Permanent magnet synchronous motor structure adopting built-in magnetic poles to weaken cogging torque
Technical Field
The invention belongs to the field of permanent magnet motors, and particularly relates to a permanent magnet synchronous motor structure adopting built-in magnetic poles to weaken cogging torque.
Background
Permanent magnet synchronous motors are widely used in industrial applications due to their performance characteristics of high efficiency, high torque density, and low vibration noise. However, the cogging torque is one of the specific problems of the permanent magnet motor, and is a key problem which must be considered and solved in the design and manufacture of the high-performance permanent magnet motor, and the weakening of the cogging torque not only can reduce the vibration and noise generated when the motor runs, but also can improve the low-speed performance of the motor in a speed control system and the high-precision positioning in a position control system.
The cogging torque weakening method of the existing permanent magnet motor mainly has the following problems:
1. many approaches reduce cogging torque while at the same time causing a reduction in motor output torque and possibly even an increase in electromagnetic torque ripple. Therefore, when the method is applied, both the cogging torque ripple and the electromagnetic torque ripple are considered comprehensively, and an appropriate weakening method is adopted according to actual conditions, wherein the weakening method can be one or a combination of several methods.
2. In a traditional permanent magnet motor, the air gap is not uniform due to the opening of a motor slot, the air gap flux density waveform is seriously distorted, great influence is generated on the cogging torque and the torque ripple of the motor, and the cogging torque can be reduced due to the small opening of the slot, but the processing and offline difficulty is also caused, and the slot filling rate of the motor is also reduced.
3. Although many methods can achieve the purpose of reducing the cogging torque, some methods have obvious disadvantages and are difficult to be widely applied in practice, for example, the fractional slot winding causes uneven magnetic field distribution and produces unbalanced magnetic pull force; the stator chute reduces the area of a stator slot, influences the embedding of a winding and increases the stray loss and magnetic leakage of the motor; the rotor oblique pole can generate axial unbalanced magnetic pull force; the thickness of the unequal magnetic sheets is easy to cause the idle-load back electromotive force of the motor to be overlarge and the temperature field to be partially saturated; the permanent magnet is complicated in segmented dislocation structure and difficult in manufacturing process.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a permanent magnet synchronous motor structure which adopts built-in magnetic poles to weaken cogging torque, and aims to solve the problems of torque fluctuation caused by the cogging torque, reduction in control characteristics and operation reliability of a permanent magnet motor servo drive system, influence on control precision of the system, vibration, noise and the like.
In order to achieve the purpose, the invention adopts the following technical scheme:
a permanent magnet synchronous motor structure adopting built-in magnetic poles to weaken cogging torque comprises a stator, a rotor and a rotating shaft, wherein the rotating shaft is fixedly sleeved on a middle shaft hole of the rotor, the rotor is located on the inner side of a ring-shaped stator, multi-pole stator slots are arranged in the stator in a surrounding mode along the circumferential direction, concentrated windings are distributed in the stator slots, multi-pole permanent magnet mounting grooves are arranged in the rotor in a surrounding mode along the circumferential direction, each permanent magnet mounting groove comprises two permanent magnet slots which are symmetrically arranged, a U-shaped structure is formed between the two permanent magnet slots, an iron core bridge is fixedly embedded in one end, close to the rotating shaft, of each permanent magnet slot and the mutual connection position of the two permanent magnet slots, the two ends of each iron core bridge abut against the.
Furthermore, a plurality of auxiliary grooves are formed in the inner surface of the stator facing the air gap at intervals along the circumferential direction.
Furthermore, the concentrated windings have three phases, and the windings in the same phase are connected in series.
Further, the thickness of the iron core bridge embedded and fixed at the joint of the two permanent magnet slots is the same.
Furthermore, the ratio of the length of the magnetic pole of the permanent magnet to the thickness of the permanent magnet is 4.5-5.5, and the length of the permanent magnet is not less than one third of the length of the permanent magnet slot.
