Permanent magnet motor electromagnetic simulation model analysis method

Abstract

An analytical method for electromagnetic simulation modeling of permanent magnet synchronous motors includes the following steps: Meshing the stator and rotor of the permanent magnet synchronous motor using a 2D finite element model and a meshing method capable of calculating the skin effect; performing simulation when the permanent magnet synchronous motor is under no-load to obtain the no-load air gap magnetic flux density, and performing Fourier decomposition analysis on the no-load air gap magnetic flux density; performing simulation when the permanent magnet synchronous motor is under rated load to obtain the load air gap magnetic flux density, and performing Fourier decomposition analysis on the load air gap magnetic flux density; and, with the volume remaining constant, deriving the formula for calculating eddy current loss of the permanent magnet based on the harmonic order and amplitude values ​​of the air gap magnetic flux density, in order to find the specific tooth harmonic that generates eddy current loss of the permanent magnet, and weaken or eliminate it to maximize the reduction of the eddy current loss value of the permanent magnet.

Description

Technical fields:

[0001] This invention relates to a method for analyzing electromagnetic simulation models of permanent magnet motors. Background technology:

[0002] In pumping stations and related water conservancy projects, low-speed, high-torque permanent magnet motor drive systems are receiving increasing attention. These systems employ a new transmission technology that directly drives low-speed pumps using a low-speed permanent magnet synchronous motor. This eliminates the need for a traditional reducer, effectively reducing unit failures caused by gearbox wear, improving system reliability and lifespan, and reducing maintenance costs.

[0003] Compared with commonly used induction motors and electrically excited synchronous motors, permanent magnet synchronous motors are not only smaller and lighter, but also have higher operating efficiency and power factor under rated load and light load, which is of great significance for large pump drives with flow control requirements.

[0004] When a permanent magnet synchronous motor (PMSM) is running, an electromagnetic field exists within its internal space. This electromagnetic field is generated jointly by the permanent magnet and the armature magnetic field. The distribution and variation of the electromagnetic field in different media, as well as its interaction with the current, determine the operating state and performance of the electrodes. Therefore, simulation modeling of PMSMs is of great importance. Traditional analytical methods are mainly divided into direct analytical methods based on Maxwell's equations and equivalent magnetic circuit analysis methods. Direct analytical methods can only be used for relatively simple solution domains. For more complex motor structures, the solutions obtained by analytical methods are lengthy and complex. On the other hand, equivalent magnetic circuit analysis can achieve an effective balance between computation time and accuracy, but it is only applicable to the initial design of the motor, with a narrow scope of application, and the accuracy and reliability of the analytical results cannot be guaranteed. Summary of the Invention:

[0005] This invention provides an analytical method for electromagnetic simulation models of permanent magnet motors. The method features a reasonable structural design and employs a 2D finite element electromagnetic simulation model to perform simulation analyses of both no-load and loaded states of the permanent magnet synchronous motor. It obtains the influence of stator straight slots, rotor magnetic bridges, and high-order harmonic currents on the air gap magnetic flux density, simplifying the calculation and analysis steps, improving simulation efficiency, and ensuring accurate and reliable results. This allows for accurate evaluation of the motor's operating state and performance, facilitating calculations of permanent magnet losses and solving problems existing in the prior art.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] A method for analyzing the electromagnetic simulation model of a permanent magnet motor, the method comprising the following steps:

[0008] S1. The stator and rotor of the permanent magnet synchronous motor are meshed using a 2D finite element model and a meshing method that can calculate the skin effect, respectively, to determine the magnetic field distribution and the meshing of the permanent magnet.

[0009] S2, when the permanent magnet synchronous motor is in an unloaded state, the simulation is carried out to obtain the unloaded air gap magnetic flux density of the motor. Fourier decomposition analysis is performed on the unloaded air gap magnetic flux density of the motor to obtain the influence of the stator straight slot on the unloaded air gap magnetic flux density, thereby increasing the eddy current loss of the permanent magnet.

[0010] S3, when the permanent magnet synchronous motor is under rated load, the simulation is carried out to obtain the load air gap magnetic flux density of the motor. Fourier decomposition analysis is performed on the load air gap magnetic flux density of the motor to obtain the influence of rotor magnetic bridge and high-order harmonic current on the load air gap magnetic flux density, thereby increasing the eddy current loss of permanent magnet.

