Studies on Power Quality and, an LSE & PSOPC based Harmonic Estimation to Real Time Data

Abstract

Electric power as a commodity is very different from other products – it is generated far from the point of use, is fed to the grid together with the output of many other generators and arrives at the point of use via several transformers and many kilometers of overhead and possibly underground cabling. Quality check of power is very important. But it has constantly been polluted by both consumers (non-linear loads) and utility companies (due to increased use of semi conductor based power processors). Assuring the quality of delivered power to be good enough for the application at hand calls for measurement and study of power quality at the point of common coupling.

There are various categories of Power Quality issues. Issues related to voltage amplitude variations will include voltage sags/dips and voltage swells. Issue related to frequency is harmonics in the power system. Short term problems include transients and momentary interruptions. We have carried out a brief study of all these PQ issues, and problems caused by them.

Developments in the field of power electronics has brought tremendous power processing capability to engineers but it has also polluted the power system with harmonics. Then there are non linear loads that inject harmonics in the power system. Measurement and estimation of harmonics in power system has become one of the most important tasks in the hands of power system engineers for increasing reliability and quality of supplied power. For harmonic analysis FFT based schemes are unable to give enough information for PQ mitigation. So researchers have been attempting other methods to estimate harmonics in sampled voltage and current signals. Among these; least square estimation, for estimating amplitudes and particle swarm optimization with passive congregation, for estimating phase and frequency used together has most attractive features of compactness and fastness. We have developed a harmonic estimator based on LSE and PSOPC to estimate amplitude, phase and frequency of the sampled signal. We have used the estimator on real time data acquired using a digital storage oscilloscope in Electrical Machines Laboratory of Department of Electrical Engineering at NIT Rourkela. The results for estimating integral harmonics are attractive and encourage researchers to modify the estimator code to make it able to estimate inter-harmonics and sub-harmonics also.