A new method for calculating iron loss of stator permanent magnet motor

Abstract

The present invention proposes a novel method for calculating the iron loss of a stator permanent magnet motor, which comprises the following steps: firstly, selecting representative points for analyzing the variation law of the magnetic flux density in the iron core; then obtaining an elliptical magnetization trajectory diagram through simulation; decomposing the elliptical harmonic magnetic field; calculating the magnetic flux density amplitude and the DC bias amplitude on the long axis and short axis of each elliptical harmonic; and finally calculating the iron loss through the proposed formula. The novel method for calculating the iron loss of a stator permanent magnet motor proposed in the present invention takes into account the influence of multiple factors, including: elliptical rotating magnetization phenomenon, DC bias phenomenon, small hysteresis loop phenomenon and PWM harmonic current, and has the outstanding advantages of high accuracy, simple calculation process, and can be used to calculate the iron loss of different motors under different working conditions, thus providing guidance for the design and optimization of motors.

Description

Technical Field

[0001] The invention relates to the field of motor iron loss calculation, and in particular to a novel stator permanent magnet motor iron loss calculation method taking into account the influence of elliptical rotating magnetization phenomenon, direct current bias magnetization phenomenon, small hysteresis loop phenomenon and PWM harmonic current. Background Art

[0002] With global warming, fossil fuel shortages and environmental pollution, how to use energy more efficiently has become a problem that humans must face in the process of development. Permanent magnet synchronous motors have the advantages of small size, high power density, high efficiency, high output torque and reliable operation. They have been widely used in many fields, especially in the automotive industry. Permanent magnet synchronous motors play an important role in the development of new energy vehicles.

[0003] Most traditional permanent magnet motors use surface mount, plug-in or embedded processes to fix permanent magnets to the rotor. In this way, during the operation of the motor, there will be problems such as heat dissipation difficulties, excessive temperature rise leading to irreversible demagnetization of permanent magnets, thereby limiting the motor output. In response to this problem, as early as the 1950s, scholars conducted research on stator permanent magnet motors. Unlike rotor permanent magnet motors, stator permanent magnet motors place both permanent magnets and armature windings on the stator. The simple rotor structure not only improves the reliability of the motor operation, but also acts as a fan when the rotor rotates, enhancing the heat dissipation performance of the motor.

[0004] Stator permanent magnet motors have attracted more and more attention due to their significant advantages such as sturdy structure, high power (torque) density, good heat dissipation performance, and strong fault tolerance. It is considered to be a combination of switched reluctance motors and traditional permanent magnet brushless motors, and is increasingly used in many electrical industrial applications. However, few scholars have studied the iron loss calculation model of stator permanent magnet motors. Since the structure of this motor is completely different from that of traditional permanent magnet motors, resulting in completely different loss distribution, it is very important to study the losses of this motor.

[0005] After searching, the Chinese patent application number CN202110629757.7 discloses a method and model for quickly calculating the iron loss of a high-speed motor based on the speed. The motor is a high-speed motor. The method and model are based on the classic iron loss calculation model, and a variable coefficient iron loss calculation model considering factors such as high-order harmonics, rotating magnetization, skin effect and small hysteresis loop is obtained. The model can fully reflect the change of iron loss with the magnetic flux density waveform distortion rate, magnetic flux density amplitude and motor frequency. The relationship between iron loss and speed is obtained by fitting the calculation results of the motor iron loss at different speeds through nonlinear curve fitting, thereby obtaining an iron loss calculation model related to the speed. The model can quickly obtain the corresponding iron loss at different motor speeds, and has a high calculation accuracy. The method for establishing the iron loss rapid calculation model proposed in the present invention has a wide range of applications, not only suitable for high-speed permanent magnet motor iron loss calculation, but also can be used for other types of high-speed motors.

