CN100381720C - A Design Method of Permanent Magnetic Bias Inner Rotor Radial Hybrid Magnetic Bearing - Google Patents

Abstract

A design method for a radial hybrid magnetic bearing with a permanent magnet biased inner rotor. The method takes the displacement stiffness of the radial hybrid magnetic bearing with a permanent magnet biased inner rotor as the starting point, and takes the maximum bearing capacity, saturation magnetic density, and slot fullness as the starting point. Compared with the existing magnetic bearing design method targeting at the best working point of the permanent magnet, this method is more conducive to the control of the magnetic bearing, and the size of the obtained permanent magnet is more reasonable. This method is accurate High precision, simple and feasible, and its design concept can be used in the design of various permanent magnet bias inner rotor radial hybrid magnetic bearings.

Description

A Design Method of Permanent Magnetic Bias Inner Rotor Radial Hybrid Magnetic Bearing

technical field

The invention relates to a design method of a non-contact magnetic suspension bearing, in particular to a design method of a permanent magnetic bias inner rotor radial hybrid magnetic bearing for a magnetic suspension flywheel, a magnetic suspension control moment gyroscope, and other devices that require magnetic suspension support. As a design for various types of permanent magnet bias inner rotor radial hybrid magnetic bearings.

Background technique

Magnetic suspension bearings are divided into pure electromagnetic bearings and hybrid magnetic suspension bearings with permanent magnetic bias and electromagnetic control. The former uses large current and consumes a lot of power, and the hybrid magnetic suspension bearings with permanent magnetic bias and electromagnetic control. The magnetic field generated by the permanent magnet bears the main load. Bearing capacity, the electromagnetic field provides auxiliary adjustment bearing capacity, so this kind of bearing can greatly reduce the control current and reduce the loss. The commonly used magnetic bearing control method adopts the traditional PID control method. The controller parameters to realize this method are determined by the bearing stiffness and damping. After a lot of practice, it has been proved that in order to make the magnetic bearing have excellent characteristics, the bearing stiffness should be matched with the The displacement stiffness is on the same order of magnitude, so the displacement stiffness of the magnetic bearing is crucial for the control of the magnetic bearing. The existing magnetic bearing design methods all use the best working point of the permanent magnet to design, the purpose is to minimize the volume of the permanent magnet, but the size of the permanent magnet calculated by this method will be small, and the processing will be very difficult. The method does not consider the influence of the displacement stiffness on the control system, so the existing design methods have the defects of poor accuracy and unfavorable control. What needs to be explained here is that the design ideas of the inner rotor magnetic bearing and the outer rotor magnetic bearing are different. For the inner rotor structure, the idea is to design the magnetic bearing rotor assembly first, and then design the stator assembly (including the permanent magnet); for the outer rotor magnetic Bearings, first design the magnetic bearing stator assembly, and then design the magnetic bearing rotor assembly (including permanent magnets), and the magnetic circuit structure of the inner rotor radial hybrid magnetic bearing and the outer rotor magnetic bearing with different structures is completely different, so it cannot be simple The design method of outer rotor magnetic bearing is applied to the design of inner rotor magnetic bearing.

Contents of the invention

The technical problem of the present invention is to overcome the deficiencies of the prior art, and provide a design method of a permanent magnetic bias inner rotor radial hybrid magnetic bearing.

The technical solution of the present invention is: a design method of a permanent magnet bias inner rotor radial hybrid magnetic bearing, which needs to determine: the radial outer height D _s1 of the stator core, the inner diameter D _s2 of the stator core, and the radial outer height H of the stator slot , stator core width b _s , stator core axial length L _sfe , rotor core outer diameter D _r1 , rotor core axial length L _rfe , permanent magnet outer diameter D _pm1 (rotor core inner diameter D _r2 ), permanent magnet axial length h _pm , the notch width L _c and the number of turns N of the coil.

