Three-phase permanent magnet servo motor with double eccentric stator and rotor and non-uniform air gap

Abstract

A three-phase permanent magnet servo motor with double eccentric stator and rotor, which solves the positioning torque problem of square wave permanent magnet servo motor and sine wave permanent magnet servo motor. The motor is a fractional slot concentrated winding motor with the number of slots per pole per phase q=Z / (2Pm)≤1 / 2, where 2P is the number of poles and Z is the number of slots. Its rotor core is an eccentric rotor with a rotor eccentricity P r =r1 / r2=(1.05~(1+2δcos(180° / 2P)); Its stator core is an eccentric stator, and the stator eccentricity P R =R1 / R2=(0.95~1 / (1+δcos(180° / Z)), (where r1 is the rotor radius, r2 is the rotor eccentric radius, R1 is the stator radius, and R2 is the stator eccentric radius). This motor is a non-uniform air gap motor with double eccentricity of the stator and rotor. When P r =P R =1When there is no eccentricity, the equivalent uniform motor air gap length δ = R1-r1.

Description

Technical Field

[0001] The invention discloses a three-phase permanent magnet servo motor, in particular to a three-phase permanent magnet servo motor with double eccentricity of stator and rotor and non-uniform air gap. The motor is suitable for direct drive and position and speed servo control applications. Background Art

[0002] Permanent magnet motors can be divided into two categories according to the driving current and back EMF waveform: sine wave and square wave. Sine wave permanent magnet motors are generally called permanent magnet synchronous motors (PMSM) or sine wave AC servo motors; the other type of square wave permanent magnet motor is called square wave brushless DC motor (BLDCM).

[0003] The biggest drawback of square wave permanent magnet motors is the large fluctuation of the fundamental commutation torque. In response to this, researchers have proposed a variety of compensation measures, but the actual application results are not ideal.

[0004] The torque fluctuation of the sine wave permanent magnet motor is much smaller than that of the square wave permanent magnet motor, and it has become the mainstream of industrial applications today. However, in order to reduce its torque fluctuation, the traditional sine wave permanent magnet motor adopts the "fractional slot distributed winding structure". The air gap harmonic magnetic field and positioning torque of the "fractional slot distributed winding motor" are small, but it will lead to the complication of the motor structure and manufacturing process. In addition, the complexity of the control system of the sine wave permanent magnet motor leads to a significant increase in the cost of the motor. More importantly, the power energy index of the motor has also decreased.

[0005] Contemporary sinusoidal permanent magnet motors have begun to adopt "fractional slot concentrated winding structure", the most typical example is: 10 poles and 12 slots "fractional slot concentrated winding motor". Since the number of poles and slots of the fractional slot concentrated winding motor are very close, its positioning torque (cogging positioning torque) is relatively large, so the biggest design and manufacturing difficulty of the concentrated winding motor is: how to reduce its positioning torque (cogging positioning torque). Although there have been many studies on it at home and abroad, and there are many methods, these methods all require sacrificing other performance as a prerequisite, and the effect is poor. The reasons are analyzed as follows:

[0006] Since the number of poles and slots of the fractional slot concentrated winding motor is very close, its winding coefficient is very large, that is, the winding utilization rate is very high, and the winding end is minimized, the motor copper loss is small, and the efficiency is high. However, the cogging torque of the fractional slot concentrated winding motor may be very large and difficult to suppress. In the extreme case, the cogging torque reaches the maximum value when the number of poles is equal to the number of slots.

[0007] The traditional methods are: selecting reasonable tooth-slot matching, using closed slots or small slots, appropriately increasing the air gap, using rotor skew slots, using rotor eccentricity, and other commonly used methods to suppress the detent torque. However, the above methods will make the winding coefficient smaller, the leakage magnetic flux larger, the air gap magnetic density smaller, and the motor material utilization rate reduced. This is at the expense of the motor's power energy index and performance, and it is not enough to suppress the detent torque to less than a few ten-thousandths. Even if the above methods are used at the same time, it is difficult to suppress the detent torque to less than a few ten-thousandths in many engineering applications. Therefore, suppressing the detent torque is still a major problem in the current design and manufacture of permanent magnet motors. In particular, large-diameter torque motors in direct drive systems still use the traditional "fractional slot distributed winding structure", although the motor structure and manufacturing process are complex and the production cost is high. Summary of the invention

