WO2022110274A1

WO2022110274A1 - Loss analysis and suppression method for magnetic field-modulated permanent-magnet electric motor

Info

Publication number: WO2022110274A1
Application number: PCT/CN2020/133832
Authority: WO
Inventors: 徐亮; 赵文祥; 蒋婷婷; 刘国海
Original assignee: 江苏大学
Priority date: 2020-11-24
Filing date: 2020-12-04
Publication date: 2022-06-02
Also published as: CN112436706A; CN112436706B

Abstract

A loss analysis and suppression method for a magnetic field-modulated permanent-magnet electric motor. A magnetomotive force and magnetic conduction model is established according to the structures of a stator (1), a rotor (2), permanent magnets (21) and armature windings (3) of a magnetic field-modulated permanent-magnet electric motor, and air-gap magnetic field harmonic distributions of the armature windings (3) and the permanent magnets are derived; the order, frequency and rotation characteristics of a magnetic field harmonic wave are analyzed, and whether each order of magnetic field harmonic wave can contribute to a torque and a loss; and contribution values of each order of magnetic field harmonic wave to the torque and the loss are calculated, and a high-hazard magnetic field harmonic wave which generates the loss but does not generate the torque is measured. A rotor magnetic flux barrier structure is designed, the adjustment effect of a magnetic flux barrier on a magnetic field harmonic wave is analyzed, the magnetic resistance on a magnetic flux path where the armature windings (3) generate high-hazard magnetic field harmonic waves is increased, and magnetic field harmonic components of high-hazard armature windings (3) are reduced in a targeted manner without affecting a magnetic field harmonic component that generates the torque. By means of the method, a high-hazard magnetic field harmonic wave can be directionally suppressed, thereby achieving a loss suppression effect on the premise of guaranteeing a high torque density of an electric motor.

Description

A Loss Analysis and Suppression Method of Magnetic Field Modulation Permanent Magnet Motor

technical field

The invention relates to a loss analysis and suppression method of a magnetic field modulation permanent magnet motor, belongs to the field of motors, and is particularly suitable for motor systems requiring high torque and high efficiency, such as electric vehicles, ship propulsion and wind power generation.

Background technique

The direct-drive permanent magnet motor can save the intermediate transmission mechanism such as gearbox and has the advantages of high reliability, high efficiency and low vibration and noise. At present, direct-drive permanent magnet motors have been used in various industries including electric vehicle in-wheel motors, large wind turbines and ship propulsion systems. However, the rapid development of electric vehicles, ship propulsion and wind power generation also requires higher and higher performance of motor systems. For example, miniaturization and light weight are the development trends of electric vehicle drive motors. At the same time, in order to ensure that the drive motor can provide sufficient power for electric vehicles under the condition of miniaturization and light weight, the torque density of the drive motor is the key. The in-wheel motor drive method installs the drive motor in the wheel, which can omit a large number of transmission components, make the vehicle structure simpler, and realize the advantages of a complex electric vehicle drive method. However, the narrow space in the wheel requires the motor to have a high torque density. In order to improve the torque density of permanent magnet motors, scholars from various countries have proposed various new permanent magnet motor structures, such as double stator permanent magnet motors, double rotor permanent magnet motors, axial flux permanent magnet motors, and transverse flux permanent magnet motors. Although the proposal of these structures effectively improves the torque density of the permanent magnet motor, the structure of the motor is complex, the processing and manufacturing are difficult, and the cost is high.

The magnetic field modulation permanent magnet motor is a new type of permanent magnet motor, and its working principle is different from that of the conventional permanent magnet motor. Traditional permanent magnet motors only use a single magnetic field harmonic to generate torque, and there are a large number of useless magnetic field harmonics in the air gap that cannot be used to generate torque. The magnetic field modulated permanent magnet motor operates on the basis of the magnetic gear effect and can take advantage of various magnetic field harmonic components in the air gap, thus having the advantage of high torque density. The research results show that the torque density of the magnetic field modulated permanent magnet motor has obvious advantages compared with the conventional permanent magnet motor under the same conditions, and the structure of the magnetic field modulated permanent magnet motor adopts the torque boosting technology such as double rotor, double stator and axial magnetic flux. The structure of the permanent magnet motor is relatively simple, so it has received extensive attention in the direct drive permanent magnet motor system.

The magnetic field harmonic content of the magnetic field modulation permanent magnet motor is rich, among which various magnetic field harmonics can generate torque. Under the cooperative work of various magnetic field harmonic magnetic fields, the average torque of the motor can be greatly improved. But it is worth noting that the harmonic magnetic field of the magnetic field modulation permanent magnet motor is rich, which will lead to the increase of the electromagnetic loss of the motor. The high loss of the motor will cause the temperature of the motor to rise, which will reduce the performance of the motor and shorten the service life of the motor. The rich magnetic field harmonics and the magnetic gear effect of the magnetic field modulated permanent magnet motor make it very difficult to carry out accurate loss analysis. On the other hand, simply suppressing the magnetic field harmonic content will result in a reduction in motor torque, losing the advantages of field-modulated permanent magnet motors. Therefore, when reducing the loss of the magnetic field modulation permanent magnet motor, it is necessary to take into account the influence on the torque, which further increases the difficulty of suppressing the loss of the magnetic field modulation permanent magnet motor. However, there are few researches on the research loss of the magnetic field modulation permanent magnet motor, and there is a lack of loss analysis and suppression methods for the magnetic field modulation permanent magnet motor.

