External rotor magnetic field modulation permanent magnet motor temperature detection and regulation method

Abstract

The invention discloses an outer rotor magnetic field modulation permanent magnet motor temperature detection and regulation method. The method comprises the steps of obtaining motor fixed parameters and working parameters and constructing a motor three-dimensional model; according to the harmonic angle, constructing a mathematical model between the air gap harmonic and iron core heat, armature winding heat and permanent magnet eddy current heat in the motor; obtaining iron core heat, armature winding heat and permanent magnet eddy current heat in a working state; establishing a temperature field mathematical model of the motor according to the heat transfer coefficients among the components, and analyzing the temperature field distribution of the motor; temperature regulation and control measures are formulated in a targeted manner according to the analysis result; from the perspective of harmonic waves, the relation between air gap harmonic waves and iron core heat, the relation between permanent magnet eddy current and an armature winding are constructed, the harmonic waves and motor heat are fused, the motor heat is obtained from the inside by means of parameters of the motor, temperature field analysis is conducted on the obtained heat, and the temperature distribution condition in the working process of the motor is obtained. And a temperature control scheme can be formulated in a targeted manner.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer substation safety, and in particular to a temperature detection and control method for an outer rotor magnetic field modulation permanent magnet motor. Background Art

[0002] The use of wheel hub drive in electric vehicles can improve the transmission efficiency of the vehicle and enable more flexible control of the vehicle. However, during use, due to the limitation of wheel hub size, the motor size and the contact area with the outside air are limited, which will cause the heating of the motor to be more serious; and the reduction of the total volume of the motor will be unfavorable for heat dissipation. When the temperature is too high, there is a risk of irreversible demagnetization of the rotor permanent magnet; it is also more likely to cause many problems that affect the reliability of the motor, such as motor insulation failure and motor structural deformation.

[0003] In order to prevent the motor temperature from being too high, temperature sensors are generally used in the prior art to measure the temperature of the motor. Since the hub motor structure is relatively compact and sealed, the temperature sensor can only detect the temperature of a partial area. Due to the different heating positions and heat transfer coefficients inside the motor, it is easy to cause uneven temperature distribution of the motor. At this time, it is difficult to effectively detect the motor temperature using a temperature sensor. Summary of the invention

[0004] The main technical problem solved by the present invention is to provide a temperature detection and control method for an outer rotor magnetic field modulated permanent magnet motor, which uses harmonics as the main factor to obtain the heat generated by the motor and perform temperature field analysis, so as to control the temperature according to the temperature distribution and reduce the impact of temperature on motor performance.

[0005] In order to solve the above technical problems, a technical solution adopted by the present invention is: to provide a temperature detection and control method of an outer rotor magnetic field modulation permanent magnet motor, the steps of which are:

[0006] Step 1: Obtain the fixed parameters and working parameters of the motor and build a three-dimensional model of the motor;

[0007] Step 2: construct a mathematical model between air gap harmonics and the heat of the iron core, the heat of the armature winding and the eddy current heat of the permanent magnet in the motor according to the harmonic angle;

[0008] Step 3: Obtain the core heat, armature winding heat and permanent magnet eddy current heat under working conditions according to the constructed mathematical models of core heat, armature winding heat and permanent magnet eddy current heat, and obtain the motor heat;

[0009] Step 4: According to the heat transfer coefficients between the stator core and the armature winding, between the rotor core and the permanent magnet, between the stator and the rotor through the air gap, and between the rotor and the external air, a temperature field mathematical model of the motor is established, and the temperature field distribution of the motor is analyzed by using the finite element method;

[0010] Step 5: Develop targeted temperature control measures based on the analysis results.

[0011] Furthermore, in step 2, the process of modeling the air gap harmonics and the heat of the iron core in the motor is as follows:

[0012] The abnormal eddy current heat is defined to be very small, so only the hysteresis heat and the classical eddy current heat need to be considered in the calculation. When the motor is running, the radial flux and the tangential flux are dominant in the tooth and yoke respectively, and the corresponding tooth tangential flux and yoke radial flux are ignored in the calculation.

[0013] According to the existing units in the motor, the area is divided, and the geometric center points of the stator and rotor teeth and yoke in the same unit are used to replace the overall magnetic flux density; the iron loss generated by each harmonic of the stator and rotor is summed to obtain the total core heat of the motor;

[0014] Since the air gap harmonics pass through the core to generate core harmonics, the frequency is the same as f i Air gap harmonic group Q(f i ) is equal to the sum of the heat generated by the core in the motor teeth and yoke with the same frequency f i The heat generated by the i-th core harmonic is summed, thereby establishing the frequency and amplitude relationship between the air gap harmonic and the core harmonic;

[0015] The air gap harmonics are replaced into the iron core thermal mathematical model to obtain the iron core harmonic mathematical model dominated by the air gap harmonics.

