Optimal Energy Management Based On Super Capacitor Assisted Electric Bus

In the paste few years, the super capacitor has been widely used in electric cars because of its high power density, long time life and high efficiency during discharge and re-charging.Buses often started and braked when traveling in the city. If super capacitor and battery are used together, we can not only take the advantage of battery high energy density and super capacitor high power density, utilizing super capacitor short-time power charging and discharging characteristics to improve the electric car's starting, climbing and braking performance, but also reduce the battery charge and discharge current to extend its life, and improve the dynamic and economic performance of the vehicle.Firstly, key components of vehicles like super capacitor, battery and power converter features and principle are introduced in detail. Then a simulation model of the key parts is set up and the choose of capacity ratio between battery and super capacitor under all the working conditions are analyzed in detail. In order to make full use of fixed path characteristics of buses, the velocity and acceleration of buses when driving are estimated according to the historical data and real-time data, the bus stop's characteristics of road slope and site is sought out by using GPS/GIS(global satellite navigation information system). Finally, we use all of this information to calculate each moments' power demand when heading for next stop.For electric bus power's management problems, this paper puts forward the super capacitor and battery power pre-allocated of bus stop site according to the average power of the next section, add-subtract speed double fuzzy control in the running process of the energy management strategy. In order to improve bus starting, acceleration and energy recovery efficiency as far as possible, super capacitor SOC(the State of Charge) predict control strategy is brought in. This control method calculates the bus super capacitor SOC reference value in every moment according to the previous bus stop site SOC pre-allocated initial value and some predicting information. Then the predictive control strategy and fuzzy control adjust the bidirectional DC/DC converter to control the vehicle energy flow by different weight factor. It turns out that when super capacitor SOC predictive control strategy has different weight factor, it will have different influence on energy management system.Using the ADVISOR software, taking the New York and Nuremberg, Germany movement condition as example, Matlab/simulink as a research tool, systematically analyze the suggested energy management. The result of simulation shows: The proposed method can better meet the needs of electric buses starting, acceleration and energy utilization efficiency,reduce the battery charge and discharge current, extend the life of battery.