Intelligent monitoring system based on rare earth permanent magnet variable frequency motor

Abstract

The invention relates to the technical field of motor monitoring, and particularly discloses an intelligent monitoring system based on a rare earth permanent magnet variable frequency motor. A surface-mounted rare earth permanent magnet synchronous motor adopts a surface-mounted design, the motor is embedded into a magnetic material, a rotor and a stator magnetic field operate synchronously during normal work, and a rotor winding has no induced current; rotor resistance and hysteresis loss do not exist, the efficiency of the motor is improved, and the permanent magnet variable frequency motor not only can reduce resistance loss, but also can effectively improve a power factor; magnetic stability analysis, operation simulation and temperature screening are integrated, a section temperature extreme point is excavated, a time sequence trend of the section temperature extreme point is tracked, a core heat source is accurately positioned, and a heat source area is divided according to a preset threshold value based on a triangular mesh, so that real-time identification and partitioning of the internal heat source of the motor are realized, the internal core heat source is accurately positioned, and overheating of a blind area is avoided; and in combination with the temperature-dependent demagnetization boundary, the magnetic safety margin is calculated in real time, early warning or load limiting is performed in time, and irreversible demagnetization is prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of motor monitoring, and more specifically, to an intelligent monitoring system based on a rare earth permanent magnet variable frequency motor. Background Art

[0002] With the continuous improvement of global energy demand and environmental protection requirements, the energy efficiency and reliability of motors in the household appliance field, especially in refrigerators, have become key technical bottlenecks. Most existing refrigerators use induction motors or traditional permanent magnet motors, which have problems such as low energy efficiency, large volume, poor temperature tolerance, and high cost. Existing literature (Zheng Fei. General Control Research on Permanent Magnet Synchronous Motors for Refrigerator Compressors [D]. Guizhou University, 2021. DOI: 10.27047 / d.cnki.ggudu.2021.002924.) has carried out research on the general control of permanent magnet synchronous motors for refrigerator compressors, and given surface-mounted permanent magnet synchronous motors as shown in Figure 2 and interior permanent magnet synchronous motors as shown in Figure 3 Although variable frequency technology has been widely used in refrigerators, it is still difficult to achieve more precise variable frequency control. The refrigeration demand of a refrigerator changes frequently due to factors such as ambient temperature, door opening times, and food storage volume, and the variable frequency system is required to be able to adjust the speed and power of the compressor in real time and accurately. When operating at low frequencies, the compressor needs to maintain a stable operating state and good refrigeration effect. However, problems such as lubrication and refrigerant flow control of the compressor are more prominent at low frequencies, which are likely to lead to problems such as a decrease in refrigeration efficiency, an increase in energy consumption, and a shortening of the compressor life. Moreover, the variable frequency circuit in a variable frequency refrigerator will generate electromagnetic interference, which may affect the normal operation of the refrigerator itself and surrounding electronic devices.

[0003] In order to adapt to the development trend of product miniaturization, energy conservation, and high efficiency, sintered neodymium iron boron (NdFeB) permanent magnet materials have been increasingly widely used due to their high remanence density. However, sintered NdFeB permanent magnet materials also have their deficiencies, that is, poor temperature characteristics, specifically reflected in two aspects: lower Curie temperature and higher temperature coefficient. The higher temperature coefficient results in poor thermal stability of its magnetic properties and large magnetic losses when used at high temperatures. Based on the above, traditional variable frequency technology has low control accuracy and insufficient low-frequency performance when dealing with frequent switching and complex working conditions; it is difficult to locate the core heat source inside the motor, resulting in local overheating leading to insulation aging or coil burnout. To solve the above problems, a technical solution is provided herein. Summary of the Invention

