Citation: Hajihosseini, M.; Leši´ c, V.; Shaheen, H.I.; Karimaghaee, P. Sliding Mode Controller for Parameter-Variable Load Sharing in Islanded AC Microgrid. Energies 2022, 15, 6029. https://doi.org/10.3390/ en15166029 Academic Editor: Gianfranco Chicco Received: 19 July 2022 Accepted: 18 August 2022 Published: 19 August 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Sliding Mode Controller for Parameter-Variable Load Sharing in Islanded AC Microgrid Mojtaba Hajihosseini 1 , Vinko Leši´ c 1 , Husam I. Shaheen 1, * and Paknoosh Karimaghaee 2 1 Laboratory for Renewable Energy Systems, Faculty of Electrical Engineering and Computing, University of Zagreb, 10000 Zagreb, Croatia 2 School of Electrical and Computer Engineering, Shiraz University, Shiraz 71441-65186, Iran * Correspondence: hshaheen@fer.hr; Tel.: +385-955535396 Abstract: Controlling voltage, frequency, and current in an islanded microgrid is a challenging problem because the distributed generation sources, stochastic and intermittent in nature, are not connected to the main electricity network to provide stable and clean energy. Therefore, the design of a robust controller to control the output parameters of the islanded microgrid and suppress load variations and disturbances is essential. In this paper, a hysteresis controller is proposed and designed to control the output voltage of an islanded AC microgrid and an improved sliding mode controller (SMC) based on adaptive control principle is designed to control the current of the microgrid. The current controller consists of two parts: An adaptation part, which aims to eliminate disturbances and system uncertainties, and a second part, which aims to deal with the tracking problem of the system under parameter-varying topologies. The adaptation strategy has the advantage of solving the gain tuning problem and chattering reduction. It also requires limited information about disturbance and uncertainties of the system. To validate the proposed control methodology and show its effectiveness, a case study of a simulated islanded microgrid is presented. The results show that the proposed controllers can effectively control the current and voltage underload changes and increase the stability and resilience of the microgrid. The results also reveal that the performance of the proposed controller in terms of total harmonic distortion (THD) and dynamic response overcome the performance of conventional controller by a 4× reduction in THD and 40–200× reduction in settling time. Keywords: hysteresis controller; improved sliding mode controller; distributed generation sources; current control; voltage control; islanded AC microgrid 1. Introduction A microgrid (MG) generally consists of various distributed generation (DG) resources (renewable and non-renewable resources), storage systems, and loads. Usually, DGs and storage systems are connected to a point of common coupling (PCC), shared DC or AC bus, through power converters. Microgrids have two modes of operation: grid-connected mode and islanded mode. In a grid-connected mode, voltage, and frequency are controlled by the main power network, while in the islanded mode, they are controlled by the distributed generation units or, if necessary, by the distributed storage units. Mathematical modelling of uncertainties and parameter changes in microgrids are identified as one of the greatest challenges for advanced control application [1]. Parameter variations in inverter output filters, internal and external fault disturbances, unpredicted load variations, and harmonic currents generated by nonlinear loads are inevitable events in an islanded microgrid [1]. Therefore, to improve the control performance and suppress the disturbances, robust control techniques are adopted [2–5]. One of the most challenging technical problems for the internal control design of a microgrid is the control of renewable energy sources (RES), such as wind or solar energy. The intermittent availability of these sources is known to be one of the major threats to Energies 2022, 15, 6029. https://doi.org/10.3390/en15166029 https://www.mdpi.com/journal/energies