A Modeling Method for the Electromechanical Coupling Characteristics of an Electric Drive Fracturing System

Abstract

The present invention discloses a modeling method for the electromechanical coupling characteristics of an electric-driven fracturing system, which relates to the field of electromechanical coupling modeling. First, the present invention uses a multi-level method to structurally divide the electric-driven fracturing system, divides the system into several independent subsystems according to the composition and functional characteristics of the system, and determines the vibration type studied by the system. Then, each subsystem is simplified and the simplified model is modeled to obtain the finite element and mathematical model of each subsystem, calculate the dynamic parameters of the shaft system, and then select the coupling method according to the relationship between the basic units to establish the system shaft system vibration model. Finally, the model is solved and the electromechanical coupling characteristics of the system are obtained, thereby establishing a modeling method for the electromechanical coupling characteristics of an electric-driven fracturing system. The present invention uses a multi-level method as a means and aims to establish a model that takes into account the mutual influence between the driving end and the load end of the electric-driven fracturing system, effectively solving the problem of accurate and rapid modeling of the electromechanical coupling of the electric-driven fracturing system.

Description

Technical Field

[0001] The present invention relates to the field of electromechanical coupling modeling, specifically to an electromechanical coupling characteristic modeling method that can consider the mutual influence between the driving end and the load end of an electric-driven fracturing system under electromechanical coupling, and study the free vibration and forced vibration characteristics of the shaft system of the electric-driven fracturing system, as well as the performance changes of the motor and fracturing pump. Background Art

[0002] Since the turn of the century, humanity has faced increasingly severe energy challenges. Developing traditional energy sources and acquiring new energy sources have become key solutions. In-depth research into fracturing, a key technology for developing shale gas in deep geological formations, is becoming increasingly necessary. Electric fracturing technology has gained significant attention, offering superior environmental performance and vibration and noise control compared to traditional diesel engine-driven technology.

[0003] Electric motor-driven fracturing systems often connect the drive and load ends of the system through an intermediate connecting component, forming a single unit. However, conventional research methods separate the drive and load ends of the system, preventing them from interfering with each other. This fails to consider the overall integrity of the system and makes it impossible to study the vibration of the connecting shafts. In reality, the drive and load ends of an electric fracturing system interact during operation, simultaneously affecting the intermediate shafting, causing torsional and longitudinal and lateral vibrations, exacerbating system vibration and noise. Furthermore, many research methods fail to examine the inherent vibration characteristics of electric fracturing systems.

[0004] Conventional modeling and research methods fail to investigate the characteristics of the drive-end motor and the vibration characteristics of the intermediate shaft system in an electromechanically coupled electric fracturing system. This results in insufficient in-depth research, an inability to study the system's operational characteristics under fault conditions, and an inability to ensure safe system operation. The electromechanically coupled modeling method disclosed in this invention fully considers the interactions between the various system components, allowing for the study of the overall characteristics of the electric fracturing system. Summary of the Invention

[0005] In response to the problem of electromechanical coupling modeling of electric-driven fracturing systems, that is, it is impossible to consider the mutual influence between the driving end and the load end of the electric-driven fracturing system under electromechanical coupling, and it is impossible to study the free vibration and forced vibration characteristics of the connecting shaft system under electromechanical coupling. The present invention provides a modeling method for the electromechanical coupling characteristics of an electric-driven fracturing system, which can not only consider the mutual influence between the driving end and the load end of the electric-driven fracturing system, but also study the torsional and longitudinal and lateral vibrations of the connecting shaft system, making the research more in-depth and providing more methods for the overall characteristics of the electric-driven fracturing system under electromechanical coupling and subsequent system safety issues.

[0006] A method for modeling the electromechanical coupling characteristics of an electric-driven fracturing system is characterized by being able to consider the mutual influence between the drive end and the load end, studying the vibration of the system shaft system, and further studying the overall characteristics of the electric-driven fracturing system. The specific implementation process of the method is as follows:

[0007] Step 1: Divide the electric drive fracturing system into independent subsystems:

[0008] The electric-driven fracturing system structure is divided into three independent subsystems: the drive subsystem, the intermediate shaft subsystem, and the load subsystem, using a multi-level approach based on the structural and functional characteristics of the multiple drive sources between the system's components.