[0004] To overcome the above-mentioned defects of the prior art, the present invention provides an intelligent monitoring system based on a rare-earth permanent magnet variable-frequency motor. By using a surface-mounted rare-earth permanent magnet synchronous motor and integrating magnetic stability analysis, operation simulation, and temperature screening, the internal core heat source is accurately located, aiming to solve the problems of low control accuracy in traditional variable-frequency technology, difficulty in locating the internal core heat source of the motor, resulting in local overheating leading to insulation aging or coil burnout, reducing the total loss, and avoiding overheating in the "blind area" to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An intelligent monitoring system based on a rare-earth permanent magnet variable-frequency motor, comprising a surface-mounted rare-earth permanent magnet synchronous motor and a motor heat source monitoring subsystem; the surface-mounted rare-earth permanent magnet synchronous motor includes a stator, a rotor, a non-uniform air-gap structure, a sensorless control system, and a variable-frequency drive unit; the stator adopts a 12-slot 10-pole fractional-slot flat-bottom slot punching sheet and a short-pitch concentrated winding; the rotor adopts surface-mounted permanent magnets embedded radially, and the permanent magnets and the rotor body are reinforced by Kevlar fiber binding; the non-uniform air-gap structure adopts a non-uniform air-gap design, forming a local magnetic bridge between the stator and the rotor to reduce torque ripple; the sensorless control system estimates the rotor position based on the zero-crossing detection of the back electromotive force; the variable-frequency drive unit integrates the DSP control algorithm and electromagnetic compatibility design; the motor stability monitoring subsystem is used to integrate magnetic stability analysis, operation simulation, and temperature screening, accurately locate the core heat source by excavating the extreme points of the cross-section temperature and tracking its time-series trend, and divide the heat source area based on a triangular grid according to a preset threshold to realize the real-time identification and zoning of the internal heat source of the motor.

[0007] The present invention adopts a surface-mounted design of a permanent magnet synchronous motor. The permanent magnets of the surface-mounted permanent magnet motor are installed on the outer surface of the rotor. The magnetic flux generated by the permanent magnets directly enters the air gap without any medium, and can provide a larger air-gap magnetic flux density than that of an inner-rotor type. The permanent magnets in this structure are not fixed radially. By embedding a certain depth and binding them to the rotor with Kevlar fiber, the structural strength of the permanent magnets and the rotor is increased, and the torque power density and starting torque can be improved.

[0008] The no-load air-gap magnetic field in a permanent magnet motor is generated by the excitation of permanent magnets. Therefore, the selection of the magnetic steel material and the size of the magnetic steel in a permanent magnet motor have an important impact on the performance of the motor. The three parameters of the axial length of the permanent magnet, the length of the permanent magnet magnetization direction, and the pole arc width are the most important dimensions of the permanent magnet. Therefore, the design of the rotor punching sheet needs to design the size of the magnetic steel slot according to the size of the permanent magnet and the limit fit of the magnetic steel slot, and at the same time, considering the strength of the rotor punching sheet, the distance between adjacent magnetic steel slots, between the magnetic steel slot and the inner hole, and between the magnetic steel slot and the outer circle needs to be ensured to ensure the performance of the rotor.

[0009] As a further solution of the present invention, the permanent magnet is a sintered NdFeB magnet steel with a remanence retention rate ≥ 85% at 140 °C.

[0010] As a further solution of the present invention, the motor heat source monitoring subsystem includes a magnetic stability analysis module, an operation simulation module, a temperature analysis and screening module, a heat source position determination module, and a triangular heat source marking module.

[0011] As a further solution of the present invention, the magnetic stability analysis module is used to test and plot the magnetic polarization - magnetic field strength curve through a hysteresis loop tester, calculate and plot the magnetic flux density - magnetic field strength curve based on the magnetic polarization - magnetic field strength curve, and obtain the intrinsic coercivity curve and demagnetization curve at different temperatures to analyze the magnetic stability of the motor.

[0012] As a further solution of the present invention, the operation simulation module is used to perform motor operation simulation to obtain the temperature distribution data of the motor in real time; the temperature distribution data includes the temperature distribution data of the motor cross-section.

[0013] The temperature analysis and screening module is used to plot the first temperature distribution curve based on the temperature distribution data of the motor cross-section at the same moment, respectively obtain the maximum point and the minimum point of the first temperature distribution curve, and then plot the second curve according to the change of the temperature distribution data of the motor cross-section at the maximum point and the minimum point over time, and screen the peak and valley values of the second curve as the first analysis points.

[0014] As a further solution of the present invention, the heat source position determination module is used to obtain the possibility of the core heat source position in the motor for the two extreme points in the first temperature distribution curve at the same moment, based on the difference between each extreme point and the data on the second curve at the corresponding time point, and the difference in the change trends between the first temperature distribution curve and the two second curves.

