CN1301583C - Passive magnetic suspension brushless D.C. motor - Google Patents

Abstract

A passive magnetic levitation brushless DC motor, which consists of a housing, a stator, a rotor, a rotating shaft, and two passive magnetic bearings with symmetrical structures. The stator core of the motor is placed in the middle of the housing, and two sets of passive magnetic bearings are placed on the left and right. The permanent magnet outer ring, the motor rotor and the permanent magnet inner ring of two passive magnetic bearings are fixed on a rotating shaft made of non-magnetic material. The permanent magnet ring of the magnetic bearing adopts axial magnetization, and the permanent magnet of the motor rotor adopts radial magnetization , the invention realizes the motor magnetic levitation without control of the levitation force, saves the rotor displacement detection and levitation force control device, improves the operation reliability and system efficiency, and is especially suitable for the artificial heart rotary blood pump requiring small size and maintenance-free Application, the passive magnetic levitation structure proposed by the present invention is not only suitable for brushless DC motors, but also suitable for motors with other structural forms.

Description

Passive Magnetic Levitation Brushless DC Motor

technical field

The invention belongs to a motor, in particular to a passive magnetic levitation brushless DC motor.

Background technique

Due to the absence of mechanical wear and noise, non-contact magnetic bearings are widely used in high-speed motors and special applications requiring maintenance-free bearings such as artificial heart rotary blood pumps. There are many kinds of non-contact rotating motors, the most attractive of which is the bearingless motor structure, the rotational torque and levitation force of the rotor are generated by the stator and rotor of the motor itself, without any traditional or magnetic bearings, however The complexity of torque and magnetic levitation force decoupling control technology limits the practical application of bearingless motors. Although the motor with active magnetic bearing can realize the decoupling control of electromagnetic torque and levitation force, its control technology is relatively simpler than that of the bearingless motor, but it still needs dynamic detection of multiple degrees of freedom of the rotor position and real-time measurement of levitation force. Control, its control technology is still relatively complex. If magnetic levitation can be realized without complex control technology, it will have a significant role in promoting the practical application of magnetic levitation technology in motors.

Contents of the invention

Aiming at the problem that a bearingless motor and an active magnetic bearing motor need to perform dynamic detection of rotor positions with multiple degrees of freedom and real-time control of levitation force, the present invention provides a passive magnetic levitation brushless DC motor that does not require levitation force control.

The invention adopts a passive magnetic force bearing structure composed of permanent magnets, and realizes stable magnetic levitation of motor rotors without levitation force control through rational design. The passive magnetic levitation motor of the present invention is composed of a casing, a stator and a rotor of the motor, a rotating shaft and two passive magnetic force bearings with symmetrical structures. The passive magnetic bearing consists of two sets of permanent magnet inner rings and outer rings with the same geometric size and magnetic performance. The axial magnetization directions of each set of permanent magnet rings are the same, while the axial magnetization directions of the two sets of permanent magnet rings are opposite. The inner ring of each set of permanent magnet rings has an axial displacement to the left or right relative to the outer ring, and the axial displacements between the inner and outer rings of the two sets of permanent magnet rings are equal but opposite in direction. The air gap between the inner and outer rings of the magnetic bearing is much smaller than the air gap between the stator and rotor of the motor. The axial offset between the inner and outer rings of the magnetic bearing must be greater than a certain value, that is, it must be greater than the axial offset value corresponding to the maximum axial force. To ensure the stable radial suspension and axial stability of the motor rotor. The shell can be made of metal or non-metal material into a cylindrical shape. The stator core of the motor is placed in the middle of the casing, and the permanent magnet outer rings of two sets of passive magnetic bearings are respectively placed on the left and right sides. The motor rotor and the permanent magnet inner rings of the two passive magnetic bearings are fixed on a rotating shaft made of non-magnetic material. The stator core is made of laminated electrical steel sheets with a certain number of slots, and the stator winding is placed in the slots. The rotor of the brushless DC motor is fixed on the magnetically conductive or non-magnetically conductive rotor yoke by tile-shaped permanent magnets with a certain number of poles and magnetization directions, and then fixed on the rotating shaft. Both the permanent magnets of the magnetic bearing and the motor rotor are made of high-performance rare earth permanent magnet NdFeB material, the permanent magnet ring of the magnetic bearing is magnetized in the axial direction, and the permanent magnet of the rotor of the motor is magnetized in the radial direction.

The key technology of the invention is how to solve the stability problem of the passive magnetic force bearing. According to the classical magnetic bearing theory, a passive magnetic bearing composed of permanent magnets cannot obtain a stable balance, and at least one additional constraint needs to be imposed in the direction of one degree of freedom. The invention adopts two sets of permanent magnet rings with the same structural size and magnetic properties, and skillfully realizes the radial and axial stability of the passive magnetic force bearing by utilizing their symmetry. Theoretical analysis and prototype experiments prove that the axial force of the passive magnetic bearing is related to the axial displacement between the inner and outer permanent magnet rings, and there is a maximum value. When the axial displacement is less than a certain value, the axial force increases with the axial displacement. When the axial displacement is greater than a certain value, the axial force decreases with the increase of the axial displacement. The axial stability of the entire motor rotor system can be ensured by applying an axial offset displacement to avoid the unstable region and utilizing the axially symmetrical relationship of the two magnetic bearings. Through the reasonable matching of parameters such as the width and thickness of the permanent magnetic rings of the magnetic bearing, the air gap between them and the air gap between the stator and rotor of the motor, the stable magnetic levitation of the motor rotor in the radial direction can be realized.

