A minimum direct-axis flux linkage approximation type permanent magnet flat wire driving motor and a design method thereof

Abstract

The application discloses a minimum direct-axis flux linkage approximation type permanent-magnet flat wire driving motor and a design method thereof. Eight permanent-magnet groups and eight irregular rectangular magnetic barriers are uniformly arranged on the rotor in the circumferential direction. Each permanent-magnet group is symmetric along the d-axis, and each irregular rectangular magnetic barrier is symmetric along the q-axis. Each permanent-magnet group on the radial cross section is composed of two outer layer permanent magnets and one inner layer permanent magnet. The inner layer permanent magnet is perpendicular to the d-axis. An L-shaped magnetic barrier is arranged between the end of the outer layer permanent magnet on the same side of the d-axis and away from the d-axis and the end of the inner layer permanent magnet. The leakage magnetic component is introduced into the direct-axis flux linkage. The direct-axis flux linkage amplitude is calculated based on the direct-axis flux linkage. The key structure parameters and ranges are determined according to the direct-axis flux linkage amplitude. The key structure parameters are optimized by selecting typical working condition representative points. The optimal key structure parameters are obtained according to the minimum direct-axis flux linkage amplitude approximation 0. The widening of the constant power speed regulation range is realized. The multi-target requirements under different working conditions are met.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of motor manufacturing, in particular to a structure of a permanent magnet flat wire motor and a design method of main structure parameters thereof, and relates to a design method of an electric vehicle motor. BACKGROUND

[0002] In recent years, with the gradual popularization of new energy vehicles and the rapid development of modern transportation, more stringent performance requirements are put forward for new energy vehicle drive motors. Since the permanent magnet flat wire motor has a significant effect on improving power density, it has become the main choice for new energy vehicle motors. For example, the power density index needs to be as high as 4.0 kW / kg or more, and the flat wire motor technology is one of the important directions to effectively improve the power density index of the motor. As the name implies, the biggest feature of the flat wire motor is that the winding wire of the motor is flat. Therefore, high slot fill rate is an inherent feature of the flat wire motor, and the motor can output more power under the same volume, thereby effectively improving the power density of the motor. However, compared with the round wire of the traditional round wire motor, the flat wire of the flat wire motor is generally larger in size, and thus the skin effect is obvious when high-frequency current is applied, which to a large extent highlights the temperature rise problem of the motor. In addition, the forming and automatic wiring of the flat wire winding are also key problems affecting the rapid development of the flat wire motor. Therefore, current flat wire motor research is mostly focused on winding structure (for example, Chinese Patent No. 202210514571.1) and winding welding technology (for example, Chinese Patent No. 202121253140.1). It needs to be clear that since the permanent magnet flat wire motor has a significant effect on improving power density, it has become the main choice for new energy vehicle motors. However, the permanent magnet flat wire motor still faces the inherent problem of difficult adjustment of the motor magnetic field, and thus the performance of such motor is insufficient in various working conditions such as "narrow constant power speed range", "low efficiency in high-speed field weakening region", and "weak load capacity at low speed", which is a key problem that needs to be solved for its application in electric vehicles.

[0003] For a traditional permanent magnet flat wire motor, when the motor reaches the base speed, it needs to be controlled by field weakening to achieve the continued expansion of the motor. However, since the air gap magnetic field of the permanent magnet motor remains basically constant and cannot be directly adjusted, it can only be adjusted by adjusting the direct-axis demagnetizing current, and it is difficult to achieve an ideal field weakening effect to a large extent. Therefore, the existing permanent magnet flat wire motor for electric vehicles has performance deficiencies in various working conditions such as "narrow constant power speed range", "low efficiency in high-speed field weakening region", and "weak load capacity at low speed", which to some extent restricts the large-scale application of the permanent magnet flat wire motor in the field of electric vehicle drive motors, and also becomes one of the many unfavorable factors that delay the rapid development of electric vehicles.

[0004] The document with Chinese patent number 201810293025.3 proposes a hybrid excitation motor, which adopts excitation winding and permanent magnet for common excitation, and controls the size of air gap magnetic flux by adjusting excitation current to realize wide speed range operation of the permanent magnet motor. However, it has the problem of increasing winding copper loss and improving mechanical structure complexity, so it is difficult to promote in the field of electric vehicle application. The document with Chinese patent number 201610537453.7 proposes a magnetic field enhancement type motor, which solves the problem of small constant power speed range of traditional built-in permanent magnet motor to a certain extent. However, due to the existence of d-axis permanent magnet, the structure of this type of motor produces a certain magnetic resistance, so there is an irreconcilable contradiction between adjusting inductance characteristics and ensuring torque output in the design of motor structure.

[0005] It can be seen that the constant power speed range of the current traditional driven permanent magnet motor is almost limited by the reasonable adjustment of the permanent magnet air gap magnetic field, which makes it difficult to achieve the ideal performance index of high torque and high speed of the vehicle driving motor. Therefore, it has become one of the problems to be solved in the field of vehicle driving motor to research and explore the demand of electric vehicle under multiple operating conditions, solve the problem of weak load capacity and narrow speed range caused by poor adjustment of permanent magnet air gap magnetic field in the design of traditional vehicle motor. SUMMARY

[0006] The present application aims at the defects of the prior art, and proposes a minimum direct-axis flux linkage approximation type permanent magnet flat wire driving motor and a design method of key parameters thereof. The structure of double magnetic flux leakage loop is adopted and the design idea of minimum direct-axis flux linkage approximation 0 is adopted to realize the widening of ideal constant power speed range, so as to meet the multi-objective demand under different conditions such as low-speed heavy-load high torque, high-speed cruising high efficiency and the like.

[0007] The technical scheme of the minimum direct-axis flux linkage approximation type permanent magnet flat wire driving motor is: it comprises a stator and a rotor coaxially arranged from outside to inside, a plurality of permanent magnet groups and a plurality of irregular rectangular magnetic barriers are uniformly arranged on the rotor in the circumferential direction, each permanent magnet group and each irregular rectangular magnetic barrier are staggered with each other, each permanent magnet group is symmetrical along the d-axis, and each irregular rectangular magnetic barrier is symmetrical along the q-axis; each permanent magnet group on the radial section comprises two outer layer permanent magnets and one inner layer permanent magnet, the inner layer permanent magnet is perpendicular to the d-axis, the two outer layer permanent magnets are the same in structure, are not in contact, and are arranged in a V-shaped opening outward in the radial direction; a L-shaped magnetic barrier is arranged between the end of the outer layer permanent magnet on the same side of the d-axis and the end of the inner layer permanent magnet away from the d-axis, the two L-shaped magnetic barriers on the same pole are the same in structure; the irregular rectangular magnetic barrier and the L-shaped magnetic barrier are self-leakage magnetic bridges, the outer side wall of the rotor forms a semi-elliptical small magnetic barrier on the outer side of the irregular rectangular magnetic barrier, the semi-elliptical small magnetic barrier and the irregular rectangular magnetic barrier are inter-pole leakage magnetic bridges, the magnetization directions of the two outer layer permanent magnets and the inner layer permanent magnet on the same pole are the same, and the magnetization directions of the two outer layer permanent magnets and the inner layer permanent magnet on the adjacent poles are opposite.

