Low-voltage direct-current power distribution network over-transient voltage protection method based on dynamic threshold principle

Abstract

The invention discloses a low-voltage direct-current power distribution network over-transient voltage protection method based on a dynamic threshold principle, and belongs to the field of low-voltage direct-current power distribution networks. The method comprises the steps that the protection device in the low-voltage direct-current power distribution network collects and monitors the voltage at the position of the protection device in real time; when the voltage is lower than 90% of the rated voltage, the voltage and the voltage change rate at the current moment + delta t are obtained to serve as the first voltage and the first voltage change rate; the voltage and the voltage change rate at the current moment + 2 delta t are obtained as the second voltage and the second voltage change rate, and delta t is the reciprocal of the collection frequency of the protection device; taking the second voltage change rate as a dynamic protection threshold value, comparing the first voltage change rate with the second voltage change rate, and if the first voltage change rate is greater than the second voltage change rate and is greater than 0, taking a first measure; and taking a second measure under other conditions. The method is simple and easy to implement, the operation stability of the system is guaranteed, and a fixed protection threshold value does not need to be set.

Description

Technical Field

[0001] The present invention relates to the field of low-voltage direct current distribution networks, and in particular to a low-voltage direct current distribution network over-transient voltage protection method based on a dynamic threshold principle. Background Art

[0002] Low-voltage DC distribution networks have been considered an effective way to relieve the pressure on existing power grids. At the same time, the rapid development of power electronics technology and the widespread application of low-voltage DC electrical appliances have made low-voltage DC power supply technology an auxiliary and alternative to traditional AC power supply and distribution technology in different areas of "new infrastructure" (such as 5G base stations, data centers, new energy charging piles, DC green buildings, smart homes, industrial Internet, rural and remote areas, etc.), prompting the existing low-voltage AC distribution network to develop towards a hybrid AC / DC and DC distribution network. The energy-saving advantages and enhanced controllability brought by DC distribution technology have been demonstrated by demonstration projects at home and abroad. At the same time, in order to promote the wider application of low-voltage DC distribution technology, the International Electrotechnical Commission has also strongly supported the formulation of technical guidelines and signs. However, reliable DC fault protection is considered a key technical challenge to ensure high stability, high reliability, and high flexibility of low-voltage DC distribution systems.

[0003] Existing low-voltage DC high-speed fault protection methods mostly directly use the voltage change rate and current change rate to determine the protection action. However, due to the fast-changing characteristics of DC fault voltage and current signals, existing methods mostly rely on signal acquisition equipment with ultra-high sampling frequency (for example, 2MHz) to ensure accurate instantaneous current and voltage change rates are obtained and compared with the preset protection thresholds to accurately determine the protection action. However, the large-scale use of these devices in low-voltage distribution networks will increase the application cost of low-voltage distribution technology and cause waste of resources. In addition, existing non-unit protection methods mostly use fixed protection threshold methods. Considering the large-scale application of low-voltage DC distribution technology, when the signal sampling frequency is reduced, the voltage change rate caused by the high-resistance fault will be lower than the fixed threshold, resulting in inaction of the protection. Summary of the invention

[0004] In order to solve the problems in the prior art, the present invention proposes a low-voltage DC distribution network transient voltage protection method based on a dynamic threshold principle.

[0005] The technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention discloses a method for protecting a low-voltage DC distribution network from transient voltage based on a dynamic threshold principle, wherein a protection device is installed on a connecting cable between a main bus and a branch bus and / or between a branch bus and a branch bus in the low-voltage DC distribution network, and the protection device can collect and monitor the voltage at its own position in real time, and control the on and off of the cable; the method comprises:

[0007] 1) Monitor the real-time voltage value. When the voltage value is lower than 90% of the rated voltage, proceed to step 2);

