Fault protection systems, methods and devices applicable to bipolar DC distribution networks

Abstract

This invention discloses a fault protection system, method, and apparatus suitable for bipolar DC distribution networks. The system includes a bipolar DC distribution network, a control module, and two circuit breakers. The first circuit breaker is installed on the connection line between the primary side of the bipolar DC distribution network and the input terminal of the sending-end converter. The second circuit breaker is installed on the connection line between the primary side of the bipolar DC distribution network and the output terminal of the sending-end converter. The control module is connected to both circuit breakers and to the primary side of the bipolar DC distribution network and the output terminal of the sending-end converter. This invention can determine the fault type by detecting the change in the amplitude of the AC line current on the sending-end converter and the magnitude of the positive and negative sequence components of the current. By installing an AC circuit breaker on the AC side of the sending-end converter, system fault isolation and fault protection are achieved in the event of a grid-side fault.

Description

Technical Field

[0001] This invention relates to the technical field of power grid fault protection, and in particular to a fault protection system, method and apparatus suitable for bipolar DC distribution networks. Background Technology

[0002] As power transmission equipment in remote rural areas ages, voltage at the transmission ends becomes severely insufficient, leading to a growing problem of low voltage qualification rates in these areas. To address this issue, a common approach is to use DC power distribution to appropriately increase the transmission and distribution voltage, thereby extending the power supply radius.

[0003] One commonly used type of power distribution equipment is the bipolar DC power distribution system, which incorporates power electronic converters to achieve low-voltage DC power distribution. Because bipolar DC power distribution systems are expensive, if a fault occurs during use, the entire system will stop operating, and technicians will conduct on-site inspections to determine the cause of the fault and perform appropriate repairs.

[0004] However, the above-mentioned fault protection methods have the following technical problems: the whole machine stops running, which will cause insufficient power supply to the terminal, making it difficult to meet the user's needs. Moreover, manual verification of the fault cause and maintenance protection are inefficient and costly. Summary of the Invention

[0005] This invention proposes a fault protection system, method, and device suitable for bipolar DC distribution networks. The system is equipped with a control module and a circuit breaker in the distribution network. The control module detects the change in the amplitude of the AC line current on the sending-end converter and the magnitude of the positive and negative sequence components of the current to determine the fault type and controls the circuit breaker to disconnect the system fault, thereby realizing fault protection of the power grid.

[0006] A first aspect of the present invention provides a fault protection system suitable for a bipolar DC distribution network, the system comprising: a bipolar DC distribution network, a control module, and two circuit breakers;

[0007] The first circuit breaker is installed on the connection line between the primary side of the bipolar DC distribution network and the input end of the sending-end converter, and the second circuit breaker is installed on the connection line between the primary side of the bipolar DC distribution network and the output end of the sending-end converter. The control module is connected to the two circuit breakers and to the primary side of the bipolar DC distribution network and the output end of the sending-end converter, respectively.

[0008] The control module is used to detect the current change amplitude and positive and negative sequence components of the AC side line of the sending-end converter of the bipolar DC distribution network, and to determine whether a line fault has occurred based on the current change amplitude and the positive and negative sequence components of the current. If a fault occurs, the control module will start the circuit breaker.

[0009] In one possible implementation of the first aspect, the control module includes: a current inner loop unit, a synchronous phase-locked loop (PLL) unit, a pulse modulation (PWM) unit, and two proportional-integral (PI) regulator units;

[0010] The output terminal of the first PI unit is connected to the input terminal of the current inner loop unit. The output terminal of the PLL unit is connected to the connection terminal of the first PI unit and the current inner loop unit. The input terminal of the PLL unit is connected to the current inner loop unit. The output terminals of the second PI unit, the current inner loop unit, and the PLL unit are connected together. The line signals at the connection terminals are summed and then connected to the input terminal of the PWM unit.

