INVESTIGATION - OF HARMONICS ON POWER DISTRIBUTION SYSTEM

Abstract

Investigation of harmonics on power distribution system is presented, i.e. qualitative overview study of the distribution power system with the goal of understanding harmonics waveform distortion within it, and to provide a detailed analysis, that gives quantitative answers to the distortion due to the specific sources of harmonics and to take preventive measures for control of the same is done and presented in this work. A complete analytical model for the most common load type, i.e. single-phase power electronic load, is derived and investigation of the cumulative harmonic current characteristics of a large number of such loads is done. This model is then used to investigate the impact of 1) interaction due to shared source impedance, 2) variation in power level, and 3) variations in circuit parameters, on individual and cumulative current harmonics. Derivation of harmonic domain models suitable for the study of conventional three-phase, six pulse harmonic converters is performed. Modulation theory based on switching functions and discrete convolutions are the cornerstone of these models. Inrush current phenomenon, arising during transformer energization, and containing a slowly decaying transient response, with connection to harmonic domain technique is presented. A need to reduce the harmonics and reactive power in the system has occurred mostly due to large use of power electronic apparatus. The comparison of the technologies developed for handling harmonic and reactive power reveals that the strategy of hysteresis current control provides best results with regard to THD confirming well to IEEE — 519 standards. But the major limitation is the high and variable switching frequency of operation of the devices, which results in complexity in design of filters needed to meet the EMI standards. This led to selection of control techniques suitable for APF which employing constant switching frequency. Hence adaptive hysteresis band current controller is proposed and modeled. Analytical results are presented to show the effectiveness of the proposed shunt active filter.