Fault prediction control method for low-damping direct current system based on parallel sampling of inductance voltage

Abstract

The application relates to the technical field of direct current transmission and distribution protection, in particular to a low-damping direct current system fault prediction control method based on parallel sampling of inductive voltage; the method comprises the following steps: synchronously collecting main loop current and additional inductive voltage, using the inductive voltage to calculate the current change rate and taking the maximum value of the current differential value as a detection value, and predicting the current at the next sampling time according to the detection value; comparing the detection value with preset first and second threshold values, if the detection value exceeds the first threshold value, switching to a transfer branch, and then deciding whether to operate a mechanism to disconnect and transfer a power consumption branch to isolate a fault or reset according to whether the actual or predicted current is out of limit; if the detection value exceeds the second threshold value, switching and directly disconnecting at the same time, and then isolating a fault or resetting according to the out-of-limit result; the application realizes early prediction of a fault current, graded and rapid disposal of false faults and real faults, shortens the cutting time, and reduces the short-circuit current peak value.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission and distribution protection technology, specifically to a fault prediction and control method for low-damped DC systems based on parallel sampling of inductor voltage. Background Technology

[0002] As the capacity of DC transmission and distribution systems continues to increase, the equivalent resistance of the lines is small and the time constant is low, exhibiting typical low-damping characteristics. This results in an extremely high current rise rate when a short-circuit fault occurs, posing a severe challenge to the speed and accuracy of the protection and control system. In low-damped DC systems, the fault current can rise to a level that endangers equipment safety within milliseconds. Therefore, protection devices are required not only to accurately detect the current amplitude but also to capture the current change trend in a timely manner so as to predict and take control measures in advance before the current reaches the dangerous limit.

[0003] In existing protection schemes, the method of calculating the rate of change based on the difference of current sampled values ​​can reflect the trend of current change, but its accuracy is affected by the sampling frequency and the location of the sampling point relative to the time of the fault. At the same time, relying solely on the instantaneous value of the current for fault identification is difficult to fully distinguish between a real short circuit and a transient disturbance in the system, which may lead to insufficient selectivity of the protection action. As a common energy storage element in DC systems, the inductor has a clear physical relationship between the voltage across its terminals and the rate of change of current. Parallel sampling of the inductor voltage can provide an independent and synchronous information path for obtaining the rate of change of current.

[0004] By organically combining inductor voltage information with current sampling information, it is expected to improve the ability to perceive the development trend of fault current. On this basis, hierarchical control logic can be constructed, which can not only respond quickly to severe faults, but also leave room for handling recoverable disturbances. Therefore, studying a fault prediction control method that integrates parallel sampling of inductor voltage is of great significance for improving the power supply safety and operational flexibility of low-damped DC systems. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the background technology by proposing a fault prediction and control method for low-damped DC systems based on parallel sampling of inductor voltage.

[0006] The technical solution of this invention: a fault prediction and control method for a low-damping DC system based on parallel sampling of inductor voltage, comprising the following specific implementation steps: S1. Synchronously collect the instantaneous value of the main circuit current and the instantaneous value of the voltage across the additional inductor at a fixed sampling period. Calculate the current change rate at the current moment using the inductor voltage sampling value. At the same time, calculate the current change rate based on the current sampling using two adjacent current sampling points. Take the maximum value of the two as the current change rate detection value at the current moment. S2. After completing each current sampling and obtaining the current change rate detection value at the current moment, the instantaneous current value at the next sampling moment is predicted using the detection value to obtain the predicted current value. S3. Compare the current rate of change detection value with the preset first threshold and second threshold of current rate of change. The second threshold is greater than the first threshold. If the detection value is greater than the first threshold but not greater than the second threshold, execute strategy one: switch to the transfer branch and continuously predict the current. If the actual current or the predicted current reaches the preset current amplitude limit, issue an operating mechanism disconnect command and switch to the energy consumption branch to isolate the fault after disconnection. If the limit is not exceeded and the detection value falls back to within the limit, reset. If the detection value is greater than the second threshold, execute strategy two: switch to the transfer branch and immediately issue an operating mechanism disconnect command, continuously predict the current. If the actual current or the predicted current reaches the current amplitude limit, switch to the energy consumption branch to isolate the fault. If the limit is not exceeded and the detection value falls back to within the limit, reset. If the detection value is not greater than the first threshold, do not execute the switching action. S4. Repeat the above steps until the fault isolation or reset is completed.

