基于勒让德多项式拟合的变谐波阻抗估计方法

Estimation method for variable harmonic impedance based on Legendre polynomial fitting

传统的谐波阻抗估计方法往往在研究时段内将其假设为恒定值,但伴随着光伏等新能源接入电网,以及可能存在的运行方式改变,这种假设不再成立。为此,提出一种基于勒让德多项式拟合的变谐波阻抗估计方法。采用勒让德多项式对谐波阻抗曲线进行拟合,根据系统侧谐波电压和谐波阻抗的变化特性建立目标函数约束。求解目标函数最小值得到拟合函数的系数,进而实现变谐波阻抗估计。基于此,同时讨论了勒让德多项式阶数的选取和谐波阻抗突变点识别方法,提高了方法的适用性。基于诺顿等效电路和10节点测试系统进行了仿真。仿真结果表明,与传统方法相比,所提方法可以跟踪谐波阻抗的变化,提高谐波阻抗估计的精度。

Traditional harmonic impedance estimation methods tend to assume it as a constant value during the study period.However,along with the connection of new energy sources such as photovoltaics to the grid and the possible changes in operation,this assumption no longer holds.For this,a variable harmonic impedance estimation method based on Legendre polynomial fitting is proposed.The harmonic impedance curve is fitted with Legendre polynomial,and then the objective function constraint is established according to the variation properties of harmonic voltage and harmonic impedance.The coefficients of the fitting func⁃tion are obtained by solving the minimum of the objective function,and then the variable harmonic impedance estimation is realized.Based on this,the selection of Legendre polynomial order and the identifica⁃tion method of harmonic impedance mutation point are also discussed to improve the applicability of the method.Simulations are carried out in Norton equivalent circuit and 10-bus test system.The simulative re⁃sults show that compared with the traditional method,the proposed method can track the variation of har⁃monic impedance and improve the accuracy of harmonic impedance estimation.