Vacuum | deep low temperature | high temperature | radiation resistance and automation solutions
05
2024
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01
Simulation analysis of three-dimensional magnetic field distribution of weak magnetic type permanent magnet motor
1 Overview
In recent years, with the increasingly severe environmental and energy crisis, electric vehicles have received attention and policy support from governments around the world. As one of the core components of electric vehicles, the motor drive system is different from the ordinary industrial motor drive system in design and manufacturing, such as high power density, high efficiency in the whole working area, high performance (low speed, large torque, wide constant power area, high dynamic response), high environmental adaptability and low cost. Due to the advantages of high power density and high efficiency, permanent magnet motor has become the choice of electric vehicle motors. However, the permanent magnet motor also has the disadvantages of difficult to adjust the magnetic field and small range of weak magnetic expansion. At present, the problem of weak magnetic field of permanent magnet motor is mainly from two aspects: control strategy and motor body structure. The most common method of control strategy is to apply direct axis demagnetization current in the stator winding, and rely on armature reaction field to weaken the main field. The main structure of the motor body is to use a special structure scheme to achieve the purpose of convenient adjustment of the air gap flux. The weak magnetic type permanent magnet motor proposed in this paper adopts a conical rotor structure, which can adjust the size of the air gap magnetic flux through the axial displacement of the rotor, and can take into account the operation performance requirements of low speed and large torque and wide constant power area, which is especially suitable for the operation condition of electric vehicles.
In this paper, the Flux software of Altair Company is used to simulate and analyze the weak magnetic permanent magnet motor model. Flux is a professional 2D and 3D electrical, magnetic and thermal analysis software for electromagnetic equipment such as motors, sensors and transformers. The software is based on Maxwell differential equations and finite element method to optimize the electromagnetic and electrothermal design of the product. It has the characteristics of reliability, accuracy and efficiency, and can provide accurate simulation results and shorten the research and development cycle. Flux12.3 was used in this analysis.
2 Structural characteristics of weak magnetic permanent magnet motor
The structure of the weak magnetic type permanent magnet motor proposed in this paper is shown in Figure 1. The inner cavity of the stator and the outer circle of the rotor are conical, and the rotor components are supported by the detachable cylindrical roller bearings, which can move along the axis in a small range. As shown by the dotted line in Figure 1, when the axial displacement of the rotor Δz=0, the air gap length is minimum (the initial design value of the air gap length), the magnetic load is maximum, and the torque output capacity is close to that of a cylindrical motor of similar size. As shown by the solid line in Figure 1, when δZ >0, the air gap length Δ increases and the magnetic load decreases, which can conveniently realize the operation of weak magnetic expansion speed.
1 Overview
In recent years, with the increasingly severe environmental and energy crisis, electric vehicles have received attention and policy support from governments around the world. As one of the core components of electric vehicles, the motor drive system is different from the ordinary industrial motor drive system in design and manufacturing, such as high power density, high efficiency in the whole working area, high performance (low speed, large torque, wide constant power area, high dynamic response), high environmental adaptability and low cost. Due to the advantages of high power density and high efficiency, permanent magnet motor has become the choice of electric vehicle motors. However, the permanent magnet motor also has the disadvantages of difficult to adjust the magnetic field and small range of weak magnetic expansion. At present, the problem of weak magnetic field of permanent magnet motor is mainly from two aspects: control strategy and motor body structure. The most common method of control strategy is to apply direct axis demagnetization current in the stator winding, and rely on armature reaction field to weaken the main field. The main structure of the motor body is to use a special structure scheme to achieve the purpose of convenient adjustment of the air gap flux. The weak magnetic type permanent magnet motor proposed in this paper adopts a conical rotor structure, which can adjust the size of the air gap magnetic flux through the axial displacement of the rotor, and can take into account the operation performance requirements of low speed and large torque and wide constant power area, which is especially suitable for the operation condition of electric vehicles.
In this paper, the Flux software of Altair Company is used to simulate and analyze the weak magnetic permanent magnet motor model. Flux is a professional 2D and 3D electrical, magnetic and thermal analysis software for electromagnetic equipment such as motors, sensors and transformers. The software is based on Maxwell differential equations and finite element method to optimize the electromagnetic and electrothermal design of the product. It has the characteristics of reliability, accuracy and efficiency, and can provide accurate simulation results and shorten the research and development cycle. Flux12.3 was used in this analysis.
2 Structural characteristics of weak magnetic permanent magnet motor
The structure of the weak magnetic type permanent magnet motor proposed in this paper is shown in Figure 1. The inner cavity of the stator and the outer circle of the rotor are conical, and the rotor components are supported by the detachable cylindrical roller bearings, which can move along the axis in a small range. As shown by the dotted line in Figure 1, when the axial displacement of the rotor Δz=0, the air gap length is minimum (the initial design value of the air gap length), the magnetic load is maximum, and the torque output capacity is close to that of a cylindrical motor of similar size. As shown by the solid line in Figure 1, when δZ >0, the air gap length Δ increases and the magnetic load decreases, which can conveniently realize the operation of weak magnetic expansion speed.
FIG. 2 3D model of permanent magnet motor
3.2 Mesh generation
The splitting module of Flux 12.3 is upgraded to "Mesh Gems", replacing the previous "Flux mesher", which greatly improves the splitting quality and efficiency. Taking a single stator slot as an example, the comparison results of split quality between the two are shown in Figure 3.
FIG. 4 3D magnetic field distribution of weak magnetic type permanent magnet motor
4.2 Simulation analysis and experimental test of no-load back potential
In order to verify the correctness of the theory and simulation analysis, a prototype was designed and manufactured in this study, and the relevant experimental research was carried out. The theoretical calculation, simulation analysis and experimental test results of no-load back potential are shown in FIG. 5. As the axial displacement of the rotor increases, the length of the air gap increases, and the back potential decreases approximately linearly, which proves the feasibility of realizing weak magnetic field from the body structure of the weak magnetic type permanent magnet motor. It is worth noting that the results of finite element simulation are in good agreement with the experimental values, which indicates the accuracy and effectiveness of Flux software calculation.
FIG. 5 Comparison of theoretical calculation, 3D finite element simulation and experimental test values of no-load back potential
5 Conclusions
In this paper, the structural characteristics and principle of weak magnetic field permanent magnet motor are introduced. The low-frequency electromagnetic field simulation software Flux of Altair is used to simulate and analyze the motor model, and a prototype is designed and manufactured. The simulation results and experimental test results show that the weak magnet motor has the same low speed and high torque output capacity as the cylindrical motor of similar size, and has approximately linear weak magnet ability, which can conveniently achieve a wide range of weak magnetic expansion speed operation, especially suitable for the operation condition of electric vehicles. The simulation results are in good agreement with the experimental test values, indicating that the Flux software has the characteristics of accuracy and efficiency, which can significantly improve the work efficiency and optimize the design accuracy.
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