[0008] 2) Assuming that the time when the voltage value is lower than 90% of the rated voltage is t, the voltage and the voltage change rate at the time t+Δt are obtained as the first voltage and the first voltage change rate; and the voltage and the voltage change rate at the time t+2Δt are obtained as the second voltage and the second voltage change rate; wherein Δt is the reciprocal of the acquisition frequency of the protection device;

[0009] 3) Taking the second voltage change rate as the dynamic protection threshold, the first voltage change rate is compared with the second voltage change rate. If the first voltage change rate is greater than the second voltage change rate and both are greater than 0, a fault occurs within the protection area of ​​the protection device, and the protection device takes the first measure; in other cases, a fault occurs outside the protection area of ​​the protection device, and the protection device takes the second measure.

[0010] Furthermore, two protection devices are provided on the cables connecting the main busbar and the branch busbar and / or connecting the branch busbar and the branch busbar, and the two protection devices are respectively installed at two ends of the cable.

[0011] Furthermore, the protection devices each include a voltage sensor, an auxiliary inductor, a protection relay and a circuit breaker for protecting a low-voltage DC distribution network. The voltage sensor is used to collect the voltage of the protection relay in real time and obtain the voltage change rate, and to continuously detect the collected voltage. The auxiliary inductor, voltage sensor, protection relay and circuit breaker are connected in series with each other; the protection area of ​​the protection relay is isolated between the two protection devices by the auxiliary inductor.

[0012] In a second aspect, the present invention discloses an electronic device, including a processor and a memory, wherein the memory stores machine executable instructions that can be executed by the processor, and the processor executes the machine executable instructions to implement the low-voltage DC distribution network transient voltage protection method based on the dynamic threshold principle.

[0013] In a third aspect, the present invention discloses a machine-readable storage medium, which stores machine-executable instructions. When the machine-executable instructions are called and executed by a processor, they are used to implement the low-voltage DC distribution network transient voltage protection method based on the dynamic threshold principle.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The present invention proposes a transient voltage protection method based on the dynamic threshold principle, which effectively solves the problem in the prior art that it is difficult to achieve accurate protection under low sampling frequency and high resistance fault conditions due to reliance on fixed thresholds and transient voltages. Under the same size of protective auxiliary inductance and sampling frequency, the high resistance fault resistance value that can be identified by the present invention is about four times that of the prior art; and when distinguishing the same high resistance fault, the auxiliary inductance required by the present invention is only about one-fourth of that of the prior art. The present invention significantly improves the fault differentiation capability under low sampling frequency voltage sensors, thereby ensuring the protection reliability of low-voltage DC systems. In addition, the method greatly reduces the implementation cost of low-voltage DC distribution networks, simplifies the implementation process, and the system operation stability is also fully guaranteed. In addition, the present invention does not require a preset fixed protection threshold, reflecting higher adaptability and flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a system diagram of a low voltage DC distribution network;

[0017] Figure 2 It is a partial system diagram of a low voltage DC distribution network;

[0018] Figure 3 It is a flow chart of the low voltage DC distribution network transient voltage protection method of the present invention;

[0019] Figure 4 It is a logic diagram for realizing the algorithm of the low voltage DC distribution network transient voltage protection method of the present invention;

[0020] Figure 5 It is the common connection point PCC, protection relay R a1 and protection relay R a2 Time-voltage response diagram of F1 fault;

[0021] Figure 6 Is the protection relay R a1 Time-voltage change rate response diagram at F1 fault;

[0022] Figure 7 It is the common connection point PCC and the protection relay R a1 Time-current response diagram at F1 fault;

[0023] Figure 8 Is the protection relay R a1 Response diagram of time-voltage change rate at F2 fault;

[0024] Fig. 9 Is the protection relay Ra1 Response diagram of transient voltage change rate at different fault resistance and sampling frequency;

[0025] Fig.10 Is the protection relay R a1 Response diagram of transient voltage rate of change amplitude at different fault resistances and sampling frequencies;

