IPMSMにおける電磁共振条件の検討

抄録

IPMSM (Interior permanent Magnet Synchronous Motor) is widely used for many industrial applications because of its high power density and high efficiency. Also, in recent years, the product’s rotational speed has become faster and the size has become lighter and more compact. On the other hand, these changes have increased magnetic flux density inside the motor and radial electromagnetic excitation, which causes large noises as a result of the sound and vibration. It is known that one of the causes of the noise is the resonance between the electromagnetic excitation force and the stator core. Although it is necessary to clarify the resonance condition of the electromagnetic excitation force and the stator core to reduce noise, the condition when the resonance happens has not become clear enough yet. In this report, we carried out the research on the resonance condition of the electromagnetic excitation force and the stator core. IPMSM can be regarded as a periodic structure, and one equation of motion with 48 degree of Freedom (DOF) is transformed into 48 equations of motion with 1 DOF using the coordinate transformation specific to cycle-symmetric structures. By solving these 48 equations of motion, it became clear that the resonance occurred when the excitation frequency matches the natural frequency and the excitation mode order matches the natural vibration mode order. This resonance condition was also consistent with the experimental results. In addition to that, for IPMSMs with 8 interior permanent magnets and 48 slots, it became clear that the stator core is excited in the vibration modes which is multiples of 8 and the occurrence of resonance can be suppressed by avoiding the use of the frequency which satisfies the resonance condition.