[0015] As a further solution of the present invention, the triangular heat source marking module is used to divide triangular grid cells centered on the core heat source point in the motor cross-section area, compare the distance between the triangular grid cells and the heat source center with the preset threshold range [r1, r2] and mark them; if the distance between the triangular grid cell and the heat source center is less than r1, then mark the triangular grid cell as "high heat source area"; if the distance between the triangular grid cell and the heat source center is less than r1, then mark the triangular grid cell as "medium heat source area"; if the distance between the triangular grid cell and the heat source center is less than r1, then mark the triangular grid cell as "low heat source area".

[0016] As a further solution of the present invention, the possibility of the core heat source position in the motor is determined by the same diffusion direction and slope difference of the heat source.

[0017] As a further solution of the present invention, for the diffusion direction of the heat source, for the selected maximum points, record the spatial coordinates (x i , y i ) of the extreme points on the first temperature distribution curve at n consecutive moments respectively, and splice the spatial coordinates into a trajectory according to the time series to preliminarily judge the diffusion direction of the heat source.

[0018] As a further solution of the present invention, the slope difference is determined by, for each extreme point P j , extracting the temperature data sequence of this point on the second curve at the corresponding moment and calculating the slope difference between this sequence and the temperature sequence {T ne (t)} of adjacent points on the first temperature distribution curve.

[0019] The calculation formula of the slope difference is:

[0020]

[0021] In the formula: ΔT j (t) is the slope difference at moment t, is the temperature data sequence, and T ne (t) is the temperature sequence of adjacent points.

[0022] The technical effects and advantages of an intelligent monitoring system based on a rare earth permanent magnet variable frequency motor of the present invention: In the present invention, through the surface-mounted design of the surface-mounted rare earth permanent magnet synchronous motor, the motor is embedded with magnetic materials. When working normally, the rotor and the stator magnetic field run synchronously, there is no induced current in the rotor winding, and there is no rotor resistance and hysteresis loss, improving the motor efficiency. The permanent magnet variable frequency motor can not only reduce the resistance loss, but also effectively improve the power factor; and integrate magnetic stability analysis, operation simulation and temperature screening. By excavating the cross-section temperature extreme points and tracking their time series trends, accurately locate the core heat source, divide the heat source area based on the triangular grid according to the preset threshold, realize the real-time identification and zoning of the internal heat source of the motor, accurately locate the internal core heat source, avoid overheating in the "blind area", combine the temperature-dependent demagnetization boundary, calculate the magnetic safety margin in real time, give early warning or limit the load in time, and prevent irreversible demagnetization; the present invention reduces extreme thermal stress and local aging through online monitoring and early warning, reduces the failure rate, and prolongs the mechanical and insulation life. Description of the Drawings

[0023] Figure 1 is the production process route diagram of the rare earth permanent magnet variable frequency motor provided by the present invention

[0024] Figure 2 is the surface-mounted permanent magnet synchronous motor of the prior art provided by the present invention;

[0025] Figure 3 is the interior permanent magnet synchronous motor of the prior art provided by the present invention;

[0026] Figure 4 The thermal analysis diagram of the motor provided by MotorCAD for the present invention;

[0027] Figure 5 The schematic diagram of the demagnetization curve and the recoil curve provided by the present invention;

[0028] Figure 6 The schematic structural diagram of an intelligent monitoring system based on a rare earth permanent magnet variable frequency motor provided by the present invention. Detailed implementation manners

[0029] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the accompanying drawings in the present invention. Obviously, the described technical solutions are only a part of the present invention, rather than all of them. All other technical solutions obtained by those of ordinary skill in the art based on the technical solutions in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] Embodiment 1

[0031] Figure 6 The schematic structural diagram of an intelligent monitoring system based on a rare earth permanent magnet variable frequency motor provided by the present invention is shown as follows. An intelligent monitoring system based on a rare earth permanent magnet variable frequency motor includes a surface-mounted rare earth permanent magnet synchronous motor and a motor heat source monitoring subsystem; the surface-mounted rare earth permanent magnet synchronous motor is connected to the motor heat source monitoring subsystem;

[0032] The motor stability monitoring subsystem is used to integrate magnetic stability analysis, operation simulation and temperature screening. By excavating the extreme points of the cross-section temperature and tracking its time series trend, the core heat source is accurately located, and the heat source area is divided based on the triangular grid according to a preset threshold, so as to realize the real-time identification and zoning of the internal heat source of the motor.

