An asymmetric radial electromagnetic bearing and a method of designing the same

Abstract

The application discloses an asymmetric radial electromagnetic bearing and a design method thereof, wherein the asymmetric radial electromagnetic bearing comprises an asymmetric radial electromagnetic bearing stator, an asymmetric radial electromagnetic bearing rotor and winding coils. The design method of the asymmetric radial electromagnetic bearing comprises the following steps: determining parameters in advance; calculating electromagnetic forces of the asymmetric radial electromagnetic bearing in X and Y directions; and calculating various structural parameters of the asymmetric radial electromagnetic bearing. Compared with a conventional symmetric radial electromagnetic bearing structure and a currently disclosed asymmetric electromagnetic bearing, the asymmetric radial electromagnetic bearing has the advantages of small electromagnetic force coupling in horizontal and vertical directions, low electromagnetic loss, and low rotor temperature rise.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic bearing technology, and specifically to a low-power radial electromagnetic bearing and its design method. Background Technology

[0002] Electromagnetic bearings offer advantages such as non-contact operation, wear-free operation, lubrication-free operation, high speed, long lifespan, and controllability, leading to their widespread use in flywheel energy storage systems, medical equipment, turbine machinery, and machine tool manufacturing. However, the realization of these advantages depends to some extent on the rationality of the electromagnetic bearing's structure and design.

[0003] In existing magnetic levitation technologies, horizontal rotating machinery often employs symmetrical radial electromagnetic bearings for support. In this case, the radial electromagnetic bearings continuously need to counteract the gravity of the rotor system during operation. Based on differential control theory, the controller of the radial electromagnetic bearing constantly generates a large control current to counteract gravity, resulting in significant electromagnetic losses during operation. If the rotor operates in a vacuum, the temperature rise of the electromagnetic bearing due to these losses will affect the equipment's performance and may even lead to safety accidents.

[0004] Furthermore, prior art CN115111265A discloses an asymmetric electromagnetic bearing, including a rotor and a stator with multiple magnetic poles. The cross-sectional area S of the magnetic poles in the first and second quadrants is the same, and the cross-sectional area s of the magnetic poles in the third and fourth quadrants is the same, with S > s. The number of coil turns wound around each group of magnetic poles is the same. Prior art CN115095602A discloses an asymmetric electromagnetic bearing, including a rotor and a stator with multiple magnetic poles. The cross-sectional area of ​​the magnetic poles in the first, second, third, and fourth quadrants is the same, but the number of coil turns in the first and second quadrants is N, and the number of coil turns in the third and fourth quadrants is M, with N > M.

[0005] In the above two inventions, the magnetic pole structure is relatively complex, and the actual electromagnetic force generated in any quadrant will affect the electromagnetic force in the horizontal and vertical directions, which is not conducive to control. Summary of the Invention

[0006] This invention provides an asymmetric radial electromagnetic bearing and its design method.

[0007] The asymmetric radial electromagnetic bearing of this invention specifically includes: an asymmetric radial electromagnetic bearing rotor, an asymmetric radial electromagnetic bearing stator, and winding coils. Both the rotor and stator are constructed from laminated silicon steel sheets. The stator's magnetic poles are divided into four groups: an upper pole pair, a right pole pair, a lower pole pair, and a left pole pair. The area of ​​the pole column of the upper pole pair is greater than that of the right pole pair, which equals that of the left pole pair, which is greater than that of the lower pole pair. This ratio of pole column areas is given during calculation. The winding coils are wound with enameled wire. The number of turns in the upper winding is greater than that in the right winding, which equals that in the left winding, which is greater than that in the lower winding. The specific number of turns is determined by a formula in the design method. The winding coils are wound with enameled wire.

[0008] The design method in this invention specifically includes the following steps:

[0009] Step (1): Predetermine the parameters;

[0010] Specifically, this includes determining the material of the electromagnetic bearing and the maximum magnetic flux density B. max Determine the number of magnetic poles N P The value is 8. Based on the rotor mass M and the maximum dynamic unbalance force F of the horizontal rotating machinery, calculate the actual maximum load-bearing capacity F required for each magnetic pole pair. imax Determine the inner diameter d1 of the asymmetric radial electromagnetic bearing rotor based on the outer diameter of the rotor of the horizontal rotating machinery; the air gap size s0; and the maximum coil current I. max And the maximum current density J and the slot fill factor λ.

[0011] Step (2): Calculate the electromagnetic force of the asymmetric radial electromagnetic bearing in the X and Y directions. The specific solution process is as follows:

[0012] Based on the principle of virtual displacement, the electromagnetic force of each pair of magnetic poles on the rotor can be obtained.

