Automatic fault-tolerant permanent magnet synchronous motor for high-torque-density turn-to-turn short circuit fault

Abstract

The utility model discloses an automatic fault-tolerant permanent magnet synchronous motor for a high-torque-density turn-to-turn short circuit fault, and belongs to the field of fault-tolerant motors. The motor is a radial magnetic field circular rotating motor, and a stator part of the motor comprises a stator iron core, a stator winding, a magnetic conduction bridge and independent teeth. According to the utility model, the motor realizes an automatic fault-tolerant function through the magnetic conductive bridge, and the torque density of the motor is improved through the independent teeth. When the motor works normally, magnetic circuits in the magnetic conductive bridge offset each other and are completely consistent with the magnetic circuit without the magnetic conductive bridge, the effective magnetic circuit path of the motor is relatively long at the moment, so that the torque density of the motor is relatively low, and the independent teeth are additionally arranged on the stator, so that the magnetic circuit path is shortened, and meanwhile, the path of the magnetic circuit trend is increased; and the torque density of the motor is greatly improved. When a turn-to-turn short circuit occurs in the motor, magnetic circuits in the magnetic conductive bridges cannot offset each other to form a loop, so that short-circuit current can be suppressed, meanwhile, torque, current and voltage hardly change, and capacity-reduction-free output can be realized.

Description

Technical Field

[0001] This utility model belongs to the field of fault-tolerant motors, and more specifically, relates to a radial flux permanent magnet synchronous motor with relatively high torque density and automatic fault tolerance for inter-turn short circuit faults. Technical Background

[0002] In recent years, with the continuous development of permanent magnet synchronous motors (PMSMs), various faults have become a focus of attention, among which inter-turn short circuit faults are the most common. Inter-turn short circuit faults reduce motor output capacity, cause asymmetry in three-phase voltage and current, intensify motor vibration, and lead to excessive heat generation and even winding burnout due to excessive short-circuit current. They are also a source of other faults, thus posing a significant threat to the motor. However, due to the uncertainty of the short-circuit location, inter-turn short circuits are the most difficult fault to handle in PMSMs. Currently, axial PMSMs can automatically tolerate inter-turn short circuit faults without changes in motor torque, voltage, or current. However, if this principle is directly applied to radial flux and circular rotating motors, the utilization rate of the winding coils is low, resulting in low motor torque density. Therefore, how to enable radial flux PMSMs to automatically tolerate inter-turn short circuit faults while maintaining relatively high torque density is a key issue in the field of fault-tolerant motors and urgently needs to be addressed. Utility Model Content

[0003] The problem to be solved by this utility model is to provide a high torque density inter-turn short-circuit fault automatic fault-tolerant permanent magnet synchronous motor.

[0004] To solve the above-mentioned technical problems, the technical solution proposed by this utility model is: a high torque density inter-turn short-circuit fault automatic fault-tolerant permanent magnet synchronous motor, wherein the motor is a circular rotary motor; the motor includes a stator, a rotor, and an air gap between them; the stator includes a stator core and stator windings; the stator windings are m-phase windings, where m is an integer greater than or equal to 2, and each phase of the stator winding includes 2z stator coils, where z is an integer greater than or equal to 1; the stator core has through slots along the axial direction on the side near the rotor, forming stator slots and stator teeth; the stator core includes zm magnetic bridges, each magnetic bridge connecting two adjacent stator teeth, and each stator tooth connected to a specific magnetic bridge... The number of magnetic bridges does not exceed one, forming zm stator tooth pairs; the electrical angle value of the included axis angle of the two stator teeth in each stator tooth pair is 340° to 380°; the electrical angle value spanned by the tooth tip arc length of each stator tooth in each stator tooth pair is 130° to 230°; the stator tooth pairs are evenly distributed along the circumference of the stator core; each magnetic bridge is located at the top of the slot between the two stator teeth it connects; each pair of stator teeth contains two stator teeth, each of which is wound with a stator coil; the two stator coils wound on the two stator teeth in each pair of stator teeth have the same number of turns, the same winding direction, belong to the same phase winding, and are connected in series.

[0005] In a preferred embodiment, the per-unit value of the inductance of each stator coil is not less than 2.

[0006] In a preferred embodiment, the stator core contains stator teeth that are not connected to the magnetic bridge, i.e., independent teeth. The number of independent stator teeth is equal to the number of stator tooth pairs. The independent stator teeth and the stator tooth pairs are arranged alternately along the circumference of the stator core. The stator independent teeth are not wound with stator coils.