[0008] Further, the side wall direction of the V-shaped formed by the two outer layer permanent magnets is the width direction of the outer layer permanent magnet, the width direction of the inner layer permanent magnet is the direction perpendicular to the d-axis, and the widths of the outer layer permanent magnet and the inner layer permanent magnet are equal.

[0009] Further, the inner ends of the two outer layer permanent magnets form an intermediate magnetic conduction bridge, the end of the inner layer permanent magnet and the corresponding end of the L-shaped magnetic barrier form an inner magnetic conduction bridge, and the end of the outer layer permanent magnet and the corresponding end of the L-shaped magnetic barrier form an outer magnetic conduction bridge.

[0010] The technical scheme of the design method of the minimum direct-axis flux linkage approximation type permanent magnet flat wire driving motor is as follows:

[0011] Step 1): introduce the leakage flux component ψ σ (i d , i q ) into the direct-axis flux linkage, wherein the direct-axis flux linkage

[0012] ψ d (i d , i q ) = ψ pm (i d , i q ) + L d (i d , i q ) · i d - ψ σ(i d ,i q ), ψ pm (i d ,i q ) is permanent magnet flux linkage, L d (i d ,i q ) is direct axis inductance, i d ,i q are d, q axis rated current respectively;

[0013] Step 2) calculating direct axis flux linkage amplitude | ψ d (i d ,i q ) based on the direct axis flux linkage ψ According to the direct axis flux linkage amplitude | ψ d | determine motor shaft length l, inner and outer permanent magnet width w i , inner and outer permanent magnet thickness h i , self-leakage magnetic bridge width l 11 , inter-pole leakage magnetic bridge width l 12 These key structural parameters and their ranges; μ0 is air gap permeability, μ r is relative permeability, N is the number of turns per phase winding, i = 1, 2, w i = w1, w2, are the inner and outer permanent magnet width respectively, h i = h1, h2, are the inner and outer permanent magnet thickness respectively, l is the motor shaft length; B pm is the permanent magnet flux density;

[0014] Step 3) select a typical working condition representative point to optimize the key structural parameters, calculate the minimum direct axis flux linkage amplitude | ψ d | according to the optimized key structural parameters, and obtain the optimal key structural parameters based on the minimum direct axis flux linkage amplitude | ψ d || approximation to 0.

[0015] Further, the range of the key structural parameters is: h1 = 1.5h2 ~ 1.8h2, l 12 = R 42 -R 41 , l 11 = 1.85l 12 ~ 2.25l 12 , R 41 = 0.65R1 ~ 0.67R1, R 42 = 1.05R 41 ~ 1.08R 41 , i = 1, 2; the outer side of the semi-elliptical magnetic barrier and the irregular rectangular magnetic barrier is on two concentric circles respectively, R 41R is the radius of the semi-elliptical small magnetic barrier 42 R is the radius of the irregular rectangular magnetic barrier outer side.

[0016] Further, the leakage magnetic component

[0017] The present application has the beneficial effects after adopting the above technical solutions:

[0018] 1. The present application arranges two layers of permanent magnets inside and outside the rotor symmetrically about the d-axis and sets L-shaped magnetic barriers between the two layers of permanent magnets, which, together with the semi-elliptical small magnetic barriers and irregular rectangular magnetic barriers symmetrically arranged about the q-axis, form a double leakage magnetic circuit with appropriate size, the self-leakage magnetic bridge bears the main leakage magnetic part, and the inter-pole leakage magnetic bridge bears the auxiliary leakage magnetic part, the leakage magnetic is controlled by adjusting the q-axis current, which can effectively adjust the air gap magnetic field, increase the output torque of the motor under heavy load climbing working condition, and improve the operating efficiency of the motor under high-speed cruising working condition.

[0019] 2. The combination design of the two layers of permanent magnets in the present application makes the magnetic flux generated by the d-axis field weakening current under high-speed working condition transition more effectively inside the rotor, which is beneficial to the improvement of the field weakening effect under this working condition.

[0020] 3. The present application establishes multiple magnetic bridges, which can enhance the mechanical strength of the motor body and provide conditions and possibilities for constant power operation under high speed.

[0021] 4. The design concept of minimum direct-axis flux linkage approximation proposed in the present application introduces a leakage magnetic component to solve the problems of difficult field weakening and difficult adjustment of air gap magnetic field in traditional permanent magnet motors, which can make the field weakening and leakage magnetic synchronous under the high-speed cruising working condition, weaken the d-axis air gap magnetic field together, and more easily realize the approximation of the minimum direct-axis flux linkage to 0, so as to achieve the widening of the ideal constant power speed regulation range and more easily obtain the beneficial effect of wide-area constant power under all working conditions.

[0022] 5. The present application proposes a multi-working-condition high-efficiency design method, which can effectively adjust the air gap magnetic field by adjusting the q-axis current to control the leakage magnetic under different working conditions, effectively regulate the saturation degree of the leakage magnetic region, and make the leakage magnetic flux change accordingly under different working conditions, so as to meet the multi-working-condition and multi-target performance requirements of "low-speed heavy load large torque, high-speed cruising high efficiency".