[0013]

[0014] Where α is half the angle between the two magnetic poles of the electromagnetic bearing.

[0015] In differential drive mode, the magnitude of the electromagnetic force generated by the right magnetic pole on the rotor is...

[0016]

[0017] The magnitude of the electromagnetic force generated by the left magnetic pole on the rotor is

[0018]

[0019] Its electromagnetic resultant force in the X direction can be expressed as:

[0020] f x =f x+ -f x- (4)

[0021] Similarly, the magnitude of the electromagnetic force generated by the upper magnetic pole on the rotor is

[0022]

[0023] The magnitude of the electromagnetic force generated by the lower magnetic pole on the rotor is

[0024]

[0025] Its electromagnetic resultant force in the Y direction can be expressed as:

[0026] f y =f y+ -f y- (7)

[0027] Step (3): Calculate the various structural parameters of the asymmetric radial electromagnetic bearing. The specific solution process is as follows:

[0028] Stator pole width:

[0029]

[0030] t1:t2:t3:t4=6:5:4:5 (9)

[0031] The width of both the stator yoke and the rotor core should not be less than the width of the stator poles, and is generally taken as C = (1~1.5)t. i In this invention, the width of the stator yoke is:

[0032] C = t1 (10)

[0033] Rotor core width:

[0034] c = t1 (11)

[0035] Rotor outer diameter:

[0036] d2=d1+2c (12)

[0037] Stator inner diameter:

[0038] D1=d2+2s0 (13)

[0039] Air gap cross-sectional area:

[0040] A i =t i l (14)

[0041] In the formula, l is the axial width of the stator. From formula (1) and formula (14), the axial length of the stator can be obtained by taking i = 1.

[0042]

[0043] Rotor axial length:

[0044] L = l + 5 (16)

[0045] Substituting the actual maximum load capacity and maximum current value into formula (1), the number of turns of the winding coil for each magnetic pole pair can be obtained:

[0046]

[0047] Minimum bare wire diameter:

[0048]

[0049] Furthermore, the diameter d of the enameled wire is determined based on the minimum bare wire diameter.

[0050] Based on the number of turns and structure of the winding coil, the coil slot area can be obtained as follows:

[0051]

[0052] To allow sufficient space for installing the winding coil, the radial height of the magnetic pole is:

[0053] H=(1~1.4)H' (20)

[0054] Winding coil slot bottom diameter:

[0055] D2 = D1 + 2H (21)

[0056] Stator outer diameter:

[0057] D3 = D2 + 2C (22)

[0058] Beneficial effects:

[0059] Compared with traditional symmetrical radial electromagnetic bearing structures and currently disclosed asymmetrical electromagnetic bearings, this invention has the following advantages: firstly, its electromagnetic force has less coupling in the horizontal and vertical directions, which is beneficial for control; secondly, its electromagnetic loss is low, which can reduce rotor temperature rise. Attached Figure Description

[0060] Figure 1 A schematic diagram showing the structure of an asymmetric radial electromagnetic bearing;

[0061] Figure 2 Equivalent magnetic circuit diagram representing an asymmetric radial electromagnetic bearing;

[0062] Figure 3 A schematic diagram showing the structural parameters of an asymmetric radial electromagnetic bearing;

[0063] Figure 4 A magnetic flux density distribution diagram showing the working state of an asymmetric radial electromagnetic bearing;

[0064] Figure 5 The characteristic curves of the electromagnetic force (Y direction) of the asymmetric radial electromagnetic bearing as a function of the control current under different rotor displacements are shown.

[0065] Figure 6 This graph compares the total power loss of an asymmetric radial electromagnetic bearing and a traditional symmetric radial electromagnetic bearing when supporting the rotor of the same horizontal machine. Detailed Implementation

[0066] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0067] like Figure 1 As shown, the asymmetric radial electromagnetic bearing of this invention includes: an asymmetric radial electromagnetic bearing rotor 1, an asymmetric radial electromagnetic bearing stator 2, and winding coils 3. Both the asymmetric radial electromagnetic bearing rotor 1 and the asymmetric radial electromagnetic bearing stator 2 are constructed from laminated silicon steel sheets. The magnetic poles of the asymmetric radial electromagnetic bearing stator 2 are divided into four groups: an upper pole pair, a right pole pair, a lower pole pair, and a left pole pair. The area of ​​the pole column of the upper pole pair is greater than that of the right pole pair, which equals that of the left pole pair, which is greater than that of the lower pole pair. The pole column area ratio is given during calculation. The winding coils 3 are made of enameled wire, with the number of turns in the upper winding coil greater than that in the right winding coil, which equals that in the left winding coil, which is greater than that in the lower winding coil. The specific number of turns is determined by calculation using formulas in the design method.

