CN103915925A - Rotor structure for permanent magnet synchronous motor with step-shaped permanent magnets - Google Patents

Abstract

The invention relates to a permanent magnet synchronous motor rotor structure with stepped permanent magnets. In the rotor structure, the permanent magnets of each pole are stepped, and the maximum value of the thickness of the permanent magnet magnetization direction appears in the middle of a magnetic pole, and the minimum value appears in the middle of a magnetic pole. On both sides of the pole permanent magnet, the thickness of the permanent magnet in the direction of magnetization transitions from the thickest part in the middle to the thinnest part in the direction of magnetization on both sides, and the transition process is a step transition. Through such a structure, the magnetic potential of the permanent magnet can be stepped, so that the odd harmonic content of the air-gap flux density waveform of the motor increases. For the inline magnet, the waveform of the air-gap flux density can be obtained A certain degree of improvement, which will improve the back electromotive force waveform of the winding, thereby reducing the eddy current loss of the motor.

Description

A permanent magnet synchronous motor rotor structure with stepped permanent magnets

technical field

The invention belongs to the technical field of motors, and in particular relates to a permanent magnet synchronous motor rotor structure with stepped permanent magnets.

Background technique

With the gradual maturity and completion of the design, development and control technology of permanent magnet synchronous motors, as well as the continuous development of permanent magnets in terms of performance and industrialization, permanent magnet synchronous motors have both good speed regulation characteristics of DC motors and AC motors. Due to the advantages of simple structure, convenient maintenance, stable operation and reliable performance, the demand in various fields is increasing, and the development prospect is getting better and better. At present, permanent magnet synchronous motors are widely used in various servo motors, wind power generation fields, electric vehicle drive fields, and CNC machine tool electric spindle motors.

However, the permanent magnet synchronous motors at this stage, especially the fractional slot permanent magnet synchronous motors, have relatively large harmonic content in the back EMF of the AC winding, especially in the permanent magnet synchronous motors with embedded concentrated windings. The eddy current loss of the motor increases, the temperature rise increases, and the efficiency of the motor decreases, which has a serious impact on the performance of the motor. The main reason for the high harmonic content of the back electromotive force in the permanent magnet synchronous motor winding is that the waveform of the air-gap flux density of the motor is poor in sinusoidality, and more even-order harmonics are mixed in, so that the air-gap flux density of the motor presents a trapezoidal wave, so the winding The harmonic content of the back EMF will be relatively large. In the design of salient pole induction motors, designers often use the method of non-uniform air gap to obtain the sinusoidal air gap flux density waveform, but this method is not suitable for permanent magnet synchronous motors, so looking for a suitable The method of improving the air-gap magnetic density waveform of the permanent magnet synchronous motor is particularly important.

According to the magnetic circuit Ohm's law, the magnetic flux Φ is equal to the magnetic potential F divided by the magnetic resistance R _m . Under the same magnetic pole of the motor, the magnetic circuit is basically the same, and the magnetic resistance is also basically the same, so the place where the magnetic potential is large will produce larger The magnetic flux will also generate a larger magnetic density in the air gap. According to this principle, as long as the magnetic potential generated by the permanent magnet is reasonably controlled, the waveform of the no-load air gap flux density can be controlled. The magnetic potential of the permanent magnet is proportional to the length of the permanent magnet in the direction of magnetization, so the reasonable design of the length of the permanent magnet in the direction of magnetization can control the waveform of the air-gap flux density and achieve the purpose of improving the waveform of the air-gap flux density.

Therefore, how to improve the waveform of the air-gap magnetic field and the waveform of the back electromotive force is a technical problem to be solved by those skilled in the art.

Contents of the invention

technical problem to be solved

In order to avoid the deficiencies of the prior art, the present invention proposes a permanent magnet synchronous motor rotor structure with ladder-shaped permanent magnets to solve the problem of poor sinusoidality of the air gap flux density waveform of the fractional slot concentrated winding permanent magnet synchronous motor.

Technical solutions

A permanent magnet is a step-shaped permanent magnet synchronous motor rotor structure, including a rotor core 2, a permanent magnet 3, a magnetic isolation bridge 4, a magnetic isolation air gap 6, and a rotating shaft 5; it is characterized in that one side of the permanent magnet 3 is stepped , one side is an in-line stepped magnetic steel, the stepped opening faces the center of the rotor core and the center of the stepped shape coincides with the axis of the rotor core 2; the stepped shape of the permanent magnet 3 has a thickness in the middle of The step of H _max is the center, with N equal-width steps on both sides, and the magnetization direction of the permanent magnet is perpendicular to the bottom surface of the step permanent magnet.

The maximum thickness H _max and the minimum value H _min of the arc-shaped magnetization direction of the permanent magnet 3 satisfy the relational expression:

Among them: α _p is the pole arc coefficient of the motor.