[0033] Specifically, the surface-mounted rare earth permanent magnet synchronous motor includes a stator, a rotor, a non-uniform air-gap structure, a sensorless control system and a variable frequency drive unit;

[0034] The stator adopts a 12-slot 10-pole fractional slot flat-bottom slot punching sheet and a short-pitch concentrated winding;

[0035] The rotor adopts surface-mounted permanent magnets embedded radially, and the permanent magnets and the rotor body are reinforced by Kevlar fiber binding;

[0036] The non-uniform air-gap structure adopts a non-uniform air-gap design, and reduces the torque ripple by forming a local magnetic bridge between the stator and the rotor;

[0037] The sensorless control system estimates the rotor position based on the zero-crossing detection of the back electromotive force;

[0038] The variable-frequency drive unit integrates a DSP control algorithm and electromagnetic compatibility design.

[0039] Specifically, the stator slot type adopts a flat-bottom slot punching structure, and a fractional-slot concentrated winding with 12 slots and 10 poles is used.

[0040] Specifically, the non-uniform air-gap structure includes 4 equally spaced magnetic bridges, and the thickness of the magnetic bridges is 0.3 mm.

[0041] Specifically, the permanent magnet is selected as a sintered NdFeB magnet with a remanence retention rate of ≥85% at 140°C.

[0042] In order to reduce the noise and vibration of the motor system, in addition to performing mechanical structure analysis on the developed motor, the torque ripple should also be reduced as much as possible. Through reasonable electromagnetic design and rotor structure design, the air-gap magnetic density is made close to a sinusoidal distribution. Adopting a non-uniform air gap is the most obvious method. During the development process, simulations and verifications are carried out on different magnetic bridges for magnetic isolation and different implementation methods of non-uniform air gaps to seek the minimum torque ripple and the highest efficiency value.

[0043] When designing a permanent magnet variable-frequency motor, multiple aspects need to be considered. The windings generally include single-layer windings, double-layer windings, and hybrid windings. As the name implies, a single-layer winding means that there is only one set of windings in a slot and it is only connected to the windings in other slots to form a loop. A double-layer winding means that there are upper and lower layers of windings in a slot. The selection of the winding should minimize the high-order harmonics as much as possible. In order to weaken the harmonic electromotive force, the winding factor needs to be made as small as possible. When a short-pitch winding is used, the winding factor is 0. At the same time, increasing the number of slots per pole per phase can also effectively suppress the harmonics. The selection of the number of slots per pole per phase needs to consider the size and number of poles of the motor. The selection of the number of poles of the motor is generally related to the motor speed. The present invention intends to adopt a fractional-slot concentrated winding method with 12 slots and 10 poles to achieve a basic high-order harmonic of 0 and improve the motor efficiency at the same time.

[0044] The working principle of a rare-earth permanent magnet variable-frequency motor is the same as that of an electrically excited synchronous motor. The difference is that the former uses a permanent magnet to replace the excitation winding for excitation. When three-phase alternating current with a frequency of f passes through the three-phase stator of the permanent magnet motor (each phase is 120° electrical angle apart), a rotating magnetic field that moves at the synchronous speed will be generated. Under steady-state conditions, the main pole magnetic field rotates synchronously with the rotating magnetic field. Therefore, the rotor speed is also the synchronous speed. The stator rotating magnetic field always remains relatively stationary with respect to the main pole magnetic field established by the permanent magnet. They interact with each other and generate an electromagnetic torque to drive the motor to rotate and perform energy conversion.

