VSC-HVDC (Voltage Source Converter-High Voltage Direct Current) system protection method and system based on two-mode transient characteristic collaboration

Abstract

The invention belongs to the technical field of fault protection of a flexible direct-current power transmission system, and provides a VSC-HVDC system protection method based on two-mode transient characteristic collaboration. Comprising the following steps: constructing a VSC-HVDC system mathematical model and constructing a simulation platform; extracting and analyzing typical fault transient characteristics of the direct current side; and designing a protection scheme based on two-mode transient characteristic collaboration. The invention discloses a VSC-HVDC system protection method based on two-mode transient characteristic collaboration by researching transient characteristics of single-pole grounding, bipolar short circuit and high-resistance faults of a direct current side of a VSC-HVDC system. Establishing a system simulation model through a Simulink platform, injecting three types of typical faults, collecting transient voltage data, and analyzing the mapping correlation between the transient voltage change rate, the transient voltage acceleration and the faults under different faults to obtain key modal transient characteristics; a protection action logic based on cooperation of two modal thresholds is constructed, interference signals which may cause misjudgment, such as load disturbance, are effectively eliminated, and the effective information density of fault identification is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fault protection of flexible HVDC system, and particularly relates to a VSC-HVDC system protection method and system based on two-mode transient voltage feature cooperation, which is suitable for solving the problems of accurate identification and rapid removal of typical faults such as single-pole grounding, bipolar short circuit, high resistance fault and the like of the DC side of the VSC-HVDC system, and is particularly suitable for the safe and stable operation of the flexible HVDC system in the high-proportion new energy grid-connected scene. BACKGROUND

[0002] The global energy structure is accelerating the transformation to clean and low-carbon, and the grid-connected proportion of fluctuating new energy such as wind power and photovoltaic is continuously increasing. The limitations of traditional AC power transmission systems in terms of bidirectional power flow regulation and weak grid support are increasingly prominent. The VSC-HVDC technology has become a core supporting technology for long-distance high-power power transmission and new energy grid connection in new power systems due to its advantages of flexible and controllable power, no need for grid commutation, and independent regulation of active and reactive power, and is widely used in non-fall point high-power power transmission, island power supply and other engineering scenarios.

[0003] However, the fault protection of the VSC-HVDC system still faces key technical bottlenecks: the transient process of the DC side fault is complex, and the electrical quantity characteristics of different fault types are significantly different, so the traditional protection strategy based on a single electrical quantity (such as voltage amplitude and current amplitude) cannot balance reliability and speed.

[0004] Existing protection methods cannot comprehensively capture the multi-dimensional characteristics of the fault transient state, and are difficult to adapt to the complex fault scenarios of the VSC-HVDC system. A new type of protection strategy that can integrate multi-dimensional transient information, has strong anti-interference ability and fast action speed is urgently needed to ensure the safe and stable operation of the flexible HVDC system. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the existing VSC-HVDC system protection method, such as low identification accuracy for complex faults, weak anti-interference ability and slow action speed, and to provide a protection method and system based on two-mode transient feature cooperation, which realizes accurate and rapid removal of DC side faults by constructing a technical chain of "model building-feature extraction-scheme design-verification optimization".

[0006] The technical solution is as follows: On the one hand, the present application provides a VSC-HVDC system protection method based on two-mode transient feature cooperation, comprising the following steps: S1, a VSC-HVDC system mathematical model and a simulation platform are constructed, and the power and voltage data of the double converter stations are monitored in real time; S2, extraction and analysis of typical fault transient characteristics on the DC side: extract and analyze the distribution law of the transient voltage rate of change characteristic quantity and the transient voltage acceleration characteristic quantity under normal and fault conditions, and preset the transient voltage rate of change threshold and the transient voltage acceleration threshold according to the distribution law; according to the voltage data collected in S1, the transient voltage rate of change characteristic quantity and the transient voltage acceleration characteristic quantity are calculated; S3, judgment of typical faults on the DC side: compare the transient voltage rate of change characteristic quantity with the preset transient voltage rate of change threshold, and compare the transient voltage acceleration characteristic quantity with the preset transient voltage acceleration threshold.

