CN112994539B - A method for suppressing cogging torque ripple of permanent magnet synchronous motor - Google Patents

Abstract

The invention provides a method for suppressing the cogging torque ripple of a permanent magnet synchronous motor. The method aims at suppressing the cogging torque ripple of a permanent magnet synchronous motor. From the perspective of motor dynamic control, a method based on dynamic magnetic compensation is proposed. The cogging torque weakening scheme, in order to improve the existing weakening method, needs to change the motor structure design, increase the complexity of the motor manufacturing process, and solve the problem of torque ripple existing in the motor itself and the problem that it can only be used in specific occasions. .

Description

A method for suppressing cogging torque ripple of permanent magnet synchronous motor

technical field

The invention belongs to the field of permanent magnet synchronous motor control, and in particular relates to a method for suppressing cogging torque ripple of a permanent magnet synchronous motor.

Background technique

With the development of science and technology and industrial progress, electric drive systems and motors have become more and more widely used in various fields, including electric products, industrial manufacturing, transportation, and defense technology. Among them, permanent magnet synchronous motors are widely used due to their remarkable advantages such as high efficiency, large power factor, strong reliability, light weight, simple structure, small size and low noise. But inevitably, PMSM also has some defects, among which torque ripple is an inherent defect of PMSM. Torque ripple is affected by motor structure and parameters, control strategy and other factors, including torque ripple caused by armature reaction, torque ripple caused by electromagnetic factors, torque ripple caused by current commutation, and torque caused by cogging effect. Torque pulsation caused by pulsation and machining, in which the cogging torque pulsation exists due to the physical structure of the cogging of the motor itself, and is an oscillating rotation caused by the fluctuation of the tangential component force of the interaction between the permanent magnet and the armature teeth. torque, the force that tries to keep the position of the armature teeth and the permanent magnets aligned, even when the windings of the permanent magnet motor are not energized. The torque ripple will cause vibration and noise of the motor, which will affect the motor system in applications, such as affecting the low-speed performance of the motor speed control system, affecting the high-precision positioning in the position control system, and affecting the control characteristics of the servo control system. and operation reliability. For wind power systems, there is a starting resistance torque, which affects the efficiency of wind power. When the torque ripple frequency is the same as the resonant frequency of the motor stator or rotor, the vibration and noise in the motor will be amplified, and the performance of the motor will be greatly affected.

Traditional methods to suppress cogging torque ripple include magnetic pole offset, stator skew or rotor skew, pole slot fit, permanent magnet shape optimization, pole arc coefficient combination, auxiliary slot, unequal tooth width and unequal slot width, etc. methods, and have been verified by many experiments and practical applications. However, the traditional methods are optimized from the design of the motor body, which changes the structure of the motor, makes the motor manufacturing process more complicated, increases the motor manufacturing cost, and even introduces torque ripple caused by machining factors due to the complex process. Moreover, after the motor is manufactured, it is irreversible, and different motor designs are required in different occasions or working conditions, which reduces the utilization rate of the motor. Therefore, it is very important to suppress torque ripple.

In view of this, it is urgent to propose a method for suppressing cogging torque ripple of permanent magnet synchronous motor with certain dynamic adaptability, so as to optimize the operation performance of the motor in various occasions without increasing the manufacturing cost of the motor.

SUMMARY OF THE INVENTION

(1) Technical problems to be solved

In view of the deficiencies of the prior art, the present invention proposes a method for suppressing the cogging torque ripple of a permanent magnet synchronous motor. The method aims at suppressing the cogging torque ripple of a permanent magnet synchronous motor. A weakening scheme of cogging torque based on dynamic magnetic compensation is proposed, in order to improve the existing weakening method, it needs to change the structural design of the motor, increase the complexity of the motor manufacturing process, solve the problem of torque ripple after the motor is manufactured, and Questions that can only be used for specific occasions.