[0011] In one possible implementation of the first aspect, the current inner loop unit includes: a proportional regulator unit and a current inner loop signal intersection point, wherein the current inner loop signal intersection point is connected to the output terminal of the first PI unit and the input terminal of the PLL unit, respectively, and the output terminal of the current inner loop signal intersection point is connected to the input terminal of the proportional regulator unit.

[0012] A second aspect of this invention provides a fault protection method suitable for bipolar DC distribution networks, the method being applicable to the fault protection system for bipolar DC distribution networks described above. The method includes:

[0013] Collect the current amplitude on the AC side of the sending-end converter of the DC distribution network;

[0014] When the current amplitude is greater than the preset value, the three-phase voltage value of the sending-end converter on the AC side is collected;

[0015] Based on the three-phase voltage values, it is determined whether a line fault has occurred, and if a line fault is determined to have occurred, the circuit breaker is triggered to start.

[0016] In one possible implementation of the second aspect, the line fault includes a three-phase short-circuit fault;

[0017] The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes:

[0018] If the three-phase voltage values ​​suddenly drop to zero, then the line fault is determined to be a three-phase short-circuit fault.

[0019] In one possible implementation of the second aspect, the line fault includes a two-phase short-circuit fault;

[0020] The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes:

[0021] If the voltage value of one phase of the three-phase voltage drops suddenly while the voltage values ​​of the remaining two phases are normal, then the line fault is determined to be a two-phase short circuit fault.

[0022] In one possible implementation of the second aspect, the line fault includes a single-phase short-circuit fault;

[0023] The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes:

[0024] If two of the three-phase voltage values ​​are equal and the voltage amplitude is half of the rated voltage, and the voltage value of the remaining phase is normal, then the line fault is determined to be a single-phase short-circuit fault.

[0025] In one possible implementation of the second aspect, the acquisition of the current amplitude on the AC side of the sending-end converter of the DC distribution network includes:

[0026] Collect the three-phase current values ​​on the AC side of the sending-end converter of the DC distribution network;

[0027] The three-phase current values ​​are transformed using coordinates to obtain two-phase current values.

[0028] The current amplitude is calculated based on the two-phase current values.

[0029] In one possible implementation of the second aspect, the coordinate transformation of the three-phase current values ​​to obtain two-phase current values ​​includes:

[0030] A three-phase stationary coordinate system is used to obtain the three-phase current values. This three-phase stationary coordinate system is then transformed into a two-phase stationary coordinate system, as shown in the following transformation formula:

[0031]

[0032] In the above formula, α represents the value of the α axis in the two-phase stationary coordinate system, β represents the value of the β axis in the two-phase stationary coordinate system, and a, b, and c represent the three phases in the three-phase stationary coordinate system, respectively.

[0033] A third aspect of the present invention provides a fault protection device suitable for bipolar DC distribution networks, the device being applicable to the fault protection system for bipolar DC distribution networks as described above, the device comprising:

[0034] The current acquisition module is used to acquire the current amplitude on the AC side of the sending-end converter of the DC distribution network;

[0035] The voltage acquisition module is used to acquire the three-phase voltage value of the sending-end converter on the AC side when the current amplitude is greater than the preset value;

[0036] The fault protection module is used to determine whether a line fault has occurred based on the three-phase voltage values, and to trigger the circuit breaker to start when a line fault is determined to have occurred.

[0037] Compared with the prior art, the fault protection system, method and device for bipolar DC distribution networks provided by the embodiments of the present invention have the following advantages: The present invention can determine the fault type (three-phase short circuit, two-phase short circuit, single-phase grounding) by detecting the change in the amplitude of the AC line current on the sending-end converter and the magnitude of the positive and negative sequence components of the current, and can realize the system fault isolation when the grid side fault occurs by adding an AC circuit breaker on the AC side of the sending-end converter, and realize the fault protection of the sending-end converter by blocking the switching tube of the sending-end converter. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a fault protection system suitable for bipolar DC distribution networks provided in an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of a fault protection system suitable for bipolar DC distribution networks provided in an embodiment of the present invention;

[0040] Figure 3 This is a flowchart illustrating a fault protection method applicable to a bipolar DC distribution network according to an embodiment of the present invention.

