Recent Advance of Hybrid Energy Storage Systems for Electrified Vehicles

A hybrid energy storage system (HESS) that combines batteries and ultracapacitors (UCs) presents unique electric energy storage capability over traditional Energy Storage Systems (ESS) made of pure batteries or UCs. As a critical powertrain component of an electrified vehicle (EV), the performance and life of the ESS dominate the performance and life-cycle cost of the pure electric vehicle (PEV) and plug-in hybrid electric vehicle (PHEV) due to the large size of their ESS. Different from traditional power density and energy density considerations, the use of battery and UC HESS today is more geared toward the use of UCs to take over the high frequency, dynamic charge and discharge to ensure quick system response and to extend battery life by reducing its frequent charge and discharge. In this paper, the recent advance of HESS and relevant technologies have been reviewed. The state-of-the-art of battery ESS and modeling method, considering its performance degradation under different use patterns are first presented. Methods for modeling the UC and DC/DC converter in the HESS, along with various HESS architectures, are also overviewed. Energy management methods of HESS are then reviewed according to recent literature to derive appropriate energy split strategies between the batteries and UCs. Finally, various HESS-based applications from public transportation to construction machinery are discussed to illustrate the benefits of HESS.