(2) Technical solutions

In order to overcome the above problems or at least partially solve the above problems, the present invention provides a method for suppressing the cogging torque ripple of a permanent magnet synchronous motor. It is assumed that the motor cogging is simplified into a rectangle, and the magnetic permeability of the permanent magnet is infinite. Under the conditions, the method includes the following steps:

表示；其中，W是电机内部的能量，α是定转子相对位置角；Step S1: Determine the cogging torque expression; when the rotor of the permanent magnet synchronous motor is in any position, its cogging torque can be calculated by

Representation; among them, W is the energy inside the motor, α is the relative position angle of the stator and rotor;

Step S2: Determine the energy inside the motor

Among them, μ ₀ is the vacuum permeability, μ ₀ =4π×10 ^-7 H/m, B(θ,α) is the magnetic flux density, θ is the angle at which the centerline of the magnetic pole deviates from the zero position of the cogging torque, V is the air-gap magnetic field volume.

得

其中，B_r(θ)为θ角处的剩磁密度，h_m为永磁体磁化方向长度，函数g(θ,α)为有效气隙长度；Step S3: At any location, the magnetic flux density is

have to

Among them, B _r (θ) is the remanence density at the angle θ, h _m is the length of the magnetization direction of the permanent magnet, and the function g(θ, α) is the effective air gap length;

进行傅里叶分解，得到离散的分解式

Step S4: respectively for B _r ² (θ) and

Perform Fourier decomposition to get the discrete decomposition

Among them, n is the harmonic order, p is the number of pole pairs, Q _S is the number of motor slots, G ₀ is the relative air gap permeability function, B _r0 =αB _r ² (θ), G _n and B _rn are Fourier coefficients of the expansion;

其中，L_a为电枢轴向长度，R₁为电枢外径，R₂为定子轭内径；Step S5: Substitute the discrete decomposition formula into the cogging torque to obtain the cogging torque expression

Among them, L _a is the axial length of the armature, R ₁ is the outer diameter of the armature, and R ₂ is the inner diameter of the stator yoke;

其中g为气隙长度，r为永磁体的位置，μ_r为r处的磁导率，F_PM1和F_gap1分别为永磁体和气隙磁场的基波幅值，a为极弧系数,

其中I_a为三相电流的有效值；Step S6: According to the mechanical characteristics of the motor, the torque T _C ' required to cancel the n-th harmonic is:

where g is the air gap length, r is the position of the permanent magnet, μ _r is the permeability at r, F _PM1 and F _gap1 are the fundamental amplitudes of the permanent magnet and the air gap magnetic field, respectively, a is the pole arc coefficient,

Wherein I _a is the effective value of the three-phase current;

Step S7: inject a three-phase current with an effective value of I _a into the stator side of the motor, and I _a is obtained from T _C =T _C ′.

Further, the permanent magnet synchronous motor is specifically a surface-mounted permanent magnet synchronous motor or a built-in permanent magnet synchronous motor.

On the other hand, as a method suitable for software implementation, the present invention also discloses a permanent magnet synchronous motor cogging torque ripple suppression system, comprising:

At least one processor and at least one memory communicatively connected to the processor, wherein: the memory stores program instructions executable by the processor, the processor invoking the program instructions to perform any of the above The method for suppressing cogging torque ripple of a permanent magnet synchronous motor described in Item 1.

In another aspect, the present invention also discloses a non-transitory computer-readable storage medium, the non-transitory computer-readable storage medium stores computer instructions, and the computer instructions cause the computer to execute any of the above. The method for suppressing the cogging torque ripple of a permanent magnet synchronous motor described above.

(3) Beneficial effects

Compared with the prior art, the technical key points of the present invention are: a) Fourier transform the formula of cogging torque to obtain harmonic expressions of different orders; b) respectively inject currents of different frequencies to convert each The harmonics of the cogging torque of the order are eliminated to achieve the purpose of weakening the cogging torque of the motor. Therefore, the present invention proposes a new method for weakening the cogging torque of the motor from the perspective of the dynamic control of the motor. This method can reduce the cost and complexity of the design and manufacture of the motor. The cogging torque of the motor is weakened, which effectively increases the utilization rate of the motor, and can be realized through software calculation and control, so that the same type of motor can be effectively used in various occasions.

Description of drawings

The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way, in which:

FIG. 1 is a schematic diagram of the position of the stator and rotor of the permanent magnet synchronous motor in the present invention.