By adopting the technical scheme, the invention has the following technical effects:
1. on the basis of the traditional V-shaped permanent magnet motor, a pair of iron core bridges are additionally arranged on the inner side of the rotor close to the rotating shaft section to separate magnetic poles, a magnetic pole mounting groove is U-shaped, and two permanent magnets are arranged in the permanent magnet pole mounting groove, so that the rotor structure can be greatly weakened by tooth space torque at the cost of sacrificing less electromagnetic torque, the dynamic performance of the built-in permanent magnet motor is improved, the consumption of the permanent magnets is reduced, and the cost of the motor is saved;
2. the permanent magnet slots on the inner side of the rotor can be connected into a whole by adding the iron core bridge, so that the assembly difficulty of the motor is greatly reduced, and the production and the manufacture of the motor are facilitated;
3. and an auxiliary groove is formed on the inner surface of the stator facing the air gap, so that the cogging torque can be effectively reduced.
Drawings
The invention is described in further detail below with reference to the accompanying drawings and the detailed description;
FIG. 1 is a cross-sectional view of the present invention;
FIG. 2 is an enlarged view of a portion of FIG. 1;
FIG. 3 is a comparison of cogging torque for open assist notch versus no assist notch;
FIG. 4 is a comparison of cogging torque for different auxiliary flute sizes;
fig. 5 is a schematic illustration of the cogging torque attenuation effect using different permanent magnet thicknesses.
Detailed Description
The generation mechanism of the permanent magnet motor cogging torque is as follows: cogging torque is the torque produced by the interaction between the permanent magnets and the iron core when the permanent magnet motor windings are not energized, and is caused by the tangential component of the interaction force between the permanent magnets and the armature teeth. When the stator and the rotor move relatively, the magnetic conductance between the armature teeth and the permanent magnet is basically unchanged, so that the magnetic field around the armature teeth is also basically unchanged, and the magnetic conductance is greatly changed in a small section area corresponding to two side faces of the permanent magnet and formed by one or two armature teeth, so that the energy storage of the magnetic field is changed, and the cogging torque is generated. Cogging torque is defined as the negative derivative of the magnetic field energy W when the motor is not energized to the stator and rotor relative position angle α, i.e.:
currently, weakening the cogging torque of a permanent magnet synchronous motor can be achieved by two methods: firstly, the structure of the motor is changed. And the other is to adopt different control strategies. The invention adopts the first method to achieve the purpose of weakening the cogging torque.
As shown in fig. 1 and 2, the permanent magnet synchronous motor structure adopting the built-in magnetic poles to weaken cogging torque comprises a stator 1, a rotor 5 and a rotating shaft 7, wherein the rotating shaft 7 is fixedly sleeved on a central shaft hole of the rotor 5, the rotor 5 is positioned on the inner side of a ring-shaped stator 1, a multi-pole stator slot 4 is arranged inside the stator 1 in a surrounding manner along the circumferential direction, concentrated windings 2 are distributed in the stator slot 4, the concentrated windings 2 share three phases, and the same-phase windings are mutually connected in series.
The inside multipolar permanent magnetism mounting groove 6 that encircles along the circumferencial direction of following of rotor 5, permanent magnetism mounting groove 6 includes the permanent magnet groove that two symmetries set up, forms U type structure between two permanent magnet grooves, and two permanent magnet grooves are close to the one end of pivot 7 and interconnect department embedded iron core bridge 9 that is fixed with thickness such as respectively, the both ends of iron core bridge 9 are respectively near in rotor 5, and the middle part in two permanent magnet grooves is embedded permanent magnet 3 that is fixed with respectively.