[0008] In view of the shortcomings of the above-mentioned prior art that the distributed motor with fractional slots has a complex structure and manufacturing process, has a high production cost, and cannot take into account both the force and energy indicators and the positioning torque of the concentrated winding motor with fractional slots, the present invention proposes a three-phase permanent magnet servo motor with double eccentricity of stator and rotor and non-uniform air gap. The motor adopts a double eccentricity structure of the motor stator and rotor, which can effectively suppress the positioning torque, reduce the air gap harmonic magnetic field, and comprehensively improve the performance of the motor in all aspects.

[0009] The technical solution adopted by the present invention to solve the technical problem is: a three-phase permanent magnet servo motor with double eccentricity of stator and rotor and non-uniform air gap, the motor is an inner rotor motor, the rotor is equipped with more than one pair of permanent magnets, the slots of the stator are equipped with three-phase windings,

[0010] The motor is a fractional slot concentrated winding motor with the number of slots per pole per phase q=Z / (2Pm)≤1 / 2, where Z is the number of slots, 2P is the number of poles, and m is the number of phases;

[0011] The rotor core of the motor is an eccentric rotor core.

[0012] Rotor eccentricity P r =r1 / r2=(1.05~(1+2δcos(180° / 2P))), where r1 is the rotor radius and r2 is the eccentric rotor radius.

[0013] The stator core of the motor is an eccentric stator core.

[0014] Stator eccentricity P R =R1 / R2=(0.95~1 / (1+δcos(180° / Z))), where R1 is the stator radius, R2 is the eccentric stator radius, and the tooth pitch angle θ=360 / Z,

[0015] The motor is a non-uniform air gap motor with double eccentricity of the stator and rotor;

[0016] The length of the equivalent uniform air gap between the stator and the rotor is: δ=R1-r1.

[0017] The technical solution adopted by the present invention to solve the technical problem further includes:

[0018] The number of slots of the motor is Z=9N, the number of poles is 2P=8N or the number of poles is 2P=10N, wherein N=2, 3, 4, 5, ... is a natural number greater than or equal to 2.

[0019] The length of the equivalent uniform air gap between the stator and the rotor is: δ=R1-r1, which is 0.2-10 mm.

[0020] For a motor with slot number Z=12 and pole number 2P=10, the length of the equivalent uniform air gap between the stator and the rotor is: δ=R1-r1, which is 0.2-2 mm.

[0021] The stator core of the motor is an eccentric stator core.

[0022] Stator eccentricity P R =R1 / R2=(0.95~1 / (1+0.95δcos(180° / Z))), where R1 is the stator radius, R2 is the eccentric stator radius, and the tooth pitch angle θ=360 / Z.

[0023] The stator core is assembled from more than one identical stator pole slots through inner circle or outer circle positioning.

[0024] The stator pole slots have the same eccentricity.

[0025] The beneficial effects of the present invention are as follows: the non-uniform air gap three-phase permanent magnet servo motor with double eccentricity of stator and rotor proposed in the present invention can better suppress the detent torque, reduce the air gap harmonic magnetic field, and comprehensively improve the performance of the motor in all aspects. The method is applicable to both square wave and sine wave permanent magnet motors, and is also particularly suitable for large diameter torque motors in direct drive systems. The three-phase permanent magnet servo motor of the present invention has the advantages of concentrated windings, can be driven by three-phase square wave current or three-phase sine wave current, can generate stable torque, and has a series of advantages such as minimizing winding ends, minimizing air gaps, minimizing materials, minimizing detent torque, and minimizing losses.

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the eccentric structure of the motor rotor in a preferred embodiment of the present invention.

[0028] Figure 2It is a schematic diagram of the eccentric structure of the motor stator in a preferred embodiment of the present invention.

[0029] Figure 3 It is a schematic diagram of the stator eccentric structure of a 12-slot 10-pole motor in a preferred embodiment of the present invention.

