Method for transient stability analysis of a parallel power supply system of a synchronous machine-grid type MMC

Abstract

The application discloses a kind of for synchronous machine-structure network type MMC parallel power supply system transient stability analysis method, this method includes: based on synchronous machine-structure network type MMC parallel power supply system, establish the transient stability analysis model after system fault;According to the transient stability analysis model, the power angle of synchronous machine at stable equilibrium point, unstable equilibrium point of synchronous machine-structure network type MMC parallel power supply system is obtained, and the critical cut angle of system is calculated;The critical cut time of system is calculated using the critical cut angle of system as the evaluation index of system transient stability.This application can accurately and quantitatively evaluate the transient stability of system by using the critical cut time of system as the evaluation index, and has good robustness for various working conditions, and has guiding significance for the time setting of relay protection device.

Description

Technical Field

[0001] This application relates to the field of power system transmission and distribution technology, and in particular to a transient stability analysis method for synchronous machine-structured grid-type MMC parallel power supply systems. Background Technology

[0002] With the rapid development of power electronic devices, flexible DC transmission (VSC-HVDC) technology based on voltage source converters has been widely applied. Among them, the modular multilevel converter (MMC) has become the preferred voltage source converter for large-scale renewable energy base grid connection due to its advantages such as lower harmonic components and the elimination of the need for power device series connection technology. At the same time, as an important asynchronous power source, MMC-HVDC can replace synchronous power sources in future power systems to supply power to the system.

[0003] When used as a asynchronous power source, MMCs primarily employ two typical control strategies: grid-connected and grid-connected. Grid-connected MMCs typically use current vector control, with the outer loop controller achieving decoupled control of active and reactive power. The active power control loop usually maintains a constant active power, while the reactive power loop can use a constant reactive power / AC voltage control strategy. A phase-locked loop (PLL) is used to track the grid connection point voltage, achieving synchronization with the active power grid. The core idea of ​​grid-connected MMCs is to control the amplitude and phase of the grid connection point voltage, which can simulate the inertia and damping characteristics of a generator, offering unique advantages when supplying power to passive networks. However, current research on the transient stability analysis of grid-connected MMCs and synchronous machines connected in parallel to supply power to loads is limited. Therefore, it is difficult to quantitatively measure the system's transient stability and stability mechanism, and also difficult to provide a reference for the timing setting of system relay protection devices. Summary of the Invention

[0004] The purpose of this application is to provide a transient stability analysis method for synchronous machine-structured grid-type MMC parallel power supply systems, in order to solve the problem that existing technologies are unable to quantitatively measure the transient stability and stability mechanism of the system, and at the same time cannot provide objective guidance for the time setting of the system's relay protection devices.

[0005] To achieve the above objectives, this application provides a transient stability analysis method for a synchronous machine-structured MMC parallel power supply system, comprising:

[0006] Based on the synchronous machine-structure network type MMC parallel power supply system, a transient stability analytical model is established after system failure.

[0007] Based on the transient stability analytical model, the power angle of the synchronous machine at the stable equilibrium point and the unstable equilibrium point of the synchronous machine-network type MMC parallel power supply system is obtained, and the critical cut-off angle of the system is calculated.

[0008] The critical cut-off time of the system is calculated using the critical cut-off angle of the system, and is used as an evaluation index for the transient stability of the system.

[0009] Furthermore, the establishment of the transient stability analytical analysis model after a system failure includes:

[0010] For the synchronous machine-grid type MMC parallel power supply system after a fault, the grid-type MMC converter with a control strategy of constant AC voltage amplitude and frequency is modeled using a voltage source, and the grid-type MMC converter with a control strategy of constant AC voltage amplitude and frequency is modeled using a current source.

