Method for estimating subtransient reactance of surface-mounted permanent magnet motor based on finite element method

Abstract

The invention provides a method for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on a finite element method, and relates to the technical field of motors, and the method comprises the steps: constructing a finite element model, setting the angular frequency of a rotor, and calculating the amplitude of back electromotive force and the synchronous reactance under a specific working condition; setting at least two groups of parameters of the model to enable three phases of a winding circuit to be short-circuited, and calculating a three-phase short-circuit current waveform; for three-phase short-circuit current waveforms under different groups of parameters, selecting a specific phase to calculate a waveform difference value; performing spectral analysis on the waveform difference value, and calculating a transient reactance parameter under the initial position condition of the rotor according to a specific spectral component related parameter, a back electromotive force amplitude and a synchronous reactance; and changing the initial position of the rotor, and solving the next transient reactance parameter average value of multiple positions as a final result. According to the method, the rotor eddy current influence is considered, the subtransient reactance is accurately and efficiently estimated through multi-step calculation and parameter adjustment based on the finite element method, and power system optimization is assisted.

Description

Technical Field

[0001] The present invention relates to the technical field of motors, and in particular to a method for estimating subtransient reactance of a surface-mounted permanent magnet motor based on a finite element method. Background Art

[0002] In the field of modern power engineering, with the continuous optimization of high-performance rare earth permanent magnet materials and the continuous progress of advanced electromagnetic design technology, permanent magnet motors, especially permanent magnet wind turbines, have achieved significant improvements in power density, reliability, and adaptability to complex working conditions. Its application in wind turbines is becoming more and more extensive, and it has gradually become one of the key technical solutions in the field of wind power generation. With its unique advantages, permanent magnet wind turbines have shown great potential in improving energy conversion efficiency and reducing maintenance costs, making important contributions to the development of sustainable energy.

[0003] Subtransient reactance is a crucial parameter in the field of motors. For wound-rotor synchronous motors, it plays an irreplaceable role in describing the current characteristics of the initial stage of motor short-circuit faults or other sudden disturbances. Although there is no damping winding in the traditional sense on the rotor of a permanent magnet wind turbine generator, eddy currents will be generated between its rotor permanent magnets and the iron core due to the alternating magnetic field, which will produce an effect similar to the damping winding of a wound-rotor synchronous motor, making the subtransient reactance parameter also a key indicator for evaluating the performance of a permanent magnet wind turbine generator. Accurate calculation of subtransient reactance is of great significance for evaluating the short-circuit current level of the generator. This parameter is directly related to the optimization of the protection configuration of the power system and the improvement of operational reliability. In the actual operation of the power system, the setting value of the protection device must be accurately set according to the subtransient parameters of the generator. Accurate calculation of subtransient reactance can effectively improve the response accuracy of the relay protection device, reduce the risk of false operation, ensure that the power system can quickly isolate the fault when a fault occurs, minimize the scope of the fault impact, and ensure the safe and stable operation of the power system.

[0004] For wound-rotor synchronous motors, there are relatively mature methods for calculating subtransient reactance parameters. However, due to the essential difference between the rotor structure of permanent magnet wind turbines and wound-rotor synchronous motors, there are no windings on their rotors. Although the eddy currents between the rotor permanent magnets and the iron core can produce a similar effect to damping windings, the eddy current distribution is usually uneven. This structural difference makes it impossible to directly apply the calculation method of wound-rotor synchronous motors to the calculation of subtransient reactance parameters of permanent magnet wind turbines, and it cannot accurately reflect the current characteristics of permanent magnet wind turbines during short-circuit faults or transient processes.

