The distribution STATCOM for reducing the effect of voltage sag and swell

The concept of Flexible Alternating Current Transmission Systems(FACTs) and Custom Power is widly studied by the researcher. FACTs use Power electronic devices and methods to control the high-voltage side of the network for improving the power flow. Custom Power is for low-voltage distribution, and improving the poor power quality and reliability of supply affecting factories, offices and homes. Power quality and Reliability are becoming important issues for critical and sensitive loads after introducing the term of Custom Power by Hingorani in early 1980s. Custom Power Devices is classified into three categories by their structures such as Dynamic Voltage Restorer(DVR), Distribution STATCOM(DSTATCOM) and Unified Power Quality Compensator(UPQC). Among these devices, the main purpose of DVR that injects voltage in series with a distribution feeder is reducing the effect of short-term voltage sags, dips, swells and momentary interruptions. The DVR is capable of generating and absorbing the voltage independently controllable real and reactive power. It consists of three-phase voltage source inverter, injection transformer, DC LINK and Rectifier for charging the DC LINK or Battery. As you know, Rectifier is generating the harmonic problem in distribution lines. Rectifier or devices for charging DC LINK is useless in this proposed system by their structure. The proposed system have a function of generating and absorbing voltage by self-charging control technique. This system has three states : 1) normal operation, 2) charging operation and 3) recharging operation. The paper discusses control issues and the proposed control algorithm. The proposed control technique is applied to DSTATCOM for protecting voltage sags, swell and momentary interruption. The dynamic performance is analysed and verified through the simulation.