[0011] Furthermore, the grid-type MMC converter employing a control strategy with constant AC voltage amplitude and frequency is modeled equivalently using a voltage source, including:

[0012] The electromagnetic power P of the synchronous machine in a grid-type MMC parallel power supply system after a fault is determined. pos for:

[0013]

[0014] In the formula, the grid connection point voltage command value of the grid-connected MMC is E. ref The internal potential of the synchronous machine is E q The synchronous machine's power angle is δ. g The equivalent ground branch conductances of the synchronous machine node and the network-type MMC are G, respectively. 12p G 13p The mutual admittance amplitude between the synchronous machine and the network-type MMC is Y. 12p The phase angle is

[0015] Furthermore, the grid-type MMC converter employing a control strategy with constant AC voltage amplitude and frequency is modeled equivalently using a current source, including:

[0016] Determine the injected current vector I of the network-type MMC during the fault. sfau for:

[0017]

[0018] In the formula, I max This is the current limit value for the MMC. The phase setting value for the injection current of the MMC, where j is a complex unit;

[0019] Then the grid connection point voltage vector U of MMC s for:

[0020]

[0021] In the formula, Y 12f Y 13f Y 23f These represent the mutual admittance between the synchronous machine and the network-type MMC during the fault, the ground branch admittance of the synchronous machine, and the ground branch admittance of the network-type MMC, respectively.

[0022] Let the intermediate admittance term Y g1 Y g2 They are respectively:

[0023]

[0024] In the formula, G g1 B g1 Y g1 The conductivity and susceptance of Y g2 , Y g2 The amplitude and phase angle;

[0025] Then the injection current I of the synchronous machine g for:

[0026] I g =Y g1 E q ′-Y g2 I sfau ;

[0027] According to the internal potential vector E of the synchronous machine q 'and injection current I g The electromagnetic power P of the system synchronizer during the fault was obtained. fau for:

[0028]

[0029] Furthermore, obtaining the power angle of the synchronous machine at the stable equilibrium point and the unstable equilibrium point of the synchronous machine-structured MMC parallel power supply system, and calculating the critical cutoff angle of the system, includes:

[0030] Based on the power flow calculation results, the mechanical power P of the prime mover is obtained. m If the mechanical power of the prime mover is equal to the steady-state output electromagnetic power of the synchronizer, then the power angle δ of the synchronizer at the system's stable equilibrium point and unstable equilibrium point is... s and δ u They are respectively:

[0031]

[0032] Furthermore, the critical cut-off angle of the calculation system includes:

[0033] Using the equal area rule, when the critical cut-off angle δ of the system... CCA To ensure that the acceleration area equals the deceleration area, the fault clearing angle of the synchronous machine satisfies the following equation:

[0034]

[0035] Solving the equation yields the critical cut-off angle δ of the system. CCA The value of .

[0036] Furthermore, the calculation of the critical resection time of the system using the critical resection angle of the system includes:

[0037] The rotor motion equations of the synchronous machine at the time of the fault are determined to be a system of differential equations:

[0038]

[0039] In the formula, ω g This indicates the rotor speed of the synchronous machine, ω0 is the rated angular frequency of the system, and T J Let be the generator's inertial constant;

[0040] The system of differential equations is solved using the Euler method:

[0041]

[0042] In the formula, t is time, and Δt is the integration time step;

[0043] Then the critical resection time t of the system c The following criteria must be met:

[0044] δ g (t c )≤δ CCA ≤δ g (t c +Δt);

[0045] The synchronous machine power angle δ is saved at each moment during the calculation process. g and rotor angular frequency ω g The critical resection time of the system is obtained based on the value of the criterion.

[0046] This application also provides a transient stability analysis system for a synchronous machine-structured MMC parallel power supply system, comprising:

[0047] The model building unit is used to establish a transient stability analytical analysis model after a system fault based on a synchronous machine-structure network type MMC parallel power supply system.

[0048] The critical cut-off angle determination unit is used to obtain the power angle of the synchronous machine at the stable equilibrium point and the unstable equilibrium point of the synchronous machine-grid type MMC parallel power supply system according to the transient stability analytical analysis model, and to calculate the critical cut-off angle of the system.

[0049] The critical cut-off time determination unit is used to calculate the critical cut-off time of the system using the critical cut-off angle of the system, as an evaluation index of the system's transient stability.