[0041] Figure 4 This is an operation flowchart of a three-phase short-circuit detection process provided in an embodiment of the present invention;

[0042] Figure 5 This is a waveform diagram of the three-phase short-circuit AC side voltage and current provided in an embodiment of the present invention;

[0043] Figure 6 This is an operation flowchart of a two-phase short-circuit detection process provided in an embodiment of the present invention;

[0044] Figure 7 This is a waveform diagram of the two-phase short-circuit AC side voltage and current provided in an embodiment of the present invention;

[0045] Figure 8 This is an operation flowchart of a single-phase short-circuit detection process provided in an embodiment of the present invention;

[0046] Figure 9 This is a waveform diagram of the single-phase short-circuit AC side voltage and current provided in an embodiment of the present invention;

[0047] Figure 10 This is a voltage and current waveform diagram after a three-phase short-circuit and locked converter provided in an embodiment of the present invention;

[0048] Figure 11This is a voltage and current waveform diagram after a two-phase short-circuit and locked converter provided in an embodiment of the present invention;

[0049] Figure 12 This is a voltage and current waveform diagram after a single-phase short-circuit and locked converter provided in an embodiment of the present invention;

[0050] Figure 13 This is a schematic diagram of the structure of a fault protection device suitable for bipolar DC distribution networks provided in an embodiment of the present invention. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] One commonly used type of power distribution equipment is the bipolar DC power distribution system, which incorporates power electronic converters to achieve low-voltage DC power distribution. Because bipolar DC power distribution systems are expensive, if a fault occurs during use, the entire system will stop operating, and technicians will conduct on-site inspections to determine the cause of the fault and perform appropriate repairs.

[0053] However, the above-mentioned fault protection methods have the following technical problems: the whole machine stops running, which will cause insufficient power supply to the terminal, making it difficult to meet the user's needs. Moreover, manual verification of the fault cause and maintenance protection are inefficient and costly.

[0054] To address the aforementioned issues, the following detailed embodiments will be used to illustrate a fault protection system suitable for bipolar DC distribution networks provided in this application.

[0055] Reference Figure 1-2 The diagrams show a structural schematic of a fault protection system for a bipolar DC distribution network according to an embodiment of the present invention and a structural schematic of a fault protection system for a bipolar DC distribution network according to an embodiment of the present invention.

[0056] As an example, the fault protection system applicable to bipolar DC distribution networks may include:

[0057] Bipolar DC distribution network, control module and two circuit breakers;

[0058] The first circuit breaker is installed on the connection line between the primary side of the bipolar DC distribution network and the input end of the sending-end converter, and the second circuit breaker is installed on the connection line between the primary side of the bipolar DC distribution network and the output end of the sending-end converter. The control module is connected to the two circuit breakers and to the primary side of the bipolar DC distribution network and the output end of the sending-end converter, respectively.

[0059] The control module is used to detect the current change amplitude and positive and negative sequence components of the AC side line of the sending-end converter of the bipolar DC distribution network, and to determine whether a line fault has occurred based on the current change amplitude and the positive and negative sequence components of the current. If a fault occurs, the control module will start the circuit breaker.

[0060] Reference Figure 1-2 In one embodiment, the control module includes: a current inner loop unit, a synchronous phase-locked loop (PLL) unit, a pulse modulation (PWM) unit, and two proportional-integral (PI) regulator units;

[0061] The output terminal of the first PI unit is connected to the input terminal of the current inner loop unit. The output terminal of the PLL unit is connected to the connection terminal of the first PI unit and the current inner loop unit. The input terminal of the PLL unit is connected to the current inner loop unit. The output terminals of the second PI unit, the current inner loop unit, and the PLL unit are connected together. The line signals at the connection terminals are summed and then connected to the input terminal of the PWM unit.

