Research on electric vehicles

With ever increasing concern on energy diversification, energy efficiency and environmental protection, electric vehicles (EVs) including the pure EV (PEV), hybrid EV (HEV) and fuel-cell EV (FEV) are becoming attractive for road transportation. Although some of them have become commercially available, there are many challenges and opportunities for EV development and transition. This paper gives an overview of key research on various types of EVs, with emphasis on their challenges, opportunities and emerging technologies. Firstly, the classification of EVs is conducted based on their energy sources and propulsion devices, leading to deduce the PEV, HEV and FEV as well as to subdivide the HEV into the conventional version (the micro HEV, mild HEV and full HEV) and the gridable version (the plug-in HEV and range-extended EV). Then, their energy diversification, energy efficiency and overall harmful emissions are briefly introduced. Secondly, the challenges and opportunities of the PEV, HEV, gridable HEV and FEV are discussed in details. Thirdly, emerging technologies including the energy sources, electric propulsion, battery charging and vehicle-to-grid that are promising for application to EVs are reviewed. For the energy source technology, the batteries, fuel cells, ultracapacitors and ultrahigh-speed flywheels are discussed, while the concept of on-board renewable energy sources is put forward. For the electric propulsion technology, the requirements of electric machines for EVs are identified so that research activities on advanced machines and machine systems are described. For the battery charging technology, the concepts of park-and-charge and move-and-charge are presented, and hence the arrangements of inductive charging and wireless charging are described. For the vehicle-to-grid technology, the corresponding framework and operation are discussed, hence the concept of energy arbitrage is delineated. Finally, a conclusion on research priorities of EV technologies is given.