Hybrid excitation radial two-degree-of-freedom DC magnetic bearing

Abstract

The application discloses a hybrid excitation radial two-degree-of-freedom DC magnetic bearing, which comprises a stator, a rotor and a rotating shaft. The stator comprises a stator core, four excitation poles and four suspension poles which are arranged on the inner side of the stator core and are spaced apart, a suspension winding is wound on the suspension poles, and a permanent magnet and an excitation winding are arranged on the excitation poles; the suspension windings on the two suspension poles in the X direction and the Y direction are respectively connected in series in the same direction to form X and Y direction suspension windings, two pairs of excitation windings which are oppositely arranged on the excitation poles are reversely connected in series and then are connected in series or parallel to form an excitation winding, the rotor is sleeved on the rotating shaft, and a radial air gap is arranged between the rotor and the stator. Compared with the prior art, the application provides basic bias magnetic flux by the permanent magnet, provides additional bias magnetic flux by the excitation winding, realizes stable suspension of the rotor, has the advantages of less use of permanent magnet material, low cost, low power consumption and convenience in assembly.

Description

Technical Field

[0001] This invention relates to the field of magnetic levitation bearing technology, and specifically to a hybrid excitation radial two-degree-of-freedom DC magnetic bearing. Background Technology

[0002] Hybrid magnetic bearings utilize permanent magnets to generate a static bias flux. Only when the rotor deviates from its equilibrium position is the levitation winding energized to generate a control flux to adjust the air gap flux, pulling the rotor back to its equilibrium position and achieving stable levitation operation. Compared to electromagnetic bearings, hybrid magnetic bearings offer lower power consumption, require less copper, and have significant technological advantages. Based on the placement of the permanent magnets and the direction of the bias flux, hybrid magnetic bearings mainly include two types: same-pole and opposite-pole. Same-pole hybrid magnetic bearings typically use a ring-shaped permanent magnet to provide the bias flux, and the permanent magnet is axially magnetized. Opposite-pole bearings use radial magnetization, with the permanent magnet and winding placed on the same plane. The determination methods for the main parameters of all hybrid magnetic bearing structures are basically the same: based on the given maximum levitation force technical requirements, the material and air gap saturation magnetic flux density are determined. Then, assuming that the air gap bias flux density generated by the permanent magnets and the air gap flux density generated when the levitation winding carries the maximum current are both half of the saturation flux density, the permanent magnet parameters and levitation winding parameters are finally calculated.

[0003] This type of hybrid magnetic bearing presents several technical challenges in industrial applications: 1. Since the bias flux is generated only by the permanent magnet, the permanent magnet is thick, requiring a large quantity and resulting in high cost; 2. Once the hybrid magnetic bearing is designed and manufactured, the air gap magnetic flux density generated by the bias flux must reach half of the saturation magnetic flux density, resulting in a huge magnetic attraction between the stator and rotor. This places extremely high demands on the precision of prototype manufacturing and assembly, and the huge magnetic attraction makes debugging and buoyancy difficult.

[0004] Therefore, in order to solve the above-mentioned technical problems of hybrid magnetic bearings, this invention proposes a hybrid excitation radial two-degree-of-freedom DC magnetic bearing, in which part of the bias magnetic flux is generated by the permanent magnet and the rest can be generated by the excitation winding. In addition, during assembly and floating, the excitation winding can generate an excitation magnetic flux in the opposite direction to the magnetic flux of the permanent magnet, so that the bias magnetic flux is 0, making assembly simple and convenient. Summary of the Invention

[0005] Purpose of the invention: This invention aims to solve the problems of existing DC hybrid magnetic bearings, such as the large amount of permanent magnets required, the difficulty in manufacturing, assembly, and debugging due to the magnetic attraction force generated by the bias magnetic field, and the high precision requirements. It proposes a hybrid excitation radial two-degree-of-freedom DC magnetic bearing that uses permanent magnets and excitation windings together to generate bias magnetic flux. Whether the excitation winding needs to be energized to generate bias magnetic flux is determined by the control system, which is flexible and controllable. The levitation winding provides the control magnetic flux, and the levitation winding flux is decoupled from the permanent magnet magnetic field. It also features a small amount of permanent magnets, low cost, and simple manufacturing and assembly.