To sum up, for the magnetic field modulated permanent magnet motor, the rich magnetic field harmonics improve its torque density, but at the same time it will cause high losses to affect the performance and operation of the motor. Therefore, in addition to considering the torque density when designing a magnetic field modulated permanent magnet motor, its loss also needs to be studied.

SUMMARY OF THE INVENTION

The purpose of the present invention is to propose a loss analysis and suppression method of the magnetic field modulation permanent magnet motor in view of the deficiencies in the loss analysis and suppression of the existing magnetic field modulation permanent magnet motor. According to the stator, rotor, permanent magnet and winding structure of the magnetic field modulated permanent magnet motor, the magnetomotive force and permeance model are established, and the magnetic field harmonic distribution of the armature winding and the permanent magnet air gap is deduced; the order, frequency and magnetic field harmonics are analyzed. Rotation characteristics, determine whether each magnetic field harmonics can contribute to torque and loss; calculate the contribution of each magnetic field harmonics to torque and loss, and find out the high-hazard magnetic field harmonics that generate loss but not torque . Design the rotor magnetic flux barrier structure, analyze the adjustment effect of the magnetic flux barrier on the magnetic field harmonics, increase the magnetic resistance on the magnetic flux path of the armature winding to generate high-hazard magnetic field harmonics, and reduce the high-hazard armature winding magnetic field harmonics in a targeted manner components without affecting the harmonic components of the magnetic field that generate torque. The invention analyzes the action mechanism of the magnetic field harmonics of the magnetic field modulation permanent magnet motor on the loss, can quantitatively calculate the contribution value of the magnetic field harmonics to the loss and torque, and at the same time can directionally suppress the high-harm magnetic field harmonics, so as to ensure the high torque of the motor Loss suppression effect under the premise of density.

Specifically, the motor of the present invention is realized by adopting the following technical solutions: a loss analysis and suppression method of a magnetic field modulation permanent magnet motor, comprising the following steps:

Step 1: Ignore the magnetic field generated by the armature winding on the stator and the cogging structure on the stator, and only consider the magnetic flux path formed by the permanent magnetic field generated by the permanent magnet on the rotor; according to the symmetry and periodicity of the rotor magnetic circuit, select the rotor structure The basic unit, establishes the permanent magnet magnetomotive force expression;

Step 2: Ignore the permanent magnet magnetic field on the rotor, only consider the cogging structure on the stator and the connection and energization mode of the armature windings, establish the magnetomotive force expression of the armature windings of each phase in turn, and calculate the magnetomotive force of the armature windings of each phase. The mathematical expressions are added together to obtain the synthetic armature winding magnetomotive force expression considering the stator cogging effect;

Step 3: Considering the unequal magnetic permeability of the teeth and slots on the stator on the circumference of the motor air gap, select the basic unit of the tooth and slot structure on the stator, and establish the stator permeability expression;

Step 4: The permanent magnets on the rotor are attached to the rotor core, and the permeance of the rotor core does not change with time and space as a constant, and the stator and rotor permeance expressions can be obtained by multiplying the stator permeance and the rotor permeance;

Step 5: Multiply the permanent magnet magnetomotive force, the stator and rotor permeability and the permeability coefficient to obtain the permanent magnet air gap flux density expression;

Step 6: Multiply the magnetomotive force of the synthetic armature winding considering the stator cogging effect and the permeance of the rotor to obtain the expression of the air-gap flux density of the armature winding;

Step 7: Identify the harmonics of the air gap flux density that can contribute to the average torque and those that cannot contribute to the average torque; analyze and compare the order and rotational speed of the harmonic components of the permanent magnet air gap flux density and the armature winding air gap flux density, When the speed and order of the two magnetic density harmonics are equal, the magnetic density harmonic can contribute to the average torque for the working wave, otherwise it cannot contribute to the average torque for the non-working wave;

Step 8: Identify the air-gap flux density harmonics that contribute to the average torque and those that cannot contribute to the average torque; analyze the permanent magnet air-gap flux density and the armature winding air-gap flux density harmonics relative to the rotor rotational speed, which is equal to the rotor rotational speed The magnetic density harmonics do not generate rotor loss, and the magnetic density harmonics that are not equal to the rotation speed of the rotor generate rotor loss; the rotor loss is calculated by the calculation formula of rotor core loss and permanent magnet eddy current loss;

Step 9: For the air-gap flux density harmonics that generate losses but do not contribute to the average torque, design several magnetic flux barriers on the motor rotor to increase the reluctance on the magnetic flux path of the armature windings that generate high-hazard magnetic field harmonics, so that Reduce the content of high-hazard harmonics to ensure that the air-gap flux density harmonics contributing to the average torque are not affected.

