Over-current direction protection method and system for energy storage and current collection circuit

Abstract

The invention discloses an energy storage and current collection circuit overcurrent direction protection method and system. The protection method comprises the following steps: cyclically recording a positive sequence current and a positive sequence voltage of a first time interval data window; when the element is started, recording a fault positive sequence current, a fault negative sequence current and a fault positive sequence voltage of the second time interval data window; and calculating the vector difference of the positive sequence current of the data window at the two time intervals, and calculating the phase difference between the fault positive sequence voltage and the positive sequence current of the second data window. And when the negative sequence current module value of the second data window is greater than the threshold value, judging the fault as a positive direction fault, when the phase difference between the fault positive sequence voltage and the positive sequence current of the second data window meets the action equation and the vector difference module value of the positive sequence current of the two data windows is greater than the threshold value, judging the fault as a positive direction fault, and if the conditions are not met, judging the fault as a negative direction fault. According to the invention, the problem of possible maloperation of overcurrent protection in the energy storage charging and discharging states is solved based on the steady-state information of the fault voltage and current.

Description

Technical Field

[0001] The present invention relates to the technology of collector line protection, and in particular to an overcurrent direction protection method and system for collector lines considering energy storage and centralized PV power output. Background Art

[0002] Under the background of the continuous increase in global energy demand and the increasingly severe climate change, countries have been promoting the evolution of the power system towards adapting to large-scale and high-proportion new energy. However, the instability of new energy output will affect the safe and reliable operation of the power system and severely limit its large-scale consumption and utilization. Energy storage technology has significant advantages in areas such as suppressing new energy fluctuations, peak shaving and valley filling, frequency modulation and voltage regulation, and improving power quality, and can play an important role in the large-scale grid connection of new energy. However, the bidirectional flow of energy in the energy storage power station under charge / discharge states and the introduction of power electronic devices make the system fault characteristics more complex, presenting a four-quadrant change in the fault current phase and a non-linear characteristic with limited amplitude. This poses a huge challenge to the relay protection of the energy storage power station grid-connected system, and there is an urgent need to study a new principle for the protection of AC transmission lines that can adapt to the charge / discharge state switching of the energy storage power station.

[0003] The maximum output current of the energy storage system connected to the grid through an inverter is limited to 1.3 times the rated current, which further complicates the setting of overcurrent protection. Especially under different conditions of charge and discharge modes, it is difficult for the protection scheme to balance sensitivity and selectivity. Under discharge conditions, the energy storage is similar to an inverter-type power source. Early overcurrent protection schemes mainly relied on inverse-time current protection. Although the sensitivity was improved to a certain extent, the current characteristics under charging conditions were not fully considered, resulting in the protection setting being difficult to meet the actual requirements. The adaptive current quick-break protection technology based on the positive-sequence voltage-current relationship for inverter-type power sources can improve the protection performance, but it is insufficient in protection setting, especially prone to protection mismatch or refusal to operate when facing different mode conversions. In addition, the setting scheme of distribution network current protection considering the change of access capacity can cope with the change of access capacity. Currently, there are many studies on current quick-break protection, but there are few studies on the protection setting and coordination of the second and third sections of overcurrent protection, as well as the impact on starting elements and direction elements.

[0004] During the charging state, energy storage is similar to the charging of electric vehicles. Although it does not have randomness and can be equivalent according to load nodes, it will introduce additional load increase, which has an adverse impact on distribution network protection. Traditional technologies have not been able to effectively cope with interferences such as harmonics and voltage offsets caused by power electronic devices, and these factors pose challenges to information acquisition, digital filtering, and protection calculation. When the energy storage is converted from the discharge mode to the charging mode, it may cause the protection device to malfunction or refuse to operate. In addition, only by increasing the overcurrent protection setting value to avoid the influence of the maximum load current will significantly reduce the protection sensitivity at the line end and increase the system operation risk.

