Flexible power transmission active current limiting method and system based on Internet of Things

Abstract

The invention relates to the technical field of flexible power transmission, in particular to a flexible power transmission active current limiting method and system based on the Internet of Things. According to the scheme, the method comprises the following steps: constructing a control model based on a half-bridge MMC based on visual programming; setting a visual programming scheme of the active current limiting control strategy; judging whether a fault occurs or not according to the active current limiting control strategy, outputting a control instruction according to a control model of the half-bridge MMC when no fault occurs, and updating an output control instruction value according to the minimum voltage value when the fault occurs; the limit value of the fault current is obtained online; comparing the limit value of the fault current with a preset circuit breaker breaking capacity curve to obtain a target circuit breaker; and selecting the full-bridge proportion as the optimal scheme according to the target circuit breaker. According to the scheme, the negative voltage output characteristic of the full-bridge module is carried out by utilizing the Internet of Things, and online active current limiting control is completed by combining online control of a direct current modulation ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible power transmission, and more specifically, to a flexible power transmission active current limiting method and system based on the Internet of Things. Background Art

[0002] The core method for suppressing the fault current in a flexible DC grid is to limit the short-circuit current. The traditional method for limiting the short-circuit current is to break the current value through a circuit breaker. However, in actual situations, a circuit breaker generally requires a zero-crossing point, and it is difficult for DC power transmission to have a zero-crossing point. Therefore, in the prior art, there is already a method to generate a situation where the current crosses zero through oscillation.

[0003] Before the technology of the present invention, in the prior art, in addition to the DC circuit breaker solution, there is also a solution that uses an active current limiting control technology to achieve the isolation and clearing of the fault current, and overcome the defect that the half-bridge modular multilevel converter cannot clear the fault due to the reverse parallel diode freewheeling effect. Summary of the Invention

[0004] In view of the above problems, the present invention proposes a flexible power transmission active current limiting method and system based on the Internet of Things, which utilizes the negative voltage output characteristics of the full-bridge module of the Internet of Things, combined with the online control of the DC modulation ratio, to complete the online active current limiting control.

[0005] According to the first aspect of the embodiments of the present invention, a flexible power transmission active current limiting method based on the Internet of Things is provided.

[0006] In one or more embodiments, preferably, the flexible power transmission active current limiting method based on the Internet of Things includes:

[0007] Build a control model based on the half-bridge MMC through visual programming;

[0008] Set a visual programming scheme for the active current limiting control strategy;

[0009] Judge whether a fault occurs according to the active current limiting control strategy. When there is no fault, output a control instruction according to the control model of the half-bridge MMC. When there is a fault, update the output control instruction value according to the lowest voltage value;

[0010] Obtain the limit value of the fault current online;

[0011] Compare the limit value of the fault current with the pre-set circuit breaker breaking capacity curve to obtain the target circuit breaker;

[0012] Select the full-bridge ratio as the optimal solution according to the target circuit breaker.

[0013] In one or more embodiments, preferably, the control model of the half-bridge MMC is built based on visual programming, which specifically includes:

[0014] Set up a visual programming platform based on the Internet of Things;

[0015] On the visual programming platform, a control model of the half-bridge MMC is set up, and online control is performed by controlling the active power and reactive power;

[0016] Set up the control model of the half-bridge MMC through the Internet of Things, use visual programming to modify the model parameters online, and output the upper arm voltage command values of A, B, and C and the lower arm voltage command values of A, B, and C.

[0017] In one or more embodiments, preferably, the visual programming scheme for setting the active current limiting control strategy specifically includes:

[0018] Set up to extract the voltage value on all DC buses as the input signal for the visual programming of the active current limiting control strategy;

[0019] Set up the number of sub-modules of 6 arms as the output signal for the visual programming of the active current limiting control strategy.

[0020] In one or more embodiments, preferably, to judge whether a fault occurs according to the active current limiting control strategy, when there is no fault, output control instructions according to the control model of the half-bridge MMC, and when there is a fault, update the output control instruction value according to the lowest voltage value, which specifically includes:

[0021] Judge whether there is a fault at the current moment. If no DC fault occurs, divide the reference voltage of 6 arms output by the control model of the half-bridge MMC by the rated value Vcn of the sub-module capacitor voltage to obtain the number of sub-modules Nref to be put into each arm, which is used as the control instruction of the valve controller;

[0022] When it is judged that there is a fault at the current moment, start timing the time delay. When the time delay satisfies the first calculation formula, switch to the fault current limiting control strategy;

[0023] When in the fault current limiting control strategy, calculate the lowest voltage value using the second calculation formula for fast tracking of the fault point voltage;

[0024] Calculate and generate the number of sub-modules of 6 arms according to the lowest voltage value using the third calculation formula;

[0025] The first calculation formula is:

[0026] SY>KY

[0027] Wherein, SY is the time delay and KY is the control test;

[0028] The second calculation formula is as follows:

[0029] zz = Min(Vdc3, Vdc2, Vdc)

[0030] Wherein, zz is the minimum voltage value, Vdc is the DC voltage, VA, VB, and VC are the voltage values of the lines Vdc3, Vdc2, and Vdc connected to the current DC bus in sequence, and Min() is the minimum value extraction function;

[0031] The third calculation formula is as follows:

[0032]

[0033] Wherein, VFAP, VFBP, VFCP, VFAN, VFBN, and VFCN are the upper bridge arm voltage command values of A, B, and C and the lower bridge arm voltage command values of A, B, and C in sequence, and S1, S2, S3, S4, S5, and S6 are the number of inserted sub-modules of the 6 bridge arms in sequence.