[0016] Furthermore, the core heat mathematical model is:

[0017]

[0018] Where M t and M y are the masses of the motor teeth and yoke, respectively, and f qi and f pi are the i-th harmonic frequency of the core at point q and point p, respectively. q and p are the geometric center points of the stator and rotor teeth and yoke, respectively. qi and B pi are the amplitudes of the corresponding i-th harmonic, K h is the hysteresis heat coefficient, K c is the eddy current heat coefficient.

[0019] Furthermore, the frequency and amplitude relationship between the air gap harmonics and the core harmonics is:

[0020] B E1 :B E2 :…:B En =B q1 :B q2 :…:Bqn =B p1 :B p2 :…:B pn (3)

[0021]

[0022] In the formula, B qv and B pv are the harmonic amplitudes of the vth harmonic in the air gap at points q and p, respectively, and f i is the i-th core harmonic frequency at points q and p, B En is the effective amplitude of the corresponding nth air gap harmonic.

[0023] Furthermore, in step 2, the process of modeling the air gap harmonics and the eddy current heat of the permanent magnet in the motor is as follows:

[0024] The definition ignores the influence of magnetic saturation, and the total permanent magnet eddy current heat is expressed as the sum of the permanent magnet eddy current heat generated by each air gap harmonic;

[0025] Assume the permanent magnet to be a simplified rectangle, and use four resistors connected in series to represent the size of the permanent magnet, and get the equivalent resistance.

[0026] According to the law of electromagnetic induction, the amplitude of the induced electromotive force generated in the permanent magnet eddy current circuit is obtained, and combined with the equivalent resistance, the eddy current heat of the motor permanent magnet is obtained.

[0027] Furthermore, the mathematical model of the permanent magnet eddy current heat is:

[0028]

[0029] In the formula, is the amplitude of the induced electromotive force generated in the permanent magnet eddy current circuit, and R is the equivalent resistance.

[0030] Furthermore, in step 2, the process of modeling the heat of the armature winding in the motor is as follows: the winding is energized to generate a magnetic field, and the heat generated by the air gap harmonics is negligible. Here, the heat of the motor winding is obtained only based on the resistance of the winding and the current flowing through it, as shown in the following formula:

[0031] P cu =mI 2 R cu (6)

[0032] In the formula, m is the number of motor phases, I is the equivalent resistance, R cu is the phase resistance of the motor.

[0033] Furthermore, in step three, the heat of the iron core, the heat of the armature winding and the eddy current heat of the permanent magnet under working conditions are obtained according to the constructed mathematical model, and the heat of the motor is obtained, as shown in the following formula:

[0034] P heat =P cu +P eddy +P Fe (7)

[0035] In the formula, p cu is the armature winding heat, p eddy is the eddy current heat of the permanent magnet, p Fe The heat of the core.

[0036] Furthermore, in step 4, the temperature field analysis model is:

[0037]

[0038] Where T is the temperature that changes with time, λ x , y , z are the thermal conductivity of the material along the x, y, and z directions, respectively, and q v is the heat generated per unit volume per unit time, ρ m is the material element density, c m is the specific heat capacity of the material; s1 is the first type of boundary surface, T(t) is the boundary temperature at any given time, which can be a constant; s2 is the second type of boundary surface, λ is the thermal conductivity of the surface normal, n is the surface normal direction, q(t) is the boundary heat flux density at any given time; s3 is the third type of boundary surface, α s is the heat dissipation coefficient of the surface, T f is the temperature of the medium around the boundary surface.

[0039] Furthermore, in step 4, the thermal conductivity of the winding is:

[0040]

[0041] In the formula, δ i is the thickness of each heat conducting medium, λ i is the thermal conductivity of each heat-conducting medium;

[0042] The thermal conductivity of the motor stator and rotor core in the axial, radial and circumferential directions are:

[0043]

[0044] In the formula, δ Fe is the dielectric thickness of silicon steel sheet, δ0 is 0, λ iis the thermal conductivity of silicon steel sheet, λ0 is the thermal conductivity of insulation material, k Fe is the core lamination coefficient;

[0045] The air gap convection thermal conductivity is:

[0046]

[0047] In the formula, λ air is the thickness of silicon steel sheet, D1 is the outer diameter of motor stator, D2 is the inner diameter of motor rotor, Re air 、Re cr is the air gap Reynolds coefficient and the critical Reynolds coefficient;

[0048] The heat dissipation coefficient of the motor rotor outer surface is:

[0049]

[0050] In the formula, v r is the rotor surface speed.