[0007] Preferably, in step S1, the calculation of the current change rate at the current moment using the inductor voltage sampling value is specifically as follows: the collected voltage value across the inductor is divided by the additional inductance value; the calculation of the current change rate based on current sampling using two adjacent current sampling points is specifically as follows: the current difference between two adjacent sampling moments is divided by the sampling time interval; the maximum value of the two is taken as the current change rate detection value at the current moment.

[0008] Preferably, the formula for predicting the instantaneous current value at the next sampling moment using the detected value in step S2 is: the predicted current value equals the current sampled value at the current moment plus the current change rate detected value at the current moment multiplied by the sampling time interval.

[0009] Preferably, strategy one includes the following steps: A1. At the moment when the detected current change rate value is greater than the first threshold, immediately send a conduction command to the transfer branch and at the same time send a turn-off command to the power electronic switch of the main branch to switch the current of the main branch to the transfer branch. A2. After commutation, the instantaneous current value is continuously predicted in real time based on the prediction formula; A3. If the actual current sampling value or the predicted current value is detected to reach or exceed the current amplitude limit at a later time, a disconnection command for the operating mechanism is issued. After the operating mechanism is completely disconnected, a turn-off command is sent to the power electronic switch of the transfer branch to switch the current of the transfer branch to the energy consumption branch. A4. If no actual current or predicted current exceeds the limit, and the current change rate is detected to have returned to the limit at a certain moment, it is judged as a false fault. A conduction command is sent to the main branch power electronic switch, and a turn-off command is sent to the transfer branch power electronic switch to commutate the transfer branch current back to the main branch for reset.

[0010] Preferably, strategy two includes the following steps: B1. At the moment when the detected current change rate value is greater than the second threshold, immediately send a conduction command to the transfer branch and at the same time send a turn-off command to the power electronic switch of the main branch to switch the current of the main branch to the transfer branch. B2. At the same time as or immediately after switching the main branch current to the transfer branch, a disconnection command is immediately issued for the operating mechanism, and the operating mechanism begins to perform the tripping action. B3. During and after the operating mechanism performs the tripping action, the instantaneous current value is continuously predicted in real time based on the prediction formula; B4. If the actual current sampling value or the predicted current value is detected to reach or exceed the current amplitude limit at some later time, the fault is confirmed, and a shutdown command is sent to the power electronic switch of the transfer branch to switch the current of the transfer branch to the energy consumption branch. B5. If no actual current or predicted current exceeds the limit, and the current change rate is found to have returned to the limit at a certain moment, it is judged as a false fault. A closing command for the operating mechanism is issued. After the operating mechanism is fully closed, a conduction command is sent to the main branch power electronic switch, and a turn-off command is sent to the transfer branch power electronic switch to switch the transfer branch current back to the main branch for reset.

[0011] Preferably, a first threshold for the rate of change of current, a second threshold for the rate of change of current, and a limit for the current amplitude are preset, wherein the second threshold is greater than the first threshold; a sampling time interval is set, and the synchronous sampling frequency of current sampling and inductor voltage sampling is determined.

[0012] Preferably, the reset operation is as follows: When a false fault is identified, for Strategy 1, a turn-on command is sent directly to the main branch power electronic switch, and a turn-off command is sent to the transfer branch power electronic switch at the same time. For strategy two, first issue a closing command for the operating mechanism. After the operating mechanism is fully closed, send an on command to the main branch power electronic switch and simultaneously send an off command to the transfer branch power electronic switch.

[0013] Preferably, in Strategy 1, the condition for judging a false fault is: at a certain moment after the commutation, the actual current sample value is less than the current amplitude limit and the predicted current value is also less than the current amplitude limit, while the current change rate detection value has fallen back to no greater than the first threshold.

