Permanent magnet motor and design method

Abstract

The invention provides a permanent magnet motor and a design method. Comprising the following steps of: preparing a material of a stator core / rotor permanent magnet and the initial number of turns of a stator winding, generating a magnetization curve ps2-i2 of the stator winding when a rotor angle is an electric rotation angle theta0, judging that i2N is greater than or equal to i2bo, determining the initial magnetic steel thickness, generating a magnetization curve of the stator winding when a rotor angle is theta1, determining an electromagnetic torque # imgabs0 # under a rated current i2N of the stator winding, judging that TemN is greater than or equal to TemN, and the like. According to the design method, the magnitude of the electromagnetic torque is correspondingly converted into the magnitude of the magnetic co-energy area difference value (under the same fixed tiny corner difference), and the electromagnetic torque can be visually and clearly reflected from the geometric area.

Description

Technical Field

[0001] The invention relates to a permanent magnet motor and a design method thereof, belonging to the technical field of permanent magnet motor design. Background Art

[0002] The main components of a permanent magnet motor are the stator (including the stator core and the stator winding wound thereon) and the rotor permanent magnet (magnetic steel). When designing a permanent magnet motor, its electromagnetic torque characteristics (the relationship between the electromagnetic torque and the stator winding current, also known as the torque coefficient) are important design indicators. Therefore, the electromagnetic torque is crucial in the design.

[0003] There are two main methods for analyzing electromagnetic torque characteristics in the prior art: Maxwell tensor analysis and virtual displacement principle. The Maxwell tensor analysis method obtains electromagnetic torque by solving the path integral equation of magnetic induction intensity; the virtual displacement principle obtains electromagnetic torque by solving the partial differential equation of magnetic storage energy (or magnetic common energy) to the motor rotor angle.

[0004] In the existing permanent magnet motor design, the permanent magnet motor is optimized by finite element modeling of the magnetic steel thickness, the number of stator winding turns, etc., and by simulating the model (the basis of the simulation is the integral equation based on the above-mentioned Maxwell tensor analysis method or the partial differential equation based on the virtual displacement principle method). The accuracy of the magnetic steel thickness model directly affects the accuracy of the design. At the same time, the models such as the magnetic steel thickness are complex and the simulation calculation amount is large. Especially when the magnetic steel thickness is parameterized and the electromagnetic torque characteristics of the motor are solved, it is necessary to solve the above-mentioned integral equation or differential equation many times (that is, each magnetic steel thickness value needs to calculate the equation, and this is only for one current, and the current parameterization solution must be performed under different currents), the number of iterations is numerous, and the calculation amount is huge. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a permanent magnet motor and design method that is intuitive, clear, and easy to calculate.

[0006] The technical solution of the present invention is a permanent magnet motor design method, comprising the following steps:

[0007] The first step is to determine the material of the stator core, the initial number of turns of the stator winding, and the material of the rotor permanent magnet;

[0008] The second step is to generate the magnetization curve Ψ2-i2 of the stator winding when the rotor angle is the electrical angle θ0 according to the stator core material and the number of turns of the stator winding, where Ψ2 is the full magnetic flux of the stator winding and i2 is the stator winding current;

[0009] The third step is to determine the rated current i of the stator winding 2N The stator winding current i corresponding to the inflection point of the magnetization curve in the second step 2boThe size of i 2N ≥i 2bo , then adjust the number of stator winding turns, return to step 2, and repeat steps 2 and 3 until i is satisfied 2N <i 2bo , go to step 4;

[0010] Step 4: Determine the initial magnetic steel thickness;

[0011] The fifth step is to generate the magnetization curve Ψ′2-i2 of the stator winding when the rotor angle is θ1 according to the magnetic steel thickness and the number of turns determined in the third step, where Ψ′2 is the full magnetic flux of the stator winding when the rotor angle is θ1, and θ1≠θ0;

[0012] Step 6: Determine the stator winding rated current i according to the magnetization curves Ψ2-i2 and Ψ′2-i2 2N Electromagnetic torque under Where ΔW m ′ is the difference in magnetic energy, ΔW m ' is the magnetization curve Ψ2-i2, Ψ'2-i2, the ordinate and the numerical axis i2=i 2N The area enclosed;

[0013] Step 7: Compare the electromagnetic torque Tem obtained in step 6 with the rated electromagnetic torque Tem under the rated current of the stator winding. N Compare, if Tem≥Tem N Then determine the number of turns and magnetic steel thickness to complete the design.

