Differential protection sensitivity optimization and improvement method and device based on flexible direct current regulation and control characteristics

Abstract

The invention discloses a differential protection sensitivity optimization and improvement method based on a flexible direct current regulation and control characteristic, and discloses a device with the differential protection sensitivity optimization and improvement method based on the flexible direct current regulation and control characteristic. The method comprises the following steps: mapping a positive sequence power factor angle break variable difference into an adaptive braking coefficient by utilizing the significant difference of small positive sequence power factor angle break variable and large system side positive sequence power factor angle break variable caused by the control characteristics of an internal fault flexible direct current converter, and dynamically adjusting an equivalent braking coefficient according to the positive sequence power factor angle break variable on the two sides, the braking amount is greatly reduced when an internal fault occurs, the protection sensitivity is improved, the reliability of original differential protection can also be ensured when an external fault occurs, the protection sensitivity and reliability can be considered, and the main protection action performance of a near-area alternating-current line of a flexible direct access system is improved.

Description

Technical Field

[0001] The present invention relates to the field of power systems and automation technologies, and in particular to a method and device for optimizing and improving the sensitivity of differential protection based on flexible direct current regulation characteristics. Background Art

[0002] Flexible DC transmission technology based on modular multilevel converters (MMCs) is widely used in large-scale renewable energy transmission and grid-connected projects in recent years. Due to its superior selectivity, phasor differential protection has become the primary protection for transmission lines of 110 kV and above. This technology eliminates commutation failures, offers four-quadrant operation, eliminates the need for large-scale reactive power support, and provides flexible DC networking. It effectively meets the frequency and voltage support requirements of renewable energy sources such as wind and photovoltaic power.

[0003] The existing technology has conducted an in-depth analysis of the phase relationship of the short-circuit current of each phase of the flexible DC converter and its influencing factors, pointing out that the phasor current differential protection currently used by mainstream protection manufacturers has the problem of insufficient sensitivity in the flexible DC input scenario. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes an improved method for phasor differential protection based on flexible direct current regulation characteristics, which significantly improves sensitivity while ensuring reliability.

[0005] The present invention also proposes a device with an improved method for phasor differential protection based on flexible direct current regulation characteristics.

[0006] According to the first aspect of the present invention, a method for optimizing and improving the sensitivity of differential protection based on flexible direct current regulation characteristics comprises the following steps:

[0007] Obtain the three-phase voltage and current phasors of the protection installation points on both sides of the protected line;

[0008] Calculate the positive sequence voltage and current on both sides and the memorized positive sequence voltage and current two cycles ago;

[0009] Based on the positive sequence voltage and positive sequence current, the positive sequence power factor angle PF of the current sampling point is calculated respectively. 1m And the two-wave front positive sequence power factor angle PF 1m00 ; and calculate the positive sequence power factor angle mutation ΔPF 1m =|PF 1m -PF 1m00 |;

[0010] According to the difference in the positive sequence power factor angle mutation on both sides of the line, the adaptive braking coefficient K is dynamically adjusted.C , and generate improved criteria.

[0011] The method for optimizing and improving the sensitivity of differential protection based on the flexible direct current regulation characteristics according to the embodiment of the present invention has at least the following beneficial effects: the method introduces the positive-sequence power factor angle mutation information on both sides into the braking criterion, utilizes the significant difference between the smaller positive-sequence power factor angle mutation amount and the larger positive-sequence power factor angle mutation amount on the system side caused by the control characteristics of the flexible direct current converter due to the fault in the zone, maps the difference in the positive-sequence power factor angle mutation amount to the adaptive braking coefficient, and dynamically adjusts the equivalent braking coefficient according to the positive-sequence power factor angle mutation amount on both sides. The braking amount is greatly reduced in the event of a fault in the zone, thereby improving the protection sensitivity. The reliability of the original differential protection can also be guaranteed in the event of a fault outside the zone, and the protection sensitivity and reliability can be taken into account, thereby improving the main protection action performance of the AC line in the vicinity of the flexible direct current access system.

