Active distribution network active injection type relay protection method and device

Abstract

The invention belongs to the field of active distribution networks, and relates to an active injection type relay protection method and device for an active distribution network. Firstly, a fault type is judged, and then whether an injection starting criterion is met is judged; if the injection starting criterion is met, the IIDG is controlled to actively inject a characteristic signal with fundamental current information into the power grid; and the information of the detected characteristic signal is utilized at the protection part to calculate the fundamental current which is not influenced by the IIDG. According to the method, the flexibility and rapidity of the IIDG are considered and utilized, the IIDG is controlled to actively inject certain characteristic signals into the power grid during the fault period, the available fault information at the protection position is increased, and then coordination and cooperation between control and protection are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of active distribution network, relates to an inverter-type distributed power source, and in particular to an active distribution network active injection type relay protection method and device. Background Art

[0002] With the rapid development of new energy power generation technology, the penetration rate of inverter-type distributed power sources (IIDG) represented by direct-drive wind turbines and photovoltaics in the distribution network has increased year by year, and its impact on distribution network protection has become more and more significant. The output characteristics of IIDG during power grid faults are greatly affected by environmental factors and control strategies, which brings a series of new problems to the protection of active distribution networks: 1) The short-circuit current output by IIDG during faults is limited, generally 1-2 times the rated current, and its fault characteristics are not obvious; 2) The current amplitude and phase of IIDG output during faults are difficult to determine; 3) The access of IIDG makes the distribution network no longer a single-ended network, and its fault current will help increase or decrease the current flowing through the line protection, changing the fault characteristics of the distribution network. The above problems bring many difficulties to the setting and coordination of distribution network protection, and traditional protection is difficult to meet the technical requirements of active distribution network protection.

[0003] At present, the methods for improving distribution network protection in IIDG access scenarios include: adaptive current protection with online real-time updates of constant values ​​and centralized network protection based on regional information. Adaptive current protection is a protection method that uses local information or information from other nodes in the power grid to update constant values ​​in real time based on traditional current protection. Centralized network protection is a protection method that uses multi-point and multi-type information related to the fault to determine the fault location. The above methods help to improve protection performance, but they are too dependent on various measuring devices and communication equipment. Moreover, since the above methods only passively adapt to the fault characteristics of new energy, their protection schemes have the problems of complex configuration and relatively single applicable scenarios. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an active distribution network active injection relay protection method and device to solve the problems of protection setting and coordination difficulties existing in traditional passive protection methods.

[0005] The technical solution adopted by the present invention to solve the technical problem is:

[0006] The first aspect of the present invention is to provide an active distribution network active injection relay protection method, which controls the IIDG to actively inject characteristic signals into the power grid during a fault, and the protection department uses the detected characteristic signals to obtain the fundamental information of the IIDG, thereby eliminating the influence of the IIDG on the current of each branch and the existing current protection. Since the fault characteristics used by the protection department are actively injected by the IIDG, this method has good applicability in different scenarios and working conditions, and does not require the addition of additional communication and detection equipment, and has the advantages of good economy and high practicality. The simulation results verify the effectiveness of the proposed method.

[0007] The first aspect of the present invention is to provide an active distribution network active injection relay protection method, the process is as follows:

[0008] S1 determines the fault type;

[0009] S2 determines whether the injection start criterion is met;

[0010] If the injection start criterion is met in S3, the IIDG is controlled to actively inject a characteristic signal with fundamental current information into the power grid. If the injection start criterion is not met, the process returns to S1.

[0011] The S4 protection uses the information of the detected characteristic signal to calculate the fundamental current that is not affected by the IIDG.

[0012] Furthermore, the protection department first determines whether there is a negative sequence component. If so, it further determines whether the characteristic signal is stable. If so, the short-circuit current is calculated according to formula (8); if there is no negative sequence component, it further determines whether the characteristic signal is stable. If so, the short-circuit current is calculated according to formula (5);

[0013]

[0014] I p,new =I p -I p,DG Formula (5)

[0015] In the formula, I p,DG The fundamental current provided by the protection IIDG, I p,new To protect the fundamental current from being affected by IIDG, I Bp and I Cp They are respectively the current flowing through the fault phase (here phase B and phase C are used for illustration) of the protection, I kBp ,I kCp They are characteristic signals of the fault phases (here phase B and phase C are used for illustration) flowing through the protection.

