Feature signal injection-based pilot protection method and system for double-end weak feed system

Abstract

The invention provides a pilot protection method and system for a double-end weak feedback system based on characteristic signal injection. The pilot protection method comprises the following steps: injecting a characteristic frequency signal based on high controllability of a voltage source type current converter; constructing a double-end weak feedback system characteristic frequency equivalent circuit on the basis of characteristic frequency signal injection, and judging whether a fault starting condition is met or not according to a characteristic frequency signal; when a starting condition is met, a setting value is formulated by measuring the difference of the relation between the characteristic frequency impedance and the system characteristic frequency; and in combination with the setting value and the impedance difference of the measured characteristic frequencies at the two sides of the internal and external faults, establishing a criterion and judging the internal and external faults. Through injection of the characteristic frequency signal and analysis of the equivalent circuit, the problem that traditional protection cannot be applied when the new energy is connected to the weak feedback system is solved, the adaptability, sensitivity and rapidity of protection are improved, safe and stable operation of a power grid is guaranteed, and wide application of the new energy technology is promoted.

Description

Technical Field

[0001] The present invention belongs to the field of protection of weak power transmission lines connected to new energy sources, and in particular to a longitudinal protection method and system for a double-terminal weak-feedback system based on characteristic signal injection. Background Art

[0002] The transient characteristics unique to renewable energy generation technology show diverse characteristics, and these characteristics are significantly different from those of traditional synchronous generators. When a fault occurs in renewable energy generation, such as wind power and photovoltaic power generation, the frequency components in the short-circuit current are relatively complex, and contain a large proportion of attenuated speed frequency components. The existence of this frequency component makes the electrical characteristics of in-zone and out-of-zone faults on renewable energy transmission lines extremely similar, making it difficult to effectively distinguish them by conventional methods.

[0003] In addition, renewable energy power generation systems are often connected to weak power sources, which have relatively limited voltage support capabilities in the power grid. When a renewable energy power generation system fails or is disturbed, the weak power source may not be able to quickly provide stable and sufficient voltage support, resulting in greater system voltage fluctuations, further affecting the stable operation of the power grid.

[0004] Due to the above characteristics, traditional power system protection equipment and methods are prone to malfunction or refusal to operate when applied to renewable energy power generation systems. Malfunction may cause the fault-free part to be mistakenly cut off, affecting the power supply reliability and stability of the power grid; while refusal to operate may make it impossible to isolate and eliminate the fault in time, thereby expanding the scope of the fault and causing more serious consequences. Summary of the invention

[0005] The object of the present invention is to provide a double-terminal weak-feedback system longitudinal protection method and system based on characteristic signal injection to solve the above problems.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a double-terminal weak-feedback system pilot protection method based on characteristic signal injection, comprising:

[0008] Realize characteristic frequency signal injection based on high controllability of voltage source converter;

[0009] Based on the injection of characteristic frequency signal, a characteristic frequency equivalent circuit of the double-terminal weak-feedback system is constructed, and whether the fault start condition is met is determined according to the characteristic frequency signal;

[0010] When the start-up conditions are met, the setting value is determined by measuring the difference between the characteristic frequency impedance and the system characteristic frequency;

[0011] Combining the setting value and the difference in characteristic frequency impedance measured on both sides of the fault inside and outside the zone, a judgment criterion is constructed to determine the fault inside and outside the zone.

[0012] Furthermore, the characteristic frequency signal injection is realized based on the high controllability of the voltage source converter, including:

[0013] The fifth harmonic signal injection is achieved by changing the duty cycle of the modulation wave:

[0014]

[0015] Where U det is the amplitude of the detection signal, ω det is the angular frequency of the detection signal, is the initial phase U of the detection signal deta---c To inject harmonic detection signal.

[0016] Furthermore, based on the injection of the characteristic frequency signal, a characteristic frequency equivalent circuit of the double-terminal weak-feedback system is constructed, and whether the fault start condition is met is determined according to the characteristic frequency signal, including:

[0017] During the photovoltaic side fault, the converter uses the low voltage characteristics to start the fault ride-through control characteristics, and then constructs the characteristic frequency signal injection start-up criterion suitable for various short-circuit scenarios:

[0018]

[0019] In the formula, is the per unit voltage of the converter station grid connection point. Except for the single-phase grounding, the minimum phase voltage is taken. For other faults, the minimum line voltage is taken. * is the starting threshold value, which is 0.9; U N and U L.N They are the rated values ​​of phase voltage and line voltage respectively;

[0020] when After the startup criteria are met, the new energy converter station switches to the active harmonic signal injection mode.