[0068] The asymmetric radial electromagnetic bearing of the present invention includes an asymmetric radial electromagnetic bearing rotor, an asymmetric radial electromagnetic bearing stator, and winding coils. The following is a detailed description of its features:

[0069] Asymmetric Radial Electromagnetic Bearing Rotor and Stator: Both the rotor and stator of the asymmetric radial electromagnetic bearing are constructed from laminated silicon steel sheets. Silicon steel sheets possess excellent magnetic permeability and low hysteresis loss, which are crucial for the performance of the electromagnetic bearing. The rotor and stator are designed with an asymmetric structure, which helps reduce electromagnetic force coupling in the horizontal and vertical directions, thereby improving control stability and accuracy.

[0070] Stator Pole Design: The stator poles are divided into four groups: upper pole pair, right pole pair, lower pole pair, and left pole pair. This grouping design not only helps to achieve an asymmetrical electromagnetic force distribution but also optimizes the load-bearing capacity and control performance of the electromagnetic bearings. The pole column areas of these four pole pairs are not equal but are arranged in the order of upper pole pair pole column area > right pole pair pole column area = left pole pair pole column area > lower pole pair pole column area, with a given pole column area ratio. This area ratio is set based on the precise calculation and optimization of electromagnetic forces, aiming to further reduce electromagnetic losses and improve efficiency.

[0071] Winding Coil Design: The winding coil, made of enameled wire, is a key component in the electromagnetic bearing used to generate electromagnetic force. Corresponding to the stator's magnetic pole design, the number of turns in the winding coil is asymmetrical, specifically: upper winding coil turns > right winding coil turns = left winding coil turns > lower winding coil turns. This turn distribution, combined with the area ratio of the magnetic pole posts, allows the electromagnetic bearing to generate a more balanced and controllable electromagnetic force in both the horizontal and vertical directions. Simultaneously, this design helps reduce electromagnetic losses and rotor temperature rise, thereby improving the reliability and lifespan of the electromagnetic bearing. Furthermore, the number of turns and material selection for the winding coil are based on precise calculations and optimizations to ensure that electromagnetic losses and temperature rise are minimized while meeting load-bearing requirements. The use of enameled wire ensures the insulation performance and stability of the winding coil.

[0072] The design method of this invention is as follows: The design method includes three main steps, namely, pre-determining parameters, calculating the electromagnetic force of the asymmetric radial electromagnetic bearing in the X and Y directions, and calculating the structural parameters of the asymmetric radial electromagnetic bearing. The following is a detailed description of these three steps.

[0073] Step (1): Predetermine the parameters.

[0074] Before designing an asymmetric radial electromagnetic bearing, a series of key parameters need to be determined in advance. These parameters directly affect the performance and structural design of the electromagnetic bearing. Specific parameters include: the material of the electromagnetic bearing: selecting a suitable material is crucial for the performance of the electromagnetic bearing. Typically, the stator and rotor are made of laminated silicon steel sheets to reduce eddy current losses and hysteresis losses. Maximum magnetic flux density B. max This is a crucial parameter in electromagnetic bearing design, determining its load-bearing capacity and electromagnetic losses. Number of poles N p The choice of the number of magnetic poles needs to be determined based on actual needs and application scenarios. In this method, the number of magnetic poles N... P The value is determined to be 8. Rotor mass M and maximum dynamic unbalance force F. max These parameters are used to calculate the actual maximum load-bearing capacity F required for each magnetic pole pair.imax This ensures the electromagnetic bearing can stably support the rotor. Rotor outer diameter: used to determine the inner diameter d1 of the asymmetric radial electromagnetic bearing rotor. Air gap size s0: The air gap is the distance between the stator and rotor in the electromagnetic bearing; its size directly affects the electromagnetic force and electromagnetic losses. Maximum coil current I. max Maximum current density J: These parameters are used to design the winding coil to ensure that the coil does not exceed its load-bearing limit during operation. Slot fill factor λ: The slot fill factor refers to the degree of filling of the winding coil in the slot, which affects the heat dissipation and electrical performance of the electromagnetic bearing. When determining these parameters, it is necessary to comprehensively consider factors such as the application scenario, performance requirements, and cost of the electromagnetic bearing to ensure the rationality and feasibility of the design.

