New energy sending line protection method and system based on control strategy switching

Abstract

The application relates to the technical field of relay protection, in particular to a new energy sending-out line protection method and system based on control strategy switching. Whether a voltage amplitude fluctuation rate exceeds a voltage allowable fluctuation limit value is used as a switching criterion of a control strategy, a voltage modulation signal of a grid-side converter is changed, the grid-side converter is switched from a steady-state control branch to a fault control branch at the time of a fault, fault characteristic signal enhancement is realized, and the speed and sensitivity of differential protection are greatly improved under the premise of ensuring reliability. The application aims to solve the problem of how to enhance fault characteristics when a fault occurs in a new energy power system, thereby providing a reliable criterion for system fault detection.

Description

Technical Field

[0001] This application relates to the field of relay protection technology, and in particular to a method and system for protecting new energy transmission lines based on control strategy switching. Background Technology

[0002] In traditional power systems, synchronous generators exhibit typical voltage source characteristics, with large inertia and strong short-circuit capability, providing high-amplitude power frequency short-circuit currents during faults, thus laying the foundation for relay protection. However, in new energy power systems, with the continuous large-scale integration of high-proportion new energy sources and high-proportion power electronic equipment into the power system, the power grid is gradually evolving from a traditional structure dominated by synchronous generators to a new type of power system with "high-inertia and high-power" characteristics.

[0003] Traditional current differential protection relies on the vector sum of current information across the protected element, and its effectiveness depends on a clear relationship between the current amplitude and phase during a fault. However, in high-voltage and high-efficiency power generation systems, new energy units are connected to the grid via power electronic converters. Their fault response is controlled by internal control strategies and power device limits, exhibiting characteristics such as limited fault current amplitude, controlled phase, high harmonic content, and weak feeder characteristics. These characteristics result in complex fault current waveforms, low fundamental components, and difficulty in distinguishing them from load currents, severely impacting the accuracy and reliability of traditional current differential protection criteria.

[0004] In view of this, this application proposes a protection method for new energy transmission lines to overcome the shortcomings of the traditional current differential protection principle and achieve reliable protection for transmission lines in new energy power systems. Summary of the Invention

[0005] The main objective of this application is to provide a protection method for new energy transmission lines based on control strategy switching, which aims to solve the problem of how to enhance the fault characteristics when faults occur in new energy power systems, thereby providing a reliable criterion for system fault detection.

[0006] To achieve the above objectives, this application provides a new energy transmission line protection method based on control strategy switching, applied to a new energy power system. The new energy power system is equipped with a grid-side converter including a steady-state control branch and a fault control branch. The new energy transmission line protection method based on control strategy switching includes the following steps:

[0007] S10, acquire the first voltage amplitude and the second voltage amplitude of the three-phase voltage of the new energy side transmission line collected by the voltage transformer at two adjacent moments.

[0008] S20, determine the voltage amplitude fluctuation rate based on the first voltage amplitude and the second voltage amplitude;

[0009] S30, when the voltage amplitude fluctuation rate is greater than the preset fluctuation rate threshold, the control grid-side converter switches to the fault control branch, wherein the fault control branch is used to increase the amplitude and fundamental component of the fault current signal;

[0010] S40, after the grid-side converter switches to the fault control branch, the current of the new energy side and the grid side are collected at the current moment, and the longitudinal current differential protection strategy is executed based on the current of the new energy side and the grid side.

[0011] Optionally, the expression for calculating the voltage amplitude fluctuation rate is:

[0012]

[0013] In the formula, Voltage amplitude fluctuation rate, The first voltage amplitude, This is the second voltage amplitude collected at the previous moment. This is the rated voltage.

[0014] Optionally, in step S30, the step of switching the control grid-side converter to the fault control branch includes:

[0015] S31, set the time when the voltage amplitude fluctuation rate is greater than the preset fluctuation rate threshold and the corresponding time when the fault signal sent by the relay protection device is received as t0;

[0016] S32, when the time t in the timer of the grid-side converter is greater than or equal to t0, a control signal is sent to the grid-side converter through the communication link to request the grid-side converter to switch to the fault control branch.