[0051] The beneficial effects of the present invention are:

[0052] The present invention starts from the harmonic angle, constructs the theoretical connection between the air gap harmonic and the iron core heat, the permanent magnet eddy current and the armature winding, realizes the fusion of the harmonic and the motor heat, and finally obtains the heat of the motor from the inside by using the motor parameters, solves the problem of inaccurate measurement by using an external temperature sensor, and performs temperature field analysis on the obtained heat to obtain the temperature distribution during the operation of the motor, so as to facilitate the targeted formulation of a temperature control scheme. For example, a heat dissipation device is added at the temperature gathering place, and the temperature is reversed according to the temperature to achieve temperature control by controlling the harmonic. Since the harmonic is related to the stator and rotor teeth, yoke and magnetic field modulation parameters, a new idea is provided for adjusting the motor temperature by changing the stator and rotor teeth, yoke and magnetic field modulation parameters in the future. In the process of obtaining the iron core heat, the motor is divided into several areas, and the representative point iron core magnetic density of each divided area is taken to replace the overall magnetic density. Finally, the iron core heat of each area is superimposed and calculated to obtain the motor iron core heat, thereby improving the calculation accuracy compared with the traditional separate iron loss calculation model.

[0053] In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specifically cites preferred embodiments and describes them in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only five of the drawings in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0055] Figure 1 It is a flowchart of the application method;

[0056] Figure 2 It is a schematic diagram of the motor yoke unit;

[0057] Figure 3 It is a simplified model diagram of permanent magnet;

[0058] Figure 4 It is the stator temperature field cloud diagram under natural cooling conditions;

[0059] Figure 5 It is the temperature field cloud diagram of the rotor winding under natural cooling conditions. DETAILED DESCRIPTION

[0060] In order to facilitate the understanding of the present invention, the present invention is described in more detail below in conjunction with the accompanying drawings and specific embodiments. Preferred embodiments of the present invention are provided in the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0061] It should be noted that, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in this specification includes any and all combinations of one or more related listed items.

[0062] See also Figure 1-4 , Figure 1 The present invention shows a method for detecting and controlling the temperature of an outer rotor magnetic field modulation permanent magnet motor, the steps of which are:

[0063] Step S1, obtaining fixed parameters and working parameters of the motor and constructing a three-dimensional model of the motor;

[0064] Step S2, constructing a mathematical model between air gap harmonics and the heat of the iron core, the heat of the armature winding and the eddy current heat of the permanent magnet in the motor according to the harmonic angle;

[0065] Step S3, obtaining the iron core heat, armature winding heat and permanent magnet eddy current heat in the working state according to the constructed mathematical models of iron core heat, armature winding heat and permanent magnet eddy current heat, and obtaining the motor heat;

[0066] Step S4, establishing a temperature field mathematical model of the motor according to the heat transfer coefficients between the stator core and the armature winding, between the rotor core and the permanent magnet, between the stator and the rotor through the air gap, and between the rotor and the external air, and using the finite element method to analyze the temperature field distribution of the motor;

[0067] Step S5: formulate targeted temperature control measures according to the analysis results.

[0068] In step S1, the fixed parameters and working parameters of the motor are obtained by actual measurement or from relevant instruction documents, and the construction of a three-dimensional model facilitates the subsequent analysis of the temperature field distribution of the motor, making the temperature change of the motor axial direction more intuitive.

[0069] In step S2, the process of modeling the air gap harmonics and the heat of the iron core in the motor is as follows:

[0070] The abnormal eddy current heat is defined to be very small, so only the hysteresis heat and the classical eddy current heat need to be considered in the calculation. When the motor is running, the radial flux and the tangential flux are dominant in the tooth and yoke respectively, and the corresponding tooth tangential flux and yoke radial flux are ignored in the calculation.

