Improved Couplers for Charging Stationary and Moving Electric Vehicles

Abstract

Inductive Power Transfer (IPT) uses a varying magnetic field to transfer energy without contact. The contactless nature of IPT makes it an ideal method in the context of Electric Vehicle (EV) charging. The driver no longer needs remove a plug from an unsightly and vandal prone charging stand then "plug in" the vehicle-rather the charging is done invisibly and out of mind. Well designedd magnetic couplers enable energy to be directed across an air gap to an EV with little loss. The focus of this thesis is to find the best topologies suitable for both stationary charging and dynamically powering and EV while on the move. The performance of the couplers determines the overall feasibility and cost effectiveness of the complete charging system. Stationary charging is envisaged where the transmitting coupler is buried in the ground and a receiver is mounted underneath an EV, thus the driver simply needs to park over the transmitter. Couplers in a dynamic system need to transfer significantly higher power levels to a moving vehicle with adequate tolerance across the lane. Both applications are especially demanding because power levels of 2-60kW need to be transferred over 150-300mm air gaps with sufficient tolerance to horizontal misalignment, especially if automatic guidance is not desired. The magnetic field emissions also need to be controlled to ensure the systems comply with international guidelines and regulations. The performance of circular shaped couplers is initially investigated as these are the most common in the literature and industry. Existing designs are optimised but still offer necessarily poor coupling due to the shape of their fundamental flux paths. Bar shaped couplers were investigated as an alternative due to theoretically better flux paths but these were found to produce a two sided magnetic field, one side of which must be shielded resulting in very inefficient systems. A novel coupler topology called the Double D (DD) pad is proposed with a high single-sided flux path that enables it to outperform circular couplers. DD pads that are smaller and lower cost than circular couplers enable equivalent power transfer over an area five times larger when operating under the same conditions. Due to the prevalence of circular couplers, an interoperability investigation is done and shows that a DD receiver will work better with a circular transmitter than a circular receiver. Finally, DD pads are considered for dynamic powering and measurements taken on a laboratory scale system show this is a feasible option.