I. Introduction
Energy management strategies (EMSs) determines the fuel economy of plug-in hybrid electric vehicles (PHEVs) [1], there are multifarious EMSs that have been researched, which can be mainly divided into three categories.: rule-based, optimization-based, and learning-based [2], [3]. Rule-based EMSs are derived from engineering experience, which have strong practicability but lack of adaptability to different driving cycles [4].