Research On Control Strategy Of Electric Machinery Continuously Variable Transmission System

Due to the increasingly serious problems caused by the traditional automobile industry such as air,noise pollution and high energy consumption,new energy vehicles have become the research direction of the modern automobile industry.Electric vehicles are also a kind of new energy vehicles.They have advantages of zero emissions,energy saving and low noise,therefore,governments,enterprises and research scholars all actively participate in the research and development of electric vehicles,continuously improve the sustainable development level of the automobile industry,and accelerate the pace of development of electric vehicles.The electric vehicle transmission system mainly includes two aspects: power transmission system hardware and control system software.At present,pure electric vehicle is still mainly driven by the single-motor matching reductor which has the advantage of low cost and simple structure,but the economic performance is not high in middle and high-speed segment,and the motor efficiency is low.Therefore,the design of suitable transmission for electric vehicles has become the main direction of research,the main performance includes high-power stepless,wide range of speed,simple structure and better transmission performance.In addition,the control strategy is the core of the vehicle controller,because a reasonable and efficient control strategy can improve the utilization rate of the high-efficiency area of the motor and the transmission efficiency of the whole vehicle.This paper is a research on a dual-motor stepless variable speed drive system and its control strategy applied to electric vehicles,where the main motor provides the great majority of driving force,and the speed-regulated motor serves as the auxiliary system to regulate output speed,which has the advantages of wide speed regulation range,compact structure and easy control.According to the control strategy based on high system efficiency,which is matched by cyclic driving conditions,the utilization rate of high efficiency zone of motors and system efficiency of transmission are greatly improved.The main contents of the work are as follows:(1)Studied the transmission scheme of the electro-mechanical continuously variable transmission,and according to the general law of the transmission characteristics of planetary gear mechanism,analyzed the characteristics of rotational speed torque and power flow change of transmission based on differential planetary wheel in different working modes.(2)Parameter matched of power machinery continuously variable transmission system,including power system parameter matching and motor demand power based on cycle conditions and motor high efficiency zone matching.Given the parameters matching method of the dual motors,vehicle transmission ratio and battery according to the basic parameters of the vehicle,which are based on the dynamic index.At the same time,considered the cycle condition of the whole vehicle,the demand drive under NEDC condition is analyzed in the electric vehicle simulation software ADVISOR.Power and motor high efficiency zone distribution.(3)Studied the control strategy of the dual motor drive system,analyzed the calculation method of the transmission system efficiency in a working section,designed the distribution strategy of the dual motor drive torque based on the high system efficiency;analyzed the demand drive torque of the dual motor in different working segments.The calculation method reflected the driving intention by judging opening degree of accelerate-pedal and the rate of change,then compensates the demand driving torque by using the fuzzy control algorithm.According to the control mechanism of the transmission system and design,the simulation model based on Simulink is built,and the simulation is carried out in ADVISOR to analyze the dynamic performance of the vehicle and the efficiency of the transmission system.(4)Set up the bench test of the dual-motor continuously variable transmission system,analyzed the working points of the two motors and system efficiency under drive conditions.According to the simulation results,record the characteristics of the output speed regulation,and verify the control strategy.Tested and verified the transmission system has a higher utilization rate of motor and system efficiency.