[0026] Fig.11 This is the response diagram of the fault resistance size when the auxiliary inductance size is different. DETAILED DESCRIPTION

[0027] The present invention is further described and illustrated below in conjunction with specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0028] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

[0029] The purpose of the present invention is to provide a low-voltage DC power distribution network transient voltage protection method based on the dynamic threshold principle in view of the shortcomings of the current technology. The transient voltage protection method of the present invention can effectively distinguish between faults within the protection area of ​​the protection relay and faults outside the protection area under the condition of low signal sampling frequency, and is a low-voltage DC power distribution system protection method that can provide high stability and high reliability.

[0030] The present invention is directed to a low voltage DC distribution network, such as Figure 1 As shown in the figure, it is a system diagram of low voltage DC distribution network. Figure 1 In the figure, the bold mark at the position of Bus1 is the main bus of the low-voltage DC distribution network, and the bold mark at the position of Bus2, Bus3, Bus4 and Bus5 is the branch bus of the low-voltage DC distribution network. The main bus is the bus that transmits voltage to the user end, and the branch bus is the bus that receives the voltage transmitted by the main bus and transmits voltage to the electrical appliances at the user end. The main bus and the branch bus are connected by cables, and the branch bus is connected by cables. Figure 1In the invention, two protection devices are installed on the connecting cables between the main bus and the branch bus and between the branch bus and the branch bus, and the two protection devices are installed at both ends of the cable. The protection device can collect and monitor the voltage at its own position in real time, and control the on and off of the cable. The protection device includes a voltage sensor, an auxiliary inductor, a protection relay and a circuit breaker for protecting the low-voltage DC distribution network. The protection area of ​​the protection relay is isolated between the two protection devices by the auxiliary inductor. Figure 1 a1, a2, b1, b2, c1, c2, d1, d2 in the figure all represent protection relays. The area between each protection device and its adjacent protection device located upstream is the upstream protection zone of the protection device, and the area between each protection device and its adjacent protection device located downstream is the downstream protection zone of the protection device. The upstream protection zone and downstream protection zone of a protection device constitute the protection zone of the protection device, and the protection zone of the protection device is the protection zone of the protection relay in the protection device.

[0031] Part of the system topology of the low voltage DC distribution network is shown in the figure below: Figure 2 As shown. Since DC protection mainly considers the capacitor discharge stage, fault detection and protection selectivity should be completed before the diode freewheeling stage. In the capacitor discharge stage, the converter can be simplified to a combination circuit of capacitor C, cable resistance R and inductance L in the fault path. The common connection point is the main inverter, and its port capacitance is the main capacitance component in the line because the cable capacitance is much smaller than the capacitance of the main inverter. There are multiple protection devices in the low-voltage DC distribution network, each of which includes a protection relay, a solid-state circuit breaker (i.e., a circuit breaker, Figure 2 The circuit breaker and protection relay in the figure are drawn together), a voltage sensor and an auxiliary inductor. The auxiliary inductor, voltage sensor, protection relay and circuit breaker are connected in series, and the low-voltage DC distribution network area between two adjacent auxiliary inductors is the protection area of ​​the two protection relays. The auxiliary inductor, voltage sensor, protection relay and circuit breaker are connected in series, and the auxiliary inductor is used to define the fault boundary, that is, its size will affect the high-resistance fault resistance that can be identified. Figure 2 R a1 , R a2 and R c1 Both represent protection relays, with protection relay R a1 For example, when the fault is located at the protection relay R a1 and protection relay R a2 When R a1 Fault F1 is defined as an inter-pole fault, that is, the protection relay R a1 The fault in the protection zone (fault in the protection zone) and the protection relay R a2 Fault F2 is defined as a remote bus fault, that is, the protection relay Ra2 The fault in the area, protection relay R a1 Out-of-zone fault, fault F3 is defined as the protection relay R a1 Out-of-zone fault and protection relay R a2 Out-of-area faults, such as Figure 2 The following description is based on the protection relay R a1 Speaking of.

