PHEV Charging Strategies for Maximized Energy Saving

This paper studies the charging strategies of an Li-ion battery with a focus on the battery's power loss model. It is found that when the temperature is assumed constant, constant current/constant voltage (CC/CV) is near optimal for energy loss minimization. However, when the temperature is considered as a state variable, an optimal profile different from CC/CV is found. This new profile can be used to warm-up batteries during cold days, hence reducing the need for existing battery heating systems. As a result of the elevated battery temperature, significant energy savings can be achieved if the vehicle is used soon after the charging process ends. In this paper, the form of the optimization problem resembles a classic form, with the peculiarity of being highly nonlinear and time varying. The charging strategies resulting from this study will have significant impact on how plug-in hybrid electric vehicles (PHEVs) are charged and utilized.