[0005] In summary, there is little research on the feeder direction protection for the charging and discharging characteristics of electrochemical energy storage at present. Summary of the Invention

[0006] To solve the above problems existing in the prior art, based on the fault voltage, fault current phase characteristics, and the amplitude-phase change characteristics of the current before and after the fault in the four-quadrant operating state of the energy storage, the present invention proposes an overcurrent direction protection based on the problem electrical quantity information to solve the problem that the overcurrent protection of the energy storage centralized outgoing feeder may malfunction.

[0007] The present invention specifically adopts the following technical solutions:

[0008] An overcurrent direction protection method for an energy storage feeder line, characterized in that the protection method includes:

[0009] Step 1: Cyclically collect the positive-sequence current and positive-sequence voltage at the protection installation location at a first time interval;

[0010] Step 2: When the current mutation satisfies the action condition of the current mutation starting element, the protection starts, and the positive-sequence current vector and positive-sequence voltage vector at the protection installation location before starting are cached, and then enter Step 3; otherwise, return to Step 1;

[0011] Step 3: Collect the positive-sequence current, negative-sequence current, and positive-sequence voltage after the fault at the protection installation location at a second time interval. When the negative-sequence current is less than or equal to the negative-sequence current threshold value, enter Step 4; otherwise, enter Step 5;

[0012] Step 4: Compare the phase of the positive-sequence voltage after the fault with the positive-sequence current, and calculate the angular difference between the positive-sequence voltage after the fault and the positive-sequence current after the fault as the first action equation; calculate the vector difference between the positive-sequence current after the fault and the positive-sequence current vector before the fault, and compare the vector difference modulus value with the action threshold as the second action equation; when both the first action equation and the second action equation meet the conditions, it is judged as a positive-direction fault; otherwise, enter Step 5;

[0013] Step 5: When the post-fault phase current meets the operating threshold and the negative-sequence current is greater than the negative-sequence current threshold value or meets the positive-direction fault condition in Step 4, it is determined that an in-zone fault has occurred, and the protection operates to trip. Otherwise, it is determined that an out-of-zone fault has occurred.

[0014] Further preferably,

[0015] In Step 2, the operating conditions of the current mutation starting element include a first operating condition and a second operating condition. When either operating condition is met, the protection starts:

[0016] The first operating condition is ΔI ΦMAX > 1.25ΔI T + ΔI set ,

[0017] The second operating condition is

[0018] where ΔI ΦMAX is the maximum value of the half-wave integrals of the effective values of the three-phase currents, ΔI ΦΦMAX is the maximum value of the half-wave integrals of the effective values of the three-phase-interphase currents, ΔI set is a settable fixed threshold, and ΔI T is a floating threshold.

[0019] Further preferably,

[0020] ΔI set has a value range of 0.04I N ~0.5I N , and the floating threshold ΔI T automatically changes according to the fluctuation of the load current and is equal to the magnitude of the load current fluctuation at the previous moment.

[0021] Further preferably,

[0022] In Step 3, it is judged whether the negative-sequence current after the fault is greater than the negative-sequence current threshold value after the protection starts as follows:

[0023] I2 > I 2_set

[0024] I2 is the negative-sequence current value in the second time interval after the protection starts, and I 2_set is the negative-sequence current threshold value.

[0025] Further preferably,

[0026] The first time interval is 40 ms; the second time interval is 20 ms.

[0027] Further preferably,

[0028] I 2_setSet according to the maximum unbalanced negative sequence current during system operation.

[0029] Further preferably,

[0030] Step 4 includes two direction discrimination conditions, namely the phase comparison condition based on positive sequence voltage and positive sequence current, and the action condition of the vector difference between the positive sequence current after the fault and the positive sequence current before the fault.

[0031] Further preferably,

[0032] The first action equation in Step 4 is shown as follows:

[0033]

[0034] Wherein, are respectively the positive sequence voltage and positive sequence current at the protection installation location after the fault;

[0035] The second action equation in Step 4 is shown as follows:

[0036]

[0037] Wherein, is the positive sequence current recorded at the protection installation location before the fault, and I dset is the action threshold value of the current change amount direction.