[0017] Optionally, after S20, the method further includes:

[0018] S50, if the voltage amplitude fluctuation rate is less than or equal to the preset fluctuation rate threshold, the grid-side converter remains in the steady-state control branch and returns to step S10.

[0019] Optionally, in step S40, the longitudinal current differential protection strategy is executed based on the current on the new energy side and the current on the grid side, including:

[0020] S41, calculate the differential current based on the new energy side current and the grid side current respectively. and braking current :

[0021]

[0022]

[0023] In the formula, For the current on the new energy side, This refers to the grid-side current.

[0024] S42, Determine differential current and braking current Does it meet the criteria for longitudinal current differential protection?

[0025]

[0026] In the formula, The operating threshold for differential protection, This is the braking coefficient;

[0027] If S43 is satisfied, a trip command is sent to the circuit breaker; otherwise, a lockout command is sent to the circuit breaker.

[0028] This application has at least the following beneficial effects:

[0029] 1. Use whether the voltage amplitude fluctuation rate exceeds the allowable voltage fluctuation limit as the switching criterion for the control strategy to ensure that the control strategy switching command is accurate and reliable.

[0030] 2. By changing the voltage modulation signal of the grid-side converter, the grid-side converter is switched from the steady-state control branch to the fault control branch during a fault, thereby enhancing the fault characteristic signal and greatly improving the speed and sensitivity of the differential protection while ensuring reliability. Attached Figure Description

[0031] Figure 1 This is a topology diagram of the new energy power system involved in the embodiments of this application;

[0032] Figure 2 This is a flowchart illustrating the new energy transmission line protection method based on control strategy switching involved in the embodiments of this application;

[0033] Figure 3 This is a topology diagram of the control strategy involved in the embodiments of this application;

[0034] Figure 4 This is a schematic diagram of the differential current and braking current under steady-state control branch I according to the second embodiment of this application;

[0035] Figure 5 This is a schematic diagram of the differential current and braking current under the fault control branch II according to the second embodiment of this application;

[0036] Figure 6 This is a schematic diagram of the differential current and braking current under steady-state control branch I according to the third embodiment of this application;

[0037] Figure 7 This is a schematic diagram of the differential current and braking current under fault control branch II according to the third embodiment of this application;

[0038] Figure 8 This is a schematic diagram of the hardware operating environment of the computer system involved in the embodiments of this application.

[0039] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0040] To better understand the above technical solutions, exemplary embodiments of this disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0041] First Embodiment

[0042] This embodiment provides a new energy transmission line protection method based on control strategy switching. The method is applied to a new energy power system, which is equipped with a grid-side converter including a steady-state control branch and a fault control branch.

[0043] For example, a new energy power system can be provided for such Figure 1 The topology shown.

[0044] Reference Figure 2 The new energy transmission line protection method based on control strategy switching includes the following steps:

[0045] Step S10: Obtain the first voltage amplitude and the second voltage amplitude of the three-phase voltage of the new energy side transmission line collected by the voltage transformer at two adjacent time points.

[0046] In this embodiment, the three-phase voltage signal of the new energy side of the transmission line is first acquired using a high-precision voltage transformer. The acquired three-phase voltage signal is then filtered and converted from analog to digital to obtain a voltage amplitude sequence. The voltage amplitudes at two adjacent moments are selected from the voltage amplitude sequence and used as the first voltage amplitude and the second voltage amplitude, respectively.

[0047] Step S20: Determine the voltage amplitude fluctuation rate based on the first voltage amplitude and the second voltage amplitude;

[0048] Furthermore, the voltage amplitude fluctuation rate is used as the criterion to determine whether it exceeds the standard limit. Optionally, the voltage amplitude fluctuation rate is calculated using the following expression:

[0049]

[0050] In the formula, Voltage amplitude fluctuation rate, The first voltage amplitude, This is the second voltage amplitude collected at the previous moment. This is the rated voltage.

[0051] when If the voltage amplitude fluctuation rate exceeds the standard limit, proceed to step S30.