[0062] Specifically, the current inner loop unit includes: a proportional regulator unit (P) and a current inner loop signal intersection point. The current inner loop signal intersection point is connected to the output terminal of the first PI unit and the input terminal of the PLL unit, respectively. The output terminal of the current inner loop signal intersection point is connected to the input terminal of the proportional regulator unit (P).

[0063] In this embodiment, the present invention provides a fault protection system suitable for bipolar DC distribution networks. Its advantages are as follows: the present invention can monitor the current parameters of the sending-end converter of the bipolar DC distribution network in real time through the control module, and determine whether the distribution network has a fault and its fault type based on the current parameters. When a fault is determined, the circuit breaker can be immediately controlled to disconnect the circuit, thereby protecting the distribution network. On the one hand, there is no need for manual inspection of the fault type, which improves the accuracy of detection. On the other hand, the distribution network can be protected quickly, improving protection efficiency and avoiding equipment damage.

[0064] Reference Figure 3 The diagram shows a flowchart of a fault protection method for bipolar DC distribution networks according to an embodiment of the present invention.

[0065] In one embodiment, the method is applicable to the fault protection system for bipolar DC distribution networks described in the above embodiments.

[0066] As an example, the fault protection method applicable to bipolar DC distribution networks may include:

[0067] S11. Collect the current amplitude of the sending-end converter on the AC side of the DC distribution network.

[0068] Reference Figure 1 The current amplitude of the sending-end converter on the AC side can be collected through the control module.

[0069] To accurately calculate the current amplitude of the sending-end converter on the AC side, step S11, as an example, may include the following sub-steps:

[0070] S111. Collect the three-phase current values ​​on the AC side of the sending-end converter of the DC distribution network.

[0071] S112. Perform coordinate transformation on the three-phase current values ​​to obtain two-phase current values;

[0072] Specifically, the two-phase current values ​​are calculated as follows:

[0073] A three-phase stationary coordinate system is used to obtain the three-phase current values. This three-phase stationary coordinate system is then transformed into a two-phase stationary coordinate system, as shown in the following transformation formula:

[0074]

[0075] In the above formula, α represents the value of the α axis in the two-phase stationary coordinate system, β represents the value of the β axis in the two-phase stationary coordinate system, and a, b, and c represent the three phases in the three-phase stationary coordinate system, respectively.

[0076] S113. Calculate the current amplitude based on the two-phase current values.

[0077] Specifically, the current amplitude can be obtained by adding the square of α and the square of β, and then taking the square root of the sum.

[0078] S12. When the current amplitude is greater than the preset value, the three-phase voltage value of the sending-end converter on the AC side is collected.

[0079] The current amplitude is compared with the preset value. If the current amplitude is less than or equal to the preset value, the distribution network is considered to be normal. If the current amplitude is greater than the preset value, the distribution network may be faulty. The three-phase voltage values ​​of the sending-end converter on the AC side can be collected.

[0080] S13. Determine whether a line fault has occurred based on the three-phase voltage values, and trigger the circuit breaker to start when a line fault is determined to have occurred.

[0081] In one embodiment, the presence or absence of a line fault can be determined based on the three-phase voltage values, and the type of line fault in the distribution network can be determined based on the magnitude of the three-phase voltage values. When a fault occurs, the circuit breaker can be immediately tripped to disconnect the line, preventing damage to the distribution network. Simultaneously, based on the type of line fault, technicians can be notified to carry out appropriate repairs.

[0082] Reference Figure 4-5 The diagrams show the operation flowchart of the three-phase short-circuit detection process provided in one embodiment of the present invention and the voltage and current waveform diagram of the three-phase short-circuit AC side provided in one embodiment of the present invention.