[0016] Furthermore, the criterion formula for judging whether the characteristic signal is stable is as follows. When it is satisfied 5 times in a row, the characteristic signal can be judged to be stable;

[0017] |I m+1 -I m |<ε

[0018] Where: I m is the characteristic signal amplitude obtained after FFT decomposition; ε is the allowable error of the characteristic signal.

[0019] Furthermore, the fault types are divided into two-phase short circuit and three-phase short circuit. If there is a negative sequence component in the fault current, it means that the fault is a two-phase short circuit, otherwise it is a three-phase short circuit.

[0020] Furthermore, the injection start criteria include three, and satisfying any one of them is sufficient.

[0021] First, when the minimum phase voltage U min <0.9U N When U N is the rated voltage of IIDG, then the injection start criterion is met;

[0022] Second, if the fault in the system is an asymmetric fault, the amplitude characteristics of the negative sequence voltage are used as one of the criteria for injection start. - ≥0.01U N When , the injection start criterion is met;

[0023] Third, if there are multiple IIDGs in the system, the characteristic signal current amplitude is used as a supplementary criterion for injection start. k ≥I set When , it indicates that the characteristic signal injection link of some IIDGs in the system has been started, so that some IIDGs far away from the fault point can also start the injection of characteristic signals. set The value of takes into account the background harmonics in the power grid and the sensitivity of injection startup, and its value is 2%-5%I DG,N .

[0024] Furthermore, the injection process of the characteristic signal is as follows: after the converter of the IIDG calculates the current command through the control algorithm, the characteristic signal current loop is used to track the characteristic signal current command, and then the control signal output by the current loop is transmitted to the IIDG, thereby realizing the control of the characteristic signal. The characteristic frequency control loop adopts proportional resonance control to achieve rapid tracking of the current command, and in addition, the characteristic frequency negative sequence voltage component is fed forward to the modulation wave to suppress the characteristic frequency negative sequence current.

[0025] Furthermore, the frequency of the characteristic signal adopts 8 times the frequency current, 400 Hz.

[0026] Furthermore, the maximum amplitude of the characteristic signal is set to 10% of IIDG. DG,max , where I DG，max It is the output current corresponding to the maximum output of DG.

[0027] The second aspect of the present invention is to provide an active distribution network active injection type relay protection device, comprising the following modules:

[0028] A fault type determination module is used to determine whether the fault is a two-phase short circuit or a three-phase short circuit;

[0029] An injection start criterion judgment module is used to judge whether the characteristic signal injection conditions are met;

[0030] The characteristic signal injection module is used to control the IIDG to actively inject characteristic signals with fundamental current information into the power grid;

[0031] The calculation module uses the information of the detected characteristic signal to calculate the fundamental current not affected by the IIDG.

[0032] Furthermore, the injection start criterion judgment module has three judgment units, namely:

[0033] The first judgment unit is used to judge whether the minimum phase voltage of the IIDG grid connection point meets U min <0.9U N , U N is the rated voltage of IIDG;

[0034] The second judgment unit is used to judge whether the negative sequence voltage of the grid connection point meets U - ≥0.01U N ;

[0035] The third judgment unit is used to judge whether the characteristic current amplitude satisfies I k ≥I set .

[0036] The third aspect of the present invention is to provide a computer-readable storage medium, in which computer-executable instructions are stored. When the computer-executable instructions are executed by a processor, they are used to implement the active distribution network active injection relay protection method.

