MODELLING OF UNIFIED POWER QUALITY CONDITIONER (UPQC) FOR POWER QUALITY IMPROVEMENT

Abstract

With the advent of power electronics and digital control technology, the renewable energy sources are increasingly being connected to the distribution systems in terms of wind, solar, hydro etc due to their free availability and low conversion cost. However, with the proliferation of the power electronics devices, unbalanced loads and nonlinear loads, the quality of the power evacuated from these renewable sources have degraded to large extent, which may often leads to distorted voltage and currents in the distribution network thereby affecting the reliability of the system. Thus, stable operation of the distribution system amidst variety of unbalance at the connected load is a challenging task. Among various custom power devices, UPQC is considered to be the most promising solution for balanced operation of the system. It has the capability to offer control from both series as well as shunt end, thereby providing compensation to various power quality problems associated with the system. The thesis proposes a control scheme for UPQC to enhance the quality and reliability of the electrical power generated in the distribution system particularly when connected to diode rectifier type non-linear load. Unified PQ conditioner (UPQC) is a versatile custom power device which consists of two VSCs connected back-to-back to compensate for both distorted PCC voltage and supply current imperfections. For a Non-Linear load, UPQC is designed to compensate the harmonic injected by the non- load from entering into the source terminal and regulation of voltage at the point of common is carried out by series connected converter. SRF based current control method is used for current compensation by the shunt device and Hysteresis voltage control technique is used for series device which simultaneously act as shunt and series active power filters. Also, maintaining a constant value for dc link voltage is necessary for UPQC to perform normally which is here carried out by shunt connected VSC. MATLAB based simulation is carried out to demonstrate the effectiveness of the proposed control scheme.