[0052] in, This refers to the allowable voltage fluctuation limit.

[0053] It should be noted that, Adjustments need to be made based on factors such as the voltage level of the transmission line, the access capacity of the new energy power station, and the voltage quality requirements of the regional power grid. When a transient voltage fluctuation occurs on the line but does not constitute a fault, it is necessary to continuously monitor the voltage amplitude changes at multiple sampling points. If the fluctuation returns to the normal range within a short period of time, it can be determined as a non-fault fluctuation, and the process returns to step S10 to continue monitoring. In some optional implementations, at a voltage level of 220kV, Set to 1.6%.

[0054] Optionally, after S20, the method further includes:

[0055] S50, if the voltage amplitude fluctuation rate is less than or equal to the preset fluctuation rate threshold, the grid-side converter remains in the steady-state control branch and returns to step S10.

[0056] Step S30: When the voltage amplitude fluctuation rate is greater than the preset fluctuation rate threshold, the control grid-side converter switches to the fault control branch, wherein the fault control branch is used to increase the amplitude and fundamental component of the fault current signal.

[0057] In step S30, when the voltage amplitude fluctuation rate is determined to be greater than the preset fluctuation rate threshold, it means that a fault has occurred in the new energy power system. In order to achieve step S30, an additional control strategy module is added to the control system of the grid-side converter in this embodiment. This module adjusts the output voltage modulation signal of the converter in real time based on the modulation signal adjustment mechanism.

[0058] By modifying the voltage modulation signal of the grid-side converter, the voltage signal output by the converter during a fault possesses specific characteristics, thereby guiding the fault current to exhibit a more pronounced fundamental component and amplitude variation, thus addressing the issue of weak fault current characteristics in new energy sources. The expression for 's' in the additional control is:

[0059]

[0060] In some optional implementations, the relay protection device on the new energy side sends digital or pulse signals to the grid-side converter via a communication link. The signal content includes an instruction to request switching to the fault control mode. A standardized communication protocol must be used to achieve the docking between the relay protection device and the converter control system. After receiving the switching request signal, the grid-side converter control immediately switches from steady-state control branch I to fault control branch II.

[0061] For ease of understanding, please refer to Figure 3 The diagram shows the topology of the control strategy implementing the method of this application. In the dual closed-loop vector control strategy of the grid-side converter of the direct-drive wind turbine, the grid-side converter is essentially a voltage source converter, and the amplitude of its output AC current is directly related to the difference between the converter modulation voltage and the grid voltage. Based on the working principle of PWM modulation, the mechanism by which it deepens the voltage drop and enhances the fault current amplitude after a fault is as follows:

[0062] In the synchronous rotating dq coordinate system, the dynamic AC current of the grid-side converter satisfies the following relationship:

[0063]

[0064] In the formula, U sd , U sq These are the d-axis and q-axis components of the modulation voltage of the grid-side converter; i sd , i sq These are the d-axis and q-axis components of the modulation voltage of the grid-side converter; U gd , U gq These are the d-axis and q-axis components of the grid voltage; R The equivalent resistance of the line; L For grid-side filter inductance; This represents the angular velocity of the power grid.

[0065] When a fault occurs, the grid voltage U gd , U gd A voltage drop will occur. If the modulation voltage amplitude of the converter is actively reduced at this time, it will... U sd - U gd and U sq - U gq The difference further increases. With the filter inductance L remaining constant, this increase in difference directly increases the rate of change of current. and This causes the amplitude of the fault current to rise rapidly.

[0066] In addition, in PWM modulation, the modulation ratio m = U ref / ( U dc / 2) Directly affects the amplitude of the output voltage. The fault control branch reduces... U ref This reduces the modulation ratio, ultimately leading to a decrease in the amplitude of the AC voltage output by the converter. For grid-side converters, the output current is driven by the difference between the converter modulation voltage and the grid voltage. In fault scenarios where the grid voltage has already dropped, a further reduction in the converter modulation voltage amplifies this voltage difference, thereby generating a larger induced electromotive force in the filter inductor. This forces a significant increase in the amplitude of the fault current, thus enhancing the identifiability of the fault characteristics.