Further, the expression of the permanent magnet magnetomotive force F _PM (θ) expression in step 1 is:

In the formula, F _PMn is the Fourier coefficient, θ is the circumferential position of the motor air gap, P _r is the number of pole pairs of the rotor permanent magnet, and n is a positive odd number.

Further, in step 2: if it is a five-phase centralized winding, the five-phase windings are successively passed into sinusoidal currents with a mutual difference of π/5 electrical angle, and the synthetic armature winding magnetomotive force F _aq (θ, t considering the stator cogging effect) ) expression is:

In the formula, F _aq is the magnitude of the magnetomotive force of the armature winding, N is the number of turns of each set of windings, I _max is the amplitude of the alternating current, ω _PM is the rotational speed of the stator relative to the rotor and the permanent magnet, and q is the magnetic force of the armature winding. Potential harmonic order, P _r is the number of pole pairs of the rotor permanent magnet, r is a positive integer, θ ₁ and θ ₂ are the

coordinate positions

1 and 2 on both sides of the first stator split tooth of phase A, the difference between θ ₁ and θ ₂ The value is the width of a split tooth, and t is the time.

Further, in step 3: the expression of the stator permeance Λ _s (θ, t) is:

In the formula, Λ ₀ and Λ _k are the Fourier coefficients, k is a positive integer, ω _PM is the rotational speed of the stator relative to the rotor and the permanent magnet, θ ₀ is the initial position of the rotor, and N _s is the number of stator teeth;

In step 4: the permanent magnets on the rotor are attached to the rotor core, and the rotor magnetic permeability Λ _or (θ, t) is expressed as:

Λ _or (θ,t)=Λ _r1

Among them, Λ _r1 is the rotor flux;

In step 5: the permanent magnetic air gap flux density B _PM (θ, t) is expressed as:

where F _PMn is the Fourier coefficient, g is the equivalent air gap thickness, and μ ₀ is the vacuum permeability;

In step 6: the armature winding air gap flux density B _or (θ, t) is expressed as:

Further, the specific process of step 7 is:

Step 7.1: The permanent magnet air gap flux density contains two types of flux density harmonics: the order is nP _r , the rotational speed is 0, the angular frequency is 0, the order is |nP _r ±kN _s |, and the rotational speed is kN _s ω _PM / (P _r ±kN _s ), angular frequency kN _s f_ _PM ; the armature winding flux density contains two types of flux density harmonics: order is q=10r-9, rotational speed is (qP _r )ω _PM /q, angular frequency is |qP _r |f_ _PM , the order is q=10r-1, the rotational speed is (q+P _r )ω _PM /q, and the angular frequency is |q+P _r |f_ _PM , where f_ _PM is the frequency of the permanent magnet , the harmonics with the same order and rotation speed are determined according to the air-gap flux density harmonics and armature winding flux density harmonic formulas;

Step 7.2: The average torque contributed by harmonics with the same order and rotational speed is calculated as:

In the formula: B _v is the magnetic density amplitude of the permanent magnet air gap of the v order, A _Wv is the electric load harmonic amplitude of the v order, D _ri is the diameter of the air gap, a is the axial length of the motor, and θ _v is The phase angle between the v-order permanent magnet air-gap flux density harmonics and the electrical load harmonics, the average torque of the magnetic field-modulated permanent magnet motor can be obtained by adding the average torques contributed by the air-gap flux density harmonics;

The electrical load harmonic A _Wv can be expressed as:

A _Wv =m(Nk _wv )I _max /(πD _ri )

In the formula: m is the number of phases of the motor armature winding, _kwv is the winding factor of the v order, N is the number of turns of the motor winding, and I _max is the amplitude of the alternating current passing through the armature winding.

Further, the specific process of step 8 is: select the representative points on the rotor core and the permanent magnet, use the finite element method to calculate the change of the magnetic density of the representative point with time, and determine the representative point according to the change period of the armature current and the space change period of the permanent magnet. The period of the point magnetic density changing with time, the harmonic analysis is performed on the representative point magnetic density, and the amplitude, order and angular frequency of each magnetic density harmonic are calculated:

Step 8.1: Calculate the permanent magnet eddy current loss and rotor core loss of the motor according to the amplitude, order and angular frequency of each magnetic density harmonic at the representative point. The calculation formula of the permanent magnet eddy current loss is:

In the formula, a, b and d are the axial length, width and thickness of the permanent magnet, respectively, σ is the electrical conductivity of the permanent magnet, ω _k is the magnetic density harmonic rotation speed of order k, and B _PMk is the order of The magnetic density harmonic amplitude of k;

Step 8.2: The core loss calculation formula is:

where A _e is the core eddy current loss coefficient, A _h is the core hysteresis loss coefficient, f _k is the alternating frequency of the k-order magnetic density harmonic, and B _Corek is the k-order rotor core magnetic density amplitude.