[0011] S4. Under the condition of constant volume, the formula for calculating permanent magnet eddy current loss is obtained based on the harmonic order and amplitude value of the air gap magnetic flux density. The specific tooth harmonic that causes permanent magnet eddy current loss is found and weakened or eliminated to maximize the reduction of permanent magnet eddy current loss value.

[0012] The partitioning method is the SkinDepth partitioning method, used to calculate the eddy current loss of the permanent magnet.

[0013] The 6th, 8th, 10th, and 12th harmonics with higher amplitudes in the unloaded air gap magnetic flux density harmonics are all tooth harmonics.

[0014] The parsing module of the parsing method includes:

[0015] A 2D finite element model meshing module is used to mesh the stator and rotor of a permanent magnet synchronous motor using a 2D finite element model and a meshing method that can calculate the skin effect, respectively, to determine the magnetic field distribution and the meshing of the permanent magnet.

[0016] The no-load simulation analysis module is used to simulate the permanent magnet synchronous motor when it is in no-load state, obtain the no-load air gap magnetic flux density of the motor, perform Fourier decomposition analysis on the no-load air gap magnetic flux density of the motor, and obtain the influence of stator straight slots on the no-load air gap magnetic flux density, thereby increasing the eddy current loss of permanent magnets.

[0017] The load simulation analysis module is used to simulate the permanent magnet synchronous motor under rated load to obtain the load air gap magnetic flux density of the motor. The load air gap magnetic flux density of the motor is subjected to Fourier decomposition analysis to obtain the influence of rotor magnetic bridge and high-order harmonic current on the load air gap magnetic flux density, thereby increasing the eddy current loss of permanent magnet.

[0018] The permanent magnet eddy current loss calculation module is used to obtain the permanent magnet eddy current loss calculation formula based on the harmonic order and harmonic amplitude value of the air gap magnetic flux density while keeping the volume constant. This allows the module to find the specific tooth harmonic that causes permanent magnet eddy current loss and weaken or eliminate it, thereby maximizing the reduction of permanent magnet eddy current loss.

[0019] The formula for calculating the eddy current loss of the permanent magnet is as follows:

[0020] P e =k c f 2 B m 2 V

[0021] Among them, P e Here, f represents the eddy current loss of the permanent magnet, f is the harmonic amplitude of the air gap magnetic flux density, and k is the value of the eddy current loss of the permanent magnet. c The harmonic order of the air gap magnetic flux density;

[0022] The formula for calculating the specific number of the tooth harmonic is as follows:

[0023] V = Q / p ± 1 = 2mq ± 1

[0024] Where Q represents the total number of slots in the motor, p represents the number of pole pairs in the motor, m represents the number of phases in the motor, and q represents the number of slots per pole per phase.

[0025] This invention employs the aforementioned structure. A 2D finite element model meshing module uses a 2D finite element model and a meshing method capable of calculating the skin effect to mesh the stator and rotor of the permanent magnet synchronous motor, respectively, to determine the magnetic field distribution and the meshing of the permanent magnets. An unloaded simulation analysis module simulates the permanent magnet synchronous motor under no-load conditions to obtain the no-load air gap magnetic flux density. Fourier decomposition analysis of the no-load air gap magnetic flux density reveals the influence of stator straight slots on the no-load air gap magnetic flux density, thereby increasing the eddy current losses of the permanent magnets. A load simulation analysis module simulates the permanent magnet synchronous motor under rated load conditions to obtain the load air gap magnetic flux density. Fourier decomposition analysis of the load air gap magnetic flux density reveals the influence of rotor magnetic bridges and higher harmonic currents on the load air gap magnetic flux density. This approach offers advantages such as accuracy, efficiency, reliability, and practicality. Attached image description:

[0026] Figure 1 This is a schematic diagram of the process of the present invention.

[0027] Figure 2 This is a schematic diagram of the structure of the present invention. Detailed implementation method:

[0028] To clearly illustrate the technical features of this solution, the invention will be described in detail below through specific implementation methods and in conjunction with the accompanying drawings.

