Study On Control Strategy For Powertrain Of Pure Electric Bus

Electric vehicle (EV) is an effective way to solve the problems of energy crisis andenvironment pollution. However, driving mileage is a restriction to the popularity anddevelopment of EV. The best way to increase driving mileage is to study the energy storagedevice and improve energy utilization rate. In a short time, energy storage device can hardlymake a breakthrough. As a result, the best solution to increase driving mileage is to improvethe energy utilization rate on the basis of current vehicle energy storage technology. Thecarrier of energy transmission for EV is powertrain, so studying and developing thepowertrain of high performance is the best way to improve the energy utilization rate andsolve the problem of driving mileage for EV. The paper is based on the project of study onpure electric experiment vehicle and the study on key technology and industrialization forextended-range heavy commercial vehicle, which develops powertrain and control system ofhigh efficiency for pure electric bus. The main researches are as follows:(1) Recognition of the driving intention. Driving comfort and habit should be consideredin the development of powertrain control strategy for EV due to driving differences betweenEV and traditional vehicle. So it is necessary to study on the driving intention to make surethat the responses to the same driving intention between EV and traditional vehicle areidentical. According to the relationship between driving behavior and driving intention, thepaper built as a double layer hidden markov model which first layer is the driving behaviormodel and the second layer is the driving intention model. And then the experiment data ofdifferent driving behavior and driving intention is achieved according to the road experiment.The driving behavior model and driving intention model is trained off line and identified withMatlab software, the result of which indicates that the recognition method of driving behaviorand driving intention based on double layer hidden markov model put forward in the paperhas the advantages of high accuracy, short process time and strong timeliness.(2) The building of mathematical model of powertrain for pure electric bus. The buildingof mathematical model of powertrain for pure electric bus is based on detailed analysis andthe combination of theory modeling and reality modeling. Detailed studies were done on whole vehicle model, pedal model, motor model, transmission system model, wheel model,battery model, super capacitor model, power module model, hydraulic brake system modeland motor regenerative braking system model, all of which provide a reliable simulationplatform for the development of powertrain control system.(3) The design and study on control strategy for main circuit of battery–super capacitordouble power source. Main circuit of battery–super capacitor double power source wasdesigned per the requirement of pure electric bus power source system, including high powerfor starting, acceleration and climbing, enough energy for long-distance driving and fastenergy regeneration during braking. To control the main circuit DC/DC converter based onthe fuzzy self-adaptive PID control strategies. Finally, the simulations of mathematical modelof the pure electric bus power source system and control system were done, the result ofwhich indicates that main circuit of battery–super capacitor double power source can meet thepower source system requirement of pure electric bus.(4) The study of powertrain driving control strategy for pure electric bus. Consideringthe Complexity of environment, difficulty to foresee and driving randomness, regarding thepure electric bus driving system should meet the accurate control speed, impedance drivingresistance mutation and adapt to the requirements of different driving habits, thespeed-electric current double closed loop speed-adjusting system is used to control the drivingsystem of pure electric bus. In which fuzzy self-adaptive PID control strategy is used forspeed control, Bang-Bang control strategy is used for current control to meet the requirementof driving system for pure electric bus. Finally, the simulations of mathematical model of pureelectric bus powertrain driving control system was done, the result of which indicates thatspeed-electric current double closed loop speed-adjusting system can realize the floating ofvehicle speed as well as the sudden changing of impedance driving resistance during driving,which makes the control system in a good dynamic and static characteristics.(5) The study of powertrain braking control strategy for pure electric bus. Consideringthe multi-objective coexistence of safety and economy during braking for pure electric bus, aresearch was done by applying multi-objective programming theory to study the braking force distribution strategy in composite braking system according to the driving intention and speed,while considering the restriction of distribution ratio of braking force upon front and rear,ECER13braking regulation, slip ratio, motor characteristic, energy storage characteristic andtransmission system, to ensure braking system of pure electric bus achieve the maximumrecycling brake energy under premise of safety. Finally, the simulation of control strategy ofcomposite braking system was done under nine operating mode, the result of which indicatesthat hydraulic braking system and motor regenerative braking system can work coordinatelyand steadily under the control strategy in various operating mode, and well meet the dualrequirement of safety and economy during braking.(6) The design and development of powertrain control system for pure electric bus. Thedesign of primary controller is based on Freescale MC9S12DG128B singlechip, EUPECFF800R12KF4IGBT driver is based on CONCEPT2SD315AI chip, to achieving IGBTdriven and controlled by primary controller. For the differences exist in display and functionbetween the instrument of pure electric bus and traditional vehicle, an intelligent instrumentfor pure electric bus is designed based on MCGS embedded software. Following the softwareengineering design concept, the powertrain control system software is divided intomanagement layer, task layer and function layer with the design method of modularization.And then the program of each layer is designed. The powertrain control system designed inthe paper will meet complex driving condition for pure electric bus, with high output power,high output current, high output voltage, strong ant-interference ability, fast response andgood tacking characteristic, all of which will meet the requirement of pure electric bus withpower performance, economy, safety, reliability and comfortableness.(7) The experiment study on pure electric bus performance. To verify the effectivenessand stability of powertrain control system for pure electric bus, the experimental research ofpower, economy and braking for independent research and development pure electric bus areconducted according to the national standard and experiment method, the results of whichindicate the maximum speed can reach to94.09km/h and the driving mileage to163km withan excellent braking performance. The power, economy and braking characteristics not only meet the national standard, but also meet the operational requirements of ordinarymedium-sized bus, which has a good universal significances and development prospects.