On Optimization of Wireless Power Transfer Systems

The main objective of this paper is a study with reference to the optimal electromagnetic power wireless transfer, and with direct application on battery chargers. The main elements impacting the optimal operation of the wireless battery charging systems are: load resistance, mutual coupling factor and the parameters of secondary coil. It is assumed that the two magnetically coupled coils operate at the same resonance frequency, which has a common value for both circuits, source and receiver. The mode the two coils are connected, influences the values of the optimum efficiency and maximum amount of active power transferred to the load, with the best results for the "series-series" connection. The magnetically coupled systems must be able to ensure a fast and reliable charging of ultra-capacitors used for the storage of energy. Whereas charging the ultra-capacitors is a fast process, the standard inductively coupled circuits can deliver maximum power only if the impedance of the load reaches a well determined value. This value strongly depends on the shape and dimensions of each coil, as well as the space between the coils. The impedance of the load must be brought to an optimum value, according to the request for optimum efficiency in conditions maximum active power transfer. The procedure involves inductivity adjustment for the secondary coil, accompanied by determination of tuning capacitance at resonance. Optimal efficiency value and maximum real power transferred to the load have been determined through parameter analysis.