[0005] In the document "Short - Circuit Analysis of Permanent - Magnet Generators", a method for calculating the subtransient reactance parameters of a permanent magnet wind turbine is proposed. This method is based on the structural parameters of the generator. First, the inductance coefficient of the generator is solved, and then the inductance parameters are separated into the main air gap inductance and the slot leakage inductance. The main inductance is multiplied by a coefficient related to k to calculate the subtransient inductance under the influence of the rotor eddy current. However, this method has obvious defects: Calculation accuracy problem: Subtransient reactance parameters mainly play a significant role in fault conditions or transient processes. However, the existing technology obtains subtransient reactance parameters through the generator operating parameters under steady-state operation, which cannot accurately capture the true electromagnetic characteristics of the motor in the early stage of a fault or transient, resulting in inaccurate calculation results and unable to provide a reliable basis for power system protection configuration.

[0006] Difficulty in implementation and error issues: In terms of implementation means, this method requires separation of the main inductance of the air gap, which involves complex calculations and physical model processing and is difficult to implement. In addition, various errors are easily introduced during the separation process, such as inductance parameter measurement errors, model simplification errors, etc. These errors accumulate continuously during the calculation process, ultimately resulting in a large deviation between the calculated subtransient reactance parameters and the actual values, affecting the safe and stable operation of the power system.

[0007] In summary, the existing technology has many shortcomings in the calculation of subtransient reactance parameters of permanent magnet wind turbines. There is an urgent need for a method that can accurately and efficiently calculate these parameters to meet the power system's needs for performance evaluation and protection configuration of permanent magnet wind turbines. Summary of the invention

[0008] To this end, an embodiment of the present invention provides a method for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on the finite element method, which is used to solve the problem that the calculation method of the wound synchronous motor in the prior art is not applicable due to the special rotor structure of the permanent magnet wind turbine generator, and the existing permanent magnet wind turbine generator calculation method has defects in accuracy, implementation difficulty and error, and thus cannot accurately evaluate the generator short-circuit current level and optimize the protection configuration of the power system.

[0009] In order to solve the above problem, an embodiment of the present invention provides a method for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on a finite element method, the method comprising: S1: constructing a finite element model of a surface-mounted permanent magnet wind turbine, setting the rotor angular frequency in the finite element model to a specific value, and calculating the back electromotive force amplitude and synchronous reactance of the finite element model under specific working conditions; S2: performing at least two different sets of parameter settings on the finite element calculation model, wherein the winding circuit is in a three-phase short-circuit state under each set of parameter settings, and calculating the three-phase short-circuit current waveform within one electrical cycle, wherein each set of parameter settings includes stator winding resistance settings, rotor core and permanent magnet conductivity settings, and rotor initial position settings; S3: for the three-phase short-circuit current waveforms obtained under different sets of parameter settings, the short-circuit current waveform of a specific phase is selected for difference calculation to obtain the difference of the short-circuit current waveform of the specific phase under different sets of parameter settings; S4: performing spectrum analysis on the short-circuit current waveform difference to determine relevant parameters of specific spectrum components, and calculating subtransient reactance parameters under the condition of the rotor initial position according to the relevant parameters, the back electromotive force amplitude and the synchronous reactance; S5: Return to step S2, and change the initial position of the rotor to obtain subtransient reactance parameters under multiple initial positions of the rotor, and calculate the average value thereof as the final subtransient reactance parameter.

[0010] Preferably, in step S1, the specific operating condition is a normal operating state of the motor, and the specific value is a rated value.

[0011] Preferably, in step S2, the stator winding resistance is set to zero.

[0012] Preferably, in step S2, the electrical conductivity settings of the rotor core and the permanent magnet include at least two different setting values, one of which is a zero value, and the other is a value within a conventional range.

[0013] Preferably, the conventional range is 10 4 S / m - 10 6 S / m.

[0014] Preferably, in step S4, the method of performing spectrum analysis on the short-circuit current waveform difference and determining relevant parameters of specific spectrum components is: The short-circuit current waveform difference is subjected to Fourier decomposition, and the first harmonic amplitude of the short-circuit current waveform difference is selected.

[0015] Preferably, in step S4, the method for calculating the subtransient reactance parameters under the condition of the rotor initial position according to the relevant parameters, the back electromotive force amplitude and the synchronous reactance is: ; in represents the subtransient reactance, represents the back electromotive force amplitude, represents the synchronous reactance, Indicates the 1st harmonic amplitude of the short-circuit current waveform difference.

