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Title: Application of key-off cooling and partial charging in plug-in electric vehicles
Author: Shojaei, Sina
ISNI:       0000 0004 7961 1647
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2018
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Ambient conditions can have a significant impact on the temperature of the battery of electrified vehicles. In hot geographical locations, high battery temperatures can be experienced when the vehicle is parked and cooling is absent. This has three negative implications for the vehicle performance attributes: first, it accelerates the ageing mechanisms of the battery and leads to short battery lifetime; second, it necessitates inhibition of the battery power as a safety measure and leads to low traction in electric vehicles or poor fuel economy in hybrid electric vehicles; third, it increases the battery cooling load which reduces the cooling power available to the cabin and leads to poor passenger thermal comfort. Eliminating the high battery temperatures that result from exposure to hot ambient conditions requires a comprehensive battery cooling strategy; one in which the battery can be cooled when the vehicle is driven or when parked. In the current state of the art battery cooling strategy, cooling is only available when the vehicle is driven and when it is plugged in. Practical concerns such as the associated energy consumption have discouraged battery cooling when the vehicle is parked and not plugged in (key-off). Since passenger vehicles typically experience long key-off intervals, the existing battery cooling strategies are insufficient in hot ambient conditions. The main contribution of this research is proposing the application of key-off battery cooling and developing an underpinning methodology for evaluating the benefits of key-off cooling in a plug-in hybrid electric vehicle. Key-off cooling is defined as an optimal control problem and solved in view of the 24-hour duty cycle of the vehicle evaluated by a representative model. This new methodology enables applying key-off cooling based on the requirements of one or more of the attributes of battery lifetime, thermal comfort and fuel economy, enabling consideration of these attributes in applying battery cooling in an optimal manner. The results show that while the effectiveness of key-off cooling depends on the duty cycle of the vehicle, it generally improves the battery lifetime and benefits the thermal comfort and the fuel economy attributes. To enable further improvements in the battery lifetime, integration of key-off cooling and partial charging of the battery is proposed, advancing the existing state of the art where partial charging is optimised independently of cooling. A new methodology is developed that determines the combination of the battery charge and key-off cooling control strategy that maximises the battery lifetime, while also considering the thermal comfort and the fuel economy attributes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TL Motor vehicles. Aeronautics. Astronautics