[0067] Optionally, in S30, the steps for switching the control network-side converter to the fault control branch include:

[0068] S31, set the time when the voltage amplitude fluctuation rate is greater than the preset fluctuation rate threshold and the corresponding time when the fault signal sent by the relay protection device is received as t0;

[0069] S32, when the time t in the timer of the grid-side converter is greater than or equal to t0, a control signal is sent to the grid-side converter through the communication link to request the grid-side converter to switch to the fault control branch.

[0070] Specifically, upon receiving the switching request signal, the grid-side converter control immediately switches from steady-state control branch I to fault control branch II. The switching triggering time condition is t≥t0, where t0 is the moment when the grid-side converter control system receives the signal from the relay protection device. No additional delay is required, ensuring rapid fault response.

[0071] The switching condition for switching from steady-state control branch I to fault control branch II is:

[0072]

[0073] The switching must be performed immediately at time t≥t0 without additional delay, ensuring that fault control branch II is activated as soon as possible after a fault occurs to avoid attenuation of fault characteristic signals. The grid-side converter control system must have the ability to quickly switch between the two branch control logics, using a programmable logic controller or digital signal processor to implement the switching of control branches. During the switching process, the control signal of steady-state control branch I must be cut off, while the control signal of fault control branch II is activated to ensure no control conflicts.

[0074] Step S40: After the grid-side converter switches to the fault control branch, the current collected at the current time of the new energy side current and the grid side current are obtained, and the longitudinal current differential protection strategy is executed based on the current collected at ...

[0075] In step S40, after the grid-side converter switches to the fault control branch, the fault characteristics in the fault signal are amplified, and current sampling can be performed on this branch to more accurately execute the longitudinal current differential protection strategy.

[0076] Optionally, a longitudinal current differential protection strategy is implemented based on the current on the new energy side and the current on the grid side, specifically including:

[0077] S41, calculate the differential current based on the new energy side current and the grid side current respectively. and braking current :

[0078]

[0079]

[0080] In the formula, For the current on the new energy side, This refers to the grid-side current.

[0081] S42, Determine differential current and braking current Does it meet the criteria for longitudinal current differential protection?

[0082]

[0083] In the formula, The operating threshold for differential protection, This is the braking coefficient;

[0084] If S43 is satisfied, a trip command is sent to the circuit breaker; otherwise, a lockout command is sent to the circuit breaker.

[0085] In the technical solution provided in this embodiment, the switching criterion for the control strategy is based on whether the voltage amplitude fluctuation rate exceeds the voltage allowable fluctuation limit. By changing the voltage modulation signal of the grid-side converter, the grid-side converter is switched from the steady-state control branch to the fault control branch during a fault, thereby enhancing the fault characteristic signal and greatly improving the speed and sensitivity of the differential protection while ensuring reliability.

[0086] Second Embodiment

[0087] Based on the first embodiment, this embodiment provides a simulation experiment as an example to compare the effect of current collected by the grid-side converter under different branches. In this embodiment, the parameters of the simulation model are set as follows: the power of a single wind turbine is 2MW, there are 100 wind turbines, the system capacity is 200MVA, the capacity of the main transformer is 200MVA, the total length of the wind farm's AC transmission line is 100km, and the voltage level is 220kV. A transient ground fault of phase A occurs 30km away from the M side of the line, the transition resistance is 200Ω, and the fault duration is 0.2s.

[0088] See results Figure 4 and Figure 5 The diagrams shown in the second embodiment illustrate the differential current and braking current under steady-state control branch I and the differential current and braking current under fault control branch II, respectively. As can be seen from the figures, the difference in amplitude between the differential current and braking current is more pronounced under fault control branch II compared to steady-state control branch I.