[0009] The drive subsystem mainly includes the rotor and output shaft of the drive motor, the intermediate shaft subsystem mainly includes the intermediate connecting shaft section and coupling, and the load subsystem mainly includes the fracturing pump, etc.

[0010] Step 2: Determine the vibration type for the electric drive fracturing system study:

[0011] The research on electric-driven fracturing systems should focus on two key components: the motor and the fracturing pump. The main research structure and the appropriate modeling method should be selected based on the project requirements and actual conditions.

[0012] At the same time, the vibration type of the shaft system is selected according to the actual situation and the vibration type that is most harmful to the system, including longitudinal and transverse vibration and torsional vibration;

[0013] After determining the focus and vibration type of the system research, it will facilitate subsequent modeling and improve calculation efficiency;

[0014] Step 3: Simplify and build models of each independent subsystem:

[0015] According to the research focus of electromechanical coupling characteristics and the vibration type, the drive, intermediate shaft system and load subsystem are simplified modeled as follows:

[0016] 1) Modeling the drive subsystem: In industrial sites, asynchronous motors are often used as drive motors. A more sophisticated finite element model is established for the asynchronous motor based on the following mathematical model. The stator and rotor flux equations of the asynchronous motor are:

[0017]

[0018] Where: s , ψ r is the stator and rotor flux matrix; L ss 、L rr is the stator and rotor self-inductance matrix; L sr 、Lrs is the mutual inductance matrix between the stator and rotor; I s , I r is the stator and rotor current matrix;

[0019] The voltage equation of an asynchronous motor is:

[0020]

[0021] Where: U s is the stator voltage matrix; R s 、R r is the stator and rotor resistance matrix;

[0022] The electromagnetic torque equation of the asynchronous motor is:

[0023]

[0024] Where: T e is the electromagnetic torque of the motor; p is the number of pole pairs;

[0025] The mechanical motion equation of an asynchronous motor is:

[0026]

[0027] Where: T L is the load torque; J is the rotor moment of inertia; ω r Motor rotor speed;

[0028] 2) Simplify the modeling of the load subsystem: Since the load subsystem is mainly composed of several crank-connecting rod mechanisms in the fracturing pump working together to perform fracturing, and the fracturing pump has a relatively complex structure;

[0029] First, the fracturing pump is simplified. According to the number of cylinders of the fracturing pump, the fracturing pump is simplified into a crankshaft with several crank-connecting rod mechanisms. In order to ensure uniform force on the crankshaft, the phase angles of two adjacent crank-connecting rod mechanisms differ by a certain angle.

[0030] The working process of the fracturing pump is divided into the fracturing fluid suction and fracturing fluid discharge process, and the force analysis of the crankshaft crank-connecting rod mechanism is carried out to obtain the connecting rod force P acting on the connecting rod in the working state. ij The connecting rod force mainly includes the friction force generated by the piston, the guide sleeve and the connection during the movement of the piston, the inertia force generated by the rotation of the crank and the reciprocating motion of the piston, and the force acting on the piston and then on the connecting rod during the discharge of the fracturing fluid. The connecting rod force P of the i-th connecting rod is ij satisfy:

[0031]

[0032] Where: f is the friction factor between the plunger and the guide sleeve; m is the mass of the connecting rod group; a is the acceleration of the plunger; p c is the force acting on the plunger during the fracturing fluid discharge process; φ, are the crank angle and the initial position angle of the crank respectively;

[0033] Calculate the torque M acting on the crankshaft using the connecting rod force i , M i satisfy:

[0034]

[0035] The total torque M acting on the crankshaft by all connecting rods z satisfy:

[0036]

