Magnetic pole optimization method for reducing torque ripple of permanent magnet synchronous motor

Abstract

The invention discloses a magnetic pole optimization method for reducing torque ripple of a permanent magnet synchronous motor. The magnetic pole optimization method comprises the following steps: step 1, analyzing a stator magnetomotive force and a stepped permanent magnet excitation magnetic potential during load operation by using an analytical method; step 2, obtaining air gap flux density harmonic amplitudes and orders respectively generated by the armature magnetic potential and the permanent magnet excitation magnetic potential; 3, solving a resultant magnetic field under the combined action of the permanent magnet and the armature magnetic potential, calculating the total output torque during load operation, and obtaining the relation between the working harmonic wave and the average output torque and the torque pulsation; and 4, based on the relationship between the working harmonic waves of the magnetic field and the output torque, the air gap flux density amplitude of the order related to the average torque is kept unchanged by adjusting the parameters of the stepped magnetic poles, and the air gap flux density amplitude of the order related to the torque pulsation is reduced. The motor obtained through the method can output the expected average torque, meanwhile, the torque pulsation is reduced, and the better torque performance is achieved; and good economic benefits can be generated.

Description

Technical Field

[0001] The invention belongs to the field of permanent magnet synchronous motors, and in particular relates to a magnetic pole optimization method for reducing torque pulsation of permanent magnet synchronous motors. Background Art

[0002] Permanent magnet synchronous motors have been widely used in the automotive, aerospace, home appliances and other fields in recent years because of their stable operation reliability and effective improvement of motor efficiency and power density.

[0003] The permanent magnet synchronous motor is composed of stator, rotor, housing, end cover and other components. The stator is basically the same as the asynchronous induction motor, and adopts a laminated design to reduce the iron loss of the core. The rotor core is solid or laminated. The permanent magnet synchronous motor rotor has the advantages of simple structure, high power density, high efficiency, etc., which can significantly improve the transmission performance of the entire system. However, with the continuous development of industrial technology, the requirements for motor operation accuracy are getting higher and higher. Therefore, it is necessary to design a magnetic pole optimization method to reduce the torque pulsation of the permanent magnet synchronous motor, so as to reduce the motor torque pulsation, thereby improving the dynamic performance of the motor and adapting to the current market demand. Summary of the invention

[0004] In order to solve the above technical problems, the inventors have developed a magnetic pole optimization method for reducing the torque pulsation of a permanent magnet synchronous motor based on their rich experience in the motor field.

[0005] The technical solution adopted by the present invention is: a magnetic pole optimization method for reducing the torque pulsation of a permanent magnet synchronous motor, comprising the following steps:

[0006] Step 1, using an analytical method to analyze the stator magnetomotive force and the step-type permanent magnet excitation magnetomotive force harmonics during load operation;

[0007] Step 2, respectively obtaining the amplitude and order of the air gap magnetic flux harmonic generated by the armature magnetic potential harmonic and the permanent magnet excitation magnetic potential;

[0008] Step 3, obtaining the synthetic magnetic field under the combined action of permanent magnet excitation and armature magnetic potential, and then calculating the total output torque when the load is running, and obtaining the relationship between the working harmonic and the average output torque and torque ripple;

[0009] Step 4, based on the relationship between the magnetic field working harmonics and the output torque, the air gap flux density amplitude of the order related to the average torque is maintained unchanged by adjusting the stepped magnetic pole parameters, and the air gap flux density amplitude of the order related to the torque pulsation is reduced.

[0010] Further, step 3 solves the total output torque expression when the motor is running under load:

[0011]

[0012] Among them, D si is the inner diameter of the stator, δ is the air gap length, p is the number of permanent magnet pole pairs; μ0 is the air permeability, which is 4π*10 -7 H / m; B sν is the amplitude of each harmonic of the armature magnetic field; B rn is the amplitude of each harmonic of the permanent magnetic field; ω is the electrical angular velocity of the input current, ν t is the time harmonic order of the armature magnetic field; ν is the spatial harmonic order of the armature magnetomotive force; n is the spatial harmonic order of the permanent magnet magnetomotive force; θ sr is the initial position angle of the stator and rotor.

