Design Optimization and Control of High-Power Wireless Power Transfer Systems for Electric Vehicle Applications

Abstract

The employment of power electronics systems is essential in the development of environmentally-friendly electric technologies and more specifically for energy-efficient transportation systems. Given the volume of road transportation worldwide, electric mobility in the form of passenger cars, buses, trucks, etc., is an excellent alternative to conventional vehicles based on internal combustion engine (ICE). Benefits can be achieved regarding the polluting emissions (i.e. exhaust levels and geo-location), vehicle drivetrain efficiency, and fossil-fuel dependency. However, there is still a strong need for high performance electric vehicle drivetrains that are reliable, user-friendly and cost-effective. The main issue that still needs to be tackled, is the heavy and costly battery in an electric vehicle (EV). Moreover, in the EV drivetrains, the battery charging process up to now involves the possession of dedicated cables to connect the vehicle to a supply and considerable down-time to replenish the battery state of charge (SoC). Nowadays, wireless power transfer (WPT) systems are one of the promising charging technologies that cannot only improve the charging process, but also can reduce the on-board battery systems thanks to the introduction of dynamic charging system. This WPT comprises two parts: 1) on-board part (defined as secondary WPT winding and its power electronics interfaces that are installed inside the vehicle) and 2) off-board (defined as primary winding and its power electronics interfaces that are mounted on ground and connected to the grid. There are many design and control challenges; resulting in oversizing the drivetrain system and in low power quality and efficiency that should be overcome and improved. Thus, one of the main objectives of this PhD thesis is to improve the battery charging process by making it more user-friendly and by reducing the charging process and time. This might result in simultaneously re-scaling of the required battery pack in electric vehicles with improved charging concepts. Therefore, the research focuses on the development of wireless power transfer (WPT) systems for the charging and of the propulsion systems of electric vehicles (such electric buses with wirelessly connected picking-up coils) and their charging energy-management strategies. These wirelessly connected picking-up coils are well-known as secondary winding of the WPT system. In addition, this study also includes the investigation of various (plug-in hybrid) electric vehicle drivetrains and their components. Where the literature study phase is followed by evaluation and measurement of the newest generation of electric vehicles. During this PhD research, to optimally design the charging management strategy and to define the technical specifications of a WPT system, advanced vehicle simulation models are developed, fine-tuned and implemented by use of a commercial software package (Matlab/Simulink). With these simulations, insight is gained in the power flows in electric vehicles that might use different energy sources (i.e. batteries, ultra-capacitors, inductive charging systems, etc.). The requirements for electric vehicles (especially electric buses propelled by inductive power transfer systems) are investigated thoroughly by way of simulation. This research also provides the required power and energy levels along the trajectories during driving. Moreover, advanced charging management strategies for the combined use of inductive power transfer systems and rechargeable energy-storage systems like batteries are developed. This serves as a motivation for the dimensioning and configuration of the proposed WPT systems. During this work, innovative inductive power transfer systems are developed, and their performance is studied for different scenarios. Various simulation studies are included using commercial software packages (Matlab/Simulink & Infolytica FEM). A special focus is put on innovative bidirectional charging systems. Furthermore, the power electronics realization of an inductive energy transfer system is optimally designed and controlled for electric vehicles, where the wireless power transfer system consists of a primary coil at road side and a secondary carried in the vehicle. The primary is coupled to the grid supply system, while the secondary powers the vehicle propulsion system or the on-board battery. These energy couplings are realized with innovative power electronics interfaces, whereby this research focuses on the practical implementation of an optimized converter prototype, considering real losses, and control strategy. Additionally, the magnetic design of the WPT has been also verified using Infolytica FEM program, where the misalignment and impact of the airgap on the coupling coefficient have been fully addressed in this dissertation. Then, A 22kW prototype has been developed and built in ETEC laboratory to experimentally validate the operational performance of the proposed modular and scalable WPT. The final attention is focused on achieving improved energy efficiency and cost for Vehicle-to-Grid (V2G) and Grid-to-Vehicle (G2V) scenarios, based on inductive power transfer systems and on improving the interoperability of those systems. This will enable the vehicle to act as a smart mobile battery system that could be integrated in smart home network equipped with solar panels achieving high cost benefits.

Date of Award	13 Sep 2018
Original language	English
Supervisor	Joeri Van Mierlo (Promotor)