A Rule Based Power Split Strategy for Battery/Ultracapacitor Energy Storage Systems in Hybrid Electric Vehicles

摘要

This paper presents a simple and efficient rule based power split strategy for a combinedbattery/ultracapacitor energy storage system having electrochemical characteristics in hybrid electricvehicles. For this purpose, a novel rule based controller with three stages is introduced. The first stageis determination of the operation modes (i.e. either charge or discharge commands) of the energysources based on the direction of the power request (i.e. either in traction or regen request) and thecharge/discharge states (i.e. energy sources either in charging or discharging phase). In the secondstage, new weighting parameters used in rule tables are formulated based on the state of charge levels(SOC) of the energy sources to ensure the charge sustainability (i.e. SOC within limits). In the laststage, the power split rules are defined in rule tables based on the operation modes, states of the energysources and the weighting parameters. The performance of the proposed strategy has been tested on ahybrid electric city bus developed in MATLAB/Simulink and compared with alternative rule basedpower split strategy through comprehensive simulation studies under different drive cycle conditions.For comparison purpose, two different case studies have been conducted. First, the results have beencompared with the battery only system and then the effectiveness of the proposed strategy has beencompared with that of alternative one. The simulation results showed that the proposed strategysignificantly reduces the frequency of high C-rate current drawn from the battery and provides a moresmooth change in battery current during sudden acceleration events when comparing with alternativestrategy.