[0006] Technical Solution: This invention discloses a hybrid excitation radial two-degree-of-freedom DC magnetic bearing, comprising a stator, a rotor, and a shaft. The stator includes a stator core, with four suspension poles and four excitation poles evenly arranged around the inner circumference of the stator core, and the suspension poles and excitation poles are arranged alternately along the circumference. Each excitation pole has a permanent magnet embedded in it and an excitation winding wound around it, and each suspension pole has a suspension winding wound around it. Two suspension poles arranged opposite each other in the horizontal direction form an X-direction suspension pole pair; two suspension poles arranged opposite each other in the vertical direction form a Y-direction suspension pole pair. The rotor is sleeved on the shaft, and a radial air gap is provided between the rotor and the stator. The control magnetic flux generated when the suspension winding is energized, and the bias magnetic flux generated by the permanent magnet and the excitation winding, respectively realize the dynamic adjustment and static suspension of the rotor.

[0007] Furthermore, the suspension windings on the X-direction suspension pole pair are connected in series in the same direction to form the X-direction suspension winding; the suspension coils on the Y-direction suspension pole pair are connected in series in the same direction to form the Y-direction suspension winding.

[0008] Furthermore, a pair of oppositely arranged excitation windings are connected in reverse series, and another oppositely arranged excitation winding is also connected in reverse series, and then connected in series or in parallel in the same direction to form an excitation winding, with the outer polarity of the permanent magnets being the same.

[0009] Furthermore, when the X-direction suspension winding is energized, it generates an X-direction control magnetic flux; when the Y-direction suspension winding is energized, it generates a Y-direction control magnetic flux; both the X-direction and Y-direction control magnetic circuits consist of a closed-loop path formed by the stator core, its own suspension pole, the radial air gap, and the rotor. The X-direction control magnetic flux and the Y-direction control magnetic flux interact with the bias magnetic flux to generate suspension forces in the X and Y directions, respectively, thereby controlling the rotor to levitate in the X and Y directions.

[0010] Furthermore, the excitation winding is supplied with DC current to generate excitation flux, and the permanent magnet generates permanent magnet flux. The excitation flux and the permanent magnet flux pass through the same magnetic path, respectively passing through adjacent suspension poles, radial air gaps, rotor and stator core yoke to form a closed path. The bias flux is provided by the permanent magnet flux or by the superposition of the excitation flux and the permanent magnet flux.

[0011] Furthermore, the hybrid-excitation radial two-degree-of-freedom DC magnetic bearing is controlled by an excitation control system and a suspension control system respectively. The excitation control system includes an excitation power amplifier; the suspension control system includes two suspension power amplifiers, corresponding to the X and Y directions respectively. Displacement sensors detect the real-time displacement signals of the rotor in the X and Y directions. After processing by the controller, the corresponding suspension currents are independently controlled by the suspension power amplifiers to output to the X-direction suspension winding and the Y-direction suspension winding respectively. The controller adjusts the output current of the excitation power amplifier to the excitation winding according to the following preset control strategy based on the magnitude of the suspension current:

[0012] The permanent magnet is equivalent to a magnet with an ampere-turn number of N. s I ps For the winding, establish the intervention criterion for the excitation current: let the equivalent current I be applied. ps The generated air gap magnetic flux density and the air gap magnetic flux density B provided by the permanent magnet p Equal to each other, we obtain the equivalent current. , This is the rated current of the levitation winding. This represents the number of turns of the wire in the levitation coil.

[0013] Will I ps and When comparing, At that time, only the permanent magnet generates the bias magnetic flux, in which and These represent the currents in the floating windings in the X and Y directions, respectively.

[0014] when At that time, an excitation current is applied, the magnitude of which is h m The thickness in the magnetizing direction of the permanent magnet. μ is the radial air gap length. r N is the relative permeability of the permanent magnet. l The number of turns of the excitation winding conductor is given by the superposition of the excitation flux and the permanent magnet flux.

[0015] Furthermore, under normal operating conditions, a forward current is applied to the excitation winding, and the resulting excitation flux is in the same direction as the permanent magnet flux generated by the permanent magnet. The two fluxes are superimposed to form a bias flux. Under installation and commissioning conditions, to eliminate the unilateral attraction of the permanent magnet on the rotor, a reverse current is applied to the excitation winding to generate an excitation flux that cancels out the permanent magnet flux, thus equivaling the permanent magnet to an equivalent number of N ampere-turns. l I pl The winding of the excitation winding, wherein the magnitude of the reverse current flowing through the excitation winding is: .