[0014] Preferably, in Strategy 2, the operation of immediately issuing the operating mechanism disconnection command and the operation of commutating the main branch current to the transfer branch are performed simultaneously, or are performed within a very short time immediately following the completion of the commutation.

[0015] Preferably, if the current change rate detection value at the current moment is not greater than the first threshold, the system continues to operate normally, does not perform any commutation action, and continues sampling and detection in the next sampling cycle.

[0016] Compared with the prior art, the above-mentioned technical solution of the present invention has the following beneficial technical effects: This invention designs a fault prediction and control method for low-damped DC systems based on parallel sampling of inductor voltage. By synchronously acquiring the instantaneous values ​​of inductor voltage and current, the method calculates the current change rate in real time using the inductor voltage and takes the maximum of the current difference, significantly improving the detection accuracy and response speed of the current change rate, providing a reliable basis for subsequent fault prediction. Based on a hierarchical control strategy using predicted current values ​​and preset dual thresholds, the method can identify fault trends in advance before the current exceeds the limit, and distinguish between false and real faults, reducing the system's false tripping rate and minimizing the wear and tear from frequent operation of mechanical operating mechanisms, thus extending equipment lifespan. The method also addresses different severity levels of faults. The current change rate is handled according to strategy one and strategy two respectively. When the change rate is large, the tripping action is performed directly, and when the change rate is small, the tripping action is performed only after the current exceeds the limit. This differentiated treatment ensures rapid isolation of serious faults and provides recovery space for minor disturbances, taking into account both the speed and selectivity of protection. Continuous sampling of inductor voltage enables real-time prediction of future current, allowing control commands to be issued in advance. This significantly compresses the time window from the occurrence of a fault to the actual disconnection, effectively suppressing the continuous rise of short-circuit current, thereby reducing the stringent requirements on the disconnection capacity of DC circuit breakers and improving the overall safety margin and power supply reliability of the system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the topology of a low-damping DC interruption system provided in an embodiment of the present invention; Figure 2 A schematic diagram illustrating the logical judgment and timing relationship between control strategy 1 and strategy 2 provided in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the principle of parallel sampling of inductor voltage and current and calculation of current change rate provided in an embodiment of the present invention; Figure 4 This is a flowchart of the overall control logic provided in an embodiment of the present invention; Figure 5 The schematic diagram of the simulation verification circuit provided for the embodiments of the present invention; Figure 6 The above is a simulation waveform diagram of fault current detection and disconnection using the traditional current sampling method in the comparative example of this invention. Figure 7 Simulation waveform diagram of the fault prediction control method based on parallel sampling of inductor voltage provided in the embodiments of the present invention; Figure 8 Simulation waveforms of the actual current and its rate of change provided for embodiments of the present invention; Figure 9 The above is a comparison diagram of the current change rate calculated using only the sampled current and the simulation waveform of the actual sampled current in the comparative example of this invention. Detailed Implementation

[0018] Example 1: The fault prediction and control method for low-damped DC systems based on parallel sampling of inductor voltage proposed in this invention is applied to, for example... Figure 1 In the DC interruption system shown, the main branch of the DC interruption system is composed of an operating mechanism and a power electronic switch connected in series, which is used to conduct the normal load current of the DC system; the transfer branch is composed of multiple power electronic switches, which is used to carry pseudo faults or fault currents for short time; the energy consumption branch is composed of multiple metal oxide varistors (MOVs), which is used to consume the fault energy of the DC system; an additional inductor L is connected in series in the main circuit of the system to increase the system damping. It should be noted that before the system is put into operation, the inductance value of the additional inductor L should first be determined according to the rated parameters of the DC system. The inductance value is determined by the following formula: ; In the formula, This refers to the DC system voltage. This is the maximum rate of change of current that the DC system can withstand. At the same time, a first threshold for the rate of change of current is preset. Second threshold for rate of change of current And satisfy ; Preset current amplitude limit ; Set the sampling time interval to Determine the synchronous sampling frequency for current sampling and inductor voltage sampling.

