基于电网阻抗的并网逆变器准比例谐振控制

随着新能源大规模接入电网，新能源并网逆变器在与电网交互引发的次/超同步振荡问题引起了广泛关注。此类振荡问题与并网逆变器的输出阻抗和电网阻抗特性密切相关。采用谐波线性化方法建立了三相LCL型并网逆变器的小信号输出阻抗模型，分析了不同电流控制策略对其输出阻抗的影响，通过阻抗比奈奎斯特判据分析了电网阻抗变化对系统稳定的影响。采用无源阻尼与有源阻尼相结合的方法抑制LCL滤波器的固有谐振尖峰，再根据公共耦合点电网阻抗的变化调节准比例谐振（quasi proportional resonance，QPR）控制器参数以及电容电流反馈系数，使系统阻尼基本保持不变，增强系统鲁棒性，确保系统稳定运行。时域仿真与数值分析结果证明了所提控制策略的有效性。

Quasi-Proportional Resonance Control of Grid-Connected Inverter Based on Grid Impedance

With the large-scale integration of renewable energy to the grid, the problem of sub/super-synchronous oscillations caused by the interaction of renewable energy grid-connected inverters with the grid has drawn great public attention. Such oscillation problems are closely related to the output impedance of the grid-connected inverter and the characteristics of grid impedance. Therefore, a small-signal output impedance model of the three-phase LCL–type grid-connected inverter is developed in this paper with harmonic linearization method, and the impacts of different current control strategies on its output impedance are evaluated, and the influence of grid impedance on system stability is analyzed with the impedance ratio Nyquist criterion. The inherent resonance peak of LCL filter is suppressed by combining passive damping with active damping, and the parameters of quasi-proportional resonance (QPR) controller and the feedback coefficient of capacitance current are adjusted according to the change of grid impedance at the point of common coupling, which enhances the robustness of the system without changing the system damping, and ensures the stable operation of the system. Finally, the effectiveness of the proposed control strategy is verified by combination of time-domain simulation and numerical analysis.