Design method of double-shaft excitation synchronous motor for power flow control

Abstract

The invention provides a design method of a double-shaft excitation synchronous motor for power flow control, and belongs to the technical field of motors. In electromagnetic design, main design indexes of the double-shaft excitation synchronous motor are determined according to power flow control requirements; judging whether the output voltage is full-amplitude and full-phase or not and whether the core flux density is saturated or not; calculating electromagnetic performance under different slot division degrees, layer numbers and DQ axis included angles, and preliminarily screening a scheme; voltage distortion and loss of the preliminary screening scheme under the load are calculated, and optimal winding arrangement is determined; in the fluid-heat design, a universe ventilation fluid network of the double-shaft excitation synchronous motor is established, rotor three-dimensional fluid-heat transfer coupling calculation is carried out, and a surface heat dissipation coefficient is extracted; optimizing the ventilation structure by adopting a thermal network method; and the temperature rise and the thermal unbalance of the DQ-axis winding are verified. The method is provided for comprehensive design of the double-shaft excitation motor under power flow control in a novel power system, and the forward design problem of the double-shaft excitation motor under the series connection condition is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of motors, and in particular to a design method of a dual-axis excitation synchronous motor for power flow control. Background Art

[0002] The modern power system has developed into a large-scale complex power grid with AC and DC interconnection, and complementary new and traditional energy sources. The uneven distribution of energy and load in the region will lead to blockage of some transmission lines. Solving the problem by upgrading the grid structure is the traditional way of power grid development, but due to restrictions such as urban planning, the construction space is increasingly limited and the investment cost has increased significantly. With the construction of new power systems and low-carbon energy systems, new uncertain power sources and loads represented by new energy power generation and new energy vehicles are accelerating, and the demand for control of power grid trends has further expanded. The new power flow controller composed of rotating synchronous motors can not only be used to solve the blockage of transmission lines and realize the optimization and regulation of power grid trends, but also provide the urgently needed rotational inertia to high-proportion new energy systems, and make full use of the high overload capacity of motor equipment to improve the operational resilience of flexible power grids under extreme conditions.

[0003] Since the dual-axis excitation motor is connected in series in the line through a series transformer, its operating environment is different from that of traditional phase regulators and traditional dual-axis excitation motors, and its design method is also quite different from the traditional method. How to determine the main parameters, electromagnetic structure, mechanical structure that withstands power grid impact, and heat dissipation structure of the dual-axis excitation motor required for power flow control are all key and difficult technologies at present. At present, there is a lack of relevant electromagnetic and thermal design methods for dual-axis excitation motors. Summary of the invention

[0004] The purpose of the present invention is to provide a dual-axis excitation synchronous motor design method for power flow control, propose to meet the power demand of power flow control, full amplitude of output voltage, and full-phase output requirements, suppress the temperature rise and uneven thermal stress of DQ axis windings due to different excitation currents and losses, ensure the safe and stable operation of the motor, and solve the power flow control problem of the power system.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a dual-axis excitation synchronous motor design method for power flow control, including electromagnetic design: determining the dual-axis excitation motor design indicators according to power flow control requirements; determining the number of stator and rotor slots, the number of DQ shaft turns, and the wire diameter; judging whether the output voltage is full amplitude and full phase, and whether the core magnetic flux is saturated; calculating the electromagnetic performance under different slot division numbers, number of layers, and DQ shaft angles and preliminarily screening schemes; calculating the voltage distortion and loss of the preliminarily screened schemes under load, and determining the optimal winding arrangement.

[0007] Furthermore, it also includes fluid-heat transfer design: determine the cooling method and fan type; calculate the rotor sub-slot size, the alternating radial ventilation groove size of the DQ shaft winding, the stator ventilation groove size, and the ventilation duct size of the end structural parts; establish a full-domain ventilation fluid network for the dual-axis excitation synchronous motor, and adjust the ventilation duct structure according to the calculation results; perform three-dimensional fluid-heat transfer coupling calculations on the rotor and extract the surface heat dissipation coefficient; use the thermal network method to optimize the ventilation structure; verify the temperature rise and thermal imbalance of the DQ shaft winding; and verify the temperature rise of the stator and end structural parts.

