A hybrid DC circuit breaker, control protection device and method

Abstract

The invention discloses a hybrid DC circuit breaker, a control and protection device and a control and protection method. Three independent merging units of the device are used to collect the line current of the total outgoing line at one end of the hybrid DC circuit breaker, the main branch current, the transfer branch current, the total current of the energy-consuming branch and the branch current of the energy-consuming branch; the communication module of the control and protection host realizes the communication between the main branch, the transfer branch, the converter station control equipment and the converter station protection equipment; the protection judgment module performs overcurrent judgment of the circuit breaker according to the current of the merging unit; the three-out-of-two logic module performs three-out-of-two logic judgment of overcurrent according to the judgment result of the protection judgment module; the control module realizes the circuit breaker opening and closing timing and equipment fault judgment, and sends the control and protection instructions to the main branch commutation component and the semiconductor component of the transfer branch through the communication module and the interface unit; the protection method based on the device can quickly execute the opening and closing process, quickly detect the equipment status and implement effective protection.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current circuit breaker control and protection, and in particular to a hybrid direct current circuit breaker, a control and protection device and a control and protection method. Background Art

[0002] DC circuit breakers are used in DC transmission systems, especially in multi-terminal DC and DC network systems, to break DC fault currents and isolate DC line faults. Hybrid DC circuit breakers combine the technical characteristics of low conduction losses of traditional mechanical circuit breakers and high breaking speed of solid-state circuit breakers, and have become a hot topic in DC circuit breaker research.

[0003] Hybrid DC circuit breakers have high requirements for the speed and accuracy of their control and protection devices. After a DC line fault occurs, the short-circuit current increases linearly and the converter voltage drops rapidly, so the DC circuit breaker needs to be disconnected within milliseconds. The disconnection process of the DC circuit breaker involves the coordination of multiple components such as semiconductor components, mechanical switches, and energy-consuming devices, and requires two large-circuit commutations under a high voltage of hundreds of kilovolts. Since the mechanical switch in the hybrid DC circuit breaker does not have the ability to break current, it is necessary to ensure that the current is zero before disconnection. The main branch current is collected for zero-crossing judgment, and sampling, communication, and filtering delays will extend the circuit breaker disconnection time. In addition, due to the rapid changes in voltage and current during the circuit breaker opening and closing process, the fault needs to be identified within hundreds of microseconds to avoid the expansion of the fault.

[0004] The existing hybrid DC circuit breaker control protection device and method have a large delay, which affects the overall breaking time of the DC circuit breaker, and the fault protection speed cannot meet the rapid requirements of the DC circuit breaker. Summary of the invention

[0005] Therefore, the embodiments of the present invention provide a hybrid DC circuit breaker, a control protection device and a control protection method, which overcome the problems in the prior art that the hybrid DC circuit breaker control protection device and method have a large delay, affect the overall breaking time of the DC circuit breaker, and the fault protection speed cannot meet the fast requirements of the DC circuit breaker.

[0006] In a first aspect, the present invention provides a hybrid DC circuit breaker, comprising: a main branch, a transfer branch and an energy-consuming branch, wherein: the main branch is used for normal current flow, and comprises a mechanical switch and a commutation component, wherein the mechanical switch comprises: a mechanical switch control module, a switch body, an opening repulsion mechanism, a closing repulsion mechanism and a switch state sensor module; the switch body comprises: a vacuum arc extinguishing chamber, a static contact and a moving contact; the opening repulsion mechanism comprises: an opening discharge coil, a fast-breaking capacitor, a slow-breaking capacitor, a fast-breaking trigger thyristor and a slow-breaking trigger thyristor; the closing repulsion mechanism comprises: a closing discharge coil, a closing capacitor and a closing trigger thyristor; the commutation component comprises: a semiconductor device and a passive device; the transfer branch is used for breaking current, and is composed of a plurality of valve sections connected in series, each valve section comprising a plurality of semiconductor devices connected in series; the energy-consuming branch is used for dissipating energy, and is composed of a plurality of valve sections connected in series, each valve section comprising a plurality of parallel lightning arresters, and all parallel lightning arresters of each valve section are evenly divided into two groups, each group being a branch.

[0007] Furthermore, the mechanical switch control module includes: two mechanical switch controllers, and the two mechanical switch controllers are redundant to each other.

[0008] Furthermore, the switch state sensor module adopts a non-contact sensor, including: an open position sensor, a closed position sensor and a pressure-resistant position sensor.

[0009] In a second aspect, an embodiment of the present invention provides a hybrid DC circuit breaker control and protection device, comprising: three independent merging units, a control and protection host and an interface unit, wherein the three independent merging units are all used to collect the line current of the total outgoing line at one end of the hybrid DC circuit breaker, the main branch current, the transfer branch current, the total current of the energy-consuming branch and the branch current of the energy-consuming branch; the control and protection host comprises: a communication module, a control module, a protection judgment module and a three-out-of-two logic module, wherein the communication module is used to realize communication with the main branch, the transfer branch, the converter station control equipment and the converter station protection equipment; the protection judgment module performs overcurrent judgment of the hybrid DC circuit breaker according to the current of the three independent merging units; the three-out-of-two logic module is used to perform three-out-of-two logic judgment of overcurrent according to the judgment result of the protection judgment module; the control module realizes the hybrid DC circuit breaker opening and closing timing and DC circuit breaker equipment fault judgment; the control module sends the control and protection instructions to the main branch commutation component and the transfer branch semiconductor component of the hybrid DC circuit breaker through the communication module and the interface unit.

[0010] Furthermore, the control and protection host is redundantly configured, wherein one set of devices is in a duty state and the other set of devices is in a standby state, and the control and protection host performs cross communication with the mechanical switch controller.