[0016] Furthermore, the bias air gap magnetic flux density B generated by the permanent magnet p Acting on the radial air gap, the value is taken as air gap saturation magnetic flux density B. s One-quarter; the excitation magnetic flux density B generated by the excitation winding under rated maximum current. w Acting on the radial air gap, the saturation magnetic flux density B of the air gap is... s One-quarter; the magnetic flux density B generated by the levitation winding under rated maximum current. m The radial air gap acting under the levitation pole is the air gap saturation magnetic flux density B. s One-half of.

[0017] Furthermore, the levitation pole and excitation pole, stator core and rotor are all made of silicon steel sheets stacked together, with a thickness of 0.1~0.3mm and a stacking coefficient ≥0.95; the permanent magnet is made of rare earth permanent magnet material and is radially magnetized.

[0018] Furthermore, the parameter design method for the hybrid-excitation radial two-degree-of-freedom DC magnetic bearing includes the following steps:

[0019] Step 1: Determine the core material and radial air gap length of the stator and rotor. Select air gap saturation magnetic flux density B s According to the maximum levitation force index F max Determine the area S of the levitation pole, and make the area of ​​the excitation pole equal to the area of ​​the levitation pole, and establish a levitation force model;

[0020] Step 2: Based on the magnetic flux density B generated by the permanent magnet p air gap saturation magnetic flux density B s One-quarter of the thickness of the permanent magnet in the magnetization direction. H c For the coercivity of a permanent magnet, μ r denoted as the relative permeability of the permanent magnet, and μ0 as the permeability of free space.

[0021] Step 3: Based on the excitation magnetic flux density B w Calculate the ampere-turns of the excitation winding. , where N l I is the number of turns of the excitation winding conductor. l This is the rated current of the excitation winding;

[0022] Step 4: Based on the levitation magnetic flux density B m Calculate the ampere-turns of the levitation winding ,in, The number of turns of the levitation winding conductor. This is the rated current of the suspension winding.

[0023] Compared with the prior art, the present invention has the following obvious advantages:

[0024] 1. This invention configures the excitation winding and levitation winding independently. The bias magnetic flux density generated by the excitation winding is adaptively adjusted according to the magnitude of the levitation current. When the levitation current is small, the excitation winding does not work, and only the permanent magnet provides the bias magnetic field, with the system operating in a low-power state. When the levitation current increases to exceed a preset threshold, the excitation current intervenes, dynamically enhancing the bias magnetic field and enabling the system to provide a larger controllable levitation force. Compared to traditional fixed-bias hybrid magnetic bearings, the controllable levitation force of this invention can be dynamically matched according to load requirements, resulting in lower power consumption under light loads and stronger load-bearing capacity under heavy loads. While ensuring a linear force-current relationship, it achieves a balance between low power consumption and high load-bearing capacity. The control strategy of this invention is simple; the timing and magnitude of the excitation current intervention can be determined by comparing the detected value of the levitation current with a preset threshold, making it easy to implement on the controller.

[0025] 2. This invention only requires the permanent magnet to provide a low bias air gap magnetic flux density, which reduces the cost of permanent magnet materials and the dependence on heavy rare earth elements while meeting performance requirements. Attached Figure Description

[0026] Figure 1 This is a schematic diagram showing the specific parameters of the hybrid excitation radial DC hybrid magnetic bearing of the present invention.

[0027] Figure 2 This is a schematic diagram of the excitation flux of the hybrid excitation radial DC hybrid magnetic bearing of the present invention;

[0028] Figure 3 This is a schematic diagram of the X-direction control flux of the hybrid excitation radial DC hybrid magnetic bearing of the present invention.

[0029] Figure 4 This is a schematic diagram of the Y-direction control flux of the hybrid excitation radial DC hybrid magnetic bearing of the present invention;

[0030] Figure 5 This is a schematic diagram of the magnetic flux in the assembled state of the hybrid excitation radial DC hybrid magnetic bearing of the present invention;

[0031] Figure 6 This is a control principle diagram of the hybrid excitation radial DC hybrid magnetic bearing of the present invention;

[0032] Figure 7 This invention relates to the permanent magnet air gap magnetic flux density distribution of the hybrid excitation radial DC hybrid magnetic bearing.