Detailed ways

The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. The following examples are intended to illustrate the present invention, but not to limit the scope of the present invention.

As shown in the position diagram of the stator and rotor of the permanent magnet synchronous motor in Fig. 1, it is assumed that the slot is simplified as a rectangle, and the magnetic permeability of the permanent magnet is infinite. Therefore, the present invention proposes a A new method weakens the cogging torque of the motor. The expression of the cogging torque is analyzed by using the Fourier transform method, and a concept of dynamic magnetic compensation is proposed. Harmonics, by injecting currents of different frequencies to cancel the pulsation of the cogging torque they produce. At the same time, the formula of current injection is given, and a cogging torque ripple suppression method that can eliminate multiple harmonics is proposed.

Under the assumption that the motor cogging is simplified into a rectangle and the magnetic permeability of the permanent magnet is infinite, the method for suppressing the cogging torque ripple of the permanent magnet synchronous motor proposed by the present invention specifically includes the following steps:

表示；其中，W是电机内部的能量，α是定转子相对位置角；Step S1: Determine the cogging torque expression; when the rotor of the surface-mounted permanent magnet synchronous motor and the built-in permanent magnet synchronous motor is at any position, the cogging torque can be calculated by

Representation; among them, W is the energy inside the motor, α is the relative position angle of the stator and rotor;

Step S2: Determine the energy inside the motor

Among them, μ ₀ is the vacuum permeability, μ ₀ =4π×10 ^-7 H/m, B(θ,α) is the magnetic flux density, and θ is the angle at which the centerline of the magnetic pole deviates from the zero position of the cogging torque (specifically See Figure 1), V is the air gap magnetic field volume;

将其代入步骤S2中的公式后，即得

Step S3: The relative position between the permanent magnet and the slotted armature can be seen in Figure 1, then at any position, the magnetic flux density is

After substituting it into the formula in step S2, we get

Among them, B _r (θ) is the remanence density at the angle θ, h _m is the length of the magnetization direction of the permanent magnet, and the function δ(θ,α) is the effective air gap length;

进行傅里叶分解，得到离散的分解式

Step S4: respectively for B _r ² (θ) and

Perform Fourier decomposition to get the discrete decomposition

Among them, n is the harmonic order, p is the number of pole pairs, Q _S is the number of motor slots, G ₀ is the relative air-gap permeability function, B _r0 =αB _r ² (θ), G _n and B _rn are Fourier coefficients of the expansion;

其中，L_a为电枢轴向长度，R₁为电枢外径，R₂为定子轭内径；Step S5: Substitute the decomposition formula into the cogging torque to obtain the cogging torque expression

Among them, L _a is the axial length of the armature, R ₁ is the outer diameter of the armature, and R ₂ is the inner diameter of the stator yoke;

其中g为气隙长度，r为永磁体的位置，μ_r为r处的磁导率，F_PM1和F_gap1分别为永磁体和气隙磁场基波幅值，a为极弧系数,

其中I_a为三相电流的有效值；Step S6: According to the mechanical characteristics of the permanent magnet motor, the torque T _C ' required to offset the n-th harmonic is:

where g is the length of the air gap, r is the position of the permanent magnet, μ _r is the magnetic permeability at r, F _PM1 and F _gap1 are the fundamental wave amplitudes of the permanent magnet and the air gap magnetic field, respectively, a is the pole arc coefficient,

Wherein I _a is the effective value of the three-phase current;

Step S7: inject a three-phase current with an effective value of I _a into the stator side of the motor, and I _a is obtained from T _C =T _C ′.

It can be seen from this that the present invention proposes a new electronic cogging torque ripple suppression method, analyzes the expression of cogging torque by using the Fourier transform method, and proposes a concept of dynamic magnetic compensation. The harmonics of each order of cogging torque are injected with currents of different frequencies to eliminate the pulsation of cogging torque they generate. At the same time, the formula of current injection is given, and a cogging torque ripple suppression method that can eliminate multiple harmonics is proposed. Therefore, the method of the present invention reduces the cost and complexity of motor design and manufacture, can weaken the cogging torque of the motor according to the requirements of different working conditions, and increases the utilization rate of the motor.