[0071] According to the existing units in the motor, the area is divided, and the geometric center points of the stator and rotor teeth and yoke in the same unit are used to replace the overall magnetic flux density; the iron loss generated by each harmonic of the stator and rotor is summed to obtain the total core heat of the motor;

[0072] Since the air gap harmonics pass through the core to generate core harmonics, the frequency is the same as f i Air gap harmonic group Q(f i ) is equal to the sum of the heat generated by the core in the motor teeth and yoke with the same frequency f i The heat generated by the i-th core harmonic is summed, thereby establishing the frequency and amplitude relationship between the air gap harmonic and the core harmonic;

[0073] The air gap harmonics are replaced into the iron core thermal mathematical model to obtain the iron core harmonic mathematical model dominated by the air gap harmonics.

[0074] Since the internal magnetic field of the motor changes alternately when it is running, the magnetization characteristics at different positions are also different; the traditional separate iron loss calculation model can calculate the core heat of the motor under the action of sinusoidal alternating magnetic flux. In order to ensure the accuracy of the core heat calculation, the motor is usually divided into several equal areas, and the core magnetic density of the representative points of each divided area is taken to replace the overall magnetic density. Finally, the core heat of each area is superimposed and calculated, such as Figure 2 shown.

[0075] Because the magnetic field modulated permanent magnet motor has the characteristics of symmetry, the magnetization waveforms at different tooth and yoke positions are basically consistent, with only a phase difference. Therefore, it is only necessary to take the geometric center points of the stator and rotor teeth and yoke in one unit of the motor to analyze the core magnetic flux.

[0076] Since the abnormal eddy current heat is very small, only the hysteresis heat and the classical eddy current heat need to be considered in the calculation. When the motor is running, the radial flux and tangential flux are mainly in the tooth and yoke respectively, and the corresponding tooth tangential and yoke radial flux are ignored in the calculation. It can be concluded that the motor core heat corresponding to the i-th core harmonic is:

[0077]

[0078] Where M t and M y are the masses of the motor teeth and yoke, respectively, and f qi and f pi are the i-th harmonic frequency of the core at point q and point p, respectively. q and p are the geometric center points of the stator and rotor teeth and yoke, respectively. qi and B pi are the amplitudes of the corresponding i-th harmonic, K h is the hysteresis heat coefficient, K c is the eddy current heat coefficient.

[0079] The heat of the iron core is the sum of the heat generated by each harmonic of the stator and rotor, that is:

[0080]

[0081] Formula (1) shows that the heat of the iron core is mainly related to the frequency and amplitude of the motor iron core harmonics. At the same time, the air gap harmonics generated when the motor is running also have corresponding harmonic frequencies and amplitudes. First, when the air gap harmonics rotate, they are functions of position x and time t at the same time, and their trajectory equation is:

[0082]

[0083] In the formula, v is the air gap harmonic order, x is the spatial position, B mv is the harmonic amplitude of the vth harmonic, r g is the air gap radius, ω mv is the speed of harmonic v. From this, we can conclude that the time frequency of the air gap harmonic with harmonic order v is:

[0084] f v =vω mv (4)

[0085] When the motor is running, there must be relative motion between the stator and the rotor, which will cause the electrical frequency of the air gap harmonic to be different relative to the stator and the rotor. When the speed of the vth air gap harmonic is ω mv When the air gap harmonic takes the stator as the reference system, the relative electrical frequency can be expressed as:

[0086] f sv =vω mv (5)

[0087] Since the iron core is used as the reference system, in order to further simplify the analysis, Figure 2 Point q and point p are representative points. The magnetic density expressions of points q and p are only related to time t and can be expressed as:

[0088]

[0089] In the formula, B iq 、f iq and B ip 、f ip is the amplitude and frequency of each harmonic of the core at points q and p, θ iq and θ ip are the initial phase values ​​corresponding to the two points.

[0090] According to the continuity of the magnetic flux inside the motor, it can be known that the magnetic flux is continuous when it passes through the air gap and any position of the stator and rotor teeth or yoke. Therefore, when v is any harmonic of the air gap, there must be a certain i-th harmonic inside the stator core such that:

[0091] f sv =f iq =f ip (7)

[0092] Similarly, there must be a certain u-order rotor core magnetic flux harmonic in the rotor core, so that:

[0093] f Rv =f uq =f up (8)

[0094] From this, it can be seen that the necessary and sufficient condition for the vth air gap harmonic to generate core heat is that the electrical frequency of the harmonic relative to the rotor and stator is not zero.