[0050] This application also provides a terminal device, including:

[0051] One or more processors;

[0052] A memory, coupled to the processor, for storing one or more programs;

[0053] When the one or more programs are executed by the one or more processors, the one or more processors implement the transient stability analysis method for synchronous machine-structured MMC parallel power supply systems as described in any of the preceding claims.

[0054] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the transient stability analysis method for a synchronous machine-structured MMC parallel power supply system as described in any of the preceding claims.

[0055] Compared to existing technologies, the advantages of this application are as follows:

[0056] 1) This application is applied to the transient stability analysis and evaluation of a synchronous machine-network type MMC parallel power supply system. After the fault, the MMC in the system is modeled with a voltage source, and during the fault, the MMC in the system is modeled with a current source, which can accurately reflect the operating characteristics of the system.

[0057] 2) This application proposes an overall framework for the analytical calculation of transient stability of synchronous machine-structured grid-type MMC parallel power supply systems, and proposes analytical calculation methods for the critical cut-off angle and critical cut-off time of the system, which can provide a theoretical basis for the quantitative assessment of the transient stability of power systems.

[0058] 3) The analytical solution obtained by the transient stability analytical calculation method proposed in this application can quantitatively evaluate the transient stability of the system with high accuracy, thus providing a reference for the time setting of relay protection devices, which is of great significance in practical engineering.

[0059] 4) The transient stability analytical calculation method proposed in this application has good robustness to various operating conditions, and therefore can be used for the transient stability mechanism analysis of the system, and can serve as the theoretical basis for the transient stability analysis of synchronous mechanism-grid type MMC parallel power supply system. Attached Figure Description

[0060] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0061] Figure 1 This is a flowchart illustrating a transient stability analysis method for a synchronous machine-structured network (MMC) parallel power supply system according to a certain embodiment of this application.

[0062] Figure 2 This is a schematic diagram of the topology of a synchronous mechanism-structure network-type MMC parallel power supply system provided in one embodiment of this application;

[0063] Figure 3 A comparison of transient stability analytical calculation results and time-domain simulation results when the phase of the injected current in a mesh-type MMC is changed, according to a certain embodiment of this application;

[0064] Figure 4 A comparison diagram of transient stability analytical calculation results and time-domain simulation results when the fault location is changed, provided for a certain embodiment of this application;

[0065] Figure 5 A comparison diagram of transient stability analytical calculation results and time-domain simulation results when the load power supply ratio is changed, provided for a certain embodiment of this application;

[0066] Figure 6 This is a schematic diagram of the transient stability analysis system for a synchronous machine-structured grid-type MMC parallel power supply system provided in a certain embodiment of this application;

[0067] Figure 7 This is a schematic diagram of the structure of a terminal device provided in a certain embodiment of this application. Detailed Implementation

[0068] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0069] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0070] It should be understood that the terminology used in this application specification is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this application specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0071] The terms “comprising” and “including” indicate the presence of the described feature, whole, step, operation, element and / or component, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0072] The term “and / or” refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes these combinations.

[0073] Please see Figure 1 This application provides a method for transient stability analysis of a synchronous machine-structured network (MMC) parallel power supply system, according to one embodiment. Figure 1 As shown, the transient stability analysis method for a synchronous machine-structured network (MMC) parallel power supply system includes steps S10 to S30. The specific steps are as follows:

[0074] S10. Based on the synchronous machine-structure network type MMC parallel power supply system, establish a transient stability analytical analysis model after system failure.

[0075] In one specific implementation, for a synchronous mechanism-structure network type MMC parallel power supply system after a fault, the construction of a transient stability analytical analysis model specifically includes the following two parts:

[0076] 1) Equivalent modeling of a grid-type MMC converter employing a constant AC voltage amplitude and frequency control strategy using a voltage source:

[0077] For the post-fault system, let the grid connection point voltage command value of the grid-type MMC be E. ref The internal potential of the synchronous machine is E q The synchronous machine's power angle is δ. g The equivalent ground branch conductances of the synchronous machine node and the network-type MMC are G, respectively. 12p G 13p The mutual admittance amplitude between the synchronous machine and the network-type MMC is Y. 12p The phase angle is Then the electromagnetic power P of the system synchronizer after the fault pos The format is:

[0078]

[0079] 2) Equivalent modeling of grid-type MMC converters employing a constant AC voltage amplitude and frequency control strategy using current sources:

[0080] Determine the injected current vector I of the network-type MMC during the fault. sfau for:

[0081]

[0082] In the formula, I max This is the current limit value for the MMC. The phase setting value for the injection current of the MMC, where j is a complex unit;

[0083] Then the grid connection point voltage vector U of MMC s for:

[0084]

[0085] In the formula, Y 12f Y 13f Y 23f These represent the mutual admittance between the synchronous machine and the network-type MMC during the fault, the ground branch admittance of the synchronous machine, and the ground branch admittance of the network-type MMC, respectively.

[0086] Let the intermediate admittance term Y g1 Y g2 They are respectively:

[0087]

[0088] In the formula, G g1 B g1 Y g1 The conductivity and susceptance of Y g2 , Y g2 The amplitude and phase angle;

[0089] Then the injection current I of the synchronous machine g for:

[0090] I g =Y g1 E q ′-Y g2 I sfau ;

[0091] According to the internal potential vector E of the synchronous machine q 'and injection current I g The electromagnetic power P of the system synchronizer during the fault was obtained. fau for:

[0092]

[0093] S20. Based on the transient stability analytical analysis model, obtain the stable equilibrium point and the power angle of the synchronous machine at the unstable equilibrium point of the synchronous machine-network type MMC parallel power supply system, and calculate the critical cut-off angle of the system.

[0094] In this step, based on the model obtained in step S10, the critical cut-off angle of the system is further calculated.

[0095] Specifically, based on the power flow calculation results, the mechanical power P of the prime mover is obtained. m If the mechanical power of the prime mover is equal to the steady-state output electromagnetic power of the synchronizer, then the power angle δ of the synchronizer at the system's stable equilibrium point and unstable equilibrium point is... s and δ u They are respectively:

[0096]

[0097] According to the equal area rule, when the critical cut-off angle δ of the system... CCA To ensure that the acceleration area equals the deceleration area, the fault clearing angle of the synchronous machine satisfies the following equation:

[0098]

[0099] Solving the equation yields the critical cut-off angle δ of the system. CCA The value of .

[0100] S30. Calculate the critical cut-off time of the system using the critical cut-off angle of the system, and use it as an evaluation index for the transient stability of the system.

[0101] In this step, the rotor motion equations of the synchronous machine at the time of the fault are first determined to be a system of differential equations:

[0102]

[0103] In the formula, ω g This indicates the rotor speed of the synchronous machine, ω0 is the rated angular frequency of the system, and T J Let be the generator's inertial constant;

[0104] The system of differential equations is solved using the Euler method:

[0105]

[0106] In the formula, t is time, and Δt is the integration time step;

[0107] Then the critical resection time t of the system c The following criteria must be met:

[0108] δ g (t c )≤δCCA ≤δ g (t c +Δt);

[0109] The synchronous machine power angle δ is saved at each moment during the calculation process. g and rotor angular frequency ω g The critical resection time of the system is obtained based on the value of the criterion.

[0110] In summary, the transient stability analysis method for synchronous machine-structured grid-type MMC parallel power supply systems provided in this application can accurately and quantitatively evaluate the transient stability of the system by using the critical disconnection time of the system as the evaluation index. It also has good robustness under various operating conditions and provides guidance for the time setting of relay protection devices.

[0111] To aid understanding, in one specific embodiment, a synchronous mechanism-network type MMC parallel power supply system topology is provided, such as... Figure 2 As shown in the diagram. The synchronous machine and the grid-type MMC are connected to the load nodes via lines 1 and 2, respectively, to supply power to the load. The MMC has a transmission capacity of 600MW. The synchronous machine has a transmission capacity of 200MW, and the load's rated power is 800MW.