[0007] In a preferred embodiment, the electrical angle spanned by the arc length of the stator independent tooth tip is not less than 110° and not more than 280°.

[0008] The motor employing the technical solution described in this utility model maintains balanced current in each phase under inter-turn short-circuit faults, with amplitude and phase almost identical to those under normal operating conditions. Therefore, the torque under inter-turn short-circuit faults is no different from that under normal operating conditions, while the short-circuit current is significantly suppressed. The entire fault-tolerance process is automatically implemented, thus enabling the motor to have automatic inter-turn short-circuit fault tolerance. Furthermore, by cleverly utilizing adjacent stator teeth with an electrical angle difference of approximately 360° to form stator tooth pairs, a coil side of each stator coil that originally did not undertake electromechanical energy conversion is transformed into an effective coil side that also undertakes electromechanical energy conversion. Simultaneously, the use of independent stator teeth with reasonable tooth tip angles significantly improves the motor's torque density. Attached Figure Description

[0009] Figure 1 This is a cross-sectional schematic diagram of the motor described in Specific Embodiment 1;

[0010] Figure 2 This is a cross-sectional schematic diagram of the motor described in Specific Embodiment 2;

[0011] Figure 3 This is a cross-sectional schematic diagram of the motor described in Specific Embodiment 3;

[0012] Figure 4 This is a schematic diagram of the compensation leakage magnetic circuit;

[0013] Figure 5 This is a schematic diagram of the winding connection of the motor described in Embodiments 1, 2, and 3 of this utility model;

[0014] Figure 6 This is a local region division diagram of the motor model;

[0015] Figure 7 A partial schematic diagram of magnetic flux leakage caused by slotting in the motor;

[0016] Figure 8 This is a partial schematic diagram of magnetic leakage between adjacent teeth of the motor.

[0017] In the diagram, 1-stator core, 2-rotor core, 3-stator winding, 4-permanent magnet, 5-stator tooth, 6-stator independent tooth, 7-magnetic bridge. Detailed Implementation

[0018] This invention provides a high torque density, inter-turn short-circuit fault-tolerant permanent magnet synchronous motor according to a typical embodiment. The motor is a circular rotating motor. It includes a stator, a rotor, and an air gap between them. The stator includes a stator core 1 and stator windings. The stator windings are m-phase windings, where m is an integer greater than or equal to 2. Each phase of the stator winding includes 2z stator coils 3, where z is an integer greater than or equal to 1. The stator core has axially spaced slots on the side near the rotor, forming stator slots and stator teeth. The stator core includes zm magnetic bridges 7, each magnetic bridge connecting two adjacent stator teeth, and the number of magnetic bridges connected to each stator tooth is... The quantity does not exceed 1, forming zm stator tooth pairs 5; the electrical angle value of the included axis angle of the two stator teeth in each stator tooth pair is 340° to 380°; the electrical angle value spanned by the tooth tip arc length of each stator tooth in each stator tooth pair is 130° to 230°; the stator tooth pairs are evenly distributed along the circumference of the stator core; each magnetic bridge is located at the top of the slot between the two stator teeth it connects to; each pair of stator tooth pairs contains two stator teeth, each of which is wound with a stator coil; the two stator coils wound on the two stator teeth in each pair of stator tooth pairs have the same number of turns, the same winding direction, belong to the same phase winding, and are connected in series.

[0019] According to the above implementation method, the motor achieves automatic fault tolerance through a magnetic bridge and improves torque density through independent teeth. During normal operation, the magnetic circuits in the magnetic bridge cancel each other out, resulting in a completely identical magnetic circuit without the bridge. This leads to a longer effective magnetic path and lower torque density. Adding independent teeth to the stator not only shortens the magnetic path but also increases the number of paths, significantly improving torque density. When an inter-turn short circuit occurs, the magnetic circuits in the magnetic bridge cannot cancel each other out to form a loop, suppressing the short-circuit current. Simultaneously, the torque, current, and voltage remain almost unchanged, achieving output without derating.

[0020] The stator core of the motor may also contain stator teeth that are not connected to the magnetic bridge. In this paper, stator teeth that are not connected to the magnetic bridge are referred to as independent stator teeth. The number of independent stator teeth is equal to the number of stator tooth pairs. The independent stator teeth are evenly distributed along the circumference of the stator core, and the independent stator teeth and the stator tooth pairs are alternately arranged along the circumference of the stator core. The independent stator teeth are not wound with stator coils. The electrical angle spanned by the arc length of the tooth tip of the independent stator teeth is not less than 110° and not more than 280°.

