CN106160388B - A kind of Low gullet torque brshless DC motor optimization method - Google Patents

Abstract

The invention discloses a method for optimizing a brushless DC motor with low cogging torque, which adopts an arc structure notch as the stator structure of the optimized slot to form a motor; and the rotor structure type adopts tile magnetic steel radially punching magnets; specifically includes Step 1, select n sets of pole-slot coordination according to the design index; Step 2, calculate the power P _i ′; Step 3, calculate the inner diameter of the armature; Step 4, calculate the length of the armature iron core and other steps, the present invention can reduce the cogging torque.

Description

A low cogging torque brushless DC motor optimization method

technical field

The invention relates to an optimization method for a brushless DC motor with low cogging torque.

technical background

The cogging torque is the reluctance torque generated by the interaction between the stator cogging and the rotor permanent magnet. The cogging torque causes speed fluctuation, motor vibration and noise, and increases the initial starting torque of the motor, thus reducing the cogging torque. Torque is one of the main goals in brushless DC motor design. The amplitude of the fundamental cogging torque of the brushless DC motor is related to the least common multiple of the number of stator slots Z and the number of poles 2p. Therefore, the amplitude of the cogging torque of different pole slots is different. How to optimize the cogging torque? Pole-slot coordination with large slot torque amplitude plays an important role in improving the performance of brushless DC motors.

The existing technology usually adopts the method of stator skew or rotor magnetic pole skew. Practice shows that this method can reduce the cogging torque to a certain extent, but the stator skew and rotor skew increase the difficulty of stator and rotor processing and will reduce the The slot fullness of the stator reduces the output electromagnetic torque of the motor, which is not conducive to the improvement of the power density of the motor.

Contents of the invention

purpose of invention

The purpose of the present invention is to provide a low cogging torque brushless direct current motor optimization method, which can reduce the cogging torque of the brushless direct current motor.

Technical solutions

The invention relates to an optimization method for a brushless DC motor with low cogging torque, wherein arc-shaped slots are used as the stator structure of the optimized groove-formed motor;

A method for optimizing a brushless DC motor with low cogging torque as described above, which specifically includes the following steps:

Step 1. Select n sets of pole-slot coordination according to the design index, n is the specified number of sets; among them, the number of motor slots Z _i , the number of motor poles 2p _i , i≤n; find the least common multiple LCM _i of Z _i and 2p _i , Select the largest LCM _i , and obtain the number of motor slots Z _i and the number of motor poles 2p _i , then the final number of slots Z=Z _i , and the final number of poles 2p=2p _i ;

Step 2. Calculate the power P′ _i . If the motor runs for a long time, then If the motor is running for a short time, then Among them, P _N is the rated power of the motor, and η' is the prefetch efficiency of the motor;

Step 3. Calculate the inner diameter of the armature B' _δ is the prefetching air gap magnetic density, A' _δ is the prefetching line load, α _i is the prefetching calculation pole arc coefficient, λ' is the prefetching length-to-diameter ratio, and the outer diameter of the armature satisfies: D ₁ >D _il , n _N motor rated speed;

Step 4. Calculate the armature core length L≈λ′D _i1 ;

Step 5. Select the slot type, take the slot width b ₀₁ ≤1mm, and specify other structural parameters: slot depth h ₀₁ , slot shoulder width b _x1 , slot shoulder depth h _x1 ;

Step 6. Take the notch depth h _x1 as the base, make an isosceles triangle with an apex angle of 150°, and the apex of the isosceles triangle is located in the notch; draw a circle with the three vertices of the isosceles triangle as three points arc, forming an arc structure notch; using this structure as the optimized slot to form the stator structure of the motor;

Step 7. The structure type of the rotor adopts tile magnetic steel radial impact magnetization;

Step 8, calculating the outer diameter of the permanent magnet D _m =D _i1 -2δ, the inner diameter of the permanent magnet D _mi =D _m -2H _m , δ is the width of the air gap, and H _m is the thickness of the magnetization direction of the permanent magnet;

Step 9: Take the outer diameter D ₂ of the rotor tight ring, D _m < D ₂ < D _i1 ;

Step 10: Take the rotor magnetic steel length L _c =L to complete the optimization.