[0021] Furthermore, when the start-up conditions are met, the setting value is determined by measuring the difference between the characteristic frequency impedance and the system characteristic frequency, including:

[0022] According to the construction of characteristic frequency equivalent circuit, the characteristic frequency electrical quantity in each voltage and current signal is extracted by discrete Fourier transform, and the characteristic frequency impedance measured at the protection installation on both sides when the fault occurs inside and outside the zone is written by writing Kirchhoff's voltage law:

[0023]

[0024] By calculating the characteristic frequency line of the system, the impedance value of the back system characteristic frequency at different frequencies is analyzed by using the sweep frequency method; by formulating the characteristic frequency impedance difference S between the M end and the N end of the field transmission line m and S n ;

[0025]

[0026] When a fault occurs within the zone, S m Amplitude greater than zero, S n The amplitude is equal to zero. When the out-of-zone fault occurs on the back side of M, both amplitudes are zero. When the out-of-zone fault occurs on the back side of N, both amplitudes are greater than zero.

[0027] Set the protection threshold. The following are the action conditions when the zone is in effect:

[0028]

[0029] Furthermore, the selection of the setting value meets the following selection principles:

[0030] S m.max mset <min(S m1.min ,S m2.min )(7)

[0031] max(S n1.max ,S n2.max ) nset n.min (8).

[0032] Where: S m1min 、Sm 2min They are respectively the fault within the area and the fault on the back side of the N-terminal busbar. m Minimum value; S mmin The fault S is the back side fault of the busbar at the M end. m Maximum value; S n1max , S n2max are the maximum values ​​of Sn for the fault within the area and the fault on the back side of the busbar at the M end; S nmin It is the minimum value of Sn of the N-end bus backside fault.

[0033] Furthermore, by combining the setting value and the characteristic frequency impedance difference measured on both sides of the fault inside and outside the zone, a criterion is constructed to judge the fault inside and outside the zone, including:

[0034] When the fault action condition is met, the fault is identified as an internal fault, otherwise it is an external fault. m and S n With threshold value S mset and S nset If it satisfies the formula: ​​​

[0035] If it is identified as an internal fault, the protection will trip; otherwise, the protection will not operate.

[0036] In a second aspect, the present invention provides a double-terminal weak-feedback system pilot protection system based on characteristic signal injection, comprising:

[0037] A signal injection module, used to implement characteristic frequency signal injection based on the high controllability of the voltage source converter;

[0038] A starting condition acquisition module is used to construct a characteristic frequency equivalent circuit of a double-terminal weak-feedback system based on the injection of a characteristic frequency signal, and to determine whether the fault starting condition is met according to the characteristic frequency signal;

[0039] A setting value acquisition module is used to determine the setting value by measuring the difference between the characteristic frequency impedance and the system characteristic frequency when the start-up conditions are met;

[0040] The judgment output module is used to combine the setting value and the characteristic frequency impedance difference measured on both sides of the fault inside and outside the zone to build a judgment criterion and judge the fault inside and outside the zone.

[0041] Furthermore, the characteristic frequency signal injection is realized based on the high controllability of the voltage source converter, including:

[0042] The fifth harmonic signal injection is achieved by changing the duty cycle of the modulation wave:

[0043]

[0044] Where U det is the amplitude of the detection signal, ω det is the angular frequency of the detection signal, is the initial phase of the detection signal, U deta---c To inject harmonic detection signal.

[0045] In a third aspect, the present invention provides a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method for longitudinal protection of a two-terminal weakly fed system based on characteristic signal injection when executing the computer program.

[0046] In a fourth aspect, the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the method for longitudinal protection of a two-terminal weakly fed system based on characteristic signal injection are implemented.

[0047] Compared with the prior art, the present invention has the following technical effects:

[0048] The present invention constructs a protection method that is independent of the operating conditions and control strategies of the new energy side by injecting characteristic frequency signals, thereby significantly improving the adaptability and reliability of the protection.