[0095] Based on the basic theory of electromagnetic field, the relationship between the core magnetic flux harmonic amplitude and the air gap harmonic amplitude is established. When the leakage flux is ignored, the magnetic flux generated by the vth air gap harmonic passing through the tooth is:

[0096]

[0097] in,

[0098] In the formula, w t for Figure 2 The effective width of the salient pole teeth shown in the figure, z is the axial length of the motor core, B Ev v is the effective amplitude of the subharmonic.

[0099] From equation (9), we can see that the effective amplitude determines the flux capacity of the air gap harmonic passing through the core. Due to the continuity of the magnetic flux, the vth harmonic in the air gap is Figure 2 The core magnetic flux amplitude generated at the middle point q and point p and the effective amplitude of the air gap harmonic B Ev That is, the ratio of the core magnetic flux density generated by any harmonic of order v at point q and point p can be expressed as:

[0100] B E1 :B E2 :…:B En =B q1 :B q2 :…:B qn =B p1 :B p2 :...:B pn (10)

[0101]

[0102] In the formula, B qv and B pv are the harmonic amplitudes of the vth harmonic in the air gap at points q and p, respectively, and f i is the i-th core harmonic frequency at points q and p, B En is the effective amplitude of the corresponding nth air gap harmonic.

[0103] Through the simultaneous equations of (10) and (11), the relationship between the air gap magnetic flux harmonics and the core heat of the motor is established, that is, the air gap harmonic amplitude and frequency are the main factors affecting the motor core heat.

[0104] In step S2, the process of modeling the air gap harmonics and the eddy current heat of the permanent magnet in the motor is as follows:

[0105] The definition ignores the influence of magnetic saturation, and the total permanent magnet eddy current heat is expressed as the sum of the permanent magnet eddy current heat generated by each air gap harmonic;

[0106] Assume the permanent magnet to be a simplified rectangle, and use four resistors connected in series to represent the size of the permanent magnet, and get the equivalent resistance.

[0107] According to the law of electromagnetic induction, the amplitude of the induced electromotive force generated in the permanent magnet eddy current circuit is obtained, and combined with the equivalent resistance, the eddy current heat of the motor permanent magnet is obtained.

[0108] A large number of harmonics will appear in the air gap magnetic field of the motor, some of which are relatively static harmonics, and there are also some harmonics that are inconsistent with the movement of the permanent magnets on the motor rotor, which will cause corresponding induced electromotive force on the permanent magnets, thereby forming an eddy current loop, which will generate permanent magnet eddy current heat when passing through the permanent magnets.

[0109] Since the influence of magnetic saturation is ignored, the total eddy current heat of the permanent magnet can be expressed as the sum of the eddy current heat of the permanent magnet generated by each air gap harmonic; the permanent magnet is assumed to be a simplified rectangle, such as Figure 3 (a) shows the eddy current path in the conductor, and the size of a permanent magnet can be represented by four series resistors, as shown in Figure 3 (b). Then the equivalent resistance R can be obtained as:

[0110]

[0111] The permanent magnet eddy current heat mathematical model is:

[0112]

[0113] In the formula, E m is the amplitude of the induced electromotive force generated in the permanent magnet eddy current circuit.

[0114] From formula (13), it can be seen that the permanent magnet heat is mainly determined by the size of the motor permanent magnet and the air gap harmonic amplitude and relative frequency, and the permanent magnet eddy current heat generated by each harmonic can be calculated by the above formula. Therefore, when designing the motor, under the premise of not changing the amount and size of the permanent magnet, the main factors affecting the eddy current heat of the motor permanent magnet are the air gap harmonic amplitude and frequency, which provides a new angle for reducing the eddy current heat of the permanent magnet.

[0115] Through the above analysis of the principle of air gap harmonic generation, it can be seen that changes in motor structural parameters usually affect the magnetic potential characteristics and magnetic permeance distribution under two magnetic fields, thereby affecting the air gap magnetic density harmonic distribution. In addition, for permanent magnet motors, the lower the heat, the higher the motor operating efficiency, and the performance also improves accordingly. According to the analysis of equations (11) and (13), the amplitude and frequency of the motor air gap harmonics are the key factors affecting the comprehensive heat of the motor. The frequency is related to the speed, and the harmonic order generated by the motor during actual operation will not change with the change of frequency. Therefore, with air gap harmonics as the intermediate bridge, the motor heat is adjusted by considering the main motor structural parameters that affect the air gap harmonics.