[0038] Further preferably,

[0039] In Step 5, the judgment condition for the post-fault phase current to meet the action threshold is shown as follows:

[0040]

[0041] Wherein, is any phase current at the protection installation location after the fault, and I set is the phase current action threshold value;

[0042] Further preferably,

[0043] I dset has a value range of 1.1I N ~1.3I N ;

[0044] I set has a value range greater than 1.1I N ;

[0045] When amplitude is greater than 0.1U N , take the positive sequence voltage after the fault; when amplitude is not greater than 0.1U N , Obtain the positive-sequence voltage before the fault

[0046] Wherein, I N is the rated current output by a single photovoltaic and energy storage device, and U N is the rated voltage of the collector bus, and is the voltage of the collector bus before the protection starts.

[0047] This application also claims protection for a collector line protection system based on the foregoing protection method, including a data acquisition unit, a protection start unit, and a fault range judgment unit; characterized in that:

[0048] The data acquisition unit is used to cyclically acquire the current and voltage at the installation location of the photovoltaic and energy storage protection at the first time interval; after the protection starts, it is used to acquire the fault current and fault voltage at the protection installation location at the second time interval;

[0049] A current mutation start element is set in the protection start unit. When the sudden change amount of the current acquired at the first time interval is greater than the set start threshold, the protection starts;

[0050] In the fault range discrimination unit, calculate the negative-sequence current after the fault, calculate the phase difference between the positive-sequence voltage and the positive-sequence current after the fault, and calculate the vector difference between the positive-sequence current after the fault and the positive-sequence current before the fault; when the negative-sequence current after the fault meets the action threshold, or when the phase comparison between the positive-sequence voltage and the positive-sequence current after the fault results in meeting the positive-direction phase condition, and the calculated vector difference between the positive-sequence current after the fault and the positive-sequence current before the fault meets the action threshold, it is judged as a positive-direction fault.

[0051] The present invention also discloses an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that when the computer program is loaded into the processor, it implements the overcurrent direction protection method for an energy storage collector line according to the foregoing method.

[0052] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it implements the above-mentioned overcurrent direction protection method for an energy storage collector line.

[0053] Compared with the prior art, the present invention has the following remarkable advantages:

[0054] The present invention adaptively adjusts the overcurrent direction protection of the positive-sequence fault component ratio phase element based on the negative-sequence current and the change amount of the positive-sequence current, and solves the problem that the overcurrent protection may malfunction during the energy storage charging and discharging states. This method uses the steady-state quantity information based on the power frequency components of voltage and current, with small data calculation amount and is easy to implement in existing relay protection devices. Brief Description of the Drawings

[0055] Figure 1 This is the flow chart of the overcurrent direction protection method for the energy storage collector line of the present invention;

[0056] Figure 2 This is the typical energy storage centralized transmission system diagram and fault point setting diagram of the present invention;

[0057] Figure 3 This is the phase relationship diagram of the positive direction voltage and current of the phase comparison type of the present invention;

[0058] Figure 4(a) shows the energy storage charging state after the F1 fault of the present invention. When 0.2U N <U PPC <0.85U N , it is the phase relationship diagram of the fault voltage and fault current;

[0059] Figure 4(b) shows the energy storage charging state after the F1 fault of the present invention. When U PPC <0.2U N , it is the phase relationship diagram of the fault voltage and fault current;

[0060] Figure 4(c) shows the energy storage discharging state after the F1 fault of the present invention. When 0.2U N <U PPC <0.85U N , it is the phase relationship diagram of the fault voltage and fault current;

[0061] Figure 4(d) shows the energy storage discharging state after the F1 fault of the present invention. When U PPC <0.2U N , it is the phase relationship diagram of the fault voltage and fault current;

[0062] Figure 5(a) shows the energy storage charging state after the F2 fault of the present invention. When 0.2U N <U PPC <0.85U N , it is the phase relationship diagram of the fault voltage and fault current;

[0063] Figure 5(b) shows the energy storage charging state after the F2 fault of the present invention. When U PPC <0.2U N , it is the phase relationship diagram of the fault voltage and fault current;

[0064] Figure 5(c) shows the energy storage discharging state after the F2 fault of the present invention. When 0.2U N <U PPC <0.85U N , it is the phase relationship diagram of the fault voltage and fault current;