[0037] 3) Each subsystem is simplified into an inertial concentrated mass disk and a virtual massless shaft joint to obtain the basic unit of the system: Based on the similarity principle of the real model and system dynamics, the material properties of each subsystem must be basically the same before and after simplification to ensure that the components of the subsystem have the same or similar free properties and dynamic characteristics before and after simplification; the geometry must be similar to ensure that the corresponding linear dimensions of the same component have the same proportional relationship; the motion of the components of the subsystem must also be similar before and after simplification to ensure that the displacements of all corresponding points before and after simplification have the same direction or the same proportional constant;

[0038] The driving end, intermediate shaft section, and load end are simplified into an inertial concentrated mass disk and a massless shaft joint in sequence. The inertial concentrated mass disk has rotational inertia and damping, and the shaft joint has torsional stiffness and damping. The calculation method for the rotational inertia and torsional stiffness of the components is:

[0039] The calculation of the moment of inertia includes the calculation of the moment of inertia of rotating parts and reciprocating parts;

[0040] The calculation of the moment of inertia of a rotating moving part is as follows:

[0041]

[0042] Where: m is the total mass of the rotating object; R is the radius of inertia;

[0043] The calculation of the moment of inertia of reciprocating motion parts is converted into rotational moment of inertia by the equivalent kinetic energy method. The calculation formula is as follows:

[0044]

[0045] Where: m1 and m2 are the masses of the plunger group and the connecting rod group; r is the crank radius; k is the rotation coefficient;

[0046] For the calculation of torsional stiffness, the calculation formula is as follows:

[0047]

[0048] Where: G is the shear modulus of the shaft end material; I p is the polar moment of inertia of the cross section of the shaft segment; L is the length of the shaft segment with equal cross section;

[0049] The above steps obtain the basic units of each component with kinetic parameters;

[0050] Step 4: Select the coupling method between subsystems:

[0051] According to the assembly, motion and force coupling relationship between the basic units, and by selecting appropriate intermediate transmission parameters including speed, torque, angular velocity and angular acceleration, the inertial concentrated mass disks and the massless shaft joints are combined into a whole. At the same time, the shaft system model of the overall system is modeled using the Lagrange equation. The longitudinal and transverse vibrations and torsional vibrations respectively satisfy:

[0052]

[0053]

[0054] Where: M is the mass matrix; J is the moment of inertia matrix; C is the damping matrix; K is the stiffness matrix; F is the external excitation force matrix; T is the external excitation torque matrix;

[0055] Step 5: Solve the model:

[0056] According to the above steps, the electromechanical coupling model of the electric drive fracturing system is obtained and the calculation is performed;

[0057] Select appropriate motor or fracturing pump performance parameters as system status monitoring signals. System status monitoring signals are usually selected at the motor end, which is easier to obtain and process. The system operating status can be quickly monitored through the system status monitoring signals.

[0058] Step 6: Obtain the electromechanical coupling characteristics of the electric drive fracturing system:

[0059] Based on the research content of the system, the electromechanical coupling performance of the electric drive fracturing system is obtained and analyzed;

[0060] Based on the obvious fracturing pump load or motor characteristics in the performance curve, or the changes in the corresponding frequency orders after fast Fourier decomposition, the observation method and Fourier decomposition method are used to verify the effectiveness of the electromechanical coupling model. Specifically:

[0061] First, run the system long enough to obtain stable operating results. Then observe the motor speed, torque, etc. or the total torque of the fracturing pump on the crankshaft or perform fast Fourier decomposition to determine whether the corresponding frequency orders are coupled with each other:

[0062] If they are coupled to each other, it means that this electromechanical coupling characteristic modeling method has achieved beneficial results;

[0063] If they are not coupled to each other, modify the inherent parameters of the system, change the coupling mode between the components, and re-model.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] 1. The electromechanical coupling model of the electric-driven fracturing system established in this invention can fully consider the mutual influence between the electric motor as the drive subsystem and the fracturing pump as the load subsystem under the specific working conditions of the fracturing system, thereby providing new ideas for studying the electromechanical coupling characteristics of the electric-driven fracturing system.