[0012] According to some embodiments of the present invention, the improved criterion includes:

[0013]

[0014] in, and are the fault current phasor amplitudes on both sides of the line, i qd is the minimum operating current;

[0015] The adaptive braking coefficient K C The calculation formula is:

[0016]

[0017] Where Ks is the fixed braking coefficient, and its value range is 0.7 to 0.9.

[0018] According to some embodiments of the present invention, the positive sequence voltage and positive sequence current The calculation formula is:

[0019]

[0020] Among them, a is the rotation factor,

[0021] According to some embodiments of the present invention, the memorized positive sequence voltage Memory positive sequence current Extracted by the following formula:

[0022]

[0023] The subscript |0| indicates the memory amount of the first two cycles.

[0024] According to some embodiments of the present invention, when an in-zone fault occurs, the braking coefficient K is reduced. C Improve sensitivity; when an out-of-zone fault occurs, maintain the original fixed braking coefficient Ks to ensure reliability.

[0025] According to a second aspect of the present invention, a device for optimizing and improving the sensitivity of differential protection based on flexible direct current regulation characteristics is characterized by comprising:

[0026] A data acquisition module is used to obtain the three-phase voltage and current phasors of the protection installation points on both sides of the protected line;

[0027] The voltage and current module is used to calculate the positive sequence voltage and current on both sides and the memorized positive sequence voltage and current from two cycles ago;

[0028] The power factor angle module is used to calculate the positive sequence power factor angle PF of the current sampling point based on the positive sequence voltage and positive sequence current. 1m And the two-wave front positive sequence power factor angle PF 1moo , and calculate the positive sequence power factor angle mutation ΔPF 1m =|PF 1m -PF 1m00 |;

[0029] Improved judgment module, used to dynamically adjust the adaptive braking coefficient K according to the difference in the positive sequence power factor angle mutation on both sides of the line C , and generate improved criteria.

[0030] According to some embodiments of the present invention, the improved criterion includes:

[0031]

[0032] in, and are the fault current phasor amplitudes on both sides of the line, i qd is the minimum operating current;

[0033] The adaptive braking coefficient K C The calculation formula is:

[0034]

[0035] Where Ks is the fixed braking coefficient, and its value range is 0.7 to 0.9.

[0036] According to some embodiments of the present invention, the positive sequence voltage and positive sequence current The calculation formula is:

[0037]

[0038] Among them, a is the rotation factor,

[0039] According to some embodiments of the present invention, the memorized positive sequence voltage Memory positive sequence current Extracted by the following formula:

[0040]

[0041] The subscript |0| indicates the memory amount of the first two cycles.

[0042] According to some embodiments of the present invention, when an in-zone fault occurs, the braking coefficient K is reduced. C Improve sensitivity; when an out-of-zone fault occurs, maintain the original fixed braking coefficient Ks to ensure reliability.

[0043] The third aspect of the present invention provides a terminal, which includes: a memory, a processor, and a computer program stored in the memory and runnable on the processor. When the processor executes the computer program, it implements the above-mentioned method for optimizing and improving the sensitivity of differential protection based on flexible direct current regulation characteristics.

[0044] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0046] Figure 1 Schematic diagram of the steps of a method for optimizing and improving the sensitivity of differential protection based on flexible direct current regulation characteristics according to an embodiment of the present invention;

[0047] Figure 2 A topology diagram of a flexible direct current (FDC) AC system provided in an embodiment of the present invention;

[0048] Figure 3 Schematic diagram of the sudden change characteristics of the positive sequence power factor angle on both sides of the fault zone provided by the embodiment of the present invention;

[0049] Figure 4 Schematic diagram of the sudden change characteristics of the positive sequence power factor angle on both sides of an out-of-zone fault provided by an embodiment of the present invention;

[0050] Figure 5 Schematic diagram of sensitivity verification of the optimization solution for intra-area BC faults provided by an embodiment of the present invention;

