Fault current clearing circuit, method and control device based on DC transformer

Abstract

The present application relates to a fault current clearing circuit based on a DC transformer, comprising N cascaded sub-clearing circuit modules, any of which comprises a DAB DC transformer and a half-bridge circuit, wherein the DAB DC transformer is used to convert a medium-voltage DC signal into a low-voltage DC signal to provide electrical energy for a low-voltage DC distribution network; the half-bridge circuit is connected in parallel with the DAB DC transformer, and is used to act according to a control signal to cut off the fault circuit between the medium-voltage DC distribution network and the DAB DC transformer, thereby clearing the fault current. In the above-mentioned fault current clearing circuit, when a transient short circuit fault occurs in the medium-voltage DC distribution network, by controlling the on and off of the half-bridge circuit arm switch, the medium-voltage DC capacitor in the DAB DC transformer can be isolated from the fault point, thereby cutting off the fault current, while preventing a power outage on the low-voltage side.

Description

Technical Field

[0001] The present application relates to the technical field of direct current power transmission and distribution, and in particular to a fault current clearing circuit, method and control device based on a direct current transformer. Background Art

[0002] With the increasing number of power electronic equipment in medium voltage AC distribution network and the extension of DC technology from transmission level to distribution level, medium voltage DC distribution network has gradually attracted people's attention. In medium voltage DC distribution network, DC transformer is the key conversion equipment to complete power transmission and voltage conversion.

[0003] At present, using the series and parallel combination of DC / DC conversion sub-modules to construct a reasonable medium-voltage DC transformer is one of the hot spots in the development of DC transformer topology. For example, existing literature has conducted a detailed analysis of the control and operating performance of the DC transformer based on dual-active-bridge (DAB) input series-output parallel. When a transient short-circuit fault occurs in the medium-voltage DC bus, all sub-DAB DC transformer modules need to be powered off to clear the fault current, which prolongs the power outage time and reduces the power quality. How to clear the fault current has become the key to the further development of the DAB DC transformer and the entire DC distribution network. Summary of the invention

[0004] Based on this, it is necessary to provide a fault current clearing circuit, method and control device based on a DC transformer to address the above technical problems, so as to solve the problem that the power outage time of the existing DAB DC transformer is prolonged due to clearing DC fault current.

[0005] On one hand, the present application provides a fault current clearing circuit based on a DC transformer, which is used to be connected between a medium-voltage DC distribution network and a low-voltage DC distribution network to clear the fault current in the medium-voltage DC distribution network. The clearing circuit includes a first preset number of cascaded sub-clearing circuit modules, and any of the sub-clearing circuit modules includes a DAB DC transformer and a half-bridge circuit. The DAB DC transformer is used to convert a medium-voltage DC signal into a low-voltage DC signal to provide electrical energy for the low-voltage DC distribution network; the half-bridge circuit is connected in parallel with the DAB DC transformer and is used to act according to a control signal to cut off the fault circuit between the medium-voltage DC distribution network and the DAB DC transformer, thereby clearing the fault current.

[0006] In the fault current clearing circuit in the above embodiment, by setting a half-bridge circuit connected in parallel with the DAB DC transformer, when an instantaneous short circuit fault occurs in the medium-voltage DC distribution network, the medium-voltage DC capacitor in the DAB DC transformer and the fault point can be isolated by controlling the on and off of the half-bridge circuit bridge arm switch, thereby cutting off the fault current, and the electric energy stored in the medium-voltage DC capacitor can be supplied to the low-voltage DC grid, so that there is no power outage on the low-voltage side. After the instantaneous fault current is cleared, the half-bridge circuit bridge arm switch is controlled to enter a steady-state working state, so that the system can quickly restore the steady-state working state, thereby greatly reducing the power outage loss. On the other hand, by cascading N sub-clearing circuit modules (the input end is connected in series and the output end is connected in parallel), the medium-voltage side can obtain the maximum withstand voltage value and the low-voltage side can obtain the maximum working current value under the same number of sub-clearing circuit modules.

[0007] In one embodiment, the half-bridge circuit comprises a first controllable switch unit and a second controllable switch unit connected in series, and two ends of the second controllable switch unit are set as two input ends of the sub-clearing circuit module;

[0008] The half-bridge circuit is configured as:

[0009] When a fault current is detected in the medium voltage DC distribution network, the first controllable switch unit is locked and the second controllable switch unit is turned on to cut off the fault circuit between the medium voltage DC distribution network and the DAB DC transformer.