[0029] like Figure 1-2 The method for analyzing the electromagnetic simulation model of a permanent magnet motor, as shown in the figure, includes the following steps:

[0030] S1. The stator and rotor of the permanent magnet synchronous motor are meshed using a 2D finite element model and a meshing method that can calculate the skin effect, respectively, to determine the magnetic field distribution and the meshing of the permanent magnet.

[0031] S2, when the permanent magnet synchronous motor is in an unloaded state, the simulation is carried out to obtain the unloaded air gap magnetic flux density of the motor. Fourier decomposition analysis is performed on the unloaded air gap magnetic flux density of the motor to obtain the influence of the stator straight slot on the unloaded air gap magnetic flux density, thereby increasing the eddy current loss of the permanent magnet.

[0032] S3, when the permanent magnet synchronous motor is under rated load, the simulation is carried out to obtain the load air gap magnetic flux density of the motor. Fourier decomposition analysis is performed on the load air gap magnetic flux density of the motor to obtain the influence of rotor magnetic bridge and high-order harmonic current on the load air gap magnetic flux density, thereby increasing the eddy current loss of permanent magnet.

[0033] S4. Under the condition of constant volume, the formula for calculating permanent magnet eddy current loss is obtained based on the harmonic order and amplitude value of the air gap magnetic flux density. The specific tooth harmonic that causes permanent magnet eddy current loss is found and weakened or eliminated to maximize the reduction of permanent magnet eddy current loss value.

[0034] The partitioning method is the SkinDepth partitioning method, used to calculate the eddy current loss of the permanent magnet.

[0035] The 6th, 8th, 10th, and 12th harmonics with higher amplitudes in the unloaded air gap magnetic flux density harmonics are all tooth harmonics.

[0036] The parsing module of the parsing method includes:

[0037] A 2D finite element model meshing module is used to mesh the stator and rotor of a permanent magnet synchronous motor using a 2D finite element model and a meshing method that can calculate the skin effect, respectively, to determine the magnetic field distribution and the meshing of the permanent magnet.

[0038] The no-load simulation analysis module is used to simulate the permanent magnet synchronous motor when it is in no-load state, obtain the no-load air gap magnetic flux density of the motor, perform Fourier decomposition analysis on the no-load air gap magnetic flux density of the motor, and obtain the influence of stator straight slots on the no-load air gap magnetic flux density, thereby increasing the eddy current loss of permanent magnets.

[0039] The load simulation analysis module is used to simulate the permanent magnet synchronous motor under rated load to obtain the load air gap magnetic flux density of the motor. The load air gap magnetic flux density of the motor is subjected to Fourier decomposition analysis to obtain the influence of rotor magnetic bridge and high-order harmonic current on the load air gap magnetic flux density, thereby increasing the eddy current loss of permanent magnet.

[0040] The permanent magnet eddy current loss calculation module is used to obtain the permanent magnet eddy current loss calculation formula based on the harmonic order and harmonic amplitude value of the air gap magnetic flux density while keeping the volume constant. This allows the module to find the specific tooth harmonic that causes permanent magnet eddy current loss and weaken or eliminate it, thereby maximizing the reduction of permanent magnet eddy current loss.

[0041] The formula for calculating the eddy current loss of the permanent magnet is as follows:

[0042] P e =k c f 2 B m 2 V

[0043] Among them, P e Here, f represents the eddy current loss of the permanent magnet, f is the harmonic amplitude of the air gap magnetic flux density, and k is the value of the eddy current loss of the permanent magnet. c The harmonic order of the air gap magnetic flux density;

[0044] The formula for calculating the specific number of the tooth harmonic is as follows:

[0045] V = Q / p ± 1 = 2mq ± 1

[0046] Where Q represents the total number of slots in the motor, p represents the number of pole pairs in the motor, m represents the number of phases in the motor, and q represents the number of slots per pole per phase.

[0047] The working principle of the electromagnetic simulation model analysis method for permanent magnet motors in this embodiment of the invention is as follows: a 2D finite element electromagnetic simulation model is used to simulate and analyze the no-load and loaded states of the permanent magnet synchronous motor, respectively, to obtain the influence of stator straight slots, rotor magnetic bridges and high-order harmonic currents on air gap magnetic flux density, simplify the calculation and analysis steps, improve the simulation analysis efficiency, and ensure that the analysis results are accurate and reliable, thereby accurately evaluating the operating status and performance of the motor, facilitating users to calculate the permanent magnet losses of the motor, making it easy to popularize and apply, and applicable to permanent magnet motors of different application scenarios or different specifications.