[0066] 2. The shafting model established using the method of the present invention can not only calculate the free vibration characteristics of the shafting of the electric-driven fracturing system, but also calculate the forced vibration characteristics of the shafting after adding excitation to the shafting, laying the foundation for the study of the shafting vibration between the motor and the fracturing pump.

[0067] 3. When establishing the model, mathematical modeling and finite element modeling of the motor end and the fracturing pump end are performed according to the research focus and actual situation, which can improve the efficiency of modeling and calculation and provide a new method for the accurate and rapid modeling of the electromechanical coupling model. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] To facilitate the explanation of the use of this method, the present invention takes a five-phase asynchronous motor driving a five-cylinder fracturing pump electromechanical coupling system and studies the torsional vibration of the shaft system as an example, and is described in detail by the following specific implementation and drawings.

[0069] Figure 1 Flowchart of the modeling method for the electromechanical coupling characteristics of the electric drive fracturing system;

[0070] Figure 2 This is a diagram of the multi-level structure division of the electric drive fracturing system;

[0071] Figure 3 It is the finite element model of five-phase asynchronous motor;

[0072] Figure 4 Simplified model of the fracturing pump crankshaft;

[0073] Figure 5 This is the shafting diagram of the electric drive fracturing system;

[0074] Figure 6 This is the simulink simulation model diagram of the shaft torsional vibration of the electric drive fracturing system;

[0075] Figure 7 This is the frequency domain decomposition diagram of the fracturing pump load torque;

[0076] Figure 8 This is a time domain comparison diagram of electromagnetic torque of the motor with constant load and fracturing pump load under electromechanical coupling;

[0077] Figure 9 This is the frequency domain decomposition diagram of the electromagnetic torque of the motor with constant load and fracturing pump load under electromechanical coupling;

[0078] Figure 10 This is a time domain comparison diagram of the A-phase stator current of the motor with constant load and fracturing pump load under electromechanical coupling;

[0079] Figure 11 The frequency domain decomposition diagram of the A-phase stator current of the motor with constant load and fracturing pump load under electromechanical coupling;

[0080] Figure 12 This is the torsional vibration curve of the system shaft system under electromechanical coupling;

[0081] Explanation of the accompanying numbers: 1 is the stator of a five-phase motor; 2 is the rotor of a five-phase motor; 3 is the crankshaft of a fracturing pump; 4 is the crank of a fracturing pump; 5 is the connecting rod of a fracturing pump; 6 is the plunger of a fracturing pump; 7 is the inertial concentrated mass disk in the shaft section diagram; 8 is the virtual massless elastic shaft section in the shaft section diagram. DETAILED DESCRIPTION

[0082] In order to make the purpose, technical solutions and effects of the present invention more clear, the method described in the present invention will be described in detail below through the specific implementation shown in the accompanying drawings, but it should be understood that these descriptions are exemplary and are not intended to limit the scope of the present invention.

[0083] Implementation Example 1:

[0084] according to Figure 1 The modeling process is completed as shown in the flow chart of the electromechanical coupling characteristics modeling method of the electric drive fracturing system:

[0085] Step 1: Divide the electric drive fracturing system into independent subsystems:

[0086] according to Figure 2 As shown in the figure, the structure of the electric-driven fracturing system is first divided. Using the multi-level method, according to the structure and functional characteristics of the multiple driving sources between the various components of the system, the electric-driven fracturing system is divided into three independent subsystems: the driving subsystem, the intermediate shafting subsystem, and the load subsystem.

[0087] The drive subsystem mainly includes the rotor and output shaft of the drive motor, the intermediate shaft subsystem mainly includes the intermediate connecting shaft section and coupling, and the load subsystem mainly includes the fracturing pump crankshaft;

[0088] Step 2: Determine the vibration type for the electric drive fracturing system study:

[0089] This example focuses on the five-phase asynchronous motor and establishes a finite element model with higher computational accuracy for the five-phase asynchronous motor. A five-cylinder fracturing pump is also mathematically modeled. In this example, the shafting torsional vibration has a greater impact on the system, so the shafting torsional vibration is selected as the vibration type for systematic research to improve the computational efficiency and accuracy of the system model.

