Power Demand Analysis and Performance Estimation for Active-Combination Energy Storage System Used in Hybrid Electric Vehicles

Because of the drawbacks of ultracapacitors (UCs) and batteries, an active combination of UCs and Li-ion batteries has been proposed as an energy storage system (ESS) for hybrid electric vehicles (HEVs). Given the complexity of the active control system in an active-combination energy storage system (ACES), the performance match for the ACES used in an HEV is much more complex. In this paper, a widely applicable method to analyze the design process of the ESS used in HEVs is presented. The concept of the power-energy (PE) function is proposed to illustrate the power demand from the HEV and the energy and power capability of the ESS. This concept draws a clear contrast between demand and capability, particularly for the ACES. At the same time, the efficiency of the ACES could be estimated on the basis of this method. Furthermore, by using operating data from a hybrid electric bus in Changchun, China, power demand analysis and performance estimation are carried out for the optimal design of the ACES.