[0023] 6、The design method provided by the application is also reflected on the optimization means, in order to improve the overall design efficiency, the application selects typical working condition representative points in different working conditions of "low speed heavy load" and "high speed cruise", establishes the correlation of key parameters, reasonably comprehensively optimizes the key structural parameters of the motor, matches them with the corresponding working conditions, sets a threshold to judge the optimization progress, and selects the optimal structural parameters as the optimal size according to the relationship between the minimum direct-axis flux linkage amplitude and the set threshold size as the judgment basis under the requirement of torque output. Meanwhile, the method has universal applicability and multi-objective global convergence, and is suitable for motor optimization design application. BRIEF DESCRIPTION OF DRAWINGS

[0024] The application will be further described in detail below in combination with the drawings and specific embodiments;

[0025] Figure 1 is a radial cross-sectional structure schematic diagram of a minimum direct-axis flux approximation type permanent magnet flat wire driving motor according to the application;

[0026] Figure 2 is a stator structure schematic diagram in Figure 1 ;

[0027] Figure 3 is an enlarged schematic diagram of the rotor direct-axis local structure and geometric size marking in Figure 1 ;

[0028] Figure 4 is an enlarged schematic diagram of the rotor cross-axis local structure and geometric size marking in Figure 1 ;

[0029] Figure 5 is an enlarged schematic diagram of the magnetizing direction marking of the permanent magnet on the rotor in Figure 1 ;

[0030] Figure 6 is a schematic diagram of the motor leakage magnetic circuit when the permanent magnet works in Figure 5 ;

[0031] Figure 7 is a relationship schematic diagram of the current limit circle and the voltage limit ellipse of the traditional permanent magnet flat wire motor;

[0032] Figure 8 is a relationship schematic diagram of the current limit circle and the voltage limit ellipse of the permanent magnet flat wire driving motor of the application after introducing the leakage magnetic component;

[0033] Figure 9 is a d, q axis equivalent magnetic circuit diagram of the motor shown in Figure 1 ;

[0034] Figure 10 is a corresponding working condition representative point selection diagram according to the running working condition and motor parameters of the application;

[0035] Figure 11 is the flow chart of the optimization method of the key parameters of the electric machine;

[0036] Figure 12 is Figure 1 the schematic diagram of the magnetic field distribution of the electric machine of the application under the low-speed heavy-load working condition;

[0037] Figure 13 is Figure 1 the schematic diagram of the magnetic field distribution of the electric machine of the application under the high-speed cruising working condition;

[0038] Figure 14 is Figure 1 the comparison diagram of the torque performance of the electric machine of the application and the conventional permanent-magnet flat-line electric machine;

[0039] Figure 15 is Figure 1 the comparison diagram of the power performance of the electric machine of the application and the conventional permanent-magnet flat-line electric machine.

[0040] In the figure: 1. stator; 2. rotor; 3. armature winding; 4. outer layer permanent magnet; 5. inner layer permanent magnet; 6. L-shaped magnetic barrier; 7. irregular rectangular magnetic barrier; 8. semi-elliptical small magnetic barrier; 9. rotating shaft; 10. self-leakage magnetic bridge; 11. inter-pole leakage magnetic bridge; 12. middle magnetic bridge; 13. inner magnetic bridge; 14. outer magnetic bridge; 15. stator tooth; 16. stator slot; 17. stator yoke. DETAILED DESCRIPTION

[0041] Referring to Figure 1 and Figure 2 the application is a minimum direct-axis flux linkage approximation type permanent-magnet flat-line driving electric machine, which comprises a stator 1, a rotor 2 and a rotating shaft 9 arranged coaxially from outside to inside, the rotor 2 is located inside the stator 1, the center of the rotor 2 is used for placing the rotating shaft 9, the stator 1 and the rotor 2 are both composed of silicon steel sheets with equal thickness and the lamination coefficient is 0.95. The rotating shaft 9 is composed of non-magnetic material. The stator 1 is provided with an armature winding 3 in the stator slot; there is an air gap between the inner wall of the stator 1 and the outer wall of the rotor 2, and the air gap length is related to the power level of the electric machine, the permanent-magnet material and the processing and assembling technology.

[0042] The stator 1 is composed of stator teeth 15, stator slots 16 and a stator yoke 17. The armature winding 3 is placed in the stator slot 16.

[0043] The rotor 2 is uniformly provided with a plurality of permanent magnet groups and a plurality of irregular rectangular magnetic barriers 7 in the circumferential direction, and each permanent magnet group and each irregular rectangular magnetic barrier 7 are arranged with spacing staggered in the circumferential direction. Figure 1Only eight permanent magnet groups and eight irregular rectangular magnetic barriers 7 are shown. The center line of each permanent magnet group is the d-axis, and it is symmetrical along the d-axis; the center line of each irregular rectangular magnetic barrier 7 is the q-axis, and it is symmetrical along the q-axis. Therefore, the center line between two adjacent permanent magnet groups is the q-axis, and the number of permanent magnet pole pairs of the motor is 4.

[0044] In combination Figure 3 and Figure 4 In the radial cross section, each permanent magnet group is composed of three rectangular neodymium iron boron permanent magnets, which are fixedly embedded in the inside of the rotor 2. The three rectangular neodymium iron boron permanent magnets are two outer layer permanent magnets 4 and one inner layer permanent magnet 5. The two outer layer permanent magnets 4 have the same structure, are symmetrical with respect to the d-axis, and are arranged in a V shape on the radial cross section. The opening of the V shape faces outward in the radial direction. The side wall direction of the V shape formed by the two outer layer permanent magnets 4 is the width direction of the outer layer permanent magnet 4, and the thickness direction of the outer layer permanent magnet 4 is the inside-outside direction. The width of the two outer layer permanent magnets 4 is w1, and the thickness is h1.

[0045] The two outer layer permanent magnets 4 do not contact each other, and a middle magnetic conduction bridge 12 with a tangential width of l 21 is formed between the inner ends of the two outer layer permanent magnets 4. The middle magnetic conduction bridge 12 itself is symmetrical along the d-axis, and the function of the middle magnetic conduction bridge 12 is to appropriately increase the d-axis inductance and improve the speed regulation performance to a certain extent.

[0046] The inner layer permanent magnet 5 is perpendicular to the d-axis, and its width direction is perpendicular to the d-axis. The width of the inner layer permanent magnet 5 is w2, and the thickness in the inside-outside direction is h2. The width of the outer layer permanent magnet 4 is equal to the width of the inner layer permanent magnet 5, i.e., w1=w2. The thickness h1 of the outer layer permanent magnet 4 is greater than the thickness h2 of the inner layer permanent magnet 5.

[0047] Referring to Figure 3 and Figure 4 , on the same side of the d-axis, between the end of the outer layer permanent magnet 4 and the end of the inner layer permanent magnet 5, and away from the d-axis, an L-shaped magnetic barrier 6 is arranged. Therefore, there is one L-shaped magnetic barrier 6 on each side of the d-axis, and the two L-shaped magnetic barriers 6 on the same pole have the same structure and are symmetrical along the d-axis. The L-shaped magnetic barrier 6 can limit the excessive uncontrollable ineffective leakage magnetic field generated by the single layer permanent magnet, and at the same time make the inside-outside double layer permanent magnet magnetic circuit connected.

