Overview of Power Networks in Hybrid Electric Vehicles

Abstract

In hybrid electric vehicles (HEVs), the power network takes an ever-important role, which functions to adjust the engine operating region for less emissions, to incorporate the electric machine for higher overall efficiency, and to feed the increasing demand of electric loads with different voltage levels. Furthermore, more and more mechanically, pneumatically or hydraulically driven systems are gradually superseded by electrically driven systems. In this paper, the key issues, the main components, the powertrain arrangements and the voltage levels of the power network in HEVs are discussed. Keywords hybrid electric vehicle, power network, DC microgrid, powertrain, voltage level 1. INTRODUCTION Although electric vehicles (EVs) have the advantages of zero emissions, high energy efficiency and quiet operation, their process of commercialization has been hindered due to some limitations, such as the short driving range, the lack of charging infrastructure, the time-consuming recharge and the high initial cost [Chan, 1993]. Rather than simply an interim solution, the hybrid electric vehicles (HEVs) form an individual family of EVs and exhibit strong competence in the auto market. The HEVs incorporate an internal combustion engine (ICE) and electric machine to ensure the ICE operating in its efficient mode. Hence, they have even longer driving range than ICE vehicles. By refuelling the gasoline from the existing gas station, the HEVs are well accepted by general publics [Chan and Chau, 2001]. Generally, the HEVs are classified into four kinds: the series hybrid, parallel hybrid, series-parallel hybrid, and complex hybrid, based on the powertrain arrangement [Chau and Wong, 2002]. Recently, another way to categorize the HEVs has also been accepted, namely the micro hybrid, mild hybrid and full hybrid , based on the operating features and power level of HEVs [Ebron and Cregar, 2005; Yu et al., 2008]. Additionally, in order to further improve the energy diversification and energy efficiency of HEVs, two gridable HEVs, namely the plug-in HEV (PHEV) and the extended-range EV (E-REV), have also been developed [Van Wieringen and Pop-Iliev, 2010]. For all