[0013] Furthermore, the amplitudes of the harmonics of the air gap flux generated by the stepped permanent magnet assembly at the initial moment can be expressed as:

[0014]

[0015] Where p is the number of permanent magnet pole pairs, c is the number of permanent magnet layers; α p1 =θ m1 p / π, α p2 =θ m2 p / π,…,α pc =θ mc ·p / π are the pole arc coefficients of the permanent magnets of each layer, where θ m1 ,θ m2 ,…,θ mc are the central angles of the arc lengths of the permanent magnets of each layer, in radians; h m1 、h m2 ,…,h mc They are respectively the thickness of each layer of the permanent magnet of the stepped permanent magnet assembly.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The present invention uses an analytical method to establish an expression for magnetic pole parameters and magnetic field working harmonics, and then according to the relationship between the magnetic field working harmonics and the total torque, by adjusting the stepped magnetic pole parameters, the air gap flux density amplitude of the order related to the average torque is maintained unchanged, and the air gap flux density amplitude of the order related to the torque pulsation is reduced, thereby reducing the workload of motor design and saving motor optimization time.

[0018] 2. The motor obtained by using the magnetic pole optimization method proposed in the present invention can output the expected average torque while reducing torque pulsation, and has better torque performance.

[0019] 3. At the same time, the motor magnetic pole of the present invention is a non-skewed pole structure, which can avoid the adverse effect of introducing the skewed pole effect and reducing the electromagnetic torque compared with the traditional skewed pole and magnetic pole offset methods. It can meet the current market needs and create better economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A flow chart for reducing motor torque pulsation of the present invention;

[0021] Figure 2 A stepped magnetic pole permanent magnet motor topology structure designed for the magnetic pole optimization method of the present invention;

[0022] Figure 3 The schematic diagram of the axial cross-sectional structure of the stepped magnetic pole rotor of the present invention, the magnetization direction of the permanent magnet, the thickness of the multi-layer permanent magnet and the pole arc coefficient;

[0023] Figure 4 It is a schematic diagram of the axial cross-sectional structure of the conventional surface-mounted permanent magnet motor rotor and the permanent magnet magnetization direction, permanent magnet thickness and pole arc coefficient parameters;

[0024] Figure 5 is the main operating harmonic order related to the average torque and torque ripple in the air gap magnetic field of the embodiment of the present invention;

[0025] Figure 6 A comparison diagram of the harmonics of the permanent magnetic field of the embodiment of the present invention and the conventional surface-mounted permanent magnet motor;

[0026] Figure 7 The output torque waveform diagram of the embodiment of the present invention and the traditional surface-mounted permanent magnet motor. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0028] like Figure 1 As shown, a flow chart of a magnetic pole optimization method for reducing torque ripple of a permanent magnet synchronous motor according to the present invention is provided, comprising the following steps:

[0029] Step 1: Use analytical method to analyze the stator magnetomotive force and the harmonics of the step-type permanent magnet excitation magnetomotive force during load operation, and obtain the stator magnetomotive force and permanent magnet excitation magnetomotive force under a pair of poles as follows:

[0030]

[0031] Among them, F sν (t,θ) is the expression of the stator magnetomotive force changing with time and space angle; F sν is the amplitude of each harmonic of the stator magnetomotive force, ω is the electrical angular velocity of the input current, ν is the spatial harmonic order of the armature magnetomotive force; θ is the spatial angle; F m (t,θ) is the expression of the change of permanent magnet excitation magnetic potential with time and space; F mn is the harmonic amplitude of the permanent magnet excitation order, n is the spatial harmonic order of the permanent magnet magnetomotive force; θ sris the initial position angle of the stator and rotor.