[0019] The specific control process of this embodiment includes the following detailed steps: S1. During normal system operation, a fixed sampling period is used. The instantaneous values ​​of the main circuit current and the voltage across the additional inductor L are collected simultaneously. Set at the k-th sampling time The collected current value is The collected voltage across the inductor is The rate of change of current at the current moment is calculated using the sampled inductor voltage value, and the calculation formula is as follows: ; Simultaneously, the rate of change of current based on current sampling is calculated using two adjacent current sampling points, and the calculation formula is as follows: ; Then, compare the rate of change of current obtained at the same time using the two methods described above. and Take the maximum of the two as the current time. The detected value of the rate of change of current, i.e.: ; Combination Figure 2 As shown, simply sampling the current not only fails to accurately predict the rate of change of current, but in some cases, the obtained rate of change of current may even be much smaller than the actual value; for example... Figure 2 The second green sampling point The calculated rate of change of current is significantly smaller than the actual value, in extreme cases... At the sampling point, the rate of change of current is zero; however, if the inductor voltage is sampled at the same time, a more accurate rate of change of current can be obtained. Figure 2 The second orange sampling point The obtained current change rate is too large. Increasing the current before the next sampling point can improve accuracy. Even if the current does not increase, it is acceptable to improve conservatism. Therefore, the method of taking the maximum of the two values ​​in this step can effectively solve the above problem. The maximum current change rate detection value... Used for selecting subsequent control strategies and predicting faults.

[0020] S2. After each current sampling is completed, the current change rate detection value at the current moment is obtained. Then, the instantaneous current value at the next sampling moment is predicted using the calculated rate of change of current. The prediction formula is as follows: ; In the formula, For prediction The current value at time (i.e., the next sampling time); It should be noted that the predicted current value is used to determine in advance whether the current will exceed the limit before the next actual sampling point arrives.

[0021] S3. Calculate the current change rate detection value obtained in step S1 at the current moment. Compared with the preset first threshold of current change rate and the second threshold of the rate of change of current The comparison automatically selects either strategy 1 or strategy 2 to execute. Figure 3As shown: Scenario 1: When detected When the time comes, execute strategy 1; The specific execution process of strategy 1 is as follows: A1, at time The current change rate was detected to be above the limit (i.e., greater than the limit). Immediately send a conduction command to the transfer branch and a turn-off command to the main branch power electronic switch to switch the current from the main branch to the transfer branch, so that the transfer branch can carry current. A2, Time Subsequently, the instantaneous current value is continuously predicted in real time based on the prediction formula in step S2; A3. If at some later time... Actual current sampling value detected Reaching or exceeding the current amplitude limit Or the predicted current value obtained from the prediction formula. Reaching or exceeding That is, the following conditions must be met: or If a real fault occurs, the system is judged to have a fault. At this time, a disconnection command is issued for the operating mechanism, and the operating mechanism begins to perform the tripping action. After the operating mechanism is completely disconnected, a shutdown command is sent to the power electronic switch of the transfer branch, so that the current of the transfer branch is switched to the energy consumption branch, and the system energy is consumed through the MOV, and the fault is finally completely isolated. A4. If at time... No instantaneous current value exceeding the limit was detected (i.e., the following conditions are met simultaneously): and ), and at some point The current change rate has been detected to have returned to within the limit, i.e., the following conditions are met: If the fault is detected, it is determined to be a false fault. At this time, a conduction command is sent to the main branch power electronic switch, and a turn-off command is sent to the transfer branch power electronic switch to switch the current of the transfer branch back to the main branch and reset the system. It should be noted that the above times With time They do not have a fixed order on the timeline; they are judged independently based on their respective real-time detection conditions. Scenario 2: When detected At that time, execute strategy 2; The specific execution process of strategy 2 is as follows: B1, at time The current change rate was detected to be above the limit (i.e., greater than the limit). Immediately send a conduction command to the transfer branch and a turn-off command to the main branch power electronic switch to switch the current from the main branch to the transfer branch, so that the transfer branch can carry current. B2. At the same time as or immediately after switching the main branch current to the transfer branch, a disconnection command is immediately issued for the operating mechanism, and the operating mechanism begins to perform the tripping action. This process does not require waiting for the judgment result of whether the current amplitude exceeds the limit. B3. During and after the operating mechanism performs the tripping action, the instantaneous current value is continuously predicted in real time according to the prediction formula in step S2. B4. If at some subsequent moment... Actual current sampling value detected Reaching or exceeding the current amplitude limit Or the predicted current value obtained from the prediction formula. Reaching or exceeding That is, satisfying: or If a real fault is confirmed, a shutdown command is sent to the power electronic switch of the transfer branch, causing the current of the transfer branch to be switched to the energy consumption branch, and the system energy is consumed through the MOV, ultimately completely isolating the fault. B5. If at time... No instantaneous current value exceeding the limit was detected (i.e., the following conditions are met simultaneously): and ), and at some point The current change rate has been detected to have returned to within the limit, i.e., the following conditions are met: If the fault is detected, it is determined to be a false fault. At this time, a closing command for the operating mechanism is issued. After the operating mechanism is fully closed, a conduction command is sent to the main branch power electronic switch, and a turn-off command is sent to the transfer branch power electronic switch to switch the current of the transfer branch back to the main branch and reset the system. Similarly, the above moments and time They do not have a fixed chronological order on the timeline, and each is judged independently.