[0034] In one or more embodiments, preferably, obtaining the limit value of the fault current online specifically includes:

[0035] After determining that a DC fault has occurred, the number of sub-modules of the 6 bridge arms is switched through the controller of the commutation valve after a fault detection delay;

[0036] After starting to suppress the fault current, the DC fault current is automatically detected;

[0037] Extract the maximum value of the fault current as the limit value of the fault current.

[0038] In one or more embodiments, preferably, comparing the limit value of the fault current with the pre-set breaker opening capacity curve to obtain the target breaker specifically includes:

[0039] Set the opening capacity curves of DC breakers at several different prices;

[0040] Extract the maximum breaking current of different opening capacity curves;

[0041] When the maximum breaking current is greater than the limit value of the fault current, it is used as an optional breaker;

[0042] Extract the breaker with the lowest price among all the optional breakers as the target breaker.

[0043] In one or more embodiments, preferably, selecting the full-bridge ratio according to the target breaker as the optimal solution specifically includes:

[0044] Obtain the maximum breaking current of the target circuit breaker;

[0045] Calculate the additional full-bridge ratio using the fourth calculation formula;

[0046] Add the additional full-bridge ratio to ten percent of the total number of modules as the optimal solution;

[0047] The fourth calculation formula is:

[0048] E = 1.2×CG÷kd

[0049] Where E is the additional full-bridge ratio, kd is the maximum breaking current, and CG is the limit value of the fault current.

[0050] According to the second aspect of the embodiments of the present invention, a flexible transmission active current limiting system based on the Internet of Things is provided.

[0051] In one or more embodiments, preferably, the flexible transmission active current limiting method based on the Internet of Things includes:

[0052] A model building module for building a control model based on a half-bridge MMC using visual programming;

[0053] An active current limiting interaction setting module for setting a visual programming solution for the active current limiting control strategy;

[0054] An online instruction generation module for determining whether a fault has occurred according to the active current limiting control strategy. When there is no fault, control instructions are output according to the control model of the half-bridge MMC. When there is a fault, the output control instruction value is updated according to the lowest voltage value;

[0055] A fault current extreme value module for obtaining the limit value of the fault current online;

[0056] A circuit breaker selection module for obtaining the target circuit breaker by comparing the limit value of the fault current with the preset circuit breaker breaking capacity curve;

[0057] An optimal extraction module for selecting the full-bridge ratio as the optimal solution according to the target circuit breaker.

[0058] According to the third aspect of the embodiments of the present invention, a computer-readable storage medium is provided, on which computer program instructions are stored. When the computer program instructions are executed by a processor, the methods described in any one of the first aspects of the embodiments of the present invention are implemented.

[0059] According to the fourth aspect of the embodiments of the present invention, an electronic device is provided, including a memory and a processor. The memory is used to store one or more computer program instructions. Among them, the one or more computer program instructions are executed by the processor to implement the methods described in any one of the first aspects of the embodiments of the present invention.

[0060] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0061] In the solution of the present invention, a flexible control and strategy setting method based on visual programming is provided. First, by setting up a visual programming platform based on the Internet of Things and building a control model based on the half-bridge MMC on it, it is possible to use this platform to achieve online control by controlling the active power and reactive power, and the model parameters can be modified online using visual programming. The voltage command values of the upper and lower bridge arms of each phase can also be output. At the same time, a visual programming solution for the active current limiting control strategy is set up. The voltage value of the entire DC bus is extracted as the input signal, and the number of sub-modules of the 6 bridge arms is used as the output signal. In this way, a flexible system from the construction of the control model to the setting of the active current limiting control strategy is built based on visual programming, which is convenient for corresponding adjustment and control command output according to different situations.

[0062] In the solution of the present invention, a method for accurately selecting the optimal solution to deal with faults and reasonably limiting the current is provided. After a fault occurs, first, the limit value of the fault current is obtained online. After judging the occurrence of a DC fault, the number of sub-modules of the 6 bridge arms is switched through the controller of the commutation valve after a fault detection delay, and the DC fault current is automatically detected after the fault current suppression is started, and its maximum value is extracted as the limit value. Then, the limit value of the fault current is compared with the opening capacity curves of different-price DC circuit breakers set in advance, and the optional circuit breakers with the maximum breaking current greater than the fault current limit value are selected, and the circuit breaker with the lowest price is selected as the target circuit breaker. Finally, according to the maximum breaking current of the target circuit breaker, the additional full-bridge ratio is calculated using a specific fourth calculation formula, and it is added to 10% of the total number of modules to determine the optimal solution. The entire process realizes the purpose of reasonable current limiting from fault detection to accurately selecting a response solution.