[0089] Third Embodiment

[0090] Based on the first embodiment, this embodiment provides another simulation experiment as an example to compare the effect of current collected by the grid-side converter under different branches. In this embodiment, the parameters of the simulation model are set as follows: the power of a single wind turbine is 2MW, there are 100 wind turbines, the system capacity is 200MVA, the capacity of the main transformer is 200MVA, the total length of the wind farm's AC transmission line is 100km, and the voltage level is 220kV. A transient ground fault of phase A occurs 80km away from the M side of the line, the transition resistance is 100Ω, and the fault duration is 0.2s.

[0091] See results Figure 6 and Figure 7 The diagrams shown in the third embodiment illustrate the differential current and braking current under steady-state control branch I and the differential current and braking current under fault control branch II, respectively. As can be seen from the figures, the difference in amplitude between the differential current and braking current is more pronounced under fault control branch II compared to steady-state control branch I.

[0092] As one implementation scheme, Figure 8 This is a schematic diagram of the hardware operating environment of the computer system involved in the embodiments of this application.

[0093] like Figure 8As shown, the computer system may include: a processor 1001, such as a CPU; a memory 1005; a user interface 1003; a network interface 1004; and a communication bus 1002. The communication bus 1002 is used to enable communication between these components. The user interface 1003 may include a display screen or an input unit such as a keyboard; optionally, the user interface 1003 may also include a standard wired interface or a wireless interface. The network interface 1004 may optionally include a standard wired interface or a wireless interface (such as a Wi-Fi interface). The memory 1005 may be high-speed RAM or non-volatile memory, such as a disk drive. Optionally, the memory 1005 may also be a storage device independent of the aforementioned processor 1001.

[0094] Those skilled in the art will understand that Figure 8 The computer system architecture shown does not constitute a limitation on the computer system and may include more or fewer components than shown, or combine certain components, or have different component arrangements.

[0095] like Figure 8 As shown, the memory 1005, as a storage medium, may include an operating system, a network communication module, a user interface module, and computer programs. The operating system is a program that manages and controls the hardware and software resources of the computer system, as well as the operation of the computer programs and other software or programs.

[0096] exist Figure 8 In the computer system shown, the user interface 1003 is mainly used to connect to the terminal and communicate with the terminal; the network interface 1004 is mainly used to communicate with the backend server; and the processor 1001 can be used to call the computer program stored in the memory 1005.

[0097] In this embodiment, the computer system includes: a memory 1005, a processor 1001, and a computer program stored in the memory and executable on the processor, wherein:

[0098] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0099] S10, acquire the first voltage amplitude and the second voltage amplitude of the three-phase voltage of the new energy side transmission line collected by the voltage transformer at two adjacent moments.

[0100] S20, determine the voltage amplitude fluctuation rate based on the first voltage amplitude and the second voltage amplitude;

[0101] S30, when the voltage amplitude fluctuation rate is greater than the preset fluctuation rate threshold, the control grid-side converter switches to the fault control branch, wherein the fault control branch is used to increase the amplitude of the fault current signal;

[0102] S40, after the grid-side converter switches to the fault control branch, the current of the new energy side and the grid side are collected at the current moment, and the longitudinal current differential protection strategy is executed based on the current of the new energy side and the grid side.

[0103] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0104] The formula for calculating the voltage amplitude fluctuation rate is as follows:

[0105]

[0106] In the formula, Voltage amplitude fluctuation rate, The first voltage amplitude, This is the second voltage amplitude collected at the previous moment. This is the rated voltage.

[0107] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0108] S31, set the time when the voltage amplitude fluctuation rate is greater than the preset fluctuation rate threshold and the corresponding time when the fault signal sent by the relay protection device is received as t0;

[0109] S32, when the time t in the timer of the grid-side converter is greater than or equal to t0, a control signal is sent to the grid-side converter through the communication link to request the grid-side converter to switch to the fault control branch.

[0110] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0111] S41, calculate the differential current based on the new energy side current and the grid side current respectively. and braking current :

[0112]

[0113]

[0114] In the formula, For the current on the new energy side, This refers to the grid-side current.

[0115] S42, Determine differential current and braking current Does it meet the criteria for longitudinal current differential protection?

