Consequent pole pseudo direct drive motor with magnetic flux switching permanent magnet structure

Abstract

The invention discloses a consequent pole pseudo direct drive motor with a magnetic flux switching permanent magnet structure, which is characterized in that a permanent magnet is moved from a high-speed rotor to a low-speed rotor, and the magnetic flux switching permanent magnet structure is introduced, so that the eddy current loss in the permanent magnet is reduced, and the high-speed rotor has higher robustness. Compared with a magnetic gear of a magnetic flux switching structure, although the output torque density of the magnetic flux switching magnetic gear is lower than that of a traditional magnetic gear, the magnetic flux switching consequent pole pseudo direct drive motor has higher degree of freedom in design due to the existence of direct drive torque. The motor is optimally designed through a multi-target genetic algorithm, and is compared with a conventional consequent-pole pseudo direct-drive motor for analysis, and the superiority of the motor is verified.

Description

Technical Field

[0001] The present invention belongs to the field of high-speed driving, and more specifically, relates to an alternating-pole pseudo direct-drive motor with a flux-switching permanent magnet structure. Background Art

[0002] Pseudo direct drive motors play an important role in many fields, especially in areas that require low-speed high torque, high torque density and high efficiency, such as medical, petrochemical, aerospace, etc. Based on the magnetic field modulation theory, the pseudo direct drive motor consists of a permanent magnet synchronous motor and a magnetic gear. In the pseudo direct drive motor, the permanent magnet synchronous motor mainly generates electromagnetic torque, the magnetic gear is responsible for torque transmission, and the permanent magnet of the stator generates a small amount of reverse flux torque. The pseudo direct drive motor is a flux modulation motor, and each of its components can constitute an element of flux modulation. The modulation ring of the pseudo direct drive motor plays the role of flux filtering and outputs torque.

[0003] Traditional mechanical gears have problems with loud noise and friction, which can easily lead to increased wear and even serious failure consequences. However, magnetic gears have the natural advantage of not requiring lubrication or regular maintenance. They can work without losing steps and overloading, and the maintenance-free life of magnetic gears exceeds 10 years. A coaxial magnetic gear with double-layer permanent magnets and spoke structure is proposed, which has better performance.

[0004] The multi-pole permanent magnet array of the pseudo direct drive motor is attached to the stator teeth of the motor. By coupling the inner rotor of the permanent magnet synchronous motor and the high-speed rotor of the magnetic gear, the electromagnetic torque can be transmitted and output on the outer rotor. Compared with the traditional radial series-connected magnetic gear motor, the pseudo direct drive motor has only two air gaps in the structure, making its structure more compact and simple. Therefore, the processing accuracy and process requirements are lower, but the torque density of the pseudo direct drive motor is relatively low compared with the radial series-connected magnetic gear motor of the same size. However, the conventional pseudo direct drive has a disadvantage that the permanent magnets fixed on the stator teeth have a large resistance to the magnetic flux generated by the winding, reducing the electromagnetic torque. Therefore, the alternating pole pseudo direct drive motor with permanent magnets embedded in the slot came into being, which does not affect the magnetic flux of the winding, thereby improving the back electromotive force and electromagnetic torque.

[0005] The disadvantage of the alternating pole pseudo direct drive motor is that there is a large flux leakage in the permanent magnets in the slots, which affects the utilization of the permanent magnets and the electromagnetic performance of the motor. By adding auxiliary teeth outside the alternating pole permanent magnets, the structure of the permanent magnets can be made more stable and the problem of flux leakage can be improved. Recently, a new type of flux switching magnetic gear has been proposed to adapt to high-speed operation. Under high-speed operation, the eddy current loss of the motor is reduced and the stability of the high-speed rotor is enhanced. By applying the characteristics and structure of the flux switching magnetic gear in the alternating pole pseudo direct drive motor, the good performance of the flux switching magnetic gear at high speed can be inherited, reducing losses and improving efficiency.

