Innovative Load Shedding Scheme to Restore Synchronous Generator Based Microgrids during FIDVR

Fault induced voltage recovery (FIDVR) phenomenon may occur in microgrids ( $\mu $ Gs) and distribution systems due to the induction motors (IMs) behavior after system voltage sags especially short circuit faults. For the case that motors reaccelerate, system voltage may recover to its nominal value after few seconds. However, it may remain low during motor stalling condition, which result in unstable (non-recoverable) FIDVR. In this paper, an adaptive load shedding scheme is proposed to mitigate unstable FIDVR in $\mu $ Gs containing synchronous dispersed generators (SDGs) to enhance system dynamic behavior. Derivative of the imaginary part of equivalent admittance seen from the distribution feeders with respect to time is utilized to discriminate stable FIDVR from unstable ones. In addition, a new criterion is proposed to determine SDG stability margin during the FIDVR phenomenon. Then, a new load shedding scheme is presented based on the proposed SDG stability margin and IM reacceleration index. Moreover, the load shedding time delay is adaptively calculated based on motor reacceleration time. Performance of the proposed method is evaluated by comprehensive simulation studies on two realistic networks. These investigations fairly reveal security and reliability of the proposed method in various conditions.