[0075] Step (2): Calculate the electromagnetic force of the asymmetric radial electromagnetic bearing in the X and Y directions.

[0076] After determining the key parameters, the next step is to calculate the electromagnetic forces of the asymmetric radial electromagnetic bearing in the X and Y directions. This step is crucial in the design process because the magnitude and direction of the electromagnetic forces directly affect the bearing's load-bearing capacity and control performance. Based on the principle of virtual displacement, the formulas for the electromagnetic forces of each pair of magnetic poles to the rotor can be derived. In differential drive mode, the electromagnetic forces of the right and left magnetic pole pairs in the X direction, and the electromagnetic forces of the upper and lower magnetic pole pairs in the Y direction, can be calculated separately. Then, by combining these electromagnetic forces, the resultant electromagnetic force of the asymmetric radial electromagnetic bearing in the X and Y directions can be obtained. The calculation results of this step will provide an important basis for subsequent structural parameter design, ensuring that the electromagnetic bearing can meet the requirements of load-bearing capacity and control performance.

[0077] Step (3): Calculate the structural parameters of the asymmetric radial electromagnetic bearing.

[0078] After determining the electromagnetic force, the next step is to calculate the various structural parameters of the asymmetric radial electromagnetic bearing. These parameters include stator pole width, stator yoke width, rotor core width, rotor outer diameter, stator inner diameter, air gap cross-sectional area, stator axial length, rotor axial length, number of turns in the winding coil, minimum bare wire diameter, enameled wire diameter, coil slot area, pole radial height, and winding coil slot bottom diameter, etc.

[0079] The calculation of these structural parameters requires the results of electromagnetic force calculations and the working principle of electromagnetic bearings. Through a series of formula derivations and calculations, the specific values ​​of these structural parameters can be obtained. These parameters will directly guide the machining and assembly process of the electromagnetic bearings, ensuring that the electromagnetic bearings can operate stably according to design requirements.

[0080] When calculating structural parameters, special attention must be paid to the interactions and constraints between the parameters to ensure the rationality and feasibility of the calculation results. At the same time, the actual processing and assembly conditions must be considered, and the calculation results should be appropriately corrected and adjusted.

[0081] This example uses the actual rotor structure of a horizontal machine, with a total rotor mass of 20 kg, a maximum unbalanced force of 263.19 N, and an outer diameter of 36 mm. The design method of this invention will be described in detail below.

[0082] In practical design, a 3x margin is used, resulting in a bearing capacity of 789.57 N for the asymmetric radial electromagnetic bearing to counteract the rotor's dynamic imbalance force. Since the rotor is horizontal, the asymmetric radial electromagnetic bearing also needs to provide a static bearing capacity (to counteract gravity) of 200 N. Therefore, the maximum electromagnetic bearing capacity F that a single radial electromagnetic bearing needs to provide to the rotor in the four directions (up, right, down, left) is... 1max F 2max、 F 3max、 F 4max The values ​​are 494.79 N, 394.79 N, 294.79 N, and 394.79 N, respectively. Additionally, based on the actual properties of the material, B is chosen. max =1.2T, based on the rotor outer diameter, d1 = 36mm. Take the air gap value s0 = 0.5mm, and the maximum coil current I. max The current is 4A, and the maximum current density J is 3.5A / mm. 2 The fill factor λ is 0.7.

[0083] Figure 2 The equivalent magnetic circuit diagram of an asymmetric radial electromagnetic bearing, along with the definitions of the X and Y directions, are presented, and combined with... Figure 2 The electromagnetic force expressions of the asymmetric radial electromagnetic bearing in the X and Y directions can be derived from formulas (1)-(7).

[0084] Figure 3 The structural parameters required to be solved for the asymmetric radial electromagnetic bearing are marked. By combining design formulas (8), (9), (11), (12), and (13), t1, t2, t3, t4, D1, and d2 can be calculated. C can be calculated from formula (10). By combining formulas (1) and (14) and removing i=1, l can be obtained. L can be calculated from formula (16). By substituting the actual maximum load capacity and maximum current values ​​of the upper, right, lower, and left sides into formula (1), the winding coil turn values ​​of the four magnetic pole pairs on the upper, right, lower, and left sides are N1, N2, N3, and N4, respectively. d can be calculated from formula (18). w And according to d wThe value of d can then be determined. Using formulas (19), (20), and (21) and taking i = 1, H and D2 can be obtained. D3 can be obtained using formula (22). After solving, the specific numerical results of each parameter are shown in the table below.

