Analysis of fuel economy and battery life depending on the types of HEV using dynamic programming

Increasing demands of eco-friendly vehicles, various types of hybrid electric vehicle (HEV) have been researched and released. Recently, some research has interest in not only the efficiency of the vehicle but also the durability of battery because the life of battery has influence on the cost of maintenance, stability and performance of the vehicle. In this study, backward simulation based on dynamic programming depending on the type of HEV which is consists of engine and battery or engine, battery and ultra-capacitor was conducted. The developed backward simulation algorithm can calculate the optimal fuel economy according to the driving cycle and other vehicle and components conditions. For the analysis of battery life, a battery capacity fade model was applied to the result of backward simulation. Battery life was estimated with an assumption that the vehicle drives repeatedly to follow the result of backward simulation derived to find the optimal fuel economy. From the simulation results, it is shown that HEV with ultra-capacitor has better fuel economy though it is almost similar with HEV without ultra-capacitor. However, the battery life of HEV with ultra-capacitor was estimated better because of the difference of battery power usage. Consequently, applying the ultra-capacitor to the typical parallel HEV has no large advantage in terms of fuel economy but has significant benefit in terms of battery life.