并网逆变器dq阻抗灰箱辨识方法与应用

Gray-box Identification Method of Grid-connected Inverters dq Impedance and Its Applications

为实现“双碳”目标,并网逆变器大量接入配电网,与弱电网间形成复杂交互,谐波劣化问题凸显。并网逆变器dq阻抗的准确获取是进行谐波劣化分析的关键之一。现有阻抗测量方法存在无法适应并网逆变器运行工作点时变,加窗快速傅里叶变换(fast Fourier transform,FFT)频域计算存在差异的缺陷。针对这些缺陷,提出一种以白箱建模结果为目标,以黑箱算法为求解途径的灰箱辨识方法,基于并网逆变器端口电压、电流时域数据,对不同运行工作点下的dq阻抗进行在线辨识。首先,在逆变器并网点串联注入多正弦波电压扰动,获取辨识模型所需数据;然后,建立灰箱辨识模型,通过递推最小二乘算法对并网逆变器dq阻抗进行在线辨识;最后,基于RT-LAB搭建半实物实时仿真平台,验证所提方法的有效性。基于阻抗辨识结果,绘制回率矩阵特征函数奈奎斯特曲线,对不同运行工作点下系统相角裕度进行求解,实现所提方法在谐波劣化风险在线评估中的应用。

In order to achieve the goal of “carbon peaking and carbon neutralization”, a large number of grid-connected inverters are connected to the distribution network. A complex interaction with the weak grid is formed, and the problem of harmonic degradation is prominent. Accurate acquisition of dq impedance of grid-connected inverters is one of the keys to analysis harmonic degradation. The existing impedance measurement methods are not suitable since the operating points of grid-connected inverters maybe time-varying and the calculation results of windowed fast Fourier transform(FFT) in frequency domain is distinct. Aiming at these defects, this paper presented a gray-box identification method, which took the white-box modeling results as the goal and the black-box algorithm as the solution. Based on the time-domain data of voltage and current of ports, the dq impedance at different operating points was identified online. Firstly, multiple sinusoidal voltage disturbances were injected into point of common coupling of the inverters in series to obtain the data needed for the identification model. Secondly, the gray-box identification model was established, and the dq impedance of the grid-connected inverters was identified online through the recursive least square algorithm. Finally, a hardware in the loop real-time simulation platform was built based on RT-LAB to verify the effectiveness of the presented method. Moreover,based on the impedance identification results, the Nyquist curve of characteristic function of the return rate matrix was drawn, and the phase angle margin of the system under different operating points was solved, so as to realize the application of method presented in this paper in the online assessment of harmonic degradation risk.