[0014] A permanent magnet motor obtained by adopting any of the above-mentioned design methods.

[0015] The beneficial effects of the present invention compared with the prior art are as follows:

[0016] (1) The design method of the present invention converts the magnitude of the electromagnetic torque into the magnitude of the magnetic common energy area difference (under the same fixed small rotation angle difference), and the electromagnetic torque can be intuitively and clearly reflected from the geometric area;

[0017] (2) The design method of the present invention determines the starting point of motor design (determination of the starting saturation current) by making the inflection point of the difference in magnetic common energy area and the inflection point of the magnetization curve, i.e., the magnetic flux-current curve, correspond to the starting saturation current, thereby greatly reducing the amount of design calculations and simplifying the design calculations of the motor;

[0018] (3) The present invention provides a graphical method for determining the electromagnetic torque, which is intuitive and clear. The electromagnetic torque can be determined without the need for detailed and complex calculations (integral equation operations or differential equation operations), which greatly simplifies the design calculations of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of the present invention;

[0020] Figure 2 is the magnetization curve of the example of the present invention (the rotor angle is θ0);

[0021] Figure 3 Schematic diagram of the rated current and inflection point current of the stator winding in the magnetization curve (rotor angle is θ0) of the example of the present invention;

[0022] Figure 4 is the magnetization curve of the example of the present invention (the rotor angles are θ0 and θ1 respectively);

[0023] Figure 5 The stator winding rated current i is the magnetization curve of the present invention (the rotor angles are θ0 and θ1 respectively). 2N Schematic diagram of the corresponding electromagnetic torque;

[0024] Figure 6 The stator winding current is i under the magnetization curve of the present invention (the rotor angles are θ0 and θ1 respectively). 2b1 The corresponding ΔW m ′;

[0025] Figure 7 The stator winding current is i under the magnetization curve of the present invention (the rotor angles are θ0 and θ1 respectively). 2b2 The corresponding ΔW m ′. DETAILED DESCRIPTION

[0026] The present invention is described in detail below with reference to specific examples and accompanying drawings.

[0027] The present invention Figure 1 As shown, a permanent magnet motor design method is provided, comprising the following steps:

[0028] The first step is to determine the material of the stator core and the initial number of turns of the stator winding as well as the material of the rotor permanent magnets.

[0029] In this step, the stator core material is selected from existing conventional stator core materials, such as silicon steel, etc. The initial number of turns of the stator winding can refer to the number of turns of existing similar permanent magnet motors. The specific value of the initial number of turns has no effect on the subsequent design.

[0030] In this step, the material of the rotor permanent magnet is selected from existing conventional rotor materials, such as SmCo26, NdFeB, etc.

[0031] The second step is to generate the magnetization curve Ψ2-i2 of the stator winding when the rotor angle is the electrical angle θ0 according to the stator core material and the number of turns of the stator winding, where Ψ2 is the full magnetic flux of the stator winding and i2 is the stator winding current.

[0032] Furthermore, in this step, the total magnetic flux density of the stator winding is Ψ2 = N*Φ 2s , where N is the number of stator winding turns, Φ 2s is the magnetic flux generated by the single-turn stator winding current i2, which is a known value.

[0033] Furthermore, in this step, the position where the N magnetic pole of the rotor permanent magnet is orthogonal to the center line of the stator winding is the electrical rotation angle θ0 (corresponding to the maximum output position of the motor torque angle characteristic).

[0034] like Figure 2 As shown, this example provides a magnetization curve Ψ2-i2, i when the rotor angle is the electrical angle θ0. 2bo is the stator winding current corresponding to the inflection point of the magnetization curve.

[0035] The third step is to determine the rated current i of the stator winding 2N The stator winding current i corresponding to the inflection point of the magnetization curve in the second step 2bo The size of i 2N ≥i 2bo , then adjust the number of stator winding turns, return to step 2, and repeat steps 2 and 3 until i is satisfied 2N <i 2bo , go to step 4.

[0036] Furthermore, in this step, if i 2N ≥i 2bo , then increase the number of stator winding turns, return to step 2, and repeat steps 2 and 3 until i is satisfied 2N <i 2bo , go to step 4.

