Lorentz force type axial magnetic bearing

Abstract

The lorentz force type axial magnetic bearing comprises a stator and a rotor, the stator comprises two circular ring iron cores and a permanent magnet ring located in the middle, and the rotor comprises a rotor iron core, a rotating shaft, a collecting ring and a control winding. The rotor core is fixed on the rotating shaft, the two sides of the rotating shaft are connected with the two collecting rings through insulating materials, a working air gap exists between the rotor core and the stator, the control winding is wound on the surface of the rotor core, the left side and the right side of the control winding are opposite in winding direction, and the control winding is led out from the interior of the rotor core and connected to the collecting rings. The other side of the collector ring is connected to a bipolar switch power amplifier through a carbon brush, the bipolar switch power amplifier is controlled by a single-chip microcomputer, the magnitude and direction of current are adjusted according to axial displacement signals, and axial stable suspension of the rotor is achieved. The device is simple in structure, convenient to manufacture, free of axial unbalanced force, small in size, capable of saving materials and space, simple to control and good in dynamic and static performance, and the force / current relation is linear.

Description

Technical Field

[0001] The present invention relates to the technical field of motion control magnetic bearings, and particularly to a Lorentz force type axial magnetic bearing. Background Art

[0002] Hybrid magnetic bearings use permanent magnets to generate a bias magnetic field and suspension windings to generate a control magnetic field. The two synthesized air-gap magnetic fields are enhanced on one side and weakened on the other side, and a displacement closed-loop control system is established to generate a controllable suspension force in the direction opposite to the rotor eccentricity, realizing the stable suspension of the rotor. It has the advantages of large suspension force density and low power consumption. However, existing axial hybrid magnetic bearings all have axial unbalanced forces. And in the design, the bias magnetic field generated by the permanent magnet and the air-gap magnetic density generated by the suspension winding magnetic field can only be half of the air-gap saturation magnetic density. The suspension force mathematical model is not only related to the control current but also related to the rotor offset. The force / current relationship is non-linear. When designing the control system, approximate linearization is performed, which results in poor accuracy of the control system. In particular, the unbalanced force caused by eccentricity will deteriorate the dynamic and static performance of the magnetic bearing, increasing the control difficulty and complexity and affecting the stability and accuracy of the system. In some application scenarios with strict requirements for space and weight, such as implantable medical devices, micro air vehicles, etc., due to the excessive volume and weight of traditional hybrid axial magnetic bearings, they cannot meet the actual requirements. Summary of the Invention

[0003] Object of the Invention: Aiming at the technical problem of poor control performance of existing axial hybrid magnetic bearings caused by unbalanced forces and force / current non-linearity, the present invention proposes a Lorentz force type axial magnetic bearing, which has no axial unbalanced force, and the force / current relationship is a strict linear relationship, with good dynamic and static performance, small volume, and simple manufacturing and assembly.

[0004] Technical Solution: The present invention discloses a Lorentz force type axial magnetic bearing, which includes a rotor Ⅰ and a stator Ⅱ. The rotor Ⅰ passes through the stator Ⅱ. The rotor Ⅰ includes a rotating shaft, a rotor core, a left slip ring, a right slip ring, a left control winding, a right control winding, and a protective ring. The rotor core is sleeved on the rotating shaft, and a protective ring is provided circumferentially at the center of the rotor core. On the circumferential surface of the rotor core and on the left and right sides of the protective ring, a left control winding and a right control winding are wound. The two sides of the rotating shaft are connected to the left slip ring and the right slip ring through insulating materials. The stator Ⅱ includes a left circular ring core and a right circular ring core, and a permanent magnet ring is sandwiched between the left circular ring core and the right circular ring core. There is a working air gap between the rotor core and the left circular ring core and the right circular ring core.

[0005] Furthermore, the number of turns of the left control winding and the right control winding is equal and their winding directions are opposite, and they are connected in series with each other. At both ends of the rotor core, holes are opened in the radial position. After the left control winding and the right control winding respectively pass through the holes and come out from both sides of the rotor core, they are connected to the left slip ring and the right slip ring.