[0045] The surface-mounted design using PMSM has the characteristics of large torque power density and large starting torque. The motor is embedded with magnetic materials. During normal operation, the rotor runs synchronously with the stator magnetic field. There is no induced current in the rotor winding, and there is no rotor resistance and hysteresis loss, improving the motor efficiency. The permanent magnet variable frequency motor can not only reduce the resistance loss, but also effectively improve the power factor, with simple structure and high reliability. Using electromagnetic simulation software, the punching sheet and structure of the motor are reasonably optimized to achieve the best design of the motor, so as to reduce the volume and weight of the motor. The excitation with permanent magnet materials replaces the pole shoes and excitation coils for excitation in the original excitation motor with one or more permanent magnets, greatly reducing the number of components, greatly simplifying the structure, and at the same time greatly enhancing the mechanical reliability of the motor.

[0046] Specifically, the motor heat source monitoring subsystem includes a magnetic stability analysis module, an operation simulation module, a temperature analysis and screening module, a heat source position determination module, and a triangular heat source marking module; the operation simulation module is connected to the temperature analysis and screening module, the temperature analysis and screening module is connected to the heat source position determination module, and the heat source position determination module is connected to the triangular heat source marking module;

[0047] The magnetic stability analysis module is used to test and draw the magnetic polarization - magnetic field intensity curve through a hysteresis loop tester, calculate and draw the magnetic flux density - magnetic field intensity curve according to the magnetic polarization - magnetic field intensity curve, and obtain the intrinsic coercivity curve and demagnetization curve at different temperatures to analyze the magnetic stability of the motor;

[0048] The operation simulation module is used to perform motor operation simulation to obtain the temperature distribution data of the motor in real time; the temperature distribution data includes the temperature distribution data of the motor cross-section.

[0049] The temperature analysis and screening module is used to draw the first temperature distribution curve according to the temperature distribution data of the motor cross-section at the same moment, respectively obtain the maximum point and the minimum point of the first temperature distribution curve, and then draw the second curve according to the change of the temperature distribution data of the motor cross-section at the maximum point and the minimum point with time, and screen the peak and valley values of the second curve as the first analysis points;

[0050] The heat source position determination module is used for two extreme points in the first temperature distribution curve at the same moment. According to the difference between each extreme point and the data on the second curve at the corresponding time point, and the difference in the change trend between the first temperature distribution curve and the two second curves, obtain the possibility of the core heat source position in the motor;

[0051] The triangular heat source marking module is used to divide triangular grid units centered on the core heat source point within the cross-sectional area of the motor, and compare and mark according to the distance between the triangular grid unit and the heat source center with the preset threshold range [r1, r2]; if the distance between the triangular grid unit and the heat source center is less than r1, then mark this triangular grid unit as the "high heat source area"; if the distance between the triangular grid unit and the heat source center is less than r1, then mark this triangular grid unit as the "medium heat source area"; if the distance between the triangular grid unit and the heat source center is less than r1, then mark this triangular grid unit as the "low heat source area".

[0052] Such as Figure 4 is the thermal analysis diagram of the motor by MotorCAD for faster analysis; the colors from blue to red represent the temperature from low to high in turn. The temperature of the housing and the stator core is the lowest (dark blue), the temperature of the air gap and the stator winding is in the middle (green-yellow), and the rotor permanent magnet and the inner hub area are damaged and concentrated, and the temperature is the highest (red), which is used to visually locate the internal heat source distribution of the motor and guide the heat dissipation design and thermal protection strategy.

[0053] Specifically, the possibility of the core heat source position in the motor is determined by the same diffusion direction and slope difference of the heat source.

[0054] The diffusion direction of the heat source is obtained by recording the spatial coordinates (x i , y i ) of the extreme value points on the first temperature distribution curve at n consecutive moments for the selected extreme value points, and splicing the spatial coordinates into a trajectory according to the time series to preliminarily judge the diffusion direction of the heat source.

[0055] The slope difference is determined by extracting the temperature data sequence of each extreme value point P j on the second curve at the corresponding moment, calculating the slope difference between this sequence and the temperature sequence {T ne (t)} of adjacent points on the first temperature distribution curve; the calculation formula for the slope difference is:

[0056]

[0057] In the formula: ΔT j (T) is the slope difference at time t, is the temperature data sequence, and T ne (t) is the temperature sequence of adjacent points.

