Design of IPT Highways to Power Moving Electric Vehicles

Abstract

Modern Electric Vehicles (EVs) are an attractive and sustainable transportation alter- native to help reduce global greenhouse gas emissions and our dependence on a rapidly diminishing petroleum reserve. However due to their limited battery capacity, most current EVs need to be manually plugged into charging stands on a regular basis for recharging. This poses significant convenience and safety concerns to users; especially in wet, snowing or other adverse weather conditions. Inductive Power Transfer (IPT) is a means of wirelessly transferring power across an air-gap without the need for direct electrical contact. It relies on the fundamental principles of Amp`ere’s and Faraday’s Laws, and can allow stationary EVs to be recharged without requiring cumbersome plugs and connectors. Instead, power can be transferred from a primary coil (buried in the ground) to a secondary coil (mounted underneath the EV chassis) to recharge EVs rapidly at rates of 5 - 50 kW. If IPT systems are incorporated into the highway network, then EVs can even be powered dynamically as they move. This has the potential of ensuring that EVs have unlimited range capabilities, higher operating efficiencies, reduced battery sizes and cost, as well as shorter dedicated charging times. This thesis focusses on the design of such IPT highways to power moving EVs, with the aim of improving their practical viability. The first problem that the thesis addresses is the question of how large these IPT primary and secondary coils need to be for practical EV charging. A comprehensive method is first proposed to help designers choose suitable coil sizes for stationary EV charging design examples. With this method, practical coil sizes can be selected to charge different EV classes (e.g. sedans and Sport Utility Vehicles) in several charging locations (e.g. garage, car-park and roadside). These selected coil sizes are also shown to be capable of transferring up to 10 kW to these EVs over widely varying air-gaps (100 - 400 mm) and horizontal misalignments (±200 mm). A slight extension to this approach also enables designers to select coil sizes for IPT highways and dynamic EV powering applications. Following this, a system is developed to detect EVs travelling on IPT highways. With this detection system, buried IPT primary coils can detect an approaching EV and initiate power transfer to the EV when it is in close proximity. The prototype three coil detection system is capable of detecting EVs moving at speeds up to 1 m/s, for ground clearances less than 285 mm and a horizontal misalignment below ±300 mm. The control signal generated using this system can also control the primary power supply to energise the IPT primary coil and initiate power transfer to the EV when it is in the specified optimum charging region. Finally, the thesis examines methods to control the power transfer in IPT highways. Several methods are explored and a Double Coupled System (DCS) approach relying on an AC-AC intermediary controller is proposed for power transfer control. With this DCS, power transfer to EVs can be initiated within 2.5 ms of EV detection and can be effectively controlled as desired. Overall, the thesis has explored various design elements or issues related to IPT high- ways. Hopefully, the research presented here will help to bring dynamic charging one step closer to practical IPT EV highways in the not so distant future.