[0008] Furthermore, the power, speed and voltage design indicators of the dual-axis excitation synchronous motor are determined according to the power demand of the power flow control; the main dimensions of the motor are calculated according to the design requirements of the output voltage and phase; the number of stator slots, the number of winding turns and the wire diameter of the motor are designed; the number of rotor slots, the number of D-axis and Q-axis winding turns and the wire diameter are determined; the no-load excitation current is calculated by parameter scanning iteration, and it is determined whether the no-load back EMF effective value reaches the preset value and whether it is full-phase; if it does not meet the requirements, return to redetermine the number of rotor slots, the number of D-axis and Q-axis winding turns and the wire diameter; if it meets the requirements, the optimal two-dimensional finite element model is selected.

[0009] Furthermore, the two-dimensional finite element models with different slot division numbers, single layer, double layer, single and double layer, and different DQ axis angles are determined respectively, the DQ axis no-load excitation current and the harmonic distortion rate of the magnetic flux density of these models are calculated and compared, and several preferred schemes are selected; it is judged whether the magnetic flux density of the no-load core is saturated. If it does not meet the requirements, it returns to redetermine the number of rotor slots, the number of turns of the D-axis and Q-axis windings, and the wire diameter; if it meets the requirements, the effective value of the stator current is calculated, and the load excitation current of the preferred scheme is iteratively calculated with the output voltage range and phase angle as the target, the output voltage distortion rate and loss of the preferred scheme are compared, and the optimal dual-axis excitation winding structure arrangement is determined with the minimum distortion rate and minimum loss as the criteria.

[0010] Furthermore, check whether the load core magnetic flux density of the optimal solution is saturated; if not, return to re-determine the number of rotor slots, the number of D-axis and Q-axis winding turns and the wire diameter; if passed, with the goal of making the transient reactance and time constant as small as possible, fine-tune the air gap length and the stator and rotor slot parameters to optimize the transient synchronous reactance and time constant of the motor.

[0011] Furthermore, determine whether the transient reactance and time constant meet the optimization target. If so, check whether the electromagnetic force and heat load of the optimal solution meet the requirements. If so, check whether all electromagnetic design requirements of the dual-axis excitation synchronous motor are met. If so, perform fluid-heat transfer design.

[0012] Furthermore, determine the cooling method, fan type, and required flow rate, calculate various losses and thermal density of the rotor; determine the inner and outer diameters of the fan, the number of blades, and the installation angle; determine the size of the auxiliary slot, the size and number of radial ventilation grooves in the DQ shaft winding, and the slot wedge outlet diameter; determine the size and number of the stator radial ventilation grooves, and the size of the ventilation ducts of the end structural parts, establish a full-domain ventilation fluid network for the dual-axis excitation motor, and determine whether the calculated flow value is equal to the pre-taken flow value and whether the air volume distribution in each wind zone is reasonable. If so, establish a rotor fluid-heat transfer coupling model considering the air gap flow, and extract the heat dissipation coefficients of the ventilation groove surface and the rotor surface.

[0013] Furthermore, a rotor lumped parameter thermal network model is established to determine whether the thermal network model is accurate; if it does not meet the requirements, the rotor lumped parameter thermal network model is re-established; if it meets the requirements, a thermal network with different sub-slot sizes and ventilation groove size structural parameters is established, and the extracted ventilation groove surface and rotor surface heat dissipation coefficient are used as boundary conditions for calculation; based on the temperature change law of the DQ axis winding and iron core; the rotor ventilation structure is optimized with the goal of minimizing temperature and thermal imbalance.

[0014] Furthermore, the optimal rotor ventilation structure is selected, and the fluid-thermal coupling calculation is performed using a two-dimensional finite element model; it is determined whether the maximum temperature and thermal imbalance coefficient of the D-axis and Q-axis windings meet the requirements. If so, it is determined whether the stator and stator end structural parts meet the temperature rise requirements. If the temperature rise requirements are met, the entire size of the motor is output to complete the electromagnetic-fluid-thermal design.

[0015] Beneficial effects of the invention: The invention solves the forward design problem of a series dual-axis excitation motor under the demand for flow control in the context of a new power system. Through the proposed electromagnetic-fluid-thermal design process, a series dual-axis excitation synchronous motor that meets the full amplitude and full phase requirements of the output voltage can be designed. By designing the alternating radial ventilation structure of the DQ axis winding, the flow distribution in each radial ventilation groove is more uniform, the axial thermal imbalance is reduced, the winding temperature difference and thermal stress are reduced, and the heat dissipation capacity of the rotor is improved. Ensure the safe and reliable operation of the dual-axis excitation synchronous motor.