[0037] Further preferably, in this step, if i 2N <i 2bo , determine the stator winding current difference Δi2, Δi2 = i 2bo -i 2N , if Δi2≤k*i 2N , k is the stator winding current difference coefficient, then go directly to step 4. If Δi2≤k*i is not satisfied 2N , then reduce the number of stator winding turns, return to step 2, and repeat steps 2 and 3 until Δi2≤k*i is satisfied 2N Preferably, k∈(0,0.5], more preferably, k∈(0,0.1].

[0038] like Figure 3 As shown, in this example, the stator winding rated current i 2N The stator winding current i corresponding to the inflection point of the magnetization curve 2bo The difference Δi2 is too large, so the number of stator winding turns should be reduced to make the stator winding rated current i 2NThe stator winding current i corresponding to the inflection point of the magnetization curve 2bo Try to be as close as possible to avoid waste due to too large a design margin.

[0039] In this step, the inflection point of the magnetization curve, ie, the magnetic flux-current curve, is made to correspond to the initial saturation current, and the number of turns is limited by the inflection point of the magnetization curve, thereby reducing the number of iterations and the amount of calculation of the motor design.

[0040] The fourth step is to determine the initial magnetic steel thickness.

[0041] The initial magnetic steel thickness in this step can refer to the existing magnetic steel thickness of similar permanent magnet motors, and the specific value of the initial magnetic steel thickness has no effect on the subsequent design.

[0042] The fifth step is to generate the magnetization curve Ψ′2-i2 of the stator winding when the rotor angle is θ1 according to the magnetic steel thickness and the number of turns determined in the third step, where Ψ′2 is the full magnetic coil of the stator winding when the rotor angle is θ1, and θ1≠θ0.

[0043] Furthermore, in this step, the total magnetic flux density of the stator winding is Ψ′2=N*Φ 2s +Ψ 21 , where N is the number of stator winding turns, Φ 2s is the magnetic flux generated by the single-turn stator winding current i2, which is a known value, Ψ 21 is the mutual inductance flux generated by the rotor winding current i1 on the stator winding, which is related to the rotor angle θ1 and the rotor winding current i1. The specific calculation method is a well-known technology in the art. When the rotor angle is the electrical angle θ0, Ψ 21 =0.

[0044] In this step, the magnetic steel can be equivalent to the rotor winding current, and the magnetic steel thickness is proportional to the rotor winding current. This is the conventional theory of electrical engineering.

[0045] Furthermore, in this step, the value of the rotor angle difference Δθ=|θ1-θ0| is not greater than 0.2°; the preferred value range is 0.05° to 0.1°.

[0046] like Figure 4 As shown, in this example, a magnetization curve with a Δθ of 0.05° and rotor angles of θ0 and θ1 is provided.

[0047] Step 6: Determine the stator winding rated current i according to the magnetization curves Ψ2-i2 and Ψ′2-i2 2N Electromagnetic torque under Where ΔW m ′ is the difference in magnetic energy, ΔW m ' is the magnetization curve Ψ2-i2, Ψ'2-i2, the ordinate and the numerical axis i2=i 2N The enclosed area.

[0048] In this step, the rotor angle difference Δθ=|θ1-θ0|, and the magnetic energy difference between the two positions is ΔW′, which is equal to Figure 5 The shaded area.

[0049] The present invention uses difference instead of differential, and the approximate Δθ=|θ1-θ0| is a fixed value, so the electromagnetic torque Tem is Figure 5 The shaded area (magnetic energy difference ΔW m ′).

[0050] And from Figure 5 It can be clearly seen that as long as the stator winding current is less than the initial saturation current (inflection point of the magnetization curve), that is, when the magnetic circuit is not saturated, as the stator winding current increases, the electromagnetic torque increases in direct proportion to the stator winding current. When the initial saturation current value is exceeded, the two currents i under the saturation current are compared. 2b2 and i 2b1 The corresponding magnetic energy difference ΔW m ′(respectively Figure 7 and Figure 6 The difference between the two is very small. That is to say, as the stator winding current increases, the electromagnetic torque increases very slowly. In other words, to increase Tem, a large amount of stator winding current needs to be increased.

[0051] Step 7: Compare the electromagnetic torque Tem obtained in step 6 with the rated electromagnetic torque Tem under the rated current of the stator winding. N Compare, if Tem≥Tem N Then determine the number of turns and magnetic steel thickness to complete the design.

[0052] Furthermore, if Tem≥Tem is not satisfied in this step, N , then adjust (increase) the magnetic steel thickness, repeat steps 5 to 7 until Tem≥Tem is satisfied N .