[0058] In the embodiment of the present invention, the surface-mounted rare earth permanent magnet synchronous motor adopts a surface-mounted design, with the motor embedded with magnetic materials. During normal operation, the rotor runs synchronously with the stator magnetic field, and there is no induced current in the rotor winding, eliminating rotor resistance and hysteresis loss, thereby improving the motor efficiency. The permanent magnet variable-frequency motor can not only reduce resistance loss but also effectively improve the power factor. Additionally, magnetic stability analysis, operation simulation, and temperature screening are integrated. By identifying the extreme cross-section temperature points and tracking their temporal trends, the core heat sources are accurately located. Based on triangular meshes, the heat source areas are divided according to a preset threshold to achieve real-time identification and zoning of the internal heat sources of the motor, precisely locating the internal core heat sources and avoiding overheating in "blind spots". Combining with the temperature-dependent demagnetization boundary, the magnetic safety margin is calculated in real time to give early warnings or limit loads in a timely manner to prevent irreversible demagnetization. The present invention reduces extreme thermal stress and local aging through on-line monitoring and warning, reduces the failure rate, and extends the mechanical and insulation life.

[0059] Embodiment 2

[0060] As Figure 1 shown in the production process route diagram of the rare earth permanent magnet variable-frequency motor; the production process is divided into two major stages: "assembly line group processing" and "testing and packaging", and the specific processes are as follows:

[0061] Assembly line group processing:

[0062] Pre-processing of materials: material cutting and blank preparation;

[0063] Forming and initial inspection of stator and rotor cores: After stamping / laminating, perform QCB dimension and stacking quality inspections; if unqualified (NG), rework after QA review.

[0064] Stator processing flow: Stamp identification codes on the stator core and insert insulating paper at the bottom of the slots; install the core skeleton; wind enameled wires in the stator winding; cure and dry after the stator winding is wound.

[0065] Rotor processing flow: Polish / bore the inner hole of the rotor; insert and rivet positioning rivets; apply glue to the magnetic tiles and paste them onto the surface of the core; dry, cure, and cool the magnetic tiles after clamping them with a fixture; perform curing strength detection on the magnetic tiles; stamp identification codes on the rotor.

[0066] Intermediate inspection and assembly: Appearance and perpendicularity inspection → Installation of lead wire components → Terminal crimping and skeleton switching → Phase separation and bundling of outgoing wires → Re-inspection by QC.

[0067] QC re-inspection / rework: Finally, perform QCB inspections on the entire stator and rotor; rework the NG parts and enter the next stage after passing the inspection.

[0068] Testing and packaging:

[0069] Stator electrical and appearance inspection: QC performs electrical performance inspections on the stator winding, such as insulation, withstand voltage, and turn-to-turn short circuit; at the same time, check the appearance and dimensions.

[0070] Stator and rotor dust removal and cleaning: Remove impurities such as surface iron filings and glue residues, and perform anti-rust and anti-corrosion treatments.

[0071] QA review and spot checks: QA reviews the quality records of the entire process and eliminates batches that fail the spot checks.

[0072] Finished product packing and warehousing: Qualified units are packaged in batches according to the model and stored in the warehouse for shipment.

[0073] Example 3

[0074] The Curie temperature of sintered NdFeB permanent magnet materials is generally about 310 - 410 °C, while that of ferrite is 450 °C, that of samarium cobalt is about 800 - 850 °C, and that of alnico is even higher than that of samarium cobalt; in the temperature coefficient of NdFeB permanent magnet materials, the temperature coefficient α(Br) of the remanence Br can reach -0.13% / K, and the temperature coefficient α(HcJ) of the intrinsic coercivity HcJ reaches -(0.6 - 0.7)% / K. One standard gives the typical value of α(Br) as -0.12% / K and α(HcJ) as -0.6% / K (25 - 140 °C), and another standard gives α(Br) as -(0.1 - 0.12)% / K and α(HcJ) as -(0.45 - 0.6)% / K (20 - 100 °C). The relatively high temperature coefficient results in poor thermal stability of its magnetic properties and large magnetic losses when used at high temperatures. Generally, when NdFeB permanent magnet materials are used at high temperatures, the lower half of the demagnetization curve will bend, as Figure 5 shown in the schematic diagram of the demagnetization curve and the recoil curve. The solid line in the figure is the B–H demagnetization curve, which represents the response of the remanence B of the material when the external magnetization intensity H changes; the dotted line is the J–H intrinsic magnetization curve, which reflects the change of the magnetization intensity J (the internal magnetism of the ferrite after removing the vacuum permeability effect). The key points on the second quadrant curve include: H CJ : Intrinsic coercivity point, the H when the J–H curve passes through zero; H CB : Coercivity point, the H when the B–H curve passes through zero; H D : Demagnetization inflection point, the critical H at which the material begins to undergo irreversible demagnetization.