[0049] The characteristic frequency signal injection and equivalent circuit construction of the present invention enable accurate measurement and analysis of the characteristic frequency impedance of the protection installations on both sides when a fault occurs on a double-ended weakly fed outgoing line. By comparing these impedance characteristics, it is possible to effectively distinguish between in-zone and out-of-zone faults, avoiding misjudgment caused by the complex current frequency components in traditional protection.

[0050] The characteristic frequency signal injection strategy of the present invention (such as selecting 250 Hz as the injection frequency, the injection signal length is 100 ms, etc.), and the equivalent circuit analysis and impedance measurement based on the signal, the technical solution can respond to faults quickly and sensitively, reduce the fault clearing time, and improve the stability and reliability of the power grid.

[0051] The setting principle of the present invention takes into account various factors such as signal attenuation, data processing error, transition resistance, etc., making the selection of setting value more scientific and reasonable. At the same time, by adjusting the parameters of the injection signal (such as amplitude, frequency, etc.) and the setting of the setting value, it can flexibly adapt to different power grid structures and operating conditions, thereby improving the flexibility and configurability of the protection scheme.

[0052] The present invention effectively prevents the expansion and spread of faults by accurately distinguishing faults inside and outside the area and quickly cutting off the faulty part, thereby ensuring the safe and stable operation of the power grid. At the same time, since the injection of characteristic frequency signals has little effect on the normal operation of the power grid, it will not significantly affect the power quality of the power grid.

[0053] In summary, this technical solution solves the problem that traditional protection is not applicable when new energy is connected to the weak-feed system through the injection of characteristic frequency signals and equivalent circuit analysis, improves the adaptability, sensitivity and speed of protection, ensures the safe and stable operation of the power grid, and promotes the widespread application of new energy technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a logic block diagram of the present invention.

[0055] Figure 2 This is a structural topology of a large-scale photovoltaic flexible direct access power system in an embodiment of the present invention.

[0056] Figure 3 Inject characteristic signals into control strategy diagrams.

[0057] Figure 4 Amplitude-frequency characteristic diagram after characteristic signal injection.

[0058] Figure 5The present invention is the different transition resistance S at the fault f1 m With S n Result graph.

[0059] Figure 6 The present invention is the different transition resistance S at the fault f3 m With S n Result graph.

[0060] Figure 7 The present invention is the different transition resistance S at the fault f5 m With S n Result graph.

[0061] Figure 8 The present invention is the different transition resistance S at the faults at f1 and f3 n With the setting value S nset .

[0062] Fig. 9 The present invention is the different transition resistance S at the faults at f5 and f3 n With the setting value S nset .

[0063] Fig.10 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0064] The present invention is further described below in conjunction with the accompanying drawings and specific implementation methods.

[0065] Example 1, please refer to Fig.10 , a two-terminal weak-feedback system pilot protection method based on characteristic signal injection includes:

[0066] Realize characteristic frequency signal injection based on high controllability of voltage source converter;

[0067] Based on the injection of characteristic frequency signal, a characteristic frequency equivalent circuit of the double-terminal weak-feedback system is constructed, and whether the fault start condition is met is determined according to the characteristic frequency signal;

[0068] When the start-up conditions are met, the setting value is determined by measuring the difference between the characteristic frequency impedance and the system characteristic frequency;

[0069] Combining the setting value and the difference in characteristic frequency impedance measured on both sides of the fault inside and outside the zone, a judgment criterion is constructed to determine the fault inside and outside the zone.

[0070] By using the high controllability of the voltage source converter to inject the characteristic frequency signal, this method can use the propagation and response characteristics of this special signal in the power grid to accurately identify the fault. The characteristic frequency signal is obviously different from other signals in the power grid, so it can significantly reduce the possibility of misjudgment and missed judgment and improve the accuracy of fault identification.

[0071] The characteristic frequency equivalent circuit of the two-terminal weak-feedback system is constructed, so that the method can adapt to the special environment of the weak-feedback system connected to the renewable energy. Through the analysis of the equivalent circuit, the electrical characteristics of the fault can be described and simulated more accurately, providing strong support for the formulation of protection strategies. This adaptability enables the method to be widely used in various weak-feedback systems connected to renewable energy, improving the overall protection level of the power grid.

[0072] By measuring the difference between the characteristic frequency impedance and the system characteristic frequency, the setting value can be determined more scientifically. This setting value formulation method takes into account the actual operation of the power grid and the fault characteristics, which can ensure that the protection is promptly actuated in the event of a fault, while avoiding false actions and improving the reliability and sensitivity of the protection.