[0051] Figure 6Schematic diagram of sensitivity verification of the optimization solution for intra-area AN failure provided by an embodiment of the present invention;

[0052] Figure 7 Schematic diagram of sensitivity verification of the optimization solution for intra-area BCN faults provided by an embodiment of the present invention;

[0053] Figure 8 A schematic diagram illustrating reliability verification of an optimization solution for out-of-zone faults provided in an embodiment of the present invention;

[0054] Figure 9 This is a structural block diagram and topological diagram of a device for optimizing and improving the sensitivity of differential protection based on flexible direct current regulation characteristics provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0055] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0056] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0057] In the description of the present invention, "several" means one or more, "many" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The use of "first" and "second" in the description is solely for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, implicitly specifying the number of the indicated technical features, or implicitly specifying the order of the indicated technical features.

[0058] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0059] Example 1

[0060] The embodiment of the present invention provides a method for optimizing and improving the sensitivity of differential protection based on flexible direct current regulation characteristics, such as Figure 1 As shown, the method includes the following steps:

[0061] Step S100: Acquire the three-phase voltage and current phasors of the protection installation points on both sides of the protected line.

[0062] like Figure 2 The flexible direct current is connected to the AC system as shown. First, it is necessary to obtain the three-phase voltage and current phasors at the protection installation points on both sides of the protected line m and n. as well as The following takes the m side as an example, and the n side is the same.

[0063] Step S200 , calculating the positive sequence voltage and current on both sides and the memorized positive sequence voltage and current from two cycles ago.

[0064] Calculate positive sequence voltage and positive sequence current

[0065]

[0066] Calculate the memorized positive sequence voltage and current two cycles ago

[0067]

[0068] Where, is the rotation factor, and the subscript |0| represents the memory of the first two cycles.

[0069] Step S300: Calculate the positive sequence power factor angle PF of the current sampling point based on the positive sequence voltage and positive sequence current. 1m And the two-wave front positive sequence power factor angle PF 1m00 ; and calculate the positive sequence power factor angle mutation ΔPF 1m =|PF 1m -PF 1moo |.

[0070] Calculate the positive sequence power factor angle PF at the current sampling point 1m :

[0071]

[0072] Calculate the positive sequence power factor angle PF for two cycles ahead 1m|0| :

[0073]

[0074] Calculate the positive sequence power factor angle mutation ΔPF1 1m :

[0075]

[0076] Step S400: Dynamically adjust the adaptive braking coefficient K according to the difference in the positive sequence power factor angle mutation amount on both sides of the line.C , and generate improved criteria. The formula is:

[0077]

[0078] in, and are the fault current phasor amplitudes on both sides of the line, i qd is the minimum operating current;

[0079] The adaptive braking coefficient K C The calculation formula is:

[0080]

[0081] Where Ks is the fixed braking coefficient, ranging from 0.7 to 0.9. ΔPF1 1.max =max(ΔPF1 1m ,ΔPF1 1n ) is the larger of the positive sequence power factor angle mutation on both sides of the line, ΔPF1 1.max =min(ΔPF1 1m ,ΔPF1 1n ) is the smaller of the positive sequence power factor angular mutations on both sides of the line.

[0082] The current domestic requirement for AC side fault ride-through of flexible DC converters is to use unbalanced control during the fault period to suppress negative sequence current. [7] In order to prevent DC overvoltage caused by power surplus in the DC system, flexible DC converter stations usually adopt a fixed unity power factor control strategy to maintain active power transmission during faults. Therefore, for AC lines with flexible DC input into the AC system, when an internal fault occurs, the positive sequence power factor angle mutation ΔPF11 on the system side is close to 90°. However, due to the influence of the unity power factor control strategy and the negative sequence suppression strategy, the positive sequence power factor angle mutation ΔPF11 on the flexible DC side is very small. Figure 3 As shown in the figure, when a fault occurs within the zone, the significant difference in the positive sequence power factor angle mutation amount ΔPF11 on both sides can be used to quickly reduce the braking coefficient and achieve sensitive action for the fault within the zone. When a fault occurs outside the zone, the positive sequence power factor angle ΔPF11 on both sides is basically close, as shown in the figure. Figure 4 As shown, the original customized trip coefficient is adopted to ensure reliable protection without false tripping.