Further, the specific process of step 9 is as follows: compare the angular frequency of the magnetic density harmonics of the permanent magnet and the rotor core with the angular frequency of the armature winding and the air gap magnetic density of the permanent magnet, and determine the permanent magnet and the The rotor core magnetic density is generated by which air-gap magnetic density harmonics, and then calculate the permanent magnet and iron core losses generated by each air-gap magnetic density harmonic, and identify the air-gap magnetic density harmonics that generate a lot of losses without contributing to the average torque Wave Components:

Step 9.1: Design P _r magnetic flux barriers on the motor rotor. At this time, the calculation formula of the motor rotor magnetic permeability Λ _pr (θ, t) is:

where λ is the width of the magnetic flux barrier, Λ ₁ is the rotor permeability amplitude, and T is twice the pole pitch of the permanent magnet;

Step 9.2: After designing P _r magnetic flux barriers on the rotor, the calculation formula of the air gap flux density harmonics of the armature winding is:

Optimize the width and length of the flux barrier and increase the reluctance on the flux path where the armature windings generate high-hazard magnetic field harmonics to reduce the high-hazard harmonic content while ensuring that the air-gap flux density harmonics that contribute to the average torque are not affected. influences.

Beneficial effects:

After the present invention adopts the above-mentioned design scheme, it can have the following beneficial effects:

1. The present invention establishes a magnetomotive force and a magnetic permeability model according to the stator, rotor, permanent magnet and winding structure of a magnetic field modulation permanent magnet motor, and derives the harmonic distribution of the armature winding and the permanent magnetic air gap magnetic field; by analyzing the magnetic field harmonics The order, frequency and rotation characteristics can quickly determine whether each magnetic field harmonic can contribute to the torque loss. It avoids the blindness of the traditional parameter scanning analysis and design method, points out the direction for the loss analysis and suppression of the magnetic field modulation permanent magnet motor, reduces the workload of motor design, and shortens the optimization design cycle of the motor.

2. The present invention constructs the conversion mechanism of air gap flux density harmonics and permanent magnet and rotor core harmonic flux density, establishes an analysis and calculation model based on the harmonic angle of permanent magnet and rotor core loss, and can analyze and calculate each air gap flux density. The contribution value of the dense harmonics to the loss can be determined, and the high-hazard magnetic field harmonics that only generate loss but do not contribute to the torque can be identified, which lays a solid foundation for realizing the loss suppression under the premise of ensuring the motor torque density.

3. The present invention establishes a rotor permeability model considering the rotor magnetic flux barrier, analyzes the action mechanism of the magnetic flux barrier on the rotor on the harmonics of the armature winding, and proposes an optimal design method for the rotor magnetic flux barrier, which can be used without affecting the contribution torque. On the basis of the harmonics of the motor, it can effectively suppress the harmonics of the armature winding with high hazard, so as to reduce the loss while ensuring the high torque density of the motor. Compared with the traditional magnetic field modulation permanent magnet motor, the magnetic field modulation permanent magnet motor designed by the loss analysis and suppression method of the present invention has better torque performance and lower loss.

Description of drawings

1 is a cross-sectional view of an object of an embodiment of the present invention;

2 is a schematic diagram of a basic unit of a rotor structure and a permanent magnet magnetomotive force without a magnetic flux barrier according to an embodiment of the present invention;

Fig. 3 is the connection schematic diagram of the armature winding of the embodiment of the present invention;

4 is a schematic diagram of the magnetomotive force of each phase armature winding according to an embodiment of the present invention;

5 is a schematic diagram of a basic unit of a stator cogging structure and a stator flux guide according to an embodiment of the present invention;

6 is a schematic diagram of a rotor flux permeance without a magnetic flux barrier according to an embodiment of the present invention;

Fig. 7 is the harmonic analysis of the magnetic density of the permanent magnetic air gap without the magnetic flux barrier according to the embodiment of the present invention;

Fig. 8 is the harmonic analysis of the air gap magnetic density of the armature winding without the magnetic flux barrier according to the embodiment of the present invention;

FIG. 9 is the contribution of the air gap magnetic density harmonics to the average torque without the magnetic flux barrier according to the embodiment of the present invention;

10 is the variation of magnetic density with time and the harmonic analysis of the representative point of the permanent magnet without the magnetic flux barrier according to the embodiment of the present invention; (a) is the variation of the magnetic density with time; (b) is the harmonic analysis result;

11 is the variation of magnetic density with time and the harmonic analysis of the representative point of the rotor core without the magnetic flux barrier according to the embodiment of the present invention; (a) is the variation of the magnetic density with time; (b) is the harmonic analysis result;

12 is the contribution of the air gap magnetic density harmonics to the loss of the permanent magnet and the rotor core without the magnetic flux barrier according to the embodiment of the present invention; (a) is the contribution of the air gap magnetic density harmonics to the permanent magnet loss; (b) is the air gap magnetic density harmonic. Contribution of gap flux density harmonics to rotor core loss;

FIG. 13 is a schematic diagram of the basic unit of the rotor structure and the rotor magnetic permeability under the magnetic flux barrier according to the embodiment of the present invention;

14 is the harmonic analysis of the air gap magnetic density of the armature winding with or without the magnetic flux barrier according to the embodiment of the present invention;

15 is a comparison of the loss of permanent magnets and rotor cores with or without a magnetic flux barrier according to an embodiment of the present invention;

FIG. 16 is a comparison of average torque and torque ripple with or without a flux barrier according to an embodiment of the present invention.