[0032] Under normal circumstances, the protection relay R a1 The voltage U a Rated voltage U n , which is defined as follows:

[0033]

[0034] Among them, U t Is the protection relay R a1 Voltage near the main inverter, U a Is the protection relay R a1 The voltage at the other end, L a Is the protection relay R a1 The auxiliary inductance, I, flows through the protection relay R a1 of current.

[0035] When F1 fault occurs, based on the low voltage DC fault characteristics, the protection relay R a1 Voltage U near the main inverter t and flows through the protection relay R a1 The derivative of the current I can be expressed as formula (2) and formula (3).

[0036]

[0037]

[0038] Among them, U0 is the initial voltage of the capacitor of the main inverter, L is the inductance; C is the capacitance; s1 and s2 are the roots of the denominator of the Laplace expression of the DC fault characteristic; as shown in formula (4), the cable resistance R, inductance L and capacitance C in the fault circuit are involved.

[0039]

[0040] Among them, α is the damping coefficient; ω0 is the resonant angular frequency; R is the cable resistance.

[0041] Substituting formula (2) and (3) into formula (1), we can get the protection relay R a1 The voltage is expressed as formula (5).

[0042]

[0043] Take t = 0 and substitute formula (4) into formula (5), and we can get the protection relay R a1 The transient voltage is expressed as formula (6).

[0044]

[0045] Taking the derivative of both sides of formula (5), the protection relay R a1 The voltage derivative of is shown in formula (7).

[0046]

[0047] Assuming t = 0 in this formula, we can get the protection relay R a1 The transient voltage change rate is shown in formula (8), where the PT subscript stands for transient.

[0048]

[0049] When F1 fault occurs, the protection relay R a1 After the transient voltage drops, the protection relay R a1 The transient voltage change rate is positive, and its value is related to the protection relay R in the fault path. a1 It is related to the rated voltage, auxiliary inductance and cable impedance.

[0050] In addition, by taking the derivative of both sides of formula (7) again, the second-order voltage derivative can be expressed as formula (9).

[0051]

[0052] Substituting formula (4) and t=0 into formula (9), we obtain formula (10), which is a negative value, indicating that the rate of change of the transient voltage decreases after the F1 fault occurs.

[0053]

[0054] When F3 fault occurs, U a The voltage characteristics of Bus2 are similar to those of Bus2, which can be expressed by formula (2). At the same time, by taking the derivative of formula (2), the voltage change rate and second-order change rate at Bus2 are obtained as shown in formulas (11) and (12). Substituting t = 0 into the formula, it can be found that when F3 fails, the protection relay R a1 The voltage change rate is negative, and the rate of change is getting smaller and smaller.

[0055]

[0056]

[0057] Therefore, the protection relay R a1 The positive and negative values ​​of the voltage change rate and the voltage change rate of the second point after the fault are compared with the voltage change rate of the third point to distinguish the downstream fault. In this process, the third point after the fault occurs is used as a dynamic threshold, which changes with the different fault locations, and there is no need to set a fixed protection threshold.

[0058] For this feature, Figure 3 As shown, the technical solution of the present invention is as follows:

[0059] Step 1: The voltage sensor collects the voltage U of the protection relay in real time and obtains the voltage change rate dU / dt, and also continuously monitors the collected voltage U and the voltage change rate dU / dt to ensure that the system status of the low-voltage DC distribution network can be mastered in real time;

[0060] When it is detected that the voltage value of the protection relay is lower than 90% of the rated voltage, the process proceeds to step 2 for further processing, otherwise, the process proceeds to step 1 to continue to obtain and monitor the voltage U and the voltage change rate dU / dt in real time;

