Étude de la transmission d'énergie sans fil (WPT) basée sur la résonance couplée magnétique

RÉSUMÉ Depuis la fin du 20e siècle, les appareils électroniques portables (ordinateurs, téléphones cellulaires, tablettes, implants, …), sont de plus en plus présents dans notre vie quotidienne. Mais ces appareils électronique, bien que populaires sont fortement tributaires de la courte durée de leur alimentation (piles ou batteries). Pour l’utilisateur, la commodité de l'électronique portable est peu à peu compromise par la nécessité de recharger les batteries de plus en plus fréquemment au cours des mois, à mesure que la capacité de la batterie diminue. En ce qui concerne les appareils qui ne peuvent pas être branchés sur un chargeur comme les implants biomédicaux, le problème devient encore plus délicat à cause de l’opération chirurgicale nécessaire pour le remplacement de la pile. Après des recherches de plusieurs années, la transmission d'énergie sans fil (WPT pour Wireless Power Transmission) basée sur la résonance magnétique couplée est en train de devenir assez mature pour enfin apporter une solution aux problèmes énergétiques de nos appareils mobiles. Cependant, beaucoup d’avancements restent à faire dans le domaine des dispositifs médicaux implantables où le transfert d'énergie est fortement limité par la taille du récepteur ainsi que par les pertes du tissu humain dispersif. Parce que la gamme du bas GHz est reconnue comme la fréquence de transfert optimale à travers ces tissus, une alternative au résonateur à bobine doit être étudiée et développée. Dans ce document, une solution originale de transmetteur est présentée. Elle tient compte du besoin d’avoir un fort champ magnétique en zone de champ proche et d’un faible champ rayonné en zone de champ lointain, choses ordinairement difficile à combiner à ces fréquences.----------ABSTRACT Since the late 20th century, highly portable and mobile electronic devices such as laptops, cell phones, robots, tablets and implants, have emerged and have been playing an increasingly important role in our daily life. However, such electronic apparatus and popular gadgets are highly dependent on power supply that is enabled by various types of battery. The convenience of portable electronics has been increasingly compromised by the necessity to “refill” battery more and more frequently. As for the devices that cannot be plugged into a charger, such as biomedical implants, the problem becomes even worse because of the required surgery only for the power supply or battery replacement. After several years of investigations and developments, wireless power transmission (WPT) systems based on magnetically coupled resonance are matured enough to become a predominating technology poised to solve the energy problem of mobile devices. In the field of implantable medical devices, however, the energy transfer operation is highly limited by the size of receiver and also the loss properties of dispersive human tissue. Since the low GHz range has been considered as the optimal transfer frequency, an alternative to the lossy coil resonator should be studied and developed. In this thesis work, an original transmitter solution is presented that considers the needs for strong magnetic dominant near-field and weak far field radiation even at low GHz frequency. Chapter 2 of this thesis introduces a half-closed partially ceramic-filled cavity resonator along with an accurate but analytical model. Design parameters are also studied using a full-wave simulation software package and measurement results of a resonator-to-resonator transfer scheme. They show a good agreement with simulation results. An efficiency above 65% can be obtained within the distance comparable to the diameter of the resonator (60.5mm) in this case study. Subsequently, energy transmission between the proposed cavity resonator and a small-sized copper coil of 3mm of diameter is investigated. Measurement results show that the efficiency is above 34% within 20mm and above 8.2% within 40mm, which is much higher than the conventional coil-to-coil transmission scheme