[0112] Furthermore, the specific parameters of the system's main circuit are shown in Table 1:

[0113] Table 1

[0114]

[0115]

[0116] for Figure 2 The system shown has a fault location set at line 1, with a distance m = 0.5 from the synchronous machine side node. During the fault, the injection current phase of the MMC is set to... The electromagnetic power P of the system synchronizer after the fault, calculated in step 1. pos The expression is:

[0117] P pos =0.0064-0.8953cos(δ) g +1.6427);

[0118] The electromagnetic power P of the system synchronizer during the fault period calculated in step 2 is obtained. fau The expression is:

[0119] P fau =0.002-0.0537cos(δ) g -4.6);

[0120] According to step 3, the electromagnetic power P of the synchronizer before the fault... m Since the value is 0.1798, the power angle δ of the synchronizer at the stable equilibrium point and the unstable equilibrium point can be calculated. s and δ u They are respectively:

[0121] δ s =0.1229,δ u =2.8748;

[0122] According to the equal area rule, the analytical solution for the critical resection angle can be obtained as δ. CCA =2.0585.

[0123] Based on step 4, an analytical solution for the critical fault clearing time can be obtained. Furthermore, the critical clearing time obtained through electromagnetic transient simulation and its error are shown in Table 2 below:

[0124] Table 2

[0125]

[0126] Considering the fault location m = 0.5, at the system's initial operating point, the current injection phase is changed in four quadrants at intervals of 0.2 pu. The analytical calculation and time-domain simulation results of the critical clearing time are as follows: Figure 3 As shown.

[0127] Maintain the phase of the injected current during the fault Without changing the distance m between the fault point and the synchronizing machine-side node at the system's initial operating point, the analytical calculation and time-domain simulation results of the critical clearing time are as follows: Figure 4 As shown.

[0128] Maintain the phase of the injected current during the fault With the fault location m = 0.5 and the load power unchanged, the active power output of the synchronous motor is varied, corresponding to the output power of the generator and MMC and their ratio K under five different operating conditions. p Table 3 below shows the analytical calculation and time-domain simulation results of the critical resection time under these five operating conditions. Figure 5 As shown.

[0129] Table 3

[0130]

[0131] As shown in the table above, the analytical solution for the critical clearing time obtained by the transient stability analytical calculation method proposed in this application can accurately reflect the transient stability of the system, with an error within 10%. This is because the transient stability analytical model of this application treats the network-type MMC as an equivalent current source during the fault period, and simulates it using voltage source characteristics after the fault is cleared. The transient stability analytical calculation method proposed in this application has good robustness. Even when the MMC current injection phase changes, the fault location changes, and the proportion of synchronous machine and load power supply changes during the fault period, the analytical solution for the critical clearing time obtained by the transient stability analytical calculation method proposed in this application can reflect the changing trend of the transient stability characteristics of the system when the above factors change, and has strong applicability to various operating conditions.

[0132] Please see Figure 6 One embodiment of this application also provides a transient stability analysis system for a synchronous machine-structured network-type MMC parallel power supply system, comprising:

[0133] Model building unit 01 is used to establish a transient stability analytical analysis model after a system fault in a synchronous machine-structure network type MMC parallel power supply system.

[0134] The critical cut-off angle determination unit 02 is used to obtain the power angle of the synchronous machine at the stable equilibrium point and the unstable equilibrium point of the synchronous machine-grid type MMC parallel power supply system according to the transient stability analytical analysis model, and to calculate the critical cut-off angle of the system.

[0135] The critical resection time determination unit 03 is used to calculate the critical resection time of the system using the critical resection angle of the system, as an evaluation index of the transient stability of the system.

[0136] It is understood that the transient stability analysis system for synchronous mechanical network type MMC parallel power supply system provided in this embodiment is used to execute the transient stability analysis method for synchronous mechanical network type MMC parallel power supply system as described in any of the above embodiments, and achieve the same effect, which will not be further elaborated here.

[0137] Please see Figure 7 One embodiment of this application provides a terminal device, including:

[0138] One or more processors;

[0139] A memory, coupled to the processor, for storing one or more programs;

[0140] When the one or more programs are executed by the one or more processors, the one or more processors implement the transient stability analysis method for synchronous machine-structured MMC parallel power supply systems as described above.