[0065] Figure 5(d) shows the energy storage discharging state after the F2 fault of the present invention. When U PPC <0.2UN Phase relationship diagram of fault voltage and fault current Specific implementation mode

[0066] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the spirit of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0067] As Figure 1 shown, the present invention discloses an overcurrent direction protection method for an energy storage collector line, including the following steps:

[0068] Step 1: Collect the current and voltage at the installation location of the collector line protection at a first time interval in a loop;

[0069] The first time interval is 40 ms. Before the protection starts, record the three-phase voltage of the relay busbar and the three-phase current at the installation location of the protection, and calculate the positive-sequence voltage and positive-sequence current.

[0070] Step 2: When the current mutation satisfies the action condition of the current mutation starting element, the protection starts, and the three-phase current vector and voltage vector on the new energy side before starting are cached, and enter Step 3; otherwise, return to Step 1;

[0071] In Step 2, the starting conditions of the current mutation starting element include a first action condition and a second action condition. When either action condition is satisfied, the protection starts:

[0072] The first action condition is ΔI ΦMAX > 1.25ΔI T + ΔI set ,

[0073] The second action condition is

[0074] where, ΔI ΦMAX is the maximum value of the half-wave integral of the effective values of the three-phase currents, ΔI ΦΦMAX is the maximum value of the half-wave integral of the effective values of the three-phase interphase currents, ΔI set is a settable fixed threshold, and ΔI T is a floating threshold.

[0075] ΔI set has a value range of 0.04I N ~ 0.5I N , and the floating threshold ΔI TAutomatically change according to the fluctuation of the load current, that is, the current floating threshold is the magnitude of the load current fluctuation at the previous moment.

[0076] Step 3: Collect the fault current and fault voltage at the installation location of the collector line protection at the second time interval, calculate the negative sequence current. When the negative sequence current is less than the negative sequence current threshold value, go to Step 4; otherwise, go to Step 5.

[0077] Judge whether the fault negative sequence current is greater than the negative sequence current threshold value after the protection starts as follows:

[0078] I2>I 2_set

[0079] I2 is the amplitude of the negative sequence current in the second time interval after the protection starts, and I 2_set is the negative sequence current threshold value.

[0080] Among them, the second time interval is 20 ms. In the preferred solution of the present invention, the negative sequence current threshold value I 2_set takes 0.5I N .

[0081] Step 4: Use the post-fault positive sequence voltage and positive sequence current for phase comparison to form the first action equation; use the post-fault positive sequence current and the pre-fault positive sequence current to calculate the vector difference to form the second action equation. When the phase comparison result of the post-fault positive sequence voltage and positive sequence current meets the positive direction phase condition, and the vector difference calculated from the post-fault positive sequence current and the pre-fault positive sequence current meets the action threshold, it is judged as a positive direction fault; otherwise, go to Step 5.

[0082] The first action equation is shown as follows:

[0083]

[0084] Among them, are the post-fault positive sequence voltage and positive sequence current at the protection installation location respectively;

[0085] The second action equation is shown as follows:

[0086]

[0087] Among them, is the pre-fault positive sequence current recorded at the protection installation location, and I dset is the action threshold value of the current change amount direction;

[0088] I dset The value range of N is 1.1I N ~1.3I

[0089] I setThe value range is greater than 1.1I N .

[0090] When the amplitude is greater than 0.1U N , take the positive-sequence voltage after the fault When the amplitude is not greater than 0.1U N , take the positive-sequence voltage before the fault

[0091] Among them, I N is the rated current output by a single photovoltaic and energy storage, and U N is the rated voltage of the collector bus, is the voltage of the collector bus before the protection starts.

[0092] In the preferred embodiment of the present invention, I N = 1100A, U N = 35kV, and I dset takes 1.1I N .

[0093] Step 5: Compare the magnitudes of the three-phase currents after the fault with the action threshold value to form an action equation, which is a necessary condition for the overcurrent protection to act.

[0094]

[0095] Among them, is any phase current at the protection installation location after the fault, and I set is the phase current action threshold value;

[0096] In the preferred embodiment of the present invention, I set takes 1.1I N .