[0016] Preferably, in step S5, the range of changing the initial position of the rotor is 0-180°, and the changing step size is a preset value.

[0017] The embodiment of the present invention further provides a system for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on the finite element method. The system is used to implement the method for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on the finite element method described above, and specifically includes: A model building and parameter acquisition module, used to build a finite element model of a surface-mounted permanent magnet wind turbine, set the rotor angular frequency in the finite element model to a specific value, and calculate the back electromotive force amplitude and synchronous reactance of the finite element model under specific working conditions; A short-circuit current calculation module, used to perform at least two different sets of parameter settings on the finite element calculation model, each set of parameter settings puts the winding circuit in a three-phase short-circuit state, and calculates the three-phase short-circuit current waveform within an electrical cycle, wherein each set of parameter settings includes a stator winding resistance setting, a rotor core and permanent magnet conductivity setting, and a rotor initial position setting; The current waveform processing module is used to select the short-circuit current waveform of a specific phase for difference calculation based on the three-phase short-circuit current waveforms obtained under different sets of parameter settings, and obtain the difference of the short-circuit current waveform of the specific phase under different sets of parameter settings; A spectrum analysis and reactance calculation module, used to perform spectrum analysis on the short-circuit current waveform difference, determine relevant parameters of specific spectrum components, and calculate sub-transient reactance parameters under the rotor initial position condition based on the relevant parameters, back electromotive force amplitude and synchronous reactance; The average calculation module is used to return to the short-circuit current calculation module and change the initial position of the rotor to obtain the sub-transient reactance parameters under multiple initial positions of the rotor, and calculate the average value thereof as the final sub-transient reactance parameter.

[0018] Preferably, the short-circuit current calculation module includes: A first short-circuit current calculation unit is used to calculate a three-phase short-circuit current waveform when the stator winding resistance is a specific value, the rotor core and the permanent magnet conductivity are specific values ​​representing no rotor eddy current effect, and the rotor initial position is a specific value; The second short-circuit current calculation unit is used to calculate the three-phase short-circuit current waveform when the stator winding resistance is the same specific value, the rotor core and the permanent magnet conductivity are specific values ​​representing the actual or approximately actual rotor eddy current effect, and the rotor initial position is the same specific value.

[0019] It can be seen from the above technical solutions that the present invention has the following beneficial effects: (1) Based on the finite element method, the present invention comprehensively considers multiple factors and accurately calculates subtransient reactance parameters. By constructing a model and performing calculation and analysis under different parameter settings, the problem of inaccurate calculation in the prior art is effectively solved, providing a reliable basis for accurately evaluating the short-circuit current and dynamic response level of the generator, effectively promoting the optimization of power system protection configuration, and enhancing the stability and reliability of the power system.

[0020] (2) The present invention proposes a clear and feasible estimation method with clear operation steps. It overcomes the defects of the existing technology, such as high difficulty and large error, avoids complex operations, and has strong operability. General R&D personnel can quickly calculate parameters and improve calculation efficiency, which is convenient for wide application in the industry and promotes the development of related technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the implementation cases of the present invention or the technical solutions in the prior art, the following is a brief description of the drawings required for use in the embodiments. By referring to the drawings, the features and advantages of the present invention will be more clearly understood. The drawings are schematic and should not be understood as limiting the present invention in any way. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them: Figure 1 A flow chart of a method for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on the finite element method provided in an embodiment; Figure 2 Schematic diagram of a finite element model of a surface-mounted permanent magnet wind turbine in an embodiment; Figure 3 is a schematic diagram of a three-phase short-circuit current waveform when the rotor eddy current is not considered in the embodiment; Figure 4 Schematic diagram of three-phase short-circuit current waveform when rotor eddy current is considered in the embodiment; Figure 5 Schematic diagram of the current difference when the rotor eddy current is considered and not considered in the embodiment; Figure 6 Schematic diagram of subtransient reactance under different initial rotor positions in the embodiment; Figure 7 A block diagram of a system for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on the finite element method provided in an embodiment. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Embodiment 1