[0006] As a typical electromechanical device, the conventional alternating-pole pseudo-direct-drive motor includes a stator, radially magnetized permanent magnets, windings, rotor pole pieces, and an inner rotor. The performance of the motor depends on the complex coupling relationship between the electromagnetic field, mechanical structure, and thermal characteristics. In order to deeply verify the performance of the motor, multi-physics field analysis is required. The loss of the electromagnetic field will cause the temperature of the motor material to rise, and the temperature rise will in turn affect the performance of the permanent magnets and windings, thus forming a bidirectional coupling. The motor is subjected to various loads and excitations, and the mechanical strength and fatigue resistance of existing motors cannot meet the requirements. Summary of the invention

[0007] In view of the technical defects of existing alternating pole pseudo direct drive motors in electromagnetic performance and mechanical structure, the present invention proposes an alternating pole pseudo direct drive motor with a flux switching permanent magnet structure, which aims to improve the torque density of the motor, reduce torque pulsation, and enhance the thermal and mechanical properties of the motor, thereby improving the overall operating stability and efficiency of the motor.

[0008] To achieve the above-mentioned purpose, the present invention uses a multi-objective genetic algorithm to optimize the design of the alternating pole pseudo direct drive motor and the flux switching alternating pole pseudo direct drive motor, and compares and analyzes the electromagnetic performance of the two. Although the output torque density of the flux switching magnetic gear is lower than that of the traditional magnetic gear, due to the existence of direct drive torque, the flux switching alternating pole pseudo direct drive motor has greater flexibility in structural design than the alternating pole pseudo direct drive motor. Under the same output torque, the loss of the flux switching alternating pole pseudo direct drive motor is lower than that of the alternating pole pseudo direct drive motor when driven at high speed, and its high-speed rotor has better stability.

[0009] The specific technical scheme of the present invention is: an alternating pole pseudo direct drive motor with a flux switching permanent magnet structure, comprising: a stator, radially magnetized permanent magnets, windings, outer rotor pole pieces, inner rotor, and tangentially magnetized permanent magnets, the stator teeth of the stator are salient pole structures, the radially magnetized permanent magnets are fixed to the stator slots by auxiliary teeth on the stator teeth, and are magnetized along the inner direction of the stator slots; the windings are three-phase double-layer distributed windings; the inner rotor is a salient pole structure with four salient pole teeth; the tangentially magnetized permanent magnets are magnetized in parallel along the axial direction, and the magnetization directions of adjacent tangentially magnetized permanent magnets are opposite; the outer rotor is composed of alternating outer rotor pole pieces and tangentially magnetized permanent magnets.

[0010] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0011] 1. The present invention improves high-speed drive performance and design freedom: By moving the permanent magnet from the inner rotor to the outer rotor and introducing a flux switching permanent magnet structure, the present invention significantly improves the stability of the motor in high-speed drive and reduces the loss during high-speed operation. At the same time, the design flexibility of the motor is increased and can adapt to a variety of application scenarios.

[0012] 2. The present invention is based on multi-objective optimization design. The motor structural parameters are optimized to enhance the torque performance of the motor. While keeping the motor size unchanged, the motor can not only provide the same output torque as the conventional alternating pole pseudo direct drive motor at rated current, but also has a higher overload capacity, significantly improving the torque output under extreme working conditions, so that the motor can show stronger power and efficiency advantages in high-performance applications.

[0013] 3. The present invention proposes strong heat dissipation and structural stability of the motor based on multi-physical field analysis. By optimizing the cooling design, the temperature of the motor is kept within a reasonable range under high-speed operation, thereby extending the life of the motor. At the same time, the optimized high-speed rotor has higher mechanical strength and fatigue resistance, can adapt to high-load operating conditions, and ensure the long-term reliability of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of a flux-switching alternating-pole pseudo direct-drive motor provided for implementation of the present invention;

[0015] Figure 2 A schematic diagram of the operating principle of a flux switching alternating pole pseudo direct drive motor provided for the implementation of the present invention;

[0016] Figure 3 A parametric structure diagram of a flux-switching alternating-pole pseudo direct-drive motor provided for the implementation of the present invention;

[0017] Figure 4 A multi-objective optimization result diagram provided for the implementation of the present invention;

[0018] Figure 5 A comparison diagram of radial magnetic flux density of the outer air gap provided for the implementation of the present invention;

[0019] Figure 6 A comparison diagram of radial harmonic amplitudes of the outer air gap provided for the implementation of the present invention;

[0020] Figure 7 A comparison diagram of the torque output of the inner and outer rotors of the motor provided for the implementation of the present invention;