[0033] Figure 8 This is the air gap magnetic flux density distribution of the hybrid excitation radial DC hybrid magnetic bearing of the present invention when the maximum excitation current acts independently;

[0034] Figure 9 This is the combined air gap magnetic flux density distribution of the permanent magnet of the hybrid excitation radial DC hybrid magnetic bearing of the present invention when superimposed with the maximum excitation current;

[0035] Figure 10 This invention relates to the air gap magnetic flux density distribution when the excitation current of the hybrid excitation radial DC hybrid magnetic bearing cancels the magnetic field of the permanent magnet.

[0036] Figure 11 This invention relates to the radial magnetic flux density distribution of the hybrid excitation radial DC hybrid magnetic bearing under light load conditions in the X direction.

[0037] Figure 12 This is the radial magnetic flux density distribution of the hybrid excitation radial DC hybrid magnetic bearing of the present invention under the condition of maximum levitation force in the X direction;

[0038] Figure 13 This is a force-suspending current relationship diagram for the hybrid excitation radial DC hybrid magnetic bearing of the present invention under light load in the X direction;

[0039] Figure 14 This is a force-suspending current relationship diagram for the hybrid excitation radial DC hybrid magnetic bearing of the present invention under heavy load in the X direction. Detailed Implementation

[0040] The following is in conjunction with the appendix Figures 1-13 The present invention will be further described below. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be used to limit the scope of protection of the present invention.

[0041] This invention discloses a hybrid excitation radial two-degree-of-freedom DC magnetic bearing, see [link to relevant documentation]. Figures 1-6 The specific structure is as follows:

[0042] The hybrid-excitation radial two-degree-of-freedom DC magnetic bearing body includes a stator 1, a rotor 2 (rotor core), and a shaft 3. The shaft 3 runs through the interior of the rotor 2. The stator 1 includes a stator core, and a radial air gap 9 exists between the stator core 1 and the rotor 2. Eight magnetic poles are evenly distributed around the inner circumference of the stator core: four excitation poles 8 and four suspension poles 7. The excitation poles 8 and suspension poles 7 are alternately arranged along the circumference, with the same arc length. The suspension poles 7, excitation poles 8, stator core, and rotor 2 are all made of laminated silicon steel sheets with a thickness of 0.1~0.3mm and a lamination factor ≥0.95. The permanent magnet 6 is made of rare-earth permanent magnet material and is radially magnetized.

[0043] Each suspension pole 7 is wound with a suspension winding 4. The four suspension windings have the same number of turns, and the four excitation windings have the same number of turns. Among them, the suspension windings on two opposite suspension poles 7 in the horizontal direction (X-axis direction) are connected in series in the same direction to form the X-direction suspension winding, which generates the X-direction control magnetic flux 13 when energized. The suspension windings on two opposite suspension poles 7 in the vertical direction (Y-axis direction) are connected in series in the same direction to form the Y-direction suspension winding, which generates the Y-direction control magnetic flux 14 when energized. The X-direction and Y-direction control magnetic circuits are both closed paths formed by passing through adjacent suspension poles 7, radial air gap 9, rotor 2, and stator core yoke, respectively. The X-direction control magnetic flux 13 and the Y-direction control magnetic flux 14 interact with the bias magnetic flux 10 to generate suspension forces in the X and Y directions, respectively controlling the rotor 2 to levitate in the X and Y directions.

[0044] Each excitation pole 8 has a permanent magnet 6 radially embedded in its body. The permanent magnet 6 is radially magnetized, with the magnetization direction pointing towards the center of the rotating shaft 3. Excitation windings are wound on the excitation pole 8. A pair of oppositely arranged excitation windings are connected in series in opposite directions. Another oppositely arranged excitation winding is also connected in series in opposite directions, and then connected in series or in parallel in the same direction to form an excitation winding 5.

[0045] The magnetic circuit system of a magnetic bearing includes a bias magnetic circuit and a control magnetic circuit.

[0046] After the magnetic flux generated by the excitation winding 5 and the magnetic flux generated by the permanent magnet 6 are combined at the excitation pole 8, according to Kirchhoff's law for magnetic circuits, the bias magnetic flux Φ generated by the permanent magnet 6... p Starting from excitation pole 8, the path passes through radial air gap 9, rotor 2, radial air gap 9, adjacent floating pole 7 on one side, and stator core yoke, returning to excitation pole 8 to form a closed path. The bias magnetic flux Φ generated when excitation winding 5 is energized... w With Φ p Sharing the same closed path, the two superimpose at the excitation pole, and the total bias flux is .

