A Simple Method for Design of Adaptive Filters for Sinusoidal Signals

Filtering of input signals in algorithms for measurement of power system electrical parameters is very important. Filters are used to minimize the noise effect and eliminate the presence of higher order harmonics. In addition to that, a number of measurement algorithms apply orthogonal signal components obtained by two orthogonal finite-impulse response filters. The frequency response of the filters must have nulls at the higher order harmonic frequencies that are expected to be present in the signal and must have a unity gain at the main harmonic frequency. In the case of a time-varying frequency, the filter parameters have to be adapted during frequency estimation. In this paper, a simple method for online design of digital filters for sinusoidal signals is proposed. It is based on closed-form solutions for calculating filter coefficients. A simple linear algorithm for frequency estimation was used, and a derived algorithm for online adaptation of the filter coefficients is computationally very efficient. The number of subsections in the cascade and data window lengths can also be changed, depending on the frequency variations during measurement.

I. Introduction

Accurate measurement of power system parameters is important for control and protection of the power system. Measurements form an important basis for understanding of power quality phenomena. Different phenomena require different analysis tools. in some cases, one is purely interested in steady-state characteristics of the signal, e.g., root-mean-square (rms) voltage, frequency, or harmonic spectrum. in other cases, one is mainly interested in the voltage as a function of time, e.g., the transient due to capacitor switching. for these 1-D signal analysis problems, suitable techniques are available and in use [1], [2].