[0075] To prevent the permanent magnet motor from losing magnetism due to the poor thermal stability of the permanent magnet material, it is necessary to conduct reliability verification on the permanent magnet motor under high-temperature conditions, obtain the position of the inflection point of the demagnetization curve of each type of NdFeB permanent magnet material at the highest operating temperature, and ensure that the operating point of the motor under the most adverse conditions (including high temperature and large current) still varies above the inflection point of the permanent magnet demagnetization curve. When the motor stops running, the residual magnetic induction intensity Br of the permanent magnet material remains basically unchanged. Currently, the commonly used measurement equipment is a hysteresis loop tester, and the measurement coil used in the test process is a J-H coil. By measuring the J-H curve, the B-H curve can be calculated, and the intrinsic coercivity curve and demagnetization curve at different temperatures can be obtained to ensure the magnetic retention and stability of the permanent magnet motor.

[0076] Example 4

[0077] Take an application example of a 7-slot sample to demonstrate the complete data analysis process from simulation data to heat source localization and grid marking.

[0078] Obtain the partial cross-section probe temperature summary table shown in Table 1 output by the operation simulation module:

[0079] Slot number T (t = 100 s) [°C] T (t = 101 s) [°C] ΔT / Δt [°C / s] 1 68.0 68.2 0.2 2 72.5 73.0 0.5 3 65.4 65.6 0.2 4 70.1 70.4 0.3 5 95.0 95.8 0.8 6 64.7 64.8 0.1 7 62.0 61.8 -0.2

[0080] The first temperature distribution curve (t = 100 s): peak at slot 5 (95 °C), valley at slot 7 (62 °C).

[0081] Track between t = 100 - 110 s. The peak at slot 5 reaches 98 °C (t = 105 s), and the valley at slot 7 drops to 60 °C (t = 103 s).

[0082] The heat source position determination module analyzes that the ΔT / Δt of slot 5 is the largest (0.8 °C / s), much higher than other slots → the heat source tends to be at slot 5. The average temperature of adjacent slots 4 and 6 is 67.5 °C, and the gradient of slot 5 ≈ (95.0 - 67.5) / d ≈ 27.5 / d, which is significantly the largest. Slot 5 continuously maintains the highest temperature and rises the fastest within 100 - 110 s, and the trajectory is the most stable. The corresponding position of slot 5 is the core heat source.

[0083] The triangular heat source marking module classifies grid cells. After performing triangular grid segmentation on the cross-section and taking the center distance d of several cells:, the triangular heat source marking summary table shown in Table 2 below is obtained

[0084] Unit ID d (mm) Area classification A 1.8 High heat source area B 2.2 High heat source area C 4.5 Medium heat source area D 8.7 Medium heat source area E 12.0 Low heat source area F 15.5 Low heat source area

[0085] Set thresholds: r1 = 3, r2 = 10;

[0086] d < r1 → high heat source area; r1 ≤ d < r2 → medium heat source area; d ≥ r2 → low heat source area.

[0087] As described above, it is only the specific implementation manner of the present application. However, the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claimed rights.

[0088] Finally: The above description is only the preferred solution of the present invention and is not used to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An intelligent monitoring system based on rare earth permanent magnet variable frequency motor, comprising a surface mounted rare earth permanent magnet synchronous motor and a motor heat source monitoring subsystem; characterized in that: The surface-mounted rare earth permanent magnet synchronous motor includes a stator, a rotor, a non-uniform air gap structure, a sensorless control system and a variable frequency drive unit; the stator adopts 12-slot 10-pole fractional slot flat-bottom slot punchings and short-pitch concentrated windings; the rotor adopts surface-mounted permanent magnets embedded radially, and the permanent magnets and the rotor body are reinforced by Kevlar fiber binding; the non-uniform air gap structure adopts a non-uniform air gap design, which reduces torque pulsation by forming a local magnetic bridge between the stator and the rotor; the sensorless control system estimates the rotor position based on back-electromotive force zero-crossing detection; the variable frequency drive unit integrates DSP control algorithm and electromagnetic compatibility design; the motor stability monitoring subsystem is used to integrate magnetic stability analysis, operation simulation and temperature screening, and accurately locates the core heat source by mining the cross-sectional temperature extreme points and tracking their time series trends, and divides the heat source area according to the preset threshold based on the triangular grid, so as to realize real-time identification and zoning of the internal heat source of the motor.