[0030] Figure 4 It is a schematic diagram of the assembly of a stepless shoe double eccentric 10-pole 12-slot motor.

[0031] Figure 5 This is another schematic diagram of the assembly of a stepless shoe double eccentric 10-pole 12-slot motor.

[0032] Figure 6 It is a schematic diagram of the stator core structure composed of Z=12 identical pole slots.

[0033] Figure 7 It is a stator eccentricity parameter diagram of the best embodiment motor with 10 poles and 12 slots.

[0034] Figure 8 This is the positioning torque waveform diagram without using an eccentric magnetic pole.

[0035] Fig. 9 It is the positioning torque waveform diagram under one magnetic pole after the rotor is eccentric.

[0036] Fig.10 This is the positioning torque waveform under one magnetic pole after the rotor and stator are double eccentric.

[0037] In the figure, 1-stator core, 7-rotor assembly. DETAILED DESCRIPTION

[0038] This embodiment is a preferred implementation mode of the present invention. Other embodiments whose principles and basic structures are the same or similar to those of this embodiment are within the protection scope of the present invention.

[0039] The present invention aims to solve the problems existing in the existing square wave permanent magnet motors and sine wave permanent magnet motors, and proposes a three-phase permanent magnet servo motor with a new design principle, new structure, high performance, low cost, and a stator and rotor with double eccentricity and non-uniform air gap using fractional slot concentrated windings.

[0040] In order to solve the problem of large positioning torque in existing square wave permanent magnet servo motors and sine wave permanent magnet servo motors, in the present invention, the motor is a fractional slot concentrated winding motor with the number of slots per pole per phase q=Z / (2Pm)≤1 / 2, wherein q is the number of slots per pole per phase, Z is the number of slots, 2P is the number of poles, and m is the number of phases.

[0041] The rotor core of the motor is an eccentric rotor core, and the rotor eccentricity Pr=r1 / r2=(1.05~(1+2δcos(180° / 2P))), wherein r1 is the rotor radius, and r2 is the eccentric rotor radius;

[0042] The stator core 1 of the motor is an eccentric stator core, and the stator eccentricity P R =R1 / R2=(0.95~1 / (1+δcos(180° / Z))), where R1 is the stator radius and R2 is the eccentric stator radius.

[0043] The motor is a non-uniform air gap motor with double eccentricity of the stator and rotor, such as Figure 4 and Figure 5 .

[0044] When the eccentricity Pr=P R =1, r 1＝ r2, R1 = R2, when both the stator and the rotor are not eccentric, the motor with non-uniform air gap becomes a motor with uniform air gap. At this time, the length of the equivalent uniform air gap is: δ = R1-r1.

[0045] Since the number of poles and slots of the fractional slot concentrated winding motor are very close, its winding coefficient is very large, that is, the winding utilization rate is very high. However, the tooth slot positioning torque of the fractional slot concentrated winding motor may be very large and difficult to suppress. Its limit is that the positioning torque reaches a maximum value when the number of poles is equal to the number of slots. The traditional method is: select reasonable tooth slot matching, use closed slots or small slots, appropriately increase the air gap, use rotor skew slots, use rotor eccentricity and other commonly used methods to suppress the positioning torque. However, the above methods will make the winding coefficient smaller, the leakage magnetic flux larger, the air gap magnetic density smaller, and the motor material utilization rate reduced, at the expense of the motor's power energy index and performance, and it is not enough to suppress the positioning torque to less than a few ten-thousandths. Even if all the above methods are used at the same time, it is difficult to suppress the positioning torque to less than a few ten-thousandths for motors in many engineering applications.

[0046] Choose a reasonable tooth-slot match: the closer the number of poles is to the number of slots, the larger the winding coefficient is, the higher the utilization rate of the winding is, but the positioning torque may be greater.