[0032] Step 2, respectively obtain the air gap magnetic flux harmonics generated by the armature magnetic potential harmonics and the permanent magnet excitation magnetic potential, as follows:

[0033]

[0034] Where Bs(t,θ) is the expression of the air gap magnetic flux density generated by the armature magnetic potential changing with time and space angle; μ0 is the air magnetic permeability, which is 4π*10 -7 H / m; B sν is the harmonic amplitude of the armature magnetic field, ν t is the time harmonic order of the armature magnetic field; is the variation of air gap ratio permeability function over time and space, λ0 is the DC component of air gap ratio permeability function, λ i is the harmonic amplitude of the air gap ratio permeability function, i is the harmonic order of the air gap ratio permeability function; B r (t,θ) is the expression of the change of air gap magnetic flux density generated by permanent magnetic potential with time and space angle; B rn is the amplitude of each harmonic of the permanent magnet magnetic field.

[0035] Step 3: Calculate the resultant magnetic field B under the combined action of permanent magnet excitation and armature magnetic potential δ (t,θ) can be expressed as:

[0036] B δ (t,θ)=B s (t,θ)+B r (t,θ);

[0037] The total output torque expression when the load is running is calculated as follows:

[0038]

[0039] Among them, D si is the inner diameter of the stator, δ is the air gap length, and p is the number of permanent magnet pole pairs.

[0040] Step 4, based on the relationship between the magnetic field working harmonics and the output torque, the air gap flux density amplitude of the order related to the average torque is maintained unchanged by adjusting the stepped magnetic pole parameters, and the air gap flux density amplitude of the order related to the torque pulsation is reduced.

[0041] like Figure 2 As shown, the topology of the stepped magnetic pole permanent magnet motor designed by the magnetic pole optimization method of the present invention is shown.

[0042] like Figure 3As shown, the stepped permanent magnet assembly includes p pairs of permanent magnets, and the number of pairs of permanent magnet poles can be adjusted; each pair of permanent magnet poles includes two permanent magnets with different magnetization directions, and 2p permanent magnets are uniformly embedded on the outer surface of the rotor core; each permanent magnet is composed of multiple layers of sub-permanent magnets that are symmetrical about the radial axis but have different thicknesses and pole arc coefficients, and the number of permanent magnet layers is c; the pole arc coefficients of each layer of sub-permanent magnets are α p1 =θ m1 p / π, α p2 =θ m2 p / π,…,α pc =θ mc p / π, where θ m1 ,θ m2 ,…,θ mc are the central angles of each layer of permanent magnet arc length, in radians; the thickness of each layer of permanent magnets in the stepped permanent magnet assembly is h m1 、h m2 ,…,h mc . Among them, the pole arc coefficient of each layer of sub-permanent magnets located on the inner side of the rotor core should be smaller than the pole arc coefficient of the sub-permanent magnets located on the outer side. The amplitude of each harmonic of the air gap flux generated by the ladder-type permanent magnet assembly at the initial moment can be expressed as:

[0043]

[0044] Among them, B r is the residual magnetic induction intensity of the permanent magnet, in Tesla; δ is the air gap length of the motor; c is the number of layers of the stepped permanent magnet, which is a positive integer.

[0045] like Figure 4 The figure shows the rotor of a traditional surface-mounted permanent magnet motor, the axial cross-sectional structure of the permanent magnet, the magnetization direction of the permanent magnet, the thickness of the permanent magnet, and the pole arc coefficient parameter diagram. The traditional surface-mounted permanent magnet motor has a pole arc coefficient of α p =θ m p / π, where θ m is the central angle occupied by the arc length of the surface-mounted permanent magnet; the thickness of the permanent magnet of the traditional surface-mounted motor h m The harmonics of permanent magnet air gap flux density of traditional surface mounted permanent magnet motor are:

[0046]

[0047] The parameters of the permanent magnets of each layer of the step-type magnetic pole are selected to meet the following conditions: (1) the air gap flux density amplitude of the order related to the average torque is maintained unchanged by adjusting the parameters of the step-type magnetic pole; (2) the air gap flux density amplitude of the order related to the torque pulsation is reduced.