[0022] S4. Combining steps S1 to S3, the overall control logic of this embodiment is as follows: Figure 4 As shown, it is executed in the following sequence: With sampling period By synchronously sampling the instantaneous values ​​of the current and the voltage across the inductor, the maximum rate of change of current at the current moment is obtained through calculation and comparison. ; judge Size: like If the current exceeds the current limit, strategy 2 is executed, which involves immediately switching the main branch current to the transfer branch and disconnecting the operating mechanism; When the fault is detected, the current in the transfer branch is switched to the energy consumption branch to isolate the fault. like Execute strategy 1, which involves diverting the main branch current to the transfer branch. When the actual or predicted current value exceeds the current limit... When the fault occurs, a disconnection command is issued for the operating mechanism. After disconnection, the current in the transfer branch is switched to the energy consumption branch to isolate the fault. like If the system operates normally, it will not perform any switching action and will continue sampling and detection in the next cycle. After a fault is identified and isolated, the system completes the protection of the DC line; if it is determined to be a false fault, the system completes the reset according to the corresponding strategy and restores the normal power supply state.

[0023] Example 2, the fault prediction and control method for low-damped DC systems based on parallel sampling of inductor voltage proposed in this invention, also includes a simulation verification example of the method proposed in Example 1, specifically: To verify the effectiveness of the method proposed in Example 1, the following method was used: Figure 5 The simulation circuit shown is used for verification. In the simulation, the sampling rate is set to 1kHz, and the circuit needs to be disconnected when the instantaneous current value reaches 10kA, with the current amplitude as a limit. As the threshold for the initial action in fault diagnosis; The simulation results of the general method (sampling only the instantaneous current value and sending a command after the current exceeds the 5kA limit) are as follows: Figure 6 As shown, Figure 6 In this context, 'i' represents the actual current value in the circuit. This represents the current value obtained through sampling (using the general method); it can be seen that the current amplitude was detected to exceed 5kA at 5.2ms, at which point the DC circuit breaker started to operate and finally disconnected the line at 7.32ms. By this time, the instantaneous current value had already risen above 7kA. like Figure 5 As shown, when using the scheme proposed in this embodiment, the current change rate is detected to be approximately [value missing] at 1.1ms. Then, strategy 2 was executed and the action was started; at 5.1ms, it was predicted that the instantaneous value of the current at the next sampling point would reach the limit of 5kA, and it was determined that the line needed to be cut off. Finally, the line was cut off at 5.11ms, which was 2.21ms earlier than the traditional method, and the cutting current was more than 2kA smaller. The simulation results using the proposed scheme are as follows: Figure 7 As shown, Figure 7 In and The values ​​represent the rate of change of current and the current value obtained using the method proposed in this paper; it can be seen that at 1.1 ms, the method of this invention detects a rate of change of current of approximately [value missing]. At this time, the DC circuit breaker starts to operate (the simulation executes strategy 2 mentioned above); after 5.1ms prediction, the instantaneous current value at the sampling point reaches the limit of 5kA, and it is determined that the line needs to be disconnected. Since the circuit breaker has already performed the corresponding action, the line is finally disconnected at 5.11ms; the general method disconnects the line at 7.32ms, while the method proposed in this invention disconnects the line 2.21ms earlier. The actual current and its rate of change are as follows: Figure 8 As shown, Figure 8 In Let 'i' represent the actual rate of change of current in the circuit and the actual current value. We can see that the actual rate of change of current is approximately 1 ms. ,and Figure 7 The rate of change of current obtained by the method proposed in this invention The current is very close. When the line current value is close to but less than 5kA at 5.11ms, the line is cut off. The previous general method cuts off the line at 7.32ms, by which time the instantaneous current value has already risen above 7kA. The method proposed in this invention cuts off the line 2.21ms earlier, and the cutting current is more than 2kA smaller. Using only the sampled current and the rate of change of current calculated from the sampled current, as follows: Figure 9 As shown, Figure 9 In and This represents the current change rate calculated using only the sampled current, compared to the sampled current value; from Figure 9 As can be seen, at time 1.1 ms, the rate of change of current obtained by this method is... At the next sampling time of 1.2ms, the rate of change of current is The method proposed in this invention (using the same sampling frequency reference) detects the rate of change of current at 1.1ms. Anomalies in the rate of change of current can be detected one sampling period in advance; In summary, the solution proposed in this invention can detect circuit faults in a timely manner, quickly disconnect the line, reduce the development time of fault current, prevent the short-circuit current from continuing to rise, and effectively reduce the system's current interruption capability for DC circuit breakers.