[0006] The present invention proposes a novel method for calculating the iron loss of a stator permanent magnet motor. The method is as follows: first, representative points are selected to analyze the variation law of the magnetic flux density in the iron core; then, an elliptical magnetization trajectory diagram is obtained through simulation; the elliptical harmonic magnetic field is decomposed; the magnetic flux density amplitude and the DC bias amplitude on the long axis and short axis of each elliptical harmonic are calculated; and finally, the iron loss is calculated by the proposed formula. The novel method for calculating the iron loss of a stator permanent magnet motor proposed in the present invention takes into account the influence of multiple factors, including: elliptical rotating magnetization phenomenon, DC bias phenomenon, small hysteresis loop phenomenon and PWM harmonic current. It has the outstanding advantages of high accuracy, simple calculation process, and can be used to calculate the iron loss of different motors under different working conditions, providing guidance for the design and optimization of motors.

[0007] Compared with the above patent documents, the solution proposed in the present invention is different in that:

[0008] 1. The influencing factors considered in the present invention include elliptical rotation magnetization phenomenon, DC bias phenomenon, small hysteresis loop phenomenon and PWM harmonic current.

[0009] 2. The research object of the present invention is the stator permanent magnet motor;

[0010] The research method of the present invention is as follows: firstly, representative points are selected to analyze the variation law of magnetic flux density in the iron core; then, an elliptical magnetization trajectory diagram is obtained through simulation; the elliptical harmonic magnetic field is decomposed; the magnetic flux density amplitude and the DC bias amplitude on the long axis and short axis of each elliptical harmonic are obtained; and finally, the iron loss is calculated through the proposed formula. Summary of the invention

[0011] In order to overcome the defects of the traditional motor iron loss calculation method that few factors are considered and the result is not accurate enough, the present invention proposes a new iron loss calculation method, which is especially aimed at the stator permanent magnet motor and takes into account the influence of elliptical rotating magnetization phenomenon, DC bias phenomenon, small hysteresis loop phenomenon and PWM harmonic current.

[0012] To achieve the above object, the technical solution adopted by the present invention is:

[0013] A novel method for calculating iron loss of a stator permanent magnet motor is characterized by comprising the following steps:

[0014] Step 1: Select representative points.

[0015] Select representative points on the stator core and rotor core of the motor;

[0016] Step 2: Get the elliptical magnetization trajectory diagram,

[0017] The waveform diagram of the tangential and radial flux density at each representative point changing with the rotor position is solved by simulation using Ansys Maxwell software, and the elliptical magnetization trajectory diagram of the changing relationship between the radial flux density and the tangential flux density at each representative point is obtained;

[0018] Step 3: Elliptical harmonic magnetic field decomposition,

[0019] The irregular elliptical magnetic field of each representative point is decomposed into a series of elliptical harmonic magnetic density vectors by using the principle of harmonic analysis.

[0020] Step 4: Find B m With ΔB,

[0021] Two mutually orthogonal alternating magnetizations are used to equalize each elliptical harmonic magnetic field, that is, the elliptical magnetic flux density is decomposed into the major axis and minor axis directions to calculate the iron loss, and then the magnetic flux density amplitude B on the major axis and minor axis of each elliptical harmonic is calculated in turn. m and DC bias amplitude ΔB;

[0022] Step 5: Calculate iron loss,

[0023] The B of each elliptical harmonic of each representative point m Substitute ΔB into the iron loss calculation formula in turn to obtain the iron loss density value of each representative point. The average value of each representative point is the motor iron loss density. Finally, multiply the iron loss density by the iron loss volume to get the iron loss. The iron loss calculation formula is:

[0024]

[0025] Among them, P Fe is the total iron loss density; P h is the hysteresis loss density; P eis the eddy current loss density; k h is the hysteresis loss coefficient; k e is the eddy current loss coefficient; f is the fundamental frequency, vf is the vth elliptical harmonic frequency; B mMv and B mNv are the magnetic flux density amplitudes of the vth elliptical harmonic in the major and minor axis directions respectively; ΔB Mv and ΔB Nv are the DC bias magnitudes of the vth elliptical harmonic in the major and minor axis directions respectively.

[0026] As a preferred technical solution of the present invention: seven representative points are selected, representing the stator tooth tip, the center of the stator tooth, the stator tooth yoke, the stator yoke, the rotor tooth tip, the rotor tooth yoke and the rotor yoke respectively.

