Research On Several Crucial Problems In Rotor Dynamics Of MW Super High Speed IPM Machine

Direct-driven system of MW super high speed PM machine has been made increasing use in compressor,aerodynamics and other fields,which brings more and more electric and mechanical problems because of its super high speed.Generally,super high speed PM machine has surface-mounted few poles PM rotor covered by non-magnetic bandage.But the bandage may enlarge the thickness of air-gap so that the consumption of magnetic steel and losses of rotor surface would be more.Thickness of air-gap of laminated IPM structure is thin,but it has much magnetic flux leakage and the rotor punching's mechanical strength is insufficient.This paper focused on optimization of magnetic pole structure of MW super high speed PM machine to solve above problems.The crucial problems of rotor dynamics,such as critical speed and dynamic unbalance,were also studied.Since rotor peripheral speed of MW super high speed PM machine is very high,it has poor mechanical properties.In order to seek a rotor magnetic pole structure balancing both mechanical and electrical properties,surface-mounted magnetic pole structure covered by non-magnetic conductive sheath,common buried-type magnetic pole structure and a new-type of magnetic pole structure with high strength and non-magnetic strengthening rib between laminated interior permanent magnetic steel were respectively studied.After mechanical and electrical properties of three kinds of magnetic pole structure were compared,the optimal structure was determined.According to the size of the rotor,the shaft with reasonable structure was designed by checking the strength of the key.Energy method was presented to calculate the rigidity of each shaft segment and total deformation and the result was validated by finite element method to judge whether the rigidity meets the requirements.In order to predict the resonance of the shaft,the first order critical speed of the shaft was calculated by the equivalent diameter method and the critical speed of each order was calculated by modal analysis of finite element method.The modal analysis was also carried out to study the effect of bearing stiffness on the critical speed of the shaft.Aiming at the problem that the dynamic balance of the shaft of super high speed motor is difficult to grasp,the unbalance harmonic response analysis is carried out.After maximum unbalance mass,allowed eccentricity and unbalance magnitude was calculated,the harmonic response analysis was carried out on the given unbalance mass and eccentricity based on the assumption of the unbalance of the shaft,considering the influence of the bearing stiffness.Finally,the effect of bearing stiffness on the unbalance response of shaft is obtained.