[0047] The control magnetic path is generated by energizing the suspension winding 4, and forms a closed path through the stator core, its own suspension pole 7, the radial air gap 9, and the rotor 2.

[0048] The control magnetic circuit and the bias magnetic circuit are independent of each other, realizing the dynamic adjustment and static levitation of the rotor respectively. The air gap magnetic flux density B generated by the permanent magnet 6... p Acting on the radial air gap 9, the saturated air gap magnetic flux density B s One-quarter of the air gap magnetic flux density B generated by excitation winding 5 under rated maximum current. w The maximum value is the saturated air gap magnetic flux density B s One-quarter of the air gap magnetic flux density B generated by the levitation winding 4 under rated maximum current. m The maximum value is the saturated air gap magnetic flux density B sOne-half of.

[0049] The peripheral hardware system of the aforementioned magnetic bearing includes an excitation control system and a suspension control system. The excitation control system contains one excitation power amplifier; the suspension control system contains two suspension power amplifiers, corresponding to the X and Y directions respectively. Displacement sensors detect the real-time displacement signals of the rotor in the X and Y directions. After processing by the controller, the corresponding suspension currents are independently controlled by the suspension power amplifiers to output to the X-direction and Y-direction suspension windings. Based on the magnitude of the suspension current, the controller adjusts the output current of the excitation power amplifier to the excitation winding 5 according to a preset control strategy to dynamically adjust the bias magnetic field, achieving stable suspension of the rotor in two radial degrees of freedom and effectively reducing system power consumption. Specifically:

[0050] The permanent magnet is equivalent to a magnet with an ampere-turn number of N. s I ps The winding is such that an equivalent current I is passed through it. ps The generated air gap magnetic flux density and the air gap magnetic flux density B provided by the permanent magnet p They are equal, thus the equivalent current can be obtained. .

[0051] Will I ps and For comparison, the currents of the levitation windings in the X and Y directions are I. X I Y ,when When the rotor disturbance is small, the system generates a bias magnetic field only by the permanent magnet 6; when At that time, an excitation current is applied, the magnitude of which is h m The thickness of permanent magnet 6 in the magnetization direction. The radial air gap length is 9, μ r N is the relative permeability of the permanent magnet. l The number of turns of the excitation winding conductor is given by the bias flux 10, which is provided by the superposition of the excitation flux 11 and the permanent magnet flux 12.

[0052] like Figure 7 In operation, the excitation power amplifier supplies a positive current to the excitation winding 5, generating an excitation flux 11 that is in the same direction as the permanent magnet flux 12 generated by the permanent magnet. These two fluxes superimpose to form a bias flux 10. During installation and commissioning, the excitation power amplifier supplies a current to the excitation winding 5 that is in the same direction as the excitation current I. l When currents of the same magnitude but opposite direction are applied, the permanent magnet 6 can be equivalent to a current with an ampere-turn number of N. l I pl The magnitude of the reverse current flowing through the excitation winding 5 is: The generated excitation flux 11 is opposite in direction to the permanent magnet flux 12, and the two cancel each other out to eliminate the unilateral attraction of the permanent magnet on the rotor.

[0053] The levitation control system includes two levitation power amplifiers, which drive the levitation windings in the X and Y directions, respectively. When the rotor 2 eccentricates in any direction, the radial air gap 9 decreases in the eccentric direction, and the excitation flux 11 increases; conversely, the radial air gap 9 increases in the opposite direction, and the excitation flux 11 decreases. The currents in the levitation windings 5 ​​are superimposed, generating levitation flux. This upward control flux cancels out the lower bias flux 10 and superimposes with the upper excitation flux 11, making the upper flux greater than the lower flux. The resultant force on the rotor is upward, causing the rotor to move upward and gradually return to the equilibrium position.

[0054] The design steps for the aforementioned magnetic bearing are as follows:

[0055] Step 1: Perform magnetic circuit analysis and construct a magnetic circuit model. Select the materials for the stator core, rotor core, and permanent magnet (6), and the length of the radial air gap (9). The axial length l of the stator core and rotor core z Based on the maximum levitation force requirement F max Determine the magnetic pole area B s Let μ0 be the air gap saturation magnetic flux density and μ0 be the free permeability; further, the arc length l between the excitation pole 8 and the levitation pole 7 can be obtained. c : .