[0063] Other features and advantages of the present invention will be described in the following specification, and, in part, will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained by the structures specifically pointed out in the written specification, claims, and drawings.

[0064] The technical solutions of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0065] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0066] Figure 1 It is a flowchart of a flexible transmission active current limiting method based on the Internet of Things according to an embodiment of the present invention.

[0067] Figure 2 It is a flowchart of building a control model based on a half-bridge MMC through visual programming in a flexible transmission active current limiting method based on the Internet of Things according to an embodiment of the present invention.

[0068] Figure 3 It is a flowchart of a visual programming scheme for setting an active current limiting control strategy in a flexible transmission active current limiting method based on the Internet of Things according to an embodiment of the present invention.

[0069] Figure 4 It is a flowchart of determining whether a fault occurs according to an active current limiting control strategy in a flexible transmission active current limiting method based on the Internet of Things. When there is no fault, control instructions are output according to the control model of the half-bridge MMC. When there is a fault, the output control instruction value is updated according to the lowest voltage value.

[0070] Figure 5 It is a flowchart of online obtaining the limit value of the fault current in a flexible transmission active current limiting method based on the Internet of Things according to an embodiment of the present invention.

[0071] Figure 6 It is a flowchart of obtaining the target circuit breaker by comparing the limit value of the fault current with the pre-set circuit breaker opening capacity curve in a flexible transmission active current limiting method based on the Internet of Things according to an embodiment of the present invention.

[0072] Figure 7 It is a flowchart of selecting the full-bridge ratio as the optimal solution according to the target circuit breaker in a flexible transmission active current limiting method based on the Internet of Things according to an embodiment of the present invention.

[0073] Figure 8 It is a structural diagram of a flexible transmission active current limiting system according to an embodiment of the present invention.

[0074] Figure 9 It is a structural diagram of an electronic device in an embodiment of the present invention. Specific embodiments

[0075] In some of the processes described in the specification, claims, and above-mentioned drawings of the present invention, multiple operations appear in a specific order. However, it should be clearly understood that these operations can be performed not in the order in which they appear herein or in parallel. The serial numbers of the operations, such as 101, 102, etc., are only used to distinguish different operations, and the serial numbers themselves do not represent any execution order. Additionally, these processes can include more or fewer operations, and these operations can be executed sequentially or in parallel. It should be noted that the descriptions such as "first", "second", etc. in this article are used to distinguish different messages, devices, modules, etc., do not represent a sequence, and do not limit that "first" and "second" are different types.

[0076] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0077] The core method for suppressing the fault current in a flexible DC power grid is to limit the short-circuit current. The traditional method for limiting the short-circuit current is to break the current value through a circuit breaker. However, in actual situations, a circuit breaker generally requires a zero-crossing point, and it is difficult for DC power transmission to have a zero-crossing point. Therefore, in the prior art, there is already a method to generate a current zero-crossing situation through an oscillation method.

[0078] Before the technology of the present invention, in the prior art, in addition to the DC circuit breaker solution, there is also a solution that uses an active current limiting control technology to achieve the isolation and clearance of the fault current, and overcome the defect that the half-bridge modular multilevel converter cannot clear the fault due to the reverse parallel diode freewheeling effect.

[0079] In the embodiments of the present invention, a flexible power transmission active current limiting method and system based on the Internet of Things are provided. This solution utilizes the negative voltage output characteristics of the full-bridge module in the Internet of Things, combined with the online control of the DC modulation ratio, to complete the online active current limiting control.

[0080] According to the first aspect of the embodiments of the present invention, a flexible power transmission active current limiting method based on the Internet of Things is provided.

[0081] Figure 1 It is a flowchart of a flexible power transmission active current limiting method based on the Internet of Things according to an embodiment of the present invention.

[0082] In one or more embodiments, preferably, the flexible power transmission active current limiting method based on the Internet of Things includes:

[0083] S101. Build a control model based on a half-bridge MMC through visual programming;

[0084] S102. Set a visual programming solution for the active current limiting control strategy;

[0085] S103. Determine whether a fault occurs according to the active current limiting control strategy. When there is no fault, output control instructions according to the control model of the half-bridge MMC. When there is a fault, update the value of the output control instructions according to the lowest voltage value;

[0086] S104. Obtain the limit value of the fault current online;

[0087] S105. Compare the limit value of the fault current with the pre-set circuit breaker opening capacity curve to obtain the target circuit breaker;

[0088] S106. Select the full-bridge ratio as the optimal solution according to the target circuit breaker.

[0089] In the embodiment of the present invention, in the prior art, the construction costs of the flexible DC transmission using the full-half bridge hybrid and the pure half-bridge flexible DC transmission are 441,000 yuan / MW and 251,100 yuan / MW respectively, with an overall increase of 75.6%. Because, in the prior art, if the Internet of Things is used for parameter update and design process, the method of combining the full-bridge plate hybrid with the DC circuit breaker is preferably selected to obtain the ratio under the optimal cost.

[0090] Figure 2 It is a flowchart of building a control model based on a half-bridge MMC through visual programming in an active current limiting method for flexible power transmission based on the Internet of Things according to an embodiment of the present invention.

