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Title: Analysis, design and control of DC-DC resonant converter for on-board bidirectional battery charger in electric vehicles
Author: Liu, Chaohui
ISNI:       0000 0004 6347 9012
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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The combustion of fossil fuels, a non-renewable and finite resource, has caused increasing air pollution, ozone damage, acid rain and global warming. Electric vehicles (EVs) are eco-friendly with the attractive properties of lower greenhouse emissions, lower fuel usage and reduced air pollution. Battery and charger is one of the vital elements to analyse and develop for EVs. This research focuses on the bidirectional on-board battery charger with the emphasis on the design and analysis of the DC-DC converter. Firstly, a LLC resonant topology is selected as the initial design candidate of the DC-DC resonant converter owing to the preferred soft-switching features. Single phase chargers suffer from a second harmonic voltage/current ripple which can lead to reduction of battery life. A feedforward-proportional-integral-resonant (FF-PIR) controller has been proposed and tested for suppressing this low-frequency current ripple in the LLC resonant converter employed in EV battery chargers. Secondly, the recent developments in smart-grid technology necessitates bi-directional power flow from distributed energy storages like EV to support grid in the vehicle-to-grid (V2G) application. To achieve bi-directional power flow capability, the conventional uni-directional LLC topology is modified into bidirectional CLLC resonant converter. The characteristics have been analysed and validated by extensive simulations and experimental tests. Further improvement has been implemented to increase the power efficiency under varying battery voltages. An optimum-resonant-frequency tracking scheme is proposed and tested to maintain the operation close to the maximum efficiency point over a wide battery voltage range. Finally, in order to predict the converter efficiency accurately, this thesis presents a prediction method employing 2D and 3D finite element analysis (FEA) for calculating the power losses of magnetic components with litz wire in the converter.
Supervisor: Wang, Jiabin ; Stone, David Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available