[0083] In one embodiment, the line fault includes a three-phase short-circuit fault;

[0084] The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes:

[0085] If the three-phase voltage values ​​suddenly drop to zero, then the line fault is determined to be a three-phase short-circuit fault.

[0086] Specifically, the three-phase current values ​​of the sending-end converter of the DC distribution network on the AC side can be collected in real time, the three-phase current values ​​can be converted into two-phase current values, the current amplitude can be calculated using the two-phase current values, and when the current amplitude is greater than the preset value, the three-phase voltage values ​​can be collected. When the three-phase voltage values ​​suddenly drop to zero, the line fault is determined to be a three-phase short circuit fault.

[0087] Reference Figure 5 It can be seen that, in the case of a three-phase short circuit on the grid side, Figure 5 The simulation waveforms of voltage and current on the primary side of the transformer and the AC side of the sending-end converter are shown. The simulation shows a three-phase short circuit occurring on the primary side of the transformer at 1 second. The primary voltage of the transformer will immediately drop to zero. At this time, the AC current on the sending-end converter begins to rise, but its maximum current is limited due to the current inner loop of the control system. Simultaneously, the AC current on the sending-end converter will generate a current with a reduced transformation ratio on the primary side of the transformer.

[0088] Reference Figure 6-7 The diagrams show the operation flowchart of the two-phase short-circuit detection process provided in one embodiment of the present invention and the voltage and current waveform diagram of the two-phase short-circuit AC side provided in one embodiment of the present invention.

[0089] In one embodiment, the line fault includes a two-phase short-circuit fault;

[0090] The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes:

[0091] If the voltage value of one phase of the three-phase voltage drops suddenly while the voltage values ​​of the remaining two phases are normal, then the line fault is determined to be a two-phase short circuit fault.

[0092] Specifically, the three-phase current values ​​of the sending-end converter of the DC distribution network on the AC side can be collected in real time, the three-phase current values ​​can be converted into two-phase current values, and the current amplitude can be calculated using the two-phase current values. When the current amplitude is greater than the preset value, the three-phase voltage values ​​can be collected. When the voltage value of one phase of the three-phase voltage drops sharply and the voltage values ​​of the remaining two phases are normal, the line fault is determined to be a two-phase short circuit fault.

[0093] Reference Figure 6 It can be seen that when a two-phase short circuit occurs on the grid side, the secondary side of the transformer is equivalent to a single-phase short circuit. This AC voltage can be decomposed into positive-sequence and negative-sequence components. For the DC side voltage of the sending-end converter, since the AC side voltage contains a negative-sequence component, its current will also contain a negative-sequence component, so the capacitor voltage will fluctuate at the second harmonic of the fundamental frequency.

[0094] Under a two-phase short circuit, the AC output voltage of the sending-end converter is a positive-sequence voltage when the DC-side voltage is stable, while the transformer secondary voltage contains a negative-sequence component. Therefore, an overcurrent will be generated in the negative-sequence network. However, this overcurrent is actually much smaller than that under a three-phase short circuit. This is because, on the one hand, the DC-side voltage fluctuation of the converter causes the converter output AC voltage to also contain a negative-sequence component, and on the other hand, the amplitude of the negative-sequence component in the transformer secondary voltage is smaller.

[0095] Figure 6 To simulate the voltage and current waveforms on the grid side under a two-phase short circuit, it can be seen from the figure that a two-phase short circuit occurs at 1 second. After that, the voltages on the primary and secondary sides of the transformer will change as previously analyzed and calculated, and at the same time, a three-phase unbalanced current will be generated.

[0096] In actual operation, when a two-phase short circuit occurs on the primary side of the transformer, an increase in current will occur on the AC side of the sending-end converter, and a large amount of unbalanced current will be transmitted to the power grid. If the current-carrying capacity of the line can meet this current, it is not enough to cause danger. When the line cannot carry the current, the AC circuit breaker will be opened to isolate the fault.

