A method for designing an asymmetric rotor to reduce torque ripple of an interior permanent magnet synchronous motor

Abstract

The application discloses a built-in permanent magnet synchronous motor torque ripple asymmetric rotor design method, first modeling the motor rotor lamination, and the design variable is the magnetic steel slot magnetic barrier shape. By designing a continuous asymmetric magnetic barrier configuration, analyzing the cogging torque, reluctance torque and permanent magnet torque harmonic composition and component size, adjusting the magnetic steel slot magnetic barrier shape and asymmetry, realizing torque phase difference compensation, reducing the cogging torque, reluctance torque and harmonic torque three harmonics and harmonic component size, and achieving the effect of reducing the overall torque ripple. Experiments show that the scheme can reduce the torque ripple from 9.2% to 5.1%, while maintaining the rated torque above 29Nm, solving the problem that the prior art cannot balance multi-harmonic suppression and torque output.

Description

Technical Field

[0001] This invention relates to the field of motor design technology, and in particular to an asymmetric rotor design method for reducing torque ripple in a built-in permanent magnet synchronous motor. Background Technology

[0002] Torque pulsation is the periodic fluctuation of the output torque of a motor during operation. It reduces the control accuracy of the motor system, increases vibration and noise, and affects the lifespan of the equipment. Servo motors are characterized by high control precision, fast dynamic response, high reliability and stability. To ensure the high precision of servo motors and reduce control difficulty, it is particularly important to optimize torque pulsation on the motor itself. Currently, most servo motors adopt rotor structures with built-in magnets to achieve high torque density, but this technology still has the following defects: (1) Traditional IPM motors have high air gap magnetic flux density, high harmonic content, and large differences in magnetic reluctance between the D and Q axes, which will generate obvious torque pulsation (typical value 8.9%), causing vibration and noise. Common solutions include: optimizing rotor eccentricity, pole arc coefficient, etc., but the output torque is reduced significantly; using segmented pole misalignment can only suppress a single harmonic component. (2) There is a lack of rotor structure design schemes that can simultaneously reduce cogging torque, permanent magnet torque harmonics and magnetic reluctance torque harmonics. Summary of the Invention

[0003] This invention addresses the shortcomings of existing IPM motors by providing an asymmetric rotor design method to reduce torque ripple in built-in permanent magnet synchronous motors. By optimizing the magnetic barrier distribution, the method achieves synchronous suppression of cogging torque, permanent magnet torque harmonics, and reluctance torque harmonics, thereby reducing torque ripple.

[0004] The technical solution adopted by this invention to solve its technical problem is: an asymmetric rotor design method for reducing torque ripple in a built-in permanent magnet synchronous motor, comprising the following steps:

[0005] Step one: Determine that the torque ripple consists of cogging torque, permanent magnet torque harmonics, and reluctance torque harmonics. Analyze the torque ripple from these three aspects.

[0006] Step two, determine that the cogging torque is an interaction force generated by the interaction between the permanent magnet magnetic field and the stator slot, and its analytical expression is:

[0007] Where α is the angle between the center line of the stator teeth and the center line of the magnetic poles. L represents the axial length of the armature core; R1 and R2 are the outer radius of the armature and the inner radius of the stator yoke, respectively; n is an integer that makes nz / 2p an integer. G n This represents the coefficients of the Fourier series.

[0008] Step 3: Determine that the permanent magnet torque is the interaction between the magnetic flux generated by the permanent magnet and the magnetic flux generated by the stator current, and its analytical expression is:

[0009] Among them, E n The amplitude of the nth harmonic of the no-load back electromotive force (EMF) is represented by ω, where ω represents the fundamental angular frequency. I0 is the amplitude of the fundamental stator current. This is the phase difference between the stator current and the back electromotive force (EMF).

[0010] Step four, determine that the reluctance torque is caused by the imbalance of the rotor magnetic circuit, resulting in unequal direct-axis and quadrature-axis inductances. Its analytical expression is: T = (L d -L q )i d i q =[-L s2 -2M s2 +L s4 cos(6θ)+2M s4 cos(6θ)]i d i q .

[0011] Among them, L d L q These are the direct-axis inductance and quadrature-axis inductance of the motor, L s2 and L s4 M represents the amplitude of the second harmonic and the fourth harmonic of the stator self-inductance, respectively. s2 and M s4 These represent the amplitudes of the second and fourth harmonics of the stator mutual inductance, respectively.

[0012] Step 5: Model the permanent magnet motor rotor, determining the shape of the magnet slot using 8 points of the magnetic barrier. The magnet slot has an asymmetrical structure, with 4 points A, B, C, and D on each side, where A... L B L C L D L Located on the left side of the magnet trough, A R B R C R D R Located on the right side of the magnet trough. Point A. L and A R The Y-axis coordinates are the same, point D L and D R The Y-axis coordinates are the same, B L C L B R C R Located on the same circumference. The width of the magnetic barrier is differentiated by changing the relative positions of the points.

