A novel battery-supercapacitor power supply for electric vehicles (EVs) : design, simulation and experiment

University of Technology Sydney. Faculty of Engineering and Information Technology.Most existing electric vehicles (EVs) employ rechargeable batteries alone. As a consequence, they suffer from performance degradation such as power deprivation or battery aging, and have difficulty to cope with the whole spectrum of driving load without compromising durability or safety. A more complex design is therefore, required to address this drawback. More specifically, a Hybrid Energy Storage System (HESS) is proposed to hybridize batteries with other sources possessing higher power density such as a supercapacitor via a smart power converter to electrically regulate each power flow. This unique power sharing capability can effectively reduce power stress that would otherwise be applied to batteries alone, whilst increase the attractiveness of the EV market due to the potential power-boost capabilities. However, the novel HESS increases the cost and weight of the vehicle. This thesis is intended to resolve these conflicts and consists of following three innovative aspects. 1) A four-quadrant, supercapacitor-only drive solution is first investigated, developed and characterized to gain better insights into the unique properties of the supercapacitor and the bi-directional DC-DC converter, during both driving and regenerative braking mode – Chapter 3. 2) In order to justify various design trade-offs, a novel Multi Objective Optimization Problem (MOOP) based component sizing algorithm is developed aiming at solving two conflicting objectives – cost and total stored energy in HESS, when considering the presence of a power converter – Chapter 4. 3) Finally, an adaptive power split strategy (PSS) is developed in order to intelligently split load power between batteries and supercapacitors as a function of the ever-changing load profile. A simplified HESS model is first developed in Matlab and then, the real-time PSS is coded using Labview and deployed on a 5kW EV-HESS integrated test rig. Both simulation and experimental results prove its effectiveness in coping with even the harshest driving scenarios in real life – Chapter 5. Although I specifically present the results for HESS applications, the concept of MOOP, HESS and PSS can be easily tailored for other types of hybridized systems such as series hybrid electric vehicles, battery assisted fuel cell electric vehicles, solar-battery power systems or any dual-source power systems that need to perform load-leveling functions