What is a hollow cup brushless motor?
The electromagnetic design of high-speed hollow cup stator brushless DC motor. The air gap magnetic flux density of the conventional magnet structure hollow cup stator high-speed permanent magnet brushless DC motor is relatively low. The use of the new HALBACH magnet structure can significantly improve the air gap magnetic flux density. The magnet structure has the characteristics of magnetic shielding and sinusoidal air gap magnetic flux density distribution, which is particularly suitable for hollow cup-shaped stator high-speed permanent magnet brushless DC motors. Figures 17 and 2 show the conventional magnet structure and HALBACH magnet structure.
When designing high-speed and efficient permanent magnet
brushless DC motors, their electromagnetic design can follow the following principles:
1) Compared with the conventional magnet structure motor with parallel magnetization, the conventional magnet structure motor with radial magnetization has a small air gap flux and a large rotor yoke flux. Therefore, for conventional magnet structure motors with 6 or more poles, parallel magnetization should be used.
2) The sinusoidal distribution of air gap magnetic flux density in HALBACH magnet structure motors is much better than that in conventional magnet structure motors. The more magnet blocks per pole, the better the sinusoidal distribution of air gap magnetic flux density.
3) The magnetic flux density of the rotor yoke of the HALBACH magnet structure motor is very low, much lower than that of conventional magnet structure motors. Therefore, the HALBACH magnet structure motor can eliminate the need for magnetic rotor cores; However, for conventional magnet structure motors, if the rotor yoke is non-magnetic, the air gap magnetic flux density of the motor will be significantly reduced. Therefore, if the rotor does not have a magnetic core, the motor should adopt a HALBACH magnet structure to ensure the air gap magnetic flux density of the motor, thereby ensuring the power density and torque density of the motor.
4) For statorless magnetic core motors, whether using HALBACH magnet structure or conventional magnet structure, the permanent magnetic field of the motor has a certain radiation range. Therefore, to prevent electromagnetic interference, it is necessary to ensure that the total effective air gap of the motor is greater than 6 times the thickness of the permanent magnet. The magnetic flux density outside this range will be very small and will not cause electromagnetic interference or iron loss.
5) When the thickness of the permanent magnet is small, the air gap magnetic flux density provided by the HALBACH magnet structure is lower than that of the conventional magnet structure; When the thickness of the permanent magnet increases to a certain value, the air gap magnetic flux density provided by the HALBACH magnet structure is higher than that of the conventional magnet structure motor. Therefore, for statorless iron core motors, the HALBACH magnet structure should be adopted, and the magnet thickness should be increased as much as possible to improve the air gap magnetic flux density, thereby ensuring that the motor has a considerable power density and torque density.
