Real-time Validation of a Robust LQG based Decentralized Supplementary Control Loop to Mitigate Instability in an Islanded AC Microgrid

Microgrids comprising of inverter-interfaced distributed generations (IIDGs) can be subjected to high penetration levels of rectifier interfaced active loads (RIALs). The interaction between the control loops of these loads and the IIDGs can cause instability in these microgrids. To mitigate the instability, this letter proposes a robust decentralized linear quadratic gaussian (LQG) control loop around each IIDG unit. The LQG control combines the Kalman estimator with the linear quadratic regulator with prescribed degree of stability (LQRPDS). In order to obtain the optimal values of the diagonal weighting matrices of Kalman estimator and LQRPDS, a bi-objective optimization problem has been formulated and solved using a fast and elitist multi-objective non-dominated sorting genetic algorithm (NSGA-II). The performance of the proposed control loop in real time environment has been validated through simulations carried out in OPAL-RT eMegaSim® real-time digital simulator and is found to provide robust control under small load disturbances.