Development of a Novel Multiport Power Converter for Inductive Power Transfer Applications

The severity of human-made climate change has never been more evident than in the first two decades of the 21st century. For example, the United States averaged just two heat waves per year in the 1960s in comparison to over six per year between 2010 and 2020, while rising sea temperatures have increased the likelihood of category four and five hurricanes in the north Atlantic since the 1980s. It is scientific consensus that human-made climate change is attributed to greenhouse gases emitted by the burning of fossil fuels such as petroleum, coal and gas. Therefore, the heavy reliance on fossil fuels for energy production is of major concern to governments worldwide. Due to the rapid development of enabling technologies, the electrification of ground transportation has been the major focus over the last twenty years. However, the uptake of electrification has been slow worldwide. For example, in New Zealand, Electric Vehicles (EVs) constitute a minute 1% of the overall Light Duty Vehicle (LDV) fleet. The scientific community and industry experts agree that wireless EV charging through Inductive Power Transfer (IPT) can potentially accelerate the uptake of EVs. As opposed to plug-in charging, wireless systems enable EV charging without the need for user interaction. Hands-free initiation of the charging process makes IPT technology much safer and more convenient for the user, especially in the presence of adverse weather conditions. Unlike plug-in chargers, there are no physical connections that could wear or be damaged and wireless charging standards ensure interoperability between all systems. Although IPT based EV chargers are already commercially available, there are still a number of technological challenges that need to be addressed to achieve widespread adoption. These include the requirement to maintain nominal output power and efficiency for a large range of misaligned parking conditions and battery voltages; achieving high efficiency and maintaining soft-switching throughout the operating range; reducing the size and complexity of thermal systems; and minimising cost. Additionally, more accurate power loss models are required to optimise the overall system design with regard to efficiency, cost and size. Therefore, the focus of this thesis is to address the main technological barriers towards the widespread adoption of IPT based EV chargers and it proposes power electronic solutions that significantly improve system performance in terms of tolerance to operating conditions and system efficiency, while minimising the impact on system cost and complexity. To address the concerns above, this thesis proposes a novel multi-port power converter topology termed the Boost Active Bridge (BAB). The main improvements of this topology compared to existing power converters includes the ability to output a voltage greater than the input voltage, thus reducing switch conduction losses, as well as the ability to regulate its output voltage with minimal control action, resulting in a further reduction is switch conduction losses and a larger Zero Volt Switching (ZVS) region. The experimental results obtained from prototype BAB system showed a peak efficiency of 95.2% when delivering 7 kW to the EV battery. Overall, the proposed BAB converter offers up to 5% improvement in power transfer efficiency while also significantly increasing the operation region of IPT based EV chargers in comparison to existing technology. The BAB converter is able to address the limited operating region of existing IPT based EV chargers and can significantly improve the power transfer efficiency; however, this system utilises four additional DC inductors. As such, this thesis also proposes a BAB converter, which integrates the current splitting functionality previously achieved using DC inductors into a Double D (DD) magnetic coupler. This achieves a reduction in the magnetic volume of approximately 70%. Analysis of the proposed converter together with detailed design guidelines to maximise power transfer efficiency for a system designed to meet the SAEJ2954 specifications is also presented in this thesis. Experimentally obtained efficiencies from a 7 kW prototype system show minimal variation over the full range of loading conditions, ranging between 94.2% and 92%. A critical aspect of designing IPT systems is the accurate characterisation of power losses in the magnetic couplers. Correct loss models enable the optimisation of the magnetic coupler design procedure, while also being a major requirement for managing thermal constraints and computing optimal control parameters. To date, the power losses in magnetic couplers have mainly been predicted by the use of small-signal methods such as LCR meters or impedance analysers. However, these methods do not sufficiently energise the magnetic coupler to increase the magnetic fields and temperatures to levels that are nominally observed during operation. Therefore, in order to model the power losses in magnetic couplers at their rated energisation levels and operational temperatures the Stepped Resonant Excitation (SRE) Methodology is also proposed in this thesis. The SRE method is capable of independently quantifying the winding loss and ferrite loss of a magnetic coupler. Experimental results show that the SRE method presents less than 10% error in predicting core loss on a toroid shaped inductor with magnetic flux densities greater than 50mT.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Engineering

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2023

Author dc:creator

• Kalra, Gaurav R.

Advisors dc:contributor.advisor

• Thrimawithana, Duleepa
• Madawala, Udaya
• Neuburger, Ing Martin

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/64516

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/64516