[0090] Step 3: Simplify and build models of each independent subsystem:

[0091] 1) Model the drive subsystem. Figure 3 This is the established finite element model of the five-phase motor.

[0092] 2) Simplify the load subsystem model. The five-cylinder fracturing pump is simplified into a crankshaft with five crank-connecting rod mechanisms with phase angles of 144°. Each crank-connecting rod mechanism is as follows: Figure 4 shown.

[0093] The fracturing pump has two working states during operation. The first working state is the fracturing fluid suction process, and the second working state is the fracturing fluid discharge process. The torque acting on the crankshaft during the fracturing fluid suction and discharge processes is different. The torque acting on the crankshaft of the i-th crank-connecting rod mechanism is

[0094]

[0095] Where: P i is the connecting rod force during the process of sucking and discharging fracturing fluid; φ is the crank angle; β is the connecting rod swing angle.

[0096] The total torque M acting on the crankshaft z for

[0097]

[0098] 3) Each subsystem is simplified into a virtual massless shaft and an inertial concentrated mass disk. Based on the system dynamics relationship between the components of the system, and in accordance with the above-mentioned simplification principles of basically identical material properties, similar geometry, and similar motion, each subsystem is simplified into a virtual massless shaft and an inertial concentrated mass disk to obtain the basic unit of each independent subsystem, and the dynamic parameters such as the moment of inertia and torsional stiffness of each basic unit are calculated according to the above-mentioned calculation method. The shaft diagram established is as follows: Figure 5 As shown;

[0099] Step 4: Select the coupling method between subsystems:

[0100] According to the assembly, motion and force coupling relationship between each unit, and the electromagnetic torque and speed output by the motor are selected as the intermediate transmission parameters, the torsional vibration differential equation of each concentrated mass disk and virtual massless shaft is listed according to the Lagrange equation to meet the following requirements:

[0101]

[0102] Step 5: Solve the model:

[0103] The drive subsystem, intermediate shaft subsystem and load subsystem models and their vibration models established in steps 3 and 4 are established using simulink software as follows: Figure 6 The simulation model shown.

[0104] Step 6: Obtain the electromechanical coupling characteristics of the electric drive fracturing system:

[0105] The fluctuation of the motor performance curve and the shaft vibration curve is analyzed. First, the load torque of the fracturing pump at the rated speed of the motor is decomposed by Fourier, as shown in the following figure: Figure 7 After the fast Fourier decomposition of the fracturing pump load torque, the main frequencies are 16.248Hz, 32.504Hz, 48.752Hz and 65Hz, and the amplitudes of the other harmonics are relatively small. Since the focus of the system research is the motor, the performance curve of the motor is analyzed. In order to highlight the comparison, the motor performance curves with fracturing pump load and constant load are drawn respectively. Figure 8 The figure shows the electromagnetic torque curve of the motor. It can be seen from the figure that after the system stabilizes, the electromagnetic torque waveform of the motor with fracturing pump load clearly has the characteristics of fracturing pump load, and the torque pulsation is significantly greater than that of the motor with constant load. Figure 9 The figure shows the fast Fourier decomposition frequency domain diagram of the electromagnetic torque of the motor with two loads. Compared with the electromagnetic torque with a constant load, the 16.248Hz and 32.504Hz frequencies change significantly, and this frequency is the main frequency of the fracturing pump load. Similarly, Figure 10 and 11 The time and frequency domain distributions of the motor's stator current with two loads are shown. After the motor stabilizes, the amplitude of the stator current with the fracturing pump load fluctuates with the fracturing pump load. Fourier decomposition reveals significant changes in the amplitude of the 32.504 Hz and 65 Hz harmonics of the fracturing pump load frequency compared to the stator current with a constant load.

[0106] like Figure 12The figure shows the angular displacement vibration curve of the shaft system in an electrically driven fracturing system under electromechanical coupling. The torsional vibration of the shaft system is solely dependent on the inherent properties of the system and external excitation. When the external excitation torque generated by the motor and fracturing pump is applied to the shaft system, each shaft segment experiences torsional vibration, which fluctuates periodically over time.