[0073] By combining the set value and the difference in characteristic frequency impedance measured on both sides of the fault inside and outside the zone to build a criterion, this method can quickly determine the location of the fault. This fast fault location capability is of great significance for reducing fault losses and improving the speed of power grid recovery. At the same time, it also helps operation and maintenance personnel take timely measures to prevent the fault from further expanding.

[0074] In general, the two-terminal weak-feedback system longitudinal protection method significantly improves the safety and stability of the power grid through technical effects such as accurate fault identification, enhanced protection adaptability, optimized setting value formulation, and rapid fault location. It can effectively prevent power grid collapse or large-scale power outages caused by faults, and ensure the reliable operation of the power grid and the normal power demand of users.

[0075] Promoting the development and application of new energy technologies:

[0076] With the continuous development and application of new energy technologies, the structure and operation characteristics of the power grid are also changing. The proposal and application of this protection method provides an effective protection method for the access of new energy to the weak-feedback system, which helps to promote the further development and application of new energy technologies. At the same time, it also provides new ideas and methods for the formulation of protection strategies for new energy power grids.

[0077] Embodiment 2, as Figure 1 As shown, the longitudinal protection method of the two-terminal weak-feedback system based on characteristic signal injection specifically includes:

[0078] Step 1. Propose a characteristic frequency signal injection control strategy based on voltage source converter through PWM modulation and a characteristic frequency signal injection related parameter selection principle;

[0079] Step 2. Based on the full use of the advantages of "control and protection coordination", this chapter refers to the control characteristics of the new energy side using low-voltage characteristics to start fault ride-through, and then constructs a characteristic frequency signal injection start-up criterion suitable for various short-circuit scenarios;

[0080] Step 3. When the injected signal is stable, construct the characteristic frequency equivalent circuit. Analyze the characteristic frequency impedance characteristics measured at the protection installation on both sides when the double-ended weak feeder outgoing line system has internal and external faults, and formulate the setting value by analyzing the difference between the measured characteristic frequency impedance and the system characteristic frequency;

[0081] Step 4. Compare Sm / Sn with the set value to meet the zone action conditions to identify the zone faults and the zone faults;

[0082] Furthermore, in step 1, considering that the protection scheme is based on the parameter identification algorithm, a sine wave is used as the detection signal, and the fifth harmonic signal injection is achieved by changing the duty cycle of the modulation wave. Considering the measurement link of the injection signal and the impact on the power electronic equipment, the amplitude selection basis of the injection signal is given, and the injection amplitude of 0.15pu is selected considering the full power electronic characteristics of the double-terminal weak-feed system. Considering the frequency output capability of the injection signal, the transmission attenuation influence of the signal, and the signal frequency selection of the data processing process, the frequency is selected as 250Hz.

[0083] In order to ensure the stability of the system and the power quality of the system, as well as the accuracy of the detection signal and the reasonable reliability of the protection judgment, the injected characteristic signal needs to have a certain length. Considering the time margin required for communication delay and data processing, the length of the characteristic signal injected by each distributed power source is 100ms. The fifth harmonic signal injection is achieved by changing the duty cycle of the modulation wave.

[0084]

[0085] Where Udet is the amplitude of the detection signal, ω det is the angular frequency of the detection signal, is the initial phase of the detection signal, U deta---c To inject harmonic detection signal.

[0086] Further, in step 2, it is determined whether the fault start condition is met according to the characteristic frequency signal, and the steps are specifically as follows:

[0087] During the photovoltaic side fault, the converter uses the low voltage characteristics to start the fault ride-through control characteristics, and then constructs the characteristic frequency signal injection start-up criterion suitable for various short-circuit scenarios:

[0088]

[0089] In the formula, is the per unit value of the voltage at the grid connection point of the new energy source. Except for the case of single-phase grounding, the minimum phase voltage is taken, and the minimum line voltage is taken for other faults; ρ * is the start threshold value. To ensure a certain margin, this chapter takes 0.9. It can be adjusted appropriately according to the sensitivity requirements. N and U L.N They are the rated values ​​of phase voltage and line voltage respectively.

[0090] when After the startup criteria are met, the converter station on the new energy side switches to the active harmonic signal injection mode.