[0021] Figure 8 A comparison chart of motor overload capacity provided for the implementation of the present invention;

[0022] Fig. 9 A loss comparison diagram of a flux switching alternating pole pseudo direct drive motor provided for the implementation of the present invention;

[0023] Fig.10 Temperature rise distribution diagram of a flux switching alternating pole pseudo direct drive motor provided for the implementation of the present invention;

[0024] Fig.11 A stress-speed distribution diagram of a flux-switching alternating-pole pseudo direct-drive motor provided for the implementation of the present invention;

[0025] Fig.12 A comparison diagram of stress distribution of a high-speed rotor of a motor at 25000r / min provided for the implementation of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above-mentioned purpose, the present invention adopts the following technical scheme.

[0027] The present invention provides an alternating pole pseudo direct drive motor with a flux switching permanent magnet structure, such as Figure 1 As shown, it includes: a stator 1, radially magnetized permanent magnets 2, windings 3, outer rotor pole pieces 4, inner rotor 5, and tangentially magnetized permanent magnets 6. The stator teeth of the stator 1 are salient pole structures. The radially magnetized permanent magnets 2 are fixed to the stator slots by auxiliary teeth on the stator teeth and are magnetized along the inner direction of the stator slots. The windings 3 are three-phase double-layer distributed windings with a pitch of 4. The inner rotor 5 is a salient pole structure with 4 salient pole teeth. The tangentially magnetized permanent magnets 6 are magnetized in parallel along the axial direction, and the magnetization directions of adjacent tangentially magnetized permanent magnets 6 are opposite. The outer rotor is composed of outer rotor pole pieces 4 and tangentially magnetized permanent magnets 6 arranged alternately.

[0028] The tangentially magnetized permanent magnet 6 is located in the gap of the outer rotor pole piece 4, and forms a flux switching magnetic gear structure with the inner rotor 5 and the radially magnetized permanent magnet 2, which can transmit the torque on the inner rotor and reduce the eddy current loss in the permanent magnet; at the same time, the tangentially magnetized permanent magnet 6 forms a vernier motor structure with the stator 1 and the winding 3 to generate a direct drive torque. The key difference between the present invention and the conventional inner rotor alternating pole pseudo direct drive motor is the position of the internal permanent magnet. The permanent magnets on the inner rotor side of the conventional inner rotor alternating pole pseudo direct drive motor are radially magnetized. In contrast, the tangentially magnetized permanent magnet 6 of the flux switching alternating pole pseudo direct drive motor of the present invention is located in the gap of the rotor pole piece 4. The flux switching alternating pole pseudo direct drive motor of the present invention has two inner and outer rotors. The inner rotor 5 of the motor is composed of an iron core with a salient pole structure, which has high mechanical strength and is suitable for driving in high-speed areas. The inner rotor 5 of the flux switching alternating pole pseudo direct drive motor of the present invention is composed of an iron core with a salient pole structure, which has high mechanical strength and is suitable for driving in high-speed areas. The number of pole pairs P of the radially magnetized permanent magnet 2 in each slot o It is equal to the number of stator teeth and slots, and double-layer distributed winding is used in the slots.

[0029] The number of pole pairs of the winding of the alternating-pole pseudo direct-drive motor of the flux switching permanent magnet structure of the present invention is 4, which is equal to the number of rotor teeth Z of the inner rotor 5. i In the motor of the present invention, the number of pole pairs P of the radially magnetized permanent magnet 2 is o , the number of pole pairs P of the tangentially magnetized permanent magnet 6 m With Z i Satisfies formula (1); inner rotor speed ω r and the speed of the outer rotor ω m The ratio of G r Satisfy formula (2); formula (1)~(2) are as follows:

[0030] (1)

[0031] (2)

[0032] Figure 2 The working schematic diagram of the alternating pole pseudo direct drive motor with a flux switching permanent magnet structure of the present invention, the motor can be divided into two types of motors: rotor permanent magnets or stator permanent magnets. When the radially magnetized permanent magnets 2 in the stator are removed, the motor can be regarded as a permanent magnet vernier motor. When the tangentially magnetized permanent magnets 6 in the rotor are cut off, the motor can be regarded as a flux reversal motor. In addition, the magnetic gears generate torque on the inner rotor and the outer rotor. The composite torque on the inner rotor is close to 0, and the output torque is the composite of the torques of the permanent magnet vernier motor, the flux reversal motor and the magnetic gear. In this motor, the high-speed rotor is not connected to the load, and the low-speed rotor with low speed and high torque is connected to the mechanical load.