[0085] Asymmetric Radial Electromagnetic Bearing Structure Design Parameter Table

[0086]

[0087] Furthermore, a simulation model of the asymmetric radial electromagnetic bearing was established using the above parameters.

[0088] Figure 4 It is the magnetic flux density distribution of an asymmetric radial electromagnetic bearing in operation, which is uniform and there is no coupling between the magnetic pole pairs.

[0089] Figure 5 This is the characteristic curve of the electromagnetic force (Y direction) of the asymmetric radial electromagnetic bearing as a function of the control current under different rotor displacements. Clearly, under different rotor displacements, the asymmetric radial electromagnetic bearing can achieve half the rotor weight (F = 100N) under a certain control current. Therefore, the asymmetric radial electromagnetic bearing has the capacity to suspend the rotor in any position or to return the rotor from an eccentric position to the central operating point.

[0090] Figure 6 This graph compares the total power loss of an asymmetric radial electromagnetic bearing with that of a conventional symmetrical radial electromagnetic bearing when supporting the rotor of the same horizontal machine. Compared to a symmetrical design, the asymmetric radial electromagnetic bearing of this invention exhibits lower electromagnetic losses.

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An asymmetric radial electromagnetic bearing, characterized in that... This includes an asymmetric radial electromagnetic bearing rotor, an asymmetric radial electromagnetic bearing stator, and winding coils; among which, Both the asymmetric radial electromagnetic bearing rotor and the asymmetric radial electromagnetic bearing stator are made of laminated silicon steel sheets. The magnetic poles of the asymmetric radial electromagnetic bearing stator are divided into four groups: upper magnetic pole pair, right magnetic pole pair, lower magnetic pole pair, and left magnetic pole pair. The area of ​​the magnetic pole column of the upper magnetic pole pair is greater than that of the right magnetic pole pair, which equals that of the left magnetic pole pair, which is greater than that of the lower magnetic pole pair, and there is a given ratio of magnetic pole column areas. The winding coils are made of enameled wire, with the number of turns of the upper winding coil greater than that of the right winding coil, which equals that of the left winding coil, which is greater than that of the lower winding coil. The number of turns of each winding coil is calculated by the formula in the design method.

2. A design method for an asymmetric radial electromagnetic bearing, used to design an asymmetric radial electromagnetic bearing according to claim 1, characterized in that: The design methodology includes the following steps: Step (1): Predetermine parameters, including: determining the material of the electromagnetic bearing and the maximum magnetic induction intensity. Determine the number of magnetic poles The value is 8; based on the rotor mass of the horizontal rotating machinery. and maximum dynamic imbalance force Calculate the actual maximum load capacity required for each magnetic pole pair. Determine the inner diameter of the rotor of the asymmetric radial electromagnetic bearing based on the outer diameter of the rotor of the horizontal rotating machinery. Air gap size Maximum coil current and maximum current density and slot fill rate ; Step (2): Calculate the electromagnetic force of the asymmetric radial electromagnetic bearing in the X and Y directions. Specifically, this includes: obtaining the electromagnetic force expression of each pair of magnetic poles to the rotor according to the principle of virtual displacement, and deriving the electromagnetic resultant force expression in the X and Y directions respectively in the differential drive mode. Step (3): Calculate the structural parameters of the asymmetric radial electromagnetic bearing, including: stator pole width, stator yoke width, rotor core width, rotor outer diameter, stator inner diameter, air gap cross-sectional area, stator axial length, rotor axial length, number of turns of each pole pair winding coil, minimum bare wire diameter, enameled wire diameter, coil slot area, pole radial height, winding coil slot bottom diameter, and stator outer diameter.

3. The design method for an asymmetric radial electromagnetic bearing according to claim 2, characterized in that: In step (2), The expression for the resultant electromagnetic force in the X direction is: ； The expression for the resultant electromagnetic force in the Y direction is: ； in, It is half the angle between the two magnetic poles of the electromagnetic bearing. The permeability of free space, , These are the air gap cross-sectional areas of the upper and lower magnetic pole pairs, respectively. , These are the number of turns of the upper and lower windings, respectively. For bias current, , To control the current, , This represents the rotor displacement.

4. The design method for an asymmetric radial electromagnetic bearing according to claim 2, characterized in that: In step (3), the number of turns of the winding coil for each magnetic pole pair is calculated using the following formula: ； in, For the first The actual maximum load-bearing capacity of a single magnetic pole pair For the corresponding air gap cross-sectional area, This represents the maximum current in the coil.

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