Torsional Vibration Modeling Analysis And Active Suppression Method Of Integrated Electric Drive System

The electric drive system is the core device of pure electric vehicle,which is responsible for providing power to drive the vehicle.The integrated electric drive system,which integrates the motor,controller and transmission device highly,has become the key research and development direction in the field of pure electric vehicle technology due to its compact structure and high power density.However,due to the high coupling between the motor and the gear transmission system,the integrated electric drive system exhibits complex response characteristics,especially in the aspect of torsional vibration,which brings new challenges for the development of electric drive technology.Aiming at the problem of torsional vibration of integrated electric drive system,the research from modeling analysis to active suppression method of torsional vibration is completed this paper,mainly reflected in the following aspects:(1)Modeling of interior permanent magnet synchronous machines for vehicle.A two-dimensional finite element model of a permanent magnet synchronous motor(PMSM)is developed,and its basic performance was verified by simulation.Aiming at the limitation of traditional lumped parameter model,the nonlinear factors affecting motor torque characteristics are analyzed based on finite element simulation and electrical machinery.The necessity of considering motor flux harmonic and magnetic saturation characteristics to accurately reflect the machaine torque characteristics is proved.The electromagnetic submodel was established based on the current-flux flux inverse MAP,and the instantaneous torque ripple submodel is developed based on the magnetic coenergy theory and the construction of the mathematical analytic formula of flux linkage.The accuracy of the mathematical model is verified by simulation comparison.Finally,the machine torque model considering flux harmonic and magnetic saturation characteristics is established simultaneously.(2)Modeling of electric machine control system.The basic vector control model is established based on the analysis of the principles of vector control and SVPWM.An analytical calculation method of torque/fundamental reference current points is proposed based on the analysis of the current operating region and current distribution principle of the electric machine,which is suitable for all operating conditions by including MTPA control and flux-weakening control.The influence law of the magnetic saturation characteristic of machine on the operation characteristic is analyzed,then the necessity of considering the magnetic saturation characteristic of machine when developing the torque/fundamental reference current allocation strategy is proved.Thus,the basic reference current allocation strategy considering the magnetic saturation characteristic of machine is established based on inductance online lookup table.Finally,the fine matching performance between the electric machine control system model and the machine model is shown through the simulation results,and the average output torque of the motor can respond quickly and follow the required torque command.(3)Transmission system modeling and electromechanical coupling characteristics analysis.The nonlinear excitation such as time-varying meshing stiffness,meshing error and gear backlash is analyzed.The pure torsional dynamics model of helical gear pair meshing is established.Considering the stiffness and damping of the flexible shaft,a seven-degree-of-freedom dynamics model of the transmission system is established based on Newton’s second law,and its inherent characteristics are analyzed.The electromechanical coupling model of the integrated electric drive system is established by coupling with the torque and speed of the motor and its control system model.Then the characteristics of the electromechanical coupling under steady and transient conditions are analyzed.Based on the response analysis of the physical signals of each part of the system,the torsional vibration phenomenon and mechanism of the integrated electric drive system under the combined action of motor torque fluctuation and multiple excitation sources of gear meshing are discussed,which lays a theoretical foundation for proposing the active suppression method.(4)Research on active torsional vibration suppression method of integrated electric drive system.Considering the torque fluctuation excitation from the electric machine in the integrated electric drive system,an analytical calculation method of reference harmonic current command is proposed to suppress the torque ripple of the machine based on the coupling relationship between the torque and harmonic current reflected in the transient torque ripple model.A harmonic current proportional integral resonance(PIR)controller is designed to control the actual current to accurately follow the reference harmonic current command,thus a steady-state torsional vibration suppression method is proposed based on active harmonic current injection.A two-degree-of-freedom simplified model of the transmission system is established.Based on the analysis of the amplitudefrequency response characteristics of the system,the transient torsional vibration suppression method based on state feedback control is proposed.The proposed steady torsional vibration suppression method based on active harmonic current injection can generate additional harmonic torque to offset torque ripple caused by flux harmonic and the cogging torque effectively through injecting harmonic current.Thus the machine torque ripple effect on torsion vibration of transmission is reduced.In addition,the chattering problem of the system under the transient conditions such as rapid acceleration starting can be effectively reduced by the transient torsional vibration suppression method based on state feedback control proposed in this paper.Thus,dynamic load on the components can be reduce and the ride comfort of the vehicle can be improved.