[0037] The advantages and positive effects of the present invention are:

[0038] 1. During the fault period, the present invention controls the IIDG to actively inject characteristic signals into the power grid, and the protection department uses the detected characteristic signals to obtain the fundamental information of the IIDG, thereby eliminating the influence of the IIDG on the current of each branch and the existing current protection. Different from the traditional protection that passively adapts to the fault characteristics, since the fault characteristics used by the protection department are actively injected by the IIDG, the protection department uses the information provided by the characteristic signal to determine whether it should act. Therefore, this method has good applicability in different scenarios and working conditions, and does not require the addition of additional communication and detection equipment, and has the advantages of good economy and high practicality. The simulation results verify the effectiveness of the proposed method.

[0039] 2. The present invention considers utilizing the flexibility and rapidity of IIDG, controlling IIDG to actively inject certain characteristic signals into the power grid during a fault, increasing the fault information available at the protection point, and thereby achieving coordination between control and protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the active distribution network topology diagram of IIDG;

[0041] Figure 2 It is the injection method diagram of characteristic signal;

[0042] Figure 3 It is the composite sequence network diagram of characteristic signals when two phases downstream of IIDG are short-circuited;

[0043] Figure 4 This is a flowchart of active injection protection based on control and protection collaboration;

[0044] Figure 5 It is the three-phase current diagram output by IIDG;

[0045] Figure 6 It is the characteristic signal amplitude diagram output by IIDG and detected at the protection point;

[0046] Figure 7 The three-phase current diagram for protection 1;

[0047] Figure 8 This is the three-phase current diagram for protecting location 2. DETAILED DESCRIPTION

[0048] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0049] The present invention first analyzes the fault characteristics of IIDG in combination with its control strategy, and classifies and analyzes the impact of IIDG on current protection after access to the distribution network according to the fault location and type; then analyzes the injection mode and type of characteristic signals and their distribution in the power grid; then, based on the above analysis, proposes an active distribution network active injection protection method based on control and protection collaboration; finally, the effectiveness of the proposed method is verified through simulation.

[0050] by Figure 1 Taking the commonly used radial topology of the active distribution network shown in the figure as an example, the impact of IIDG access on the protection of the active distribution network is analyzed.

[0051] The fault characteristics of IIDG are mainly determined by the reference values ​​of the positive and negative sequence dq axis currents given by its control algorithm. For the positive sequence current component, IIDG generally adopts a control strategy that prioritizes reactive power output, and the calculation formula for the positive sequence dq axis current reference value is shown in formula (1); for the negative sequence current component, IIDG generally adopts a control strategy that suppresses the negative sequence current, that is, controls the negative sequence dq axis current reference value to 0.

[0052]

[0053] Where: i d_ref and i q_ref are the reference values ​​of positive sequence dq axis current respectively; I N and U N are the rated current and voltage of IIDG respectively; U is the grid connection point voltage; P is the power output of IIDG before the fault; i L is the current output by IIDG during the fault period.

[0054] Due to the special fault characteristics of IIDG, there are problems of protection misoperation and decreased sensitivity when traditional current protection is used in active distribution network. To this end, the present invention considers utilizing the flexibility of IIDG control strategy, injecting certain characteristic signals into the power grid by controlling IIDG, and the protection department uses the information provided by the characteristic signals to solve the problems that arise when traditional current protection is used in active distribution network. The following first explains and demonstrates the selection principle and control scheme of characteristic signals.

[0055] After a fault occurs in the system, the IIDG is at risk of being disconnected from the grid due to excessive deviations in voltage and frequency at the grid connection point. Therefore, after a fault occurs, the IIDG should quickly identify the fault and inject characteristic signals into the grid. Its implementation depends on fast and reliable injection start criteria.