[0033] exist Figure 3A fully parameterized model of the proposed motor is established in . In order to obtain higher output torque and lower torque pulsation, the key parameters are analyzed and optimized by a multi-objective genetic algorithm method. Before the optimization, the effects of some main parameters on torque density and torque pulsation are analyzed according to the design criteria of the proposed flux-switched alternating-pole pseudo-direct-drive motor. During the optimization, the total volume, current density, axial length, outer radius, etc. are kept unchanged.

[0034] Figure 4 The influence of some key parameters on the average torque output is given. Figure 4 (a) is the crack ratio d si / d so The relationship with the average torque shows that the larger the split ratio, the larger the distance between the permanent magnet and the armature winding, and the smaller the equivalent air gap radius. However, when the split ratio is too large and the magnetic saturation is serious, the average torque will decrease. In order to prevent the occurrence of magnetic saturation, a certain margin is retained. Figure 4 (b) shows that when the split ratio is 0.7, the maximum average torque and the Pareto front of the multi-objective genetic algorithm are obtained. The optimization of each parameter provides guidance for determining the parameter range of global optimization. Through sensitivity analysis, the optimization time is saved. Considering the copper loss, iron loss and eddy current loss of the outer rotor of the flux switching alternating pole pseudo direct drive motor at 300r / min and the inner rotor at 1950r / min, the objective functions of maximum average torque, minimum torque pulsation and maximum torque per unit permanent magnet volume are given, and the temperature of the winding and permanent magnet is roughly set to 100℃. Under the premise that the main parameters such as the volume, outer diameter and stack length of the permanent magnet remain unchanged, the conventional motor is also optimized. The optimized parameter values ​​of the two motors are shown in Table 1.

[0035] Table 1 Main parameters of the flux-switching alternating-pole pseudo-direct-drive motor and conventional motor after optimization

[0036] Figure 5 and Figure 6 The no-load radial flux density and corresponding harmonic spectrum of the flux-switching alternating-pole pseudo-direct-drive motor and the conventional alternating-pole pseudo-direct-drive motor are compared. Figure 6 It can be seen that the outer air gap no-load flux harmonics of the conventional alternating-pole pseudo-direct-drive motor are mainly the 4th and 30th, while the outer air gap open-circuit flux harmonics of the proposed flux-switching alternating-pole pseudo-direct-drive motor are mainly the 26th and 30th. In the conventional alternating-pole pseudo-direct-drive motor, the 4th harmonic of the outer air gap flux mainly generates electromagnetic torque to drive the inner rotor to rotate. In the proposed flux-switching alternating-pole pseudo-direct-drive motor, the 26th harmonic in the outer air gap flux is modulated by 30 stator teeth to generate electromagnetic torque.

[0037] The transient torque comparison of the two motors is as follows: Figure 7As shown. During the optimization process, the slot area, winding turns, outer radius, permanent magnet volume, and lamination length of the two motors were set to be the same for easy comparison. At the rated current density, their torque on the inner rotor is 0.

[0038] Figure 8 The overload capacity of the proposed motor and conventional motor is compared under different current densities. Although the torque performance of flux switching magnetic gears is much lower than that of conventional magnetic gears, the contribution of electromagnetic torque to output torque in the proposed motor is much higher than that of conventional pseudo direct drive motors. The electromagnetic torque of pseudo direct drive motors is mainly generated on the high-speed rotor and transmitted by magnetic gears. When the current density is 3.2A / mm 2 When the load is too high, the output torque of the proposed motor is equal to that of the conventional motor, and it has a higher torque output capacity under overload.

[0039] Fig. 9 The loss of the proposed flux switching alternating pole pseudo direct drive motor and the conventional alternating pole pseudo direct drive motor in each area is compared at rated current density and different speeds. With the increase of speed, the loss of the conventional alternating pole pseudo direct drive motor increases more than the loss of the proposed motor, and the main loss is mainly composed of the eddy current loss of the stator permanent magnet. The loss of the flux switching alternating pole pseudo direct drive motor is mainly composed of the eddy current loss of the stator permanent magnet and the rotor permanent magnet.

