Small Signal Stability Analysis Oriented Design of Hybrid Anti-Islanding Protection Technique Based on Active Disturbance Injection

Abstract

The conventional over/under voltage, over/under frequency based anti-islanding protection scheme presents significant nondetection zone (NDZ) under critical loading conditions of distribution networks. To overcome this challenge, a unique hybrid technique has been proposed in this article for the anti-islanding protection of distributed generators (DGs). The algorithm requires the injection of an active oscillatory disturbance signal of very small magnitude through the current control loop along the direct axis of the synchronously rotating reference frame of the converter. Small signal stability analysis of the system is carried out to analyze the effect of such active signal injection having different frequencies. The anti-islanding protection algorithm first involves the superimposition of d-axis voltage. Thereafter, two novel indexes are proposed based on which the trip signal logic is developed for the protection scheme. The methodology has been found to detect an unintentional islanding scenario within 90 ms from the initiation instant. The efficacy of the proposed hybrid anti-islanding protection scheme is tested under various abnormal operating conditions by performing simulations on the CIGRE LV test system. Experimental validation of the proposed methodology has also been carried out in Controller Hardware-in-the-Loop (CHIL) platform using Typhoon HIL 602+ and Speedgoat baseline real-time target machine.