electronics Article Optimal Tuning of Fractional Order Controllers for Dual Active Bridge-Based DC Microgrid Including Voltage Stability Assessment Mohamed Azab 1,2, * and Alexandre Serrano-Fontova 3   Citation: Azab, M.; Serrano-Fontova, A. Optimal Tuning of Fractional Order Controllers for Dual Active Bridge-Based DC Microgrid Including Voltage Stability Assessment. Electronics 2021, 10, 1109. https://doi.org/10.3390/ electronics10091109 Academic Editors: Mehdi Narimani and Apparao Dekka Received: 19 March 2021 Accepted: 1 May 2021 Published: 8 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 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/). 1 Electrical Engineering Technology Department, Faculty of Engineering, Benha University, Benha 13512, Egypt 2 Electrical Engineering Technology Department, Yanbu Industrial College, Yanbu 30436, Saudi Arabia 3 Department of Electrical Engineering, Technical University of Catalunya (UPC), 08028 Barcelona, Spain; alexandre.serrano@upc.edu * Correspondence: mohamed.ahmed.azab@ieee.org Abstract: In this article, three evolutionary search algorithms: particle swarm optimization (PSO), simulated annealing (SA) and genetic algorithms (GA), have been employed to determine the optimal parameter values of the fractional-order (FO)-PI controllers implemented in the dual active bridge- based (DAB) DC microgrid. The optimum strategy to obtain the parameters of these FO-PI controllers is still a major challenge for many power systems applications. The FO-PI controllers implemented in the DAB are used to control the DC link voltage to the desired value and limit the current flowing through the converter. Accordingly, the investigated control system has six parameters to be tuned simultaneously; K p1 ,K i1 , λ 1 for FO-PI voltage controller and K p2 ,K i2 , λ 2 for FO-PI current controller. Crucially, this tuning optimization process has been developed to enhance the voltage stability of a DC microgrid. By observing the frequency-domain analysis of the closed-loop and the results of the subsequent time-domain simulations, it has been demonstrated that the evolutionary algorithms have provided optimal controller gains, which ensures the voltage stability of the DC microgrid. The main contribution of the article can be considered in the successful application of evolutionary search algorithms to tune the parameters of FO-based dual loop controllers of a DC microgrid scheme whose power conditioner is a DAB topology. Keywords: DAB converter; microgrid; fractional order controller; genetic algorithms; simulated annealing; particle swarm optimization; voltage stability 1. Introduction The dual active bridge (DAB) converter is considered as one of the most critical emerging topologies that have been successfully used in many electrical power applications such as DC microgrids [1,2]. The DAB offers key advantages such as a minimum size of passive filter components and high-power density when compared with other bidirectional DC-DC converters [3]. Therefore, DAB converter has gained popularity during the last decade in applications such as electric vehicles (EVs), energy management systems or DC microgrids with energy storage systems (ESS) [4–8]. A general average model of a DAB has been proposed in [2], whereas a simple but reliable model has been proposed in [7]. In Reference [7], the DAB converter average and small-signal models have been validated through both simulations and experimental tests for the four different control modes. The DABs have also been the object of study in [9–20]. Even though several control strategies have been explored for the DAB, the most common among practitioners is the simple phase shift modulation technique [17,18] based on conventional PI controllers [20,21]. Besides, the variable structure controllers have been employed to control the DAB’s operation, as can be seen in [22]. Given the proliferation of the DC and mixed AC/DC microgrids, some research has been carried out to evaluate the capabilities of some power electronic converters for Electronics 2021, 10, 1109. https://doi.org/10.3390/electronics10091109 https://www.mdpi.com/journal/electronics