Model Reference Adaptive Controller for Simultaneous Voltage and Frequency Restoration of Autonomous AC Microgrids

Abstract

In an autonomous droop-based microgrid, the system voltage and frequency (VaF) are subject to deviations as load changes. Despite the existence of various control methods aimed at correcting system frequency deviations at the secondary control level without any communication network, the challenges associated with these methods and their abilities to simultaneously restore microgrid VaF have not been fully investigated. In this paper, a multi-input multi-output (MIMO) model reference adaptive controller (MRAC) is proposed to achieve VaF restoration while accurate power sharing among distributed generators (DGs) is maintained. The proposed MRAC, without any communication network, is designed based on two methods: droop-based and inertia-based methods. For the microgrid, the suggested design procedure is started by defining a model reference in which the control objectives, such as the desired settling time, the maximum tolerable overshoot, and steady-state error, are considered. Then, a feedback-feedforward controller is established, of which the gains are adaptively tuned by some rules derived from the Lyapunov stability theory. Through some simulations in MATLAB/SimPowerSystem Toolbox, the proposed MRAC demonstrates satisfactory performance.