[0010] In one embodiment, the first preset number is N, N is a positive integer greater than or equal to 1, and any of the sub-clearing circuit modules is configured as follows:

[0011] The first input end is connected to the second input end of the previous sub-clearing circuit module, and the second input end is connected to the first input end of the next sub-clearing circuit module, so that all the sub-clearing circuit modules are connected in series at the input end, wherein the first input end of the first sub-clearing circuit module is connected to the medium-voltage DC distribution network, and the second input end of the Nth sub-clearing circuit module is connected to the medium-voltage DC distribution network;

[0012] The first output ends of all the sub-clearing circuit modules are connected, and the second output ends of all the sub-clearing circuit modules are connected, so that all the sub-clearing circuit modules are connected in parallel at the output ends.

[0013] A second aspect of the present application provides a fault current clearing method based on a DC transformer, which is used to clear the fault current in a medium voltage DC distribution network. The method comprises:

[0014] Acquiring fault current information of the medium voltage DC distribution network;

[0015] A switch action signal is generated according to the fault current information to control the sub-clearing circuit module to operate so as to clear the fault current.

[0016] In the fault current clearing method in the above embodiment, in the event of an instantaneous short circuit fault on the medium voltage side, on the one hand, the medium voltage DC capacitor in the DAB DC transformer is disconnected from the fault point by controlling the switch unit of the half-bridge circuit to be flexibly turned on and off, thereby cutting off the instantaneous fault current, and providing a complete discharge circuit for the DC reactor on the medium voltage DC distribution network side, thereby effectively protecting the DC reactor. After clearing the instantaneous fault current, the system is returned to a steady-state working state by providing a stable switch control signal to the half-bridge circuit, thereby minimizing the power outage loss. On the other hand, in the event of a permanent short circuit fault on the medium voltage side, when the fault current cannot be removed by controlling the half-bridge circuit, the control will be triggered to lock all the switch units of the DAB DC transformer to clear the permanent short circuit fault current and ensure the safety of the system.

[0017] In one embodiment, the fault current includes an instantaneous fault current, and the step of generating a switch action signal according to the fault current information and controlling the sub-clearing circuit module to operate to clear the fault current includes:

[0018] A first controllable switch unit locking signal and a second controllable switch unit conducting signal are generated according to the fault current information to control the first controllable switch unit to lock and control the second controllable switch unit to conduct, so as to clear the instantaneous fault current.

[0019] In one of the embodiments, during the step of clearing the instantaneous fault current, the DAB DC transformer is in a steady-state working state.

[0020] In one embodiment, after the step of clearing the instantaneous fault current, the method further comprises:

[0021] A steady-state trigger control signal is provided to the first controllable switch unit and the second controllable switch unit to control the sub-clearing circuit module to enter a steady-state working state.

[0022] In one embodiment, the fault current also includes a permanent fault current, and the step of generating a switch action signal according to the fault current information and controlling the sub-clearing circuit module to operate to clear the fault current further includes:

[0023] If the fault current still exists after a preset time, a first controllable switch unit locking signal, a second controllable switch unit locking signal and a DAB DC transformer locking signal are generated to control the first controllable switch unit, the second controllable switch unit and the DAB DC transformer to be locked to clear the permanent fault current.

[0024] In one embodiment, the preset time T is calculated by the following formula:

[0025]

[0026] Wherein, 0<β≤1, N is the number of the sub-clearing circuit modules, C is the capacitance of the DC capacitor on the medium voltage side, V CN is the rated voltage of the medium voltage side DC capacitor, V min is the minimum voltage value at which the medium voltage side capacitor can provide driving energy for the DAB DC transformer, P N is the rated power of the sub-clearing circuit module.

