A research group including Professor Yoichi Hori and Associate Professor Hiroshi Fujimoto, both of the University of Tokyo Graduate School of Frontier Sciences, and researchers of Bridgestone Corporation, NSK Ltd., Rohm Co., Ltd., and Toyo Electric Mfg., Co., Ltd. is conducting elemental research on in-wheel motors and dynamic WPT. In October 2019, the group successfully conducted field testing of a 3rd generation in-wheel motor unit for a passenger car-class EV; a 25kW motor, inverter and wireless electrical supply circuitry were installed in each wheel of the test vehicle.     

3rd generation dynamic WPT test vehicle

The 400kHz band electric field coupling and 6.7MHz band magnetic field coupling are used in low power applications such as mobile devices, but in electric vehicles, 85kHz (between 79 and 90kHz) magnetic field couplings are used. Recently, magnetic resonance couplings which adeptly utilize resonance conditions are receiving attention, and this project wireless power transfer is also being conducted using 85kHz magnetic resonance.

Further, data was obtained of vehicles running on general urban public roads in Kanagawa prefecture and a simulation quantifying the percentage of time cars spent waiting in front of traffic lights was conducted. The results confirmed that, in the case that dynamic charging infrastructure was in place in the 30m area in front of traffic signal stop lines, with intermittent charging it would be possible to charge the on-board battery at these points, and the change in battery power before and after driving would be almost zero, making it possible to drive continuously without a large capacity battery installed in the vehicle.

Image of future dynamic WPT (Left: smart city, Right: highway) (Source: University of Tokyo press release)

This report introduces the contents of the committee meeting and field visit held November 8, 2019, at the University of Tokyo Kashiwa Campus on the theme of the latest trends and future developments in dynamic WPT, sponsored by the Society of Automotive Engineers of Japan (JSAE) Electric Power Technology Committee. At the opening of the meeting, University of Tokyo Professor Yoichi Hori (former director of the JSAE) gave the opening remarks, which are summarized below.

It is said that for electric vehicles, battery development is very important, but rather than increasing the capacity of batteries, charging while driving will solve a multitude of problems. As can be seen in electric trains, for example, the concept of range does not exist, and there is no need to store electricity in batteries. There are negative opinions regarding dynamic power transfer, such as the cost to install a wireless charging system throughout Japan would cost about JPY 500 billion. But, for Japan to take a position of leadership in the world, Professor Hori emphasized the need for more aggressive progress. 

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