In the figure: 1. Motor stator, 11, stator teeth, 12, split slot, 13, split teeth, 2, motor rotor, 21, permanent magnet, 22, flux barrier, 3, armature winding, 4, air gap.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as a limitation of the present invention.

As shown in FIG. 1 , the object of the embodiment of the present invention is a five-phase magnetic field modulation permanent magnet motor, including a motor stator 1 and a motor rotor 2. An air gap 4 is provided between the motor stator 1 and the motor rotor 2, and the motor stator 1 is wound on the top. The armature winding 3 is made; the motor stator 1 contains 20 stator teeth 11, each stator tooth 11 is split into 2 split teeth 13, and each split tooth 13 has split slots 12 on both sides, and there are a total of 40 on the motor stator 1. There are 62 pieces of permanent magnets 21 on the motor rotor 2, 62 pieces of permanent magnets 21 are evenly distributed on the rotor 2, and the permanent magnets 21 are alternately magnetized in the radial direction; A total of 31 magnetic flux barriers 22 are provided, and the 31 magnetic flux barriers 22 are evenly distributed on the rotor 2 .

The method for analyzing and suppressing the loss of a magnetic field modulation permanent magnet motor according to the present invention, the specific implementation object is shown in Figure 1, and includes the following steps:

A method for analyzing and suppressing loss of a magnetic field modulation permanent magnet motor, characterized in that it includes the following steps:

Step 4: The permanent magnets on the rotor are attached to the rotor core, and the permeance of the rotor core does not change with time and space as a constant. The rotor permeance is shown in Figure 6. The stator and rotor permeance can be expressed by multiplying the stator and rotor permeance. Mode;

Step 5: Multiply the permanent magnet magnetomotive force, the stator and rotor permeability and the permeability coefficient to obtain the permanent magnet air gap flux density expression:

Step 8: Identify the air-gap flux density harmonics that contribute to the average torque and those that cannot contribute to the average torque; analyze the permanent magnet air-gap flux density and the armature winding air-gap flux density harmonics relative to the rotor rotational speed, which is equal to the rotor rotational speed The magnetic density harmonics of 2000 do not produce rotor loss, and the magnetic density harmonics that are not equal to the rotation speed of the rotor produce rotor loss; the rotor loss is calculated by the calculation formula of rotor core loss and permanent magnet eddy current loss.

Further, the specific calculation method of steps 1-6 is:

Step 1: The expression of permanent magnet magnetomotive force F _PM (θ) is:

Step 2: It is a five-phase centralized winding, and the A, B, C, D, E five-phase windings are sequentially passed into sinusoidal currents with a mutual difference of π/5 electrical angle as follows:

The synthetic armature winding magnetomotive force expression considering the stator cogging effect is:

In the formula, N is the number of turns of each set of windings, I _max is the amplitude of the alternating current, ω _PM is the rotational speed of the stator relative to the rotor and the permanent magnet, q is the armature winding magnetomotive force harmonic order, r is a positive integer, θ ₁ and θ ₂ are the coordinate

positions

1 and 2 on both sides of the first stator split tooth of phase A, the difference between θ ₁ and θ ₂ is the width of one split tooth, θ ₀ is the initial position of the rotor, and t is the time.

Considering the cogging structure on the stator, the armature winding connection (Fig. 3), the magnetomotive force of each phase armature winding (Fig. 4), and the current expression of each phase, the magnetomotive force expression of each phase armature winding is established. Add the mathematical expressions of the magnetomotive force of the phase armature windings to obtain the combined armature winding magnetomotive force expression considering the stator cogging effect

Step 3: As shown in Figure 5, the stator permeability expression is:

Step 4: The permanent magnets on the rotor are attached to the rotor core. According to Fig. 6, the rotor magnetic permeability Λ _or (θ, t) is expressed as:

Λ _or (θ,t)=Λ _r1

Among them, Λ _r1 is the rotor permeance.

Step 5: The permanent magnetic air gap flux density B _PM (θ, t) is expressed as:

In the formula, F _PMn is the Fourier coefficient, g is the equivalent air gap thickness, and μ ₀ is the vacuum permeability.

Step 6: The expression of the armature winding air gap flux density B _or (θ, t) is:

Further, the specific calculation method of step 7 is:

Step 7.1: As shown in Figure 7, the permanent magnet air gap flux density contains two types of flux density harmonics: the order is nP _r , the rotational speed is 0, the angular frequency is 0, the order is |nP _r ±kN _s |, the rotational speed is is kN _s ω _PM /(P _r ±kN _s ), the angular frequency kN _s f_ _PM ; as shown in Figure 8, the armature winding flux density includes two types of flux density harmonics: the order is q=10r-9, the rotational speed is (qP _r )ω _PM /q, the angular frequency is |qP _r |f_ _PM , the order is q=10r-1, the rotational speed is (q+P _r )ω _PM /q, and the angular frequency is |q+P _r | _{f_PM} . Wherein, _{f_PM} is the permanent magnet frequency, _Pr =31, _Ns =20. According to the air gap flux density harmonic and armature winding flux density harmonic formula, the harmonics with the same order and rotation speed are 9, 11, 29, 31, etc.

