Abstract— The recent trend of distributed generation leads to several issues regarding power quality and energy efficiency. To meet the increased demand of electricity services and to increase service quality the current power grid structure should be controlled in such a way that distributed generation could be easily connected to it. The various services are becoming challenging concern to elegantly integrate distribute generation to the grid. One of these services is voltage control which provides support to the voltage under grid fault conditions. During voltage sag condition continues power supply should be provided to grid. According to grid code requirement of transmission system, several kind of voltage sag requires different voltage
Sudden increase or decrease in loads and starting of motors are the cause of internal voltage sags. Depending on the magnitude, duration of the voltage sag and sensitivity of equipment, severity of the voltage sag can be evaluated. The sensitive electronic equipment's are such as variable speed drive (VSD) controls, programmable logic controllers (PLC’s), motor starter, power supply controller etc.
A. Voltage Sag Classification and Characterization
In the grid system, voltage sag is considered as an abnormal condition. And they are significant reduction in one or several phases for a very short time. There are several classification methods. One of those is according to magnitude and phase angle jumps [17]. There are several types but following four are the basic types like Type A, B, C and D [16].
Fig. 1. Voltage sag type A, B, C and D.
According several authors the voltage sag of types B,C and D produces positive and negative sequence voltage which distorts the current and affects the power quality of grid[12].
This voltage sags are also characterized the positive, negative, and zero symmetric