[0021] The magnetic bridge can be integrated with the stator teeth in a single connection manner, such as... Figure 1 , Figure 2 as well as Figure 4As shown, in this connection method, the magnetic bridge and the stator core are a single unit, therefore the magnetic bridge and the stator teeth connected to it are continuous and seamless. The magnetic bridge can also be connected to the stator teeth in a splicing manner, such as... Figure 3 As shown, when a splicing connection method is used, the magnetic bridge is made of a high magnetic permeability material with a permeability greater than 1000.

[0022] Each of the aforementioned magnetic bridges, along with its two connected stator teeth and stator yoke, together form a leakage magnetic circuit, such as... Figure 4 As shown by the dashed line, the two series-connected coils wound on a pair of stator teeth form complementary coils when an inter-turn short circuit occurs in the motor. Under an inter-turn short circuit fault, the voltage drop and equivalent impedance across the series-connected coils remain unchanged, enabling the motor to automatically achieve inter-turn short-circuit fault-tolerant operation. The formula derivation is as follows:

[0023] When an inter-turn short-circuit fault occurs, the voltage equation of the fault coil is:

[0024]

[0025] In the formula e 0_a1 Let λ be the induced electromotive force of coil a1, λ be the percentage of short-circuited turns in the total number of turns of phase A coil, and N be the number of coil turns. The armature flux component linked with coil a1, To compensate for the leakage flux in the leakage flux circuit.

[0026] Due to short circuit,

[0027] Substituting into equation (1), we get

[0028] The voltage equation for the section without faults is:

[0029] Combining equations (3) and (4), we get:

[0030]

[0031] As shown in equation (5), the fault causes the voltage of the non-faulty part to drop to 0 as well. However, due to the effect of the compensation leakage circuit, the voltage equation of the other coil as the faulty coil is:

[0032]

[0033] In the formula φ m_a2 e is the main armature flux component linked with coil a2. 0_a2Let be the induced electromotive force of coil a2. Adding the voltages of the two coils together, i.e., equation (5) + equation (6), yields the corresponding voltage:

[0034]

[0035] Equation (7) shows that under the inter-turn short-circuit fault condition, the leakage flux in the compensation leakage flux circuit plays the role of exciting electromotive force and transferring energy. The mathematical form of the terminal voltage equation of the complementary coil pair containing the faulty coil is exactly the same as that under the normal condition. Similarly, the mathematical form of the voltage equation of all other complementary coil pairs is the same as that under the normal condition, and will not be repeated. It can be seen that under the condition that the power supply remains unchanged, the current of each phase is still almost the same as that under the normal condition, thereby achieving the same torque output as under the normal condition.

[0036] When an inter-turn short circuit occurs, the compensating leakage flux circuit not only transfers energy to ensure symmetrical current in each phase, but also suppresses the short-circuit current. The high permeability of the compensating leakage flux circuit results in a relatively large inductance in the stator coils, thus suppressing the short-circuit current. To achieve optimal fault tolerance, the per-unit reactance of each stator coil should be no less than 2.

[0037] Furthermore, since the distribution coefficient is:

[0038]

[0039] In the formula, ν is the harmonic order. As can be seen from the above formula, the electrical angle α between the axes of the two stator teeth contained in each pair of stator teeth is 340° to 380°. This can ensure that the two effective sides of each coil of the stator winding can be used efficiently, so that the motor has a relatively large torque density.

[0040] Adding independent teeth to the stator core can increase the air gap magnetic flux density of the motor, thereby significantly improving the torque density. The formula derivation is as follows:

[0041] The motor is a permanent magnet synchronous motor with radial flux and unequal tooth pitch. To simplify the calculation and ignore the influence of curvature, the curved part is treated as a straight line in the mathematical model. First, a mathematical model of the permanent magnet is established, and its surface current density J can be calculated according to Ampere's circuital law. P (x):

[0042]

[0043] In the formula b m τ is the width of the permanent magnet, τ is the pole pitch, and B is the distance between the poles. r μ0 represents the remanence of the permanent magnet, and μ0 represents the permeability of free space.

