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 and can dramatically increase the range, convenience, and safety of EV battery charging. One of the major difficulties is determining the physical sizes of the primary IPT coupler, buried in the roadway, and the EV mounted secondary coupler. 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 the best power to size ratio over typical expected air gaps is selected. As such a method to select the best design from eight approximately square DD couplers ranging from 300 to 1000 mm in length to meet the challenge of delivering high power over large air-gaps is presented. The performance of these couplers, or power pads, is simulated and the results can be used to select couplers for EV charging systems. A practical design example is presented involving the IPT charging of sedans and SUVs in multiple practical charging locations. The proposed pad sizes and systems are capable of transferring 10 kW to the EVs for realistic horizontal misalignments (±200 mm) and air-gaps (100-400 mm).