[0097] This application also discloses a collector line protection system based on the foregoing protection method, including a data acquisition unit, a protection start unit, and a fault range judgment unit.

[0098] The data acquisition unit is used to cyclically acquire the current and voltage at the first time interval of the photovoltaic and energy storage protection installation location at the first time interval; after the protection starts, it is used to acquire the fault current and fault voltage at the protection installation location at the second time interval;

[0099] A current mutation start element is set in the protection start unit. When the current mutation amount acquired at the first time interval is greater than the set start threshold, the protection starts;

[0100] In the fault range discrimination unit, calculate the negative sequence current after the fault, calculate the phase difference between the positive sequence voltage and the positive sequence current after the fault, and calculate the vector difference between the positive sequence current after the fault and the positive sequence current before the fault. When the negative sequence current after the fault meets the operating threshold, or when the phase comparison between the positive sequence voltage and the positive sequence current after the fault results in meeting the positive direction phase condition, and the calculated vector difference between the positive sequence current after the fault and the positive sequence current before the fault meets the operating threshold, it is judged as a positive direction fault.

[0101] The starting conditions of the current mutation starting element include a first operating condition and a second operating condition. When either operating condition is met, the protection starts:

[0102] The first operating condition is ΔI ΦMAX > 1.25ΔI T +ΔI set ,

[0103] The second operating condition is

[0104] where ΔI ΦMAX is the maximum value of the half-wave integral of the effective values of the three-phase currents, ΔI ΦΦMAX is the maximum value of the half-wave integral of the effective values of the three-phase line currents, ΔI set is a settable fixed threshold, and ΔI T is a floating threshold.

[0105] The method of the present invention is verified by simulation experiments below.

[0106] Build Figure 2 The model shown in which the energy storage is collected through a 35 kV collector line and then sent out through a 330 kV high-voltage transmission line. DG is an equivalent single set of energy storage connected to the 35 kV collecting bus through a collector line. The length of the collector line is 0.7 km, and the length of the outgoing line is 3.5 km. Model parameters: The maximum charge / discharge current of a single energy storage on the collector line is 1100 A. The line parameters of the collector line include: positive sequence: 0.064 + 0.169j Ω / km, zero sequence: 0.295 + 1.04j Ω / km; The line parameters of the outgoing line include: positive sequence: 0.054 + 0.321j Ω / km, zero sequence: 0.295 + 1.04j Ω / km, system impedance 10 Ω. The neutral point of the collector line side is not grounded, and the neutral point of the outgoing line side is directly grounded. Two fault points F1 and F2 are set. See Appendix Figure 3 , and the per-unit value of the negative sequence current |I2 / I N |, the per-unit values of the fault phase currents of CB1 and CB2

[0107] |I CB1 / I N |, |I CB2 / I N|, Positive sequence voltage and positive sequence current phase after fault Per-unit value of the calculated vector difference between the positive sequence current after fault and the positive sequence current before fault |(I CB1 -I CB1|0| ) / I N |, |(I CB2 -I CB2|0| ) / I N |.

[0108] Experiment 1: Fault on the collector line F2, the short-circuit capacity on the system side is more than 5 times the short-circuit capacity of the energy storage

[0109]

[0110]

[0111]

[0112] Experiment 2: Fault on the collector line F2, modify the short-circuit capacity ratio of the system side to the energy storage short-circuit capacity to 1

[0113]

[0114]

[0115]

[0116] Experiment 3: The parameters of the collector line are changed to: positive sequence: 0.157 + 0.09j Ω / km, zero sequence: 0.936 + 0.541j Ω / km; the short-circuit capacity ratio of the system side to the energy storage short-circuit capacity is 1

[0117]

[0118]

[0119]

[0120] It can be seen from the experimental results in the above table that during an external fault, the protection element does not operate reliably, and during an internal fault, the protection element operates reliably. When the fault passes through a transition resistance, the sensitivity and reliability of the protection direction element are not affected.