[0061] Step 2: When the voltage value of the protection relay is lower than the rated voltage U n When the voltage U of the protection relay is 90%, let this moment be t, and obtain the voltage U of the protection relay at the moment t+Δt. (t+Δt) and voltage change rate dU (t+Δt) / d(t+Δt); at the same time, obtain the voltage U of the protection relay at the time t+2Δt (t+2Δt) and voltage change rate dU (t+2Δt) / d(t+2Δt); where Δt is the inverse of the acquisition frequency of the voltage sensor;

[0062] Step 3: dU (t+2Δt) / d(t+2Δt) is regarded as the dynamic protection threshold, and dU (t+Δt) / dt (t+Δt) and dU (t+2Δt) / dt (t+2Δt) For comparison, if dU (t+Δt) / dt (t+Δt) Greater than dU (t+2Δt) / d(t+2Δt) and dU (t+Δt) / d(t+Δt) and dU (t+2Δt) / d(t+2Δt) are all greater than 0, it is determined that a fault has been detected in the protection area of ​​the protection relay, and the protection relay sends a disconnection signal to the circuit breaker that protects the protection area together with it, and the circuit breaker is disconnected, cutting off the fault, isolating the fault area, and the cable connection at the current position is disconnected;

[0063] In other cases, it is determined that a fault occurs outside the protection area of ​​the protection relay, the protection relay does not send any signal to the circuit breaker, the circuit breaker does not operate, and the connection of the cable at the current position remains connected.

[0064] In a specific embodiment of the present invention, the calculation formula of the voltage change rate dU / dt is:

[0065]

[0066] Among them, U t is the voltage of the protection relay at time t; U (t-Δt) is the voltage of the protection relay at time t-Δt.

[0067] Voltage change rate dU (t+Δt) The calculation formula of / d(t+Δt) is:

[0068]

[0069] Among them, U (t+Δt) is the voltage of the protection relay at time t+Δt.

[0070] Voltage change rate dU (t+2Δt) The calculation formula of / d(t+2Δt) is:

[0071]

[0072] Among them, U (t+2Δt) It is the voltage of the protection relay at the time t+2Δt.

[0073] like Figure 4 As shown, it is an algorithm implementation logic diagram of the low-voltage DC distribution network transient voltage protection method of the present invention, which specifically shows the fault differentiation and fault protection of the low-voltage DC distribution network, that is, the protection relay obtains U and dU / dt, compares the voltage signal U with 90% of the rated voltage, obtains the fault signal, and holds the voltage change rate through different delays and the "hold" module, thereby obtaining the voltage change rate under different delays, and obtains the signal comparison result through the comparison module ">" and inputs the logic gate to judge the logic result.

[0074] exist Figure 2 In the system, when fault F1 occurs, the protection relay R a1 and R a2 A transient voltage drop is detected, such as Figure 5 As shown in Figure 1, the voltage is less than 90% of the rated voltage, so a fault is detected; where PCC is the common connection point. Subsequently, the rate of change of the recorded voltage is as follows Figure 6 As shown, the protection relay R a1The captured transient voltage derivative (i.e. transient voltage change rate) dU (t+Δt) / d(t+Δt) is greater than dU (t+2Δt) / d(t+2Δt). Therefore, according to the judgment basis of the present invention, the fault is identified as the fault in the protection relay R a1 Downstream protection zone, and send trip (disconnect) signal to relevant circuit breaker. Figure 7 At the same time, the protection relay R a2 It will also be based on the protection relay R a1 The same judgment principle locates the fault F1 and issues a trip signal. Fault F1 is cleared and the voltage at the common connection point PCC recovers to the rated voltage within 2 milliseconds. Figure 5 shown.

[0075] when Figure 2 When the F2 fault occurs, Figure 8 As shown, the protection relay R a1 Captured transient voltage change rate dU (t+Δt) / d(t+Δt) is less than dU (t+2Δt) / d(t+2Δt), the protection triggering condition is not met, so the protection relay R a1 It does not operate in case of F2 fault, and can distinguish the faults.