[0116] In step S2, the process of modeling the heat of the armature winding of the motor with the air gap harmonics is as follows: the winding is energized to generate a magnetic field, and the heat generated by the air gap harmonics is negligible. Here, the heat of the motor winding is obtained only based on the resistance of the winding and the current flowing through it, as shown in the following formula:

[0117] P cu =mI 2 R cu (14)

[0118] In the formula, m is the number of motor phases, I is the equivalent resistance, R cu is the phase resistance of the motor.

[0119] In step S3, the heat of the iron core, the heat of the armature winding and the eddy current heat of the permanent magnet under working conditions are obtained according to the constructed mathematical model, and the heat of the motor is obtained, as shown in the following formula:

[0120] P heat =P cu +P eddy +P Fe (15)

[0121] In the formula, p cu is the armature winding heat, p eddy is the eddy current heat of the permanent magnet, p Fe The heat of the core.

[0122] In step S4, different heat generation conditions in different parts of the motor during operation result in different temperatures at different locations inside the motor. According to the second law of thermodynamics, there is heat transfer between the various parts of the motor. Therefore, based on the relevant theory of heat transfer, a mathematical model of the motor's temperature field is established, and a finite element analysis is performed on the distribution of the motor's temperature field.

[0123] The temperature field analysis model is:

[0124]

[0125] Where T is the temperature that changes with time, λ x , y , z are the thermal conductivity of the material along the x, y, and z directions, respectively, and q v is the heat generated per unit volume per unit time, ρ m is the material element density, c m is the specific heat capacity of the material; s1 is the first type of boundary surface, T(t) is the boundary temperature at any given time, which can be a constant; s2 is the second type of boundary surface, λ is the thermal conductivity of the surface normal, n is the surface normal direction, q(t) is the boundary heat flux density at any given time; s3 is the third type of boundary surface, α s is the heat dissipation coefficient of the surface, T f is the temperature of the medium around the boundary surface.

[0126] In step S4, the heat transfer methods mainly consider heat conduction and heat convection. Heat conduction generally occurs inside a solid and between two solids in contact with each other with a temperature difference. Heat convection is also called heat transfer, which is generally the heat transfer between the fluid-solid interface when a fluid flows over the surface of an object.

[0127] Since the motor winding is composed of copper wire, insulation and other media, the equivalent treatment method is used to treat it as copper wire wrapped by insulating material. The thermal conductivity of the winding is:

[0128]

[0129] In the formula, δ i is the thickness of each heat conducting medium, λ i is the thermal conductivity of each heat-conducting medium;

[0130] Since the heat transfer capacity of the stator and rotor in the axial direction and the radial and circumferential direction is different, the thermal conductivity of the motor stator and rotor core in the axial, radial and circumferential directions are:

[0131]

[0132] In the formula, δ Fe is the dielectric thickness of silicon steel sheet, δ0 is 0, λ i is the thermal conductivity of silicon steel sheet, λ0 is the thermal conductivity of insulation material, k Fe is the core lamination coefficient.

[0133] When the motor is running, the air in the air gap is in a state of relative motion. Therefore, there is heat convection between the motor stator, rotor and air gap, which makes the temperature field calculation more difficult. Therefore, the air gap equivalent thermal conductivity is used to make the heat exchange capacity of the moving air and the equivalent static air the same. The air gap convection thermal conductivity is:

[0134]

[0135] In the formula, λ air is the thickness of silicon steel sheet, D1 is the outer diameter of motor stator, D2 is the inner diameter of motor rotor, Re air 、Re cr is the air gap Reynolds coefficient and the critical Reynolds coefficient;

[0136] When the external rotor motor is working, there is relative movement between the outer surface and the external air, and heat convection is formed at this time. At this time, the heat transfer coefficient can be expressed using an empirical formula. The heat dissipation coefficient of the motor rotor outer surface is:

[0137]

[0138] In the formula, v r is the rotor surface speed.

[0139] In step S4, the temperature rise of the motor is caused by electromagnetic work, and the change in temperature will also cause the electromagnetic performance to change; therefore, there is coupling between the electromagnetic field and the temperature field of the motor. When solving the electromagnetic-thermal coupling problem, one-way coupling is used to solve the electromagnetic field of the motor, and then the temperature field of the motor is analyzed based on the electromagnetic field analysis results.

[0140] Obtaining the temperature distribution during the operation of the motor facilitates the formulation of targeted temperature control plans. For example, adding heat dissipation devices at the temperature concentration point, and reversely inferring based on the temperature to achieve temperature control by controlling harmonics. Since harmonics are related to the stator and rotor teeth, yoke and magnetic field modulation parameters, this provides new ideas for adjusting the motor temperature by changing the stator and rotor teeth, yoke and magnetic field modulation parameters in the future.

