| In modern agriculture,demands for green power of agricultural machinery becomes a urgent,which produces zero emission,much less pollution and low noise.Electric tractor with its new concept and promise is becoming a hot research topic.However,as for the parameters matching and optimization of electric tractor powertrain,there is no mature systematic design method in current.Meanwhile,facing the complicated operating mode of tractors,drive control method of electric tractor needs special care.Therefore,this paper took electric tractor as the research object.It first formulated the drive structure scheme of powertrain,based on which the parameter design method and drive control strategy were studied.The experiment part verified performances using the hardware in loop simulation platform and the bench test platform.The structure of this paper are as follows:Firstly,in view of overall design requirements and power demands of electric tractor,overall chassis structure scheme and control system scheme were designed.With this,a dual-motor coupling drive powertrain scheme suitable for multiple working conditions was formulated.And the mathematical model of powertrain for electric tractor was established.Secondly,by analyzing the traction and economic performance of electric tractor,the powertrain parameter matching design method was studied.The key component parameters for driving motor,power battery and the gearbox were matched with this method.On this basis,the parameter optimization design method for ratios of the transmission system was studied.The power objective function of driving power utilization ratio and economic objective functions of continuous working time were established.And the optimization constraints including allowable adhesion constraint and transmission ratio relation constraints were set up.The optimization design problem was solved using combination algorithm of mixed penalty function method and particle swarm optimization.The traction characteristics of electric tractor with two schemes before and after optimization were compared and analyzed.The results showed that the power coverage of electric tractors after optimization was more extensive,and the heavy load capacity got improved.Two motors' performance characteristics were more coordinated,and the motor driving force could be used more fully and reasonably.Thridly,according to the drive control target,the drive control strategy of electric tractor was formulated,combining input layer,recognition layer,decision layer and executive layer.The demand torque recognition control strategy of the recognition layer was carried out,and fuzzy PID algorithm is used to recognize the demand torque under constant speed working condition.Compared with PID controller,the simulation result showed that the fuzzy PID controller effectively improved the response speed and accuracy of target speed and traction resistance.On the basis,the power distribution control strategy of the decision layer was carried out.The minimum power loss was as the optimal distribution target.The power distribution algorithm was established for different coupling drive modes.The control rules were obtained by off-line simulation,Compared with the simulation based on constant proportional power distribution control strategy,the results showed that the minimum power loss based power distribution control strategy could effectively reduce the power loss of powertrain and improve the driving efficiency.Finally,based on the drive control strategy of electric tractor,the drive control system was designed and developed.Leveraging dSPACE,the hardware in loop simulation platform was set up.The effectiveness and practicability of the drive control system were simulated and verified.Furthermore,bench test platform was built,and the adaptability and effectiveness in driving the real power assembly were verified. |
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