Dynamic Characteristics Analysis Of A New Self-damping Planetary Transmission Under Unsteady Operating Conditions

The electric drive integration of electric vehicles is a current research hotspot.The electromechanical transmission system composed of a motor and a gear system is the main power transmission device of an EV（Electric Vehicle）,which determines the smoothness of the power transmission and the driving comfort of the EV.The EV often work in a variety of complex conditions,and the drive train is always subject to excitation from the motor and the road surface as well as time-varying parameter excitations of the gear system,which make the electromechanical transmission system exhibit complex dynamic behavior with load fluctuation and torsional vibration.To improve the dynamic characteristics of the electromechanical transmission system under internal and external excitation,a new type of self-damping planetary transmission called TVD-PG（Torsional Vibration Damper and Planetary Gear）is proposed,where the torsional vibration damper is used to replace the conventional manner a certain member in planetary gear fixed with a box.The dynamic characteristics of the motor-TVD-PG system under unsteady conditions are thoroughly explored.By comparing with the motor-PG（planetary gear）system,the advantages of the TVD-PG are demonstrated.The dynamic characteristics of the motor-TVD-PG system are further improved from the aspects of parameter optimization and active vibration control.The main researches of the article are as follows:（1）A translation-torsional dynamic model and a pure torsional dynamic model of the TVD-PG for variable speed conditions are built,taking into account the torsional deformation of the shaft,the time-varying meshing stiffness and the meshing error of the planetary gear.The translational and angular displacements of components are selected as the generalized coordinates of the system,and the angular displacements of the sun gear and the ring gear are obtained in a static coordinate system.The time-varying meshing stiffness model of planetary gear is improved to be suitable for variable speed situations,expressing as a function of the actual angular displacement of the sun gear.Coupling dynamics model of motor-TVD-PG system is established.（2）The natural characteristics of the motor-TVD-PG system are analyzed.Compared with the traditional motor-PG system,the TVD-PG significantly reduces the low-order natural frequencies of system and changes part of the mode shape of system.The influence of the stiffness parameters on the natural frequencies of the system is explored,which indicates that the stiffness change of the torsional vibration damper mainly affects the low-order natural frequencies of system,and the change of meshing stiffness in planetary gear mainly affects the high-order natural frequencies of system.The Campbell diagram and the modal kinetic energy method are used to identify the resonances that may occur in the system’s common operating speed range,which indicates that the TVD-PG can reduce the resonances in the system’s common speed range.（3）A motor dynamic model and a speed controller model of the motor based on rotor field oriented vector control is established.Based on the Matlab/Simulink platform,the motor dynamic model and TVD-PG are coupled for simulation,and the dynamic response curves of the electromechanical transmission system are obtained.During the startup process,the transient response dominated by the 1^st natural frequency of system and the resonance phenomenon of the system are excited.The TVD-PG significantly reduces the load fluctuations and component vibrations of the system,making the system speed increase more smoothly.During the load saltation process,the motor-TVD-PG system does not undergo a large overshoot.The time-varying meshing stiffness of the planetary gear causes the system to generate high-frequency fluctuations.The vibration amplitude increases with the increase of the load,and the frequencies changes with the speed.In addition,the TVD-PG can significantly reduce the interference of the fluctuation load on the motor and gear parts.Finally,the mechanism of electromechanical coupling is explored.The excitation frequencies of the gear part will appear in pairs in the spectrum of the stator current,in the form of adding and subtracting voltage frequency,and this can be used to monitor the resonance state of the system.（4）A multi-objective optimization model of the motor-TVD-PG system is established with the effective value and the maximum value of the meshing force fluctuations of the planetary gear during the startup process as the objective function.The Genetic Algorithm is used to optimize the mechanical parameters of the system,and a better optimization effect is obtained.Aiming at the phenomenon that the load fluctuation and torsional vibration of the transmission system increase significantly due to the speed request of the motor after the system is stabilized,an active vibration control method based on ADRC（Active Disturbance Rejection Control）is proposed.The electromagnetic torque of the motor is compensated by the ADRC controller,which effectively suppresses the load fluctuation and torsional vibration of the system.