A design method for a symmetrical six-pole constant current source excitation electromagnetic bearing for levitation force

Abstract

This invention discloses a symmetrical six-pole constant current source excitation electromagnetic bearing and its design method. The magnetic bearing includes a stator, a rotor, a constant current source winding, and a control winding. Six levitation poles are evenly distributed at 60° intervals on the stator, with equal air gap lengths between each levitation pole and the rotor. Coils with the same number of turns are wound on two poles in the X direction, connected in series to form a constant current source winding powered by a DC constant current source. Coils are wound on each of the six poles, with the coils on opposite poles connected in series to form a three-phase control winding, powered by a three-phase inverter. Based on the levitation force generation mechanism of the six-pole constant current source excitation active magnetic bearing, and constrained by the equality of the maximum levitation force in the X and Y directions, this invention designs the magnetic pole area, air gap bias flux, number of turns in the control winding, and number of turns in the constant current source winding for the poles in the X and Y directions. This scheme achieves completely equal radial levitation forces in the X and Y directions of the six-pole constant current source excitation active magnetic bearing, with low levitation force coupling and simple control.

Description

Technical Field

[0001] This invention relates to a design method for a symmetrical six-pole constant current source excitation active magnetic bearing with levitation force, specifically a design method for a symmetrical constant current source excitation six-pole active magnetic bearing with maximum levitation force. Background Technology

[0002] Hybrid magnetic bearings typically employ permanent magnets to generate bias flux and levitation windings to generate levitation control flux; the interaction between these two components produces levitation force. However, the permanent magnets in hybrid bearings demagnetize under high temperatures and vibrations, and their magnetic properties weaken over prolonged operation. In contrast, the levitation force generation mechanism of constant current source excitation magnetic bearings is similar to that of hybrid bearings, and the bias flux is generated by a constant current source winding, making them convenient to operate, structurally simple, and cost-effective, thus possessing significant industrial application value. Existing six-pole constant current source excitation magnetic bearings have six poles with equal areas, but the air gap bias flux density under the two poles in the X direction is twice that under the two poles in the Y direction. This results in a large difference in the maximum levitation force between the +X and +Y directions. This asymmetry leads to severe coupling of the levitation force in six-pole constant current source excitation magnetic bearings, making control complex and particularly difficult to achieve stable levitation control in certain specific applications. Summary of the Invention

[0003] Purpose of the invention: In order to solve the problem of unequal maximum levitation forces in the +X and +Y directions caused by the traditional design method of six-pole constant current source excitation magnetic bearing, this invention proposes a six-pole constant current source excitation active magnetic bearing with symmetrical levitation forces and its design method, in which the maximum levitation forces in the X and Y directions are equal, and the radial levitation force of the six-pole constant current source excitation magnetic bearing is completely symmetrically designed.

[0004] Technical solution: This invention is achieved through the following technical solution:

[0005] This invention relates to a design method for a symmetrical six-pole constant current source excitation active magnetic levitation bearing, specifically a symmetrical six-pole constant current source excitation electromagnetic bearing and its design method. The invention is based on the following structure: The magnetic bearing includes a stator, a rotor, a constant current source winding, and a control winding. Six levitation poles, spaced 60° apart, are evenly distributed on the stator, denoted as levitation pole M, levitation pole N, levitation pole Z, levitation pole U, levitation pole X, and levitation pole Y, respectively. The air gap length between each levitation pole and the rotor is equal. Coils with the same number of turns are wound on two poles in the X direction, then connected in series to form a constant current source winding powered by a single constant current source. The control winding on the opposite levitation pole is connected in series and powered by a three-phase inverter. A compensating inductor L and a compensating resistor R are connected in series on the Y direction control winding. The specific steps are as follows:

[0006] Step 1: Determine the bias magnetic flux and area relationship under the suspension poles M, N, Z, U, X, and Y.

[0007] Based on the structure and suspension mechanism, we can obtain: B x S x =2B y S y .

[0008] Among them B x S x B represents the bias magnetic flux and pole area under levitation poles M and N; y S y Let Z be the bias magnetic flux and area under the suspension poles Z, U, X, and Y;

[0009] The maximum magnetic levitation force F in the S1.2+X direction xmax The expression is:

[0010]

[0011] The maximum magnetic levitation force F in the S1.3+Y direction ymax The expression is:

[0012]

[0013] For F xmax =F ymax Solving the equation

[0014] We can conclude that: B x =1.232B y S x =1.623S y .

