This paper proposes a zero-sum dynamic game (ZSDG) design to mitigate frequency deviations in the secondary control layer of islanded AC microgrids. By defining a min-max optimization problem, where the control input minimizes the frequency deviations while the external disturbances maximizes the cost function, a robust control law is designed. The outcome leads to setting the frequency to its desired value and at the same time effects of disturbances are attenuated by applying the H∞ optimal controller in the secondary control level of AC microgrids. Since the basic ZSDG controller cannot eliminate adverse effects of external disturbances on the system frequency, an extended-ZSDG (EZSDG) method is introduced to design an effective H∞ controller. Due to the lack of access to the state variables of the microgrids, a full-order observer is designed to estimate these variables based on the measured output. In simulation results, the validity of the proposed EZSDG is investigated by considering uncertainties in both the communication and physical layers.