[0107] The above analysis verifies the beneficial effects of the electromechanical coupling model of the electric-driven fracturing system established in the present invention. The present invention fully considers the overall characteristics of the electric-driven fracturing system and, on this basis, makes the motor output performance and shaft vibration closer to the actual situation.

[0108] The above examples describe the basic logic and operating ideas of the patent of the present invention, but technicians in this industry should understand that the patent of the present invention is not limited by the above examples. The above examples and descriptions only illustrate the logic and ideas of the patent. Without departing from the spirit and scope of the patent of the present invention, the patent of the present invention will also have various changes and improvements, and these changes and improvements will fall within the scope of the patent of the present invention to be protected.

Claims

1. A modeling method for the electromechanical coupling characteristics of an electric-driven fracturing system, characterized by: The electromechanical coupling characteristic modeling method can consider the mutual influence between the drive end and the load end, can study the system shaft vibration, and then study the overall characteristics of the electric drive fracturing system. The specific implementation process of the method is as follows: Step 1: Divide the electric drive fracturing system into independent subsystems: The electric-driven fracturing system structure is divided into three independent subsystems: the drive subsystem, the intermediate shaft subsystem, and the load subsystem, using a multi-level approach based on the structural and functional characteristics of the multiple drive sources between the system's components. The drive subsystem mainly includes the rotor and output shaft of the drive motor, the intermediate shaft subsystem mainly includes the intermediate connecting shaft section and coupling, and the load subsystem mainly includes the fracturing pump; Step 2: Determine the vibration type for the electric drive fracturing system study: The research on electric-driven fracturing systems should focus on two key components: the motor and the fracturing pump. The main research structure and the appropriate modeling method should be selected based on the project requirements and actual conditions. At the same time, the vibration type of the shaft system is selected according to the vibration type that is most harmful to the system in actual conditions, including longitudinal and transverse vibrations and torsional vibrations; The focus and vibration type of the system research were determined, facilitating the subsequent selection of appropriate modeling methods to improve computational efficiency; Step 3: Simplify and build models of each independent subsystem: According to the focus of the electromechanical coupling characteristics research and the actual situation, the drive, intermediate shaft system and load subsystem are simplified modeled as follows: 1) Modeling the drive subsystem: In industrial sites, asynchronous motors are often used as drive motors. A more sophisticated finite element model is established for the asynchronous motor based on the following mathematical model. The stator and rotor flux equations of the asynchronous motor are: Where: s , ψ r is the stator and rotor flux matrix; L ss , L rr is the stator and rotor self-inductance matrix; L sr , L rs is the mutual inductance matrix between the stator and rotor; I s , I r is the stator and rotor current matrix; The voltage equation of an asynchronous motor is: Where: U s is the stator voltage matrix; R s 、R r is the stator and rotor resistance matrix; The electromagnetic torque equation of the asynchronous motor is: Where: T e is the electromagnetic torque of the motor; p is the number of pole pairs; The mechanical motion equation of an asynchronous motor is: Where: T L is the load torque; J is the rotor moment of inertia; ω r Motor rotor speed; 2) Simplify the modeling of the load subsystem: Since the load subsystem is mainly composed of several crank-connecting rod mechanisms in the fracturing pump working together to perform fracturing, and the fracturing pump has a relatively complex structure; First, the fracturing pump is simplified. According to the number of cylinders of the fracturing pump, the fracturing pump is simplified into a crankshaft with several crank-connecting rod mechanisms. In order to ensure uniform force on the crankshaft, the phase angles of two adjacent crank-connecting rod mechanisms differ by a certain angle. The working process of the fracturing pump is divided into the fracturing fluid suction and fracturing fluid discharge process, and the force analysis of the crankshaft crank-connecting rod mechanism is carried out to obtain the connecting rod force P acting on the connecting rod in the working state. ij The connecting rod force mainly includes the friction force generated by the piston, the guide sleeve and the connection during the movement of the piston, the inertia force generated by the connecting rod as the crank rotates and the piston reciprocates, and the force acting on the piston and then on the connecting rod during the discharge