[0040] Fig.10 To consider the temperature distribution of the flux switching alternating pole pseudo direct drive motor at the rated speed when the air gap inlet axial wind speed is 34.1m / s. Natural heat dissipation cannot meet the heat dissipation requirements. Therefore, the proposed motor needs to be cooled by air. Fig.10 From (a), we can see that at rated speed, the maximum temperature of the permanent magnet, which is the main heat source, is 73°C, which is much lower than the maximum operating temperature of N40UH. Fig.10 (b) takes a cross-section of the highest temperature area inside the proposed flux-switching alternating-pole pseudo direct-drive motor, and all parts of the motor are within the allowable operating temperature range.

[0041] like Fig.11 Comparison of the maximum stress of the proposed flux-switching alternating-pole pseudo-direct-drive motor and the conventional alternating-pole pseudo-direct-drive motor at different speeds. The faster the speed, the greater the shear force generated by the rotor rotation, so only the stress of the high-speed rotor needs to be considered. Considering the yield stress of 300MPa, the inner rotor speed of the alternating-pole pseudo-direct-drive motor should be lower than 25000r / m, while the speed of the flux-switching alternating-pole pseudo-direct-drive motor can reach 30000r / m.

[0042] When the high-speed rotor speed is 25000r / m, the stress comparison between the conventional alternating pole pseudo direct drive motor and the proposed flux switching alternating pole pseudo direct drive motor is shown in Fig.12The maximum stress of the flux switching alternating pole pseudo direct drive motor is smaller than that of the alternating pole pseudo direct drive motor, and the mechanical strength is stronger, which is more suitable for high-speed driving.

[0043] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An alternating pole pseudo direct drive motor with a flux switching permanent magnet structure, characterized in that: include: A stator (1), radially magnetized permanent magnets (2), a winding (3), an outer rotor pole piece (4), an inner rotor (5), and a tangentially magnetized permanent magnet (6). The stator teeth of the stator (1) are salient pole structures. The radially magnetized permanent magnets (2) are fixed to the stator slots by auxiliary teeth on the stator teeth and are magnetized along the inner direction of the stator slots. The winding (3) is a three-phase double-layer distributed winding. The inner rotor (5) is a salient pole structure and has four salient pole teeth. The tangentially magnetized permanent magnets (6) are magnetized in parallel along the axial direction, and the magnetization directions of adjacent tangentially magnetized permanent magnets (6) are opposite. The outer rotor is composed of outer rotor pole pieces (4) and tangentially magnetized permanent magnets (6) arranged alternately.

2. The alternating pole pseudo direct drive motor with a flux switching permanent magnet structure according to claim 1, characterized in that: The stator (1) is a fixed component, the outer rotor is connected to the load, and the inner rotor is idle, and both the inner and outer rotors are moving components.

3. The alternating pole pseudo direct drive motor with a flux switching permanent magnet structure according to claim 1, characterized in that: The tangentially magnetized permanent magnet (6) is located in the gap between the rotor pole pieces (4), and forms a flux switching magnetic gear structure with the inner rotor (5) and the radially magnetized permanent magnet (2), thereby transmitting the torque on the inner rotor and reducing the eddy current loss in the permanent magnet; at the same time, the tangentially magnetized permanent magnet (6) forms a vernier motor structure with the stator (1) and the winding (3) to generate direct drive torque.

4. The alternating pole pseudo direct drive motor with a flux switching permanent magnet structure according to claim 1, characterized in that: The inner rotor (5) of the motor is composed of an iron core with a salient pole structure, and the number of pole pairs P of the radially magnetized permanent magnet (2) in each slot is o It is equal to the number of stator teeth and slots, and double-layer distributed winding is used in the slots.

5. The alternating pole pseudo direct drive motor with a flux switching permanent magnet structure according to claim 4, characterized in that: The number of pole pairs of the motor winding is equal to the number of rotor teeth Z of the inner rotor (5) i Equally, the number of pole pairs P of the diametrically magnetized permanent magnet (2) o , the number of pole pairs P of the tangentially magnetized permanent magnet (6) m With Z i Satisfies formula (1); inner rotor speed ω r and the speed of the outer rotor ω m The ratio of G r Satisfy formula (2); formula (1)~(2) are as follows: (1) (2)。

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