[0141] If it is assumed that the heat energy of each part of the motor is evenly distributed on each component, then according to the results of electromagnetic analysis of the motor, the heat generation rate of each component of the motor can be obtained as shown in Table 1, and the thermal coefficient of the material of each component of the motor is shown in Table 2.

[0142] Table 1 Heating rate of each motor component

[0143]

[0144]

[0145] Table 2 Thermal coefficients of motor components

[0146] Motor parts name density Thermal conductivity Specific heat Stator, stator core 7872 45 radial / 4 axial 481 permanent magnet 8300 10 350 Stator winding 8933 400 385 Air 1.1614 0.026 1007

[0147] Based on the established three-dimensional model of the motor, the analysis and calculation results of each heat source, and the thermal coefficient of each motor component, a finite element analysis model of the motor temperature field is established and solved. Considering the convection heat exchange between the outer surface of the motor rotor and the external air during rotation, the ambient temperature is set to 20°C, and the motor temperature distribution under natural cooling conditions is obtained as follows: Figure 4 and Figure 5 shown.

[0148] Under natural cooling conditions, the high-temperature areas of the outer rotor magnetic field modulation permanent magnet motor during operation are mainly distributed in the motor stator core and stator winding parts, with the highest stator temperature of 217.74°C and the highest winding temperature of 228.1°C. This is because the stator core and stator winding are in the air gap harmonics, which generate high heat and generate large heat; and for the outer rotor motor, its interior is relatively closed, and due to the air gap and outer rotor blocking, the heat is difficult to dissipate, which further causes the temperature of the motor stator part to rise.

[0149] The above are only embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for detecting and controlling the temperature of an outer rotor magnetic field modulation permanent magnet motor, the steps of which are: Step 1: Obtain the fixed parameters and working parameters of the motor and build a three-dimensional model of the motor; Step 2: construct a mathematical model between air gap harmonics and the heat of the iron core, the heat of the armature winding and the eddy current heat of the permanent magnet in the motor according to the harmonic angle; Step 3: Obtain the core heat, armature winding heat and permanent magnet eddy current heat under working conditions according to the constructed mathematical models of core heat, armature winding heat and permanent magnet eddy current heat, and obtain the motor heat; Step 4: According to the heat transfer coefficients between the stator core and the armature winding, between the rotor core and the permanent magnet, between the stator and the rotor through the air gap, and between the rotor and the external air, a temperature field mathematical model of the motor is established, and the temperature field distribution of the motor is analyzed by using the finite element method; Step 5: Develop targeted temperature control measures based on the analysis results.

2. The method for detecting and controlling the temperature of an outer rotor magnetic field modulation permanent magnet motor according to claim 1, characterized in that: In step 2, the process of modeling the air gap harmonics and the heat of the iron core in the motor is as follows: The abnormal eddy current heat is defined to be very small, so only the hysteresis heat and the classical eddy current heat need to be considered in the calculation. When the motor is running, the radial flux and the tangential flux are dominant in the tooth and yoke respectively, and the corresponding tooth tangential flux and yoke radial flux are ignored in the calculation. According to the existing units in the motor, the area is divided, and the geometric center points of the stator and rotor teeth and yoke in the same unit are used to replace the overall magnetic flux density; the iron loss generated by each harmonic of the stator and rotor is summed to obtain the total core heat of the motor; Since the air gap harmonics pass through the core to generate core harmonics, the frequency is the same as f i Air gap harmonic group Q(f i ) is equal to the sum of the heat generated by the core in the motor teeth and yoke with the same frequency f i The heat generated by the i-th core harmonic is summed, thereby establishing the frequency and amplitude relationship between the air gap harmonic and the core harmonic; The air gap harmonics are replaced into the iron core thermal mathematical model to obtain the iron core harmonic mathematical model dominated by the air gap harmonics.

3. The temperature detection and control method of an outer rotor magnetic field modulation permanent magnet motor according to claim 2 is characterized in that: The core heat mathematical model is: Where M t and M y are the masses of the motor teeth and yoke, respectively, and f qi and f pi are the i-th harmonic frequency of the core at point q and point p, respectively. q and p are the geometric center points of the stator and rotor teeth and yoke, respectively. qi and B pi are the amplitudes of the corresponding i-th harmonic, K h is the hysteresis heat coefficient, K c is the eddy current heat coefficient.