[0048] In this embodiment, a conventional surface-mounted permanent magnet synchronous motor with 4 (p=4) pairs of permanent magnet poles and 4 layers of stepped permanent magnet synchronous motor is used as an example, and the permanent magnet thickness is 4 mm, the pole arc coefficient is 0.95, and the air gap length is 1 mm. Figure 2-4 shown.

[0049] Figure 5 It is the main working harmonic order related to the space and time harmonics in the permanent magnetic field and the armature magnetic field of the embodiment of the present invention, as well as the average torque and torque pulsation. The main component of the average torque is generated by the fundamental component of the permanent magnetic field space harmonics and the fundamental component of the armature magnetic field space harmonics; the main component of the torque pulsation is the 6th harmonic, which is generated by the 5th and 7th harmonic components of the permanent magnetic field space harmonics and the 5th and 7th harmonic components of the armature magnetic field space harmonics.

[0050] Among them, the air gap magnetic density base wave amplitude B generated by the traditional surface-mounted permanent magnet pole r1_0 for:

[0051]

[0052] Among them, the air gap magnetic density base wave amplitude B generated by the ladder type permanent magnet r1 for:

[0053]

[0054] Among them, the 5th and 7th harmonic amplitudes of the air gap flux density generated by the ladder permanent magnet are B r5 , B r7 They are:

[0055]

[0056] Optimization conditions for the thickness of each layer of permanent magnets and the pole arc coefficient: (1) By adjusting the stepped magnetic pole parameters, the air gap flux density amplitude of the order related to the average torque remains unchanged, that is, B r1 =B r1_0 ;

[0057] (2) Reduce the air gap flux amplitude of the order related to the torque ripple. For this embodiment, i.e., B r5 +B r7 Take the minimum value.

[0058] Figure 6 This is a comparison of the harmonics of the permanent magnetic field of the conventional surface-mounted permanent magnet motor after optimization of the embodiment of the present invention. It can be found that the air gap flux density of the embodiment of the present invention and the conventional surface-mounted permanent magnet motor is compared. The air gap flux density amplitude of the order (fundamental wave) related to the average torque remains unchanged, and the air gap flux density amplitude of the order (5th and 7th) related to the torque pulsation is significantly reduced. Correspondingly,

[0059] Figure 7It is the output torque waveform diagram of the embodiment of the invention and the traditional surface-mounted permanent magnet motor. It can be found that the average torque is 11.1Nm, and the average torque of the embodiment of the invention and the traditional surface-mounted permanent magnet motor remains unchanged; the torque pulsation of the embodiment of the invention is 3.4%, and the torque pulsation of the traditional surface-mounted permanent magnet motor is 9%, and the torque pulsation is reduced by 62%, which proves that the proposed method can effectively reduce the torque pulsation.

[0060] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present invention.

Claims

1. A magnetic pole optimization method for reducing torque ripple of a permanent magnet synchronous motor, characterized in that: The method adopts a stepped permanent magnet assembly embedded in the surface of the rotor core, and the rotor and the stator are coaxially distributed to reduce the magnetic pole of torque pulsation, and includes the following steps: Step 1, using an analytical method to analyze the stator magnetomotive force and the step-type permanent magnet excitation magnetic potential during load operation; Step 2, obtaining the air gap magnetic flux harmonic amplitude and order respectively generated by the armature magnetic potential and the permanent magnet excitation magnetic potential; Step 3, solving the synthetic magnetic field under the combined action of the permanent magnet and the armature magnetic potential, calculating the total output torque during load operation, and obtaining the relationship between the working harmonic and the average output torque and torque ripple; Step 4, based on the relationship between the magnetic field working harmonics and the output torque, the air gap flux density amplitude of the order related to the average torque is maintained unchanged by adjusting the stepped magnetic pole parameters, and the air gap flux density amplitude of the order related to the torque pulsation is reduced.

