Importance of rotor design for high-speed brushless motor
The design of high-speed motor is quite different from that of ordinary low-speed and low-frequency motor. The dynamic analysis of rotor and bearing system is of great significance to the operation reliability of high-speed motor.
The design of rotor is the key to the design of high-speed brushless motor. The main issues to be considered are: the selection of rotor diameter and length, the selection of permanent magnet materials and the protection methods adopted (permanent magnets cannot bear the huge centrifugal force received during high-speed rotation, and must be protected by some high-strength materials), the analysis of rotor strength and stiffness, and the design of bearings (ordinary bearings cannot be used in high-speed brushless motor, and non-contact air bearings or magnetic bearings must be used).
For high-speed brushless motor, the design of permanent magnet rotor should consider both electromagnetic and mechanical aspects, that is, the permanent magnet rotor provides a strong enough rotating magnetic field for the stator winding, and at the same time, the permanent magnet rotor itself has to bear the huge centrifugal force generated by high-speed rotation.
High-speed brushless motors have fewer poles, and generally adopt 2 poles or 4 poles. The 2-pole motor is convenient for permanent magnets to adopt the real structure to ensure the mechanical and electromagnetic symmetry of the permanent magnet rotor. At the same time, the magnetic field and winding current and frequency of the stator core of the 2-pole motor are only half of those of the 4-pole motor, which is beneficial to reduce the iron loss and copper loss of the motor stator. The main disadvantage of 2-pole motor is that the end of stator winding is longer and the required stator core area is larger.
Selection of permanent magnet materials for high-speed brushless motors The performance of permanent magnet materials determines the size and performance of high-speed motors to a certain extent. When selecting permanent magnet materials, consideration should be given to:
1. In order to improve the force and energy density and efficiency of the motor, materials with larger residual flux and density and coercive force combined area should be selected.
2. The demagnetization curve of the permanent magnet material should change linearly within the allowable working temperature range. In order to ensure that the working temperature of the permanent magnet rotor does not exceed the demagnetization temperature of the permanent magnet, the permanent magnet material with high temperature resistance should be selected.
Because the permanent magnet rotor of high-speed brushless motor bears huge centrifugal force, the selection of mechanical properties of permanent magnet material is a problem to be considered. Comprehensive technical requirements and material cost. At present, in the design of high-speed permanent magnet motors, sintered NdFeB permanent magnet materials with high temperature resistance are mostly used.