[0056] Considering reliability and speed, the injection start criterion of the characteristic signal should make use of the local information of IIDG as much as possible. When the system fails, the voltage at the grid connection point of IIDG will drop to a certain extent. This feature can be used as one of the criteria for the injection start of the characteristic signal, that is, when the minimum phase voltage U min <0.9U N If the fault in the system is an asymmetric fault, the amplitude characteristics of the negative sequence voltage can also be used as one of the criteria for injection start, that is, when the negative sequence voltage U - ≥0.01U N At the same time, if there are multiple IIDGs in the system, the characteristic signal current amplitude can also be used as a supplementary criterion for injection startup, that is, when the detected characteristic current amplitude I k ≥I set When , it indicates that the characteristic signal injection link of some IIDGs in the system has been started, so that some IIDGs far away from the fault point (where the voltage drop at the grid point is small) can also start the injection of characteristic signals. set The value of needs to consider the background harmonics in the power grid and the sensitivity of injection startup, and its value can be 2%-5%I DG,N When any of the above three criteria is met, it can be considered that a fault has occurred in the system, and the IIDG starts the characteristic signal injection link.

[0057] In order to achieve flexible control of the characteristic signal, the IIDG characteristic signal injection process adopted by the present invention is as follows: Figure 2 As shown in the figure, after the converter of IIDG calculates the current command through the control algorithm, it uses the characteristic signal current loop to track the characteristic signal current command, and then transmits the control signal output by the current loop to IIDG, thereby realizing the control of the characteristic signal. The characteristic frequency control loop adopts proportional resonance control to achieve rapid tracking of the current command. In addition, the characteristic frequency negative sequence voltage component is fed forward to the modulation wave to suppress the characteristic frequency negative sequence current. In the figure: and Respectively represent the base frequency positive and negative sequence active and reactive current reference values; i kdq_ref Represents the reference value of the characteristic frequency active and reactive current. The characteristic frequency current control loop adopts proportional resonance control to achieve fast tracking of the command. In addition, the characteristic frequency negative sequence voltage component is fed forward into the modulation wave to suppress the characteristic frequency negative sequence current. The transfer function of the characteristic frequency control loop is shown in formula (2).

[0058]

[0059] Where: u αβ is the component of the modulation voltage in the αβ coordinate system; ikαβ_ref and i kαβ are the reference value and actual value of characteristic frequency current respectively; k p , k r is the proportional resonance coefficient of the PR controller; ω N is the grid base frequency voltage angular frequency.

[0060] According to the above control structure, the injection of any integer harmonic characteristic signal can be achieved in theory. There are three key points:

[0061] 1) To avoid resonance and attenuation, the resonant frequency of the IIDG filter is generally between 10 times the power frequency and 1 / 2 times the carrier frequency, so the characteristic signal frequency is less than 10 times the power frequency.

[0062] 2) Due to the excessive disturbance in the initial stage of the fault, certain harmonic components will be generated in the power grid, mainly low-order harmonics. Therefore, in order to reduce the impact of the background harmonics of the power grid on the characteristic signal, the characteristic frequency should be kept as far away from the power frequency as possible.

[0063] 3) When the inverter is operating normally, odd harmonics are generated due to modulation, and the background harmonics of the power grid are also mainly odd. In order to strengthen the system fault characteristics, even harmonics should be selected as the system fault characteristic harmonics.

[0064] Therefore, 8 times the frequency current (400 Hz) or the like can be selected as the characteristic signal to optimize the current protection performance.

[0065] The amplitude of the injected signal needs to comprehensively consider the detection difficulty of the protection point and the requirements of the power quality of the power grid: if the amplitude of the injected characteristic signal is too small, it will increase the difficulty of identification and detection at the protection point; if the amplitude is too large, it will cause the disturbance in the power grid to exceed the standard, which will have a negative impact on the power quality. Taking into account the impact of both, the present invention sets the maximum amplitude of the characteristic signal to 10% of IIDG DG,max .

[0066] Taking the downstream two-phase short circuit as an example, the composite sequence network of the characteristic signal can be obtained as follows: Figure 3 As shown:

[0067] Characteristic signal I flowing through protection 1 and 2 kBp1 ,I kCp1 and I kBp2 ,I kCp2 As shown in formula (3):

[0068]

[0069] Where: I kB and I kC is the characteristic frequency current output by IIDG; Z ks , Z k1 and Z k2is the impedance of the system, lines L1 and L2 at the characteristic frequency. Comparing with formula (3), it can be seen that the distribution of the characteristic frequency current during the fault is similar to the fundamental wave. Therefore, if the magnitude and phase relationship between the two can be clearly understood, the protection can use the characteristics of the detected characteristic frequency current to calculate the fundamental wave current provided by the IIDG, thereby eliminating the impact of the IIDG on the current protection after it is connected to the distribution network.