[0007] S4, protection scheme design based on two-mode transient characteristic cooperation: when and only when the transient voltage rate of change characteristic quantity is greater than or equal to the transient voltage rate of change threshold, and the transient voltage acceleration characteristic quantity is greater than or equal to the transient voltage acceleration threshold, it is determined that a fault occurs on the DC line transient voltage acceleration threshold, and the protection device is triggered to act within 10 ms after the fault occurs.

[0008] On the other hand, the application provides a VSC-HVDC system protection system based on two-mode transient characteristic cooperation, which is used to realize the VSC-HVDC system protection method based on two-mode transient characteristic cooperation. The model construction subsystem is used to construct a VSC-HVDC system mathematical model and a simulation platform, and the model construction subsystem is configured with a data acquisition module to monitor and collect power and voltage data of double converter stations in real time. The transient characteristic extraction and analysis subsystem is used for extraction and analysis of typical fault transient characteristics on the DC side. The fault judgment subsystem is used for judging typical faults on the DC side. The protection scheme design subsystem is used for designing a protection scheme based on two-mode transient characteristic cooperation.

[0009] The technical scheme provided by the embodiment of the application has at least the following beneficial effects: 1. The application effectively distinguishes real fault transients from interference signals such as load fluctuations based on a two-mode cooperative criterion, significantly reduces the risk of misoperation, and has high reliability.

[0010] 2. The application can quickly capture the dramatic change characteristics of electrical quantities in the initial stage of the fault based on the transient rate of change and acceleration of the voltage, realize millisecond-level (<10 ms) fast action, and has high speed.

[0011] 3. The application can effectively identify various typical faults on the DC side, including high-impedance faults, solve the problem of insufficient sensitivity of traditional protection to high-impedance faults, and have strong adaptability. Attached Figure Description

[0012] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: Figure 1 A flowchart of a VSC-HVDC system protection method based on the synergy of two-modal transient features provided by the present invention is as follows: Figure 2 The following is a structural diagram of the VSC-HVDC system mathematical model and simulation platform provided by this invention: Figure 3 The present invention provides a mathematical model and simulation platform flowchart for the VSC-HVDC system. Figure 4 This invention provides a structural diagram of a VSC-HVDC system protection system based on the synergy of two-modal transient characteristics. Detailed Implementation

[0013] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0014] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0015] In the embodiments of this invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that, without emphasizing the distinction between them, they convey the same meaning. Similarly, the terms "of," "corresponding (relevant)," and "corresponding" may sometimes be used interchangeably. It should be noted that, without emphasizing the distinction between them, they convey the same meaning.

[0016] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0017] To make the technical problem to be solved, the technical solution and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments. This invention provides a protection method for VSC-HVDC systems based on the synergy of two-modal transient characteristics, such as... Figures 1-3 As shown, it includes the following steps: S1. Construct a mathematical model and simulation platform for the VSC-HVDC system, and monitor the power and voltage data of the dual converter stations in real time; In S1, the construction of the VSC-HVDC system mathematical model and simulation platform includes the following steps: S11. Analyze the core topology of the VSC-HVDC system, which includes six major components: AC system, converter transformer, AC filter, commutation reactor, voltage source converter (VSC), and DC capacitor. The VSC adopts a three-phase two-level bridge converter structure, which is composed of thyristor elements with 6 anti-parallel diodes forming a valve arm to form a three-phase full-bridge circuit to realize AC-DC power conversion.

