一种衰减直流分量精确估计新算法

A new algorithm for accurate estimation of decaying DC component

提出一种从故障电流信号中消除衰减直流分量的新算法.该算法基于纯正弦波信号在一个全波周期积分为零、而指数衰减信号在一个全波周期积分不为零的原理,用一个全波周期加上前一个采样周期的采样数据,就能精确估计指数函数型衰减直流信号的幅值和时间常数.将每个采样数据减去衰减直流分量偏移量得到校正采样数据,应用全波DFT电相量算法就能对滤除衰减直流分量的故障电流基波相量进行高精度测量.该算法对数字积分和指数函数进行了工程运算的简化,并提出衰减直流分量是否存在的简易判别算法,提高了数字保护算法的选择性.在M atlab仿真平台上进行了综合仿真试验,试验表明:所提算法测量精度高,易于用DSP实现,可应用到基于DSP的数字继电保护装置中.

A new algorithm to eliminate the decaying direct current(DC) component from fault currents is presented.This algorithm is based on the principle that a purely sinusoidal signal is integrated into zero over a full cycle of its fundamental frequency and an exponential decaying signal has nonzero integrating value.The sampled data of one full cycle plus one past sampled period can be used to exactly estimate the magnitude and time constant of an exponential decaying signal.Each sample data are subtracted by the decaying DC component offset of this sample period to obtain each correct data.The correct data are applied to the full DFT(discrete Fourier transform) power phasor algorithm,and then the fault current for the removal of the decaying DC component can be accurately measured.This algorithm simplifies the engineering computation of digital integration and exponential function.A simple and feasible discrimination algorithm for whether the decaying DC component exists is proposed to improve the selectivity of the digital protection algorithm.Simulation tests are carried out on Matlab simulation plateform.Tests show that the proposed algorithm has high measurement accuracy and easy implementation by DSP(digital signal processor) and can be applied to digital relay protection based on DSP.