[0070] Under different fault types, IIDG has different effects on the current flowing through the line, so the protection department needs to judge the fault type first. Since current protection is mainly used for phase-to-phase short circuit, when judging the fault type, it is only necessary to distinguish between two-phase short circuit and three-phase short circuit. Two-phase short circuit is an asymmetric fault, so if there is a negative sequence component in the fault current, it means that the fault is a two-phase short circuit, otherwise it is a three-phase short circuit.

[0071] The fundamental current and characteristic frequency current output by the IIDG are fixed to a 10-fold relationship, with the same phase. At this time, the relationship between the fundamental current and characteristic frequency current of the IIDG at the protection point satisfies equation (4).

[0072] I p,DG =10I kp (4)

[0073] Where: I p,DG The fundamental current provided for the protection IIDG; I kp is the characteristic frequency current at the protection point. From formula (4), the fundamental current I at the protection point that is not affected by IIDG can be obtained: p,new Calculate formula (5).

[0074] I p,new =I p -I p,DG (5)

[0075] When two-phase short circuit occurs, the influence of IIDG on upstream and downstream protection is not exactly the same. p,new , and the fault point location needs to be determined. However, the information obtained by the protection is limited, and it is difficult to accurately determine the fault point location. To avoid the above problems, a unified calculation formula is required for two-phase short circuit. Take the downstream two-phase short circuit as an example for analysis, and make the following transformation to the fault current:

[0076]

[0077] After the characteristic signal is changed, it can be obtained:

[0078]

[0079] Therefore, when the two phases downstream of the IIDG are short-circuited, the fundamental current at the protection point that is not affected by the IIDG is calculated as shown in formula (8). For the two phases upstream of the IIDG short-circuited, formula (8) is also applicable.

[0080]

[0081] It should be noted that the above analysis is for BC two-phase short circuit. For other types of two-phase short circuit, it is only necessary to change I Bp -I Cp For three-phase short circuit, protection 1 and 2 can directly update the short-circuit current according to formula (5).

[0082] Due to the large disturbance caused by the fault, a certain amount of harmonic signals will be generated in the power grid at the initial stage of the fault, but they will gradually decay to 0. Therefore, the detected characteristic signal must be stable before calculating the current. The stability criterion of the characteristic signal is shown in formula (9). When formula (9) is satisfied for 5 consecutive times, the characteristic signal can be determined to be stable.

[0083] |I m+1 -I m |<ε (9)

[0084] Where: I m is the characteristic signal amplitude obtained after FFT decomposition; ε is the allowable error of the characteristic signal, which is 0.5%I DG,N In summary, the process of active injection protection method based on control and protection collaboration is as follows: Figure 4 shown.

[0085] In order to verify the effectiveness of the proposed method, a Simulink Figure 1 The topology of the active distribution network with IIDG is shown in the figure. The rated voltage on the system side is 10.5kV, the system impedance is j0.5Ω, the line unit length impedance is 0.27+j0.365Ω / km, and the lengths of lines L1 and L2 are 10 and 6km respectively. The capacity of IIDG is 6MW, and the control strategy adopts the strategy of prioritizing reactive power output and suppressing negative sequence current.

[0086] It is assumed that a three-phase short circuit fault occurs at point f2 at t = 0.2s. After detecting the voltage drop at the grid connection point, the IIDG injects a characteristic signal with a frequency of 400Hz into the grid. The amplitude of the characteristic signal is 0.1 times the amplitude of the fundamental current, and the phases are the same. The three-phase current waveform output by the IIDG before and after the fault is as follows: Figure 5 As shown in the figure, the characteristic signal amplitude output by IIDG and detected at the protection point is as follows Figure 6 Shown

[0087] Depend on Figure 5 It can be seen that the three-phase current waveform output by IIDG is distorted to a certain extent due to the characteristic signal, but the overall output is stable. Figure 6 It can be seen that the characteristic signal tends to be stable at about 0.046s after the fault. The protection can calculate the fundamental current I that is not affected by IIDG according to the amplitude and phase of the characteristic signal according to formula (5): p,new .