[0006] Further, the permanent magnet ring is magnetized along the axial direction.

[0007] Further, the left collector ring and the right collector ring are respectively connected to the output end of the bipolar switching power amplifier through the left carbon brush and the right carbon brush. The bipolar switching power amplifier is controlled by a single-chip microcomputer, and adjusts the magnitude and direction of the current according to the axial displacement signal to achieve the axial stable suspension of Rotor I.

[0008] Further, the wire diameters of the left control winding and the right control winding are d, with a value range of 0.5 mm to 1 mm. The width of the working air gap is mm, and the magnetic flux density of the air gap magnetic field generated by the permanent magnet ring is the saturation value, designed to be above 1.2 T.

[0009] Further, the parameter design process of the permanent magnet ring, the left control winding, and the right control winding is as follows:

[0010] Step 1: Determine the working air gap length l g and the saturation value B of the air gap magnetic flux density to obtain the permanent magnet magnetic flux Φ in the magnetic circuit as:

[0011] Φ = BA g

[0012]

[0013] where A g is half of the surface area of Rotor I, R is the rotor diameter, and l z is the axial length of the rotor;

[0014] Step 2: Determine the permanent magnet reluctance R pm and the air gap reluctance R g ;

[0015]

[0016]

[0017] where l pm is the thickness of the permanent magnet, A pm is the magnetization area of the permanent magnet, and μ g and μ pm are the magnetic permeabilities of air and the permanent magnet respectively;

[0018] Step 3: The total magnetomotive force F pm generated by the permanent magnet is:

[0019] F pm = l pm H c ;

[0020] where H c is the coercivity of the permanent magnet;

[0021] Step: Bring the magnetomotive force F in Step 3 pm and the permanent magnet magnetic flux Φ and the permanent magnet reluctance R obtained in Step 1 and Step 2 pm and the air-gap reluctance R g into the magnetic flux - magnetomotive force - reluctance balance equation: F pm = Φ(R pm + 2R g ), and we can get:

[0022]

[0023] Step 5: Calculate the thickness l of the permanent magnet pm :

[0024]

[0025] wherein, the air permeability μ g and the permanent magnet permeability μ pm are considered the same, and then further simplify the expression of the thickness l of the permanent magnet pm :

[0026]

[0027] Step: Select the wire diameter d and the maximum working current I of the left control winding and the right control winding according to the required Lorentz force magnitude:

[0028] lR = Fd / BIπ.

[0029] Furthermore, the rotor core, the right circular ring core, and the left circular ring core are made of magnetic conductive materials, and the permanent magnet ring is made of neodymium iron boron material; the left slip ring and the right slip ring are made of copper alloy.

[0030] Furthermore, the left carbon brush and the right carbon brush are made of graphite material.

[0031] Beneficial effects:

[0032] In the present invention, by winding the control winding on the surface of the rotor, and the generated force is the Lorentz force as the axial suspension force instead of the traditional Maxwell force. The suspension force is only related to the number of turns of the winding and the current, and the force / current relationship is linear. Moreover, the stator does not need to be slotted, which is simple and convenient to manufacture. Especially importantly, when the rotor axially deviates, the stator has no axial unbalanced suction force on the rotor, reducing the control difficulty and improving the dynamic and static performance of the axial magnetic bearing. Brief description of the drawings

[0033] Figure 1 It is a schematic structural diagram of the Lorentz force type axial magnetic bearing of the present invention. Specific implementation

[0034] The present invention will be further described below in conjunction with specific implementation steps. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0035] The present invention discloses a Lorentz force type axial magnetic bearing, which includes a rotor Ⅰ and a stator Ⅱ. The rotor Ⅰ includes: a rotating shaft 5, a rotor iron core, two slip rings and a control winding. The stator Ⅱ includes: a right circular ring iron core 2 and a left circular ring iron core 1. A permanent magnet ring 3 is sandwiched between the two circular ring iron cores, and the permanent magnet ring 3 is magnetized axially.