[0048] The two ends of the L-shaped magnetic barrier 6 respectively extend to the end of the inner layer permanent magnet 5 and the end of the outer layer permanent magnet 4, and do not contact the end of the inner layer permanent magnet 5 and the end of the outer layer permanent magnet 4. An inner magnetic conduction bridge 13 with a width of l 22 is arranged between the end of the inner layer permanent magnet 5 and the corresponding end of the L-shaped magnetic barrier 6. An outer magnetic conduction bridge 14 with a width of l23 The inner magnetic guide bridge 13 and the outer magnetic guide bridge 14 can maintain certain mechanical strength of the rotor 2.

[0049] The width l of the intermediate magnetic guide bridge 12, the inner magnetic guide bridge 13 and the outer magnetic guide bridge 14 21 , l 22 , l 23 The width l of the intermediate magnetic guide bridge 12, the inner magnetic guide bridge 13 and the outer magnetic guide bridge 14 21 ∶l 22 ∶l 23 =2∶

[0050] The self-leakage magnetic bridge 10 is formed between the irregular rectangular magnetic barrier 7 and the L-shaped magnetic barrier 6, and the width of the self-leakage magnetic bridge 10 is l 11 The L-shaped magnetic barrier 6 can limit excessive uncontrollable ineffective leakage magnetic generated by the outer layer permanent magnet 4 and the inner layer permanent magnet 5, and simultaneously make the inner and outer double layer permanent magnetic magnetic circuit connected.

[0051] As shown in Figure 4 , on the outer side of each irregular rectangular magnetic barrier 7, a semicircular small magnetic barrier 8 is arranged on the outer wall of the rotor 2, the semicircular small magnetic barrier 8 is concave to the inner side of the rotor 2 and does not contact with the irregular rectangular magnetic barrier 7, thus forming an inter-pole leakage magnetic bridge 11 between the semicircular small magnetic barrier 8 and the irregular rectangular magnetic barrier 7, and the size of the inter-pole leakage magnetic bridge 11 can be adjusted by the semicircular small magnetic barrier 8. The center line of the semicircular small magnetic barrier 8 is the q-axis, and the semicircular small magnetic barrier 8 is symmetrical along the q-axis.

[0052] As shown in Figure 5 , the magnetization directions of the two outer layer permanent magnets 4 and the inner layer permanent magnet 5 on the same pole are the same, and the magnetization directions are along the thickness direction of each, the magnetization directions of the two outer layer permanent magnets 4 and the inner layer permanent magnet 5 on the adjacent poles are opposite, and the magnetization method of the alternate poles is adopted.

[0053] As shown in Figure 6 , the self-leakage magnetic branch is formed by the self-leakage magnetic bridge 10, and the inter-pole leakage magnetic branch is formed by the inter-pole leakage magnetic bridge 11, the magnetic flux path of the self-leakage magnetic branch is as follows: sequentially passing through the neodymium iron boron inner layer permanent magnet 5, the outer layer permanent magnet 4, the rotor 2, the self-leakage magnetic bridge 10 formed by the L-shaped magnetic barrier 6 and the irregular rectangular magnetic barrier 7, the rotor 2, and the inner layer permanent magnet 5 to form a closed loop; the magnetic flux path of the inter-pole leakage magnetic branch is as follows: sequentially passing through the inner layer permanent magnet 5, the outer layer permanent magnet 4, the rotor 2, the inter-pole leakage magnetic bridge 11 formed by the irregular rectangular magnetic barrier 7 and the semicircular small magnetic barrier 8, the rotor 2, the inner layer permanent magnet 5 on the adjacent pole, the outer layer permanent magnet 4, the rotor 2, and the inner layer permanent magnet 5 to form a closed loop. Therefore, the “double leakage magnetic branches” are formed in the motor of the present application, the magnetic flux intersection area is formed on the double leakage magnetic branches, which is convenient for effectively regulating and controlling the leakage magnetic components, and also provides a path for the q-axis magnetic flux injection.

[0054] See Figure 7 , the voltage limit ellipse center O vt (-Ψ pm / L d , 0) falls outside the current limit circle, Ψ pm is the permanent magnet flux linkage, L d is the direct axis inductance, which means that when the field current i d reaches the maximum current I lim , the d-axis flux linkage Ψ d is still greater than 0, which brings difficulties to the field weakening speed-up. In order to expand the constant power speed range of the motor, the measures that can be taken include: increasing the maximum current I lim , reducing the permanent magnet flux linkage Ψ pm and increasing the direct axis inductance L d . Increasing the maximum current I lim will inevitably lead to the improvement of the inverter capacity in the control system, which increases the cost and has certain safety hazards.

[0055] The direct axis flux linkage formula of the traditional permanent magnet flat motor is expressed as:

[0056] ψ d = ψ pm + L d · i d (1)

[0057] The ideal maximum speed Ω max that the motor can reach is:

[0058]

[0059] wherein U lim is the limit terminal voltage amplitude, I lim is the maximum current, Ψ pm is the permanent magnet flux linkage, Ψ dmin is the minimum direct axis flux linkage, p is the number of pole pairs of the permanent magnet, and L d is the direct axis inductance.

[0060] As can be seen from formula (1), when the motor is in the "high-speed cruising" working condition, when the field current i d increases to -Ψ pm / L d , at this time the d-axis flux linkage decreases to zero, and the minimum direct axis flux linkage Ψ dmin = 0, the motor will reach the infinite constant power speed state. However, for the traditional permanent magnet flat motor, the permanent magnet is usually located on the d-axis, which produces a larger magnetic resistance, thereby causing a smaller d-axis inductance. In order to offset the same size of the permanent magnet flux linkage, a larger d-axis field current is needed, which increases the additional loss and demagnetization risk. When the minimum direct axis flux linkage Ψ dmin> 0, the permanent magnet flux linkage Ψ pm Generally, it means high output torque, but it is difficult to weaken the magnetic field at high speed, and the power decreases rapidly; when the minimum direct-axis flux linkage Ψ dmin = 0, the permanent magnet flux linkage Ψ pm is equal to the maximum direct-axis demagnetizing flux linkage, at this time the constant power speed regulation range is the widest; when the minimum direct-axis flux linkage Ψ dmin < 0, because the permanent magnet field decreases, the weakening of the magnetic field at high speed becomes easy, and the speed regulation range is wider; but at the same time, the output torque of the motor will be reduced, resulting in the power at high speed will also be reduced.

