Abstract
In view of severe changes in temperature during different seasons in cold areas of northern China, the decay of battery capacity of electric vehicles poses a problem. This paper uses an electric bus power system with semi-active hybrid energy storage system (HESS) as the research object and proposes a convex power distribution strategy to optimize the battery current that represents degradation of battery capacity based on the analysis of semi-empirical LiFePO4 battery life decline model. Simulation results show that, at a room temperature of 25 °C, during a daily trip organized by the Harbin City Driving Cycle including four cycle lines and four charging phases, the percentage of battery degradation was 9.6 × 10−3%. According to the average temperature of different months in Harbin, the percentage of battery degradation of the power distribution strategy proposed in this paper is 3.15% in one year; the electric bus can operate for 6.4 years until its capacity reduces to 80% of its initial value, and it can operate for 0.51 year more than the rule-based power distribution strategy.
Highlights
As the sole power source in a traditional electric vehicle, a battery needs to satisfy the power and energy demands of a bus under different operating conditions
In order to attain the full potential of the hybrid energy storage system (HESS) to enhance the battery life of electric buses under local conditions, in this study, we considered the electric bus operating in Harbin, China as an example, and proposed a method to optimize charge/discharge current of battery through convex optimization considering the average monthly temperature change in one year
It can be observed that the battery only provides a small range of demand for power fluctuations, whereas the super capacity (SC) satisfies instantaneous high power requirements
Summary
As the sole power source in a traditional electric vehicle, a battery needs to satisfy the power and energy demands of a bus under different operating conditions. Song et al [8,9] proposed a new semi-active topology; the operation cost of the HESS, including the battery degradation cost and electricity cost, is minimized by using the dynamic programming (DP) approach They studied four topologies and proposed a rule-based power distribution strategy with four kinds of topologies based on the optimization results. In order to attain the full potential of the HESS to enhance the battery life of electric buses under local conditions, in this study, we considered the electric bus operating in Harbin, China as an example, and proposed a method to optimize charge/discharge current of battery through convex optimization considering the average monthly temperature change in one year.
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