[0076] Regarding the discrimination capability of high impedance faults, the responses of the proposed dynamic thresholds at different sampling frequencies under different fault resistances and sampling frequencies are shown in Figure 2. Fig. 9 As shown in the figure, the transient voltage change rate is always greater than the dynamic threshold, which will not cause protection failure. Fig.10 Compared with the existing method based on voltage change rate (at about 0.25Ω, the voltage change rate is less than the fixed threshold, and the protection fails), the transient voltage protection method based on the dynamic threshold principle proposed in the present invention can cover the fault resistance range from short circuit to 1Ω (the high-resistance fault resistance value that the present invention can identify is four times the existing resistance value) at a lower sampling frequency of 10kHz. This range is about four times that of the existing protection method for low-voltage DC distribution systems based on voltage change rate and fixed thresholds. Therefore, the present invention can use a low sampling frequency to achieve fault protection and fault differentiation of low-voltage DC distribution networks, reducing the implementation cost of low-voltage DC distribution networks. The implementation method is simple, the stable operation of the system can be guaranteed, and there is no need to set a fixed protection threshold. Fig.11The horizontal axis in the figure represents the size of the auxiliary inductor, and the vertical axis represents the high impedance fault discrimination capability of different methods under the current auxiliary inductor size. It can be seen from the figure that as the auxiliary inductor increases, the high impedance fault discrimination capability also increases, but at the same high impedance fault discrimination capability, the size of the auxiliary inductor of the method of the present invention is one-fourth of that of the existing method. In the present invention, the inductive reactance of the auxiliary inductor is 10%-20% of the inductive reactance value of the cable between the two mutually connected protection devices.

[0077] An embodiment of the present invention further provides an electronic device, including a memory and a processor;

[0078] The memory is used to store computer programs;

[0079] The processor is used to implement the above-mentioned low-voltage direct current distribution network transient voltage protection method based on the dynamic threshold principle when executing the computer program.

[0080] An embodiment of the present invention further provides a computer-readable storage medium having a program stored thereon. When the program is executed by a processor, the above-mentioned low-voltage DC distribution network transient voltage protection method based on the dynamic threshold principle is implemented.

[0081] The computer-readable storage medium may be an internal storage unit of any device with data processing capability described in any of the aforementioned embodiments, such as a hard disk or a memory. The computer-readable storage medium may also be an external storage device of any device with data processing capability, such as a plug-in hard disk, a smart media card (SMC), an SD card, a flash card, etc. equipped on the device. Furthermore, the computer-readable storage medium may also include both an internal storage unit and an external storage device of any device with data processing capability. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capability, and may also be used to temporarily store data that has been output or is to be output.

[0082] Obviously, the above-described embodiments and drawings are only some examples of the present application. For those of ordinary skill in the art, the present application can also be applied to other similar situations based on these drawings without creative work. In addition, it is understandable that, although the work done in this development process may be complicated and lengthy, for those of ordinary skill in the art, certain changes in design, manufacturing or production based on the technical content disclosed in this application are only conventional technical means and should not be regarded as insufficient content disclosed in this application. Without departing from the concept of the present application, several variations and improvements can also be made, which all belong to the scope of protection of the present application. Therefore, the scope of protection of the present application shall be subject to the attached claims.

Claims

1. A method for protecting low voltage DC distribution network from transient voltage based on dynamic threshold principle, characterized in that: A protection device is installed on the connecting cable between the main bus and the branch bus and / or between the branch bus in the low-voltage DC distribution network, and the protection device can collect and monitor the voltage at its own position in real time, and control the on and off of the cable; the method includes: 1) Monitor the real-time voltage value. When the voltage value is lower than 90% of the rated voltage, proceed to step 2); 2) Assuming that the time when the voltage value is lower than 90% of the rated voltage is t, the voltage and the voltage change rate at the time t+Δt are obtained as the first voltage and the first voltage change rate; and the voltage and the voltage change rate at the time t+2Δt are obtained as the second voltage and the second voltage change rate; wherein Δt is the reciprocal of the acquisition frequency of the protection device; 3) Taking the second voltage change rate as the dynamic protection threshold, the first voltage change rate is compared with the second voltage change rate. If the first voltage change rate is greater than the second voltage change rate and both are greater than 0, a fault occurs within the protection area of ​​the protection device, and the protection device takes the first measure; in other cases, a fault occurs outside the protection area of ​​the protection device, and the protection device takes the second measure.

