Hybrid Islanding Protection Scheme for V2G Connected System with Local Load

Abstract

In this paper a hybrid islanding scheme comprising a passive and active islanding detection technique is proposed for a vehicle to grid system. The passive system continuously monitors the rate of change of frequency and islanding condition is detected whenever it crossed a preset threshold value. Since transients in grid may also results in frequency deviation a higher threshold is desirable which increases the non-detection zone for passive islanding technique. An active islanding detection scheme is proposed where a linearly time varying reactive power in injected following an islanding detection by passive islanding method. Unlike conventional active islanding technique where change of frequency is compared with a threshold value, the proposed scheme evaluates correlation between the estimated rated of change of frequency (ROCOF) and measured ROCF. The value of this correlation function provides the threshold value for detection of islanding condition. Since the value of this correlation function in independent of the magnitude of the reactive power injection the proposed technique can work with lower injection of reactive power and hence distortion in power quality introduced by the proposed active islanding technique will be smaller