Enhancing Voltage Stability and Reactive Power Compensation by Replacing Mechanically Switched Capacitor Banks with Fuzzy Logic-Based DSTATCOM (A Case Study of Bishoftu No.3 Substation)

Abstract

Reactive power can cause voltage drops, inefficient power transmission, increased linelosses and reduced system stability. To mitigate such kinds of power quality issues amechanically switched capacitor bank is installed at Bishoftu No 3 substations.Mechanically switched capacitor banks, despite their economic advantage, are associatedwith several drawbacks. These includes large transient, switching time delay, wear and tearof contacts and limited switching frequency. This study analyzes the transient effectsassociated with the switching operations of the capacitor bank. The existing mechanicallyswitched capacitor bank is designed according to the specifications of its component.Simulations were conducted using Matlab/Simulink tool to assess the bank?�?s performance,first by switching in a single stage and subsequently all the three stages. The simulationrevealed that during the switching of the first stage at 0.08seconds, a total harmonicdistortion (THD) of voltage reached 16.48%, exceeding the acceptable standard of 5%.Furthermore, switching in all the three stages, each with a capacity of 1.2 MVAr totaling3.6MVAr, resulted in a THD of 17.03%. These findings indicate mechanically switchedcapacitor bank poses a significant power quality challenges when frequently switched tomeet reactive power demands. To mitigate these issues, this study proposes fuzzy logic-controlled DSTATCOMs as a replacement for the existing capacitor bank. The proposedsystem employs fuzzy logic controller techniques to regulate reactive power compensationand maintain voltage stability within acceptable levels. A DSTATCOM is designed havinga capacity of 3.6MVAr. The controller measures the variation in source voltage and makesthe decision based on rule base we set. It controls the firing angle of the DSTATCOM toeither absorb or inject the required compensation reactive power from or to thedistribution bus bar. The simulation result of FLC based DSTATCOM demonstrate itseffectiveness in maintaining voltage st