of the fracturing fluid. The connecting rod force P of the i-th connecting rod is ij satisfy: Where: f is the friction factor between the plunger and the guide sleeve; m is the mass of the connecting rod group; a is the acceleration of the plunger; p c It is the force acting on the plunger during the fracturing fluid discharge process; φ, are the rotation angle of the crank and the initial position angle of the crank respectively; Calculate the torque M acting on the crankshaft using the connecting rod force i , M i satisfy: The total torque M acting on the crankshaft by all connecting rods z satisfy: 3) Each subsystem is simplified into an inertial concentrated mass disk and a virtual massless shaft joint to obtain the basic unit of the system: Based on the similarity principle of the real model and system dynamics, the material properties of each subsystem must be basically the same before and after simplification to ensure that the components of the subsystem have the same or similar inherent properties and dynamic characteristics before and after simplification; the geometry must be similar to ensure that the corresponding linear dimensions of the same component have the same proportional relationship; the motion of the components of the subsystem must also be similar before and after simplification to ensure that the displacements of all corresponding points before and after simplification have the same direction or the same proportional constant; The driving end, intermediate shaft section, and load end are simplified into an inertial concentrated mass disk and a massless shaft joint in sequence. The inertial concentrated mass disk has rotational inertia and damping, and the shaft joint has torsional stiffness and damping. The calculation method for the rotational inertia and torsional stiffness of the components is: The calculation of the moment of inertia includes the calculation of the moment of inertia of rotating parts and reciprocating parts; The calculation of the moment of inertia of a rotating moving part is as follows: Where: m is the total mass of the rotating object; R is the radius of inertia; The calculation of the moment of inertia of reciprocating motion parts is converted into rotational moment of inertia by the equivalent kinetic energy method. The calculation formula is as follows: Where: m1 and m2 are the masses of the plunger group and the connecting rod group; r is the crank radius; k is the rotation coefficient; For the calculation of torsional stiffness, the calculation formula is as follows: Where: G is the shear modulus of the shaft end material; I p is the polar moment of inertia of the cross section of the shaft segment; L is the length of the shaft segment with equal cross section; The above steps obtain the basic units of each component with kinetic parameters; Step 4: Select the coupling method between subsystems: According to the assembly, motion and force coupling relationship between each basic unit, and the selection of appropriate intermediate transmission parameters including speed, torque, angular velocity and angular acceleration, each inertial concentrated mass disk and massless shaft joint are combined into a whole. At the same time, the shaft system model of the overall system is modeled using the Lagrange equation. The longitudinal and transverse vibrations and torsional vibrations respectively meet the following requirements: Where: M is the mass matrix, J is the moment of inertia matrix, C is the damping matrix, K is the stiffness matrix, F is the external excitation force matrix, and T is the external excitation torque matrix; Step 5: Solve the model: According to the above steps, the electromechanical coupling model of the electric drive fracturing system is obtained and the calculation is performed; Select appropriate motor or fracturing pump performance parameters as system status monitoring signals. System status monitoring signals are usually selected from the motor end, which is easier to obtain and process. The system operating status can be quickly monitored through the system status monitoring signals. Step 6: Obtain the electromechanical coupling characteristics of the electric drive fracturing system: Based on the research content of the system, the electromechanical coupling performance of the electric drive fracturing system is obtained and analyzed; Based on the obvious fracturing pump load or motor characteristics in the performance curve, or the changes in the corresponding frequency orders after fast Fourier decomposition, the observation method and Fourier decomposition method are used to verify the effectiveness of the electromechanical coupling model. Specifically: First, run the system long enough to obtain stable operating results. Then observe the motor speed and torque or the total torque of the fracturing pump on the crankshaft or perform fast Fourier decomposition to determine whether the corresponding frequency orders are coupled with each other: If they are coupled to each other, it means that this electromechanical coupling characteristic modeling method has achieved beneficial results; If they are not coupled to each other, modify the inherent parameters of the system, change the coupling mode between the components, and re-model.

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