Study On Electromechanical Coupling Nonlinear Vibration Of Electromechanical Transmission System For HEV

High-speed high-power electro-mechanical transmission is composed of permanent magnet synchronous motor(PMSM) and mechanical transmission, which is considered as a typical electro-mechanical coupling system. The dynamic characteristics of transmission system are not only related to mechanical configuration parameters, but also electromagnetic parameters and dynamic performance of electrical machine. Moreover, the permanent magnet synchronous machine itself is a electro-mechanical coupling system, i.e., changes of the PMSM’s motion have an impact on the rotor dynamics, which will in turn affect the motion of PMSM. Electro-mechanical coupling effect is essential in electro-mechanical transmission system. Therefore, it is important to study the constraint mechanisms of system component’s motion caused by electromechanical coupling, and analyze the correlative coupling mechanism between the coupling parameters and system function. These studies are crucial in prediction of odds operation condition and faulty control.The air-gap magnet field of permanent magnet synchronous motor for HEV was characteristic of saturation, temporal and spacial harmonic magnet filed. Accounting for the above characteristics, an electromagnetic torque analytic model was established by combining the classic Park’s transformation and airgap magnet field analytic model, from which the frequency characteristics of the electromagnetic fluctuation can be reflected. Thereafter, in a perspective of electromechanical coupling, the effects of both load fluctuation and rotor dynamic eccentricity on the frequency characteristics was analyzed. Results indicated that under a certain load fluctuation and dynamic eccentricity operation condition, a stator armature current would induce side band frequencies with a certain frequency around fundamental current.Based on the electromagnetic theory, electromagnetic torque was derived from the perspective of energy taking the effect of torsion angle on the angle between the stator and rotor magnetic motive force(MMF) into consideration. A nonlinear rotor torsional vibration model was established by simplifying electromagnetic torque. An approximate solution for this model was obtained by using the multiple scales method, which was followed by bifurcation analysis of the system. Stability of the system was investigated applying Lyapunov first method. Analysis on the correlations between the electromechanical parameters and the torsional vibration of rotor system was also conducted. Another contribution was defining the boundary condition of stable operation condition on the basis of system bifurcation and chaos characteristics given by Melnikov theory.In reality, the unsymmetrical air gas field of PMSM tends to yield unbalanced magnetic pull(UMP), which induces a rise to the electromechanical coupling lateral vibration. Then, taking armature reaction into consideration, the analytic model of UMP was established by Maxwell-Tensor method, and then equivalent electromagnetic stiffness coefficient was defined. Results show that such electromechanical coupling system tends to yield negative stiffness effect in terms of equivalent electromagnetic stiffness coefficient, which altered the stiffness attributes of a rotor system. Such effect was the reason for the decay of natural frequency and the system instability. The trends of the impacts of electromechanical parameters on the coupling vibration were also of interest to provide a theoretical basis for the electromechanical parameter design of motor-rotor system.Despite of the lateral excitation, the asymmetricity of the air gas field yields torsional electromagnetic excitation as well. The multi-electromechanical coupling dynamic model was finally established based on the Lagrang-Maxwell method. Nonlinear dynamics theory was applied to solve for multi-electromechanical coupling dynamic model. The rule of multi-electromechanical coupling was analyzed under different electro-magnetic parameters. Also, the possible measures and steps to reduce vibration of the electromechanical coupling system were discussed, which perhaps provides a theoretical basis of the active vibration control for electromechanical coupling system.