[0083] Example 2

[0084] In RTDS, taking a real project as an example, an electromagnetic transient model of the AC system connected to the receiving end of MMC-HVDC is built, and the fault point is set as shown in the attached figure. Figure 1 As shown, they are F1 to F5 respectively.

[0085] The flexible DC converter station adopts the fixed unity power factor control strategy and the negative sequence suppression control strategy. The fault occurrence time is 100ms. The existing differential protection action characteristics and the improved action characteristics are plotted as shown in the attached figure. Figure 5 ~Attached Figure 8 What I see.

[0086] By the attached Figure 5 ~Attached Figure 7 It can be seen that the proposed improved scheme of phasor differential protection based on flexible DC regulation characteristics greatly reduces the braking current when the fault occurs within the zone, and is superior to the existing phasor differential protection in terms of sensitivity; Figure 8 It can be seen that the proposed improved scheme of phasor differential protection based on flexible direct current regulation characteristics has the same performance as the existing phasor differential protection in the event of out-of-zone faults, which greatly improves the sensitivity of the existing differential protection while ensuring reliability.

[0087] Example 3:

[0088] In another aspect of the present application, an embodiment provides a device for optimizing and improving the sensitivity of differential protection based on flexible direct current regulation characteristics. The device 90 includes:

[0089] The data acquisition module 901 is used to obtain the three-phase voltage and current phasors of the protection installation points on both sides of the protected line;

[0090] The voltage and current module 902 is used to calculate the positive sequence voltage and current on both sides and the memorized positive sequence voltage and current from two cycles ago;

[0091] The power factor angle module 903 is used to calculate the positive sequence power factor angle PF of the current sampling point based on the positive sequence voltage and positive sequence current. 1m And the two-wave front positive sequence power factor angle PF 1m00 , and calculate the positive sequence power factor angle mutation ΔPF 1m =|PF 1m -PF 1m00 |;

[0092] Improved judgment module 904 is used to dynamically adjust the adaptive braking coefficient K according to the difference in the positive sequence power factor angle mutation amount on both sides of the line C , and generate improved criteria:

[0093]

[0094] in, and are the fault current phasor amplitudes on both sides of the line, i qd is the minimum operating current;

[0095] The adaptive braking coefficient K C The calculation formula is:

[0096]

[0097] Where Ks is the fixed braking coefficient, and its value range is 0.7 to 0.9.

[0098] The positive sequence voltage and positive sequence current The calculation formula is:

[0099]

[0100] Among them, a is the rotation factor,

[0101] Furthermore, the positive sequence voltage is memorized Memory positive sequence current Extracted by the following formula:

[0102]

[0103] The subscript |0| indicates the memory amount of the first two cycles.

[0104] Furthermore, when an in-zone fault occurs, by reducing the braking coefficient K C Improve sensitivity; when an out-of-zone fault occurs, maintain the original fixed braking coefficient Ks to ensure reliability.

[0105] Another aspect of the present invention provides a computer-readable storage medium storing computer-executable instructions for executing the above-mentioned Figure 1 The sensitivity optimization and improvement method of differential protection based on flexible direct current regulation characteristics is shown.

[0106] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, i.e., they may be located in one place or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of this embodiment.

[0107] Those skilled in the art will appreciate that all or some of the steps and systems in the method disclosed above can be implemented as software, firmware, hardware, and appropriate combinations thereof. Some physical components or all physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application-specific integrated circuit. Such software can be distributed on a computer-readable medium, and the computer-readable medium can include computer storage media (or non-transitory media) and communication media (or temporary media). As known to those skilled in the art, the term computer storage media is included in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data) and is volatile and non-volatile, removable, and non-removable. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory, or other memory technology, CD-ROM, digital versatile disks (DVD), or other optical disk storage, magnetic cassettes, magnetic tapes, disk storage, or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by a computer. Furthermore, as is well known to those skilled in the art, communication media typically embodies computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and may include any information delivery media.