[0048] The overall scheme mainly includes the following steps: First, the stator and rotor of the permanent magnet synchronous motor are meshed using a 2D finite element model and a meshing method capable of calculating the skin effect, to determine the magnetic field distribution and the meshing of the permanent magnets. Second, simulation is performed when the permanent magnet synchronous motor is under no-load to obtain the no-load air gap magnetic flux density. Fourier decomposition analysis is then performed on the no-load air gap magnetic flux density to obtain the influence of the stator straight slots on the no-load air gap magnetic flux density, thus increasing the eddy current loss of the permanent magnets. Third, simulation is performed when the permanent magnet synchronous motor is under rated load to obtain the load air gap magnetic flux density. Fourier decomposition analysis is then performed on the load air gap magnetic flux density to obtain the influence of the rotor magnetic bridge and higher harmonic currents on the load air gap magnetic flux density, thus increasing the eddy current loss of the permanent magnets. Finally, with the volume remaining constant, the eddy current loss calculation formula for the permanent magnets is obtained based on the harmonic order and amplitude values ​​of the air gap magnetic flux density. This allows for the identification of specific tooth harmonics that generate eddy current losses in the permanent magnets, which are then weakened or eliminated to maximize the reduction of eddy current losses.

[0049] In this application, a 2D finite element model is used. Compared to the 2D model, the 3D calculation model can consider issues such as permanent magnet segmentation, skewed slots, and winding end effects, resulting in calculation results closer to reality. However, in finite element calculations, the number of meshes in the 3D model is much greater than that in the 2D model, which significantly increases the calculation and analysis time, hindering the research. Therefore, in this application, considering practical application requirements, a 2D finite element model is selected.

[0050] Preferably, the SkinDepth partitioning method is used in this application to calculate the eddy current loss of the permanent magnet.

[0051] For the load simulation analysis and no-load simulation analysis of the motor, the no-load simulation shows the significant impact of the introduction of straight slots on the air gap magnetic flux density. Its presence will greatly increase the eddy current losses of the permanent magnet. Therefore, the impact of slots on electromagnetic performance should be considered from the initial stage of motor design and taken into account in subsequent design processes.

[0052] Since the permanent magnet is assembled inside the rotor, the cooling water flow outside the motor and the cooling airflow passing through the middle of the air gap have little direct effect on the heat dissipation of the built-in permanent magnet. Therefore, the best way to reduce the operating temperature of the permanent magnet is to start from the root cause of heat generation, namely, to reduce its eddy current loss.

[0053] First, let's analyze the waveform of the unloaded air gap magnetic flux density: If we disregard the influence of the straight slots, the unloaded air gap magnetic flux density waveform is approximately a flat-topped wave. Besides the fundamental component, it also contains odd-order spatially distributed harmonics such as the 3rd, 5th, and 7th orders. These harmonics rotate at the same speed as the fundamental wave and are stationary relative to the rotor, thus not cutting the permanent magnet and generating eddy current losses. Therefore, theoretically, without considering the cogging, the rotor permanent magnet does not generate eddy current losses or heat generation. However, in large permanent magnet motors, the cogging effect cannot be ignored. Assuming the magnetomotive force is sinusoidally distributed along the air gap and does not contain spatial harmonics, the order of the tooth harmonics can be determined by the following formula:

[0054] V = Q / p ± 1 = 2mq ± 1

[0055] Where Q represents the total number of slots in the motor, p represents the number of pole pairs in the motor, m represents the number of phases in the motor, and q represents the number of slots per pole per phase.

[0056] When unloaded, the air gap contains not only the fundamental frequency but also various odd-order spatial harmonics. Although these spatial harmonics themselves do not generate eddy current losses, the tooth harmonics generated by the cogging effect will produce eddy current losses on the permanent magnet. Therefore, when unloaded, the eddy current losses are all caused by the tooth harmonics generated by the introduction of the stator straight slots.