[0023] In order to solve the problem that the calculation method of the wound synchronous motor is not applicable due to the special rotor structure of the permanent magnet wind turbine in the existing technology, and the existing calculation method of the permanent magnet wind turbine has defects in accuracy, implementation difficulty and error, and thus cannot accurately evaluate the short-circuit current level of the generator and optimize the protection configuration of the power system. Figure 1 As shown, an embodiment of the present invention proposes a method for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on a finite element method, the method comprising: S1: Construct a finite element model of a surface-mounted permanent magnet wind turbine, set the rotor angular frequency in the finite element model to a specific value, and calculate the back electromotive force amplitude and synchronous reactance of the finite element model under specific working conditions; S2: performing at least two different sets of parameter settings on the finite element calculation model, wherein the winding circuit is in a three-phase short-circuit state under each set of parameter settings, and calculating the three-phase short-circuit current waveform within one electrical cycle, wherein each set of parameter settings includes stator winding resistance settings, rotor core and permanent magnet conductivity settings, and rotor initial position settings; S3: for the three-phase short-circuit current waveforms obtained under different sets of parameter settings, the short-circuit current waveform of a specific phase is selected for difference calculation to obtain the difference of the short-circuit current waveform of the specific phase under different sets of parameter settings; S4: Perform spectrum analysis on the short-circuit current waveform difference to determine relevant parameters of specific spectrum components, and calculate subtransient reactance parameters under the rotor initial position condition based on the relevant parameters, back electromotive force amplitude and synchronous reactance; S5: Return to step S2, and change the initial position of the rotor to obtain subtransient reactance parameters under multiple initial positions of the rotor, and calculate the average value thereof as the final subtransient reactance parameter.

[0024] From the above technical solution, it can be seen that the present invention proposes a method for estimating the sub-transient reactance of a surface-mounted permanent magnet motor based on the finite element method. By constructing a finite element model of a surface-mounted permanent magnet wind turbine and setting the rotor angular frequency to a specific value, the back electromotive force amplitude and synchronous reactance under specific working conditions are calculated, laying the foundation for subsequent calculations. Then, multiple groups of different parameter settings (covering the stator winding resistance, the rotor core and the permanent magnet conductivity and the initial position of the rotor) are performed, and the three-phase short-circuit current waveform is obtained under the three-phase short-circuit state. The waveform difference is calculated by selecting a specific phase, and the sub-transient reactance parameters under the rotor initial position condition are calculated after the relevant parameters are determined by spectrum analysis. Then, the rotor initial position is changed and the operation is repeated to obtain the average value. This technical solution fully considers the rotor structural characteristics of permanent magnet wind turbines and the influence of rotor eddy currents under short-circuit faults, and overcomes the defects of the prior art, such as the inapplicability of calculation methods due to the special rotor structure, poor accuracy, great difficulty in implementation, and large errors. It can accurately estimate subtransient reactance parameters, thereby precisely evaluating short-circuit currents and dynamic response levels, and effectively optimizing the protection configuration of the power system. It is easy to operate, and general R&D personnel can use it to quickly calculate, with strong operability.

[0025] In step S1, a finite element model of a surface mounted permanent magnet wind turbine is constructed using finite element simulation software, such as Figure 2 As shown ( Figure 2 PM1, PM2, ..., PM10 in the figure refer to the permanent magnet part of the surface-mounted permanent magnet wind turbine of the present invention), and its main parameters are shown in Table 1. The rotor angular frequency in the finite element model is set to the rated value, and the back electromotive force amplitude and synchronous reactance of the finite element model under the normal operation state of the motor are calculated.

[0026] Table 1 Motor parameters

[0027] Furthermore, the current expression under the three-phase short-circuit state is: ; The known quantities include the current ,time , Back EMF Amplitude , armature time constant , Synchronous Reactance ,frequency , rotor initial position angle , two unknown quantities are transient reactance and subtransient time constant .