[0027] A third aspect of the present application provides a fault current clearing control device based on a DC transformer, characterized in that it is used to control and clear the fault current in a medium voltage DC distribution network, and the control device includes:

[0028] A fault current information acquisition module, used to acquire fault current information of the medium voltage DC distribution network;

[0029] The control module is used to generate a switch action signal according to the fault current information, and control the sub-clearing circuit module to operate so as to clear the fault current. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 A schematic diagram of a fault current clearing circuit based on a DC transformer in an embodiment provided in the present application;

[0032] Figure 2 A working principle diagram of a fault current clearing circuit based on a DC transformer in a conventional method in an embodiment provided in the present application;

[0033] Figure 3A working principle diagram of a fault current clearing circuit based on a DC transformer in a transient fault condition in one embodiment provided in the present application;

[0034] Figure 4 A working principle diagram of a fault current clearing circuit based on a DC transformer under a permanent fault condition in an embodiment provided in the present application;

[0035] Figure 5 A schematic flow chart of a fault current clearing method based on a DC transformer in an embodiment provided in the present application;

[0036] Figure 6 A schematic flow chart of a fault current clearing method based on a DC transformer in another embodiment provided by the present application;

[0037] Figure 7 A schematic flow chart of a fault current clearing method based on a DC transformer in a third embodiment provided in the present application;

[0038] Figure 8 A schematic structural diagram of a fault current clearing control device based on a DC transformer in an embodiment provided in the present application. DETAILED DESCRIPTION

[0039] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0041] It can be understood that the terms "first", "second", etc. used in the present application can be used in this article to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from another element.

[0042] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element, or connected to the other element through an intermediate element. In addition, the "connection" in the following embodiments should be understood as "electrical connection", "communication connection", etc. if there is transmission of electrical signals or data between the connected objects.

[0043] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" etc. specify the presence of stated features, wholes, steps, operations, components, parts or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof.

[0044] With the development of power electronic control technology and device manufacturing technology, DC power grid has gained technical and economic advantages in many fields compared with AC power grid, especially with the growing demand for distributed new energy grid connection and the widespread use of DC loads, DC power grid is the trend of future power development. In medium voltage DC distribution network, DC transformer is the key commutation equipment to complete power transmission and voltage conversion.

[0045] At present, the DC transformer based on dual-active-bridge (DAB) input series-output parallel is one of the hot spots in the field of DC transformer topology development. However, the medium-voltage DC transformer based on DAB essentially retains the operating characteristics of DAB. Therefore, when the DC port voltage ratio is not equal to the transformation ratio of the high-frequency isolation transformer (this application defines this state as a voltage mismatch state, and similarly, the state when the DC port voltage ratio is equal to the transformation ratio of the high-frequency isolation transformer is defined as a voltage matching state), the voltage mismatch technical bottlenecks such as high current stress, soft switch loss and low transmission efficiency of DAB will limit its large-scale application. At the same time, from the perspective of DC distribution network application, due to the presence of concentrated DC capacitors in DAB, the DAB-type medium-voltage DC transformer cannot be set with fault-tolerant redundant submodules to improve the fault tolerance of internal submodule failures, which reduces the power supply continuity and reliability of the DC transformer itself. Furthermore, when the medium-voltage DC bus fails, the DC capacitors in each DAB submodule will quickly discharge to the fault point, increasing the fault interruption capacity of the system; when the fault is cleared, the DC capacitors need to be recharged, which prolongs the power outage time and reduces the power quality. Especially for instantaneous DC faults, medium-voltage DC transformers with fault blocking and rapid recovery functions are essential. At the same time, even with the cooperation of DC circuit breakers, DAB-type medium-voltage DC transformers can achieve DC fault isolation, but because DC circuit breakers require a certain amount of commutation time, the capacitor voltage of DAB-type DC transformers will not be able to support multiple reclosing of DC circuit breakers. Therefore, it is necessary to design more complex protection strategies to distinguish permanent faults from transient faults, which increases the complexity and action delay of the relay protection system.

[0046] In view of the above-mentioned shortcomings of the DAB type DC transformer, a new type of DC transformer is needed, which can automatically clear the fault current when the fault current is generated in the medium voltage DC distribution network, especially for the instantaneous fault current, and can ensure that the downstream low voltage DC distribution network will not be shut down during the fault current clearing process, thereby improving the power supply reliability.

[0047] In order to solve the above problems, the present application provides a fault current clearing circuit, method and control device based on a DC transformer, which will be described below in conjunction with specific embodiments.

[0048] In one embodiment of the present application, Figure 1 As shown, a fault current clearing circuit based on a DC transformer is provided, which is used to be connected between a medium-voltage DC distribution network and a low-voltage DC distribution network to clear the fault current in the medium-voltage DC distribution network. The clearing circuit includes N cascaded sub-clearing circuit modules, and any sub-clearing circuit module includes a DAB DC transformer 200 and a half-bridge circuit 100. The DAB DC transformer 200 is used to convert a medium-voltage DC signal into a low-voltage DC signal to provide electric energy for the low-voltage DC distribution network; the half-bridge circuit 100 is connected in parallel with the DAB DC transformer 200, and is used to act according to a control signal to cut off the fault circuit between the medium-voltage DC distribution network and the DAB DC transformer 200, thereby clearing the fault current.