[0091] As Figure 2 shown, in one or more embodiments, preferably, the building of the control model based on a half-bridge MMC through visual programming specifically includes:

[0092] S201. Set up a visual programming platform based on the Internet of Things;

[0093] S202. Set a control model based on a half-bridge MMC on the visual programming platform and perform online control by controlling the active power and reactive power;

[0094] S203. Set the control model based on a half-bridge MMC to modify the online model parameters through the Internet of Things using visual programming, and output the upper bridge arm voltage instruction values of A, B, and C and the lower bridge arm voltage instruction values of A, B, and C.

[0095] In an embodiment of the present invention, first, a visualization programming platform based on the Internet of Things needs to be set up. This platform allows users to program through a graphical interface without writing complex codes. Such a platform usually has a drag-and-drop function, and users can build programs by dragging predefined modules or components. On this visualization programming platform, a control model based on a half-bridge modular multilevel converter (MMC) will be built. MMC is a power electronic converter widely used in high-voltage direct current (HVDC) transmission and flexible alternating current transmission systems (FACTS). The half-bridge MMC is one of the topological structures, which consists of multiple identical sub-modules, and each sub-module contains a half-bridge circuit. The main task of the control model is to online control the active power and reactive power. Active power refers to the power that actually does work, such as driving a motor to rotate; reactive power refers to the power that does not do actual work, such as the exchange of magnetic field energy. By adjusting the output voltage and phase of the MMC, the flow of these powers can be controlled. To achieve online control, the control model needs to be connected to the Internet of Things. In this way, data (such as the voltage, current, and frequency of the power grid) can be collected in real time, and the working state of the MMC can be dynamically adjusted according to these data. Using the visualization programming platform, the parameters of the control model can also be modified online. For example, the set values of active and reactive powers can be adjusted, or the control strategy can be changed (such as switching from PQ control to VF control). Finally, the control model will output the upper-bridge-arm voltage command values and lower-bridge-arm voltage command values of three phases A, B, and C. These command values will be sent to each sub-module of the MMC to control the internal switching devices (such as IGBTs) to generate the required output voltage.

[0096] Figure 3 It is a flowchart of a visualization programming scheme for setting an active current limiting control strategy in an active current limiting method for flexible power transmission based on the Internet of Things according to an embodiment of the present invention.

[0097] As Figure 3 shown, in one or more embodiments, preferably, the visualization programming scheme for setting the active current limiting control strategy specifically includes:

[0098] S301. Set to extract the voltage value on all DC buses as the input signal for the visualization programming of the active current limiting control strategy;

[0099] S302. Set the number of sub-modules of 6 bridge arms as the output signal for the visualization programming of the active current limiting control strategy.

[0100] In the embodiment of the present invention, in the control strategy of a normal half-bridge MMC, half of the control signals of phases A, B, and C are divided by the rated value of the sub-module capacitor voltage to obtain the number of sub-modules that need to be transiently inserted in each arm, so that the sum of the DC voltages output by the upper and lower arm units is equal to the given control signal, and emergency step-down control of the arm is performed. Under the step-down control, the fault current will be significantly reduced, and then the DC fault will be quickly cleared. When the DC fault has been cleared by the DC circuit breaker, the converter immediately switches from the emergency step-down control of the arm to the conventional control mode, enabling the DC power grid to resume normal operation.

[0101] Figure 4 It is a flowchart of a method for actively limiting current in flexible power transmission based on the Internet of Things according to an embodiment of the present invention, which determines whether a fault occurs according to the active current limiting control strategy. When there is no fault, control instructions are output according to the control model of the half-bridge MMC. When there is a fault, the output control instruction value is updated according to the lowest voltage value.

[0102] As Figure 4 shown, in one or more embodiments, preferably, the determining whether a fault occurs according to the active current limiting control strategy, when there is no fault, outputting control instructions according to the control model of the half-bridge MMC, and when there is a fault, updating the output control instruction value according to the lowest voltage value specifically includes:

[0103] S401. Determine whether there is a fault at the current moment. If no DC fault occurs, divide the reference voltages of the 6 arms output by the control model of the half-bridge MMC by the rated value Vcn of the sub-module capacitor voltage to obtain the number of sub-modules Nref that need to be inserted in each arm, which is used as the control instruction of the valve controller;

[0104] S402. When it is determined that there is a fault at the current moment, start timing the time delay. When the time delay satisfies the first calculation formula, switch to the fault current limiting control strategy;

[0105] S403. When in the fault current limiting control strategy, calculate the lowest voltage value using the second calculation formula for fast tracking of the fault point voltage;

[0106] S404. Calculate and generate the number of sub-modules of the 6 arms according to the lowest voltage value using the third calculation formula;

[0107] The first calculation formula is:

[0108] SY > KY

[0109] where SY is the time delay and KY is the control test;

[0110] The second calculation formula is:

[0111] zz = Min(Vdc3, Vdc2, Vdc)

[0112] Among them, zz is the minimum voltage value, Vdc is the DC voltage, and the voltage values of Vdc3, Vdc2, and Vdc of the lines connected to the current DC bus are VA, VB, and VC in sequence. Min() is the minimum value extraction function;

[0113] The third calculation formula is:

[0114]

[0115] Among them, VFAP, VFBP, VFCP, VFAN, VFBN, and VFCN are the upper bridge arm voltage command values of A, B, and C and the lower bridge arm voltage command values of A, B, and C in sequence, and S1, S2, S3, S4, S5, and S6 are the number of inserted sub-modules of the 6 bridge arms in sequence.