Its characteristic is that the method is based on the displacement stiffness of the magnetic bearing, and its specific steps are as follows:

(1) Set the rotor speed n and the maximum bearing capacity F _max according to the index requirements of the required magnetic suspension support device, set the static levitation current i according to the power consumption requirements, and set the air gap length δ and laminations according to the existing processing level Coefficient K _fe , set the displacement stiffness K _x of the magnetic bearing according to the requirements of the existing magnetic bearing controller, set the magnetic leakage coefficient σ according to the magnetic field analysis, and set the saturation flux density B _s of the core according to the magnetization characteristics of the selected core material ;

(2) Determine the inner diameter of the permanent magnet D _pm2 according to the rotor speed and the strength of the material;

(3) Determine the cross-sectional area A of the stator core according to the maximum bearing capacity F _max , the saturation magnetic density B _s and the lamination coefficient K _fe ;

(4) Determine the proportional relationship between the stator core width b _s and the axial length L _sfe of the stator core according to actual requirements, and then determine the stator core width b _s , the axial length L _sfe of the stator core, and the axial length L _ref of the rotor core;

(5) Based on the analysis of the magnetic circuit, the magnetic density of each part of the stator and rotor cores is reasonably distributed, and the thickness h _rfe of the yoke of the rotor core is calculated;

(6) According to the magnetic air gap length δ between the stator and rotor, determine the axial length h _pm of the permanent magnet and the slot width L _c ;

(7) Calculate the outer diameter D _pm1 of the permanent magnet (that is, the inner diameter D _r2 of the rotor core) according to the displacement stiffness K _x , and then determine the current stiffness K _i in combination with the rotor gravity G, and determine the diameter d of the coil wire by the current density J and the static levitation current i _c ;

(8) Determine the outer diameter D _r1 of the rotor core according to the thickness h _rfe of the yoke of the rotor core, and determine the inner diameter D _r2 of the stator core by the air gap length δ;

(9) Determine the radial outer height H of the stator slot according to the slot fullness requirement, and then determine the radial outer height D _s1 of the stator core;

(10) Determine the number of coil turns N according to the current stiffness K _i .

The value range of the displacement stiffness is determined by the controller, which is -0.5N/um～-3N/um; the air gap length δ is 0.15～0.35mm; the magnetic leakage coefficient σ is 1.1 ~ 3; the lamination coefficient K _fe is obtained by the ratio of the actual stator or rotor core weight to its theoretically calculated value, and is taken as 0.75 ~ 0.95; the stator core width b _s and the stator core axial length L _sfe The proportional relationship is determined by actual requirements. If the magnetic bearing requires a short axial length, the proportional value is 4-6; otherwise, the proportional value is 1-3; the slot fullness rate is 40%-60%.

The principle of the present invention is: the present invention starts with the displacement stiffness of the radial hybrid magnetic bearing for design, sets various parameters according to requirements, and through the magnetic circuit analysis and calculation of this type of magnetic bearing, other structural dimensions of the magnetic bearing can be obtained. According to the set rotor speed n and the strength requirements of the material, the permanent magnet inner diameter D _pm2 can be obtained, and the stator core cross-sectional area A is determined by the following formula according to the maximum bearing capacity F _max , saturation flux density B _s and lamination coefficient K _fe .

$\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="s"\; filenames="C20061011426900091.png"\; state="\{\{state\}\}">s</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; fe</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, μ ₀ =4π×10 ^-7 H/m, which is the magnetic permeability of air.

Set the ratio of the width b _s of the stator core to the axial length L _{sfe of} the stator core as C, then the width b _{s of} the stator core and the axial length L _sfe of the stator core are:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; sfe</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; A</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

b _s ＝C·L _sfe (3)

In order to avoid the magnetic pull caused by the misalignment of the stator and rotor core axes, the axial length L _rfe of the rotor core can be taken as:

L _rfe =1.15·L _sfe (4)

According to the magnetic circuit analysis, the magnetic density of each part of the stator and rotor cores is reasonably distributed, and the thickness h _rfe of the yoke of the rotor core is calculated as:

${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; rfe</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="A"\; filenames="C20061011426900091.png"\; state="\{\{state\}\}">A</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; rfe</span>}}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

The coefficient 3 in the formula is to consider that the yoke of the stator core mainly passes through the electric excitation flux and does not pass through the permanent magnet flux. When the magnetic bearing bears the maximum bearing capacity, the electric excitation flux is generally 1/3 of the permanent magnet flux.

According to the set magnetic air gap length δ between the stator and rotor, the axial length h _pm of the permanent magnet and the slot width L _c can be obtained as:

h _pm =K ₁ ·δ (6)

L _c =K ₂ ·h _pm (7)

In the formula, K ₁ and K ₂ are constants, whose values are taken according to experience.