[0047] The present invention adopts a non-uniform air gap structure and electromagnetic design with double eccentricity of the stator and rotor, which doubles the ability to suppress the positioning torque, so the tooth slot matching with the closest number of poles and slots can be adopted, for example:

[0048] In this embodiment, the number of slots Z=9N, the number of poles 2P=8N or the number of poles 2P=10N, where N=2, 3, 4, 5, ..., that is, N is an integer greater than or equal to 2; the length of the equivalent uniform air gap between the stator and the rotor is: δ=R1-r1 is 0.2~10mm, then the winding coefficient of the motor is 0.945.

[0049] When N is relatively large, the diameter of the motor is also relatively large, and at this time, the length of the equivalent uniform air gap can also be relatively large. In the best embodiment of the present invention, a torque motor with slot number Z=9N=36, pole number 2P=32, and stator outer diameter of 358mm is taken as an example, and the positioning torque of the motor is better than 0.006Nm.

[0050] In this embodiment, the motor with slot number Z=12 and pole number 2P=10 is selected, and the length of the equivalent uniform air gap between the stator and the rotor is: δ=R1-r1 is 0.2-2mm. The winding coefficient of the motor is 0.933, and the positioning torque of the motor is better than 0.00045Nm.

[0051] In order to illustrate the influence of eccentricity on the suppression of the detent torque, the following example is taken as an example a motor with the number of slots Z = 12, the number of poles 2P = 10, the air gap δ = 0.4mm, the slot opening 0.2mm, and the outer diameter 110mm:

[0052] (1) When eccentricity is not used and the air gap is uniform, since the number of slots and the number of poles are close, even if the best pole-slot match and the best air gap and slot size match are used, the motor detent torque is still 0.011Nm, which is not practical. The detent torque waveform under one magnetic pole is as follows: Figure 8 The positioning torque waveform consists of a main wave with a larger amplitude and a secondary wave with a smaller amplitude caused by the slot. Relative to a pair of magnetic pole waves, the positioning torque wave is a double frequency harmonic.

[0053] (2) When the rotor is eccentric, even if the eccentricity is relatively large, the optimal positioning torque is 0.0026Nm, and the positioning torque waveform is as follows Fig. 9 , but at this time the amplitude of the positioning torque has been reduced by 4.3 times, and the side wave caused by slotting has been basically completely suppressed. However, for high-performance motors, the positioning torque index is not ideal enough.

[0054] (3) Further adopting the double eccentricity of the rotor and stator, even if the eccentricity is not too large, the positioning torque can be optimized to 0.00045Nm. The positioning torque waveform is as follows Fig.10. It can be seen that after adopting the double eccentricity of the rotor and stator, the amplitude of the positioning torque is reduced by 13.4 times compared with the case without eccentricity, and the frequency is doubled. Since the eccentricity of the rotor and stator when the rotor and stator are double eccentric is not too large, there is no obvious difference between the non-uniform air gap and the uniform air gap without eccentricity. Therefore, the average air gap magnetic flux of the non-uniform air gap motor of the present invention is also not significantly different from that of the case with uniform air gap without eccentricity. That is, for the motor with double eccentricity of the rotor and stator, the average air gap magnetic flux decreases very little.

[0055] In addition, in this embodiment, the stator core 1 of the three-phase permanent magnet servo motor is assembled from Z identical pole slots. Figure 6 The stator core 1 is assembled by inner or outer circle positioning, and the Z identical stator pole slots have the same eccentricity.

[0056] A preferred embodiment of the present invention is Figure 3 , Figure 4 As shown in the figure, it can be seen that this three-phase brushless permanent magnet DC motor is a fractional slot concentrated winding motor with the number of slots per pole and per phase q=Z / (2Pm)=12 / 10m=12 / 30≤1 / 2, in which the number of slots Z is 12, the number of poles 2P is 10, and the number of phases m is 3.

[0057] The rotor core of the motor is an eccentric rotor core, and the rotor eccentricity P r =r1 / r2=(1.05~(1+2δcos(180° / 2P))), take 2.02, where the rotor radius r1=42mm and the eccentric rotor radius r2=21mm.

[0058] The stator core 1 of the motor is an eccentric stator core, and the stator eccentricity P R = R1 / R2 = (0.95 ~ 1 / (1 + δ cos (180 ° / Z))), take 0.794, where the stator radius R1 = 40.50 mm, the eccentric stator radius R2 = 53.50 mm. Schematic diagram of the best embodiment of the 10-pole 12-slot rotor with pole shoes and double eccentric motor in this embodiment. The positioning torque can reach less than 844.9e -6 Nm.