[0056] The bias magnetic flux Φ generated when the excitation winding 5 is energized w The bias magnetic flux Φ generated by the permanent magnet 6 p When using closed paths with the same direction in the working state, the two superimposed at the excitation poles result in a total bias flux Φ. l The sum of the two:

[0057]

[0058] Among them, H c For the coercivity of permanent magnet 6, μ r The relative permeability of permanent magnet 6. The thickness of permanent magnet 6 in the magnetization direction. This refers to the number of turns in excitation winding 5. This is the current in excitation winding 5.

[0059] Furthermore, the control magnetic flux at the air gap below the levitation pole 7 is: N s I x With N s I y The ampere-turns of the floating winding 4 in the X and Y directions.

[0060] Furthermore, a levitation force model is established: Where x and y are displacements in the corresponding directions.

[0061] Taking the X direction as an example, for F x Performing a Taylor expansion near the equilibrium point yields:

[0062]

[0063]

[0064] Obtain its current stiffness for Displacement stiffness for The levitation force F in the Y direction y Similarly.

[0065] Step 2: Based on the equivalent magnetic circuit model, and according to Kirchhoff's laws for magnetic circuits, the thickness h of the permanent magnet 6 in the magnetization direction... m Determined by the following formula The permanent magnet 6 can be made of a low coercivity material to maintain the conventional thickness, or a high coercivity material can be selected to reduce the thickness while maintaining the same performance.

[0066] Specifically: A magnetic circuit model of the bias flux 10 generated by any permanent magnet 6 is selected, and the relevant parameters of the permanent magnet 6 are calculated according to Kirchhoff's laws. The magnetomotive force of the permanent magnet 6 is then... H c For the coercivity of permanent magnet materials, h m The thickness is in the direction of magnetization of the permanent magnet. The magnetic reluctance of the permanent magnet 6 within this closed path. Working air gap magnetoresistance Furthermore, the bias magnetic flux generated by the permanent magnet Setting the bias air gap magnetic flux density of the permanent magnet Solving the above equations simultaneously, we can find the thickness of the permanent magnet. S p S is the cross-sectional area of ​​the permanent magnet. g The air gap cross-sectional area is equal in size to the magnetic pole area; μ p is the absolute permeability of the permanent magnet.

[0067] Step 3: Excitation winding 5 ampere-turns N l I l Determined by the following formula: Among them, the magnetic flux density B of the excitation winding w The set air gap saturation magnetic flux density B s One-quarter of the size.

[0068] Specifically, a magnetic circuit model of the excitation flux generated by any excitation winding 5 is selected, and the ampere-turns of excitation winding 5 are calculated according to Kirchhoff's laws. The magnetomotive force generated by the excitation winding is... N l I is the number of turns of the excitation winding conductor. l This is the rated current of the excitation winding. When the permanent magnet 6 is included in the magnetic circuit and the stator and rotor core materials are the same... Expanding the reluctance and neglecting higher-order terms, The bias air gap magnetic flux density of the excitation winding is set to .

[0069] Step 4: Determine the number of 4 ampere-turns for the levitation winding .

[0070] According to the present invention, a hybrid excitation radial DC hybrid magnetic bearing is designed to meet the maximum load capacity of 420N.

[0071] Table 1 Specific parameters of magnetic levitation bearings

[0072] Rotor inner diameter 18mm Rotor outer diameter 38.4mm Stator inner diameter 39mm Stator outer diameter 75mm Number of turns of excitation winding 150 turns Number of turns of the floating winding 150 turns Air gap saturation magnetic flux density 1.2T Magnetic pole area <![CDATA[720mm 2 ]]> Maximum excitation current 5.2A Maximum floating current 2.1A

[0073] Based on the above parameters, a model was established in Maxwell2D finite element analysis software. By setting different current excitations, the magnetic field distribution and force characteristics of the present invention under different working conditions can be simulated. Table 2 shows the excitation conditions and verification objectives corresponding to each figure.

[0074] Table 2. Excitation conditions and verification objectives for each attached figure.