[0108] The above is a specific description of the preferred implementation of the present application, but the present application is not limited to the above implementation mode. Technical personnel familiar with the field can also make various equivalent modifications or substitutions without violating the spirit of the present application. These equivalent modifications or substitutions are all included in the scope defined by the claims of the present application.

Claims

1. A method for optimizing and improving the sensitivity of differential protection based on flexible direct current regulation characteristics, characterized in that: The following steps are involved: Obtain the three-phase voltage and current phasors of the protection installation points on both sides of the protected line; Calculate the positive sequence voltage and current on both sides and the memorized positive sequence voltage and current two cycles ago; Based on the positive sequence voltage and positive sequence current, the positive sequence power factor angle PF of the current sampling point is calculated respectively. 1m And the two-wave front positive sequence power factor angle PF 1moo ; and calculate the positive sequence power factor angle mutation ΔPF 1m =|PF 1m -PF 1m00 |; According to the difference in the positive sequence power factor angle mutation on both sides of the line, the adaptive braking coefficient K is dynamically adjusted. C , and generate improved criteria.

2. The method according to claim 1, characterized in that The improved criteria include: in, and are the fault current phasor amplitudes on both sides of the line, i qd is the minimum operating current; The adaptive braking coefficient K C The calculation formula is: Where Ks is the fixed braking coefficient, and its value range is 0.7 to 0.

9.

3. The method according to claim 1, characterized in that The positive sequence voltage and positive sequence current The calculation formula is: Among them, a is the rotation factor, 4. The method according to claim 3, characterized in that The memorized positive sequence voltage Memory positive sequence current Extracted by the following formula: The subscript |0| indicates the memory amount of the first two cycles.

5. The method according to claim 1, characterized in that When a fault occurs within the zone, the braking coefficient K is reduced. C Improve sensitivity; when an out-of-zone fault occurs, maintain the original fixed braking coefficient Ks to ensure reliability.

6. A device for optimizing and improving the sensitivity of differential protection based on flexible direct current regulation characteristics, characterized in that: include: A data acquisition module is used to obtain the three-phase voltage and current phasors of the protection installation points on both sides of the protected line; The voltage and current module is used to calculate the positive sequence voltage and current on both sides and the memorized positive sequence voltage and current from two cycles ago; The power factor angle module is used to calculate the positive sequence power factor angle PF of the current sampling point based on the positive sequence voltage and positive sequence current. 1m And the two-wave front positive sequence power factor angle PF 1m00 , and calculate the positive sequence power factor angle mutation ΔPF 1m =|PF 1m -PF 1m00 |; Improve the judgment module to dynamically adjust the adaptive braking coefficient K according to the difference in the positive sequence power factor angle mutation on both sides of the line C , and generate improved criteria.

7. The device according to claim 6, characterized in that The improved criteria include: in, and are the fault current phasor amplitudes on both sides of the line, i qd is the minimum operating current; The adaptive braking coefficient K C The calculation formula is: Where Ks is the fixed braking coefficient, and its value range is 0.7 to 0.

9.

8. The device according to claim 7, characterized in that The positive sequence voltage and positive sequence current The calculation formula is: Among them, a is the rotation factor, 9. The device according to claim 7, characterized in that The memorized positive sequence voltage Memory positive sequence current Extracted by the following formula: The subscript |0| indicates the memory amount of the first two cycles.

10. The device according to claim 7, characterized in that When a fault occurs within the zone, the braking coefficient K is reduced. C Improve sensitivity; when an out-of-zone fault occurs, maintain the original fixed braking coefficient Ks to ensure reliability.

11. A computer-readable storage medium storing computer-executable instructions, wherein the computer-executable instructions are used to execute the method according to any one of claims 1 to 5.

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