Resonant Inductive Coupling Wireless Power Transfer is the Future of the World Transportation System
by: Yosra Ben Fadhel, Research Laboratory of Biophysics and Medical Technology (BMT) High Institute of Medical Technologies of the University of Tunis El-ManarTunis, Tunisia, and Nabil Derbel, Laboratory of Control & Energy Management, National School of Engineers of Sfax, University of Sfax, Tunisia.
According to the International Energy Agency (IEA), 75 % of CO2 emission comes from road vehicles, with about 60% of the global oil consumption in 2020, which makes the need for a clean alternative urgent. Electric vehicles (EVs) have appeared as an important pillar in the transition towards a clean energy society. EVs presented in the current market was been significantly improved in terms of both drive range and performance. In addition, they are pollution-free and noiseless operations. Nevertheless, powering them effectively and efficiently still remains a challenge. The first electric vehicle (EV) was a plug-in electric vehicle (PEV), in which the battery is charged during the static conditions in charging stations (CSs). Mostly, CSs are located in parking areas where cables need to be connected to the EVs for charging .
However, the wire charging connections may be very dangerous, especially in bad weather conditions. Moreover, wires may cause sparking during plugging and unplugging, which makes their use impossible under certain circumstances, such as in airports or near gas stations. Wireless Power Transfer (WPT) has appeared as a more flexible and convenient charging alternative that had attracted broad attention. EVs wireless charging enables electric power transfer without any solid connections. This advantage provides a compact, flexible, and safe charging process. In addition, it reduces the system complexity and the overall charging cost. In the literature, several approaches have been proposed to develop a reliable WPT system for charging EVs batteries . Nevertheless, resonant inductive coupling gains the most attention from researchers and industries, since it ensures human safety and has a simple design circuit. The general block diagram of a RIC WPT for EVs is shown in Fig.1.
Fig1: General presentation of WPT for EVs.
B. Fundamentals of a RIC System
RIC systems are based on coupled-mode theory in an oscillating electromagnetic field with the transmitter coil (TX) and the receiver coil (RX), respectively. Figure 2 shows the TX TX and RX coils that are represented by inductors LTX and LRX with their equivalent series resistances represented by RTX and RRX, respectively. The resonant tank capacitor CTX, is connected in series with LTX, and the resonant tank capacitor CRX is connected in parallel with LRX . Both coils are connected to a compensation capacitor to reach the resonance at the same operating frequency f0, where the transmitted power and the system efficiency increases. These capacitors can be connected in various arrangements: serial-serial (SS), serial-parallel (SP), parallel-parallel (PP) and parallel-serial (PS). The load, represented by the resistance RLoad, is powered by the rectified DC voltage from the receiver circuit. The resistances RTX and RRX introduced by the coupled coils waste power when the alternating currents pass through the coil, thereby reducing the system efficiency. These losses due to the resistances decrease the power transfer efficiency. Consequently, these resistances should be as small as possible.
Fig. 2: System diagram of RIC WPT between two coils.
During the design process of a WPT system, several parameters should be considered, such as the air gap between two coils, the compensation scheme, the resonant frequency, the coil design, the power electronics topology, etc. These parameters directly influence the performance of the system operation and efficiency.
C. Safety Standards and Guidelines
Certainly, the use of time-varying currents and voltage at high levels introduces real risks and concerns to human being health and safety. These risks include fire hazards, electromagnetic field exposure, and electrical shock. Accordingly, the bigger challenge with health and safety concerns in EVs WPT systems is how to ensure total public safety. The high-frequency system operation produces varying magnetic and electric fields. The low coupling between coils makes the share of the leakage field very high. For that reason, undesirable electromagnetic interference and field exposure appears. In 2010, the international commission on Nonionizing Radiation Protection (ICNIRP) declared the recommendations for restricting field radiations and proposed guidelines to limit the impact of magnetic and electric fields on employees and the public in general. ICNIRP recommended standards focus on frequencies ranging between 1 Hz - 100 kHz, which covers almost all wireless EV charging applications . The new version of ICNIRP 2020 guidelines covers a frequency range between 100 kHz to 300 GHz .
Another important organization that set standards for high-powered wireless charging systems for EVs is the Society of Automotive Engineers (SAE). In 2016, the SAEj2954 was the first version that recommended standards for WPT. In 2020, the SAE j2954 recommended 3 standards for three power classes follows as WPT1 with 3.7kVA, WPT2 with 7.7kVA and 11kVA, WPT3 transmission standards established and 22kVA (WPT4) design standards are in the way of development .
The development of dynamic wireless charging will open a new era of electrified transportation systems with reduced battery capacity and increased vehicle driving range. The recommended future research directions include:
- More coupler (power pad) configurations with higher power transfer efficiency and better misalignment tolerance.
- Bi-directional operation of the wireless charging system should be advanced to make it technically and commercially feasible.
- Smart charging system is desired with secure and reliable sensing devices and a communication network.
- Research on electromagnetic effects on the human body should be carried out for the safe operation of EV wireless charging.
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Yosra Ben Fadhel obtained research master's degree in biophysics, radiophysics, and medical imaging (Biomedical Engineering) from the higher institute of medical technologies of Tunis (ISTMT) of the university of Tunis El-Manar in collaboration with the Faculty of Medicine of Tunis (FMT) in 2015. In 2020, she received a Ph.D. in biophysics, radiophysics, and medical imaging (electronic circuits design and fabrication). In 2022, November, she has been an Assistant Professor at ISTMT.
Her research interests include emerging technologies in power electronics. Her recent research focuses on wireless power transfer, with several possible applications, of which we particularly mention medical implants, E-textilet technology, portable medical devices integrating the Internet of Things (IoT), and wirless power transfer for electric vehicles.
|Nabil Derbel received the Engineering Diploma degree from the École Nationale d’Ingénieurs de Sfax (ENIS), Tunisia, in 1986, the “Diplôme d’Etudes Approfondies” degree in automatic control from the Institut National des Sciences Appliquées de Toulouse, France, in 1986, the “Doctorat d’Université” degree from the Laboratoire d’Automatique et d’Analyse des Systèmes, Toulouse, France, in 1989, and the “Doctorat d’État” degree from the Ecole Nationale d’Ingénieurs de Tunis (ENIT), Tunisia. Since 2003, he has been a Full Professor in electrical engineering. He is the author and co-author of more than 90 articles published in international journals and of more than 500 papers published in national and international conferences. His current research interests include optimal control, sliding mode control, sensors, robotic systems, intelligent methods, instrumentation, and renewable energies.|
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