[0018] Based on the working principle of VSC, expressions for active power P and reactive power Q are established: ; In the formula: This refers to the magnitude of the output voltage of the VSC converter. It refers to the magnitude of the AC system voltage. This refers to the effective reactance of the commutating reactor. It represents and The phase angle difference between them; S12. Build a hierarchical control system architecture. At the system level, the system receives scheduling commands, coordinates multi-terminal power distribution and DC voltage stability, and adopts master-slave control, droop control or voltage margin control strategies. At the station level, the system is based on a dual closed-loop control of "outer loop power / voltage loop + inner loop current loop" to achieve d / q axis decoupling and dynamic tracking with a response time in milliseconds. At the converter level, the system generates high-frequency trigger signals through pulse width modulation (PWM) to control IGBT switching and eliminate harmonic distortion.

[0019] S13. Based on the VSC-HVDC system mathematical model and simulation platform, set the key parameters: rated capacity 2000MVA, DC voltage ±100kV, AC voltage 230kV, discrete simulation step size 7.407μs (matching the IGBT 1.35kHz switching frequency), and configure the data acquisition module to monitor the power and voltage data of the dual converter stations in real time.

[0020] S2. Extraction and analysis of transient features of typical faults on the DC side: Extract and analyze the distribution patterns of transient voltage change rate and transient voltage acceleration features under normal and fault conditions, and preset transient voltage change rate thresholds and transient voltage acceleration thresholds based on their distribution patterns; calculate transient voltage change rate and transient voltage acceleration features based on the voltage data collected in S1.

[0021] In S2, the extraction and analysis of typical DC-side fault transient features includes the following steps: S21. Set three types of typical DC-side faults: Three types of typical DC-side faults and their simulation implementation methods are defined as follows: 1. Single-pole grounding fault: Connect a time-controlled switch between the positive / negative pole and ground, and connect a 0.01Ω fault resistor in series; 2. Bipolar short-circuit fault: Set a short-circuit switch between the positive and negative poles, with a closing time of 1.5 seconds, and connect a 0.01Ω fault resistor in series; 3. High-resistance fault: A 200Ω high-resistance resistor is used to simulate non-metallic grounding such as tree branch contact, pollution flashover, etc. S22. Unified fault simulation conditions: The fault occurrence time is set to 1.5 seconds, and the fault location is located at 10% of the transmission line. S23. Inject the above three types of faults into the VSC-HVDC system mathematical model and simulation platform, and collect DC voltage data within 30ms after the fault through the data acquisition module. S24. Extract the two core modal features of the transient voltage; 1. Transient voltage change rate: the first derivative of voltage with respect to time, with a time interval of 7.407 μs (simulation step size). 2. Transient voltage acceleration: the second derivative of voltage with respect to time; By comparing the characteristic distribution patterns under normal and fault conditions, it is clear that: the voltage drop of a single-pole grounding fault is about 15%-20%, the voltage of a double-pole short-circuit fault drops sharply to near 0, and the voltage of a high-resistance fault drops slowly by 5%-10%, providing a basis for the design of protection schemes. S25. Based on the analysis results of fault transient characteristics, set protection action thresholds: transient voltage change rate threshold and transient voltage acceleration threshold; perform data fitting and engineering verification through the VSC-HVDC system mathematical model and simulation platform.

[0022] S26. Based on the voltage data collected in S1, calculate the transient voltage change rate characteristic and the transient voltage acceleration characteristic.

[0023] S3. Typical fault judgment on the DC side: Compare the transient voltage change rate characteristic with the preset transient voltage change rate threshold, and at the same time compare the transient voltage acceleration characteristic with the preset transient voltage acceleration threshold.

[0024] S4. Protection scheme design based on two-mode transient characteristics: When the transient voltage change rate characteristic is greater than or equal to the transient voltage change rate threshold and the transient voltage acceleration characteristic is greater than or equal to the transient voltage acceleration threshold, it is determined that a fault has occurred in the DC line transient voltage acceleration threshold circuit, and the protection device is triggered to operate, and the fault is cleared within 10ms after the fault occurs.