[0027] As a preferred technical solution of the present invention: a DC bias magnetic induction phenomenon exists on the stator tooth tip, a small hysteresis loop phenomenon exists on the rotor tooth tip, and an elliptical rotation magnetization phenomenon exists in the iron core.

[0028] As a preferred technical solution of the present invention: the iron loss calculation method takes into account the influence of the elliptical rotation magnetization phenomenon on the iron loss.

[0029] As a preferred technical solution of the present invention: the iron loss calculation method takes into account the influence of DC bias magnetization on the iron loss.

[0030] As a preferred technical solution of the present invention: when DC bias magnetization only affects hysteresis loss, the hysteresis loss density P h The approximate relationship between the DC bias induction ΔB is expressed as:

[0031] P h (ΔB) = P h0 ε(ΔB)

[0032] ε(ΔB)=1+k dc ΔB β +k l ΔB 2

[0033] Where P h (ΔB) and P h0 are the hysteresis loss with and without the influence of DC bias magnetization induction, k dc , k l and β are coefficients without physical meaning. Through nonlinear fitting, they are equal to 0.4575, 0.376 and 5.5975 respectively. It can be seen from the above formula that the influence of DC bias magnetization on the iron loss calculation can be taken into account by ε(ΔB).

[0034] As a preferred technical solution of the present invention: the iron loss calculation method takes into account the influence of small hysteresis loop phenomenon on iron loss.

[0035] As a preferred technical solution of the present invention: the iron loss calculation method takes into account the influence of PWM harmonic current on iron loss.

[0036] The novel stator permanent magnet motor iron loss calculation method proposed in the present invention improves the accuracy of iron loss model calculation by taking into account the influence of multiple factors, including: elliptical rotating magnetization phenomenon, DC bias phenomenon, small hysteresis loop phenomenon and PWM harmonic current, and provides guidance for the design and optimization of the motor.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) Compared with the traditional iron loss calculation method, the iron loss calculation method proposed in the present invention takes into account the influence of multiple factors and improves the calculation accuracy.

[0039] (2) The iron loss calculation method proposed in the present invention is easy to understand, convenient to operate, has a simple calculation process, and takes less time to calculate.

[0040] (3) The iron loss calculation method proposed in the present invention can be used for iron loss calculation of all motors, not just stator permanent magnet motors.

[0041] (4) The iron loss calculation method proposed in the present invention can calculate the iron loss value of the motor under both no-load and load conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a logical structure diagram of the present invention;

[0043] Figure 2 It is a typical point position diagram and magnetic density change waveform of an example of the present invention;

[0044] Figure 3 It is a typical point magnetic density change trajectory of the example of the present invention;

[0045] Figure 4 This is an elliptical harmonic decomposition diagram of the rotor tooth tip of an example of the present invention;

[0046] Figure 5 Schematic diagram of elliptical rotational magnetization;

[0047] Figure 6 It is a schematic diagram of the DC bias magnetic phenomenon and the small hysteresis loop phenomenon;

[0048] Figure 7 Schematic diagram of the effect of PWM harmonic current on core magnetic flux density;

[0049] Figure 8 Schematic diagram of the sub-elliptical magnetic field and its harmonic decomposition.

[0050] List of reference numerals: 1. stator tooth tip; 2. center of stator tooth; 3. stator tooth yoke; 4. stator yoke; 5. rotor tooth tip; 6. rotor tooth yoke; 7. rotor yoke. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0052] The present invention proposes a novel method for calculating the iron loss of a stator permanent magnet motor, comprising the following steps:

[0053] Step 1: Select representative points.

[0054] Combination Figure 2 Taking the flux reversal motor, one of the representatives of stator permanent magnet motors, as an example, some representative points are selected on the stator core and rotor core of the motor to analyze the law of magnetic flux density change in the core. Figure 2 Points 1-7 in the figure represent stator tooth tip 1, stator tooth center 2, stator tooth yoke 3, stator yoke 4, rotor tooth tip 5, rotor tooth yoke 6 and rotor yoke 7 respectively.