[0116] In the embodiment of the present invention, first, it is necessary to determine whether there is a fault at the current moment. This can be achieved by monitoring various sensors and protection devices in the system. If a DC fault (such as overcurrent, short circuit, etc.) is detected, the fault handling program is entered. If no DC fault occurs, the reference voltages of the 6 bridge arms output by the control model of the half-bridge MMC are divided by the rated value Vcn of the sub-module capacitor voltage to obtain the number of sub-modules Nref that need to be inserted for each bridge arm. This calculation process can be expressed as: Nref = Vcn × Vref; where Vref is the reference voltage of the bridge arm and Vcn is the rated value of the sub-module capacitor voltage. Nref will be used as the control instruction of the valve controller to determine the number of sub-modules that need to be inserted for each bridge arm. When it is determined that there is a fault at the current moment, the time delay is started. When the time delay satisfies the first calculation formula SY > KY, the fault current limiting control strategy is switched. Here, SY represents the time delay and KY is a preset control test threshold. Under the fault current limiting control strategy, the second calculation formula is used to calculate the minimum voltage value zz for quickly tracking the voltage at the fault point. The second calculation formula is: zz = min(Vdc3, Vdc2, Vdc); where zz is the minimum voltage value, Vdc is the DC voltage, and Vdc3, Vdc2, and Vdc are the voltage values of the lines connected to the current DC in sequence, and min() is the minimum value extraction function. According to the calculated minimum voltage value zzzz, the third calculation formula is used to calculate and generate the number of sub-modules of the 6 bridge arms. Through the above steps, precise control of the half-bridge MMC can be achieved, ensuring the stable operation of the system whether in normal operation or in case of a fault.

[0117] Figure 5 It is a flowchart of online obtaining the limit value of the fault current in an active current limiting method for flexible power transmission based on the Internet of Things according to an embodiment of the present invention.

[0118] As Figure 5 shown, in one or more embodiments, preferably, obtaining the limit value of the fault current online specifically includes:

[0119] S501. After judging the occurrence of a DC fault, the number of sub-modules of the six arms is switched by the controller of the commutation valve after a fault detection delay;

[0120] S502. After starting to suppress the fault current, automatically detect the DC fault current;

[0121] S503. Extract the maximum value of the fault current as the limit value of the fault current.

[0122] In the embodiment of the present invention, the DC current is calculated according to the AC current, IDC = IA + IB + IC, where IDC is the DC current, IA is the AC current of phase A, IB is the AC current of phase B, and IC is the AC current of phase C; 2) Since the AC currents of the three-phase AC of A, B, and C satisfy Kirchhoff's voltage law, the following formula can be used to calculate the DC fault current: IDC = (IF)e-kt + ici, where IF is the initial value of the current, k is a constant coefficient formed by the line parameters, and ici is the transient current generated by the inserted sub-module; therefore, its fault current is decaying, and the decay speed is affected by the value of k; extracting the maximum value during this process is the limit value of the fault current.

[0123] Figure 6 is a flow chart of obtaining the target circuit breaker according to the comparison between the limit value of the fault current and the pre-set circuit breaker breaking capacity curve in an active current limiting method for flexible power transmission based on the Internet of Things according to an embodiment of the present invention.

[0124] As Figure 6 shown, in one or more embodiments, preferably, obtaining the target circuit breaker according to the comparison between the limit value of the fault current and the pre-set circuit breaker breaking capacity curve specifically includes:

[0125] S601. Set the breaking capacity curves of several DC circuit breakers with different prices;

[0126] S602. Extract the maximum breaking current of different breaking capacity curves;

[0127] S603. When the maximum breaking current is greater than the limit value of the fault current, it is used as an optional circuit breaker;

[0128] S604. Extract the circuit breaker with the lowest price among all the optional circuit breakers as the target circuit breaker.

[0129] In an embodiment of the present invention, collect data on DC circuit breakers of different models and prices and their opening capacity curves. Establish a database or spreadsheet and enter the data points of the model, price, and opening capacity curve of each circuit breaker. Design an algorithm or use a graphical tool to analyze the opening capacity curve of each circuit breaker, identify and record its maximum breaking current. Computational software or programming tools (such as Python, MATLAB, etc.) can be used to automate this step. Compare the maximum breaking current of each circuit breaker with the fault current limit value. Create a screening function or query to automatically select all circuit breakers with a maximum breaking current greater than the fault current limit value. From the list of screened circuit breakers, extract the price information of each circuit breaker. Sort these circuit breakers to find the one with the lowest price. Take the circuit breaker with the lowest price and qualified technology as the target circuit breaker. Output or display the model, price, and important performance indicators of this circuit breaker. Suppose a power system engineer needs to select an appropriate circuit breaker for a newly designed DC transmission system. He first obtains 5 circuit breaker options with different prices and their opening capacity curves from suppliers. Through an automated tool, he quickly analyzes these curves and determines the maximum breaking current of each circuit breaker. The set fault current limit is 10 kA. The system automatically screens out all circuit breakers with a maximum breaking current exceeding 10 kA, and then compares the prices of these circuit breakers. It is found that a circuit breaker with a price of $5000 meets both the technical requirements and has the lowest cost. Therefore, the engineer selects this circuit breaker as the final procurement option, thus ensuring the safety and economy of the system.