[0025] In S4, the protection scheme design based on the synergy of two-modal transient characteristics includes the following steps: S41. Set protection action logic: The protection device will be activated if and only if both the transient voltage change rate and transient voltage acceleration of the DC line exceed the corresponding thresholds. ; ; In the formula, The threshold for the rate of change of transient voltage. The transient voltage acceleration threshold; If and only if the transient voltage change rate of the DC line is ≥ Transient voltage acceleration ≥ When this occurs, the protection device is activated.

[0026] S42. Clearly define protection action requirements: Fault identification and isolation shall be completed within 10ms after a fault occurs to prevent the fault from spreading to the AC side or other converter stations and to ensure the overall stability of the system.

[0027] The effectiveness verification of the protection scheme designed for S4 includes the following steps: S51. Export the per-unit values ​​of DC line voltage collected by the VSC-HVDC system mathematical model and simulation platform to Excel through the Workspace module for data preprocessing, including but not limited to removing outliers and filling in missing data. S52. Import the preprocessed data into MATLAB and use plotting tools to visualize the transient voltage change rate and acceleration curves under single-pole grounding, double-pole short circuit, and high-resistance faults to verify whether both modes exceed the set threshold. S53. Record the protection action time and fault clearing effect under three types of faults, verify the selectivity of the protection strategy (only the faulty line operates), record the protection action time of the three types of faults, confirm that the action time is ≤10ms, and there is no failure to operate or false operation, and verify the speed and reliability of the protection strategy.

[0028] Figure 4 This is a block diagram of a VSC-HVDC system protection system based on two-modal transient characteristic coordination, according to an exemplary embodiment. This VSC-HVDC system protection system is used to implement the VSC-HVDC system protection method based on two-modal transient characteristic coordination as described above. The VSC-HVDC system protection system includes: The model building subsystem is used to build the mathematical model and simulation platform of the VSC-HVDC system. The model building subsystem is configured with a data acquisition module to monitor and acquire the power and voltage data of the dual converter stations in real time. The transient feature extraction and analysis subsystem is used for the extraction and analysis of transient features of typical DC-side faults. The fault diagnosis subsystem is used to diagnose typical faults on the DC side. The protection scheme design subsystem is used to design protection schemes based on the synergy of two-modal transient characteristics.

[0029] The above embodiments can be implemented, in whole or in part, by software, hardware (such as circuits), firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more sets of available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium. A semiconductor medium can be a solid-state drive.

[0030] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0031] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the devices, apparatuses, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0032] In the several embodiments provided by this invention, it should be understood that the disclosed devices, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another device, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0033] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0034] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0035] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0036] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A protection method for a VSC-HVDC system based on the synergy of two-modal transient characteristics, characterized in that, Includes the following steps: S1. Construct a mathematical model and simulation platform for the VSC-HVDC system, and monitor the power and voltage data of the dual converter stations in real time; S2. Extraction and analysis of transient features of typical DC side faults: Extract and analyze the distribution patterns of transient voltage change rate and transient voltage acceleration features under normal and fault conditions, and preset transient voltage change rate thresholds and transient voltage acceleration thresholds based on their distribution patterns; calculate transient voltage change rate and transient voltage acceleration features based on the voltage data collected in S1. S3. Typical fault judgment on the DC side: Compare the transient voltage change rate characteristic with the preset transient voltage change rate threshold, and at the same time compare the transient voltage acceleration characteristic with the preset transient voltage acceleration threshold. S4. Protection scheme design based on two-mode transient characteristics: When the transient voltage change rate characteristic is greater than or equal to the transient voltage change rate threshold and the transient voltage acceleration characteristic is greater than or equal to the transient voltage acceleration threshold, it is determined that a fault has occurred in the DC line transient voltage acceleration threshold circuit, and the protection device is triggered to operate, and the fault is cleared within 10ms after the fault occurs.