According to the displacement stiffness K _x , the outer diameter D _pm1 of the permanent magnet (that is, the inner diameter D _r2 of the stator core) can be obtained as:

${\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; pm</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; pm</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; pm</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="D.\; pm"\; filenames="C20061011426900091.png"\; state="\{\{state\}\}">D.</figure-callout></span><figure-callout\; id="2"\; label="D.\; pm"\; filenames="C20061011426900091.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}^{\mathrm{<span\; class="notranslate">pm</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

In the formula: $C_1=\frac{\sqrt{-\frac{{\mathrm{<figure-callout\; id="2"\; label="f\; pm"\; filenames="C20061011426900091.png"\; state="\{\{state\}\}">f</figure-callout>}}_{\mathrm{pm}}^{}\&Center\; Dot;{\mathrm{\&mu;}}_0\&Center\; Dot;A}{K_x\&Center\; Dot;{\mathrm{\&sigma;}}^2\&Center\; Dot;\mathrm{\&delta;}}}-\mathrm{\&delta;}}{2\&Center\; Dot;{\mathrm{\&mu;}}_0\&Center\; Dot;A}---\left(9\right)$

Where F _pm = H _pm h _pm is the magnetomotive force of the permanent magnet, H _pm is the coercive force of the permanent magnet, generally 760kA/m ~ 790kA/m; μ _pm is the relative permeability of the permanent magnet, generally taken as 1.03 to 1.05.

Combined with the rotor gravity G, the current stiffness K _i can be obtained:

${\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; x</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

In the formula, x is the offset between the rotor center and the magnetic center during static levitation.

The diameter d _c of the coil wire is determined by the current density J and the static levitation current i as:

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; J</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

Then take the value according to the national standard.

Determine the radial outer height H of the stator slot according to the slot fullness requirement, and then determine the radial outer height D _s1 of the stator core as:

D _s1 =D _st +2·L _sfe (12)

According to the current stiffness K _i , the number of coil turns N can be obtained as:

$\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; pmsum</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; pm</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; pmsum</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; pm</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

In the formula: R _pm is the reluctance of the permanent magnet, and R _pmsum is the total reluctance of the permanent magnet magnetic circuit.

So far, the design of the radial hybrid magnetic bearing of the entire permanent magnet biased inner rotor is completed.

Compared with the prior art, the present invention has the advantages that: the present invention adopts the design method based on the displacement stiffness of the radial hybrid magnetic bearing, which is different from that of the existing inner rotor radial hybrid magnetic bearing based on the optimum working point of the permanent magnet. Compared with the design method, it is more conducive to control and the obtained parameters are more reasonable.

Description of drawings

Fig. 1 is the structural diagram of the permanent magnetic bias inner rotor radial hybrid magnetic bearing aimed at by the present invention;

Fig. 2 is the design flowchart of the present invention;

Fig. 3 is a physical diagram of the permanent magnet bias inner rotor radial hybrid magnetic bearing designed according to the present invention, wherein (a) is the stator assembly of the inner rotor radial magnetic bearing, and (b) is the rotor of the inner rotor radial magnetic bearing components.

Detailed ways

As shown in Figure 1, the design object of the present invention is a permanent magnetic bias inner rotor radial hybrid magnetic bearing for a magnetic levitation control moment gyroscope, in which 1 is a magnetic ring, 2 is a permanent magnet, 3 is a rotor core, 4 is the magnetic air gap between the stator and rotor, 5 is the coil, and 6 is the stator core. According to the requirements of the existing magnetic bearing controller, the displacement stiffness K _x of the magnetic bearing is set to -0.8N/um, and the rotor speed n is set to 30000r/min according to the requirements of the magnetic levitation control torque gyro index, and then the permanent is set by the material strength The magnet inner diameter D _pm2 is 19mm, the air gap length δ is set to 0.2mm according to the existing processing level, the lamination coefficient K _fe is 0.85, the magnetic leakage coefficient σ is set to 1.2 according to the magnetic field analysis of the magnetic bearing, and according to the magnetic levitation control The index requirements of the torque gyroscope set the maximum bearing capacity _Fmax to 108.7N, and set the static levitation current i to 0.2A according to the power consumption requirements of the magnetic levitation control torque gyroscope. In this embodiment, the stator and rotor cores of the magnetic bearings use iron-nickel Soft magnetic alloy 0.1mm thick 1J50, according to the magnetization curve of 1J50, the saturation magnetic density B _s is determined to be 1.2T. According to the off-line level of the existing coils, the full rate of the stator slot is set to 40%.