As shown in figures 1 and 2, on the basis of the traditional built-in permanent magnet motor, the length of the permanent magnet 3 is shortened along the direction of the permanent magnet grooves from the inner side of the rotor 5, the iron core bridges 9 with equal thickness are respectively added at the connection positions of each pair of permanent magnet grooves and are always kept to be close to the rotor 5, and the permanent magnet grooves on the inner side of the rotor 5 can be connected into a whole by adding the iron core bridges 9, so that the assembly difficulty of the motor is greatly reduced, and the production and the manufacture of the motor are facilitated.
The magnetic pole length to thickness ratio of the permanent magnet 3 is 4.5-5.5, and the length of the permanent magnet 3 is not less than one third of the permanent magnet slot. A plurality of auxiliary grooves 8 are formed in the inner surface, facing the air gap, of the stator 1 at intervals along the circumferential direction, the width and the depth of the groove opening of each auxiliary groove 8 are equal to those of the groove opening of the stator groove 4 preliminarily, and the size of each auxiliary groove 8 in the inner surface of the stator 1 is optimized through parameters to obtain the most appropriate size combination.
An auxiliary groove 8 is formed on the inner surface of the stator 1. The width of the groove opening of the groove is k, the depth of the groove opening is s, and the initial size k multiplied by s is 2mm multiplied by 1 mm. Compared with the interior permanent magnet motor with a general structure, the opening of the auxiliary groove 8 is equivalent to increasing the number of teeth of the stator 1 so as to change the magnetic pole matching number of the motor, the frequency of the cogging torque is improved, so the amplitude of the cogging torque is reduced to some extent, and the peak value of the cogging torque with the auxiliary groove 8 is reduced by about 60 percent compared with that shown in fig. 3.
As shown in fig. 4, from the initial size, 0.5mm is used as an analysis size interval, the width k of the auxiliary groove 8 is selected from 0mm (without opening the auxiliary groove 8), 0.5mm, 1mm, 1.5mm and 2.0mm in sequence, the depth s of the auxiliary groove 8 is selected from 0mm (without opening the auxiliary groove 8), 0.5mm and 1mm in sequence, and the cogging torque generated by combining the two to form different groove type size combinations is shown in fig. 4. Overall, the notch width and depth dimension of the auxiliary groove 8 in combination can significantly reduce the cogging torque, and the cogging torque is minimized when the width k of the auxiliary groove 8 is 0.5mm and the groove depth s of the auxiliary groove 8 is 1mm, and the cogging torque peak value is reduced by about 35%.
The permanent magnets 3 are optimized in magnetic pole thickness along the inner side of the rotor 5 along the direction of the permanent magnet slots, and the iron core bridge 9 is abutted against the inner wall of the rotor 5 in the process. The cogging torque is optimized by taking the thickness of the magnetic steel as a parameter, and in order to obtain the optimal thickness of the permanent magnet 3, a common V-shaped built-in arrangement mode is used as a contrast, namely the length of the permanent magnet 3 is 6.4mm, and the thickness of the magnetic steel is gradually reduced from 6.4mm to 5.5mm by a step length of 0.1 mm. Four lengths of 5.5mm, 5.8mm, 6.1mm and 6.4 are selected for analysis and research.
As shown in fig. 5, the cogging torque of the motor varies with the position of the rotor 5 and decreases as the length of the permanent magnet 3 decreases. The cogging torque of the traditional V-shaped built-in motor is the maximum when the length of the permanent magnet 3 is 6.4mm, when the length of the permanent magnet 3 is changed into 5.5mm and the iron core bridge 9 is added, the cogging torque peak value is reduced by about 20%, the consumption of the permanent magnet 3 is reduced by 14%, and the thickness of the magnetic steel can be continuously optimized.
Therefore, the structure provided by the patent can effectively reduce the cogging torque of the interior permanent magnet synchronous motor, reduce the using amount of the permanent magnet 3, save the cost of the motor and further improve the dynamic performance of the interior permanent magnet motor.
While the invention has been described in connection with the above embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, which are illustrative and not restrictive, and that those skilled in the art will understand that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention, and they should be construed as being included in the following claims and description.