2. The VSC-HVDC system protection method based on the synergy of two-modal transient characteristics according to claim 1, characterized in that, In S1, the construction of the VSC-HVDC system mathematical model and simulation platform includes the following steps: S11. Analyze the core topology of the VSC-HVDC system, clarify that the VSC adopts a three-phase two-level bridge converter structure, and establish the expressions for active power P and reactive power Q: ； In the formula: This refers to the magnitude of the output voltage of the VSC converter. It refers to the magnitude of the AC system voltage. This refers to the effective reactance of the commutating reactor. This represents the phase angle difference between them; S12. Establish a hierarchical control system architecture, including system level, station level and converter level; S13. Based on the Simulink platform, build a mathematical model and simulation platform for the VSC-HVDC system, set the system rated capacity to 2000MVA, DC voltage ±100kV, AC voltage 230kV, and discrete simulation step size to 7.407μs, and configure a data acquisition module to monitor the power and voltage data of the dual converter stations in real time.

3. The VSC-HVDC system protection method based on the synergy of two-modal transient characteristics according to claim 1, characterized in that, In S2, the extraction and analysis of typical DC-side fault transient features includes the following steps: S21. Set three types of typical DC-side faults: single-pole grounding fault, bipolar short-circuit fault, and high-resistance fault. S22. Unified fault simulation conditions: The fault occurrence time is set to 1.5 seconds, and the fault location is located at 10% of the line. S23. Inject the above three types of faults into the VSC-HVDC system mathematical model and simulation platform, and collect DC voltage data within 30ms after the fault through the data acquisition module. S24. Extract two core modal features of transient voltage: transient voltage change rate and transient voltage acceleration, and compare the feature distribution patterns under normal operating conditions and fault conditions. S25. Based on the analysis results of fault transient characteristics, set the protection action thresholds: transient voltage change rate threshold and transient voltage acceleration threshold; S26. Based on the voltage data collected in S1, calculate the transient voltage change rate characteristic and the transient voltage acceleration characteristic.

4. The VSC-HVDC system protection method based on the synergy of two-modal transient characteristics according to claim 1, characterized in that, In S4, the protection scheme design based on the synergy of two-modal transient characteristics includes the following steps: S41. Set protection action logic: The protection device will be activated if and only if both the transient voltage change rate and transient voltage acceleration of the DC line exceed the corresponding threshold. S42. Clearly define protection action requirements: Fault identification and isolation shall be completed within 10ms after the fault occurs.

5. The VSC-HVDC system protection method based on the synergy of two-modal transient characteristics according to claim 1, characterized in that, The effectiveness verification of the protection scheme designed for S4 includes the following steps: S51. Export the per-unit values ​​of DC line voltage collected by the VSC-HVDC system mathematical model and simulation platform to Excel through the Workspace module for data preprocessing, including but not limited to removing outliers and filling in missing data. S52. Import the preprocessed data into MATLAB and use plotting tools to visualize the transient voltage change rate and acceleration curves under single-pole grounding, double-pole short circuit, and high-resistance faults. S53. Record the protection action time and fault clearing effect under three types of faults to verify the selectivity, speed and reliability of the protection strategy.

6. A VSC-HVDC system protection system based on two-modal transient characteristic coordination, used to implement the VSC-HVDC system protection method based on two-modal transient characteristic coordination as described in any one of claims 1-5, wherein the VSC-HVDC system protection system comprises: The model building subsystem is used to build the mathematical model and simulation platform of the VSC-HVDC system. The model building subsystem is configured with a data acquisition module to monitor and acquire the power and voltage data of the dual converter stations in real time. The transient feature extraction and analysis subsystem is used for the extraction and analysis of transient features of typical DC-side faults. The fault diagnosis subsystem is used to diagnose typical faults on the DC side. The protection scheme design subsystem is used to design protection schemes based on the synergy of two-modal transient characteristics.

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