Power Control Techniques in Wireless Power Transfer System

Department of Electrical EngineeringWireless power transfer (WPT) technology has attract the attentions of researchers and industrial for new method of power transfer mechanism. WPT technology enables contactless energy transfer between two resonators through a magnetic field. WPT is a promising method of powering electrical devices, especially in environments where wired charging is inconvenient of even dangerous. Recently, the interest of WPT has been arise with the increase of mobile devices such as cell phones, PDAs, laptops, tablets, and other handheld gadgets equipped with rechargeable batteries has been widely spreading. In recent years, WPT technology has already been applied to tooth brushes and mobile phones. In addition, many researchers are interested in applying WPT technology to electrical vehicle, cordless zone, and biomedical application and are conducting research to realize it. The area where wireless power transmission technology is most needed is biomedical. Biomedical devices to be implanted in the body are most severely limited by their small volume and battery capacity limitations. WPT technology is the most suitable technology to solve this problem. However, power loss occurs during wireless power transmission, it is necessary to overcome this problem because the harmful effects on the human body. In this dissertation, two new power control techniques are introduced to increase the efficiency of wireless power transmission in biomedical systems. The first proposed technique is a technique for transmitting power more efficiently at a place where the transmission distance is long, the size of the device is small, the position of the device is not fixed, and the efficiency is very low like a capsule endoscopy. The second proposed technique is a power control technique which can increase the power transfer efficiency for applications with close distances for implanted biomedical devices under the skin like a cardiac pacemaker. Chapter II presents a new power control technique to improve efficiency in magnetic resonance (MR)- WPT system for biomedical capsule endoscopy. Recently, capsule endoscopy technology has been developed and emerged as an alternative to small bowel endoscopy, gastroscopy, and colonoscopy, all of which cause discomfort to patients because of their relatively large-diameter and flexible cables. However, commercialized capsule endoscopy still suffers from limited battery capacity. Chapter II presents a theory for power control technique in MR-WPT system, along with its experimental verification. An MR-WPT system with a 9-mm-diameter receiver is implemented, which is small enough to fit in the current capsule endoscope. The proposed system improves the efficiency despite variations in the distance, angle, and displacement. The proposed system is found to have a low specific absorption rate, which demonstrated that it is safe to use in the human body. Chapter III proposes power control technique for inductive power transfer (IPT) battery charging system using in-band communication that aims to minimize number of power stages and increase power transfer efficiency with low-cost hardware. Constant current and constant voltage mode are needed to effectively charge Li-ion batteries to ensure long life-span and maximum capacity utilization. These two charging modes require different feedback loops and circuitry, which increase system complexity and reduces efficiency. One approach is to use additional converter stages that ensure effective battery charging, but this introduces additional conversion losses, which decreases efficiency. The IPT system using proposed step charging method tracks the proper frequency to maintain the desired constant current or voltage for battery charging without the need for additional regulation circuits, and with minimized feedback control signal. In-band communication is used to send feedback signal from secondary side to primary side of the IPT system, which enables effective feedback control without conventional wireless communication module. This power control technique is a technique to eliminate power loss in an unnecessary regulator. This technology is applicable to IPT using in-band communication and is suitable for implantable devices because it reduces receiver loss.ope

Wireless Power Transfer System for Battery-Less Body Implantable Devices

Department of Electrical EngineeringAs the life expectancy is increased and the welfare is promoted, researches on the body implantable medical devices (BIMD) are actively being carried out, and products providing more various functions are being released. On the other hand, due to these various functions, the power consumption of the BIMD is also increased, so that the primary battery alone cannot provide sufficient power for the devices. The limited capacity and life time of batteries force patients to make an additional payment and suffering for the power supply of the BIMD. Wireless power transfer technology is the technology which has been making remarkable progress mainly in wireless charging for personal portable devices and electric vehicles. Convergence of wireless power transfer technology (WPT) and rechargeable battery can extend the life time of the BIMD and reduce the suffering and the cost for battery replacements. Furthermore, WPT enables the devices which do not need to operate consistently such as body implantable sensor devices to be used without batteries. In this dissertation, techniques to support WPT for BIMD are introduced and proposed. First, basic researches on magnetic coupled WPT are presented. The basics which are important factors to analyze power transmission are introduced. In addition, circuits that make up the WPT system are described. There are three common technical challenges in WPT. Those are efficiency degradation on coil geometry, voltage gain variation with coil geometry, and power losses in WPT. The common challenges are discussed in chapter II. Moreover, additional challenges which are arisen in WPT for BIMD and approaches to resolve the challenges are addressed in chapter II. Then, efficiency improvement techniques and control techniques in WPT are presented in chapter III. The presented techniques to improve efficiency are applied in coil parts and circuit parts. In coil parts, efficiency enhancement technique by geometric variation is proposed. In circuit parts, instantaneous power consuming technique for step-down converter is suggested. Li-ion battery charger is also discussed in chapter III. Additionally, the wireless controlled constant current / constant voltage charging mode and the proposed step charging method are described. After that, WPT system for BIMD is discussed one by one with the proposed techniques for each part in chapter IV. A load transformation is suggested to improve efficiency in weak coupling, and suppress voltage gain variation under coil displacement. Power conversion efficiency improvement techniques for rectifier and converter are also proposed. By using the proposed technique for the converter, we can remove the bootstrap capacitors, and reduce the overall size of power circuits. In conclusion, techniques in coil parts and circuit parts to handle challenges in WPT for BIMD are fully investigated in this thesis in addition to the efficiency improvement and control techniques in common WPT. All the techniques are verified through simulations or experiments. The approaches realized in the thesis can be applied to other applications employing the WPT.clos