[0028] In step S2, at least two different sets of parameter settings are performed on the finite element calculation model. Under each set of parameter settings, the winding circuit is in a three-phase short-circuit state, and the three-phase short-circuit current waveform within one electrical cycle is calculated, wherein each set of parameter settings includes stator winding resistance settings, rotor core and permanent magnet conductivity settings, and rotor initial position settings, specifically including: In the above finite element model, the stator winding resistance is set to 0, the rotor core and permanent magnet conductivity is set to 0, the rotor initial position is set to 0, the winding circuit is connected to a three-phase short-circuit state, and the three-phase short-circuit current of one electrical cycle is calculated. The three-phase current waveforms are recorded as A1, B1, and C1 respectively.

[0029] Specifically, the stator winding resistance is set to 0, the rotor core and permanent magnet conductivity is set to 0, and the back electromotive force amplitude is calculated to be 800V and the synchronous reactance is 1.466Ω. At the same time, the three-phase short-circuit current waveform of the motor in one electrical cycle when the rotor initial position is 0 is calculated, as shown in Figure 3 shown.

[0030] Furthermore, based on the same finite element model, the stator winding resistance is set to 0, and the rotor core and permanent magnet conductivity are set to conventional levels, generally 10 4 S / m - 10 6 S / m, the initial position of the rotor is set to 0, the winding circuit is connected to a three-phase short-circuit state, and the three-phase short-circuit current of one electrical cycle is calculated. The three-phase current waveforms are recorded as A2, B2, and C2 respectively.

[0031] The stator winding resistance is still set to 0, the rotor core and permanent magnet conductivity are set to 9930000S / m and 625000S / m respectively, and the three-phase short-circuit current waveform of the motor in one electrical cycle when the rotor initial position is 0 is calculated, as shown in Figure 4 shown.

[0032] In step S3, for the three-phase short-circuit current waveforms obtained under different sets of parameter settings, the short-circuit current waveform of a specific phase (phase A) is selected for difference calculation, and the difference of the short-circuit current waveform of the specific phase under different sets of parameter settings is obtained to obtain the waveform as shown in FIG. Figure 5 shown.

[0033] In step S4, the short-circuit current waveform difference is Fourier decomposed, and the 1st harmonic amplitude of the short-circuit current waveform difference is selected, which is 2457.5A. The sub-transient reactance parameters under the rotor initial position condition are calculated based on the 1st harmonic amplitude, back electromotive force amplitude and synchronous reactance. : ; in, represents the back electromotive force amplitude, represents the synchronous reactance, Represents the 1st harmonic amplitude of the short-circuit current waveform difference, so the sub-transient reactance parameter under the current conditions is It can be calculated as 1.401Ω according to the above formula.

[0034] In step S5, return to step S2 and change the initial position of the rotor, wherein the range of changing the initial position of the rotor is 0 - 180°, and the change step is a preset value (preferably 10°). Repeat steps S2 to S4 to obtain the subtransient reactance parameters under multiple initial positions of the rotor. , calculate its average value as the final subtransient reactance parameter. Figure 6 As shown, the average value of the subtransient reactance under different initial rotor positions is 1.400Ω. Embodiment 2

[0035] like Figure 7 As shown, the present invention provides a system for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on the finite element method, and the system is used to implement the method for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on the finite element method of the first embodiment, specifically comprising: The model building and parameter acquisition module 100 is used to build a finite element model of the surface-mounted permanent magnet wind turbine, set the rotor angular frequency in the finite element model to a specific value, and calculate the back electromotive force amplitude and synchronous reactance of the finite element model under specific working conditions; The short-circuit current calculation module 200 is used to set at least two different sets of parameters for the finite element calculation model, and each set of parameter settings puts the winding circuit in a three-phase short-circuit state, and calculates the three-phase short-circuit current waveform within one electrical cycle, wherein each set of parameter settings includes stator winding resistance settings, rotor core and permanent magnet conductivity settings, and rotor initial position settings; The current waveform processing module 300 is used to select the short-circuit current waveform of a specific phase for difference calculation based on the three-phase short-circuit current waveforms obtained under different sets of parameter settings, and obtain the difference of the short-circuit current waveform of the specific phase under different sets of parameter settings; The spectrum analysis and reactance calculation module 400 is used to perform spectrum analysis on the short-circuit current waveform difference, determine the relevant parameters of the specific spectrum components, and calculate the sub-transient reactance parameters under the rotor initial position condition based on the relevant parameters, the back electromotive force amplitude and the synchronous reactance; The average calculation module 500 is used to return to the short-circuit current calculation module 200 and change the initial position of the rotor to obtain subtransient reactance parameters under multiple initial positions of the rotor, and calculate the average value thereof as the final subtransient reactance parameter.