[0097] Reference Figure 8-9 The diagrams show the operation flowchart of the single-phase short-circuit detection process provided in one embodiment of the present invention and the voltage and current waveform diagram of the AC side of the single-phase short circuit provided in one embodiment of the present invention.

[0098] In one embodiment, the line fault includes a single-phase short-circuit fault;

[0099] The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes:

[0100] If two of the three-phase voltage values ​​are equal and the voltage amplitude is half of the rated voltage, and the voltage value of the remaining phase is normal, then the line fault is determined to be a single-phase short-circuit fault.

[0101] Specifically, the three-phase current values ​​of the sending-end converter of the DC distribution network on the AC side can be collected in real time, the three-phase current values ​​can be converted into two-phase current values, and the current amplitude can be calculated using the two-phase current values. When the current amplitude is greater than the preset value, the three-phase voltage values ​​can be collected. When two of the three-phase voltage values ​​are equal and the voltage amplitude is half of the rated voltage, and the voltage value of the remaining phase is normal, the line fault is determined to be a single-phase short-circuit fault.

[0102] Reference Figure 9 It can be seen that since the neutral point is grounded in bipolar DC power distribution, no overvoltage will occur when a single-phase short circuit occurs on the grid side. The fault voltage is equivalent to a single-phase open circuit, but a single-phase overcurrent will be generated.

[0103] In bipolar DC power distribution, when a single-phase short circuit occurs on the grid side, the voltage on the primary side of the transformer will become:

[0104]

[0105] Therefore, assuming the transformer turns ratio is k, the voltage on the secondary side of the transformer can be obtained as follows:

[0106]

[0107] Therefore, at this point, the secondary side of the transformer is equivalent to introducing a large number of zero-sequence and negative-sequence components. Simulations of this situation yield the following results: Figure 9 These represent the voltage and current on the primary side of the transformer and the AC side of the sending-end converter after a single-phase ground fault on the grid side.

[0108] When a single-phase ground fault occurs on the grid side, the DC side voltage will not decrease, and the line can still transmit power, maintaining normal load voltage. However, due to the second-harmonic fluctuations in voltage and current on the line, line losses will increase. This type of fault is identified by detecting fluctuations in current and voltage on the line, and the entire system is isolated from the fault point using a circuit breaker.

[0109] Specifically, once a line fault is detected, the circuit breaker can be immediately triggered to disconnect the connection line of the distribution network, thereby preventing the sending-end converter from transmitting power to the short-circuit point and locking the converter to ensure the safety of the power grid.

[0110] Reference Figure 10-12The following diagrams respectively illustrate the voltage and current waveforms after a three-phase short-circuit and locked converter provided in one embodiment of the present invention, the voltage and current waveforms after a two-phase short-circuit and locked converter provided in one embodiment of the present invention, and the voltage and current waveforms after a single-phase short-circuit and locked converter provided in one embodiment of the present invention.

[0111] After the circuit breaker was activated, a grid-side fault occurred in the bipolar low-voltage DC distribution system. The fault was isolated by adding circuit breakers to the lines. The protection structure diagram of the entire system is shown below. Figure 10-12 As shown in the diagram, the six circuit breakers can be used for fault isolation and AC / DC switching. When a fault is detected on the grid side, circuit breaker S1 is disconnected to protect the converter, and S2 is disconnected to prevent overcurrent from flowing into the line. At this time, the entire distribution network is disconnected from the main grid and loses its energy source.

[0112] In this embodiment, the present invention provides a fault protection method applicable to bipolar DC distribution networks. Its beneficial effects are as follows: the present invention can determine the fault type (three-phase short circuit, two-phase short circuit, single-phase grounding) by detecting the change in the amplitude of the AC line current on the sending-end converter and the magnitude of the positive and negative sequence components of the current. Furthermore, by installing an AC circuit breaker on the AC side of the sending-end converter, the system fault is cleared when the grid side is faulty. Moreover, by blocking the switching tubes of the sending-end converter, the fault protection of the sending-end converter is achieved.