[0088] It is assumed that a two-phase short circuit fault occurs at point f2 at t = 0.2s, and the three-phase current waveform at protection 1 is as follows Figure 7 As shown, the three-phase current waveform at protection 2 is as follows Figure 8 As shown, the grey dotted line is the fault current amplitude flowing through the protection when the IIDG is not connected.

[0089] Depend on Figure 7 It can be seen that when the two phases downstream of IIDG are short-circuited, the fault phase current at protection 1 increases in one phase and decreases in the other phase. The non-fault phase current flowing through protection 1 is I provided by IIDG. AL .Depend on Figure 8 It can be seen that when the two phases downstream of the IIDG are short-circuited, the fault phase current at the protection point 2 will increase, and its simulation results are consistent with equation (8). This method can accurately calculate the fundamental current at the protection point that is not affected by the IIDG under different fault locations and fault types, and can effectively solve a series of problems that occur in current protection after the IIDG is connected.

[0090] The present invention proposes an active distribution network active injection protection method based on control and protection coordination. During a fault, the IIDG is controlled to actively inject a characteristic signal with fundamental current information into the power grid. The protection part uses the information of the detected characteristic signal to calculate the fundamental current that is not affected by the IIDG, thereby achieving coordination between control and protection. The advantages of the method are as follows:

[0091] 1) There is no need to adjust the setting scheme of the existing protection, and the fundamental current at the protection point that is not affected by the IIDG can be calculated, which eliminates the influence of the IIDG access on the existing current protection in principle.

[0092] 2) It is not affected by changes in IIDG access capacity and access quantity, and has good applicability under various fault types and operating conditions.

[0093] 3) No additional measurement and communication equipment is required, and it is economical and practical.

[0094] The present invention further establishes an active distribution network active injection relay protection device for implementing the above method, comprising the following modules:

[0095] A fault type determination module is used to determine whether the fault is a two-phase short circuit or a three-phase short circuit;

[0096] An injection start criterion judgment module is used to judge whether the characteristic signal injection conditions are met;

[0097] The characteristic signal injection module is used to control the IIDG to actively inject characteristic signals with fundamental current information into the power grid;

[0098] The calculation module uses the information of the detected characteristic signal to calculate the fundamental current not affected by the IIDG.

[0099] Furthermore, the injection start criterion judgment module has three judgment units, namely:

[0100] The first judgment unit is used to judge whether the minimum phase voltage of the IIDG grid connection point meets U min <0.9U N , U N is the rated voltage of IIDG;

[0101] The second judgment unit is used to judge whether the negative sequence voltage of the grid connection point meets U - ≥0.01U N ;

[0102] The third judgment unit is used to judge whether the characteristic current amplitude satisfies I k ≥I set .

[0103] The present invention further establishes a computer-readable storage medium based on the above method, wherein the computer-readable storage medium stores computer execution instructions, and when the computer execution instructions are executed by a processor, they are used to implement an active distribution network active injection relay protection method.

[0104] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0105] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes 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 generate 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.

[0106] 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.

[0107] 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.

[0108] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, which all belong to the protection scope of the present invention.