[0091] Furthermore, in step 3, a characteristic frequency equivalent circuit is constructed to analyze the characteristic frequency impedance characteristics measured at the protection installations on both sides when the double-ended weakly fed outgoing line system has internal and external faults. The setting value is determined by analyzing the difference in the relationship between the measured characteristic frequency impedance and the system characteristic frequency.

[0092] According to the construction of characteristic frequency equivalent circuit, DFT is used to extract the characteristic frequency electrical quantity in each voltage and current signal. By writing Kirchhoff's voltage law, the characteristic frequency impedance is measured at the protection installation on both sides when there is a fault inside and outside the zone.

[0093]

[0094] By calculating the characteristic frequency line of the system, the impedance value of the back system characteristic frequency at different frequencies is analyzed by using the sweep frequency method. The characteristic frequency impedance differences Sm and Sn at the M and N ends of the field transmission line are formulated.

[0095]

[0096] When an intra-zone fault occurs, the amplitude of Sm is greater than zero and the amplitude of Sn is equal to zero. When an extra-zone fault occurs on the back side of M, both amplitudes are zero. When an extra-zone fault occurs on the back side of N, both amplitudes are not zero.

[0097] Analyze the differences in protection schemes under faults at different locations and set the protection threshold. The following are the action conditions when the fault occurs within the zone.

[0098]

[0099] When selecting the setting value, it is necessary to consider the attenuation of the signal during line transmission, data processing errors, the influence of transition resistance, etc. The selection of the appropriate setting value must meet the following selection principles.

[0100] S m.max <S mset <min(S m1.min ,S m2.min )(7)

[0101] max(Sn1.max ,S n2.max )<S nset <S n.min (8)

[0102] Considering the errors of different types of equipment at both ends of the protection installation under faults inside and outside the transmission line area and the above-mentioned influencing factors, the setting value can be set to 50Ω.

[0103] Furthermore, in step 4, when the zone fault action condition is met, the zone fault is identified, otherwise it is an out-of-zone fault. Compare the characteristic frequency impedance difference Sm and Sn with the threshold values ​​Smset and Snset. If the zone fault action condition is met, it is identified as a zone fault and the protection trips; otherwise, the protection does not operate.

[0104] Establish as attached Figure 2 The large-scale two-terminal weak-feedback system shown in the figure is used as a simulation model. The system transmission line is set as shown in the attached figure. Figure 2 The topology shows that asymmetric faults occur at each fault point.

[0105] When AG, ABG, and AB faults occur, the electrical quantities collected at the photovoltaic and MMC side transmission line protection installation are used to extract the characteristic frequency electrical quantities in each voltage and current signal through DFT, and the measured characteristic frequency impedance value is calculated. The average amplitude is calculated through the formulated protection scheme and compared with the setting value to determine the fault direction and distinguish the fault inside and outside the area. The above simulation results are shown in the following table.

[0106] Table 1 Judgment results of different types of faults occurring at different locations of the outgoing line of the double-terminal weak-feed system

[0107]

[0108]

[0109] Establish as attached Figure 2 The large-scale two-terminal weak-feedback system shown in the figure is used as a simulation model. The system transmission line is set as shown in the attached figure. Figure 2 The topology shows that each fault point has ABC grounding faults through different transition resistances.

[0110] When ABC grounding fault occurs through different transition resistances, the electrical quantities collected at the photovoltaic and MMC side transmission line protection installation are extracted through DFT to extract the characteristic frequency electrical quantities in each voltage and current signal, and the measured characteristic frequency impedance value is calculated. The average amplitude is calculated through the formulated protection scheme and compared with the setting value to determine the fault direction and distinguish the fault inside and outside the area. The above simulation results are shown in the following table.

[0111] Table 2 Judgment results of ABC grounding faults through transition resistance at different locations of the outgoing line of the double-terminal weak-feed system

[0112]

[0113] Establish as attached Figure 2 The large-scale photovoltaic power plant shown in the figure is connected to the power system via MMC as a simulation model. The fault type is set to ABC fault, and the photovoltaic output is set to 0%, 20%, 50%, and 75% of the original value. The judgment results are shown in the following table.