[0016] Additional advantages of the present invention will be more clearly given in the following description or learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0018] Figure 1This is a flow chart of the electromagnetic-fluid-thermal design method of a dual-axis excitation synchronous motor for power flow control requirements according to an embodiment of the present invention.

[0019] Figure 2 It is a schematic diagram of the two-dimensional structure of a dual-axis excitation synchronous motor for power flow control requirements according to an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the alternating radial air ducts of the DQ axis windings of a dual-axis excitation synchronous motor for power flow control requirements according to an embodiment of the present invention.

[0021] Among them: 81- rotor auxiliary slot; 82- single radial air duct; 83- double radial air duct; 84- radial ventilation groove. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below by the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0023] It should be understood by those skilled in the art that unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs.

[0024] It should also be understood that terms, such as those defined in commonly used dictionaries, should be understood to have a meaning consistent with that in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless as defined herein.

[0025] Those skilled in the art will appreciate that, unless otherwise stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements and / or groups thereof.

[0026] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. Different embodiments or examples described in this specification and features of different embodiments or examples may be combined and combined by those skilled in the art without contradiction.

[0027] To facilitate understanding of the present invention, the present invention is further explained below with reference to specific embodiments in conjunction with the accompanying drawings, and the specific embodiments do not constitute a limitation on the embodiments of the present invention.

[0028] Those skilled in the art should understand that the drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily necessary for implementing the present invention.

[0029] Example 1

[0030] like Figures 1 to 3 As shown, in this embodiment 1, an electromagnetic-fluid-heat collaborative design method for a dual-axis excitation synchronous motor for power flow control is provided. The method includes electromagnetic design and fluid-heat transfer design, and the electromagnetic design includes the following steps: determining the main design indicators of the dual-axis excitation motor according to the power flow control requirements; designing the number of stator and rotor slots, the number of DQ shaft turns, the wire diameter, etc.; judging whether the output voltage is full amplitude and full phase, and whether the core magnetic flux is saturated; calculating the electromagnetic performance under different slot divisions, layers, and DQ shaft angles and preliminarily screening the scheme; calculating the voltage distortion and loss of the preliminarily screened scheme under load, and determining the optimal winding arrangement; verifying the electromagnetic force and thermal load of the optimal scheme, and optimizing the transient parameters into reactance and time constant. The fluid-thermal design includes the following steps: determine the cooling method, fan type, etc.; calculate the rotor auxiliary slot size, the alternating radial ventilation groove size of the DQ axis winding, the stator ventilation groove size, the end structural ventilation duct size, etc.; establish a full-domain ventilation fluid network for the dual-axis excitation synchronous motor, and adjust the ventilation duct structure according to the calculation results; perform three-dimensional fluid-heat transfer coupling calculations on the rotor and extract the surface heat dissipation coefficient; optimize the ventilation structure using the thermal network method; verify the temperature rise and thermal imbalance of the DQ axis winding; and verify the temperature rise of the stator and end structural parts. This embodiment provides a method for the comprehensive design of dual-axis excitation motors under flow control in new power systems, and solves the forward design problem of dual-axis excitation motors in series.

[0031] Specifically, in the present embodiment, an electromagnetic-fluid-thermal collaborative design method for a dual-axis excitation synchronous motor for power flow control includes an electromagnetic design step and a fluid-thermal design step. The electromagnetic design step includes: Step 1: Determine the power, speed, voltage and other design indicators of the dual-axis excitation synchronous motor according to the power demand of power flow control. Calculate the main dimensions of the motor according to the design requirements of output voltage 0-10.5kV and phase 0-360°. Step 2: Design the number of stator slots, number of winding turns and wire diameter of the motor. Step 3: Determine the number of rotor slots, number of winding turns and wire diameter of the D-axis and Q-axis. Step 4: Parameter scanning iteration calculates the no-load excitation current i d0 ,i q0 , and determine whether the effective value of the no-load back electromotive force reaches 6.06kV and whether it is full-phase. If it does not meet the requirements, return to step three; if it meets the requirements, proceed to step five. Step five: Determine the two-dimensional finite element models under different slot divisions, single-layer, double-layer, single-double-layer, and different DQ axis angles, calculate and compare the DQ axis no-load excitation current and magnetic flux harmonic distortion rate of these models, and select several preferred schemes. Step six: Determine whether the no-load core magnetic flux is saturated. If it does not meet the requirements, return to step three; if it meets the requirements, proceed to step seven. Step seven: When the effective value of the stator current is 1500A, take the output voltage range of 0-10.5kV and the phase angle of 0-360° as the target to iteratively calculate the load excitation current i of the preferred scheme. d 、i q , compare the output voltage distortion rate and loss of the optimal solution. Determine the optimal dual-axis excitation winding structure arrangement based on the minimum distortion rate and minimum loss. Step 8: Check whether the load core magnetic flux density of the optimal solution is saturated. If not, return to step three, if passed, proceed to step nine. Step nine: With the transient reactance and time constant as small as possible, fine-tune the air gap length and the stator and rotor slot parameters to optimize the transient synchronous reactance and time constant of the motor. Step ten: Determine whether the transient reactance and time constant meet the optimization target. If satisfied, proceed to step eleven, otherwise return to step nine. Step eleven: Check whether the electromagnetic force and heat load of the optimal solution meet the requirements. If not, return to step two. If passed, proceed to step twelve. Step twelve: Check whether all electromagnetic design requirements of the dual-axis excitation synchronous motor are met. If not; return to step one, if passed, proceed to step thirteen.