In the formula: B _v is the magnetic density amplitude of the permanent magnet air gap of the v order, A _Wv is the electric load harmonic amplitude of the v order, D _ri is the diameter of the air gap, a is the axial length of the motor, and θ _v is The phase angle between the v-order permanent magnet air-gap flux density harmonics and the electrical load harmonics. The average torque of the magnetic field-modulated permanent magnet motor can be obtained by summing the average torques contributed by the harmonics of the air-gap flux density, as shown in Figure 9.

The electrical load harmonic A _Wv can be expressed as:

A _Wv =m(Nk _wv )I _max /(πD _ri )

Further, the specific calculation method of step 8 is as follows. Select the representative points on the rotor core and permanent magnet, and use the finite element method to calculate the variation of the magnetic density of the representative points with time, as shown in Figures 10(a) and 11(a). According to the change period of the armature current and the space change period of the permanent magnet, the period of the magnetic density of the representative point changing with time is determined, and the harmonic analysis of the magnetic density of the representative point is carried out to calculate the amplitude, order and angular frequency of the harmonics of each magnetic density. As shown in Figures 10(b) and 11(b).

Step 8.1: The calculation formula of permanent magnet eddy current loss is:

In the formula, a, b and d are the axial length, width and thickness of the permanent magnet, respectively, σ is the electrical conductivity of the permanent magnet, ω _k is the magnetic density harmonic rotation speed of order k, and B _PMk is the order of The magnetic density harmonic amplitude of k. The eddy current loss of the permanent magnet of the motor can be calculated by substituting the amplitude, order and angular frequency of each magnetic density harmonic at the representative point of the permanent magnet, as shown in Figure 12(a).

Step 8.2: The core loss calculation formula is:

where A _e is the core eddy current loss coefficient, A _h is the core hysteresis loss coefficient, f _k is the alternating frequency of the k-order magnetic density harmonic, and B _Corek is the k-order rotor core magnetic density amplitude. The rotor core loss of the motor can be calculated by substituting the amplitude, order and angular frequency of each magnetic density harmonic at the representative point of the rotor core, as shown in Figure 12(b).

Further, the specific calculation method of step 9 is as follows. Compare the angular frequency of the magnetic density harmonics of the permanent magnet and rotor core with the angular frequency of the magnetic density harmonics of the armature winding and the permanent magnet air gap, and determine which air gaps the magnetic density of the permanent magnet and the rotor core is composed of by the difference of the angular frequency of each harmonic. The magnetic density harmonics are generated, and then the permanent magnet and iron core losses generated by the air gap magnetic density harmonics are calculated. Identify the harmonic components of the air gap flux density that generate significant losses without contributing to the average torque. Comparing Figures 9 and 12, it can be seen that the harmonic orders of 9, 11, 29, and 31 air gap flux density contribute to the average torque, and the harmonic orders of 1, 9, 11, 29, and 31 air gap flux density contribute to the loss, where The 1st order air gap flux density harmonic produces a lot of losses without contributing to the average torque and is a high hazard harmonic. Comparing Figures 7 and 8, it can be seen that the first-order air-gap flux density harmonics are all generated by the armature windings.

Step 9.1: Design P _r magnetic flux barriers on the rotor of the motor (Fig. 13). At this time, the calculation formula of the magnetic permeability of the rotor of the motor is:

In the formula, Λ ₁ is the rotor permeability amplitude, and T is twice the pole pitch of the permanent magnet.

Optimized flux barrier width and length and increased reluctance on the flux path where the armature windings generate high hazard magnetic field harmonics to reduce the high hazard harmonic content (1st harmonic) while ensuring the air gap contributing to the average torque Magnetic density harmonics are not affected.

FIG. 14 is the harmonic analysis of the air-gap flux density of the armature winding with or without the magnetic flux barrier according to the embodiment of the present invention. As shown in the figure, the designed rotor flux barrier structure effectively suppresses the generation of high-harm harmonics (1st harmonic), while other harmonics are basically unaffected. FIG. 15 is a comparison of the loss of the permanent magnet and the rotor core with or without the magnetic flux barrier in the embodiment of the present invention. As shown in the figure, by directional suppression of high-harm harmonics, the permanent magnet eddy current loss and rotor core loss of the field-modulated permanent magnet motor are effectively reduced. FIG. 16 is a comparison of average torque and torque ripple with or without a flux barrier according to an embodiment of the present invention. As shown in the figure, the embodiment of the present invention can suppress the loss on the premise of ensuring the torque density of the motor.

To sum up, the present invention discloses a loss analysis and suppression method of a magnetic field modulation permanent magnet motor. According to the stator, rotor, permanent magnet and winding structure of the magnetic field modulated permanent magnet motor, the magnetomotive force and permeance model are established, and the magnetic field harmonic distribution of the armature winding and the permanent magnet air gap is deduced; the order, frequency and magnetic field harmonics are analyzed. Rotation characteristics, determine whether each magnetic field harmonic can contribute to torque and loss; calculate the contribution value of each magnetic field harmonic to torque and loss, and find out the high-hazard magnetic field harmonic that only produces loss but not torque Wave. Design the rotor magnetic flux barrier structure, analyze the adjustment effect of the magnetic flux barrier on the magnetic field harmonics, increase the magnetic resistance on the magnetic flux path of the armature winding to generate high-hazard magnetic field harmonics, and reduce the high-hazard armature winding magnetic field harmonics in a targeted manner components without affecting the harmonic components of the magnetic field that generate torque. The invention analyzes the action mechanism of the magnetic field harmonics of the magnetic field modulation permanent magnet motor on the loss, can quantitatively calculate the contribution value of the magnetic field harmonics to the loss and torque, and at the same time can directionally suppress the high-harm magnetic field harmonics, so as to ensure the high torque of the motor Loss suppression effect under the premise of density.