[0061] Referring to Figure 9 , the relationship between the permanent magnet flux Ф pm and the leakage flux Ф σ can be expressed as:

[0062] φ σ (R σ +2R pm )=φ pm (2R g +2R pm ) (3)

[0063] Where, R σ is the leakage magnetic resistance, R pm is the permanent magnet resistance, R pm = R pmV + R pmI , R pm = R pmV + R pmI , R g is the air gap magnetic resistance, R σ = R σZ / / R σJ , R pm is the magnetic resistance of the outer permanent magnet 4, R pmI is the magnetic resistance of the inner permanent magnet 5, R σZ is the magnetic resistance of the self-leakage magnetic bridge 10, and R σJ is the magnetic resistance of the inter-pole leakage magnetic bridge 11.

[0064] If the stator and rotor magnetic resistance is not considered, the leakage coefficient α is expressed as follows:

[0065]

[0066] Then the leakage flux Ф σ and the leakage component Ψ σ (i d , i q ) can be calculated as follows:

[0067]

[0068] ψσ (i d i q )=Nφ σ (i d i q (6)

[0069] Where: R r It is the rotor reluctance, R s It is the stator reluctance, N is the number of turns per slot per phase winding, i d i q Rated currents for the d and q axes, respectively.

[0070] Therefore, by controlling the leakage flux through the q-axis current, the saturation level of the leakage flux region can be affected, thereby controlling the leakage flux component Ψ. σ (i d i q The distribution under different operating conditions enables flexible raising and lowering of the effective flux linkage of the permanent magnet, thereby satisfying the flexible transition between multiple operating conditions of the motor. This invention introduces a leakage flux component into the d-axis and q-axis equivalent magnetic circuit. Under no-load conditions, the current in the stator winding is zero, and only the magnetic flux generated by the permanent magnet acts alone. At this time, as... Figure 6 As shown, due to the establishment of the leakage flux branch, most of the permanent magnet flux forms a loop between adjacent permanent magnets and between each pole in the form of leakage flux. Only a small portion of the main flux enters the stator through the air gap, forming an induced electromotive force. Therefore, in the motor of this invention, the permanent magnet flux linkage Ψ pm and direct-axis inductor L d Represented as:

[0071] ψ pm =NB pm s = NB pm w i l (7)

[0072]

[0073]

[0074] Among them: B pm It is the magnetic flux density of the neodymium iron boron permanent magnet, i = 1, 2, w i =w1,w2, where w1 and w2 are the widths of the outer permanent magnet 4 and the inner permanent magnet 5, respectively, and h i =h1,h2, where h1 is the thickness of the outer permanent magnet 4 or the inner permanent magnet 5, l is the effective shaft length of the motor, μ0 is the air gap permeability, and μ r It is the relative permeability.

[0075] Then the leakage magnetic component Ψ σ (i d i q This can be represented as:

[0076]

[0077]

[0078]

[0079] From formula (7), (9), (12), it can be seen that the permanent magnet flux linkage Ψ pm of the motor is positively related to the width w of the permanent magnet i ; the direct axis inductance L d is positively related to the width w of the permanent magnet i , i = 1, 2. It is negatively related to the thickness h of the permanent magnet i ; in addition to the width w of the permanent magnet i , the thickness h of the permanent magnet i , the width l of the self-leakage magnetic bridge 10 11 , the width l of the inter-pole leakage magnetic bridge 11 12 , the width l of the self-leakage magnetic bridge 10 σ (i d , i q ) is also a key parameter of the leakage flux component Ψ σ (i d , i q ).

[0080] The present application is based on the concept of "minimum direct axis flux linkage approximation", introduces the leakage flux component Ψ σ (i d , i q ), and reasonably designs the permanent magnet flux linkage Ψ pm and the minimum direct axis flux linkage Ψ dmin based on the consideration of the direct axis inductance L d . In order to make the minimum direct axis flux linkage Ψ dmin approximate to 0 and obtain a relatively ideal best constant power speed regulation range, the leakage flux component Ψ σ (i d , i q ) is introduced in the direct axis flux linkage, and the direct axis flux linkage is:

[0081] ψ d (i d ,i q ) = ψ pm (i d ,i q ) + L d (i d ,i q ) · i d - ψ σ (i d ,i q ) (13)

[0082] Substitute formula (7), (9), (12) into formula (13) respectively to obtain the direct axis flux linkage amplitude | Ψ d | as follows:

[0083]

[0084] Thus, the application links the direct-axis flux linkage Ψ d With the permanent magnet flux linkage Ψ pm , the direct-axis inductance L d And the leakage flux component Ψ σ (i d , i q ) related structure parameters.

[0085] The application is based on the "minimum direct-axis flux linkage approximation" concept, introduces the leakage flux component Ψ σ (i d , i q ), and reasonably designs the permanent magnet flux linkage Ψ pm And the minimum direct-axis flux linkage Ψ dmin Based on considering the direct-axis inductance L d . The introduction of the leakage flux component Ψ σ (i d , i q ) is more inclined to the design of the minimum direct-axis flux linkage Ψ dmin Approximation to 0.

[0086] Referring to Figure 8 , when the "low speed heavy load" to "high speed cruise" working condition changes, the center of the voltage limit ellipse of the permanent magnet motor with the leakage flux component Ψ σ (i d , i q ) changes to O vt ((Ψ σ -Ψ pm ) / L d , 0), which falls on the current limit circle, which means that when the field current i d Increases to -Ψ dmin / L d , the d-axis flux linkage decreases to zero, and the minimum direct-axis flux linkage Ψ dmin = 0, that is, the minimum value of the direct-axis flux linkage amplitude |Ψ d | = 0, and the motor will approach the ideal constant power speed regulation state. Therefore, in view of the series of deficiencies such as the difficulty of field weakening and the narrow constant power operating range of the traditional flat wire permanent magnet motor, the application adds the leakage flux component Ψ σ (i d , i q ), based on the design idea of the minimum direct-axis flux linkage Ψ dmin Approximation to 0 under the maximum field weakening current, it is easier to obtain the effect of effectively widening the constant power range. When the motor is in the "low speed heavy load" working condition, with the continuous increase of the q-axis current, the intersection of the q-axis flux and the leakage flux gradually saturates, and the leakage reluctance R σAs the magnetic flux increases, the inter-pole leakage flux or self-leakage flux decreases significantly. At this point, almost all the permanent magnet flux enters the stator through the air gap to generate torque, meeting the performance requirements of low-speed, heavy-load, and high-torque operation. When the motor is in "high-speed cruising" mode, the q-axis current transforms into the d-axis demagnetizing current. The saturation at the intersection of the q-axis flux and leakage flux decreases significantly, and a large amount of permanent magnet leakage flux remains, reducing the effective flux linkage of the permanent magnet. In this state, leakage flux and field weakening occur simultaneously, jointly weakening the d-axis air gap magnetic field. This makes it easier to approach the minimum direct-axis flux linkage to zero, better meeting the load capacity and field weakening effect under high-speed field weakening operation conditions, and improving operating efficiency in the high-speed range.