[0049] Specifically, taking the i-th sub-clearing circuit module as an example, the half-bridge circuit 100 includes a first controllable switch unit Q1 and a second controllable switch unit Q2 connected in series, wherein two ends of the second controllable switch unit Q2 are set as two input ends of the i-th sub-clearing circuit module, and the connection relationship of each sub-clearing circuit module is as follows: the first input end is connected to the second input end of the previous sub-clearing circuit module, and the second input end is connected to the first input end of the next sub-clearing circuit module, so that all sub-clearing circuit modules are connected in series at the input end, wherein the first input end of the first sub-clearing circuit module is connected to the medium-voltage DC distribution network, and the second input end of the N-th sub-clearing circuit module is connected to the medium-voltage DC distribution network; the first output ends of all sub-clearing circuit modules are connected, and the second output ends of all sub-clearing circuit modules are connected, so that all sub-clearing circuit modules are connected in parallel at the output end. From the above connection relationship, it can be seen that on the medium voltage side, the voltage of the medium voltage DC distribution network is the sum of the input voltages of the N sub-clearing circuit modules, thereby reducing the withstand voltage of each sub-clearing circuit module and improving the safety of the system. On the low voltage side, the current of the low voltage DC distribution network is the sum of the output currents of the N sub-clearing circuit modules. Under the condition of the same number of sub-clearing circuit modules, the maximum output current is obtained, thereby maximizing the load capacity of the system.

[0050] Furthermore, in some embodiments, in order to optimize the DC input voltage waveform on the medium voltage side and ensure that the necessary switch action buffer time is provided for the sub-clearing circuit module in the event of a fault, a DC inductor L may be provided between the medium voltage DC distribution network and the fault current clearing circuit. dc In the case of steady-state operation of the system, the medium-voltage DC power provided by the medium-voltage DC distribution network passes through the DC inductor L dc , providing medium-voltage direct current with noise removed to the fault current clearing circuit based on the DC transformer, and providing steady-state control trigger signals to the controllable switch units inside each sub-clearing circuit module so that each sub-clearing circuit module works in a steady-state working state, which can realize step-down output of the medium-voltage direct current, and then obtain low-voltage direct current of a preset voltage level at the output end; and when a momentary short-circuit fault occurs in the medium-voltage DC distribution network, by controlling the two controllable switch units of the half-bridge circuit to work according to certain rules, while the DAB DC transformer continues to work in a steady-state working state, it can ensure that the short-circuit fault current is isolated and eliminated from the downstream normal distribution network without power outage in the downstream low-voltage DC distribution network, thereby improving the power supply reliability of the system.

[0051] In the fault current clearing circuit in the above embodiment, by setting a half-bridge circuit connected in parallel with the DAB DC transformer, when an instantaneous short circuit fault occurs in the medium-voltage DC distribution network, the medium-voltage DC capacitor in the DAB DC transformer and the fault point can be isolated by controlling the on and off of the half-bridge circuit bridge arm switch, thereby cutting off the fault current, and the electric energy stored in the medium-voltage DC capacitor can be supplied to the low-voltage DC grid, so that there is no power outage on the low-voltage side. After the instantaneous fault current is cleared, the half-bridge circuit bridge arm switch is controlled to enter a steady-state working state, so that the system can quickly restore the steady-state working state, thereby greatly reducing the power outage loss. On the other hand, by cascading N sub-clearing circuit modules (the input end is connected in series and the output end is connected in parallel), the medium-voltage side can obtain the maximum withstand voltage value and the low-voltage side can obtain the maximum working current value under the same number of sub-clearing circuit modules.