[0015] Step 2: Calculate the number of turns in the constant current source winding

[0016] S2.1 Assuming the constant current source winding has N turns, the excitation current is I, the air gap length is g, and the air permeability is μ0, based on the bias magnetic circuit, we obtain:

[0017] Step 3: Calculate control winding parameters

[0018] S3.1 When the maximum levitation force is generated in the X and Y directions respectively, the control winding is energized to generate the same control magnetic flux as the bias magnetic flux:

[0019]

[0020] Step 4: Calculate the stator inner diameter and axial length

[0021] From the structure of the magnetic bearing, we can obtain: 4S1+2S2=l×πR×ρ, where l is the axial length of the iron core, R is the inner diameter of the stator, and ρ is the ratio of the six pole arcs to the circumference, which is generally taken as 0.9. Based on the maximum levitation force requirement, the magnetic pole area can be calculated, and then the inner diameter and shaft length of the stator can be obtained.

[0022] Furthermore, to ensure the symmetry of the three-phase control windings, a compensating inductor L and a compensating resistor R need to be connected in series on the Y-direction control winding as follows:

[0023]

[0024] Where L x R x L controls the winding inductance and resistance in the X direction. y R y The inductance and resistance of the winding are controlled in the Y direction.

[0025] Furthermore, B x Less than or equal to 0.5B s B s It is the air gap saturation magnetic flux density.

[0026] Beneficial effects:

[0027] Compared to the unequal maximum levitation forces in the +X and +Y directions caused by the traditional six-pole constant current source excitation magnetic bearing, this invention achieves a completely symmetrical design of the radial levitation force of the six-pole magnetic bearing by designing the maximum levitation forces in the +X and +Y directions to be equal. It also provides a design method for the bias magnetic induction intensity, magnetic pole area, and control winding, resulting in a small coupling of levitation force and easy control. Attached Figure Description

[0028] Figure 1 Front view of the electromagnetic axis of a symmetrical hexagonal constant current source for levitation force.

[0029] Figure 2 Wiring diagram of the bias winding of the electromagnetic bearing for symmetrical six-pole constant current source excitation for levitation force.

[0030] Figure 3 Wiring diagram of the control winding of the symmetrical six-pole constant current source excitation electromagnetic bearing for levitation force.

[0031] Figure 4 Bias magnetic flux density diagram of a symmetrical hexagonal constant current source electromagnetic bearing for stable levitation.

[0032] Figure 5 The bias magnetic flux density diagram of each suspension pole of the symmetrical six-pole constant current source excitation electromagnetic bearing for levitation force

[0033] Figure 6 The electromagnetic magnetic axis F of the symmetrical hexagonal constant current source for levitation force ymax Magnetic flux density distribution map

[0034] Figure 7 For levitation force symmetrical six-stage constant current source excitation electromagnetic bearing F ymax Magnetic flux density diagram of air gap under each suspension pole

[0035] Figure 8 The electromagnetic magnetic axis F of the symmetrical hexagonal constant current source for levitation force xmax Magnetic flux density distribution map

[0036] Figure 9 For levitation force symmetrical six-stage constant current source excitation electromagnetic bearing F xmax Magnetic flux density diagram of air gap under each suspension pole Detailed Implementation

[0037] The principle upon which this invention is based is:

[0038] This invention relates to a design method for a constant current source excitation active magnetic levitation bearing, specifically a design method for a symmetrical six-pole constant current source excitation electromagnetic bearing. The invention is based on the following structure. Its structure is as follows: Figure 1 As shown, the bias magnetic flux in a stable levitation state is as follows Figure 2 As shown. The magnetic bearing includes a stator 1, a rotor 2, a constant current source winding, and a control winding. Six levitation poles, spaced 60° apart, are evenly distributed on the stator 1, denoted as levitation pole M, levitation pole N, levitation pole Z, levitation pole U, levitation pole X, and levitation pole Y, respectively. The air gap length between each levitation pole and the rotor 2 is equal. Coils with the same number of turns are wound on the two poles in the X direction, and then connected in series to form a constant current source winding powered by a constant current source. The control winding on the levitation pole is connected in series and powered by a three-phase inverter. A compensation winding 20 and a compensation inductor 19 are connected in series on the control winding in the Y direction. The following assumptions are made for the symmetrical six-pole constant current source excitation electromagnetic bearing: only the working air gap reluctance is considered, the reluctance of the left, middle, and right stator cores and the rotor core are ignored, and leakage flux and eddy current effects are ignored.

[0039] The bias magnetic flux distribution at the equilibrium position of this invention is as follows: Figure 2 As shown, the resultant force on the rotor is zero at this time, and it is in equilibrium. When in equilibrium, the constant current source windings on suspension poles M and N are energized, while the others are not. Based on the selected electromagnetic material, the bias magnetic flux on suspension poles M and N when in stable suspension is B. x The suspended electrode area is S x The bias magnetic flux on the suspension poles Z, U, X, and Y is B. y The suspended electrode area is S y .