Said N≥2.

The height of the nth step counted from the middle to both sides is:

Among them: α _p is the pole arc coefficient of the motor.

The minimum value H _min of the arc-shaped magnetization direction of the permanent magnet 3 is 0.6 to 1 times the thickness of the permanent magnet designed for the motor.

The width of the magnetic isolation air gap 6 at both ends of the permanent magnet 3 is 1 to 1.5 times the minimum thickness of the permanent magnet, and the length of the magnetic isolation air gap ensures the thickness requirement of the magnetic isolation bridge designed for the motor.

The thickness of the magnetic isolation bridge is 1-2 mm.

Beneficial effect

The present invention proposes a permanent magnet synchronous motor rotor structure in which the permanent magnets are stepped. In the rotor structure, the permanent magnets of each pole are stepped. Appearing on both sides of the permanent magnet of the magnetic pole, the thickness of the permanent magnet in the magnetization direction transitions from the thickest part in the middle magnetization direction to the thinnest part in the magnetization direction on both sides, and the transition process is a stepped transition. Through such a structure, the magnetic potential of the permanent magnet can be stepped, so that the odd harmonic content of the air-gap flux density waveform of the motor increases. For the inline magnet, the waveform of the air-gap flux density can be obtained A certain degree of improvement, which will improve the back electromotive force waveform of the winding, thereby reducing the eddy current loss of the motor.

The invention improves the counter electromotive force waveform, reduces torque ripple, reduces vibration and noise, reduces the eddy current loss of the motor, improves the efficiency of the motor, and at the same time can reduce the temperature rise of the motor rotor and permanent magnet, improve the stability of the motor operation, and improve the performance of the motor. Comprehensive performance. It has good manufacturability, low requirements on processing instruments and easy realization. And because of the stepped shape of the magnetic poles, the radial position of the magnetic poles is absolutely fixed during the rotation of the motor, and there will be no sliding or offset, and the magnetic field is stable, so that the performance of the motor is more stable.

Description of drawings

Fig. 1: The permanent magnet of the present invention is a step-shaped permanent magnet synchronous motor rotor structure schematic diagram

1 is a stator core, 2 is a rotor core, 3 is a permanent magnet, 4 is a magnetic isolation bridge, 5 is a rotating shaft, and 6 is a magnetic isolation air gap.

Detailed ways

Now in conjunction with embodiment, accompanying drawing, the present invention will be further described:

The invention provides a rotor structure with stepped permanent magnets for permanent magnet synchronous motors, especially for permanent magnet synchronous motors with fractional slot concentrated windings. The structure has a rotor core, trapezoidal permanent magnets and a magnetic isolation air gap. Each pole of the rotor core is provided with a permanent magnet and a magnetic isolation air gap.

The permanent magnets in each pole are in a stepped shape, and the maximum value of the thickness of the permanent magnet magnetization direction appears in the middle of a magnetic pole as H _max , and the minimum value appears on both sides of the permanent magnet of the magnetic pole as H _min , where H _max > H _min , and the thickness of the permanent magnet gradually transitions from H _max to H _min through N steps of equal width (excluding the step with the thickness of H _max in the middle), where N≥2 and the transition law is symmetrical about the pole centerline, the permanent magnet The magnetization direction is perpendicular to the bottom surface of the ladder permanent magnet. Assuming that the pole arc coefficient of the motor is designed as α _p , the best optimization effect will be obtained when the structural parameters meet the following two conditions:

Condition 1, H _max , H _min and α _p satisfy the relationship

Condition 2, the height of the nth step (counting from the middle to both sides, the highest step in the middle is counted as the 0th step) is

In this way, the midpoint of each step surface can be made to fall on the same sinusoidal curve, so as to achieve the best optimization effect.

The rotor structure is provided with a 1-2mm thick magnetic isolation air gap, which is set at the two ends of each pole permanent magnet near the edge of the rotor core. The setting of the magnetic isolation air gap can effectively reduce the Flux leakage between opposite poles. There is a magnetic isolation bridge between the magnetic isolation air gap and the motor air gap. The magnetic isolation bridge is actually a rotor core with a reasonably designed thickness. When performing the specific design of the thickness of the rotor magnetic bridge, stress analysis and calculation should be carried out. To ensure that the stress value of each magnetic isolation bridge meets the requirements, obtain the optimal size of the magnetic isolation bridge, thereby reducing the magnetic flux leakage between adjacent magnetic poles, so as to ensure that the performance of the motor meets the given requirements.

Specific embodiments Referring to Fig. 1, this figure is a specific implementation of the new rotor structure of the permanent magnet synchronous motor, and this figure only shows a quarter of the entire motor structure.