[0052] In one embodiment of the present application, Figure 2 As shown, a working principle diagram of a fault current clearing circuit under a traditional method when a short circuit fault occurs in a medium-voltage DC distribution network is provided. Specifically, under the traditional strategy, when a short circuit fault occurs in a medium-voltage DC distribution line, all switch tubes in any sub-clearing circuit module will be immediately locked. Since the locked power electronic switch device is equivalent to forming a breakpoint in the circuit, the medium-voltage side capacitor C1 in any sub-clearing circuit module will stop discharging to the fault point due to the presence of the first controllable switch unit Q1 in the locked state, thereby clearing the fault current. At the same time, the DC inductor L dcThe residual current in the first controllable switch unit will flow into the medium-voltage side DC capacitor C1 of each sub-clearance circuit module through the reverse-parallel diode in the first controllable switch unit. Therefore, in order to avoid overvoltage protection or burning of the DC capacitor C1 caused by the voltage increase caused by this part of the current, it is necessary to increase the capacitance C1 when designing the sub-clearance circuit module, thereby increasing the overall cost. In addition, during the DC fault current processing, since all switch tubes are in the locking stage, the power supply of the fault current clearing circuit to the downstream low-voltage side will be interrupted, reducing the power quality on the low-voltage side.

[0053] In one embodiment of the present application, Figure 3 As shown, a working principle diagram of a fault current clearing circuit when a short-circuit fault occurs in a medium-voltage DC distribution network is provided. Specifically, when a short-circuit fault current is detected on a medium-voltage DC line in the medium-voltage DC distribution network, in any sub-clearing circuit module, the first controllable switch unit Q1 of the half-bridge circuit 100 is locked, the second controllable switch unit Q2 is turned on, and the DAB DC transformer 200 works normally in a steady state. From the circuit structure, it can be seen that the medium-voltage DC capacitor C1 in the DAB DC transformer 200 is disconnected at the switch Q1 connected to the medium-voltage DC grid, and cannot discharge to the fault point, thereby cutting off the source of the fault current. On the other hand, the DC inductor L dc The residual current of the inductor is released by turning on the second controllable switch unit Q2 to achieve freewheeling. Then, the medium-voltage DC inductor C1 continues to supply power to the downstream low-voltage DC distribution network through the normally functioning DAB DC transformer. When it is only a momentary fault, after the fault current is eliminated, a normal steady-state trigger control signal is provided to the half-bridge circuit 100. The system can resume normal power supply and the downstream power supply will not be interrupted. Therefore, the stability and power supply reliability of the system can be greatly improved.

[0054] In one embodiment of the present application, Figure 4 As shown, a working principle diagram of a fault current clearing circuit when a permanent short circuit fault occurs in a medium voltage DC distribution network is provided. Specifically, when a permanent short circuit fault occurs in a medium voltage DC distribution network, the fault current clearing circuit first passes through Figure 3 In the working process shown, after a certain period of time, if the system detects that the fault current still exists, all controllable switch units in all sub-clearing modules are locked to facilitate maintenance personnel to perform fault maintenance.

[0055] In one embodiment of the present application, Figure 5 As shown, a fault current clearing method based on a DC transformer is provided, which is used to clear the fault current in a medium voltage DC distribution network, and the method comprises:

[0056] Step 22, obtaining fault current information of the medium voltage DC distribution network;

[0057] Specifically, the medium voltage DC distribution network monitors the line current in real time through the protection device, and uses the detected current value as the real-time input variable of the fault current clearing circuit control system to ensure the medium voltage DC distribution network's rapid response capability to the fault current.

[0058] Step 24: Generate a switch action signal according to the fault current information to control the sub-clearing circuit module to operate so as to clear the fault current.

[0059] In the fault current clearing method in the above embodiment, in the event of an instantaneous short circuit fault on the medium voltage side, on the one hand, the medium voltage DC capacitor in the DAB DC transformer is disconnected from the fault point by controlling the switch unit of the half-bridge circuit to be flexibly turned on and off, thereby cutting off the instantaneous fault current, and providing a complete discharge circuit for the DC reactor on the medium voltage DC distribution network side, thereby effectively protecting the DC reactor. After clearing the instantaneous fault current, the system is returned to a steady-state working state by providing a stable switch control signal to the half-bridge circuit, thereby minimizing the power outage loss. On the other hand, in the event of a permanent short circuit fault on the medium voltage side, when the fault current cannot be removed by controlling the half-bridge circuit, the control will be triggered to lock all the switch units of the DAB DC transformer to clear the permanent short circuit fault current and ensure the safety of the system.

[0060] In one embodiment of the present application, Figure 6 As shown, step 24, generating a switch action signal according to the fault current information, controlling the sub-clearing circuit module to operate to clear the fault current, includes:

[0061] Step 242: Generate a first controllable switch unit locking signal and a second controllable switch unit conducting signal according to the fault current information to control the first controllable switch unit to lock and control the second controllable switch unit to conduct, so as to clear the instantaneous fault current.