[0130] Figure 7 It is a flowchart of selecting the full-bridge ratio as the optimal solution according to the target circuit breaker in a flexible transmission active current limiting method based on the Internet of Things in an embodiment of the present invention.

[0131] As Figure 7 shown, in one or more embodiments, preferably, the selecting the full-bridge ratio as the optimal solution according to the target circuit breaker specifically includes:

[0132] S701. Obtain the maximum breaking current of the target circuit breaker;

[0133] S702. Calculate the additional full-bridge ratio using the fourth calculation formula;

[0134] S703. Add the additional full-bridge ratio to 10% of the total number of modules as the optimal solution;

[0135] The fourth calculation formula is:

[0136] E = 1.2×CG÷kd

[0137] where E is the additional full-bridge ratio, kd is the maximum breaking current, and CG is the limit value of the fault current.

[0138] In an embodiment of the present invention, to obtain the maximum breaking current of the target circuit breaker: First, it is necessary to accurately understand the maximum breaking current (kd) of the selected target circuit breaker. This data is usually provided by the equipment manufacturer or can be obtained through actual testing. Calculate the additional full-bridge ratio: Use the fourth calculation formula E = 1.2 × cg × kd to calculate the additional full-bridge ratio. Here, E represents the additional full-bridge ratio, CG represents the limit value of the fault current, and kd represents the maximum breaking current again. Multiplying by 1.2 is to ensure there is enough margin to cope with possible overload conditions. Develop an optimal solution: Add 10% of the total number of modules to the calculated additional full-bridge ratio to determine the final full-bridge ratio. This step ensures that the system design not only considers the current fault current but also has additional capacity to adapt to possible future demand changes or system upgrades. The detailed implementation steps are as follows: 1. Data collection: Obtain the maximum breaking current from the technical specifications of the target circuit breaker. Determine the limit value of the fault current in the system, which may need to be obtained through historical data analysis or system simulation. 2. Perform calculations: Input the limit value of the fault current and the maximum breaking current into the fourth calculation formula. Use a calculator or programming tool to calculate the additional full-bridge ratio. 3. Optimize the scheme design: Calculate 10% of the total number of system modules and add it to the additional full-bridge ratio. After setting the full-bridge ratio, perform system design and configuration adjustments to ensure that all components can handle this new ratio. 4. Verification and testing: Simulate the new configuration in the system simulation software to ensure its performance under various operating conditions. If possible, conduct on-site testing to verify the effectiveness of the calculations and configurations. Specifically, a practical example is as follows: Suppose a power system engineer is responsible for upgrading the DC circuit breaker of a substation. He selects a circuit breaker with a maximum breaking current of 30 kA. Given that the limit value of the fault current at this station is 25 kA. According to the fourth calculation formula, the additional full-bridge ratio is calculated as follows: E = 1.0; Considering possible future expansion of the system, he decides to add 10% of the total number of modules to the additional full-bridge ratio. If the system has 100 modules, then an additional 10 modules are added, making the final designed full-bridge ratio 1.1 (i.e., increasing the number of modules by 10% to adapt to the additional full-bridge ratio). In this way, the engineer ensures that the system can not only withstand the current electrical load but also adapt to possible future increased demands, thereby enhancing the reliability and durability of the system.

[0139] According to the second aspect of the embodiment of the present invention, a flexible power transmission active current limiting system based on the Internet of Things is provided.

[0140] Figure 8 It is a structural diagram of a flexible power transmission active current limiting system based on the Internet of Things according to an embodiment of the present invention.

[0141] In one or more embodiments, preferably, the flexible transmission active current limiting system based on the Internet of Things includes:

[0142] A model building module 801 for building a control model based on a half-bridge MMC through visual programming;

[0143] An active current limiting interaction setting module 802 for setting a visual programming solution for the active current limiting control strategy;

[0144] An online instruction generation module 803 for judging whether a fault occurs according to the active current limiting control strategy. When there is no fault, control instructions are output according to the control model of the half-bridge MMC. When there is a fault, the output control instruction value is updated according to the lowest voltage value;

[0145] A fault current extreme value module 804 for obtaining the limit value of the fault current online;

[0146] A circuit breaker selection module 805 for comparing the limit value of the fault current with a preset circuit breaker breaking capacity curve to obtain a target circuit breaker;

[0147] An optimal extraction module 806 for selecting the full-bridge ratio as the optimal solution according to the target circuit breaker.

[0148] In the embodiments of the present invention, through a series of modular designs, a system applicable to different structures is realized. This system can achieve closed-loop, reliable, and efficient execution through acquisition, analysis, and control.