The advantage of the present invention is that the levitation force does not need to be controlled in the motor magnetic levitation, and the complex rotor position dynamic detection and levitation force real-time control device of the magnetic levitation bearingless motor and the active magnetic bearing motor are omitted, which not only improves the operation reliability and the system Efficiency, and it has its special advantages for applications such as artificial heart rotary blood pumps that require small volume and maintenance-free to be placed in the human body. Since only the torque of the motor needs to be controlled, its control technology is relatively simple. For the brushless DC motor shown in the present invention, the frequency conversion speed regulation control method without position sensor is adopted. The passive magnetic levitation structure proposed by the present invention is not only suitable for brushless DC motors, but also suitable for motors with other structural forms, such as motors with induction, reluctance and permanent magnet rotors.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the magnetic bearing double inner ring offset to the stator of the motor according to the present invention.

Fig. 2 is a structural schematic diagram of the reverse offset of the double inner rings of the magnetic bearing to the stator of the motor according to the present invention.

In the figure: 1 shell, 2 stator core, 3 stator winding, 4 permanent magnet rotor, 5 rotor yoke, 6 permanent magnet outer ring of magnetic bearing, 7 permanent magnet inner ring of magnetic bearing, 8 non-magnetic rotating shaft, 9 fixed magnetic bearing The non-magnetic ring of the outer ring. The direction indicated by the arrow in the figure is the direction of magnetization.

Detailed ways

As shown in the accompanying drawings, the present invention is mainly composed of two parts, a motor and a passive magnetic bearing. The motor is composed of a stator core 2 fixed on a casing 1 , a stator winding 3 , and a permanent magnet rotor 4 fixed on a rotor yoke 5 and a non-magnetic rotating shaft 8 . The stator core is made of laminated electrical steel sheets, and has a certain number of slots for placing the stator windings, and the power wires of the windings are drawn out through the holes on the housing 1 . The permanent magnet rotor 4 consists of radially magnetized permanent magnets. The passive magnetic bearing consists of two sets of permanent magnet inner rings 7 and outer rings 6 with the same geometric size and magnetic performance. The axial magnetization direction of each set of permanent magnet rings is the same, while the axial magnetization direction of the two sets of permanent magnet rings on the contrary. The inner ring of each set of permanent magnet rings has an axial displacement to the left or right relative to the outer ring, which can constitute two types of passive magnetic bearing structures shown in the accompanying drawings. The displacements are equal in magnitude but opposite in direction. The outer ring 6 of the passive magnetic bearing is fixed on the housing 1 through the non-magnetic sleeve 9 , while the inner ring 7 is directly fixed on the non-magnetic rotating shaft 8 .

In this embodiment, the inner and outer rings of the magnetic bearing are made of axially magnetized NdFeB permanent magnet material, the thickness and length of the inner and outer rings are 5 and 10 mm respectively, the diameter of the outer ring is 26 mm, and the air gap between the inner and outer rings is 0.4 mm , the axial offset between the inner and outer rings is about 1.5mm. The stator core of the brushless DC motor is made of laminated electrical steel sheets of 0.35mm, and has 12 slots for placing symmetrical three-phase windings. The inner and outer diameters of the stator core are 18mm and 36mm respectively, and the axial length is 10mm. The rotor is bonded on the rotor yoke by radially magnetizing four NdFeB permanent magnet tiles with a length of 10mm and a thickness of 2mm. The air gap between the stator and rotor of the motor is 2mm.

Claims (3)

1. passive electromagnetic levitation type brshless DC motor, include housing, stator, rotor and rotating shaft, it is characterized in that this direct current machine also is provided with two passive magnetic bearings with symmetrical structure, the stator core of laying motor in the middle of in the housing, about respectively place the permanent magnetism outer shroud of one group of passive magnetic bearing, ring is fixed in the rotating shaft of a non-magnet material making in the permanent magnetism of rotor and two passive magnetic bearings, ring and outer shroud adopt axial charging in the permanent magnetism of magnetic bearing, the rotor permanent magnet adopts radial magnetizing, its described passive magnetic bearing is made up of ring and outer shroud in two groups of permanent magnetism with identical physical dimension and magnetic property, ring and outer shroud in every group of permanent-magnetic clamp comprises, its axial charging direction is identical, and the axial charging direction of two groups of permanent-magnetic clamps is opposite, the interior ring of every group of permanent-magnetic clamp has an axial displacement to the left or to the right with respect to outer shroud, axial displacement between two groups of permanent-magnetic clamp inner and outer rings equates and direction is opposite, air gap in the permanent magnetism of its described passive magnetic bearing between ring and the outer shroud is less than the air gap between the electric machine rotor, and the axial dipole field of ring and outer interannular must be greater than the axial dipole field value of maximum axial force correspondence in the magnetic bearing permanent magnetism.

2. passive electromagnetic levitation type brshless DC motor according to claim 1 is characterized in that described stator core is to be overrided to form by the electrical sheet that has some grooves, places stator winding in the groove.

3. passive electromagnetic levitation type brshless DC motor according to claim 1 is characterized in that described rotor is fixed on the rotor yoke of magnetic conduction or non-magnetic conduction by the tile permanent magnet with certain number of poles and direction of magnetization, is fixed in the rotating shaft then.

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