The permanent magnet synchronous motor in this example is a fractional slot permanent magnet synchronous motor with 12 slots and 10 poles. It has a stator core 1, a rotor core 2, and a rotating shaft 5 passing through the rotor core 2. The rotor core 2 drives the rotating shaft 5 to rotate relative to the stator core 1. The rotor core 2 has 10 poles, and each pole is equipped with a permanent magnet 3 and a magnetic isolation bridge 4 . The rotor core 2 is provided with magnetic isolation air gaps 6 equal to the number of permanent magnets, and the magnetic isolation air gaps 6 extend axially along the rotor core 2 throughout the entire rotor core 2 . And the permanent magnet 3 in each pole is ladder-shaped, and the maximum value of its permanent magnet magnetization direction thickness appears in the middle of a magnetic pole, and minimum value occurs on both sides of this magnetic pole permanent magnet, and the thickness of its permanent magnet magnetization direction is from the middle The place with the thickest thickness in the direction of magnetization transitions to the place with the thinnest thickness in the direction of magnetization on both sides, and the transition process is a step transition. In the figure, the permanent magnets 3 are distributed symmetrically along the center of the cross-section of the rotor core 2. This structure is conducive to reducing the content of even harmonics in the air-gap flux density waveform, making the air-gap flux density waveform closer to sinusoidal.

The specific size of this embodiment is: H _min =2mm, H _max =8.3 mm, H ₀ =H ₁ =5.8 mm, H ₂ =H _min =2 mm.

When the motor is working, the thickness of the permanent magnet 3 with a ladder-shaped unequal thickness shape structure is designed according to the optimal optimized magnetic field waveform. The permanent magnet 3 of each pole is thick in the middle and thin at both ends, so as to approach each pole The air-gap magnetic field strength on the radial axis of the permanent magnet 3 is relatively large, and the air-gap magnetic field strength away from the axis is weakened, which can make the air-gap magnetic field waveform very close to the ideal sine wave, so that the counter electromotive force generated by the winding will also be very close to the ideal sine wave. Compared with conventional permanent magnet motors, the permanent magnet synchronous motor with this rotor structure has very low eddy current loss and small torque ripple, which improves the operating efficiency and stability of the motor. The design of the magnetic isolation bridge 4 makes the magnetic flux in this part saturated, and the magnetic flux can no longer be injected, which reduces the magnetic flux leakage, and the magnetic flux leakage coefficient of the motor will also be reduced. Due to the existence of the magnetic isolation air gap 6, the permanent magnet motor of the rationally designed magnetic isolation bridge 4 has a smaller flux leakage coefficient than the conventional permanent magnet motor, and also has sufficient strength, and the motor has higher operating efficiency and reliability. sex.

Claims (7)

1. permanent magnet is a step-like permanent-magnetic synchronous motor rotor structure, comprises rotor core (2), permanent magnet (3), every magnetic bridge (4), every magnetic air gap (6) and rotating shaft (5); It is characterized in that described permanent magnet (3) is on one side stairstepping, is the stairstepping magnet steel of yi word pattern on one side, and step-like opening is towards the center of rotor core and the axis coinciding of step-like center and rotor core (2); The stairstepping of described permanent magnet (3), taking middle thickness as H _maxstep centered by, both sides are N wide ladder, the magnetizing direction of permanent magnet is vertical with the bottom surface of ladder permanent magnet.

2. permanent magnet is step-like permanent-magnetic synchronous motor rotor structure according to claim 1, it is characterized in that: the maximum thickness H of the arc magnetizing direction of described permanent magnet (3) _maxwith minimum value H _minmeet relational expression: wherein: α _pfor the pole embrace of motor.

3. permanent magnet is step-like permanent-magnetic synchronous motor rotor structure according to claim 1, it is characterized in that: described N >=2.

4. permanent magnet is step-like permanent-magnetic synchronous motor rotor structure according to claim 1, it is characterized in that: institute

State from centre to the height of n step of both sides number and be:

wherein: α _pfor the pole embrace of motor.

5. permanent magnet is step-like permanent-magnetic synchronous motor rotor structure according to claim 1, it is characterized in that: the thickness minimum value H of the arc magnetizing direction of described permanent magnet (3) _minfor the road of design of electrical motor calculating 0.6～1 times of permanent magnet thickness.

6. permanent magnet is step-like permanent-magnetic synchronous motor rotor structure according to claim 1, it is characterized in that: the width every magnetic air gap (6) at described permanent magnet (3) two ends is 1～1.5 times of permanent magnet minimum thickness, every the length of magnetic air gap ensure design of electrical motor every magnetic bridge thickness requirement.

7. permanent magnet is step-like permanent-magnetic synchronous motor rotor structure according to claim 1, it is characterized in that: described is 1～2 millimeter every magnetic bridge thickness.