[0036] Furthermore, the short-circuit current calculation module 200 includes: A first short-circuit current calculation unit is used to calculate a three-phase short-circuit current waveform when the stator winding resistance is a specific value, the rotor core and the permanent magnet conductivity are specific values ​​representing no rotor eddy current effect, and the rotor initial position is a specific value; The second short-circuit current calculation unit is used to calculate the three-phase short-circuit current waveform when the stator winding resistance is the same specific value, the rotor core and the permanent magnet conductivity are specific values ​​representing the actual or approximately actual rotor eddy current effect, and the rotor initial position is the same specific value.

[0037] A system for estimating the sub-transient reactance of a surface-mounted permanent magnet motor based on the finite element method in this embodiment is used to implement the aforementioned method for estimating the sub-transient reactance of a surface-mounted permanent magnet motor based on the finite element method. Therefore, the specific implementation method of the system for estimating the sub-transient reactance of a surface-mounted permanent magnet motor based on the finite element method can be seen in the embodiment part of the method for estimating the sub-transient reactance of a surface-mounted permanent magnet motor based on the finite element method in the preceding text. For example, the model building and parameter acquisition module 100, the short-circuit current calculation module 200, the current waveform processing module 300, the spectrum analysis and reactance calculation module 400, and the average calculation module 500 are respectively used to implement steps S1, S2, S3, S4, and S5 in the aforementioned method for estimating the sub-transient reactance of a surface-mounted permanent magnet motor based on the finite element method. Therefore, its specific implementation method can refer to the description of the corresponding various partial embodiments. In order to avoid redundancy, it will not be repeated here.

[0038] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0039] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0040] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide for implementing the process in the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0041] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A method for estimating subtransient reactance of a surface-mounted permanent magnet motor based on finite element method, characterized in that: include: S1: constructing a finite element model of a surface-mounted permanent magnet wind turbine, setting the rotor angular frequency in the finite element model to a specific value, and calculating the back electromotive force amplitude and synchronous reactance of the finite element model under specific working conditions; S2: performing at least two different sets of parameter settings on the finite element calculation model, wherein the winding circuit is in a three-phase short-circuit state under each set of parameter settings, and calculating the three-phase short-circuit current waveform within one electrical cycle, wherein each set of parameter settings includes stator winding resistance settings, rotor core and permanent magnet conductivity settings, and rotor initial position settings; S3: for the three-phase short-circuit current waveforms obtained under different sets of parameter settings, the short-circuit current waveform of a specific phase is selected for difference calculation to obtain the difference of the short-circuit current waveform of the specific phase under different sets of parameter settings; S4: performing spectrum analysis on the short-circuit current waveform difference to determine relevant parameters of specific spectrum components, and calculating subtransient reactance parameters under the condition of the rotor initial position according to the relevant parameters, the back electromotive force amplitude and the synchronous reactance; S5: Return to step S2, and change the initial position of the rotor to obtain subtransient reactance parameters under multiple initial positions of the rotor, and calculate the average value thereof as the final subtransient reactance parameter.

2. The method for estimating subtransient reactance of a surface-mounted permanent magnet motor based on finite element method according to claim 1, characterized in that: In step S1 , the specific operating condition is the normal operating state of the motor, and the specific value is a rated value.

