Citation: Hesarian, M.S.; Tavoosi, J.; Alanazi, T.I. Model Development of a Hybrid Battery–Piezoelectric Fiber System Based on a New Control Method. Polymers 2022, 14, 5428. https://doi.org/10.3390/ polym14245428 Academic Editors: Xiaoning Tang and Shaoju Fu Received: 25 October 2022 Accepted: 7 December 2022 Published: 11 December 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/). polymers Article Model Development of a Hybrid Battery–Piezoelectric Fiber System Based on a New Control Method Mir Saeid Hesarian 1, *, Jafar Tavoosi 2 and Tarek I. Alanazi 3 1 Faculty of Textile Engineering, Urmia University of Technology, Urmia 5716693188, Iran 2 Department of Electrical Engineering, Ilam University, Ilam 69315516, Iran 3 Department of Physics, College of Science, Northern Border University, Arar 73222, Saudi Arabia * Correspondence: s.hesarian@uut.ac.ir Abstract: By increasing the application of smart wearables, their electrical energy supply has drawn great attention in the past decade. Sources such as the human body and its motion can produce elec- trical power as renewable energy using piezoelectric yarns. During the last decade, the development of the piezoelectric fibers used in smart clothes has increased for energy-harvesting applications. Therefore, the energy harvesting from piezoelectric yarns and saving process is an important subject. For this purpose, a new control system was developed based on the combination of the sliding mode and particle swarm optimization (PSO). Using this method, due to the piezoelectric yarn cyclic deformation process, electrical power is produced. This power is considered the input voltage to the controlling system modeled in this article. This system supplies constant voltage to be saved in a battery. The battery supplies power for the electrical elements of smart fabric structure for different applications, such as health care. It is shown that the presence of PSO led to the improvement of system response and error reduction by more than 30%. Keywords: piezoelectric fibers; sliding mode control; PSO; wearable energy harvesting 1. Introduction Renewable energy sources have attracted more attention for several decades. The energy obtained from mechanical energy is a kind of renewable energy. Sources such as the human body and its motion can produce electrical power as renewable energy [1–5]. The flexibility, low consumption of energy, and smartness of electronic devices are important subjects in studies on topics such as wearable devices for wireless short-distance communi- cation [6,7]. The sensors and data transmitters of wearable devices consume a micro- to milli-range of watts. For example, Bluetooth transmitters need 5 mW of power to transmit a data rate of 500 kbit per second [8]. During walking, 67 W of energy can be generated and transformed from mechanical to electrical power [9]. Monitoring the vital signs of patients [10], athletes [11], and older adults [12] is the best know application of electrical stimulation. Therefore, the supply of power for wearable e-textiles and electronics [13] is an attractive topic in this field of research. Recently, low-power devices have been developed [14–17]. Heavy and bulky rechargeable batteries are used to supply power to smart textile products [18]. Because of their bulk and non-flexibility, these batteries cannot be connected to textile structures. Therefore, the development of lightweight power generation is the subject of studies [19]. Nowadays, high-tech textile products have more applications in communication, shielding, and antenna applications [20,21]. Moreover, clothes or textiles can be used as a supply source of energy [22]. Garments and fabrics with flexible, lightweight, breathable, and stretchable characteristics provide significant adaptability to deformations made by body motions. Thus, fabrics with a large surface can generate heat and mechanical energy Polymers 2022, 14, 5428. https://doi.org/10.3390/polym14245428 https://www.mdpi.com/journal/polymers