Claims

1. An active distribution network active injection relay protection method, It is characterized in that The process is as follows: S1 determines whether the fault is a two-phase short circuit or a three-phase short circuit; S2 determines whether the injection start criterion is met. The injection start criterion includes three criteria, and it only needs to meet one of them. First, when the minimum phase voltage U min <0.9U N When U N is the rated voltage of IIDG, then the injection start criterion is met; Second, if the fault in the system is an asymmetric fault, the amplitude characteristics of the negative sequence voltage are used as one of the criteria for injection start. - ≥0.01U N When , the injection start criterion is met; Third, if there are multiple IIDGs in the system, the characteristic signal current amplitude is used as a supplementary criterion for injection start. k ≥I set When , it means that the characteristic signal injection link of some IIDGs in the system has been started, then some IIDGs far away from the fault point can also start the injection of characteristic signals; If the injection start criterion is met in S3, the IIDG is controlled to actively inject a characteristic signal with fundamental current information into the power grid. If the injection start criterion is not met, the process returns to S1. The S4 protection uses the information of the detected characteristic signal to calculate the fundamental current that is not affected by the IIDG.

2. According to claim 1, the active distribution network active injection relay protection method, It is characterized in that The protection department first determines whether there is a negative sequence component. If so, it further determines whether the characteristic signal is stable. If so, the short-circuit current is calculated according to formula (8); if there is no negative sequence component, it further determines whether the characteristic signal is stable. If so, the short-circuit current is calculated according to formula (5); I p,new =I p -I p,DG Formula (5) In the formula, I p,DG The fundamental current provided by the protection IIDG, I p,new To protect the fundamental current from being affected by IIDG, I Bp and I Cp are the fault phase current flowing through the protection, I kBp ,I kCp They are respectively the characteristic signals of the fault phase flowing through the protection.

3. The active distribution network active injection relay protection method according to claim 2, It is characterized in that The criterion formula for judging whether the characteristic signal is stable is as follows. When it is satisfied 5 times in a row, the characteristic signal can be judged to be stable; |I m+1 -I m |<ε Where: I m is the characteristic signal amplitude obtained after FFT decomposition; ε is the allowable error of the characteristic signal.

4. The active distribution network active injection relay protection method according to claim 1, It is characterized in that If there is a negative sequence component in the fault current, it means that the fault is a two-phase short circuit, otherwise it is a three-phase short circuit.

5. The active injection relay protection method for active distribution network according to claim 1, It is characterized in that I set The value of takes into account the background harmonics in the power grid and the sensitivity of injection startup, and its value is 2%-5%I DG,N .

6. The active distribution network active injection relay protection method according to claim 1, It is characterized in that The injection process of the characteristic signal is as follows: after the IIDG converter calculates the current command through the control algorithm, the characteristic signal current loop is used to track the characteristic signal current command, and then the control signal output by the current loop is transmitted to the IIDG to realize the control of the characteristic signal. The characteristic frequency control loop adopts proportional resonance control to realize rapid tracking of the current command, and feeds the characteristic frequency negative sequence voltage component forward to the modulation wave to suppress the characteristic frequency negative sequence current.

7. The active distribution network active injection relay protection method according to claim 1, It is characterized in that The frequency of the characteristic signal uses 8 times the frequency of the current.

8. The active distribution network active injection relay protection method according to claim 1, It is characterized in that The maximum amplitude of the characteristic signal is set to 10% of IIDG DG,max , where I DG，max It is the output current corresponding to the maximum output of DG.

9. An active distribution network active injection type relay protection device according to the active distribution network active injection type relay protection method according to claim 1, It is characterized in that Includes the following modules: A fault type determination module is used to determine whether the fault is a two-phase short circuit or a three-phase short circuit; An injection start criterion judgment module is used to judge whether the characteristic signal injection conditions are met; The characteristic signal injection module is used to control the IIDG to actively inject characteristic signals with fundamental current information into the power grid; The calculation module uses the information of the detected characteristic signal to calculate the fundamental current not affected by the IIDG.

10. The active distribution network active injection relay protection device according to claim 9, It is characterized in that The injection start criterion judgment module has three judgment units, namely: The first judgment unit is used to judge whether the minimum phase voltage of the IIDG grid connection point meets U min <0.9U N , U N is the rated voltage of IIDG; The second judgment unit is used to judge whether the negative sequence voltage of the grid connection point meets U - ≥0.01U N ; The third judgment unit is used to judge whether the characteristic current amplitude satisfies I k ≥I set .

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