Average Absolute Frequency Deviation Value Based Active Islanding Detection Technique

An average absolute frequency deviation value based active islanding detection technique is proposed in this paper. The inverter´s classical q-axis current controller is modeled with a continuous periodic reference current of a small value. During the loss of mains, the island´s frequency deviates with respect to the variation in the reference current; this is detected by making the use of an average absolute frequency deviation value. In case of a stable island formation, there is a small periodic frequency deviation owing to the small value of the periodic reference current, and the frequency deviation is so small that it falls inside the nondetection zone (NDZ) of the frequency relay. The main advantage of the proposed algorithm is that it detects the stable island formation but without forcing the island to lose its stable operation. In case of nonislanding switching events, which may transiently impose a significant deviation in the frequency, the possibility of false detection is eliminated by reconfirming the occurrence of islanding once it is suspected. The reference current is kept to a small value to limit the degradation of the power quality and the power factor. Computer simulation is done with MATLAB.