[0044] The motor area is divided into 6 parts, such as Figure 7 As shown, region 2 is the stator, region 3 is the air gap, region 4 is the permanent magnet, region 5 is the air gap between the rotor and the permanent magnet (the air gap is very small and can be ignored, therefore g1 = 0), and region 6 is the rotor. The magnetic flux density of each region can be obtained using the Poisson equation and its six boundary conditions. The expression for the air gap magnetic flux density is as follows:

[0045]

[0046] In the formula B m1y The expression for the radial air gap magnetic flux density of the motor is given by B. m1x Here is the expression for the tangential air gap magnetic flux density of the motor, h m g1 is the thickness of the permanent magnet, and g2 is the length of the air gap in the motor.

[0047] The air gap magnetic flux density obtained above is without considering the influence of stator slotting. In reality, the influence of stator slotting on the air gap magnetic flux density cannot be ignored. Considering the influence of cogging effect on the motor magnetic field distribution, taking a single slot model as an example, the specific expression for the relative permeability distribution function within a single slot air gap can be obtained:

[0048]

[0049] In the formula, b0 is the slot width, b τ denoted as tooth pitch, and g' as equivalent air gap length.

[0050] The magnetic flux density in the radial direction at various locations in the air gap of the motor can be calculated using the above formula:

[0051] B y (x,y)=B m1y λ(x,y) (12)

[0052] By calculating the magnetic flux of each phase, it can be verified that independent teeth can significantly improve the torque density of the motor, and the optimal angle of the independent teeth that maximizes the torque density of the motor can be determined.

[0053]

[0054] Φ3=kΦ1 (15)

[0055]

[0056] Where Φ is the total magnetic flux, Φ1 is the main magnetic flux, and Φ2 is the leakage magnetic flux caused by the slotting, such as Figure 8 As shown, Φ3 is the leakage flux between adjacent teeth, and k is the leakage flux coefficient corresponding to the leakage flux between adjacent teeth, with a value of [value missing]. l is the axial length of the motor, b1 is the width of the winding tooth tip, and b0 is the slot width.

[0057] Solving equations (10), (11), (12) and (16) simultaneously reveals that when the electrical angle of the tooth tip arc of the independent tooth is not less than 110° and not greater than 280°, the increase in the magnetic flux of the motor is not less than 10%, which is beneficial for the motor to have a relatively high torque density.

[0058] To make the technical solution and advantages of this utility model clearer and more complete, the present utility model will be described in detail below with reference to the accompanying drawings and some specific embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the present utility model.

[0059] Specific Embodiment 1: The cross-sectional view of the high torque density inter-turn short-circuit fault automatic fault-tolerant permanent magnet synchronous motor described in this embodiment is as follows. Figure 1 This embodiment is a radial flux, circular rotating motor, including a stator, a rotor, and an air gap between them, employing a 6-slot, 14-pole configuration. The stator includes a stator core 1 and a stator winding 3, while the rotor includes permanent magnets 4, a rotor core 2, and a shaft. Fourteen permanent magnets are evenly distributed on the outer surface of the rotor core, with their N and S polarities alternating along the circumference of the rotor core. In this embodiment, the stator core near the rotor has axially spaced slots, forming six stator slots and six stator teeth. The stator winding is a three-phase winding, with each phase containing two stator coils. The stator core in this embodiment includes three magnetic bridges 7; each of the three magnetic bridges connects to three pairs of stator teeth 5 in an integrated connection. The stator core is a single unit; each magnetic bridge is located at the top of the slot between the two stator teeth it connects to; the electrical angle between the axes of the two stator teeth connected by the magnetic bridge is 360°, and they are adjacent to each other. These three pairs of stator teeth constitute three pairs of stator teeth. Therefore, the stator core in this embodiment contains three pairs of stator teeth; the electrical angle spanned by the arc length of the tooth tip of each stator tooth in each pair of stator teeth is 170°; the stator teeth are evenly distributed along the circumference of the stator core; each pair of stator teeth contains one stator coil wound on each of the two stator teeth; the stator coils wound on the two stator teeth in each pair of stator teeth have the same winding direction, the same number of turns, belong to the same phase winding, and are connected in series. Their connection method is as follows: Figure 5 As shown.

