Robust Nonlinear Optimal Control for Voltage-Frequency and Active-Reactive Power Regulation in Microgrids

This paper presents a novel nonlinear optimal and robust control strategy, for the dual operation mode for a microgrid. During the grid-connected operation mode, it uses PQ control mode, in order to inject or absorb active or reactive power to the microgrid AC common bus, while on the other hand after an isolation event, the microgrid uses the VF control mode in order to ensure the voltage and frequency regulation to the local load. The main contribution of this paper is to present an alternative control scheme, instead of the classical control methods based on nested linear controllers, with dedicated control loops for the current and voltage regulation. The advantages of the proposed control strategy are that the control algorithm is able to achieve the control objectives and at the same minimizes a given performance index, expressed in terms of the control expenditure and the tracking reference error. It is worth mentioning that the microgrid under study is modeled using the dq-frame and therefore output power of the system becomes a nonlinear function of the state, therefore it is necessary to apply nonlinear optimal and robust controllers in order to reject the parametric uncertainties of the system and deal with the microgrld nonlinear behavior.