[0057] Under load, the air gap magnetomotive force is synthesized from the permanent magnet magnetomotive force and the armature magnetomotive force. Since the cogging effect still exists, the methods for reducing no-load eddy current losses are still applicable to reducing eddy current losses under load. However, under load, the introduction of the armature magnetomotive force makes the sources of eddy current losses more diverse.

[0058] The armature magnetomotive force is obtained by synthesizing the three-phase spatial pulsating magnetomotive force. If a sinusoidal current without harmonics is passed through the stator winding, considering the characteristics of the winding distribution, the pulsating magnetomotive force generated by each phase is actually a step wave. Therefore, in addition to the fundamental wave content, the synthesized magnetomotive force also contains 6k±1 order forward and reverse rotating magnetomotive forces. These higher harmonics of the magnetomotive force will generate large eddy current losses.

[0059] In practice, motors are typically powered by frequency converters. The waveform flowing through the motor windings is unlikely to be a standard sine wave; it usually contains high-order harmonics near the switching frequency. These harmonics generally have small amplitudes, but their frequencies are very high. Since the magnitude of eddy current losses is proportional to the square of the frequency, they also cause significant eddy current losses.

[0060] Therefore, based on the problems mentioned above and considering the angle of the load air gap magnetic flux density, there are two ways to reduce load eddy currents on the basis of no-load eddy current losses: First, improve the sinusoidal nature of the winding to reduce the amplitude of the combined magnetomotive force caused by the winding distribution; second, reduce the harmonic ratio of the inverter output current and select inverters with better positive linearity of output current waveform and less high-order harmonic content to power the permanent magnet synchronous motor.

[0061] On the other hand, the analytical module includes: a 2D finite element model mesh generation module, which is used to mesh the stator and rotor of the permanent magnet synchronous motor using a 2D finite element model and a meshing method capable of calculating the skin effect, respectively, to determine the magnetic field distribution and the mesh generation of the permanent magnet; an unloaded simulation analysis module, used to simulate the permanent magnet synchronous motor under unload conditions, obtain the unloaded air gap magnetic flux density of the motor, perform Fourier decomposition analysis on the unloaded air gap magnetic flux density of the motor, and obtain the influence of the stator straight slots on the unloaded air gap magnetic flux density, thereby increasing the eddy current loss of the permanent magnet; negative The load simulation analysis module is used to simulate the permanent magnet synchronous motor under rated load conditions to obtain the load air gap magnetic flux density of the motor. Fourier decomposition analysis is performed on the load air gap magnetic flux density to obtain the influence of rotor magnetic bridge and high-order harmonic current on the load air gap magnetic flux density, thereby increasing the eddy current loss of the permanent magnet. The permanent magnet eddy current loss calculation module is used to obtain the permanent magnet eddy current loss calculation formula based on the harmonic order and harmonic amplitude value of the air gap magnetic flux density while keeping the volume constant. This allows for the identification of specific tooth harmonics that generate permanent magnet eddy current losses and their weakening or elimination, thereby maximizing the reduction of permanent magnet eddy current loss values.

[0062] In summary, the electromagnetic simulation model analysis method for permanent magnet motors in this embodiment of the invention adopts a 2D finite element electromagnetic simulation model to perform simulation analysis on both no-load and loaded states of the permanent magnet synchronous motor. This method obtains the influence of stator straight slots, rotor magnetic bridges, and high-order harmonic currents on the air gap magnetic flux density, simplifies the calculation and analysis steps, improves the simulation analysis efficiency, and ensures that the analysis results are accurate and reliable. This allows for accurate evaluation of the motor's operating status and performance, facilitates users in calculating the permanent magnet losses of the motor, and is easy to popularize and apply. It can be used for permanent magnet motors of different application scenarios or specifications.

[0063] The above specific embodiments should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, any alternative improvements or modifications made to the embodiments of the present invention shall fall within the scope of protection of the present invention.

