Study On Electromechanical Coupling Characteristics And Control Strategy Optimization Of An Integrated Electric Drive System For Pure Electric Vehicle

Electric drive system is the core component of new energy vehicles.The integrated design and manufacture of electric drive system can greatly improve its efficiency,power density,NVH performance and reliability.The integration of drive motor and reducer can effectively reduce the volume,weight and cost of electric drive system,which has become an important trend of its development.At present,there are researches on electrical system and gear transmission system all over the world,but the coupling effect between mechanical system and electrical system on the dynamic performance of electrical drive system is seldom considered.This paper takes an integrated electric drive system(IEDS)as the research object,which is composed of a permanent magnet synchronous motor(PMSM)and a helical gear reducer.A detailed dynamic model of surface-mounted PMSM control system and a torsional vibration model of pure electric vehicle driveline are proposed to study the electromechanical coupling characteristics of IEDS.On this basis,this paper optimizes the motor control strategy to improve the performance of the integrated electric drive system.The main research contents are as follows:(1)Based on vector control,the torque/speed control system of PMSM is established,and the control system parameters in torque mode and speed mode are designed respectively.At the same time,combined with the maximum torque per ampere(MTPA)control and flux weakening(FW)control,the stator reference current of motor is calculated to ensure that the maximum torque output can be maintained at low speed and the maximum power output can be maintained at high speed.In addition,the space vector pulse width modulation(SVPWM)algorithm is taken as the inverter switch control strategy,and the relationship between inverter dead time effect,voltage drop effect and motor electromagnetic torque harmonics is further analyzed.On this basis,the harmonic torque mathematical model of PMSM is established.(2)By analyzing the mesh process of helical gear,the relationship between the mesh stiffness and the angular displacement is obtained.Considering the influence of the nonlinear factors such as time-varying mesh stiffness and mesh error,the transient dynamic model of helical gear is established by adopting centralized parameters method.Then,the torsional vibration model of pure electric vehicle transmission system equipped with IEDS is established,and the inherent characteristics and modal vibration mode of the transmission system are further analyzed.Based on the driveline torsional vibration model,the influence of the parameters of IEDS components on the natural frequency of the whole vehicle transmission system is studied by parameter sensitivity analysis.(3)Based on the complete control system model of PMSM and the torsional vibration model of the whole vehicle transmission system,the electromechanical coupling characteristics of IEDS under the conditions of uniform speed,rapid acceleration and impact load are simulated and analyzed.By observing the changes of the stator current,the electromagnetic torque,the speed of each component of IEDS,the mesh force of reducer and the acceleration of vehicle in time and frequency domain under different conditions,the mechanism and reason of the electromechanical coupling effect of IEDS are analyzed,which provides the theoretical basis for the control strategy optimization of IEDS.(4)Based on the results of the electromechanical coupling effect analysis of IEDS under the condition of uniform speed,rapid acceleration and impact load,this paper proposed an active damping control strategy(ADCS)based on motor torque compensation,which can effectively suppress the speed fluctuation of the components of IEDS under the condition of rapid acceleration,reduce the gear meshing force,and improve the vehicle driving comfort.At the same time,the harmonic current of the motor is suppressed by injecting harmonic voltage,so as to weaken the harmonic torque,reduce the amplitude of the motor speed fluctuation and the dynamic load of IEDS.The active damping control strategy and harmonic torque reduction strategy can effectively reduce the dynamic load of IEDS,thus prolonging the life of IEDS and improving the driving comfort of the vehicle.