[0024] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A low-damping DC system fault prediction control method based on inductance voltage parallel sampling, characterized in that, The specific implementation steps include the following: S1. Synchronously collect the instantaneous value of the main circuit current and the instantaneous value of the voltage across the additional inductor at a fixed sampling period. Calculate the current change rate at the current moment using the inductor voltage sampling value. At the same time, calculate the current change rate based on the current sampling using two adjacent current sampling points. Take the maximum value of the two as the current change rate detection value at the current moment. S2. After completing each current sampling and obtaining the current change rate detection value at the current moment, the instantaneous current value at the next sampling moment is predicted using the detection value to obtain the predicted current value. S3. Compare the current rate of change detection value with the preset first threshold and second threshold of current rate of change. The second threshold is greater than the first threshold. If the detection value is greater than the first threshold but not greater than the second threshold, execute strategy one: switch to the transfer branch and continuously predict the current. If the actual current or the predicted current reaches the preset current amplitude limit, issue an operating mechanism disconnect command and switch to the energy consumption branch to isolate the fault after disconnection. If the limit is not exceeded and the detection value falls back to within the limit, reset. If the detection value is greater than the second threshold, execute strategy two: switch to the transfer branch and immediately issue an operating mechanism disconnect command, continuously predict the current. If the actual current or the predicted current reaches the current amplitude limit, switch to the energy consumption branch to isolate the fault. If the limit is not exceeded and the detection value falls back to within the limit, reset. If the detection value is not greater than the first threshold, do not execute the switching action. S4. Repeat the above steps until the fault isolation or reset is completed.

2. The fault prediction and control method for a low-damping DC system based on parallel sampling of inductor voltage according to claim 1, characterized in that, In step S1, the current change rate at the current moment is calculated using the inductor voltage sampling value as follows: the voltage value across the inductor is divided by the additional inductance value; the current change rate based on current sampling is calculated using two adjacent current sampling points as follows: the current difference between two adjacent sampling moments is divided by the sampling time interval; the maximum value of the two is taken as the current change rate detection value at the current moment.

3. The fault prediction and control method for a low-damping DC system based on parallel sampling of inductor voltage according to claim 1, characterized in that, In step S2, the formula for predicting the instantaneous current value at the next sampling moment using the detected value is: the predicted current value equals the current sampled value at the current moment plus the current change rate detected value at the current moment multiplied by the sampling time interval.