[0116]

[0117] In the formula, The operating threshold for differential protection, This is the braking coefficient;

[0118] If S43 is satisfied, a trip command is sent to the circuit breaker; otherwise, a lockout command is sent to the circuit breaker.

[0119] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0120] S50, if the voltage amplitude fluctuation rate is less than or equal to the preset fluctuation rate threshold, the grid-side converter remains in the steady-state control branch and returns to step S10.

[0121] Furthermore, those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program includes program instructions and can be stored in a storage medium, which is a computer-readable storage medium. The program instructions are executed by at least one processor in a computer system to implement the process steps of the embodiments of the above methods.

[0122] Therefore, this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the various steps of the new energy transmission line protection method based on control strategy switching as described in the above embodiments.

[0123] The computer-readable storage medium can be any computer-readable storage medium capable of storing program code, such as a USB flash drive, portable hard drive, read-only memory (ROM), magnetic disk, or optical disk.

[0124] It should be noted that, since the storage medium provided in the embodiments of this application is the storage medium used to implement the methods of the embodiments of this application, those skilled in the art can understand the specific structure and variations of the storage medium based on the methods described in the embodiments of this application, and therefore will not be repeated here. All storage media used in the methods of the embodiments of this application fall within the scope of protection of this application.

[0125] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0126] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0127] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0128] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0129] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0130] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for protecting new energy transmission lines based on control strategy switching, characterized in that, Applied to a new energy power system, wherein the new energy power system is equipped with a grid-side converter including a steady-state control branch and a fault control branch, the new energy transmission line protection method based on control strategy switching includes the following steps: S10, acquire the first voltage amplitude and the second voltage amplitude of the three-phase voltage of the new energy side transmission line collected by the voltage transformer at two adjacent moments. S20, determine the voltage amplitude fluctuation rate based on the first voltage amplitude and the second voltage amplitude; S30, when the voltage amplitude fluctuation rate is greater than the preset fluctuation rate threshold, the control grid-side converter switches to the fault control branch, wherein the fault control branch is used to increase the amplitude and fundamental component of the fault current signal; S40, after the grid-side converter switches to the fault control branch, the current of the new energy side and the grid side are collected at the current moment, and the longitudinal current differential protection strategy is executed based on the current of the new energy side and the grid side. The formula for calculating the voltage amplitude fluctuation rate is as follows: ； In the formula, For voltage amplitude fluctuation rate, The first voltage amplitude, This is the second voltage amplitude collected at the previous moment. Rated voltage; In step S30, the step of switching the control grid-side converter to the fault control branch includes: S31, set the time when the voltage amplitude fluctuation rate is greater than the preset fluctuation rate threshold and the corresponding time when the fault signal sent by the relay protection device is received as t0; S32, when the time t in the timer of the grid-side converter is greater than or equal to t0, a control signal is sent to the grid-side converter through the communication link to request the grid-side converter to switch to the fault control branch.

2. The method for protecting new energy transmission lines based on control strategy switching as described in claim 1, characterized in that, Following S20, the following is also included: S50, if the voltage amplitude fluctuation rate is less than or equal to the preset fluctuation rate threshold, the grid-side converter remains in the steady-state control branch and returns to step S10.

3. The method for protecting new energy transmission lines based on control strategy switching as described in claim 1, characterized in that, In step S40, a longitudinal current differential protection strategy is executed based on the current on the new energy side and the current on the grid side, including: S41, calculate the differential current based on the new energy side current and the grid side current respectively. and braking current : ； ； In the formula, For the current on the new energy side, This refers to the grid-side current. S42, Determine differential current and braking current Does it meet the criteria for longitudinal current differential protection? ； In the formula, The operating threshold for differential protection, This is the braking coefficient; If S43 is satisfied, a trip command is sent to the circuit breaker; otherwise, a lockout command is sent to the circuit breaker.

4. A computer system, characterized in that, The computer system includes: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is executed by the processor, it implements the steps of the new energy transmission line protection method based on control strategy switching as described in any one of claims 1 to 3.

5. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the new energy transmission line protection method based on control strategy switching as described in any one of claims 1 to 3.

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