[0036] The rotor iron core is sleeved on the rotating shaft 5. A protective ring 13 is installed circumferentially at the center of the rotor iron core. On the surface of the rotor iron core, a left control winding 8 and a right control winding 9 are respectively wound on both sides of the protective ring 13. Both sides of the rotating shaft 5 are connected to the left slip ring and the right slip ring 7 through insulating materials. The left control winding 8 and the right control winding 9 have equal number of turns and opposite winding directions, and are connected in series with each other. At both ends of the rotor iron core, holes are opened in the radial position. After the left control winding 8 and the right control winding 9 pass through the holes and come out from both sides of the rotor iron core, they are connected to the left slip ring and the right slip ring 7. The left slip ring and the right slip ring 7 are respectively connected to the output end of the bipolar switch power amplifier through the left carbon brush 11 and the right carbon brush 12. The bipolar switch power amplifier is controlled by a single-chip microcomputer, and adjusts the magnitude and direction of the current according to the axial displacement signal to realize the axial stable suspension of the rotor Ⅰ.

[0037] The rotor Ⅰ penetrates through the stator Ⅱ and is arranged oppositely. There is a working air gap 10 between the rotor iron core and the left circular ring iron core 1 and the right circular ring iron core 2.

[0038] The rotor iron core, the right circular ring iron core 2, and the left circular ring iron core 1 are made of magnetic conductive materials. The permanent magnet ring 3 is made of neodymium iron boron material. The left carbon brush 11 and the right carbon brush 12 are made of graphite materials. The left slip ring and the right slip ring 7 are made of copper alloy.

[0039] The wire diameters of the left control winding 8 and the right control winding 9 are d, with a value range of 0.5 mm to 1 mm. The width of the working air gap (10) is (d + 0.5) mm. The magnetic density of the air gap magnetic field generated by the permanent magnet ring 3 is the saturation value, generally designed to be above 1.2 T.

[0040] The parameters of the permanent magnet 3 and the specific parameters of the left control winding 8 and the right control winding 9 are determined according to the saturation value B of the air gap magnetic density, the inner diameter R of the rotor, and the axial length l of the rotor z The permanent magnetic flux Φ generated by the permanent magnet in the magnetic circuit can be obtained as follows:

[0041]

[0042] where A g is half of the surface area of the rotor Ⅰ;

[0043] Then, according to the thickness l of the permanent magnet 3pm , working air gap 10 length l g , permanent magnet 3 magnetization area A pm , air magnetic permeability μ g and the magnetic permeability μ pm , define the permanent magnet reluctance and air gap reluctance The permanent magnet 3 generates a total magnetomotive force F pm = l pm H c , where H c is the coercive force of the permanent magnet.

[0044] Combined flux-magnetomotive force-reluctance balance equation F pm =Φ(R pm +2R g ) Combining the above parameter expression equation into the following formula, we can get Calculate the axial length l of the permanent magnet pm for:

[0045]

[0046] Among them, the air magnetic permeability μ g and the permanent magnet permeability μ pm It can be considered the same, and the axial length l of the permanent magnet can be simplified pm The expression is:

[0047]

[0048] After completing the parameter design of permanent magnet 3, the wire diameter d and the maximum operating current I are selected according to the target Lorentz force F requirement and lR=Fd / BIπ.

[0049] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include technical schemes composed of any combination of the above-mentioned technical features. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

Claims

1. A Lorentz force type axial magnetic bearing, comprising a rotor I and a stator II, wherein the rotor I penetrates the stator II, and is characterized in that: The rotor I comprises a rotating shaft (5), a rotor core (4), a left collector ring (), a right collector ring (7), a left control winding (8), a right control winding (9) and a protective ring (13); the rotor core (1) is sleeved on the rotating shaft (5), a protective ring (13) is provided at the center of the rotor core (4), a left control winding (8) and a right control winding (9) are wound on the circumferential surface of the rotor core (4) and on the left and right sides of the protective ring (13), and the left collector ring (6) and the right collector ring (7) are connected to the two sides of the rotating shaft (5) by insulating material; the stator II comprises: a left annular core (1) and a right annular core (2), a permanent magnet ring (3) is sandwiched between the left annular core (1) and the right annular core (2); and a working air gap (10) exists between the rotor core (4) and the left annular core (1) and the right annular core (2).