[0064] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for analyzing the electromagnetic simulation model of a permanent magnet motor, characterized in that, The parsing method includes the following steps: S1. The stator and rotor of the permanent magnet synchronous motor are meshed using a 2D finite element model and a meshing method that can calculate the skin effect, respectively, to determine the magnetic field distribution and the meshing of the permanent magnet. S2, when the permanent magnet synchronous motor is in an unloaded state, the simulation is carried out to obtain the unloaded air gap magnetic flux density of the motor. Fourier decomposition analysis is performed on the unloaded air gap magnetic flux density of the motor to obtain the influence of the stator straight slot on the unloaded air gap magnetic flux density, thereby increasing the eddy current loss of the permanent magnet. S3, when the permanent magnet synchronous motor is under rated load, the simulation is carried out to obtain the load air gap magnetic flux density of the motor. Fourier decomposition analysis is performed on the load air gap magnetic flux density of the motor to obtain the influence of rotor magnetic bridge and high-order harmonic current on the load air gap magnetic flux density, thereby increasing the eddy current loss of permanent magnet. S4. Under the condition of constant volume, the formula for calculating permanent magnet eddy current loss is obtained based on the harmonic order and amplitude value of air gap magnetic flux density. In order to find the specific tooth harmonic that generates permanent magnet eddy current loss, and weaken or eliminate it, so as to reduce the value of permanent magnet eddy current loss to the greatest extent. The formula for calculating the eddy current loss of the permanent magnet is as follows: P e = k c f 2 B m 2 V Among them, P e Here, f represents the eddy current loss of the permanent magnet, f is the harmonic amplitude of the air gap magnetic flux density, and k is the value of the eddy current loss of the permanent magnet. c The harmonic order of the air gap magnetic flux density; The formula for calculating the specific number of the tooth harmonic is as follows: V = Q / p ± 1 = 2mq ± 1 Where Q represents the total number of slots in the motor, p represents the number of pole pairs in the motor, m represents the number of phases in the motor, and q represents the number of slots per pole per phase.

2. The analytical method for electromagnetic simulation model of permanent magnet motor according to claim 1, characterized in that: The partitioning method is the Skin Depth partitioning method, used to calculate the eddy current loss of the permanent magnet.

3. The analytical method for electromagnetic simulation model of permanent magnet motor according to claim 1, characterized in that: The 6th, 8th, 10th, and 12th harmonics with higher amplitudes in the unloaded air gap magnetic flux density harmonics are all tooth harmonics.

4. The analytical method for electromagnetic simulation model of permanent magnet motor according to claim 1, characterized in that, The parsing module of the parsing method includes: A 2D finite element model meshing module is used to mesh the stator and rotor of a permanent magnet synchronous motor using a 2D finite element model and a meshing method that can calculate the skin effect, respectively, to determine the magnetic field distribution and the meshing of the permanent magnet. The no-load simulation analysis module is used to simulate the permanent magnet synchronous motor when it is in no-load state, obtain the no-load air gap magnetic flux density of the motor, perform Fourier decomposition analysis on the no-load air gap magnetic flux density of the motor, and obtain the influence of stator straight slots on the no-load air gap magnetic flux density, thereby increasing the eddy current loss of permanent magnets. The load simulation analysis module is used to simulate the permanent magnet synchronous motor under rated load to obtain the load air gap magnetic flux density of the motor. The load air gap magnetic flux density of the motor is subjected to Fourier decomposition analysis to obtain the influence of rotor magnetic bridge and high-order harmonic current on the load air gap magnetic flux density, thereby increasing the eddy current loss of permanent magnet. The permanent magnet eddy current loss calculation module is used to obtain the permanent magnet eddy current loss calculation formula based on the harmonic order and harmonic amplitude value of the air gap magnetic flux density under the condition of constant volume, so as to find the specific tooth harmonic that generates permanent magnet eddy current loss and weaken or eliminate it, so as to reduce the value of permanent magnet eddy current loss to the greatest extent. The formula for calculating the eddy current loss of the permanent magnet is as follows: P e =k c f 2 B m 2 V Among them, P e Here, f represents the eddy current loss of the permanent magnet, f is the harmonic amplitude of the air gap magnetic flux density, and k is the value of the eddy current loss of the permanent magnet. c The harmonic order of the air gap magnetic flux density; The formula for calculating the specific number of the tooth harmonic is as follows: V = Q / p ± 1 = 2mq ± 1 Where Q represents the total number of slots in the motor, p represents the number of pole pairs in the motor, m represents the number of phases in the motor, and q represents the number of slots per pole per phase.

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