[0062] Specifically, when fault current information of the medium voltage DC distribution network is detected, the first controllable switch unit Q1 is quickly controlled to be locked, and the second controllable switch unit Q2 is controlled to be turned on, so as to clear the instantaneous fault current in the first place. The specific working principle has been introduced in detail in the above embodiment and will not be repeated here.

[0063] In one embodiment of the present application, please continue to refer to Figure 6 , step 24, after generating a switch action signal according to the fault current information and controlling the sub-clearing circuit module to operate to clear the fault current, it also includes:

[0064] Step 244: providing a steady-state trigger control signal to the first controllable switch unit and the second controllable switch unit to control the sub-clearing circuit module to enter a steady-state working state.

[0065] Specifically, when an instantaneous short circuit fault occurs in the medium voltage side DC distribution network, after the fault current clearing circuit completes the fault current clearing work through step 242, the system has normal working conditions. At this time, a steady-state trigger control signal is provided to the first controllable switch unit Q1 and the second controllable switch unit Q2 of the half-bridge circuit to restore the system to normal power supply. The specific working principle has been introduced in detail in the aforementioned embodiment and will not be repeated here.

[0066] In one embodiment of the present application, Figure 7 As shown, step 24, generating a switch action signal according to the fault current information, controlling the sub-clearing circuit module to operate to clear the fault current, also includes:

[0067] Step 246: If the fault current still exists after a preset time, generate a first controllable switch unit locking signal, a second controllable switch unit locking signal and a DAB DC transformer locking signal to control the first controllable switch unit, the second controllable switch unit and the DAB DC transformer to be locked to clear the permanent fault current.

[0068] Specifically, for a permanent fault, since the system cannot determine the fault type, when the fault current information is just detected, the fault current clearing circuit clears the fault current according to the processing method of step 242. After a preset time, if the system detects that the fault current has not been cleared, it is determined that a permanent fault has occurred. At this time, all controllable switch units of all sub-clearing circuit modules are controlled to be locked to completely cut off the connection path of the medium and low voltage DC power grid, making it convenient for staff to conduct fault detection and maintenance.

[0069] Furthermore, in some embodiments, the preset time T is calculated by the following formula:

[0070]

[0071] Where, 0<β≤1, N is the number of sub-clearance circuit modules, C is the capacitance of the medium voltage DC capacitor, V CN is the rated voltage of the medium voltage DC capacitor, V min P is the minimum voltage value that the medium voltage capacitor can provide driving energy for the DAB DC transformer. N is the rated power of the sub-clearance circuit module.

[0072] In one embodiment of the present application, Figure 8 As shown, a fault current clearing control device based on a DC transformer is also provided, which is used to control and clear the fault current in a medium voltage DC distribution network, and the control device includes:

[0073] A fault current information acquisition module 1000 is used to acquire fault current information of the medium voltage DC distribution network;

[0074] The control module 2000 is used to generate a switch action signal according to the fault current information, and control the sub-clearing circuit module to operate so as to clear the fault current.

[0075] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory or optical memory, etc. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0076] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", "ideal embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0077] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0078] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. 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 application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A fault current clearing circuit based on a DC transformer, used for connecting between a medium voltage DC distribution network and a low voltage DC distribution network to clear the fault current in the medium voltage DC distribution network, characterized in that: A first preset number of cascaded sub-clearing circuit modules are included, any of the sub-clearing circuit modules comprising: A DAB DC transformer, used to convert a medium voltage DC signal into a low voltage DC signal to provide electric energy for the low voltage DC distribution network; A half-bridge circuit is connected in parallel with the DAB DC transformer and is used to operate according to a control signal to cut off the fault circuit between the medium voltage DC distribution network and the DAB DC transformer, thereby clearing the fault current; the half-bridge circuit includes a first controllable switch unit and a second controllable switch unit connected in series, and two ends of the second controllable switch unit are set as two input ends of the sub-clearing circuit module; the fault current includes a permanent fault current; The half-bridge circuit is configured as: When a fault current is detected in the medium voltage DC distribution network, the first controllable switch unit is locked and the second controllable switch unit is turned on to cut off the fault circuit between the medium voltage DC distribution network and the DAB DC transformer; Wherein, if the fault current still exists after a preset time, the first controllable switch unit, the second controllable switch unit and the DAB DC transformer are all locked to clear the permanent fault current; The preset time T is established by the following calculation formula: Wherein, 0<β≤1, N is the number of the sub-clearing circuit modules, C is the capacitance of the DC capacitor on the medium voltage side, V CN is the rated voltage of the medium voltage side DC capacitor, V min is the minimum voltage value at which the medium voltage side capacitor can provide driving energy for the DAB DC transformer, P N is the rated power of the sub-clearing circuit module.