In addition, it should be noted that the above-mentioned method for suppressing cogging torque ripple of a permanent magnet synchronous motor of the present invention can be executed as a software program or computer instruction in a non-transitory computer-readable storage medium or in a control system with a memory and a processor. , and its calculation procedure is simple and fast. Each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically alone, or two or more units may be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware, or can be implemented in the form of hardware plus software functional units. The above-mentioned integrated units implemented in the form of software functional units can be stored in a computer-readable storage medium. The above-mentioned software functional unit is stored in a storage medium, and includes several instructions to cause a computer device (which may be a personal computer, a server, or a network device, etc.) or a processor (processor) to execute the methods described in the various embodiments of the present invention. some steps. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), magnetic disk or optical disk and other media that can store program codes .

The above embodiments are only used to illustrate the technical solutions of the present invention, but are not intended to limit the specific embodiments of the present invention. Modifications or equivalent substitutions to the specific embodiments of the present invention, without any modification or equivalent substitutions that do not depart from the spirit and scope of the present invention, are still within the scope of the claims of the present invention.

Claims (4)

1. a method for suppressing cogging torque ripple of a permanent magnet synchronous motor, characterized in that, under the condition that the motor cogging is assumed to be simplified into a rectangle, and the magnetic permeability of the permanent magnet is infinite, the method comprises the following steps: Step S1: Determine the cogging torque expression; when the rotor of the permanent magnet synchronous motor is in any position, its cogging torque can be calculated by

Representation; among them, W is the energy inside the motor, α is the relative position angle of the stator and rotor; Step S2: Determine the energy inside the motor

Among them, μ ₀ is the vacuum permeability, μ ₀ =4π×10 ^-7 H/m, B(θ,α) is the magnetic flux density, θ is the angle at which the centerline of the magnetic pole deviates from the zero position of the cogging torque, V is the volume of the air-gap magnetic field; Step S3: At any location, the magnetic flux density is

have to

Among them, B _r (θ) is the remanence density at the angle θ, h _m is the length of the magnetization direction of the permanent magnet, and the function g(θ, α) is the effective air gap length; Step S4: respectively for B _r ² (θ) and

Perform Fourier decomposition to get the discrete decomposition

Among them, n is the harmonic order, p is the number of pole pairs, Q _S is the number of motor slots, G ₀ is the relative air gap permeability function, B _r0 =αB _r ² (θ), G _n and B _rn are Fourier coefficients of the expansion; Step S5: Substitute the discrete decomposition formula into the cogging torque to obtain the cogging torque expression

Among them, L _a is the axial length of the armature, R ₁ is the outer diameter of the armature, and R ₂ is the inner diameter of the stator yoke; Step S6: According to the mechanical characteristics of the motor, the torque T _C ' required to cancel the n-th harmonic is:

where g is the air gap length, r is the position of the permanent magnet, μ _r is the permeability at r, F _PM1 and F _gap1 are the fundamental amplitudes of the permanent magnet and the air gap magnetic field, respectively, a is the pole arc coefficient,

Wherein I _a is the effective value of the three-phase current; Step S7: inject a three-phase current with an effective value of I _a into the stator side of the motor, and I _a is obtained from T _C =T _C ′. 2 . The method for suppressing cogging torque ripple of a permanent magnet synchronous motor according to claim 1 , wherein the permanent magnet synchronous motor is specifically a surface-mounted permanent magnet synchronous motor or a built-in permanent magnet synchronous motor. 3 . 3. A permanent magnet synchronous motor cogging torque ripple suppression system, characterized in that, comprising: At least one processor and at least one memory communicatively connected to the processor, wherein: the memory stores program instructions executable by the processor, the processor invoking the program instructions to execute the method of claim 1 The method for suppressing cogging torque ripple of a permanent magnet synchronous motor according to any one of to 2. 4. A non-transitory computer-readable storage medium, characterized in that, the non-transitory computer-readable storage medium stores computer instructions, the computer instructions cause the computer to perform the execution of any one of claims 1 to 2. The method for suppressing the cogging torque ripple of a permanent magnet synchronous motor described above.

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