[0059] This motor is a non-uniform air gap motor with double eccentricity of stator and rotor. R =1, r 1＝ r2, R1 = R2, when both the stator and the rotor are not eccentric, the motor with non-uniform air gap becomes a motor with uniform air gap, and the length of the equivalent uniform air gap is: δ = R1-r1 = 0.5 mm. The positioning torque of the motor of the present invention can reach the order of less than a few ten-thousandths.

[0060] The stator-rotor double eccentric non-uniform air gap three-phase permanent magnet servo motor proposed by the present invention can better suppress the positioning torque, reduce the air gap harmonic magnetic field, and comprehensively improve the performance of the motor in all aspects by adding rotor pole shoes. The method is applicable to both square wave and sine wave permanent magnet motors, and is also particularly suitable for large diameter torque motors in direct drive systems.

[0061] The three-phase permanent magnet servo motor of the present invention has the advantages of concentrated windings, can be driven by three-phase square wave current or three-phase sine wave current, can generate stable torque, and has a series of advantages such as minimizing winding ends, minimizing air gaps, minimizing materials, minimizing positioning torque, and minimizing losses.

Claims

1. A three-phase permanent magnet servo motor with double eccentricity of stator and rotor and non-uniform air gap, the motor is an inner rotor motor, the rotor is equipped with one or more permanent magnets, and the slots of the stator are equipped with three-phase windings, characterized in that: The motor is a fractional slot concentrated winding motor with the number of slots per pole per phase q=Z / (2Pm)≤1 / 2, where Z is the number of slots, 2P is the number of poles, and m is the number of phases; The rotor core of the motor is an eccentric rotor core. Rotor eccentricity P r =r1 / r2=(1.05~(1+2δcos(180° / 2P))), where r1 is the rotor radius and r2 is the eccentric rotor radius. The stator core of the motor is an eccentric stator core. Stator eccentricity P R =R1 / R2=(0.95~1 / (1+δcos(180° / Z))), where R1 is the stator radius, R2 is the eccentric stator radius, and the pitch angle θ=360 / Z, The motor is a non-uniform air gap motor with double eccentricity of the stator and rotor; The length of the equivalent uniform air gap between the stator and the rotor is: δ=R1-r1.

2. The stator-rotor double eccentric non-uniform air gap three-phase permanent magnet servo motor according to claim 1, characterized in that: The number of slots of the motor is Z=9N, the number of poles is 2P=8N or the number of poles is 2P=10N, wherein N=2, 3, 4, 5, ... is a natural number greater than or equal to 2.

3. The stator-rotor double eccentric non-uniform air gap three-phase permanent magnet servo motor according to claim 1, characterized in that: The length of the equivalent uniform air gap between the stator and the rotor is: δ=R1-r1, which is 0.2-10 mm.

4. The stator-rotor double eccentric non-uniform air gap three-phase permanent magnet servo motor according to claim 1, characterized in that: For a motor with slot number Z=12 and pole number 2P=10, the length of the equivalent uniform air gap between the stator and the rotor is: δ=R1-r1, which is 0.2-2 mm.

5. The stator-rotor double eccentric non-uniform air gap three-phase permanent magnet servo motor according to claim 1, characterized in that: The stator core of the motor is an eccentric stator core, and the stator eccentricity P R =R1 / R2=(0.95~1 / (1+0.95δcos(180° / Z))), where R1 is the stator radius, R2 is the eccentric stator radius, and the tooth pitch angle θ=360 / Z.

6. The three-phase permanent magnet servo motor with double eccentricity of stator and rotor and non-uniform air gap according to any one of claims 1 to 5, characterized in that: The stator core is assembled from more than one identical stator pole slots through inner circle or outer circle positioning.

7. The stator-rotor double eccentric non-uniform air gap three-phase permanent magnet servo motor according to claim 6, characterized in that: The stator pole slots have the same eccentricity.

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