Design of a propulsion system with double-layer power capacitors and soft-switched converters for a hybrid automobile
The increasing pollution levels, especially in cities, have made the development of more environmentally 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 amont 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 capacitors are an attractive option in hybrid vehicles due to their high power density and long lifetime. However, these devices are new, and assembling of large energy storage units has to be studies 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 minimize weight and size. The use of higher switching frequencies brings important reductions in weight mainly for the magnetic components. However, due to 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 minimize fuel consumption. The thesis also includes the formulation of an energy management strategy optimized for the vehicle characteristics and the implementation of an experimental prototype for the proposed system.
Analysis and Design of DC to AC Power Converters at 13.56MHz
An analysis and design procedure for DC to AC Converters ranging from 250 to 500 Watts working at 13.56MHz based on commercially available power VDMOS transistors is presented in this work. A systematic technique for the design and analysis of these converters is presented by making contributions in the three main areas: VDMOS transistor modeling, converter configuration identification and HF transform modeling. In terms of VDMOS modeling , the large-signal impedance VDMOS model and a parameter extraction process are proposed for both standard and RF type VDMOS converters. For converter configuration identification, impedance cancellation and transformation techniques are used to synthesize a single transistor converter with a minimum component count and well defined component values. Using a complete top-down HF transformer model based on a Multi-conductor Transmission Line (MTL) representation of the windings, a method to combine single transistor converters to obtain higher output power is demonstrated. Detailed experimental results are presented for 250W converters based on either the ARF446 or the IRFP450A with efficiencies of about 85% as well as a 500W push-pull converter based on two ARF446 with an efficiency of 78%.