3. The method for estimating subtransient reactance of a surface-mounted permanent magnet motor based on finite element method according to claim 1, characterized in that: In step S2, the stator winding resistance is set to zero.

4. The method for estimating subtransient reactance of a surface-mounted permanent magnet motor based on finite element method according to claim 1, characterized in that: In step S2, the electrical conductivity settings of the rotor core and the permanent magnet include at least two different setting values, one of which is a zero value and the other is a value within a conventional range.

5. The method for estimating subtransient reactance of a surface-mounted permanent magnet motor based on finite element method according to claim 4 is characterized in that: The conventional range is 10 4 S / m - 10 6 S / m.

6. The method for estimating subtransient reactance of a surface-mounted permanent magnet motor based on finite element method according to claim 1, characterized in that: In step S4, the method of performing spectrum analysis on the short-circuit current waveform difference and determining the relevant parameters of the specific spectrum component is as follows: The short-circuit current waveform difference is subjected to Fourier decomposition, and the first harmonic amplitude of the short-circuit current waveform difference is selected.

7. The method for estimating subtransient reactance of a surface-mounted permanent magnet motor based on finite element method according to claim 1, characterized in that: In step S4, the method for calculating the subtransient reactance parameters under the condition of the rotor initial position according to the relevant parameters, the back electromotive force amplitude and the synchronous reactance is: ； in represents the subtransient reactance, represents the back electromotive force amplitude, represents the synchronous reactance, Indicates the 1st harmonic amplitude of the short-circuit current waveform difference.

8. The method for estimating subtransient reactance of a surface-mounted permanent magnet motor based on finite element method according to claim 1, characterized in that: In step S5, the range of the rotor initial position is changed to 0 - 180°, and the step size is changed to a preset value.

9. A system for estimating subtransient reactance of a surface-mounted permanent magnet motor based on finite element method, characterized in that: The system is used to implement the method for estimating the subtransient reactance of a surface-mounted permanent magnet motor based on the finite element method as described in any one of claims 1 to 8, specifically comprising: A model building and parameter acquisition module, used to build a finite element model of a surface-mounted permanent magnet wind turbine, set the rotor angular frequency in the finite element model to a specific value, and calculate the back electromotive force amplitude and synchronous reactance of the finite element model under specific working conditions; A short-circuit current calculation module, used to perform at least two different sets of parameter settings on the finite element calculation model, each set of parameter settings puts the winding circuit in a three-phase short-circuit state, and calculates the three-phase short-circuit current waveform within an electrical cycle, wherein each set of parameter settings includes a stator winding resistance setting, a rotor core and permanent magnet conductivity setting, and a rotor initial position setting; The current waveform processing module is used to select the short-circuit current waveform of a specific phase for difference calculation based on the three-phase short-circuit current waveforms obtained under different sets of parameter settings, and obtain the difference of the short-circuit current waveform of the specific phase under different sets of parameter settings; A spectrum analysis and reactance calculation module, used to perform spectrum analysis on the short-circuit current waveform difference, determine relevant parameters of specific spectrum components, and calculate subtransient reactance parameters under the rotor initial position condition based on the relevant parameters, back electromotive force amplitude and synchronous reactance; The average calculation module is used to return to the short-circuit current calculation module and change the initial position of the rotor to obtain subtransient reactance parameters under multiple initial positions of the rotor, and calculate the average value thereof as the final subtransient reactance parameter.

10. The system for estimating subtransient reactance of a surface-mounted permanent magnet motor based on finite element method according to claim 9, characterized in that: The short-circuit current calculation module comprises: A first short-circuit current calculation unit is used to calculate a three-phase short-circuit current waveform when the stator winding resistance is a specific value, the rotor core and the permanent magnet conductivity are specific values ​​representing no rotor eddy current effect, and the rotor initial position is a specific value; The second short-circuit current calculation unit is used to calculate the three-phase short-circuit current waveform when the stator winding resistance is the same specific value, the rotor core and the permanent magnet conductivity are specific values ​​representing the actual or approximately actual rotor eddy current effect, and the rotor initial position is the same specific value.

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