[0121] The external faults in Experiments 1 to 3 correspond to Figure 4(a) to Figure 4(d) Voltage and current phase analysis. In Fig. 4(a), there is a risk of maloperation of the direction element, which is consistent with the maloperation of the direction element shown in the external faults "three-phase fault (charging) transition resistance is 1Ω, 3Ω" in Experiments 1 to 3. When the "auxiliary criterion for the change in positive sequence current after fault and positive sequence current before fault |(I CB2 -I CB2|0| ) / I NAfter that, the directional element does not operate reliably.

[0122] The external faults in Experiments 1 to 3 correspond to Figure 5(a) to Figure 5(d) voltage and current phase analysis. When an internal fault occurs, under different ratios of system short-circuit capacity to energy storage short-circuit capacity and different line impedance angles of the distribution network lines, " and |(I CB2 -I CB2|0| ) / I N |” all operate reliably, proving that this method can effectively improve the reliability of overcurrent direction.

[0123] This disclosure can be a system, a method, and / or a computer program product. The computer program product can include a computer-readable storage medium having thereon computer-readable program instructions for causing a processor to implement various aspects of this disclosure.

[0124] The computer-readable storage medium can be a tangible device that can hold and store instructions used by an instruction execution device. The computer-readable storage medium can be, for example, but is not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (non-exhaustive list) of the computer-readable storage medium include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disc (DVD), a memory stick, a floppy disk, a mechanically encoded device, such as a punched card or raised structures in grooves having instructions stored thereon, and any suitable combination of the foregoing. The computer-readable storage medium used herein is not construed as being a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagated through a waveguide or other transmission medium (e.g., an optical pulse through an optical fiber cable), or an electrical signal transmitted through a wire.

[0125] The computer-readable program instructions described herein can be downloaded from the computer-readable storage medium to various computing / processing devices, or downloaded to an external computer or external storage device through a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include a copper transmission cable, an optical fiber transmission, a wireless transmission, a router, a firewall, a switch, a gateway computer, and / or an edge server. The network adapter or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0126] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine - related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object - oriented programming languages such as Smalltalk, C++, etc., and conventional procedural programming languages such as the "C" language or similar programming languages. The computer - readable program instructions may be executed entirely on the user's computer, partially on the user's computer, executed as a stand - alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., through the Internet using an Internet service provider). In some embodiments, by using the state information of the computer - readable program instructions to customize an electronic circuit, such as a programmable logic circuit, a field - programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit can execute the computer - readable program instructions to implement various aspects of the present disclosure.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A method for overcurrent direction protection of an energy storage collector line, characterized in that, The protection method includes the following: Step 1: Collect the positive-sequence current and positive-sequence voltage at the protection installation location in a cycle at a first time interval; Step 2: When the sudden change in current satisfies the action condition of the current mutation starting element, the protection starts, and the positive-sequence current vector and positive-sequence voltage vector before starting are cached, and then enter Step 3; otherwise, return to Step 1; Step 3: Collect the positive-sequence current, negative-sequence current, and positive-sequence voltage after the fault at the protection installation location at a second time interval. When the negative-sequence current is less than or equal to the negative-sequence current threshold value, enter Step 4; otherwise, enter Step 5; Step 4: Use the positive-sequence voltage after the fault and the positive-sequence current to perform phase comparison, calculate the angle difference between the positive-sequence voltage after the fault and the positive-sequence current after the fault as the first action equation; calculate the vector difference between the positive-sequence current after the fault and the positive-sequence current vector before the fault, and compare the vector difference modulus value with the action threshold as the second action equation; when both the first action equation and the second action equation meet the conditions, it is judged as a positive-direction fault; otherwise, enter Step 5; Step 5: When the phase current after the fault meets the action threshold, and the negative-sequence current is greater than the negative-sequence current threshold value or meets the positive-direction fault condition in Step 4, it is judged that an in-zone fault has occurred, and the protection acts to trip; otherwise, it is judged that an out-of-zone fault has occurred.

2. A method for overcurrent direction protection of an energy storage collector line according to claim 1, characterized in that: In Step 2, the action conditions of the current mutation starting element include a first action condition and a second action condition. When either action condition is met, the protection starts: The first motion condition is ΔI ΦMAX > 1.25ΔI T + ΔI set , The second operation condition is where, ΔI ΦMAX is the maximum value among the half-wave integrals of the effective values of the three-phase currents, and ΔI ΦΦMAX is the maximum value among the half-wave integrals of the effective values of the three inter-phase currents, ΔI set is a settable fixed threshold, and ΔI T is a floating threshold.