2. The low voltage DC distribution network transient voltage protection method based on the dynamic threshold principle according to claim 1 is characterized in that: Two protection devices are arranged on the cables connecting the main busbar and the branch busbar and / or connecting the branch busbar and the branch busbar, and the two protection devices are respectively installed at two ends of the cable.

3. The low voltage DC distribution network transient voltage protection method based on the dynamic threshold principle according to claim 1 is characterized in that: The protection devices all include a voltage sensor, an auxiliary inductor, a protection relay and a circuit breaker. The voltage sensor is used to collect the voltage of the protection relay in real time and obtain the voltage change rate, and to continuously detect the collected voltage. The protection relay and the circuit breaker are used to protect the low-voltage DC distribution network. The auxiliary inductor, the voltage sensor, the protection relay and the circuit breaker are connected in series with each other; the protection area of ​​the protection relay is isolated between the two protection devices by the auxiliary inductor.

4. The low voltage DC distribution network transient voltage protection method based on the dynamic threshold principle according to claim 3 is characterized in that: The area between each protection device and the adjacent protection device located upstream is the upstream protection area of ​​the protection device, and the area between each protection device and the adjacent protection device located downstream is the downstream protection area of ​​the protection device. The upstream protection area and downstream protection area of ​​a protection device constitute the protection area of ​​the protection device, and the protection area of ​​the protection device is the protection area of ​​the protection relay in the protection device.

5. The low voltage DC distribution network transient voltage protection method based on the dynamic threshold principle according to claim 3 is characterized in that: The inductive reactance of the auxiliary inductor is 10%-20% of the inductive reactance value of the cable between the two mutually connected protection devices.

6. The low voltage DC distribution network transient voltage protection method based on the dynamic threshold principle according to claim 3 is characterized in that: In step 2), the rated voltage is the rated voltage of the protection relay.

7. The low voltage DC distribution network transient voltage protection method based on the dynamic threshold principle according to claim 3 is characterized in that: In step 2), the first voltage change rate is The second voltage change rate is Among them, U (t+Δt) is the voltage of the protection relay at time t+Δt; U (t+2Δt) is the voltage of the protection relay at time t+2Δt; U t is the voltage of the protection relay at time t.

8. The low voltage DC distribution network transient voltage protection method based on the dynamic threshold principle according to claim 3 is characterized in that: In step 3), the protection device takes a first measure, including: A fault occurs in the protection area of ​​the protection relay, and the protection relay sends a disconnection signal to the circuit breaker, the circuit breaker is disconnected, the fault is cut off, and the connection of the cable at the current position is disconnected; The protection device adopts a second measure, including: If a fault occurs outside the protection area of ​​the protection relay, the protection relay does not send any signal to the circuit breaker, the circuit breaker does not operate, and the cable connection at the current position remains connected.

9. An electronic device, characterized in that: It comprises a processor and a memory, wherein the memory stores machine executable instructions that can be executed by the processor, and the processor executes the machine executable instructions to implement the low-voltage direct current distribution network transient voltage protection method based on the dynamic threshold principle as described in any one of claims 1 to 8.

10. A machine-readable storage medium, characterized in that: The machine-readable storage medium stores machine-executable instructions, which, when called and executed by a processor, are used to implement the low-voltage DC distribution network transient voltage protection method based on the dynamic threshold principle as described in any one of claims 1 to 8.

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