[0075] Figure 7 <![CDATA[I X =I Y =0A]]> <![CDATA[I l =0A]]> Examine the distribution of the bias magnetic flux density generated by the permanent magnet alone. Figure 8 <![CDATA[I X =I Y =0A]]> <![CDATA[I l =5.2A]]> Examine the magnetic flux density distribution under the sole action of the maximum excitation current. Figure 9 <![CDATA[I X =I Y =0A]]> <![CDATA[I l =5.2A]]> Verification of the combined bias magnetic flux density distribution generated by the permanent magnet and the excitation current Figure 10 <![CDATA[I X =I Y 0A]]> <![CDATA[I l =-5.2A]]> During installation and commissioning, it was verified that the magnetic field of the permanent magnet could be largely canceled out. Figure 11 <![CDATA[I X =0.5A,I Y =0A]]> <![CDATA[I l =0A]]> Examine the radial magnetic flux density distribution under light load conditions in the X direction. Figure 12 <![CDATA[I X =2.1A,I Y =0A]]> <![CDATA[I l =5.2A]]> Verification of radial magnetic flux density distribution under maximum levitation force in the X direction Figure 13 <![CDATA[I Y =0A]]> <![CDATA[I l =0A]]> View the force-suspending current relationship diagram under light load conditions in the X direction. Figure 14 <![CDATA[I Y =0A]]> <![CDATA[I l =5.2A]]> View the force-suspending current relationship diagram under heavy load conditions in the X direction.

[0076] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

Claims

1. A hybrid excitation radial two-degree-of-freedom DC magnetic bearing, comprising a stator (1), a rotor (2), and a shaft (3), characterized in that: The stator (1) includes a stator core, and four suspension poles (7) and four excitation poles (8) are evenly arranged on the inner circumference of the stator core. The suspension poles (7) and excitation poles (8) are arranged alternately along the circumference. Each excitation pole (8) is embedded with a permanent magnet (6) and wound with an excitation winding (5). Each suspension pole (7) is wound with a suspension winding (4). Two suspension poles arranged opposite each other in the horizontal direction form a suspension pole pair in the X direction. Two suspension poles arranged opposite each other in the vertical direction form a suspension pole pair in the Y direction. The rotor (2) is sleeved on the rotating shaft (3). A radial air gap (9) is provided between the rotor (2) and the stator (1). The control magnetic flux generated when the suspension winding (4) is energized, and the bias magnetic flux (10) generated by the permanent magnet (6) and the excitation winding (5) respectively realize the dynamic adjustment and static suspension of the rotor.

2. The hybrid excitation radial two-degree-of-freedom DC magnetic bearing according to claim 1, characterized in that: The suspension windings on the X-direction suspension pole pair are connected in series in the same direction to form the X-direction suspension winding; the suspension coils on the Y-direction suspension pole pair are connected in series in the same direction to form the Y-direction suspension winding.

3. The hybrid excitation radial two-degree-of-freedom DC magnetic bearing according to claim 1, characterized in that: A pair of oppositely arranged excitation windings are connected in reverse series, and another oppositely arranged excitation winding is also connected in reverse series, and then connected in series or in parallel in the same direction to form an excitation winding (5). The permanent magnets (6) have the same polarity on the outside.

4. A hybrid-excitation radial two-degree-of-freedom DC magnetic bearing according to claim 2, characterized in that: When the X-direction suspension winding is energized, it generates X-direction control flux (13); when the Y-direction suspension winding is energized, it generates Y-direction control flux (14); the X-direction and Y-direction control magnetic circuits are both composed of a stator core, its own suspension pole (7), radial air gap (9), and rotor (2) forming a closed loop path. The X-direction control flux (13) and Y-direction control flux (14) interact with the bias flux (10) to generate suspension forces in the X and Y directions, respectively, which control the rotor (2) to levitate in the X and Y directions.

5. A hybrid-excitation radial two-degree-of-freedom DC magnetic bearing according to claim 3, characterized in that: The excitation winding (5) is supplied with DC current to generate excitation flux (11), and the permanent magnet (6) generates permanent magnet flux (12). The excitation flux (11) and the permanent magnet flux (12) pass through the same magnetic path, respectively passing through adjacent suspension poles (7), radial air gap (9), rotor (2) and stator core yoke to form a closed path. The bias flux (10) is provided by the permanent magnet flux (12) or by the superposition of the excitation flux (11) and the permanent magnet flux (12).