2. The circuit according to claim 1, characterized in that The first preset number is N, where N is a positive integer greater than or equal to 1, and any of the sub-clearing circuit modules is configured as follows: The first input end is connected to the second input end of the previous sub-clearing circuit module, and the second input end is connected to the first input end of the next sub-clearing circuit module, so that all the sub-clearing circuit modules are connected in series at the input end, wherein the first input end of the first sub-clearing circuit module is connected to the medium-voltage DC distribution network, and the second input end of the Nth sub-clearing circuit module is connected to the medium-voltage DC distribution network; The first output ends of all the sub-clearing circuit modules are connected, and the second output ends of all the sub-clearing circuit modules are connected, so that all the sub-clearing circuit modules are connected in parallel at the output ends.

3. The circuit according to claim 2, characterized in that The voltage of the medium voltage DC distribution network is the sum of the input voltages of the N sub-clearing circuit modules, and the current of the low voltage DC distribution network is the sum of the output currents of the N sub-clearing circuit modules.

4. A fault current clearing method based on a DC transformer, characterized in that: For clearing a fault current in a medium voltage DC distribution network, the method comprises: Acquiring fault current information of the medium voltage DC distribution network; Generate a switch action signal according to the fault current information, and control the sub-clearing circuit module to operate to clear the fault current; The fault current includes a permanent fault current, and the generating of a switch action signal according to the fault current information and controlling the sub-clearing circuit module to operate to clear the fault current includes: If the fault current still exists after a preset time, a first controllable switch unit locking signal, a second controllable switch unit locking signal and a DAB DC transformer locking signal are generated to control the first controllable switch unit, the second controllable switch unit and the DAB DC transformer to be locked to clear the permanent fault current; The preset time T is calculated by the following formula: Wherein, 0<β≤1, N is the number of the sub-clearing circuit modules, C is the capacitance of the DC capacitor on the medium voltage side, V CN is the rated voltage of the medium voltage side DC capacitor, V min is the minimum voltage value at which the medium voltage side capacitor can provide driving energy for the DAB DC transformer, P N is the rated power of the sub-clearing circuit module.

5. The method according to claim 4, characterized in that The fault current includes an instantaneous fault current, and the step of generating a switch action signal according to the fault current information and controlling the sub-clearing circuit module to operate to clear the fault current includes: A first controllable switch unit locking signal and a second controllable switch unit conducting signal are generated according to the fault current information to control the first controllable switch unit to lock and control the second controllable switch unit to conduct, so as to clear the instantaneous fault current.

6. The method according to claim 5, characterized in that During the step of clearing the instantaneous fault current, the DAB DC transformer is in a steady-state working state.

7. The method according to claim 5 or 6, characterized in that: After the step of clearing the instantaneous fault current, the method further comprises: A steady-state trigger control signal is provided to the first controllable switch unit and the second controllable switch unit to control the sub-clearing circuit module to enter a steady-state working state.

8. A fault current clearing control device based on a DC transformer, characterized in that: Used to control and clear fault current in a medium voltage DC distribution network, the control device comprises: A fault current information acquisition module, used to acquire fault current information of the medium voltage DC distribution network; A control module, used for generating a switch action signal according to the fault current information, and controlling the sub-clearing circuit module to operate so as to clear the fault current; The fault current includes a permanent fault current; the control module is further used to generate a first controllable switch unit locking signal, a second controllable switch unit locking signal and a DAB DC transformer locking signal if the fault current still exists after a preset time, so as to control the first controllable switch unit, the second controllable switch unit and the DAB DC transformer to be locked, so as to clear the permanent fault current; The preset time T is calculated by the following formula: Wherein, 0<β≤1, N is the number of the sub-clearing circuit modules, C is the capacitance of the DC capacitor on the medium voltage side, V CN is the rated voltage of the medium voltage side DC capacitor, V min is the minimum voltage value at which the medium voltage side capacitor can provide driving energy for the DAB DC transformer, P N is the rated power of the sub-clearing circuit module.

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