[0055] Step 2: Get the elliptical magnetization trajectory diagram,

[0056] The waveform diagram of the tangential and radial flux density at each representative point changing with the rotor position is solved by Ansys Maxwell software simulation, as shown in Figure 2 As shown, the elliptical magnetization trajectory diagram of the change relationship between the radial magnetic flux density and the tangential magnetic flux density at each representative point is obtained, as shown in Figure 3 shown.

[0057] according to Figure 2 and Figure 3 The conclusions can be drawn:

[0058] (1) There is obvious DC bias magnetic induction phenomenon on the stator tooth tip 1;

[0059] (2) There are some small hysteresis loops at the rotor tooth tip 5;

[0060] (3) The phenomenon of elliptical rotational magnetization is widespread in the iron core.

[0061] Step 3: Elliptical harmonic magnetic field decomposition,

[0062] The irregular elliptical magnetic field can be decomposed into a series of elliptical harmonic magnetic density vectors by using the principle of harmonic analysis, such as Figure 4 shown.

[0063] Step 4: Find B m With ΔB,

[0064] Two mutually orthogonal alternating magnetizations are used to equalize each elliptical harmonic magnetic field, that is, the elliptical magnetic flux density is decomposed into the major axis and minor axis directions to calculate the iron loss, and the magnetic flux density amplitude B on the major axis and minor axis of each elliptical harmonic is calculated in turn. m And the DC bias amplitude ΔB.

[0065] Step 5: Calculate iron loss,

[0066] The B of each elliptical harmonic at each point m Substitute ΔB into the iron loss calculation formula in turn to obtain the iron loss density value of each point. The average value of each point is the motor iron loss density. The iron loss density is finally multiplied by the iron loss volume to get the iron loss. The iron loss calculation formula is:

[0067]

[0068] Among them, P Fe is the total iron loss density; P h is the hysteresis loss density; P e is the eddy current loss density; k h is the hysteresis loss coefficient; k e is the eddy current loss coefficient; f is the fundamental frequency, vf is the vth elliptical harmonic frequency; B mMv and B mNv are the magnetic flux density amplitudes of the vth elliptical harmonic in the major and minor axis directions respectively; ΔB Mv and ΔB Nv are the DC bias magnitudes of the vth elliptical harmonic in the major and minor axis directions respectively.

[0069] In this embodiment: the iron loss calculation method takes into account the influence of elliptical rotation magnetization phenomenon on the iron loss.

[0070] Ferromagnetic materials have two types of magnetization: alternating magnetization and rotating magnetization. Rotating magnetization is further divided into circular rotating magnetization and elliptical rotating magnetization. The direction of the magnetic field of alternating magnetization remains unchanged, but the magnitude changes with time; the magnitude of the magnetic field of circular rotating magnetization remains unchanged, but the magnetization direction changes with time; for elliptical magnetization, both the magnitude and the magnetization direction change with time. The schematic diagram of elliptical rotating magnetization is shown below. Figure 5 As shown, from Figure 5 It can be seen that the major axis and minor axis of the ellipse do not coincide with the radial and tangential directions. In order to ensure the accuracy of the iron loss calculation, it is more reasonable to decompose the elliptical magnetization trajectory along the major axis and minor axis and calculate the iron loss separately. The major axis direction of the magnetization ellipse is defined as the direction of the straight line between the point of the magnetic flux density with the largest absolute value on the rotating magnetization trajectory and the origin, while the minor axis direction is the direction perpendicular to the major axis. maj and B min are the magnetic flux density amplitudes in the major and minor axis directions, respectively.