[0053] Furthermore, the present invention also provides a permanent magnet motor obtained by adopting the above-mentioned design method.

[0054] Parts of the present invention that are not described in detail are well known to those skilled in the art.

Claims

1. A permanent magnet motor design method, characterized in that: The following steps are involved: The first step is to determine the material of the stator core, the initial number of turns of the stator winding, and the material of the rotor permanent magnet; The second step is to generate the magnetization curve Ψ2-i2 of the stator winding when the rotor angle is the electrical angle θ0 according to the stator core material and the number of turns of the stator winding, where Ψ2 is the full magnetic flux of the stator winding and i2 is the stator winding current; The third step is to determine the rated current i of the stator winding 2N The stator winding current i corresponding to the inflection point of the magnetization curve in the second step 2bo The size of i 2N ≥i 2bo , then adjust the number of stator winding turns, return to step 2, and repeat steps 2 and 3 until i is satisfied 2N <i 2bo , go to step 4; Step 4: Determine the initial magnetic steel thickness; The fifth step is to generate the magnetization curve Ψ′2-i2 of the stator winding when the rotor angle is θ1 according to the magnetic steel thickness and the number of turns determined in the third step, where Ψ′2 is the full magnetic flux of the stator winding when the rotor angle is θ1, and θ1≠θ0; Step 6: Determine the stator winding rated current i according to the magnetization curves Ψ2-i2 and Ψ′2-i2 2N Electromagnetic torque under Where ΔW m ′ is the difference in magnetic energy, ΔW m ' is the magnetization curve Ψ2-i2, Ψ'2-i2, the ordinate and the numerical axis i2=i 2N The area enclosed; Step 7: Compare the electromagnetic torque Tem obtained in step 6 with the rated electromagnetic torque Tem under the rated current of the stator winding. N Compare, if Tem≥Tem N Then determine the number of turns and magnetic steel thickness to complete the design.

2. A permanent magnet motor design method according to claim 1, characterized in that: In the third step, if i 2N ≥i 2bo , then increase the number of stator winding turns, return to step 2, and repeat steps 2 and 3 until i is satisfied 2N <i 2bo , go to step 4.

3. A permanent magnet motor design method according to claim 2, characterized in that: In the third step, if i 2N <i 2bo , determine the stator winding current difference Δi2, Δi2 = i 2bo -i 2N , if Δi2≤k*i 2N , k is the stator winding current difference coefficient, then go directly to step 4. If Δi2≤k*i is not satisfied 2N , then reduce the number of stator winding turns, return to step 2, and repeat steps 2 and 3 until Δi2≤k*i is satisfied 2N , where k∈(0,0.5].

4. A permanent magnet motor design method according to claim 3, characterized in that: In the third step, k∈(0,0.1].

5. A permanent magnet motor design method according to claim 3, characterized in that: If Tem≥Tem is not satisfied in the seventh step N , then increase the thickness of the magnetic steel and repeat steps 5 to 7 until Tem≥Tem is satisfied N .

6. A permanent magnet motor design method according to claim 5, characterized in that: In the second step, the total magnetic flux density of the stator winding is Ψ2 = N*Φ 2s , where N is the number of stator winding turns, Φ 2s is the magnetic flux generated by the single-turn stator winding current i2; In the fifth step, the total magnetic flux density of the stator winding is Ψ′2=N*Φ 2s +Ψ 21 ,Ψ 21 is the mutual inductance flux generated by the rotor winding current i1 on the stator winding. When the rotor angle is the electrical angle θ0, Ψ 21 =0.

7. A permanent magnet motor design method according to claim 6, characterized in that: In the second step, the position of the rotor permanent magnet N pole when it is orthogonal to the stator winding center line is the electrical angle θ0, which corresponds to the maximum output position of the motor torque angle characteristic; on the magnetization curve Ψ2-i2 with the rotor angle being the electrical angle θ0, i 2bo is the stator winding current corresponding to the inflection point of the magnetization curve, which approximately corresponds to the initial saturation current.

8. A permanent magnet motor design method according to claim 3, characterized in that: The value of the rotor angle difference Δθ=|θ1-θ0| in the fifth step is not greater than 0.2°.

9. A permanent magnet motor design method according to claim 8, characterized in that: In the fifth step, the rotor angle difference Δθ=|θ1-θ0| ranges from 0.05° to 0.1°.

10. A permanent magnet motor obtained by using the design method described in any one of claims 1 to 9.

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