According to the above conditions, the cross-sectional area of the stator core A = 111.6mm ² can be calculated from formula (1), and the ratio of the width b _s of the stator core to the axial length L _sfe of the stator core is set to C = 2.5, then the formula (2) and (3) It can be obtained that the width of the stator core b _s = 15mm, the axial length of the stator core L _sfe = 6mm, the axial length of the rotor core L _rfe = 7mm can be obtained from the formula (4), and the rotor core can be obtained from the formula (5) Thickness of the yoke h _rfe = 2.7mm, set K ₁ = 24, K ₂ = 2, from equations (6) and (7), the axial length of the permanent magnet h _pm = 4.8mm, the slot width L _c = 9.6mm , from equations (8) and (9), the outer diameter of the permanent magnet D _pm1 = 28.2mm, considering the offset x = 0.1mm between the rotor center and the magnetic center after the general magnetic bearing is statically levitated, it can be obtained from (10) The current stiffness K _i =119.8N/A, the diameter of the coil wire d _c =0.356mm can be obtained from formula (11), which is taken as 0.35mm, and the radial outer side of the stator slot can be obtained after the program cycle according to the set slot full rate Height H=52mm, the stator core radial outer height D _s1 =64mm can be obtained from formula (12), and the number of coil turns N=87 can be obtained from formula (13). So far, the permanent magnetic bias inner rotor radial hybrid magnetic bearing has been designed.

The contents not described in detail in the description of the present invention belong to the prior art known to those skilled in the art.

Claims (7)

1. the design method of a permanent magnet bias inner rotor radial mixed magnetic bearing, it is characterized in that: this method is based on the displacement rigidity of magnetic bearing, and its concrete steps are as follows:

(1) the displacement rigidity K of setting magnetic bearing _x, rotor speed n, gap length δ, leakage coefficient σ, lamination COEFFICIENT K _Fe, maximum load capacity F _Max, static suspension current i and saturation magnetic induction B unshakable in one's determination _s

(2) determine the permanent magnet inside diameter D according to the intensity of rotor speed n and material _Pm2

(3) according to maximum load capacity F _Max, saturation magnetic induction B _sAnd lamination COEFFICIENT K _FeDetermine stator core sectional area A;

(4) require to determine stator core width b according to reality _sWith the stator core axial length L _SfeProportionate relationship, and then definite stator core width b _s, the stator core axial length L _SfeAnd rotor core axial length L _Rfe

(5) by the magnetic circuit analysis, distribute stator and rotor each several part magnetic unshakable in one's determination close, calculate rotor core yoke portion thickness h _Rfe

(6) according to the magnetic air gap length δ between the rotor, determine permanent magnet axial length h _PmAnd width of rebate L _c

(7) according to displacement rigidity K _xCalculate the permanent magnet outer diameter D _Pm1, determine current stiffness K in conjunction with rotor gravity G again _i, determine the diameter d of winding wire by current density, J and static suspension current i _c

(8) according to rotor core yoke portion thickness h _RfeDetermine the rotor core outer diameter D _R1, determine frame bore D by gap length δ _S2

(9) require to determine stator slot radial outside height H according to copper factor, and then definite stator core radial outside height D _S1

(10) according to current stiffness K _iDetermine turn number N.

2. the design method of a kind of permanent magnet bias inner rotor radial mixed magnetic bearing according to claim 1 is characterized in that: described displacement rigidity span determines by controller, be taken as-0.5N/um～-3N/um.

3. the design method of a kind of permanent magnet bias inner rotor radial mixed magnetic bearing according to claim 1, it is characterized in that: described gap length δ is taken as 0.15～0.35mm.

4. the design method of a kind of permanent magnet bias inner rotor radial mixed magnetic bearing according to claim 1, it is characterized in that: described leakage coefficient σ is taken as 1.1～3.

5. the design method of a kind of permanent magnet bias inner rotor radial mixed magnetic bearing according to claim 1 is characterized in that: described lamination COEFFICIENT K _FeBe that ratio by actual stator or rotor core weight and its calculated value obtains, be taken as 0.75～0.95.

6. the design method of a kind of permanent magnet bias inner rotor radial mixed magnetic bearing according to claim 1 is characterized in that: described stator core width b _sWith the stator core axial length L _SfeProportionate relationship require to determine that by reality if magnetic bearing requires axial length short, then this ratio value is taken as 4～6, otherwise this ratio value is taken as 1～3.

7. the design method of a kind of permanent magnet bias inner rotor radial mixed magnetic bearing according to claim 1, it is characterized in that: described copper factor is taken as 40%～60%.

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