[0060] Specific Embodiment Two: The high torque density inter-turn short-circuit fault automatic fault-tolerant permanent magnet synchronous motor described in this embodiment is as follows: Figure 2As shown, this embodiment is a radial flux, circular rotating motor, including a stator, a rotor, and an air gap between them, employing a 9-slot, 14-pole configuration. The stator includes a stator core 1 and stator windings, while the rotor includes permanent magnets, a rotor core, and a shaft. Fourteen permanent magnets are evenly distributed on the outer surface of the rotor core, with their N and S polarities alternating along the circumference of the rotor core. In this embodiment, the stator core near the rotor has axially spaced through slots, forming nine stator slots and nine stator teeth. The stator windings are symmetrical three-phase windings, with each phase containing two stator coils. The stator core in this example includes three magnetic bridges 7. Each of the three magnetic bridges connects three pairs of stator teeth 5, with each bridge located at the top of the slot between the two connected stator teeth. The electric field of the included angle between the axes of the two stator teeth connected by each magnetic bridge is... With an angle value of 360° and adjacent positions, these three pairs of stator teeth constitute three stator tooth pairs. Therefore, the stator core in this embodiment contains three pairs of stator tooth pairs. The remaining stator teeth are not connected to the magnetic bridge and are referred to as independent stator teeth 6. Thus, the stator core in this embodiment contains three independent teeth. The electrical angle spanned by the arc length of the tooth tip of each stator tooth in each stator tooth pair is 170°. The stator tooth pairs are evenly distributed along the circumference of the stator core, and the independent stator teeth are also evenly distributed along the circumference of the stator core. The independent stator teeth and the stator tooth pairs are arranged alternately along the circumference of the stator core. Each pair of stator tooth pairs contains two stator teeth, each containing one stator coil. The stator coils wound on the two stator teeth in each pair of stator tooth pairs have the same winding direction, the same number of turns, belong to the same phase winding, and are connected in series. Their connection method is as follows: Figure 5 As shown; the stator independent teeth are not wound with stator coils; the electrical angle spanned by the tooth tip arc of the independent teeth is 168°.

[0061] Specific Embodiment 3: The high torque density inter-turn short-circuit fault automatic fault-tolerant permanent magnet synchronous motor described in this embodiment is as follows: Figure 3 As shown, this embodiment is based on specific embodiment two, but the connection method between the magnetic bridge 7 and the stator slot is changed to a splicing connection.

Claims

1. A high torque density, inter-turn short-circuit fault-tolerant permanent magnet synchronous motor, characterized in that, The motor is a circular rotary motor; the motor includes a stator, a rotor, and an air gap between them; the stator includes a stator core (1) and stator windings; the stator windings are m-phase windings, where m is an integer greater than or equal to 2, and each phase of the stator winding includes 2z stator coils (3), where z is an integer greater than or equal to 1; the stator core has through slots along the axial direction on the side near the rotor, forming stator slots and stator teeth; the stator core includes zm magnetic bridges (7), each magnetic bridge connecting two adjacent stator teeth, and the number of magnetic bridges connected to each stator tooth does not exceed 1, forming zm stator tooth pairs ( 5); The electrical angle value of the included axis angle of the two stator teeth in each stator tooth pair is 340° to 380°; The electrical angle value spanned by the tooth tip arc length of each stator tooth in each stator tooth pair is 130° to 230°; The stator tooth pairs are evenly distributed along the circumference of the stator core; Each magnetic bridge is located at the top of the slot between the two stator teeth it connects to; Each pair of stator teeth contains two stator teeth, each of which is wound with a stator coil; The two stator coils wound on the two stator teeth in each pair of stator teeth have the same number of turns, the same winding direction, belong to the same phase winding, and are connected in series.

2. The high torque density inter-turn short-circuit fault automatic fault-tolerant permanent magnet synchronous motor according to claim 1, characterized in that, The per-unit value of the inductance of each stator coil is not less than 2.

3. The high torque density inter-turn short-circuit fault automatic fault-tolerant permanent magnet synchronous motor according to claim 1 or 2, characterized in that, The stator core contains stator teeth that are not connected to the magnetic bridge, namely independent teeth (6). The number of independent stator teeth is equal to the number of stator tooth pairs. The independent stator teeth and the stator tooth pairs are arranged alternately along the circumference of the stator core. The stator independent teeth are not wound with stator coils.

4. The high torque density inter-turn short-circuit fault automatic fault-tolerant permanent magnet synchronous motor according to claim 3, characterized in that, The electrical angle spanned by the arc length of the stator independent tooth tip is not less than 110° and not more than 280°.

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