[0087] Compared with the traditional magnetic weakening formula, the leakage magnetic component Ψ is added. σ (i d i q The difference between the formula after (14) and the formula is the second term on the right side, which is the minimum direct-axis flux linkage amplitude |Ψ dmin | Subject to the second term on the right side of formula (14) The direct impact of the leakage magnetic component Ψ, therefore, in order to make the leakage magnetic component Ψ σ (i d i q The effect of ) is more obvious. The key parameters of the motor of this invention are set as follows: motor shaft length l, permanent magnet width w i Permanent magnet thickness h i Self-leaking magnetic bridge 10 width l 11 Inter-electrode leakage magnetic bridge 11 width l 12 .

[0088] Reduce permanent magnet flux Ψ pm While it facilitates field weakening and speed enhancement, it reduces torque density, resulting in a decrease in load level. Therefore, increasing the direct-axis inductance L... d With reducing permanent magnet flux Ψ pm A trade-off needs to be made; according to formula (9), the direct-axis inductance L d With N 2 l positively correlated with Ψ pm -Ψ σ Positively correlated with Nl, to reduce the maximum negative demagnetizing current -i applied. d Increase direct-axis inductance L d At the same time, to ensure the permanent magnet chain Ψ pm The length of the motor shaft can remain unchanged by increasing the number of winding turns N while reducing the length of the motor shaft l.

[0089] According to the motor dimension equation, the ratio of the shaft length l to the outer diameter R1 of the rotor 2 in a traditional permanent magnet flat wire motor is generally within the following range: The preliminary selection of the ratio range between the outer diameter R1 and the inner diameter R2 of rotor 2 is as follows: The basic dimensions of the motor are determined based on R1 and R2.

[0090] See Figure 3 and Figure 4 The outer permanent magnet 4 has a width of w1 and a radial thickness of h1, while the inner permanent magnet 5 has a width of w2 and a radial thickness of h2. From formula (14), it can be seen that the direct-axis inductance L... d and Negative correlation, improve L d Amplitude, this invention constrains the four parameters as follows:

[0091] Considering that the outer permanent magnet 4 is closer to the outside of the rotor 2 so that magnetic energy can be better utilized, the thickness h1 of the outer permanent magnet 4 should be greater than the thickness h2 of the inner permanent magnet 5. To simplify the constraints, we take w1 = w2 and h1 = 1.5h2 ~ 1.8h2.

[0092] The outer edges of the semi-elliptical magnetic barrier 8 and the irregular rectangular magnetic barrier 7 lie on two concentric circles, with the center of these circles being O2. The center O2 lies on the q-axis, and the distance from the center O2 to the center O2 of rotor 2 is R3. The constraint relationship between R3 and the rotor's outer diameter R1 is: R3 = 1.3R1 ~ 1.35R1. The radius of the semi-elliptical magnetic barrier 8 is R. 41 R 41 The constraint relationship with the rotor outer diameter R1 is: R 41 =0.65R1~0.67R1, the radius of the outer side of the irregular rectangular magnetic barrier 7 is R. 42 R 41 With R 42 The constraint relationship is: R 42 =1.05R 41 ~1.08R 41 Therefore, the width l of the inter-electrode leakage magnetic bridge 11 12 =R 42 -R 41 .

[0093] Ψ pm -Ψ σ (i d i q ) and the width l of the self-leaking magnetic bridge 10 11 and the width of the inter-electrode leakage magnetic bridge 11 12 Negative correlation, while the main leakage magnetic field effect is shared by the self-leakage magnetic bridge 10, the width l of the self-leakage magnetic bridge 10 is reasonably increased. 11 Then the constraint is: l 11 =1.85l 12 ~2.25l 12 .

[0094] The self-leakage magnetic bridge 10 should keep the same distance between the L-shaped magnetic barrier 6 and the irregular rectangular magnetic barrier 7, and the L-shaped magnetic barrier 6 and the irregular rectangular magnetic barrier 7 are modified with arc-shaped corners to make the leakage magnetic flux flow through the self-leakage magnetic bridge 10 and the pole-to-pole leakage magnetic bridge 11 uniformly when the motor is accelerated, and to improve the leakage magnetic effect and the field weakening effect.

[0095] The center of the arc-shaped inner corner of the inner side of the irregular rectangular magnetic barrier 7 is O4, and the distance between the center O4 and the center O1 is R7; the center of the arc-shaped outer corner of the outer side of the irregular rectangular magnetic barrier 7 is O5, and the distance between the center O5 and the center O1 is R8, and the constraint relationship with the inner diameter R2 of the rotor is: R7 = 1.28R2 ~ 1.35R2, and R8 = 1.56R2 ~ 1.60R2.

[0096] The distance between the center O1 and the midpoint of the inner side of the irregular rectangular magnetic barrier 7 is R5, and R5 = 1.22R2 ~ 1.30R2. The center of the arc-shaped outer corner of the inner side is the same as the center O3 of the arc-shaped inner corner of the outer end of the L-shaped magnetic barrier 6, and the center O3 is inside the outer end of the L-shaped magnetic barrier 6, and the distance between the center O3 and the center O1 is R6, and R6 = 1.48R2 ~ 1.55R2.

[0097] A magnetic conducting bridge 13 is arranged between the end of the inner layer permanent magnet 5 and the inner end of the L-shaped magnetic barrier 6, and the width of the magnetic conducting bridge 13 is l 22 A magnetic conducting bridge 14 is arranged between the end of the outer layer permanent magnet 4 and the outer end of the L-shaped magnetic barrier 6, and the width of the magnetic conducting bridge 14 is l 23 The purpose of the magnetic conducting bridge 13 and the magnetic conducting bridge 14 is to maintain the mechanical strength of the rotor 2. The width of the intermediate magnetic conducting bridge 12, the inner magnetic conducting bridge 13 and the outer magnetic conducting bridge 14 is l 21 , l 22 , l 23 , and l 21 ∶ l 22 ∶ l 23 = 2:1:1.

[0098] Referring to Figure 10 , according to the performance requirements under different working conditions, a typical working condition representative point is selected, and the key structural parameters of the motor are comprehensively optimized, and the minimum direct-axis flux linkage amplitude |Ψ dmin | is used as the judgment basis to approach 0. The preferred embodiment of the present application is that the minimum direct-axis flux linkage amplitude |Ψ dmin | is compared with the threshold β of approaching 0 as the judgment basis, and the optimal structural parameters are selected as the optimal size.