[0071] In the iron loss calculation in the prior art, K. Yamazaki proposed a hysteresis loop superposition calculation method, the expression is:

[0072]

[0073]

[0074] Among them B rm and B tm N are the magnetic flux density amplitudes in the radial and tangential directions of each hysteresis loop. r and N t are the total number of hysteresis loops for the radial and tangential components, respectively. In Yamazaki’s model, the flux density trajectory is decomposed along the radial and tangential directions for calculation, as Figure 4 As shown, this will reduce the accuracy of iron loss calculation. Therefore, the present invention calculates by decomposing along the major axis and the minor axis, and the expression is converted into

[0075]

[0076]

[0077] Solving the iron loss by decomposing the elliptical rotating magnetization trajectory into the major axis and minor axis directions is more accurate than the traditional solution of decomposing the magnetic flux density into radial and tangential directions.

[0078] In this embodiment: the iron loss calculation method takes into account the influence of DC bias magnetization on the iron loss.

[0079] DC bias phenomenon such as Figure 6 As shown in the figure, due to the presence of DC bias in the alternating magnetic flux density, the corresponding hysteresis loop will be distorted and the corresponding hysteresis loss will increase. It is generally believed that DC bias only affects the hysteresis loss, and the hysteresis loss density P h The approximate relationship between the DC bias induction ΔB is expressed as:

[0080] P h (ΔB) = P h0 ε(ΔB)

[0081] ε(ΔB)=1+k dc ΔB β +k l ΔB 2

[0082] Where P h (ΔB) and P h0 They are the hysteresis loss with and without the influence of DC bias magnetizing induction. dc , k land β are coefficients without physical meaning, which are equal to 0.4575, 0.376 and 5.5975 respectively through nonlinear fitting. It can be seen from the above formula that the influence of DC bias magnetization on the iron loss calculation can be taken into account by ε(ΔB).

[0083] In this embodiment: the iron loss calculation method takes into account the influence of small hysteresis loop phenomenon on the iron loss.

[0084] Since the stator permanent magnet motor adopts a double salient pole structure, the cogging effect is significant, and the magnetic flux density waveform in the core (especially the rotor teeth) is seriously distorted, resulting in a small hysteresis loop, such as Figure 6 shown.

[0085] In this embodiment: the iron loss calculation method takes into account the influence of PWM harmonic current on the iron loss.

[0086] The inverter-powered high-speed permanent magnet brushless motor contains high-frequency current harmonics in its stator current due to PWM modulation. The high-frequency harmonic current will increase the core loss.

[0087] like Figure 7 As shown in Figure 1, compared with no-load conditions and sinusoidal current input, the distorted current injected by the inverter can produce more and smaller hysteresis loops, resulting in additional hysteresis losses. The flux density harmonics caused by the PWM carrier also produce additional eddy current losses.

[0088] In order to quickly, conveniently and accurately obtain the number and corresponding amplitude of each small hysteresis loop, the irregular elliptical magnetic field can be decomposed into a series of elliptical harmonic magnetic density vectors by using the principle of harmonic analysis, such as Figure 8 As shown. For each elliptical harmonic magnetic field, two mutually orthogonal alternating magnetizations are used along the major axis and minor axis directions to be equivalent, and considering the influence of DC bias magnetization ε(ΔB), the iron loss calculation formula is:

[0089]

[0090] In summary, the new stator permanent magnet motor iron loss calculation method proposed in the present invention improves the calculation accuracy of the iron loss model by taking into account the influence of multiple factors, including: elliptical rotating magnetization phenomenon, DC bias phenomenon, small hysteresis loop phenomenon and PWM harmonic current, and provides guidance for the design and optimization of the motor.

[0091] Compared with the prior art, the present invention has the following advantages:

[0092] (1) Compared with the traditional iron loss calculation method, the iron loss calculation method proposed in the present invention takes into account the influence of multiple factors and improves the calculation accuracy.

[0093] (2) The iron loss calculation method proposed in the present invention is easy to understand, convenient to operate, has a simple calculation process, and takes less time to calculate.

[0094] (3) The iron loss calculation method proposed in the present invention can be used for iron loss calculation of all motors, not just stator permanent magnet motors.

[0095] (4) The iron loss calculation method proposed in the present invention can calculate the iron loss value of the motor under both no-load and load conditions.

