Determining the physical size of inductive couplers for IPT EV systems

Due to increasing environmental concerns and decreasing fossil fuel supplies, Electric Vehicles (EVs) are fast becoming attractive alternatives to conventional fossil-fuel driven vehicles. Inductive power transfer (IPT) is a method that can be used to transfer power to EVs over an air-gap, without the need for physical contacts. IPT systems can dramatically increase the range, convenience and safety of EV battery charging. One of the major difficulties is in determining the physical sizes of the IPT couplers. This is mainly due to the variation in vehicle classes and charging locations that may be encountered. This paper seeks to determine if suitably sized couplers can be selected which can realize all these demands. A recently proposed EV charging coupler, known as the Double-D (DD), which has been shown to provide an excellent power to size ratio over typical expected air-gaps is selected. A method to select the best design from 8 approximately square DD couplers ranging from 300mm to 1000mm in length is presented. A practical design example is presented and possible primary and secondary coupler sizes to charge a stationary EV sedan at 10kW for realistic horizontal misalignments and air-gaps are presented.