[0032] In this embodiment, the fluid-thermal design steps include: Step 13: Determine the cooling method, fan type, required flow rate, calculate various losses and thermal density of the rotor; determine the inner and outer diameters of the fan, the number of blades, and the installation angle. Step 14: Determine the size of the auxiliary slot, the size and number of radial ventilation grooves in the DQ axis winding, and the slot wedge outlet diameter. Step 15: Determine the size and number of radial ventilation grooves in the stator, the size of the ventilation duct of the end structure, establish a full-domain ventilation fluid network for the dual-axis excitation motor, and determine whether the calculated flow value is equal to the pre-taken flow value and whether the air volume distribution in each wind zone is reasonable. If not, return to step 14, if passed, proceed to step 16. Step 16: Establish a rotor fluid-heat transfer coupling model considering air gap flow, and extract the heat dissipation coefficient of the ventilation groove surface and the rotor surface. Step 17: Establish a rotor lumped parameter thermal network model. Step 18: Determine whether the thermal network model is accurate. If it does not meet the requirements, return to step 17, otherwise proceed to step 19. Step 19: Establish a thermal network with different structural parameters such as auxiliary slot size and ventilation groove size, and calculate with step 16 as the boundary condition. Summarize the temperature variation law of the DQ axis windings and the core; optimize the rotor ventilation structure with the goal of minimizing temperature and thermal imbalance. Step 20: Select the optimal rotor ventilation structure and use finite element to perform fluid-thermal coupling calculations. Step 21: Determine whether the maximum temperature and thermal imbalance coefficient of the D-axis and Q-axis windings meet the requirements. If not, return to step 14. If passed, proceed to step 22. Step 22: Determine whether the stator and stator end structural parts meet the temperature rise requirements. If not, return to step 15. If passed, proceed to step 23. Step 23: Output all dimensions of the motor and complete the electromagnetic-fluid-thermal design.

[0033] In this embodiment, the two-dimensional finite element scheme under different slot division numbers (i.e., 32, 34, 36), different numbers of layers, and different DQ axis angles, in order to ensure the mechanical strength of the rotor tooth root, the slot division numbers are limited to 32, 34, 36, and the DQ axis angle is limited to within 90 degrees. For the case where the rotor adopts a single-layer, double-layer, and double-layer excitation winding, in order to ensure the mechanical strength of the rotor tooth root, the slot depth is not deepened, the original rotor slot shape is maintained unchanged, and the number of turns of the upper and lower layers of the excitation winding is changed to 1 / 2 of the number of turns of the single-layer excitation winding. The ventilation duct structure of the D-axis winding and the Q-axis winding is an alternating radial ventilation structure, which is formed by alternating a single radial duct and a double radial duct in series. The alternating radial ventilation structure of the D-axis winding and the Q-axis winding, the minimum number of single radial ducts and double radial ducts is 2, which can be set by optimization; the radial height of the single radial duct and the double radial duct are different, and the circumferential width is different, which can be set by optimization.