4. The fault prediction and control method for a low-damping DC system based on parallel sampling of inductor voltage as described in claim 1, characterized in that, Strategy 1 includes the following steps: A1. At the moment when the detected current change rate value is greater than the first threshold, immediately send a conduction command to the transfer branch and at the same time send a turn-off command to the power electronic switch of the main branch to switch the current of the main branch to the transfer branch. A2. After commutation, the instantaneous current value is continuously predicted in real time based on the prediction formula; A3. If the actual current sampling value or the predicted current value is detected to reach or exceed the current amplitude limit at a later time, a disconnection command for the operating mechanism is issued. After the operating mechanism is completely disconnected, a turn-off command is sent to the power electronic switch of the transfer branch to switch the current of the transfer branch to the energy consumption branch. A4. If no actual current or predicted current exceeds the limit, and the current change rate is detected to have returned to the limit at a certain moment, it is judged as a false fault. A conduction command is sent to the main branch power electronic switch, and a turn-off command is sent to the transfer branch power electronic switch to commutate the transfer branch current back to the main branch for reset.

5. The fault prediction and control method for a low-damping DC system based on parallel sampling of inductor voltage according to claim 1, characterized in that, Strategy Two includes the following steps: B1. At the moment when the detected current change rate value is greater than the second threshold, immediately send a conduction command to the transfer branch and at the same time send a turn-off command to the power electronic switch of the main branch to switch the current of the main branch to the transfer branch. B2. At the same time as or immediately after switching the main branch current to the transfer branch, a disconnection command is immediately issued for the operating mechanism, and the operating mechanism begins to perform the tripping action. B3. During and after the operating mechanism performs the tripping action, the instantaneous current value is continuously predicted in real time based on the prediction formula; B4. If the actual current sampling value or the predicted current value is detected to reach or exceed the current amplitude limit at some later time, the fault is confirmed, and a shutdown command is sent to the power electronic switch of the transfer branch to switch the current of the transfer branch to the energy consumption branch. B5. If no actual current or predicted current exceeds the limit, and the current change rate is found to have returned to the limit at a certain moment, it is judged as a false fault. A closing command for the operating mechanism is issued. After the operating mechanism is fully closed, a conduction command is sent to the main branch power electronic switch, and a turn-off command is sent to the transfer branch power electronic switch to switch the transfer branch current back to the main branch for reset.

6. The fault prediction and control method for a low-damping DC system based on parallel sampling of inductor voltage according to claim 1, characterized in that, A first threshold for the rate of change of current, a second threshold for the rate of change of current, and a limit for the current amplitude are preset, wherein the second threshold is greater than the first threshold; a sampling time interval is set, and the synchronous sampling frequency of current sampling and inductor voltage sampling is determined.

7. A fault prediction and control method for a low-damping DC system based on parallel sampling of inductor voltage as described in claim 4 or 5, characterized in that, The reset operation is as follows: When a false fault is identified, for strategy one, a turn-on command is sent directly to the main branch power electronic switch, and a turn-off command is sent to the transfer branch power electronic switch at the same time. For strategy two, first issue a closing command for the operating mechanism. After the operating mechanism is fully closed, send an on command to the main branch power electronic switch and simultaneously send an off command to the transfer branch power electronic switch.

8. The fault prediction and control method for a low-damping DC system based on parallel sampling of inductor voltage according to claim 4, characterized in that, In Strategy 1, the condition for judging a false fault is: at a certain moment after the commutation, the actual current sample value is less than the current amplitude limit and the predicted current value is also less than the current amplitude limit, while the current change rate detection value has fallen back to no greater than the first threshold.

9. The fault prediction and control method for a low-damping DC system based on parallel sampling of inductor voltage according to claim 5, characterized in that, In Strategy 2, the operation of immediately issuing the operating mechanism disconnection command and the operation of commutating the main branch current to the transfer branch are performed simultaneously, or are executed within a very short time immediately after the commutation is completed.

10. The fault prediction and control method for a low-damping DC system based on parallel sampling of inductor voltage according to claim 1, characterized in that, If the current change rate detection value at the current moment is not greater than the first threshold, the system continues to operate normally, does not perform any commutation action, and continues sampling and detection in the next sampling cycle.

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