Design of a propulsion system with double-layer power capacitors and soft-switched converters for a hybrid automobile

grantor: University of TorontoThe increasing pollution levels, especially in cities, have made the development of more environmental friendly vehicles an urgent need. Although millions of dollars have been spent on electric vehicle research, no electric vehicle capable of competing with normal vehicles based only on internal combustion engines has been developed. The problem is associated with the difficulty to store the amount of energy needed and supply it at high power levels. Hybrid electric vehicles represent a very attractive option to reduce pollution while maintaining good performance. The double-layer power capacitors are an attractive option in hybrid vehicles due to their high power density and long lifetime. However, these devices are new, and the assembling of large energy storage units has to be studied before using them in vehicle systems. Voltage sharing is especially critical since many devices have to be connected in series to reach the technically required voltages. To improve the global efficiency for the vehicle, the electric propulsion system has to be designed to minimise weight and size. The use of higher switching frequencies brings important reductions in weight mainly for the magnetic components. However, due to the switching losses, the switching frequency cannot be increased unless soft-switching technologies are used. When using an energy storage device with low energy density in a hybrid vehicle, the energy management strategy is of great importance to reduce the energy storage capability required to achieve the desired performance. The energy manager takes the actions needed to operate the energy storage unit and the engine according to the specifications and maximises the energy utilisation under different driving conditions. This thesis deals with the design of a propulsion system for a series hybrid vehicle. It includes the study of an energy storage unit using double-layer capacitors and a lightweight soft-switched converter system, two innovative components in series hybrid vehicles. Furthermore, the thesis formulates an easy-to-follow design strategy for vehicles using similar configurations and directed to minimise the fuel consumption. The thesis also includes the formulation of an energy management strategy optimised for the vehicle characteristics and the implementation of an experimental prototype for the proposed system.Ph.D