2. A Lorentz force type axial magnetic bearing according to claim 1, characterized in that: The left control winding (8) and the right control winding (9) have the same number of turns and are wound in opposite directions and are connected in series. At both ends of the rotor core (4), holes are opened along the radial position. The left control winding (8) and the right control winding (9) are connected to the left collector ring (6) and the right collector ring (7) after being led out from both sides of the rotor core (4) through the holes.

3. The Lorentz force type axial magnetic bearing according to claim 1, characterized in that: The permanent magnet ring (3) is magnetized along the axial direction.

4. A Lorentz force type axial magnetic bearing according to claim 1, characterized in that: The left collector ring (6) and the right collector ring (7) are connected to the output end of the bipolar switching power amplifier through the left carbon brush (11) and the right carbon brush (12) respectively. The bipolar switching power amplifier is controlled by a single chip microcomputer and adjusts the current magnitude and direction according to the axial displacement signal to achieve axial stable suspension of the rotor I.

5. A Lorentz force type axial magnetic bearing according to claim 1, characterized in that: The wire diameter of the left control winding (8) and the right control winding (9) is d, which is 0.5 mm to 1 mm. The width of the working air gap (10) is (d+0.5) mm. The magnetic flux density of the air gap magnetic field generated by the permanent magnet ring (3) is a saturation value, which is designed to be above 1.2 T.

6. The Lorentz force type axial magnetic bearing according to claim 5, characterized in that: The parameter design process of the permanent magnet ring (3) and the left control winding (8) and the right control winding (9) is as follows: Step 1: Determine the length l of the working air gap (10) g And the air gap magnetic flux saturation value B, the permanent magnetic flux Φ in the magnetic circuit is obtained as: Φ6 BA g Among them, A g is half of the surface area of ​​rotor I, R is the rotor diameter, l z is the axial length of the rotor; Step 2: Determine the reluctance R of the permanent magnet (3) pm and air gap reluctance R g ; Among them, l pm is the thickness of the permanent magnet (3), A pm is the magnetization area of ​​the permanent magnet (3), μ g and μ pm are the magnetic permeabilities of air and permanent magnet (3) respectively; Step 3: The permanent magnet (3) generates a total magnetomotive force F pm for: F pm =l pm H c ; Among them, H c is the coercive force of the permanent magnet; Step 1: Convert the magnetomotive force F obtained in step 3 pm And the permanent magnetic flux Φ and the magnetic resistance R of the permanent magnet (3) obtained in step 1 and step 2 pm and air gap reluctance R g Substitute into the flux-magnetomotive force-reluctance balance equation: F pm =Φ(R pm +2R g ), we can get: Step 5: Calculate the thickness l of the permanent magnet (3) pm : Among them, the air magnetic permeability μ g and the permanent magnet permeability μ pm Assuming that they are the same, we can further simplify the thickness of the permanent magnet (3) to pm expression: Steps: Select the wire diameter d and the maximum operating current I of the left control winding (8) and the right control winding (9) according to the required Lorentz force: lR=Fd / BIπ.

7. The Lorentz force type axial magnetic bearing according to any one of claims 1 to 4, characterized in that: The rotor core (4), the right annular core (1) and the left annular core (2) are made of magnetic conductive materials, and the permanent magnet ring (3) is made of neodymium iron boron material; the left collector ring (6) and the right collector ring (7) are made of copper alloy.

8. The Lorentz force type axial magnetic bearing according to claim 3, characterized in that: The left carbon brush (11) and the right carbon brush (12) are made of graphite material.

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