[0114] Table 3. Judgment results of ABC faults occurring at different locations of the transmission line under different photovoltaic outputs in the double-terminal weak-feed system

[0115]

[0116]

[0117] The present invention discloses a longitudinal protection method for a two-terminal weak-feed system considering a characteristic signal injection strategy, and belongs to the field of protection of MMC transmission lines connected to new energy sources. First, the characteristic frequency signal injection is realized based on the high controllability of a voltage source converter (VSC), and the realization method of active injection of characteristic frequency signals and the principle of parameter selection are briefly described. Secondly, on the basis of active injection of characteristic frequency signals, a characteristic frequency equivalent circuit of a two-terminal weak-feed system is constructed, and the characteristic frequency impedance characteristics measured at the protection installation on both sides of the two-terminal weak-feed transmission line system when there are faults inside and outside the area are analyzed, and the different characteristics of the impedance variables measured for faults inside and outside the area of ​​the two-terminal weak-feed system are further revealed. Then, according to the difference in characteristic frequency impedance measured on both sides of the fault inside and outside the area, a longitudinal protection scheme based on characteristic frequency impedance variables and its setting principle are proposed, and a criterion is constructed to judge faults inside and outside the area. The advantages of the present invention are: it is not affected by the operating conditions of new energy stations and low voltage crossing strategies, has low communication requirements, and has a certain ability to withstand transition resistance. The proposed scheme can reliably judge faults inside and outside the area. It is suitable for two-terminal weak-feed AC systems.

[0118] In yet another embodiment of the present invention, a double-terminal weak-feedback system pilot protection system based on characteristic signal injection is provided, which can be used to implement the above-mentioned double-terminal weak-feedback system pilot protection method based on characteristic signal injection. Specifically, the system includes:

[0119] A signal injection module, used to implement characteristic frequency signal injection based on the high controllability of the voltage source converter;

[0120] A starting condition acquisition module is used to construct a characteristic frequency equivalent circuit of a double-terminal weak-feedback system based on the injection of a characteristic frequency signal, and to determine whether the fault starting condition is met according to the characteristic frequency signal;

[0121] A setting value acquisition module is used to determine the setting value by measuring the difference between the characteristic frequency impedance and the system characteristic frequency when the start-up conditions are met;

[0122] The judgment output module is used to combine the setting value and the characteristic frequency impedance difference measured on both sides of the fault inside and outside the zone to build a judgment criterion and judge the fault inside and outside the zone.

[0123] The division of modules in the embodiments of the present invention is schematic and is only a logical function division. There may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present invention may be integrated into one processor, or may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated modules may be implemented in the form of hardware or in the form of software functional modules.

[0124] In another embodiment of the present invention, a computer device is provided, the computer device comprising a processor and a memory, the memory being used to store a computer program, the computer program comprising program instructions, and the processor being used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in a computer storage medium to implement a corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of a two-terminal weak-feedback system longitudinal protection method based on characteristic signal injection.

[0125] In another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium here can include both the built-in storage medium in the computer device and the extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the longitudinal protection method of the double-terminal weak-feed system based on characteristic signal injection in the above embodiment.

[0126] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0127] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0128] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0129] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A two-terminal weak-feedback system pilot protection method based on characteristic signal injection, characterized in that: include: Injection of characteristic frequency signal based on the high controllability of voltage source converter; Based on the injection of characteristic frequency signal, a characteristic frequency equivalent circuit of the double-terminal weak-feedback system is constructed, and whether the fault start condition is met is determined according to the characteristic frequency signal; When the start-up conditions are met, the setting value is determined by measuring the difference between the characteristic frequency impedance and the system characteristic frequency; Combining the setting value and the difference in characteristic frequency impedance measured on both sides of the fault inside and outside the zone, a judgment criterion is constructed to determine the fault inside and outside the zone.

2. The method for pilot protection of a two-terminal weakly fed system based on characteristic signal injection according to claim 1 is characterized in that: Based on the high controllability of voltage source converter, characteristic frequency signal is injected, including: The fifth harmonic signal injection is achieved by changing the duty cycle of the modulation wave: Where U det is the amplitude of the detection signal, ω det is the angular frequency of the detection signal, is the initial phase of the detection signal, U deta---c To inject harmonic detection signal.