4. The method for detecting and controlling the temperature of an outer rotor magnetic field modulation permanent magnet motor according to claim 2, characterized in that: The frequency and amplitude relationship between the air gap harmonics and the core harmonics is: B E1 :B E2 :...:B En =B q1 :B q2 :...:B qn =B p1 :B p2 :...:B pn (3) In the formula, B qv and B pv are the harmonic amplitudes of the vth harmonic in the air gap at points q and p, respectively, and f i is the i-th core harmonic frequency at points q and p, B En is the effective amplitude of the corresponding nth air gap harmonic.

5. The temperature detection and control method of an outer rotor magnetic field modulation permanent magnet motor according to claim 1, characterized in that: In step 2, the process of modeling the air gap harmonics and the eddy current heat of the permanent magnets in the motor is as follows: The definition ignores the influence of magnetic saturation, and the total permanent magnet eddy current heat is expressed as the sum of the permanent magnet eddy current heat generated by each air gap harmonic; Assume the permanent magnet to be a simplified rectangle, and use four resistors connected in series to represent the size of the permanent magnet, and get the equivalent resistance. According to the law of electromagnetic induction, the amplitude of the induced electromotive force generated in the permanent magnet eddy current circuit is obtained, and combined with the equivalent resistance, the eddy current heat of the motor permanent magnet is obtained.

6. The method for detecting and controlling the temperature of an outer rotor magnetic field modulation permanent magnet motor according to claim 5, characterized in that: The permanent magnet eddy current heat mathematical model is: In the formula, is the amplitude of the induced electromotive force generated in the permanent magnet eddy current circuit, and R is the equivalent resistance.

7. The temperature detection and control method of an outer rotor magnetic field modulation permanent magnet motor according to claim 1, characterized in that: In step 2, the process of modeling the heat of the armature winding of the motor with the air gap harmonics is as follows: the winding is energized to generate a magnetic field, and the heat generated by the air gap harmonics is negligible. Here, the heat of the motor winding is obtained only based on the resistance of the winding and the current flowing through it, as shown in the following formula: P cu =mI 2 R cu (6) In the formula, m is the number of motor phases, I is the equivalent resistance, R cu is the phase resistance of the motor.

8. The temperature detection and control method of an outer rotor magnetic field modulation permanent magnet motor according to claim 1, characterized in that: In step 3, the heat of the iron core, the heat of the armature winding and the eddy current heat of the permanent magnet under working conditions are obtained according to the constructed mathematical model, and the heat of the motor is obtained, as shown in the following formula: P heat =P cu +P eddy +P Fe (7) In the formula, p cu is the armature winding heat, p eddy is the eddy current heat of the permanent magnet, p Fe The heat of the core.

9. The temperature detection and control method of an outer rotor magnetic field modulation permanent magnet motor according to claim 1, characterized in that: In step 4, the temperature field analysis model is: Where T is the temperature that changes with time, λ x , y , z are the thermal conductivity of the material along the x, y, and z directions, respectively, and q v is the heat generated per unit volume per unit time, ρ m is the material element density, c m is the specific heat capacity of the material; s1 is the first type of boundary surface, T(t) is the boundary temperature at any given time, which can be a constant; s2 is the second type of boundary surface, λ is the thermal conductivity of the surface normal, n is the surface normal direction, q(t) is the boundary heat flux density at any given time; s3 is the third type of boundary surface, α s is the heat dissipation coefficient of the surface, T f is the temperature of the medium around the boundary surface.

10. The temperature detection and control method of an outer rotor magnetic field modulation permanent magnet motor according to claim 1, characterized in that: In the step 4, The thermal conductivity of the winding is: In the formula, δ i is the thickness of each heat conducting medium, λ i is the thermal conductivity of each heat-conducting medium; The thermal conductivity of the motor stator and rotor core in the axial, radial and circumferential directions are: In the formula, δ Fe is the dielectric thickness of silicon steel sheet, δ0 is 0, λ i is the thermal conductivity of silicon steel sheet, λ0 is the thermal conductivity of insulation material, k Fe is the core lamination coefficient; The air gap convection thermal conductivity is: In the formula, λ air is the thickness of silicon steel sheet, D1 is the outer diameter of motor stator, D2 is the inner diameter of motor rotor, Re air 、Re cr is the air gap Reynolds coefficient and the critical Reynolds coefficient; The heat dissipation coefficient of the motor rotor outer surface is: In the formula, v r is the rotor surface speed.

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