2. The magnetic pole optimization method for reducing torque ripple of a permanent magnet synchronous motor according to claim 1, characterized in that: In step 1, the stator magnetomotive force under the pole is obtained through analysis as follows: Among them, F sν (t,θ) is the expression of the stator magnetomotive force changing with time and space angle; F sν is the amplitude of each harmonic of the stator magnetomotive force, ω is the electrical angular velocity of the input current, ν is the spatial harmonic order of the armature magnetomotive force, and θ is the spatial angle.

3. The method for optimizing magnetic poles for reducing torque ripple of a permanent magnet synchronous motor according to claim 1, characterized in that: In step 1, the permanent magnet excitation magnetic potential is analyzed as follows: Among them, F m (t,θ) is the expression of the change of permanent magnet excitation magnetic potential with time and space; F mn is the harmonic amplitude of the permanent magnet excitation order, n is the spatial harmonic order of the permanent magnet magnetomotive force; θ sr is the initial position angle of the stator and rotor.

4. The method for optimizing magnetic poles for reducing torque ripple of a permanent magnet synchronous motor according to claim 1, characterized in that: In step 2, the air gap magnetic flux harmonic generated by the armature magnetic potential harmonic is as follows: Among them, B s (t,θ) is the expression of the change of air gap magnetic flux density generated by the armature magnetic potential with time and space angle; B sν is the harmonic amplitude of the armature magnetic field, ν t is the time harmonic order of the armature magnetic field; μ0 is the air magnetic permeability, which is 4π*10 -7 H / m; is the variation of air gap ratio permeability function over time and space, λ0 is the DC component of air gap ratio permeability function, λ i is the harmonic amplitude of the air gap ratio permeability function, and i is the harmonic order of the air gap ratio permeability function.

5. The method for optimizing magnetic poles for reducing torque ripple of a permanent magnet synchronous motor according to claim 1, characterized in that: In step 2, the air gap magnetic flux harmonic generated by the armature magnetic potential harmonic is as follows: Among them, B r (t,θ) is the expression of the change of air gap magnetic flux density generated by permanent magnetic potential with time and space angle; B rn is the amplitude of each harmonic of the permanent magnet magnetic field.

6. A magnetic pole optimization method for reducing torque ripple of a permanent magnet synchronous motor according to claim 1, characterized in that: Step 3: Solve the total output torque expression when the motor is running under load: Wherein, T is the total output torque when the load is running; D si is the inner diameter of the stator, δ is the air gap length, and p is the number of permanent magnet pole pairs.

7. A magnetic pole optimization method for reducing torque ripple of a permanent magnet synchronous motor according to claim 1, characterized in that: The amplitude of each harmonic of the air gap flux generated by the stepped permanent magnet assembly at the initial moment can be expressed as: Where p is the number of permanent magnet pole pairs, c is the number of permanent magnet layers; α p1 =θ m1 p / π, α p2 =θ m2 p / π,…,α pc =θ mc ·p / π are the pole arc coefficients of the permanent magnets of each layer, where θ m1 ,θ m2 ,…,θ mc are the central angles of the arc lengths of the permanent magnets of each layer, in radians; h m1 、h m2 ,…,h mc They are respectively the thickness of each layer of the permanent magnet of the stepped permanent magnet assembly.

8. The magnetic pole optimization method for reducing torque ripple of a permanent magnet synchronous motor according to claim 7, characterized in that: The stepped permanent magnet assembly includes p pairs of permanent magnets, and the number of permanent magnet poles is adjustable; each pair of permanent magnet poles includes two permanent magnets with different magnetization directions, and 2p permanent magnets are evenly embedded on the outer surface of the rotor core; each permanent magnet is composed of multiple layers of sub-permanent magnets that are symmetrical about the radial axis but have different thicknesses and pole arc coefficients.

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