Beneficial effect

The method can reduce the cogging torque of the brushless DC motor.

Description of drawings

Figure 1 is a schematic diagram of the original groove structure;

Figure 2 is a schematic diagram of building an isosceles triangle with the depth of the notch as the base;

Fig. 3 is a schematic diagram of an arc structure notch;

Fig. 4 section view of motor stator and rotor;

Fig. 5 The cogging torque obtained without arc structure notches;

Fig. 6 The cogging torque obtained by using the arc structure notch.

Detailed ways

Hereinafter, the present invention will be further described in conjunction with the drawings and specific embodiments.

The invention is an optimization method for a brushless DC motor with low cogging torque, which uses an arc-shaped notch to realize the purpose of reducing the cogging torque.

Take the following motor as an example: the parameters of a brushless DC motor are rated voltage U _N = 48V, rated speed n _N = 800rpm, rated torque T _N = 2Nm, rated power P _N = 170W, long-term operation, here, Long-term operation refers to continuous operation time greater than 30 minutes.

Follow the steps below to optimize:

Step 1. Select N sets of pole-slot coordination according to the design index, among which the number of motor slots Z _i , the number of motor poles 2p _i , i≤n, find the least common multiple LCM _i of Z _i and 2p _i , and choose the largest LCM _i , then The final number of slots Z=Z _i , the final number of poles 2p=2p _i ;

According to the design parameters, the desirable pole-slot fits are: Z ₁ =12, 2p ₁ =8, LCM ₁ =24; Z ₂ =60, 2p ₂ =10, LCM ₂ =60; Z ₃ =45, 2p ₃ =12 , LCM ₃ =180; since LCM ₃ >LCM ₂ >LCM ₁ , then LCM ₃ is selected, Z=Z ₃ =45, 2p=2p ₃ =12.

Step 2. Calculate the power P′ _i . If the motor runs for a long time, then If the motor is running for a short time, then Among them, P _N is the rated power of the motor, and η' is the prefetch efficiency of the motor.

In this embodiment, the prefetch efficiency η'=0.85, the motor runs for a long time, and the calculated power

Step 3. Calculate the inner diameter of the armature B' _δ is the prefetching air gap flux density, A' _δ is the prefetching line load, α _i is the prefetching calculation pole arc coefficient, λ' is the prefetching length-to-diameter ratio, the outer diameter of the armature D ₁ >D _il , n _N Motor rated speed.

In this embodiment, the prefetch line load A' _s =14A/mm, the prefetch air gap magnetic density B' _δ =0.7T, the prefetch calculation pole arc coefficient α _i =1, and the prefetch aspect ratio λ'=0.4 , calculate the inner diameter of the armature Armature outer diameter D ₁ =90mm.

Step 4: Calculate the armature core length L≈λ′D _i1 . Armature core length L≈λ′D _i1 =28mm.

Step 5. Select the slot type, take the slot width b ₀₁ ≤ 1mm, and determine the slot depth h ₀₁ , slot shoulder width b _x1 , slot shoulder depth h _x1 and other structural parameters. The groove structure parameters are shown in Figure 1, here is a semi-pear-shaped groove with an open bottom, the groove width is 0.5mm, the groove depth is 0.5mm, the groove shoulder width is 2.8mm, and the groove shoulder depth is 0.7mm;

Step 6. Taking the depth h _x1 of the notch as the base, make an isosceles triangle with an apex angle of 150°, and the apex angle of the isosceles triangle is located in the notch. Draw an arc with the three vertices of the isosceles triangle as three points to form an arc-shaped structural notch. This structure is used as the optimized slot type to form the stator structure of the motor;

With the depth of the notch as the base, make an isosceles triangle with an apex angle of 150°, and the apex of the isosceles triangle is located in the notch, as shown in Figure 2. Draw an arc with the three vertices of the isosceles triangle as three points to form an arc-shaped structural notch, as shown in Figure 3. The groove shape formed by the arc structure notch is used as the stator groove shape of the motor.

