Citation: Jean-Pierre, G.; Altin, N.; El Shafei, A.; Nasiri, A. Overall Efficiency Improvement of a Dual Active Bridge Converter Based on Triple Phase-Shift Control. Energies 2022, 15, 6933. https://doi.org/ 10.3390/en15196933 Academic Editors: Tibor Vince and Dobroslav Kovac Received: 4 August 2022 Accepted: 13 September 2022 Published: 22 September 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 Overall Efficiency Improvement of a Dual Active Bridge Converter Based on Triple Phase-Shift Control Garry Jean-Pierre 1 , Necmi Altin 2 , Ahmad El Shafei 1 and Adel Nasiri 3, * 1 Center for Sustainable Electrical Energy Systems, University of Wisconsin-Milwaukee (UWM), Milwaukee, WI 53211, USA 2 Electrical-Electronics Engineering Department, Faculty of Technology, Gazi University, Ankara 06560, Turkey 3 Electrical Engineering Department, College of Engineering and Computing, University of South Carolina (USC), Columbia, SC 29208, USA * Correspondence: nasiri@sc.edu Abstract: This paper proposes a control scheme based on an optimal triple phase-shift (TPS) control for dual active bridge (DAB) DC–DC converters to achieve maximum efficiency. This is performed by analyzing, quantifying, and minimizing the total power losses, including the high-frequency transformer (HFT) and primary and secondary power modules of the DAB converter. To analyze the converter, three operating zones were defined according to low, medium, and rated power. To obtain the optimal TPS variables, two optimization techniques were utilized. In local optimization (LO), the offline particle swarm optimization (PSO) method was used, resulting in numerical optimums. This method was used for the low and medium power regions. The Lagrange multiplier (LM) was used for global optimization (GO), resulting in closed-form expressions for rated power. Detailed analyses and experimental results are given to verify the effectiveness of the proposed method. Additionally, obtained results are compared with the traditional single phase-shift (SPS) method, the optimized dual phase-shift (DPS) method, and TPS method with RMS current minimization to better highlight the performance of the proposed approach. Keywords: DAB; Lagrange multiplier; power loss optimization; PSO; TPS 1. Introduction The DAB converter is capable of providing bidirectional power flow, operating un- der wide voltage gain ratios, and achieving zero-voltage switching (ZVS). It has been extensively utilized in various applications, such as energy storage systems, microgrids, solid-state transformers, on-board electrical vehicle chargers, and power electronic traction transformers [1]. Although the DAB converter has many positive characteristics, some limitations exist. When utilizing the conventional singe phase-shift (SPS) modulation technique, the performance of the DAB converter depends on the operating power range. At a low power operation, conventional SPS results in a high-circulating current, which degrades the performance significantly. This circulating current does not assist in the power transfer of the converter, but serves as a heat source, resulting in conduction and copper losses, which lead to decreased efficiency of the converter. The loss of ZVS also impacts the switching losses of the DAB converter [2]. Efficiency optimization is a research focus when it comes to enhancing the DAB con- verter performance. Achieving high efficiency while operating at non-rated conditions or low power levels can be cumbersome. Therefore, some trade-offs are made when designing DAB converters. Some researchers have addressed the need for efficiency improvement by reconfiguring the DAB converter. Such techniques include increasing the tap of the transformer, using variable inductors, and adding or rearranging the switches [3–5]. Since these techniques need additional components and increase the system complexity, the Energies 2022, 15, 6933. https://doi.org/10.3390/en15196933 https://www.mdpi.com/journal/energies