[0113] This invention also provides a fault protection device suitable for bipolar DC distribution networks, see [link to relevant documentation]. Figure 13 The diagram shows a structural schematic of a fault protection device suitable for bipolar DC distribution networks according to an embodiment of the present invention.

[0114] The device is suitable for fault protection systems applicable to bipolar DC distribution networks as described in the above embodiments.

[0115] As an example, the fault protection device suitable for bipolar DC distribution networks may include:

[0116] The current acquisition module 301 is used to acquire the current amplitude of the sending-end converter on the AC side of the DC distribution network.

[0117] The voltage acquisition module 302 is used to acquire the three-phase voltage value of the sending-end converter on the AC side when the current amplitude is greater than the preset value.

[0118] The fault protection module 303 is used to determine whether a line fault has occurred based on the three-phase voltage values, and to trigger the circuit breaker to start when a line fault is determined to have occurred.

[0119] Optionally, the line fault includes a three-phase short-circuit fault;

[0120] The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes:

[0121] If the three-phase voltage values ​​suddenly drop to zero, then the line fault is determined to be a three-phase short-circuit fault.

[0122] Optionally, the line fault includes a two-phase short-circuit fault;

[0123] The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes:

[0124] If the voltage value of one phase of the three-phase voltage drops suddenly while the voltage values ​​of the remaining two phases are normal, then the line fault is determined to be a two-phase short circuit fault.

[0125] Optionally, the line fault includes a single-phase short-circuit fault;

[0126] The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes:

[0127] If two of the three-phase voltage values ​​are equal and the voltage amplitude is half of the rated voltage, and the voltage value of the remaining phase is normal, then the line fault is determined to be a single-phase short-circuit fault.

[0128] Optionally, the current acquisition module is further used for:

[0129] Collect the three-phase current values ​​on the AC side of the sending-end converter of the DC distribution network;

[0130] The three-phase current values ​​are transformed using coordinates to obtain two-phase current values.

[0131] The current amplitude is calculated based on the two-phase current values.

[0132] Optionally, the current acquisition module is further used for:

[0133] A three-phase stationary coordinate system is used to obtain the three-phase current values. This three-phase stationary coordinate system is then transformed into a two-phase stationary coordinate system, as shown in the following transformation formula:

[0134]

[0135] In the above formula, α represents the value of the α axis in the two-phase stationary coordinate system, β represents the value of the β axis in the two-phase stationary coordinate system, and a, b, and c represent the three phases in the three-phase stationary coordinate system, respectively.

[0136] Those skilled in the art will understand that, for ease of description and brevity, the specific working process of the device described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0137] Furthermore, this application also provides an electronic device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the fault protection method for bipolar DC distribution networks as described in the above embodiments.

[0138] Furthermore, embodiments of this application also provide a computer-readable storage medium storing computer-executable instructions for causing a computer to execute the fault protection method for bipolar DC distribution networks as described in the above embodiments.