3. A method for overcurrent direction protection of an energy storage collector line according to claim 2, characterized in that: ΔI set The value range is 0.04I N ~0.5I N , and the floating threshold ΔI T automatically changes according to the fluctuation of the load current and is equal to the magnitude of the load current fluctuation at the previous moment.

4. A method for overcurrent direction protection of an energy storage collector line according to claim 1, characterized in that: In Step 3, the following is used to judge whether the negative-sequence current after the fault is greater than the negative-sequence current threshold value after the protection starts: I2 > I 2_set I2 is the negative sequence current value at the second time interval after the protection is activated, and I 2_set is the negative sequence current threshold value.

5. A method for overcurrent direction protection of an energy storage collector line according to claim 1 or 4, characterized in that: The first time interval is 40 ms; the second time interval is 20 ms.

6. A method for overcurrent direction protection of an energy storage collector line according to claim 4, characterized in that: I 2_set Set according to the maximum unbalanced negative-sequence current during system operation.

7. A method for overcurrent direction protection of an energy storage collector line according to claim 1, characterized in that: Step 4 includes two direction discrimination conditions, namely the phase comparison condition based on the positive-sequence voltage and positive-sequence current and the action condition of the vector difference between the positive-sequence current after the fault and the positive-sequence current before the fault.

8. A method for overcurrent direction protection of an energy storage collector line according to claim 1 or 7, characterized in that: The first action equation in Step 4 is shown as follows: wherein, are respectively the positive-sequence voltage and positive-sequence current at the location where the protection is installed after the fault; The second action equation in Step 4 is shown as follows: Among them, is the positive-sequence current before the fault occurs at the protection installation location, and I dset is the threshold value for the directional operation of the current change amount.

9. A method for overcurrent direction protection of an energy storage collector line according to claim 1, characterized in that: In Step 5, the judgment condition for the phase current after the fault to meet the action threshold is shown as follows: Among them, is the arbitrary phase current at the location where the protection is installed after a fault, and I set is the threshold value of the phase current operation.

10. A method for overcurrent direction protection of an energy storage collector line according to claim 8 or 9, characterized in that: I dset The value range of N is 1.1I N to 1.3I; I set The value range is greater than 1.1I N ; When the amplitude is greater than 0.1U N , take the positive-sequence voltage after the fault; When the amplitude is not greater than 0.1U N , take the positive-sequence voltage before the fault Among them, I N is the rated current for single - line PV and energy storage output, U N is the rated voltage of the collector bus, is the voltage of the collector bus before the protection starts.

11. A collector line protection system based on the protection method described in any one of claims 1-10, comprising a data acquisition unit, a protection startup unit, and a fault range determination unit; characterized in that: The data acquisition unit is used to cyclically acquire the current and voltage at the photovoltaic / storage protection installation location at the first time interval at the first time interval; after the protection is started, it is used to acquire the fault current and fault voltage at the protection installation location at the second time interval. A current mutation startup element is set in the protection startup unit. When the sudden change in current acquired at the first time interval is greater than the set startup threshold, the protection is started. In the fault range discrimination unit, calculate the negative sequence current after the fault, calculate the phase difference between the positive sequence voltage and the positive sequence current after the fault, and calculate the vector difference between the positive sequence current after the fault and the positive sequence current before the fault. When the negative sequence current after the fault meets the action threshold, or when the result of comparing the positive sequence voltage and the positive sequence current after the fault meets the positive direction phase condition, and the calculated vector difference between the positive sequence current after the fault and the positive sequence current before the fault meets the action threshold, it is determined as a positive direction fault.

12. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the computer program is loaded into the processor, it implements an overcurrent direction protection method for a collector line of an energy storage system according to any one of claims 1-10.

13. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements an overcurrent direction protection method for a collector line of an energy storage system according to any one of claims 1-10.

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