6. A hybrid-excitation radial two-degree-of-freedom DC magnetic bearing according to claim 5, characterized in that: The hybrid-excitation radial two-degree-of-freedom DC magnetic bearing is controlled by an excitation control system and a suspension control system, respectively. The excitation control system includes an excitation power amplifier; the suspension control system includes two suspension power amplifiers, corresponding to the X and Y directions, respectively. Displacement sensors detect the real-time displacement signals of the rotor in the X and Y directions. After processing by the controller, the corresponding suspension currents of the suspension power amplifiers are independently controlled to be output to the X-direction suspension winding and the Y-direction suspension winding, respectively. The controller adjusts the output current of the excitation power amplifier to the excitation winding according to the following preset control strategy based on the magnitude of the suspension current: The permanent magnet (6) is equivalent to a magnet with an ampere-turn number of N. s I ps For the winding, establish the intervention criterion for the excitation current: let the equivalent current I be applied. ps The generated air gap magnetic flux density and the air gap magnetic flux density B provided by the permanent magnet (6) p Equal to each other, we obtain the equivalent current. , The rated current of the levitation winding (4) is This represents the number of turns of the wire in the levitation coil. Will I ps and When comparing, At that time, only the permanent magnet (6) generates the bias magnetic flux, in which and These represent the currents in the floating windings in the X and Y directions, respectively. when At that time, an excitation current is applied, the magnitude of which is h m The thickness of the permanent magnet (6) in the magnetization direction. The radial air gap (9) length, μ r N is the relative permeability of the permanent magnet. l The number of turns of the excitation winding conductor is given by the bias flux (10), which is provided by the superposition of the excitation flux (11) and the permanent magnet flux (12).

7. A hybrid-excitation radial two-degree-of-freedom DC magnetic bearing according to claim 5, characterized in that: Under normal operating conditions, the excitation winding (5) is supplied with a positive current, and the excitation flux (11) it generates is in the same direction as the permanent magnet flux (12) generated by the permanent magnet (6). The two are superimposed to form a bias flux (10). Under the installation and commissioning conditions, in order to eliminate the unilateral attraction of the permanent magnet (6) on the rotor (2), the excitation winding (5) is supplied with a reverse current to generate an excitation flux (11) to cancel the permanent magnet flux (12), thus making the permanent magnet (6) equivalent to a magnet with an ampere-turns of N. l I pl The magnitude of the reverse current flowing through the excitation winding (5) is: .

8. A hybrid-excitation radial two-degree-of-freedom DC magnetic bearing according to claim 1, characterized in that: The bias air gap magnetic flux density B generated by the permanent magnet (6) p The value acting on the radial air gap (9) is taken as the air gap saturation magnetic flux density B. s One-quarter; the excitation magnetic flux density B generated by the excitation winding (5) under rated maximum current. w Acting on the radial air gap (9), it is the air gap saturation magnetic flux density B. s One-quarter; the magnetic flux density B generated by the levitation winding (4) under rated maximum current. m The radial air gap (9) acting under the levitation pole (7) is the air gap saturation magnetic flux density B. s One-half of.

9. A hybrid-excitation radial two-degree-of-freedom DC magnetic bearing according to claim 1, characterized in that: The levitation pole (7), excitation pole (8), stator core and rotor (2) are all made of silicon steel sheets with a thickness of 0.1~0.3mm and a stacking coefficient ≥0.95; the permanent magnet (6) is made of rare earth permanent magnet material and is radially magnetized.

10. A hybrid-excitation radial two-degree-of-freedom DC magnetic bearing according to any one of claims 1-9, characterized in that, The parameter design method for the hybrid excitation radial two-degree-of-freedom DC magnetic bearing includes the following steps: Step 1: Determine the core material of the stator and rotor, and the length of the radial air gap (9). Select air gap saturation magnetic flux density B s According to the maximum levitation force index F max Determine the area S of the levitation pole (7), and make the area of ​​the excitation pole (8) equal to the area of ​​the levitation pole (7), and establish a levitation force model; Step 2: Based on the magnetic flux density B generated by the permanent magnet (6) p air gap saturation magnetic flux density B s One-quarter of the thickness of the permanent magnet in the magnetization direction. H c For the coercivity of a permanent magnet, μ r denoted as the relative permeability of the permanent magnet, and μ0 as the permeability of free space. Step 3: Based on the excitation magnetic flux density B w Calculate the ampere-turns of the excitation winding (5). , where N l I is the number of turns of the excitation winding conductor. l This is the rated current of the excitation winding; Step 4: Based on the levitation magnetic flux density B m Calculate the ampere-turns of the suspension winding (4) ,in, The number of turns of the levitation winding conductor. This is the rated current of the suspension winding.

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