[0139] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A fault protection system suitable for bipolar DC distribution networks, characterized in that, The system includes: a bipolar DC distribution network, a control module, and two circuit breakers; The first circuit breaker is installed on the connection line between the primary side of the bipolar DC distribution network and the input end of the sending-end converter, and the second circuit breaker is installed on the connection line between the primary side of the bipolar DC distribution network and the output end of the sending-end converter. The control module is connected to the two circuit breakers and to the primary side of the bipolar DC distribution network and the output end of the sending-end converter, respectively. The control module is used to detect the current change amplitude and positive and negative sequence components of the current on the AC side of the sending-end converter of the bipolar DC distribution network, and to determine whether a line fault has occurred based on the current change amplitude and the positive and negative sequence components of the current. If a fault occurs, the control module will start the circuit breaker. The control module includes: a current inner loop unit, a synchronous phase-locked loop unit, a pulse modulation unit, and two proportional-integral regulator units; The output of the first proportional-integral regulator unit is connected to the input of the current inner loop unit. The output of the synchronous phase-locked unit is connected to the connection point of the first proportional-integral regulator unit and the current inner loop unit. The input of the synchronous phase-locked unit is connected to the current inner loop unit. The outputs of the second proportional-integral regulator unit, the current inner loop unit, and the synchronous phase-locked unit are connected together. The line signals at the connection points are summed and then connected to the input of the pulse modulation unit. The current inner loop unit includes: a proportional regulator unit and a current inner loop signal intersection point. The current inner loop signal intersection point is connected to the output terminal of the first proportional-integral regulator unit and the input terminal of the synchronous phase-locked unit, respectively. The output terminal of the current inner loop signal intersection point is connected to the input terminal of the proportional regulator unit.

2. A fault protection method applicable to bipolar DC distribution networks, characterized in that, The method is applicable to the fault protection system for bipolar DC distribution networks as described in claim 1, and the method includes: Collect the current amplitude on the AC side of the sending-end converter of the DC distribution network; When the current amplitude is greater than the preset value, the three-phase voltage value of the sending-end converter on the AC side is collected; Based on the three-phase voltage values, it is determined whether a line fault has occurred, and if a line fault is determined to have occurred, the circuit breaker is triggered to start.

3. The fault protection method for bipolar DC distribution networks according to claim 2, characterized in that, The line faults include three-phase short-circuit faults; The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes: If the three-phase voltage values ​​suddenly drop to zero, then the line fault is determined to be a three-phase short-circuit fault.

4. The fault protection method for bipolar DC distribution networks according to claim 2, characterized in that, The line faults include two-phase short-circuit faults; The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes: If the voltage value of one phase of the three-phase voltage drops suddenly while the voltage values ​​of the remaining two phases are normal, then the line fault is determined to be a two-phase short circuit fault.

5. The fault protection method for bipolar DC distribution networks according to claim 2, characterized in that, The line faults include single-phase short-circuit faults; The determination of whether a line fault has occurred based on the three-phase voltage values ​​includes: If two of the three-phase voltage values ​​are equal and the voltage amplitude is half of the rated voltage, and the voltage value of the remaining phase is normal, then the line fault is determined to be a single-phase short-circuit fault.

6. The fault protection method for bipolar DC distribution networks according to any one of claims 3-5, characterized in that, The acquisition of the current amplitude on the AC side of the sending-end converter of the DC distribution network includes: Collect the three-phase current values ​​on the AC side of the sending-end converter of the DC distribution network; The three-phase current values ​​are transformed using coordinates to obtain two-phase current values. The current amplitude is calculated based on the two-phase current values.

7. The fault protection method for bipolar DC distribution networks according to claim 6, characterized in that, The coordinate transformation of the three-phase current values ​​to obtain two-phase current values ​​includes: A three-phase stationary coordinate system is used to obtain the three-phase current values. This three-phase stationary coordinate system is then transformed into a two-phase stationary coordinate system, as shown in the following transformation formula: In the above formula, α represents the value of the α axis in the two-phase stationary coordinate system, β represents the value of the β axis in the two-phase stationary coordinate system, and a, b, and c represent the three phases in the three-phase stationary coordinate system, respectively.

8. A fault protection device suitable for bipolar DC distribution networks, characterized in that, The device is applicable to the fault protection system for bipolar DC distribution networks as described in claim 1, and the device comprises: The current acquisition module is used to acquire the current amplitude on the AC side of the sending-end converter of the DC distribution network; The voltage acquisition module is used to acquire the three-phase voltage value of the sending-end converter on the AC side when the current amplitude is greater than the preset value; The fault protection module is used to determine whether a line fault has occurred based on the three-phase voltage values, and to trigger the circuit breaker to start when a line fault is determined to have occurred.

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