[0096] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A novel method for calculating iron loss of a stator permanent magnet motor, characterized in that: The following steps are involved: Step 1: Select representative points. Select representative points on the stator core and rotor core of the motor; Step 2: Get the elliptical magnetization trajectory diagram, The waveform diagram of the tangential and radial flux density at each representative point changing with the rotor position is solved by simulation using Ansys Maxwell software, and the elliptical magnetization trajectory diagram of the changing relationship between the radial flux density and the tangential flux density at each representative point is obtained; Step 3: Elliptical harmonic magnetic field decomposition, The irregular elliptical magnetic field of each representative point is decomposed into a series of elliptical harmonic magnetic density vectors by using the principle of harmonic analysis. Step 4: Find B m With ΔB, Two mutually orthogonal alternating magnetizations are used to equalize each elliptical harmonic magnetic field, that is, the elliptical magnetic flux density is decomposed into the major axis and minor axis directions to calculate the iron loss, and then the magnetic flux density amplitude B on the major axis and minor axis of each elliptical harmonic is calculated in turn. m and DC bias amplitude ΔB; Step 5: Calculate iron loss, The B of each elliptical harmonic of each representative point m Substitute ΔB into the iron loss calculation formula in turn to obtain the iron loss density value of each representative point. The average value of each representative point is the motor iron loss density. Finally, multiply the iron loss density by the iron loss volume to get the iron loss. The iron loss calculation formula is: Among them, P Fe is the total iron loss density; P h is the hysteresis loss density; P e is the eddy current loss density; k h is the hysteresis loss coefficient; k e is the eddy current loss coefficient; f is the fundamental frequency, vf is the vth elliptical harmonic frequency; B mMv and B mNv are the magnetic flux density amplitudes of the vth elliptical harmonic in the major and minor axis directions respectively; ΔB Mv and ΔB Nv are the DC bias magnitudes of the vth elliptical harmonic in the major and minor axis directions respectively.

2. The method for calculating the iron loss of a novel stator permanent magnet motor according to claim 1 is characterized in that: Seven representative points are selected, which respectively represent the stator tooth tip (1), the stator tooth center (2), the stator tooth yoke part (3), the stator yoke (4), the rotor tooth tip (5), the rotor tooth yoke part (6) and the rotor yoke (7).

3. The method for calculating the iron loss of a novel stator permanent magnet motor according to claim 2 is characterized in that: There is a DC bias magnetic induction phenomenon on the stator tooth tip (1), there is a small hysteresis loop phenomenon on the rotor tooth tip (5), and there is an elliptical rotation magnetization phenomenon in the iron core.

4. A novel method for calculating iron loss of a stator permanent magnet motor according to claim 1 or 3, characterized in that: The iron loss calculation method takes into account the influence of elliptical rotation magnetization phenomenon on the iron loss.

5. A novel method for calculating iron loss of a stator permanent magnet motor according to claim 1 or 3, characterized in that: The iron loss calculation method takes into account the influence of DC bias magnetization on the iron loss.

6. The method for calculating the iron loss of a novel stator permanent magnet motor according to claim 5 is characterized in that: When DC bias magnetization only affects hysteresis loss, the hysteresis loss density P h The approximate relationship between the DC bias induction ΔB is expressed as: P h (ΔB)=P h0 ε(ΔB) ε(ΔB)=1+k dc ΔB β +k l ΔB 2 Where P h (ΔB) and P h0 are the hysteresis loss with and without the influence of DC bias magnetization induction, k dc , k l and β are coefficients without physical meaning, which are equal to 0.4575, 0.376 and 5.5975 respectively through nonlinear fitting. It can be seen from the above formula that the influence of DC bias magnetization on the iron loss calculation is taken into account through ε(ΔB).

7. A novel method for calculating iron loss of a stator permanent magnet motor according to claim 1 or 3, characterized in that: The iron loss calculation method takes into account the influence of small hysteresis loop phenomenon on the iron loss.

8. A novel method for calculating iron loss of a stator permanent magnet motor according to claim 1 or 3, characterized in that: The iron loss calculation method takes into account the influence of PWM harmonic current on the iron loss.

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