[0099] The torque-speed distribution diagram is divided into subdomains I and II according to the constant torque region and the constant power region, and a typical working condition representative point O I (nI , T I ), O II (n II , T II ), n I , n II are the rotational speeds of the representative points O I , O II , T I , T II are the torques of the representative points O I , O II , the working condition representative point O I (n I , T I ) represents the "low-speed heavy load" working condition, and the working condition representative point O II (n II , T II ) represents the "high-speed cruising" working condition.

[0100] The working condition representative point O I (n I , T I ) corresponds to the "low-speed heavy load" working condition, and the optimization objective a1 is selected, that is, the output torque. The working condition representative point O II (n II , T II ) corresponds to the "high-speed cruising" working condition, and the optimization objective a2 is selected, that is, the minimum value of the direct-axis flux linkage amplitude |Ψ d |, that is, the minimum direct-axis flux linkage amplitude |Ψ dmin |, and the key structural parameter design variables of the motor shaft length l, the effective width w i , the radial thickness h i , the self-leakage magnetic bridge width l 11 , and the inter-pole leakage magnetic bridge width l 12 are represented by b1, b2, b3, b4, and b5, respectively.

[0101] According to the optimization objective and the structural parameters, a torque optimization model f1(b k ) min =F(b k , a1) is established, and the optimization model of the minimum value of the direct-axis flux linkage amplitude |Ψ d | is formula (14), wherein the function F is a mathematical relationship between the structural parameters b k and the optimization objective a1, k is the number of structural parameters, and k≤5 is satisfied. The torque optimization model is a normal model of the motor, and can be obtained by using conventional simulation software.

[0102] According to the constraint ranges of the structural parameters, that is, w1=w2, h1=1.5h2~1.8h2, l12 = R 42 - R 41 , R 41 = 0.65R1~0.67R1, R 42 = 1.05R 41 ~1.08R 41 , l 11 = 1.85l 12 ~2.25l 12 , the minimum value of each constraint range is selected as the initial value, substituted into the optimization model, and the output result is each structure parameter b k specific value:

[0103] First, according to the "low speed heavy load" working condition, the torque a1 output in the torque optimization model f1(b k ) min = F(b k , a1) reaches the requirement, if the torque a1 output reaches the set requirement value, the corresponding structure parameter specific value is substituted into formula (14), and the minimum direct axis flux linkage amplitude |Ψ dmin | is calculated, that is, the minimum value of the direct axis flux linkage amplitude |Ψ d |. Then the minimum direct axis flux linkage amplitude |Ψ dmin | and the size relationship of the set threshold β are used as the judgment basis, and the minimum direct axis flux linkage amplitude |Ψ dmin | is used as the basis to approximate 0, and the present application selects β=0.0002, when |Ψ dmin |≤β, that is, it meets the requirements, and the current each optimal parameter is output; when |Ψ dmin |>β, that is, it does not meet the requirements, then the value of the design variable is increased by a set step in the constraint range of each structure parameter, and the optimization model f1(b k ) min = F(b k , a1) is substituted again, and finally the minimum direct axis flux linkage amplitude |Ψ dmin | is output, and then compared with the set threshold β again, and so on until |Ψ dmin |≤β, the current each optimal parameter is obtained. If the torque a1 output does not reach the set requirement value, then the value of the design variable is increased by a set step in the constraint range of each structure parameter, and the optimization model f1(b k ) min = F(b k , a1) is substituted again.

[0104] The present application finally selects the optimal structure parameter as the optimal size through such comprehensive optimization, and realizes the effect of wide area constant power operation.

[0105] Referring to Table 1 below, the parameters of the motor before and after optimization are provided to prove the effectiveness of the design optimization method.

[0106] Table 1

[0107]

[0108] Referring to Figure 1 A 36-slot 8-pole permanent magnet flat wire motor with a rated speed of 1200 rpm and a rated torque of 28 Nm is taken as an example. Referring to Figure 12 and Figure 13 When running at low speed and heavy load, the inner and outer permanent magnets 5, 4 are magnetized, and current is applied to the flat wire armature winding 3, effectively blocking the magnetic flux leakage path, so that the leakage flux component Ψ σ gradually decreases, and the main flux flowing to the stator core 1 gradually increases, improving the torque density. As the speed rises, the inner and outer permanent magnets 4, 5 are gradually demagnetized, and the leakage flux component Ψ σ (i d , i q ) gradually increases, and the leakage flux flows into the adjacent permanent magnet or itself through the leakage flux path on both sides of the self-leakage flux bridge 10 and the inter-pole leakage flux bridge 11, realizing high-speed operation. Under this working condition, the introduction of the leakage flux component Ψ σ (i d , i q ) reduces the difficulty of field weakening control. Due to the reduction of field weakening current, on the one hand, it reduces the risk of irreversible demagnetization of the permanent magnet, and on the other hand, it reduces the loss, thereby widening the speed range of the permanent magnet flat wire motor while improving the operating efficiency of the motor.

[0109] Referring to Figure 14 and Figure 15 , through finite element simulation analysis, the torque-speed performance comparison chart of the embodiment of the application and the conventional permanent magnet flat wire motor is obtained, which verifies the advantages of high torque and wide speed regulation of the minimum direct-axis flux linkage approximation type permanent magnet flat wire drive motor. When the motor runs at low speed, due to the saturation of the leakage flux region, the output torque of the motor under this working condition is improved, so that the total torque is slightly larger than that of the conventional permanent magnet motor; when running at high speed, due to the introduction of the leakage flux component Ψ σ (i d , i q ), it is easier to realize the approximation of the minimum direct-axis flux linkage to 0, and the widening of the ideal constant power speed regulation range can be realized, which verifies the effectiveness of the design method.

Claims

1. A minimum direct-axis flux linkage approximation type permanent-magnet flat wire drive motor comprising a stator and a rotor disposed coaxially from the outside to the inside, characterized by: The rotor is uniformly provided with a plurality of permanent magnet groups and a plurality of irregular rectangular magnetic barriers (7) in the circumferential direction, each of the permanent magnet groups and each of the irregular rectangular magnetic barriers (7) are arranged alternately with each other, each of the permanent magnet groups is symmetrical along the d-axis, and each of the irregular rectangular magnetic barriers (7) is symmetrical along the q-axis; each of the permanent magnet groups on the radial section is composed of two outer layer permanent magnets (4) and an inner layer permanent magnet (5), the inner layer permanent magnet (5) is perpendicular to the d-axis, the two outer layer permanent magnets (4) are identical in structure, do not contact each other, and are arranged in a V-shaped structure with an opening facing outward in the radial direction; an L-shaped magnetic barrier (6) is arranged between the end of the outer layer permanent magnet (4) on the same side of the d-axis and away from the d-axis and the end of the inner layer permanent magnet (5); the two L-shaped magnetic barriers (6) on the same pole are identical in structure; a self-leakage magnetic bridge (10) is arranged between the irregular rectangular magnetic barrier (7) and the L-shaped magnetic barrier (6); on the outer side of each irregular rectangular magnetic barrier (7), the outer side wall of the rotor (2) forms a semicircular magnetic barrier (8); a pole-to-pole leakage magnetic bridge (11) is arranged between the semicircular magnetic barrier (8) and the irregular rectangular magnetic barrier (7); the magnetization directions of the two outer layer permanent magnets (4) and the inner layer permanent magnet (5) on the same pole are the same, and the magnetization directions of the two outer layer permanent magnets (4) and the inner layer permanent magnet (5) on adjacent poles are opposite.

