Design Of Loosely Coupled Wireless Charging System

In recent years, the improving in the function, performances, and operating time ofdifferent kinds of electronic devices is pushing up their power requirement. As thetraditional implantable batteries and percutaneous cords are suffering from low reliability,the Loosely-Coupled Wireless Charging System (LCWCS) as a new power transmissiontechnology, has received an extensive concern in the international scope especially in themost electronically developed countries such as USA, Japan and China. LCWCS has manyapplications in today’s electronic world, and it is a promising way to safely provide moreenergy or enable longer lifetime for modern electronic devices such as biomedicalmicrosystems devices, medical implants, etc. However, its development andimplementation encountered some problems, which made it not very applicable asexpected.The main application of this design is in medical area for the biomedical microsystems,medical implantable devices charging system. Therefore, the receiver loop is located insidethe human body, while the transmitter loop is outside. Consider the thickness of the humanskin (0.5~4mm), the skin fold thickness, and the size of the transceiver coils, the transferdistance has to be more than15mm. Hence, the loosely coupled has been chosen for thiswireless charging system design.During this LCWCS design, we conducted the resonant coils system modeling usingANSYS Maxwell according to the design requirements and applications. The primary andsecondary coils diameters are58mm and18mm respectively, and the transfer distance isabout20mm. The model designed has a coupling coefficient of0.067. After a deep analysisof different compensation topologies, SP topology has been chosen. With the coils modelcreated using Maxwell, we designed the LCWCS main circuit using ANSYS Simplorer.The system main circuit consists of the AC source, primary and secondary compensations,secondary rectifier, secondary driver, the load resistance, and the magnetic link. Afterdifferent simulations, the system output voltage and the output power are5.2V and50Wrespectively. The system transfer efficiency is about56.5%. In order to get the best charging results, the LCWCS have to be optimized. Therefore,different compensation topologies (Series-Series, Series-Parallel, Parallel-Series, andParallel-Parallel) mutual inductance and Q factor optimizations are deeply studied. Theoptimization is conducted according two different analysis indexes: the maximumtransmission power, and system performance. The system performance takes into accountthe system transmission power, transfer efficiency, coils size, reliability, etc. As result, thesystem maximum output power has a slight reduction of about11%, but the system powertransfer efficiency is enhanced to reach about67%.