A Study of Energy Management System of Electric Vehicles

Current electric vehicle power trains comprise on-board energy generation, energy storage and traction drive, where the battery used for energy storage is heavy or expensive or both and requires regular maintenance. Best practice is to use super-capacitors with batteries, reducing the deep charge-discharge cycle and battery size. According to the energy requirements of the EV bus, the control strategies of the energy management system about the dynamic battery and super-capacitor EV bus are studied. With batteries and super-capacitors electric vehicle as the main research subjects, which runs between system and parts time after time, different parts of the dynamic model was built, which include road-load model, super-capacitors model, direct current link model, power transform model and system circuit model etc. The electric vehicle simulation model with the control system of the multi-energy dynamic assembly is built, and simulated, in the ECE 15 which is an urban driving cycle and EDUC (extra urban driving cycle). Simulation results show that the dynamic performance is increased with super-capacitors in the same condition. Based on simulation, average energy consumptions with super-capacitors and without super-capacitors are calculated in typical urban driving and suburb driving cycles respectively. Calculations show that whilst average energy consumption with super-capacitors in urban driving cycle is reduced, this is not so in the suburb driving cycle. The developing low floorboard EV bus (BK6121EV) with multi-energy dynamic assembly system was used to experiment on the test road surface of Tong county in Beijing city, under the different states of the super-capacitors controller on-off. The trend of tested data curve is consistent with the simulation. With super-capacitors, dynamic performance is improved, and both traction battery current and average energy consumption are decreased. The simulation and the control system based CAN bus are both verified by experiment of the low floorboard EV bus