2. The minimum direct-axis flux linkage approximation type permanent-magnet flat motor drive motor according to claim 1, characterized in that: The side wall direction of the V-shaped structure formed by the two outer layer permanent magnets (4) is the width direction of the outer layer permanent magnet (4), the width direction of the inner layer permanent magnet (5) is the direction perpendicular to the d-axis, and the widths of the outer layer permanent magnet (4) and the inner layer permanent magnet (5) are equal.

3. The minimum direct-axis flux linkage approximation type permanent-magnet pancake motor according to claim 1, characterized in that: The thickness of the outer layer permanent magnet (4) is greater than the thickness of the inner layer permanent magnet (5).

4. The minimum direct-axis flux linkage approximation type permanent-magnet pancake motor according to claim 3, characterized in that: width l of the intermediate magnetic conducting bridge (12), of the inner magnetic conducting bridge (13), of the outer magnetic conducting bridge (14) 21 、 22 、 23 satisfies l 21 ∶l 22 ∶l 23 = 2:1:

1.

5. The minimum direct-axis flux linkage approximation permanent-magnet pancake motor drive machine of claim 3, characterized by: The outer side of the semi-elliptical small magnetic barrier (8) and the outer side of the irregular rectangular magnetic barrier (7) are on two concentric circles, the center of the concentric circles is O2 and on the q axis, the distance from the center O2 to the center of the rotor O2 is R3, the constraint relationship between R3 and the outer diameter R1 of the rotor is: R3=1.3R1~1.35R1, the radius of the semi-elliptical small magnetic barrier (8) is R 41 , the constraint relationship between R 41 and the outer diameter R1 of the rotor is: R 41 =0.65R1~0.67R1, the radius of the outer side of the irregular rectangular magnetic barrier (7) is R 42 , the constraint relationship between R 41 and R 42 is: R 42 =1.05R 41 ~1.08R 41 .

6. A design method of a minimum direct-axis flux linkage approximation type permanent-magnet flat motor as claimed in claim 1, The inner ends of the two outer layer permanent magnets (4) form a middle magnetic bridge (12), the end of the inner layer permanent magnet (5) and the corresponding end of the L-shaped magnetic barrier (6) form an inner magnetic bridge (13), and the end of the outer layer permanent magnet (4) and the corresponding end of the L-shaped magnetic barrier (6) form an outer magnetic bridge (14). The method comprises the following steps: Step 1): introducing a leakage component ψ σ (i d , q ) into the direct-axis flux linkage, said direct-axis flux linkage ψ d (i d , q ) = ψ pm (i d , q ) + L d (i d , q ) · i d - ψ σ (i d , q ), ψ pm (i d , q ) being the permanent magnet flux linkage, L d (i d , q ) being the direct-axis inductance, i d , q being the d, q-axis rated currents, respectively; Step 2) : Based on the direct axis flux linkage ψ d (i d , q ) the direct axis flux linkage amplitude | ψ | is calculated Based on the direct axis flux linkage amplitude | ψ | d | the motor shaft length l, the inner and outer permanent magnet width w i , the inner and outer permanent magnet thickness h i , the self leakage magnetic bridge (10) width l 11 , the inter pole leakage magnetic bridge (11) width l 12 These key structural parameters and their ranges; μ0 is the air gap permeability, μ r is the relative permeability, N is the number of turns per phase winding, i = 1, 2, w i = w1, w2, are the inner and outer layer permanent magnet (5, 4) width, h i = h1, h2, are the inner and outer layer permanent magnet (5, 4) thickness, l is the motor shaft length; B pm is the permanent magnet flux density; Step 3): Selecting representative points of typical working conditions to optimize the key structural parameters, and calculating the minimum direct-axis flux linkage amplitude |Ψ d | according to the optimized key structural parameters. d | to approach 0 to obtain the optimal key structural parameters.

7. The method of designing a minimum direct-axis flux linkage approximation permanent-magnet pancake motor drive according to claim 6, characterized in that: The range of the key structure parameters is: w1 = w2, h1 = 1.5h2 ~ 1.8h2, l 12 = R 42 - R 41 , l 11 = 1.85l 12 ~ 2.25l 12 , R 41 = 0.65R1 ~ 0.67R1, R 42 = 1.05R 41 ~ 1.08R 41 , i = 1, 2; the outer side of the semi-elliptical small magnetic barrier (8) and the irregular rectangular magnetic barrier (7) are on two concentric circles, R 41 is the radius of the semi-elliptical small magnetic barrier (8), R 42 is the radius of the outer side of the irregular rectangular magnetic barrier (7).

8. The method of designing a minimum direct-axis flux linkage approximation permanent-magnet pancake motor drive according to claim 6, characterized in that: The magnetic flux leakage component 9. The method of designing a minimum direct-axis flux linkage approximation permanent-magnet pancake motor drive according to claim 7, characterized in that: In the constant torque region of the motor, a typical working condition representative point is selected, and a torque optimization model is established with torque as the optimization target. In the constant power region of the motor, a typical working condition representative point is selected, and the minimum direct-axis flux linkage amplitude |Ψ d | is taken as the optimization target. The minimum value of each structural parameter range is selected as the initial value, the torque is obtained through the torque optimization model, and if the torque meets the requirements, the minimum direct-axis flux linkage amplitude |Ψ d | is calculated. The optimal key structural parameter is obtained according to the minimum direct-axis flux linkage amplitude |Ψ d | approaching 0.

10. The method of designing a minimum direct-axis flux linkage approximation permanent-magnet pancake motor drive according to claim 9, characterized in that: If the output of the torque does not reach the requirement, the value of the structure parameter is increased in the set step within the constraint range of each structure parameter, and the torque and the minimum direct-axis flux linkage amplitude |Ψ d | are obtained again through the torque optimization model.

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