3. The method for pilot protection of a two-terminal weakly fed system based on characteristic signal injection according to claim 1, characterized in that: Based on the injection of characteristic frequency signal, a characteristic frequency equivalent circuit of the double-terminal weak-feedback system is constructed, and whether the fault start condition is met is determined according to the characteristic frequency signal, including: During the photovoltaic side fault, the converter uses the low voltage characteristics to start the fault ride-through control characteristics, and then constructs the characteristic frequency signal injection start-up criterion suitable for various short-circuit scenarios: In the formula, is the per unit voltage of the converter station grid connection point. Except for the single-phase grounding, the minimum phase voltage is taken. For other faults, the minimum line voltage is taken. * is the starting threshold value, which is 0.9; U N and U L.N They are the rated values ​​of phase voltage and line voltage respectively; when After the startup criteria are met, the PV-side converter switches to the active harmonic signal injection mode.

4. The method for pilot protection of a two-terminal weakly fed system based on characteristic signal injection according to claim 1, characterized in that: When the start-up conditions are met, the setting value is determined by measuring the difference between the characteristic frequency impedance and the system characteristic frequency, including: According to the construction of the characteristic frequency equivalent circuit, the characteristic frequency electrical quantity in each voltage and current signal is extracted by using DFT, and the characteristic frequency impedance measured at the protection installation on both sides when the fault occurs inside and outside the zone is written by writing Kirchhoff's voltage law: By calculating the characteristic frequency line of the system, the impedance value of the back system characteristic frequency at different frequencies is analyzed by using the sweep frequency method; by formulating the characteristic frequency impedance difference S between the M end and the N end of the field transmission line m and S n ; When a fault occurs within the zone, S m Amplitude greater than zero, S n The amplitude is equal to zero. When the out-of-zone fault occurs on the back side of M, both amplitudes are zero. When the out-of-zone fault occurs on the back side of N, both amplitudes are greater than zero. Set the protection threshold. The following are the action conditions when the zone is in effect:

5. The method for pilot protection of a two-terminal weakly fed system based on characteristic signal injection according to claim 4 is characterized in that: The selection of the setting value meets the following selection principles: S m.max mset <min(S m1.min ,S m2.min )(7)​ max(S n1.max ,S n2.max )<S nset <S n.min (8) Where: S m1min 、Sm 2min They are respectively the fault within the area and the fault on the back side of the N-terminal busbar. m Minimum value; S mmin The fault S is the back side fault of the busbar at the M end. m Maximum value; S n1max , S n2max are the maximum values ​​of Sn for the fault within the area and the fault on the back side of the busbar at the M end; S nmin It is the minimum value of Sn of the N-end bus backside fault.

6. The method for pilot protection of a two-terminal weakly fed system based on characteristic signal injection according to claim 1, characterized in that: Combine the setting value and the difference in characteristic frequency impedance measured on both sides of the fault inside and outside the zone to build a criterion and judge the fault inside and outside the zone, including: When the fault action condition is met, the fault is identified as an internal fault, otherwise it is an external fault; compare the characteristic frequency impedance mutation difference S m and S n With threshold value S mset and S nset If it satisfies the formula: If it is identified as an internal fault, the protection will trip; otherwise, the protection will not operate.

7. A two-terminal weak-feedback system pilot protection system based on characteristic signal injection, characterized in that: include: A signal injection module, used for injecting characteristic frequency signals based on the high controllability of the voltage source converter; A starting condition acquisition module is used to construct a characteristic frequency equivalent circuit of a double-terminal weak-feedback system based on the injection of a characteristic frequency signal, and to determine whether the fault starting condition is met according to the characteristic frequency signal; A setting value acquisition module is used to determine the setting value by measuring the difference between the characteristic frequency impedance and the system characteristic frequency when the start-up conditions are met; The judgment output module is used to combine the setting value and the characteristic frequency impedance difference measured on both sides of the fault inside and outside the zone to build a judgment criterion and judge the fault inside and outside the zone.

8. The double-terminal weak-feedback system pilot protection system based on characteristic signal injection according to claim 7 is characterized in that: Characteristic frequency signal injection based on the high controllability of voltage source converter, including: The fifth harmonic signal injection is achieved by changing the duty cycle of the modulation wave: Where U det is the amplitude of the detection signal, ω det is the angular frequency of the detection signal, is the initial phase U of the detection signal deta---c To inject harmonic detection signal.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method for longitudinal protection of a two-terminal weakly fed system based on characteristic signal injection as described in any one of claims 1 to 6 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method for longitudinal protection of a two-terminal weakly fed system based on characteristic signal injection as described in any one of claims 1 to 6 are implemented.

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