[0149] According to the third aspect of the embodiments of the present invention, a computer-readable storage medium is provided, on which computer program instructions are stored. When the computer program instructions are executed by a processor, the method described in any item of the first aspect of the embodiments of the present invention is realized.

[0150] According to the fourth aspect of the embodiments of the present invention, an electronic device is provided. Figure 9 It is a structural diagram of an electronic device in an embodiment of the present invention. Figure 9 The shown electronic device is a general flexible transmission active current limiting device based on the Internet of Things. Refer to Figure 9 , the electronic device may be a smart phone, a tablet computer and other devices. The electronic device 900 includes a processor 901 and a memory 902. Among them, the processor 901 is electrically connected to the memory 902.

[0151] The processor 901 is the control center of the electronic device 900, connecting various parts of the entire electronic device through various interfaces and circuits. By running or calling the computer programs stored in the memory 902 and calling the data stored in the memory 902, it executes various functions of the electronic device and processes data, thereby monitoring the electronic device as a whole.

[0152] In this embodiment, the processor 901 in the electronic device 900 will load the instructions corresponding to the processes of one or more computer programs into the memory 902 according to the following steps, and the processor 901 will run the computer programs stored in the memory 902 to implement various functions, such as: building a control model based on a half-bridge MMC based on visual programming; setting a visual programming solution for the active current limiting control strategy; judging whether a fault occurs according to the active current limiting control strategy. When there is no fault, output control instructions according to the control model of the half-bridge MMC. When there is a fault, update the output control instruction value according to the lowest voltage value; obtain the limit value of the fault current online; compare the limit value of the fault current with the pre-set breaker opening capacity curve to obtain the target breaker; select the full-bridge ratio as the optimal solution according to the target breaker.

[0153] In some embodiments, the electronic device 900 may further include: a display 903, a radio frequency circuit 904, an audio circuit 905, a Wi-Fi module 906, and a power supply 907. Among them, the display 903, the radio frequency circuit 904, the audio circuit 905, the Wi-Fi module 906, and the power supply 907 are respectively electrically connected to the processor 901.

[0154] The display 903 can be used to display information input by the user or information provided to the user, as well as various graphical user interfaces, which can be composed of graphics, text, icons, videos, and any combination thereof. The display 903 may include a display panel. In some embodiments, the display panel may be configured in the form of a liquid crystal display (LCD) or an organic light-emitting diode (OLED), etc.

[0155] The radio frequency circuit 904 can be used to transmit and receive radio frequency signals to establish wireless communication with a network device or other electronic devices and transmit and receive signals between the network device or other electronic devices.

[0156] The audio circuit 905 can be used to provide an audio interface between the user and the electronic device through a speaker and a microphone.

[0157] The Wi-Fi module 906 can be used for short-range wireless transmission, which can help users send and receive emails, browse websites, access streaming media, etc. It provides users with wireless broadband Internet access.

[0158] The power supply 907 can be used to supply power to various components of the electronic device 900. In some embodiments, the power supply 907 can be logically connected to the processor 901 through a power management system, so as to realize functions such as management of charging, discharging, and power consumption management through the power management system.

[0159] Although Figure 9 not shown in the figure, the electronic device 900 may further include a camera, a Bluetooth module, etc., which will not be elaborated here.

[0160] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0161] In the solution of the present invention, an active current limiting method for adaptively and quickly adjusting the full-half bridge hybrid is combined with Internet of Things-based visual programming.

[0162] In the solution of the present invention, the full-bridge ratio selection in the case of the optimal cost circuit breaker is carried out through the fast and extreme breaking ability.

[0163] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories and optical memories, etc.) containing computer-usable program code.

[0164] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, and the combination of processes and / or blocks in the flowchart and / or block diagram, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for realizing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0165] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means that implement the function specified in one or more of the processes and / or blocks Figure 1 one or more of the processes and / or blocks Figure 1 specified in the block or blocks.

[0166] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable apparatus provide steps for implementing the function specified in one or more of the processes and / or blocks Figure 1 one or more of the processes and / or blocks Figure 1 specified in the block or blocks.

[0167] It is apparent that those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A flexible power transmission active current limiting method based on the Internet of Things, characterized in that: The method includes: Build a control model based on half-bridge MMC based on visual programming; A visual programming solution for setting active current limiting control strategy based on the constructed control model; Determine whether a fault occurs according to the active current limiting control strategy. If there is no fault, output the control command according to the control model of the half-bridge MMC. If there is a fault, update the output control command value according to the minimum voltage value. Obtain the limit value of fault current online; Obtain the target circuit breaker by comparing the limit value of the fault current with the preset circuit breaker breaking capacity curve; The full bridge ratio is selected as the optimal solution according to the target circuit breaker.

2. A flexible power transmission active current limiting method based on the Internet of Things as claimed in claim 1, characterized in that: The construction of a control model based on a half-bridge MMC based on visual programming specifically includes: Set up a visual programming platform based on the Internet of Things; A control model based on a half-bridge MMC is set up on the visual programming platform, which performs online control by controlling active power and reactive power; A control model based on a half-bridge MMC is set up through the Internet of Things, and visual programming is used to modify the model parameters online, and the upper arm voltage command values ​​of A, B, and C and the lower arm voltage command values ​​of A, B, and C are output.

