Development of Wireless In-Wheel Motor Using Magnetic Resonance Coupling

In-wheel motors (IWMs) in electric vehicles are particularly important for motion control. A conventional IWM is powered from a battery aboard the vehicle via cables. Since power cables and signal cables of an IWM are exposed to harsh environments, they can possibly become disconnected by high acceleration or vibration. In order to overcome this problem, the wireless-in wheel motor (W-IWM) has been proposed. The risk of disconnection would disappear if the cables of the IWM are removed. One way to implement wireless power transfer is by utilizing the magnetic resonance coupling method. However, motion of the W-IWM, and thus, a misalignment between the wheel and the vehicle, leads to variations in the secondary-side voltage provided. To account for this, this paper discusses two new control methods. One proposed method maintains the secondary voltage using a hysteresis comparator. The other proposed method estimates the secondary inverter output power, applying it to a feedforward controller in order to keep the secondary dc-link voltage constant. Experimental results show that these methods can drive a W-IWM effectively with high efficiency.