[0040] Based on the energizing method of the constant current source excitation active magnetic bearing to generate the maximum levitation force in the +X direction, the control windings on the levitation poles M and N are supplied with the maximum control current i in the +X direction. xmaxThe control windings on the floating poles Z, U, X, and Y are supplied with a maximum control current of -0.5i in the Y direction. xmax The maximum magnetic levitation force F in the +X direction xmax The expression is:

[0041]

[0042] Based on the energizing method that generates the maximum levitation force in the Y direction, the control windings on the levitation poles X and Y are supplied with the maximum control current i in the Y direction. ymax The control windings on the floating poles Z and U are supplied with the maximum control current -i in the Y direction. ymax This makes the control winding current on the levitation poles M and N zero, and the maximum magnetic levitation force F in the +Y direction... ymax The expression is:

[0043]

[0044] Furthermore, when the maximum levitation force is generated in the X and Y directions respectively, the control winding is energized to generate the same control magnetic flux as the bias magnetic flux:

[0045]

[0046] To further ensure the symmetry of the three-phase control windings, a compensating inductor L and a compensating resistor R need to be connected in series on the Y-direction control winding as follows:

[0047]

[0048] Further on F xmax =F ymax Solving the equation, we get the following equation:

[0049]

[0050] Further, there are:

[0051]

[0052] Further, there are:

[0053]

[0054] According to the constraints, we have B. x S x =2B y S y (2)

[0055] Based on the control winding parameters, we have 4S1 + 2S2 = l × πR × ρ (3)

[0056] Substituting (2) and (3) into (1), we can determine the following proportional relationship:

[0057] B x =1.232B y (4)

[0058] Substituting (4) into (2) yields the following proportional relationship:

[0059] S x =1.623S y (5)

[0060] This invention designs a six-pole constant current source excitation electromagnetic bearing with symmetrical levitation force to satisfy the maximum levitation force F in the positive X and Y directions. xmax =F ymax =387N, and the analysis and verification were performed using Maxwell 2D finite element analysis software. Specific parameters of the magnetic bearing are as follows:

[0061] As shown in Table 1.

[0062] name parameter Stator outer diameter 100mm Stator inner diameter 72mm Rotor outer diameter 32mm Rotor inner diameter 16mm Number of turns of bias winding 30 turns X-direction control winding turns 30 turns Y-direction control winding turns 30 turns X-direction suspended polar area <![CDATA[632mm 2 ]]> Y-direction suspended electrode area <![CDATA[390mm 2 ]]>

[0063] Table 1 shows the relevant parameters for stator, rotor, pole area, and number of turns. The maximum levitation force is further calculated based on the design parameters.

[0064]

[0065] F xmax F ymax The results approximately equally satisfy the design requirements, as shown below. Figure 9 As shown.

[0066] 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 symmetrical six-pole constant current source excitation electromagnetic bearing for levitation force, comprising a stator (1), a rotor (2), a constant current source winding, and a control winding, characterized in that, Both the stator (1) and the rotor (2) are made of stacked silicon steel sheets. Six floating poles with a 60° interval are evenly distributed on the stator (1), which are denoted as floating pole M, floating pole N, floating pole Z, floating pole U, floating pole X, and floating pole Y respectively. The air gap length between each floating pole and the rotor (2) is equal. The second coil (4) and the seventh coil (9) with the same number of turns are wound on the floating poles M and N, and then connected in series to form a constant current source winding and powered by a DC constant current source. The fourth coil (6), the eighth coil (10), the fifth coil (7), the first coil (3), the third coil (5), and the sixth coil (8) are wound on the six poles. The coils on the opposite poles are connected in series to form a three-phase winding. The fourth coil (6), the eighth coil (10), the fifth coil (7), the first coil (3), the third coil (5), and the sixth coil (8) are wound on the six poles. The coils on the opposite poles are connected in series to form a three-phase winding. The number of turns of the control winding composed of the eight coils (10), the fifth coil (7), the first coil (3), the third coil (5), and the sixth coil (8) is not equal. The two-phase winding composed of the fourth coil (6), the eighth coil (10), the fifth coil (7), and the first coil (3) is connected in series with the compensation inductor (19) and the compensation resistor (20) to power the three-phase inverter. The areas of the floating poles M and N are not equal to the areas of the floating poles Z, U, X, and Y. The bias magnetic flux density under the floating poles M, N, Z, U, X, and Y is not equal. The number of turns of the three-phase control winding is not equal. The three-phase control winding composed of these three-phase control windings powers the three-phase inverter. The maximum current is equal.

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