Step 7. The structure type of the rotor adopts tile magnetic steel with radial impact magnetization.

Step 8, calculating the outer diameter of the permanent magnet D _m =D _i1 -2δ, the inner diameter of the permanent magnet D _mi =D _m -2H _m , δ is the width of the air gap, and H _m is the thickness of the magnetization direction of the permanent magnet;

Here, taking the air gap width δ=0.8mm, the outer diameter of the permanent magnet D _m =D _i1 -2δ=68.4mm. Assuming that the magnetization direction thickness of the permanent magnet is H _m =5 mm, then the inner diameter of the permanent magnet is D _mi =D _m -2H _m =58.4 mm.

Step 9: Take the outer diameter D ₂ of the tight ring of the rotor, D _m < D ₂ < D _i1 . Here, take the rotor tight ring outer diameter D ₂ =69mm;

Step 10: Take the rotor magnetic steel length L _c =L. Here, the rotor magnetic steel length L _c =L=28mm is taken.

The cross-sectional view of the stator and rotor of the motor is shown in Figure 4.

The finite element analysis is carried out on the model of notch motor without arc structure and the model of notch motor with arc structure, and the obtained cogging torques are shown in Fig. 5 and Fig. 6 respectively. It can be seen from the simulation results that the maximum cogging torque of the motor model with arc-shaped slots is 8mNm, and the maximum cogging torque of the motor model without arc-shaped slots is 13mNm. The results show that the arc structure notch optimization can reduce the cogging torque of brushless DC motor.

The above description does not limit the present invention, and various modifications and changes can be made without departing from the gist of the present invention.

Claims (1)

1. A low cogging torque brushless DC motor optimization method is characterized in that, adopting the arc-shaped structure notch as the stator structure of the motor after optimization; and the rotor structure type adopts the tile magnetic steel radial punch , including the following steps: Step 1. Select n sets of pole-slot coordination according to the design index, n is the specified number of sets; among them, the number of motor slots Z _i , the number of motor poles 2p _i , i≤n; find the least common multiple LCM _i of Z _i and 2p _i , Select the largest LCM _i , and obtain the number of motor slots Z _i and the number of motor poles 2p _i , then the final number of slots Z=Z _i , and the final number of poles 2p=2p _i ; Step 2. Calculate the power P′ _i . If the motor runs for a long time, then If the motor runs for a short time, then Among them, P _N is the rated power of the motor, and η' is the prefetch efficiency of the motor; Step 3. Calculate the inner diameter of the armature B' _δ is the prefetching air gap magnetic density, A' _δ is the prefetching line load, α _i is the prefetching calculation pole arc coefficient, λ' is the prefetching length-to-diameter ratio, and the outer diameter of the armature satisfies: D ₁ >D _il , n _N motor rated speed; Step 4. Calculate the armature core length L≈λ′D _i1 ; Step 5. Select the slot type, take the slot width b ₀₁ ≤1mm, and specify other structural parameters: slot depth h ₀₁ , slot shoulder width b _x1 , slot shoulder depth h _x1 ; Step 6. Take the notch depth h _x1 as the base, make an isosceles triangle with an apex angle of 150°, and the apex of the isosceles triangle is located in the notch; draw a circle with the three vertices of the isosceles triangle as three points arc, forming an arc structure notch; using this structure as the optimized slot to form the stator structure of the motor; Step 7. The structure type of the rotor adopts tile magnetic steel radial impact magnetization; Step 8, calculating the outer diameter of the permanent magnet D _m =D _i1 -2δ, the inner diameter of the permanent magnet D _mi =D _m -2H _m , δ is the width of the air gap, and H _m is the thickness of the magnetization direction of the permanent magnet; Step 9: Take the outer diameter D ₂ of the rotor tight ring, D _m < D ₂ < D _i1 ; Step 10: Take the rotor magnetic steel length L _c =L to complete the optimization.