3. The method for active current limiting of flexible power transmission based on the Internet of Things as claimed in claim 1, characterized in that: The visual programming scheme for setting the active current limiting control strategy specifically includes: Set to extract all the voltage values ​​on the DC bus as the input signal for the visual programming of the active current limiting control strategy; The number of sub-modules of the six bridge arms is set as the output signal of the visual programming of the active current limiting control strategy.

4. The method for active current limiting of flexible power transmission based on the Internet of Things as claimed in claim 1, characterized in that: The method of judging whether a fault occurs according to the active current limiting control strategy, outputting a control instruction according to the control model of the half-bridge MMC when there is no fault, and updating the output control instruction value according to the minimum voltage value when there is a fault, specifically includes: Determine whether there is a fault at the current moment. If no DC fault occurs, divide the reference voltage of the six bridge arms output by the control model of the half-bridge MMC by the rated value Vcn of the submodule capacitor voltage to obtain the number of submodules Nref required for each bridge arm as the control instruction of the valve controller; When it is determined that there is a fault at the current moment, the time delay is started, and when the delay satisfies the first calculation formula, the fault current limiting control strategy is switched; When in the fault current limiting control strategy, the second calculation formula is used to calculate the minimum voltage value for fast tracking of the fault point voltage; The number of submodules for generating six bridge arms is calculated using a third calculation formula according to the minimum voltage value, wherein the number of submodules for generating six bridge arms is the number of submodules that need to be invested; The first calculation formula is: SY>KY Among them, SY is the time delay, KY is the control test; The second calculation formula is: zz=Min(Vdc3,Vdc2,Vdc) Wherein, zz is the lowest voltage value, Vdc is the DC voltage, VA, VB and VC are the voltage values ​​of the lines Vdc3, Vdc2, Vdc connected to the current DC bus, respectively, and Min() is the minimum value extraction function; The third calculation formula is: Among them, VFAP, VFBP, VFCP, VFAN, VFBN, and VFCN are the upper bridge arm voltage command values ​​of A, B, and C and the lower bridge arm voltage command values ​​of A, B, and C respectively, and S1, S2, S3, S4, S5, and S6 are the number of sub-modules put into operation in the six bridge arms respectively.

5. The method for active current limiting of flexible power transmission based on the Internet of Things as claimed in claim 1, characterized in that: The online obtaining of the limit value of the fault current specifically includes: After determining that a DC fault has occurred, the number of submodules in the six bridge arms is switched after a fault detection delay using the controller of the converter valve; After starting the fault current suppression, the DC fault current detection is automatically performed; The maximum value of the fault current is extracted as the limit value of the fault current.

6. The method for active current limiting of flexible power transmission based on the Internet of Things as claimed in claim 1, characterized in that: The step of obtaining a target circuit breaker by comparing the limit value of the fault current with a preset circuit breaker breaking capacity curve specifically includes: Set up several breaking capacity curves of DC circuit breakers at different price points; Extract the maximum breaking current of different breaking capacity curves; When the maximum breaking current is greater than the limit value of the fault current, it serves as an optional circuit breaker; Among all the optional circuit breakers, the circuit breaker with the smallest price is extracted as the target circuit breaker.

7. The method for active current limiting of flexible power transmission based on the Internet of Things as claimed in claim 1, characterized in that: The method of selecting the full-bridge ratio as the optimal solution according to the target circuit breaker specifically includes: Get the maximum breaking current of the target circuit breaker; Calculate the additional full-bridge ratio using the fourth calculation formula; The extra full-bridge ratio plus 10 percent of the total number of modules is taken as the optimal solution; The fourth calculation formula is: E=1.2×CG÷kd Where, E is the additional full-bridge ratio, kd is the maximum breaking current, and CG is the limit value of the fault current.

8. A flexible power transmission active current limiting system based on the Internet of Things, characterized in that: The system is used to implement the method according to any one of claims 1 to 7, and the system comprises: Model building module, used to build a control model based on half-bridge MMC based on visual programming; Active current limiting interactive setting module, used to set the visual programming scheme of active current limiting control strategy; An online instruction generation module is used to determine whether a fault occurs according to the active current limiting control strategy. When there is no fault, the control instruction is output according to the control model of the half-bridge MMC. When there is a fault, the output control instruction value is updated according to the minimum voltage value. Fault current extreme value module, used to obtain the limit value of fault current online; A circuit breaker selection module is used to obtain a target circuit breaker according to the comparison between the limit value of the fault current and the preset circuit breaker breaking capacity curve; The optimal extraction module is used to select the full-bridge ratio as the optimal solution according to the target circuit breaker.

9. A computer-readable storage medium storing computer program instructions, characterized in that: The computer program instructions implement the method according to any one of claims 1 to 7 when executed by a processor.

10. An electronic device comprising a memory and a processor, characterized in that: The memory is used to store one or more computer program instructions, wherein the one or more computer program instructions are executed by the processor to implement the method according to any one of claims 1-7.

Images