2. The intelligent monitoring system based on rare earth permanent magnet variable frequency motor according to claim 1 is characterized in that: The permanent magnet is made of sintered NdFeB magnetic steel with a residual magnetic retention rate of ≥85% at 140°C.

3. The intelligent monitoring system based on rare earth permanent magnet variable frequency motor according to claim 1 is characterized in that: The motor heat source monitoring subsystem includes a magnetic stability analysis module, an operation simulation module, a temperature analysis and screening module, a heat source location determination module, and a triangular heat source marking module.

4. The intelligent monitoring system based on rare earth permanent magnet variable frequency motor according to claim 3 is characterized in that: The magnetic stability analysis module is used to draw the magnetic polarization-magnetic field strength curve through the hysteresis loop tester test, calculate and draw the magnetic flux density-magnetic field strength curve based on the magnetic polarization-magnetic field strength curve, and obtain the intrinsic coercive force curve and demagnetization curve at different temperatures to analyze the magnetic stability of the motor.

5. The intelligent monitoring system based on rare earth permanent magnet variable frequency motor according to claim 3 is characterized in that: The operation simulation module is used to simulate the operation of the motor and obtain the temperature distribution data of the motor in real time; the temperature distribution data includes the temperature distribution data of the motor cross section; The temperature analysis and screening module is used to draw a first temperature distribution curve based on the temperature distribution data of the motor cross section at the same moment, obtain the maximum point and the minimum point of the first temperature distribution curve respectively, and then draw a second curve according to the change of the motor cross section temperature distribution data of the maximum point and the minimum point over time, and screen the peak value and the valley value of the second curve as the first analysis point.

6. The intelligent monitoring system based on rare earth permanent magnet variable frequency motor according to claim 5 is characterized in that: The heat source position determination module is used to obtain the possibility of the core heat source position in the motor for two extreme points in the first temperature distribution curve at the same time, based on the difference between each extreme point and the data on the second curve at the corresponding time point, and the difference in the changing trend of the first temperature distribution curve and the two second curves.

7. The intelligent monitoring system based on rare earth permanent magnet variable frequency motor according to claim 6 is characterized in that: The triangular heat source marking module is used to divide the triangular mesh units in the motor cross-sectional area with the core heat source point as the center, and compare and mark the triangular mesh units according to the distance between the triangular mesh units and the heat source center and the preset threshold range [r1, r2]; if the distance between the triangular mesh units and the heat source center is less than r1, the triangular mesh units are marked as "high heat source area"; if the distance between the triangular mesh units and the heat source center is less than r1, the triangular mesh units are marked as "medium heat source area"; if the distance between the triangular mesh units and the heat source center is less than r1, the triangular mesh units are marked as "low heat source area".

8. The intelligent monitoring system based on rare earth permanent magnet variable frequency motor according to claim 6 is characterized in that: The probability of the location of the core heat source in the motor is determined by the same diffusion direction and different slope of the heat source.

9. The intelligent monitoring system based on rare earth permanent magnet variable frequency motor according to claim 8, characterized in that: The diffusion direction of the heat source is determined by recording the spatial coordinates (x i ,y i ), the spatial coordinates are pieced together into a trajectory in time series to preliminarily determine the diffusion direction of the heat source.

10. The intelligent monitoring system based on rare earth permanent magnet variable frequency motor according to claim 8, characterized in that: The slope difference is determined by j , extract the temperature data sequence of the point on the second curve at the corresponding time, and calculate the slope difference between the sequence and the temperature sequence of the adjacent point on the first temperature distribution curve.

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