In the description of this specification, reference to the terms "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples", etc., is meant to incorporate the embodiments A particular feature, structure, material, or characteristic described by an example or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, The scope of the invention is defined by the claims and their equivalents.

Claims

A method for analyzing and suppressing loss of a magnetic field modulation permanent magnet motor, characterized in that it includes the following steps:

Step 1: Ignore the magnetic field generated by the armature winding on the stator and the cogging structure on the stator, and only consider the magnetic flux path formed by the permanent magnetic field generated by the permanent magnet on the rotor; according to the symmetry and periodicity of the rotor magnetic circuit, select the rotor structure The basic unit, establishes the permanent magnet magnetomotive force expression;

Step 2: Ignore the permanent magnet magnetic field on the rotor, only consider the cogging structure on the stator and the connection and energization mode of the armature windings, establish the magnetomotive force expression of the armature windings of each phase in turn, and calculate the magnetomotive force of the armature windings of each phase. The mathematical expressions are added together to obtain the synthetic armature winding magnetomotive force expression considering the stator cogging effect;

Step 3: Considering the unequal magnetic permeability of the teeth and slots on the stator on the circumference of the motor air gap, select the basic unit of the tooth and slot structure on the stator, and establish the stator permeability expression;

Step 4: The permanent magnets on the rotor are attached to the rotor core, and the permeance of the rotor core does not change with time and space as a constant, and the stator and rotor permeance expressions can be obtained by multiplying the stator permeance and the rotor permeance;

Step 5: Multiply the permanent magnet magnetomotive force, the stator and rotor permeability and the permeability coefficient to obtain the permanent magnet air gap flux density expression;

Step 6: Multiply the magnetomotive force of the synthetic armature winding considering the stator cogging effect and the permeance of the rotor to obtain the expression of the air-gap flux density of the armature winding;

Step 7: Identify the harmonics of the air gap flux density that can contribute to the average torque and those that cannot contribute to the average torque; analyze and compare the order and rotational speed of the harmonic components of the permanent magnet air gap flux density and the armature winding air gap flux density, When the speed and order of the two magnetic density harmonics are equal, the magnetic density harmonic can contribute to the average torque for the working wave, otherwise it cannot contribute to the average torque for the non-working wave;

Step 8: Identify the air-gap flux density harmonics that contribute to the average torque and those that cannot contribute to the average torque; analyze the permanent magnet air-gap flux density and the armature winding air-gap flux density harmonics relative to the rotor rotational speed, which is equal to the rotor rotational speed The magnetic density harmonics do not generate rotor loss, and the magnetic density harmonics that are not equal to the rotation speed of the rotor generate rotor loss; the rotor loss is calculated by the calculation formula of rotor core loss and permanent magnet eddy current loss;

Step 9: For the air-gap flux density harmonics that generate losses but do not contribute to the average torque, design several magnetic flux barriers on the motor rotor to increase the reluctance on the magnetic flux path of the armature windings that generate high-hazard magnetic field harmonics, so that Reduce the content of high-hazard harmonics to ensure that the air-gap flux density harmonics contributing to the average torque are not affected.
A kind of magnetic field modulation permanent magnet motor loss analysis and suppression method according to claim 1, is characterized in that, the expression of permanent magnet magnetomotive force F PM (θ) expression in step 1 is:

In the formula, F PMn is the Fourier coefficient, θ is the circumferential position of the motor air gap, P r is the number of pole pairs of the rotor permanent magnet, and n is a positive odd number.
A method for analyzing and suppressing loss of a magnetic field modulation permanent magnet motor according to claim 1, characterized in that, in step 2: if it is a five-phase concentrated winding, the five-phase windings are sequentially connected to sinusoids with a mutual difference of π/5 electrical angle. Current, the synthetic armature winding magnetomotive force F aq (θ, t) considering the stator cogging effect is expressed as:

In the formula, F aq is the magnitude of the magnetomotive force of the armature winding, N is the number of turns of each set of windings, I max is the amplitude of the alternating current, ω PM is the rotational speed of the stator relative to the rotor and the permanent magnet, and q is the magnetic force of the armature winding. Potential harmonic order, P r is the number of pole pairs of the rotor permanent magnet, r is a positive integer, θ 1 and θ 2 are the coordinate positions 1 and 2 on both sides of the first stator split tooth of phase A, the difference between θ 1 and θ 2 The value is the width of a split tooth, and t is the time.
A method for analyzing and suppressing loss of a magnetic field modulation permanent magnet motor according to claim 3, characterized in that, in step 3: the expression of the stator permeance Λs (θ, t) is:

In the formula, Λ 0 and Λ k are the Fourier coefficients, k is a positive integer, ω PM is the rotational speed of the stator relative to the rotor and the permanent magnet, θ 0 is the initial position of the rotor, and N s is the number of stator teeth;

In step 4: the permanent magnets on the rotor are attached to the rotor core, and the rotor magnetic permeability Λ or (θ, t) is expressed as:

Λ or (θ,t)=Λ r1

Among them, Λ r1 is the rotor flux;

In step 5: the permanent magnetic air gap flux density B PM (θ, t) is expressed as:

where F PMn is the Fourier coefficient, g is the equivalent air gap thickness, and μ 0 is the vacuum permeability;

In step 6: the armature winding air gap flux density B or (θ, t) is expressed as:
A kind of loss analysis and suppression method of magnetic field modulation permanent magnet motor according to claim 4, is characterized in that, the specific process of step 7 is:

Step 7.1: The permanent magnet air gap flux density contains two types of flux density harmonics: the order is nP r , the rotational speed is 0, the angular frequency is 0, the order is |nP r ±kN s |, and the rotational speed is kN s ω PM / (P r ±kN s ), angular frequency kN s f_ PM ; the armature winding flux density contains two types of flux density harmonics: order is q=10r-9, rotational speed is (qP r )ω PM /q, angular frequency is |qP r |f_ PM , the order is q=10r-1, the rotational speed is (q+P r )ω PM /q, and the angular frequency is |q+P r |f_ PM , where f_ PM is the frequency of the permanent magnet , the harmonics with the same order and rotation speed are determined according to the air-gap flux density harmonics and armature winding flux density harmonic formulas;

Step 7.2: The average torque contributed by harmonics with the same order and rotational speed is calculated as:

In the formula: B v is the magnetic density amplitude of the permanent magnet air gap of the v order, A Wv is the electric load harmonic amplitude of the v order, D ri is the diameter of the air gap, a is the axial length of the motor, and θ v is The phase angle between the v-order permanent magnet air-gap flux density harmonics and the electrical load harmonics, the average torque of the magnetic field-modulated permanent magnet motor can be obtained by adding the average torques contributed by the air-gap flux density harmonics;

The electrical load harmonic A Wv can be expressed as:

A Wv =m(Nk wv )I max /(πD ri )

In the formula: m is the number of phases of the motor armature winding, kwv is the winding factor of the v order, N is the number of turns of the motor winding, and I max is the amplitude of the alternating current passing through the armature winding.
A method for analyzing and suppressing loss of a magnetic field modulated permanent magnet motor according to claim 1, wherein the specific process of step 8 is: selecting a representative point on the rotor core and the permanent magnet, and calculating the magnetic field of the representative point by using a finite element method. The change of density with time, according to the change period of the armature current and the space change period of the permanent magnet, determine the period of the change of the magnetic density at the representative point with time, carry out the harmonic analysis of the magnetic density at the representative point, and calculate the amplitude of the harmonics of each magnetic density. , order and angular frequency:

Step 8.1: Calculate the permanent magnet eddy current loss and rotor core loss of the motor according to the amplitude, order and angular frequency of each magnetic density harmonic at the representative point. The calculation formula of the permanent magnet eddy current loss is:

In the formula, a, b and d are the axial length, width and thickness of the permanent magnet, respectively, σ is the electrical conductivity of the permanent magnet, ω k is the magnetic density harmonic rotation speed of order k, and B PMk is the order of The magnetic density harmonic amplitude of k;

Step 8.2: The core loss calculation formula is:

where A e is the core eddy current loss coefficient, A h is the core hysteresis loss coefficient, f k is the alternating frequency of the k-order magnetic density harmonic, and B Corek is the k-order rotor core magnetic density amplitude.
A kind of magnetic field modulation permanent magnet motor loss analysis and suppression method according to claim 1, it is characterized in that, the specific process of step 9 is as follows: compare permanent magnet and rotor core magnetic density harmonics with armature winding and permanent magnet air gap magnetic The angular frequency of the dense harmonics, through the difference of the angular frequencies of the harmonics, to determine which air-gap magnetic density harmonics are generated by the permanent magnet and rotor core magnetic densities, and then calculate the permanent magnets generated by the air-gap magnetic density harmonics. Magnet and core losses, specifying the harmonic components of the air gap flux density that generate substantial losses without contributing to the average torque:

Step 9.1: Design P r magnetic flux barriers on the rotor of the motor. At this time, the calculation formula of the magnetic permeability of the rotor of the motor Λ pr (θ, t) is:

where λ is the width of the magnetic flux barrier, Λ 1 is the rotor permeability amplitude, and T is twice the pole pitch of the permanent magnet;

Step 9.2: After designing P r magnetic flux barriers on the rotor, the calculation formula of the air gap flux density harmonics of the armature winding is:

Optimize the width and length of the flux barrier and increase the reluctance on the flux path where the armature windings generate high-hazard magnetic field harmonics to reduce the high-hazard harmonic content while ensuring that the air-gap flux density harmonics that contribute to the average torque are not affected. influences.