High-speed brushless motors for laboratory agitators usually operate at speeds ranging from 20,000 RPM to 30,000 RPM /min. The design of a high-speed motor is very different from the common low-speed and low-frequency motor. The dynamic analysis of the rotor and bearing system is of great significance to the operation reliability of the high-speed motor.
The design of the rotor is the key to the design of a high-speed brushless motor. The main considerations are as follows: Selection of rotor diameter and length, the choice of permanent magnetic material and using the way of protection (permanent magnets can't bear the large centrifugal force of high-speed rotating when received, must adopt some of the material to protect the high strength, the strength and stiffness analysis of the rotor, the design of the bearing (the high-speed brushless motor cannot adopt ordinary bearing must adopt non-contact air bearings and magnetic bearings), etc.
For a high-speed brushless motor, the design of a 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, while the permanent magnet rotor itself has to bear the huge centrifugal force generated by high-speed rotation.
A high-speed brushless motorhas fewer poles, generally using 2 or 4 poles. The 2-pole motor facilitates the use of the real structure of a permanent magnet to ensure the mechanical and electromagnetic symmetry of the real structure of the permanent magnet rotor. At the same time, the magnetic field and winding current and frequency of stator core of 2-pole motor are only half of that of 4-pole motor, which is beneficial to reduce the iron and copper consumption of stator. The main disadvantage of the 2-pole motor is that the end of the stator windings is longer and the required area of the stator core is larger.
The performance of a permanent magnet subject determines the size and performance of a high-speed brushless motor to a certain extent. When choosing permanent magnet material, we need to consider:
1. To improve the force-energy density and efficiency of the motor, the material with a larger area of residual flux and density and coercivity should be selected.
2. The demagnetization curve of permanent magnet materials should show linear changes within the allowable operating temperature range. To ensure that the working temperature of the permanent magnet rotor does not exceed the demagnetization temperature of the permanent magnet, high temperature resistant permanent magnet material should be selected.
Since the permanent magnet rotor of a high-speed brushless motor bears huge centrifugal force, the mechanical properties of permanent magnet material should be considered. Comprehensive technical requirements and material costs. At present, high temperature resistant sintered NdFeB permanent magnet material is mostly used in the design of high-speed permanent magnet motor.
Sintered NdFeB is a similar powder metallurgy permanent magnet material, one of the methods to protect the permanent magnet, in the outside of the permanent magnet with a high strength non-magnetic conductive protective cover, permanent magnet sports protection kit with an interference fit. Another method of protection is to bind the permanent magnet with altar fiber.