[0034] Example 2

[0035] This embodiment 2 provides an electromagnetic-fluid-thermal design method for a dual-axis excitation synchronous motor for power flow control requirements, which can meet the full amplitude and full phase requirements of the output voltage of a series dual-axis excitation synchronous motor. By designing the alternating radial ventilation structure of the DQ axis winding, the flow distribution in each radial ventilation groove is more uniform, the axial thermal imbalance is reduced, the winding temperature difference and thermal stress are reduced, and the rotor heat dissipation capacity is improved. Ensure the safe and reliable operation of the dual-axis excitation synchronous motor.

[0036] like Figure 1 As shown, the method includes: 1. Determine the main design indicators of the dual-axis excitation motor according to the power flow control requirements; 2-Design the number of stator and rotor slots, the number of DQ shaft turns, the wire diameter, etc., and calculate the no-load excitation current; 3-Calculate the electromagnetic performance under different slot divisions, number of layers, and DQ shaft angles and preliminarily screen the scheme; 4-Calculate the voltage distortion and loss of the preliminarily screened scheme under load, determine the optimal winding arrangement, and check the magnetic flux saturation; 5-Optimize the transient reactance parameters and time constant; 6-Verify the electromagnetic force, thermal load and electromagnetic requirements of the optimal scheme. 7-Determine the cooling method, fan type and size, etc.; 8-Calculate the size of the rotor auxiliary slot 81, the size of the alternating radial ventilation groove (82, 83, 84) of the DQ axis winding, the size of the stator ventilation groove, the size of the ventilation duct of the end structure, etc.; 9-Establish a full-domain ventilation fluid network for the dual-axis excitation synchronous motor, and adjust the ventilation duct structure according to the calculation results; 10-Perform a three-dimensional fluid-heat transfer coupling calculation of the air gap flow rotor, extract the heat dissipation coefficient of the ventilation groove surface and the rotor surface as the boundary conditions of the thermal network model; 11-Establish a rotor lumped parameter thermal network model, and perform thermal network calculation by changing the auxiliary slot and ventilation groove structural parameters to optimize the rotor ventilation structure; 12-Check the temperature rise and thermal imbalance of the DQ axis winding, and check the temperature rise of the stator and the end structure. The ventilation duct structure of the D axis winding and the Q axis winding is an alternating radial ventilation structure, which is formed by alternating series connection of a single radial duct 82 and a double radial duct 83. The minimum number of the single radial air duct 82 and the double radial air duct 83 is 2, which can be set by optimization; the radial heights and circumferential widths of the single radial air duct 82 and the double radial air duct 83 are different, which can be set by optimization.

[0037] In this embodiment, the forward design problem of the series dual-axis excitation motor under the demand of flow control is solved. Through the proposed electromagnetic-fluid-thermal design process, a series dual-axis excitation synchronous motor that meets the full amplitude and full phase requirements of the output voltage can be designed. By designing the alternating radial ventilation structure of the DQ axis winding, the flow distribution in each radial ventilation groove is more uniform, the axial thermal imbalance is reduced, the winding temperature difference and thermal stress are reduced, and the heat dissipation capacity of the rotor is improved. Ensure the safe and reliable operation of the dual-axis excitation synchronous motor.

[0038] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative work on the basis of the technical solution disclosed in the present invention should be included in the scope of protection of the present invention.

Claims

1. A design method for a dual-axis excitation synchronous motor for power flow control, characterized in that: Electromagnetic design includes: determining the design indicators of the dual-axis excitation motor according to the power flow control requirements; determining the number of stator and rotor slots, the number of DQ shaft turns, and the wire diameter; judging whether the output voltage is full amplitude and full phase, and whether the core magnetic flux is saturated; calculating the electromagnetic performance under different slot divisions, number of layers, and DQ shaft angles and preliminarily screening the scheme; calculating the voltage distortion and loss of the preliminarily screened scheme under load, and determining the optimal winding arrangement.

2. The design method of a dual-axis excitation synchronous motor for power flow control according to claim 1, characterized in that: It also includes fluid-heat transfer design: determine the cooling method and fan type; calculate the rotor auxiliary slot size, the alternating radial ventilation groove size of the DQ shaft winding, the stator ventilation groove size, and the ventilation duct size of the end structural parts; establish a full-domain ventilation fluid network for the dual-axis excitation synchronous motor, and adjust the ventilation duct structure according to the calculation results; perform three-dimensional fluid-heat transfer coupling calculations on the rotor and extract the surface heat dissipation coefficient; use the thermal network method to optimize the ventilation structure; verify the temperature rise and thermal imbalance of the DQ shaft winding; and verify the temperature rise of the stator and end structural parts.

