许多情况下,电网并非理想的电压源,而是存在感性阻抗的弱电网。传统的光伏逆变器设计并没有考虑电网阻抗的影响,逆变器?电网级联系统阻抗不匹配容易导致逆变器的稳定性能降低,甚至不稳定。该文从阻抗的角度,分析L滤波和LCL滤波的光伏逆变器在感性电网阻抗下的稳定性,并分别对稳定判据和输出导纳模型展开研究。通过模型降阶和矩阵近似,简化广义奈奎斯特稳定判据对逆变器?电网级联系统的稳定性分析。借鉴直流电源导纳模型建立的方法,简化由闭环状态矩阵推导d轴输出导纳的计算过程。最后根据所提出的简化判据和建立的d轴输出导纳模型,分析两种滤波方式下级联系统的稳定性,并研究滤波器参数与对级联系统稳定裕度的影响。通过实验对所进行的稳定性分析进行了验证。

In many cases, the grid is not ideal voltage source but a weak grid which contains inductive grid impedance. The influence of grid impedance is not considered in the conventional design of photovoltaic （PV） inverters. Impedance mismatch is likely to deteriorate the stability of the cascaded system of PV inverter and grid, even making the system unstable. From the perspective of the impedance, this paper analyzed the stability of PV inverter with L-filter and LCL-filter under the condition of inductive grid impedance, and the stability criterion and output admittance model were researched respectively. Through the model order reduction and matrix approximating, the stability analysis of inverter cascaded with grid which was usually complemented based on the generalized Nyquist stability criterion （GNC） is simplified. Drawing on the method in which the admittance models of the DC power are built, the calculation process of the d channel output admittance which was usually derived from the closed-loop state matrices is simplified. According to the proposed simplified criterion and the established d channel output admittance model, the stability of PV inverter cascaded with grid was analyzed, and the influence of filter parameters on stability margin of the cascaded system was studied. Experimental results validate the proposed theoretical stability analysis.