Dependence of Efficiency on Wire Type and Number of Strands of Litz Wire for Wireless Power Transfer of Magnetic Resonant Coupling

Abstract

Wireless power transfer is expected to be applied to portable devices and electric automobiles in the future. To achieve this, it is necessary to improve the transmission efficiency of the coils used in wireless power transfer, that is, to improve the quality factor and coupling coefficient of the coils. To improve the quality factor of the coils, the authors propose the use of a litz wire with a magnetoplated wire (MPW), which is a copper wire plated with a thin iron film. The MPW increases the quality factor of the coils by reducing the AC resistance owing to the proximity effect. In this study, the effect of the number of strands of a litz wire on the quality factor of the coils and efficiency characteristics is considered. Moreover, the quality factor of the coils and efficiency characteristics using three types of coil-a solid copper wire (COW), a litz wire with a copper wire (LCW), and a litz wire with an MPW (LMW)-are considered. At the transmission frequency f = 13.56 MHz, it is experimentally demonstrated that many strands, whose number becomes the highest in terms of the quality factor of the coils, exist. The transmission efficiencies of the COW, LCW and LMW coils at an output power of 5 W and a transmission distance of 9 mm are 89%, 84%, and 91%, respectively, and the efficiency of the LMW coil is the highest. Also, in this case, the temperature increases of the COW, LCW, and LMW coils are 12 • , 16 • , and 10 • , respectively, and the LMW coil reduces the temperature increase.

Examination of Wireless Power Transfer Combined With the Utilization of Distance Detection

“…Common types of coils are spiral coil, solenoid coil, opened helical coil, and a coil that the iron core is inserted in each of types of coils [2]- [5]. As an example, the transmitting and receiving coils are spiral coils in this paper.…”

“…However, the transmission efficiency is reduced as the transmission distance changes and as position misalignment occurs [5]. Implementation of wireless power transfer requires the position information of the receiving coil to realize high efficiency transmission, to determine a range of power transfers, and to transfer power to moving objects.…”

Improvement of equivalent magnetic coupling coefficient of wireless power transfer system with multiwinding transmission coil

“…EV and PHV charging is performed using a cable in most cases . However, inductive wireless power transfer (IPT) systems that can supply power without electric contact are extensively studied in terms of convenience and protection against electric shock from the charger's housing …”

“…2,3 However, inductive wireless power transfer (IPT) systems that can supply power without electric contact are extensively studied in terms of convenience and protection against electric shock from the charger's housing. [4][5][6][7][8][9] With nonresonant IPT, transmitted power and power factor in AC link heavily depend on the strength of magnetic coupling between primary and secondary windings. 7 In case of weak magnetic coupling, high voltage must be induced in the secondary winding in order to deliver power to a load, which means higher excitation current.…”

Design and simulation of networks for midrange wireless power transfer

“…Increasing Q of the coils will give a reduction of their parasitic resistances which reduces losses in the system. In recent development of WPT it is found that quality factor Q of the coils can be improved in different approaches, one which are employed in this system design are using Litz wires [7] and by increasing the spacing between turns [8].…”