energies Article Modeling and Analysis of the Power Conditioning Circuit for an Electromagnetic Human Walking-Induced Energy Harvester Ludwin Molina Arias 1, * , Joanna Iwaniec 2 and Marek Iwaniec 1   Citation: Molina Arias, L.; Iwaniec, J.; Iwaniec, M. Modeling and Analysis of the Power Conditioning Circuit for an Electromagnetic Human Walking-Induced Energy Harvester. Energies 2021, 14, 3367. https://doi. org/10.3390/en14123367 Academic Editor: Luigi Costanzo Received: 10 May 2021 Accepted: 7 June 2021 Published: 8 June 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 Department of Process Control, Faculty of Mechanical Engineering and Robotics, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków, Poland; iwaniec@agh.edu.pl 2 Department of Robotics and Mechatronics, Faculty of Mechanical Engineering and Robotics, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków, Poland; jiwaniec@agh.edu.pl * Correspondence: arias@agh.edu.pl; Tel.: +48-575-651-834 Abstract: Among the various alternative energy sources, harvesting energy from the movement of the human body has emerged as a promising technology. The interaction between the energy harvesting structure and the power conditioning circuit is nonlinear in nature, which makes selecting the appropriate design parameters a complex task. In this work, we present an electromagnetic energy harvesting system suitable for recovering energy from the movement of the lower limb joints during walking. The system under study is modeled and simulated, considering three different scenarios in which the energy source is the hip, knee, and ankle joint. The power generated by the energy harvester is estimated from kinematic data collected from an experimental gait study on a selected participant. State-space representation and Recurrence plots (RPs) are used to study the dynamical system’s behavior resulting from the interaction between the electromagnetic structure and the power conditioning circuit. The maximum power obtained through the simulation considering a constant walking speed of 4.5 km/h lays in the range of 1.4 mW (ankle joint) to 90 mW (knee joint) without implementing a multiplier gear. Keywords: energy harvesting; human walking; power conditiong circuit; electromagnetic induction; recurrence plot 1. Introduction In recent years, as a result of the wide usage of small-scale electronic devices, the re- quirement for portable and efficient energy sources has been increasing. The energy demanded by portable electronic devices is conventionally supplied by batteries. However, the energy stored in the batteries is limited, which leads to the need to recharge it after a limited period of operation or eventually replace it [1]. This fact entails an important limi- tation for portable electronic devices, mainly when the user performs fieldwork and cannot guarantee the supply of electrical energy. As a consequence of this situation, alternative methods for supplying portable electronic devices are explored. Energy harvesting from human body motion has become a promising technology for powering portable electronic devices [2]. Numerous investigations have estimated the energy associated with the motion of the joints of the human body during daily activities [3]. Among the daily activities performed by an average person, walking is one of the most engaging activities to recover energy. During walking, lower limb muscles perform positive and negative work to accelerate and decelerate the movements. These movements have been widely studied, and researchers know well the angular displacements, velocities, and accelerations of each joint during walking. Numerous walking-based energy harvesters have been designed, employing mainly electromagnetic, electrostatic, and piezoelectric transducers [4]. Donelan et al. [5] developed an energy harvester consisting of an ortho- pedic knee brace. The knee joint drives a gear train in the proposed device, transmitting Energies 2021, 14, 3367. https://doi.org/10.3390/en14123367 https://www.mdpi.com/journal/energies