3. The design method of a dual-axis excitation synchronous motor for power flow control according to claim 2, characterized in that: Determine the power, speed, and voltage design indicators of the dual-axis excitation synchronous motor according to the power demand of the power flow control; calculate the main dimensions of the motor according to the design requirements of the output voltage and phase; design the number of stator slots, number of winding turns, and wire diameter of the motor; determine the number of rotor slots, number of D-axis and Q-axis winding turns, and wire diameter; calculate the no-load excitation current through parameter scanning iteration, and determine whether the no-load back EMF effective value reaches the preset value and whether it is full phase; if it does not meet the requirements, return to re-determine the number of rotor slots, number of D-axis and Q-axis winding turns, and wire diameter; If it meets the requirements, the optimal two-dimensional finite element model is selected.

4. The design method of a dual-axis excitation synchronous motor for power flow control according to claim 3, characterized in that: Determine the two-dimensional finite element models under different slot division numbers, single layer, double layer, single and double layer, and different DQ axis angles respectively, calculate and compare the DQ axis no-load excitation current and magnetic flux harmonic distortion rate of these models, and select several preferred schemes; judge whether the no-load core magnetic flux is saturated. If it does not meet the requirements, return to redetermine the number of rotor slots, the number of D-axis and Q-axis winding turns and the wire diameter; if it meets the requirements, calculate the effective value of the stator current, iteratively calculate the load excitation current of the preferred scheme with the output voltage range and phase angle as the target, compare the output voltage distortion rate and loss of the preferred scheme, and determine the optimal dual-axis excitation winding structure arrangement with the minimum distortion rate and minimum loss as the criteria.

5. The design method of a dual-axis excitation synchronous motor for power flow control according to claim 4, characterized in that: Check whether the load core magnetic flux density of the optimal solution is saturated; if not, return to re-determine the number of rotor slots, the number of D-axis and Q-axis winding turns and the wire diameter; if passed, with the goal of making the transient reactance and time constant as small as possible, fine-tune the air gap length and the stator and rotor slot parameters to optimize the transient synchronous reactance and time constant of the motor.

6. The design method of a dual-axis excitation synchronous motor for power flow control according to claim 5, characterized in that: Determine whether the transient reactance and time constant meet the optimization target. If so, verify whether the electromagnetic force and heat load of the optimal solution meet the requirements. If so, check whether all electromagnetic design requirements of the dual-axis excitation synchronous motor are met. If so, perform fluid-heat transfer design.

7. The design method of a dual-axis excitation synchronous motor for power flow control according to claim 6, characterized in that: Determine the cooling method, fan type, and required flow rate, calculate various losses and thermal density of the rotor; determine the inner and outer diameters of the fan, the number of blades, and the installation angle; determine the size of the auxiliary slot, the size and number of radial ventilation grooves in the DQ shaft winding, and the slot wedge outlet diameter; determine the size and number of the stator radial ventilation grooves, and the size of the ventilation ducts of the end structural parts, establish a full-domain ventilation fluid network for the dual-axis excitation motor, and determine whether the calculated flow value is equal to the pre-taken flow value and whether the air volume distribution in each wind zone is reasonable. If so, establish a rotor fluid-heat transfer coupling model considering the air gap flow, and extract the heat dissipation coefficients of the ventilation groove surface and the rotor surface.

8. The design method of a dual-axis excitation synchronous motor for power flow control according to claim 7, characterized in that: A rotor lumped parameter thermal network model is established to determine whether the thermal network model is accurate. If it does not meet the requirements, the rotor lumped parameter thermal network model is re-established. If it meets the requirements, a thermal network with different auxiliary slot sizes and ventilation groove size structural parameters is established, and the heat dissipation coefficient of the extracted ventilation groove surface and rotor surface is used as the boundary conditions for calculation. Based on the temperature change law of the DQ axis winding and iron core, the rotor ventilation structure is optimized with the goal of minimizing temperature and thermal imbalance.

9. The design method of a dual-axis excitation synchronous motor for power flow control according to claim 8, characterized in that: Select the optimal rotor ventilation structure and use a two-dimensional finite element model to perform fluid-thermal coupling calculations; determine whether the maximum temperature and thermal imbalance coefficient of the D-axis and Q-axis windings meet the requirements. If so, determine whether the stator and stator end structural parts meet the temperature rise requirements. If they do, output all motor dimensions and complete the electromagnetic-fluid-thermal design.

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