[0141] The processor controls the overall operation of the terminal device to complete all or part of the steps described above for the transient stability analysis method of a synchronous machine-structured network (MMC) parallel power supply system. The memory stores various types of data to support the operation of the terminal device. This data may include, for example, instructions for any application or method operating on the terminal device, as well as application-related data. The memory can be implemented using any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read-Only Memory (EPROM), Programmable Read-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0142] In an exemplary embodiment, the terminal device may be implemented by one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), controllers, microcontrollers, microprocessors, or other electronic components to perform the transient stability analysis method for synchronous machine-structured network-type MMC parallel power supply systems as described in any of the foregoing embodiments, and to achieve the same technical effects as the methods described above.

[0143] In another exemplary embodiment, a computer-readable storage medium including a computer program is also provided. When executed by a processor, the computer program implements the steps of the transient stability analysis method for a synchronous mesh-type MMC parallel power supply system as described in any of the foregoing embodiments. For example, the computer-readable storage medium may be the aforementioned memory including the computer program, which may be executed by a processor of a terminal device to complete the transient stability analysis method for a synchronous mesh-type MMC parallel power supply system as described in any of the foregoing embodiments, and achieve the same technical effects as the aforementioned method.

[0144] The above description is the preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A transient stability analysis method for a synchronous machine-structured grid-type MMC parallel power supply system, characterized in that, include: Based on the synchronous machine-structure network type MMC parallel power supply system, a transient stability analytical model is established after system failure. Based on the transient stability analytical model, the power angle of the synchronous machine at the stable equilibrium point and the unstable equilibrium point of the synchronous machine-network type MMC parallel power supply system is obtained, and the critical cut-off angle of the system is calculated. The critical cut-off time of the system is calculated using the critical cut-off angle of the system, and is used as an evaluation index of the system's transient stability. The process of obtaining the stable equilibrium point and the power angle of the synchronous machine at the unstable equilibrium point of the synchronous machine-structured MMC parallel power supply system, and calculating the critical cutoff angle of the system, includes: Based on the power flow calculation results, the mechanical power of the prime mover is obtained. P m If the mechanical power of the prime mover is equal to the steady-state output electromagnetic power of the synchronizer, then the power angle of the synchronizer at the system's stable equilibrium point and unstable equilibrium point is... δ s and δ u They are respectively: ； In the formula, the grid connection point voltage command value of the grid-connected MMC is... E ref The internal potential of the synchronous machine is E q ' The phase angle is φ 12p The equivalent ground branch conductances of synchronous machine nodes and network-type MMCs are respectively G 12p , G 13p The mutual admittance amplitude between the synchronous machine and the network-type MMC is Y 12p .

2. The transient stability analysis method for a synchronous machine-structured grid-type MMC parallel power supply system according to claim 1, characterized in that, The established transient stability analytical analysis model after system failure includes: For the synchronous machine-grid type MMC parallel power supply system after a fault, the grid-type MMC converter with a control strategy of constant AC voltage amplitude and frequency is modeled using a voltage source, and the grid-type MMC converter with a control strategy of constant AC voltage amplitude and frequency is modeled using a current source.

3. The transient stability analysis method for a synchronous mechanical-structured MMC parallel power supply system according to claim 2, characterized in that, The equivalent modeling of the grid-type MMC converter employing a control strategy with constant AC voltage amplitude and frequency using a voltage source includes: Electromagnetic power of the synchronous machine in a grid-type MMC parallel power supply system after a fault is determined. P pos for: ； In the formula, the grid connection point voltage command value of the grid-connected MMC is... E ref The internal potential of the synchronous machine is E q ' The power angle of the synchronous machine is δ g The equivalent ground branch conductances of synchronous machine nodes and network-type MMCs are respectively G 12p , G 13p The mutual admittance amplitude between the synchronous machine and the network-type MMC is Y 12p The phase angle is φ 12p .

