基于修正独立随机矢量的系统侧谐波阻抗估计

System-side Harmonic Impedance Estimation Based on Modified Independent Random Vectors

随着新能源、电力电子装备的接入,电网中存在大量的谐波源,谐波污染和谐波谐振问题愈发严重。背景谐波波动变大,且用户侧通常装有滤波装置使得用户侧谐波阻抗并非远大于系统侧。系统侧谐波阻抗的准确估计对谐波的管控及谐波谐振分析等具有重要意义,而现有的谐波阻抗计算方法往往需假设背景谐波稳定且用户侧谐波阻抗远大于系统侧谐波阻抗,不符合工程实际,导致估计误差较大。因此,在独立随机矢量法的基础上,文中提出了基于公共连接点谐波电压和电流不同时间间隔的弱相关性来估计谐波阻抗的方法。通过对公共连接点谐波电压和谐波电流的相关性分析,对归一化相关系数设定阈值筛选出弱相关时段,在该时段内不同时间间隔所对应的系统侧谐波电流的相关性恒为弱相关,解得系统侧谐波阻抗。跟现有方法相比,所提方法可用较少的样本点计算出系统侧谐波阻抗,且背景谐波波动和两侧谐波阻抗比变化对所提方法的影响较小,适用范围更广泛。仿真以及工程实测数据的分析验证了该方法的有效性。

With the access of new energy and power electronic equipment, there are a large number of harmonic sources in the power grid, which makes harmonic pollution and harmonic resonance problems more serious. Since background harmonic fluctuations become larger and the customer side is usually equipped with filter devices, the harmonic impedance of customer side is not much larger than that of the system side. Accurate estimation of system-side harmonic impedance is of great significance for harmonic control and harmonic resonance analysis. However, the existing methods for estimating harmonic impedance usually assume that the background harmonic is stable or harmonic impedance of customer side is much larger than that of the system side, which are not always satisfied in practical cases and lead to larger estimation error. Therefore, based on the independent random vector method, this paper proposes a method for estimating the harmonic impedance based on the weak correlation between harmonic voltage and harmonic current at different time intervals. By analyzing the correlation of harmonic voltage and harmonic current measured at the point of common coupling(PCC), the threshold of the normalized correlation coefficient is set to screen out the weak correlation period, in which the correlation of the harmonic current of system side in different time intervals is always weak. Thus, the harmonic impedance of system side can be obtained. Compared with the existing methods, the proposed method requires less data and can significantly eliminate the negative effects of the background harmonic fluctuation and impedance ratio of two sides, and has a wider application range. Simulation and field cases are conducted to verify the effectiveness of the proposed method.