[0013] Step 6: Use simulation software to calculate the cogging torque, air gap magnetic flux density, no-load radial force, and torque fluctuation of the permanent magnet motor. Perform Fourier decomposition on the air gap magnetic flux density to analyze the magnitude of the fundamental and harmonic components of the air gap magnetic flux density.

[0014] Step 7: Based on the simulation results and design requirements, change the positions of 8 points of the magnetic barrier in the magnet slot, and iteratively optimize the torque pulsation and air gap magnetic flux density waveforms until the magnitude of the torque pulsation meets the design requirements.

[0015] The beneficial effects of this invention are: This invention achieves synchronous suppression of harmonics, reducing permanent magnet torque pulsation by 1.7%, reluctance torque pulsation by 2.6%, and overall torque pulsation by 5.1% in the continuous asymmetric rotor structure; the output torque is reduced by only 1.4%, ensuring the basic performance of the motor; at the same time, the amplitude of the 8th harmonic of the no-load radial force is reduced by more than 40%, which plays a certain role in suppressing vibration and noise. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0017] Figure 1 This is a schematic diagram of an asymmetric rotor structure.

[0018] Figure 2 This is a schematic diagram of a continuous asymmetric rotor structure.

[0019] Figure 3 A comparison of cogging torque between a traditional IPM and a continuous asymmetric rotor structure.

[0020] Figure 4 A comparison of air gap flux density between a traditional IPM and a continuous asymmetric rotor structure.

[0021] Figure 5 A comparison of torque ripple between a traditional IPM and a continuous asymmetric rotor structure.

[0022] Figure 6 The unloaded radial force is for a continuous asymmetric rotor structure.

Claims

1. An asymmetric rotor design method for reducing torque ripple in a built-in permanent magnet synchronous motor, characterized in that, include: Step one: Determine that the torque ripple consists of cogging torque, permanent magnet torque harmonics, and reluctance torque harmonics. Analyze the torque ripple from these three aspects. Step two, determine that the cogging torque is an interaction force generated by the interaction between the permanent magnet magnetic field and the stator slot, and its analytical expression is: Where α is the angle between the center line of the stator teeth and the center line of the magnetic poles. L represents the axial length of the armature core; R1 and R2 are the outer radius of the armature and the inner radius of the stator yoke, respectively; n is an integer that makes nz / 2p an integer. G n This represents the coefficients of the Fourier series. Step 3: Determine that the permanent magnet torque is the interaction between the magnetic flux generated by the permanent magnet and the magnetic flux generated by the stator current, and its analytical expression is: Among them, E n The amplitude of the nth harmonic of the no-load back electromotive force (EMF) is represented by ω, where ω represents the fundamental angular frequency. I0 is the amplitude of the fundamental stator current. This is the phase difference between the stator current and the back electromotive force (EMF). Step four, determine that the reluctance torque is caused by the imbalance of the rotor magnetic circuit, resulting in unequal direct-axis and quadrature-axis inductances. Its analytical expression is: T = (L d -L q )i d i q =[-L s2 -2M s2 +L s4 cos(6θ)+2M s4 cos(6θ)]i d i q . Among them, L d L q These are the direct-axis inductance and quadrature-axis inductance of the motor, L s2 and L s4 M represents the amplitude of the second harmonic and the fourth harmonic of the stator self-inductance, respectively. s2 and M s4 These represent the amplitudes of the second and fourth harmonics of the stator mutual inductance, respectively. Step 5: Model the permanent magnet motor rotor, determining the shape of the magnet slot using 8 points of the magnetic barrier. The magnet slot has an asymmetrical structure, with 4 points A, B, C, and D on each side, where A... L B L C L D L Located on the left side of the magnet trough, A R B R C R D R Located on the right side of the magnet trough. Point A. L and A R The Y-axis coordinates are the same, point D L and D R The Y-axis coordinates are the same, B L C L B R C R Located on the same circumference. The width of the magnetic barrier is differentiated by changing the relative positions of the points. Step 6: Use simulation software to calculate the cogging torque, air gap magnetic flux density, no-load radial force, and torque fluctuation of the permanent magnet motor. Perform Fourier decomposition on the air gap magnetic flux density to analyze the magnitude of the fundamental and harmonic components of the air gap magnetic flux density. Step 7: Based on the simulation results and design requirements, change the positions of 8 points of the magnetic barrier in the magnet slot, and iteratively optimize the torque pulsation and air gap magnetic flux density waveforms until the magnitude of the torque pulsation meets the design requirements.

2. The structure as described in claim 1, characterized in that, The magnetic barrier unit adopts a continuous asymmetric distribution. The magnetic steel slots of two adjacent magnetic poles are asymmetric structures, evenly distributed on the circumference, with a period of 8, thereby achieving torque phase lag offset.

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