4. The transient stability analysis method for a synchronous machine-structured grid-type MMC parallel power supply system according to claim 3, characterized in that, The grid-type MMC converter employing a control strategy with constant AC voltage amplitude and frequency is modeled equivalently using a current source, including: Determine the injected current vector of the network-type MMC during the fault. I sfau for: ； In the formula, I max This is the current limit value for the MMC. φ I The phase setting value for the injection current of the MMC, where j is a complex unit; Then the grid connection point voltage vector of MMC U s for: ； In the formula, Y 12f , Y 13f , Y 23f These represent the mutual admittance between the synchronous machine and the network-type MMC during the fault, the ground branch admittance of the synchronous machine, and the ground branch admittance of the network-type MMC, respectively. Let intermediate admittance term Y g1 , Y g2 They are respectively: ； In the formula, G g1 , B g1 They are respectively Y g1 The conductivity and susceptance, Y g2 , φ g2 They are respectively Y g2 The amplitude and phase angle; The injection current of the synchronous machine I g for: ； Based on the internal potential vector of the synchronizer E q ' and injected current I g The electromagnetic power of the system synchronizer during the fault was obtained. P fau for: 。 5. The transient stability analysis method for a synchronous mechanical-structured MMC parallel power supply system according to claim 1, characterized in that, The critical cut-off angle of the calculation system includes: Using the principle of equal area, when the system has a critical cut-off angle δ CCA To ensure that the acceleration area equals the deceleration area, the fault clearing angle of the synchronous machine satisfies the following equation: ； Solving the equation yields the critical cut-off angle of the system. δ CCA The value of .

6. The transient stability analysis method for a synchronous machine-structured grid-type MMC parallel power supply system according to claim 1, characterized in that, The calculation of the critical resection time of the system using the critical resection angle of the system includes: The rotor motion equations of the synchronous machine at the time of the fault are determined to be a system of differential equations: ； In the formula, ω g This indicates the rotor speed of the synchronous machine. ω 0 represents the system's rated angular frequency. T J Let be the generator's inertial constant; Solve the system of differential equations using the Euler method: ； In the formula, t For time Δ t This is the integration time step; The critical resection time of the system t c The following criteria must be met: ； The synchronous machine power angle is saved at each moment during the calculation process. δ g and rotor angular frequency ω g The critical resection time of the system is obtained based on the value of the criterion.

7. A transient stability analysis system for a synchronous machine-structured network-type MMC parallel power supply system, characterized in that, include: The model building unit is used to establish a transient stability analytical analysis model after a system fault based on a synchronous machine-structure network type MMC parallel power supply system. The critical cut-off angle determination unit is used to obtain the power angle of the synchronous machine at the stable equilibrium point and the unstable equilibrium point of the synchronous machine-grid type MMC parallel power supply system according to the transient stability analytical analysis model, and to calculate the critical cut-off angle of the system. The critical cut-off time determination unit is used to calculate the critical cut-off time of the system using the critical cut-off angle of the system, as an evaluation index of the system's transient stability. The process of obtaining the stable equilibrium point and the power angle of the synchronous machine at the unstable equilibrium point of the synchronous machine-structured MMC parallel power supply system, and calculating the critical cutoff angle of the system, includes: Based on the power flow calculation results, the mechanical power of the prime mover is obtained. P m If the mechanical power of the prime mover is equal to the steady-state output electromagnetic power of the synchronizer, then the power angle of the synchronizer at the system's stable equilibrium point and unstable equilibrium point is... δ s and δ u They are respectively: ； In the formula, the grid connection point voltage command value of the grid-connected MMC is... E ref The internal potential of the synchronous machine is E q ' The phase angle is φ 12p The equivalent ground branch conductances of synchronous machine nodes and network-type MMCs are respectively G 12p , G 13p The mutual admittance amplitude between the synchronous machine and the network-type MMC is Y 12p .

8. A terminal device, characterized in that, include: One or more processors; A memory, coupled to the processor, for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the transient stability analysis method for a synchronous machine-structured MMC parallel power supply system as described in any one of claims 1-6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the transient stability analysis method for a synchronous machine-structured MMC parallel power supply system as described in any one of claims 1-6.

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