[0011] In a third aspect, an embodiment of the present invention provides a control and protection method for a hybrid DC circuit breaker. Based on the hybrid DC circuit breaker control and protection device described in the second aspect of the embodiment of the present invention, the hybrid DC circuit breaker is controlled and protected in the closing state, the opening state, the opening process and the closing process.

[0012] Furthermore, the control and protection process of the hybrid DC circuit breaker in the closed state includes the following steps: the control module controls the main branch and the transfer branch to be in the on state through the communication module, and the control module detects in real time whether the components of the transfer branch and the main branch are faulty; when it is detected that the components of the transfer branch and the main branch are faulty and the opening operation cannot be completed, the circuit breaker is prohibited from opening, otherwise when it is detected that the components of the transfer branch and the main branch are not faulty, the three-out-of-two logic module is used to determine whether the line current is greater than the preset current; when the line current is not greater than the preset current, the circuit breaker is allowed to close; according to the fast opening or slow opening instruction issued by the converter station control protection, the circuit breaker is subjected to a fast opening process or a slow opening process.

[0013] Furthermore, the preset current is set according to the breaking capacity of the transfer branch and is calculated by the following formula:

[0014]

[0015] Among them, I 3 is the preset current, I 4 is the maximum current that the circuit breaker transfer branch can break, t open is the breaking time of the circuit breaker, is the maximum fault current rise rate of the DC system, I mar is the current margin.

[0016] Furthermore, the control and protection process during the hybrid DC circuit breaker opening process includes the following steps: when the control module executes a fast opening or slow opening process on the circuit breaker, the control module sends an instruction through the communication module to shut down the main branch commutation component; after a preset waiting time, the mechanical switch slow opening or fast opening instruction is issued; when the communication module detects that the displacement of the mechanical switch reaches a withstand voltage position or the transfer branch is overcurrent, the control module sends an instruction to shut down the transfer branch and turn on the main branch commutation component; it is determined whether the degree of uneven current between the two groups of lightning arresters in each valve section of the energy-consuming branch exceeds a preset threshold; when the threshold is exceeded, it is considered that the lightning arrester of the valve section is broken down and closing is prohibited; when the preset threshold is not exceeded, the opening is completed.

[0017] Furthermore, the preset waiting time is calculated by the control module in real time according to the main branch current, the main branch and the transfer branch equivalent circuit parameters. When the transfer branch cannot pass the current due to a fault, the preset time t 1 Calculated by the following formula:

[0018] t1 =t 0 -t sam -t swd -t comm +t mar

[0019] Among them, t 0 is the time required for the main branch current to become 0, t sam is the sampling delay, t swd The delay from when the switch receives the command to when the break occurs, t comm is the communication delay from the circuit breaker control protection to the mechanical switch command, t mar is the waiting time margin;

[0020] When there is a module in the transfer branch that cannot flow due to a fault and the breakdown voltage of the transfer branch fault is lower than the breakdown voltage of the main branch converter module, the preset time t 1 Calculated by the following formula:

[0021] t 1 =t z -t sam -t swd -t comm +t mar

[0022] Among them, t z The time required for the total voltage of the transfer branch fault open module to reach the breakdown voltage, t sam is the sampling delay, t swd It is the delay from the switch receiving the command to the break opening, t comm is the communication delay from the circuit breaker control protection to the mechanical switch command, t mar is the waiting time margin.

[0023] Furthermore, when the communication module detects that the displacement of the mechanical switch reaches the withstand voltage position or the transfer branch is overcurrent, if the transfer branch has a valve section with an excess redundant number of faulty modules, all modules in the valve section are delayed in shutting down, and the delay time should be greater than the falling time of the DC system fault current after the DC circuit breaker is disconnected.

[0024] Furthermore, the step of judging whether the degree of current imbalance between the two groups of lightning arresters exceeds a preset threshold value includes: the protection judgment module respectively obtains the sampling values ​​of the three sets of sensors to calculate the current deviation ratio of the energy-consuming branch, and judges whether the three calculated current deviation ratios exceed the preset threshold value, and the three-out-of-two logic module performs a three-out-of-two logic judgment on it. If two or more judgment results are exceeded, it is determined that the lightning arrester of the valve section of the energy-consuming branch is broken down, and the closing operation is prohibited. If all valve sections of the energy-consuming branch of the circuit breaker do not exceed the preset threshold value, the disconnection process ends.

[0025] Furthermore, the control and protection process of the hybrid DC circuit breaker under the split state includes the following steps: the control module makes the mechanical switch of the main branch in the disconnected state, the commutation component in the on state, and the transfer branch in the disconnected state through the communication module; the control module detects the component status of the main branch and the transfer branch in real time. When the main branch or the transfer branch fails and the circuit breaker cannot complete the closing operation, or the closing operation can be completed but the circuit breaker can no longer be opened after closing, the circuit breaker is prohibited from closing.

[0026] Furthermore, the control and protection process during the closing process of the hybrid DC circuit breaker includes the following steps: when executing the closing process, the control module sends an instruction through the communication module to open the transfer branch and start timing; before the preset timing time is reached, if the circuit breaker equipment fails, or the line current collected by the current acquisition module is judged by the protection judgment module and processed by the three-out-of-two logic module to exceed the overcurrent set value, the transfer branch is shut down through the communication module, the closing process is terminated, and the switch-off state is returned; if there is no equipment failure or line overcurrent when the preset timing time is reached, the mechanical switch closing instruction is sent through the communication module, and after all the mechanical switch ports return to the closed state within the preset time, the closing is completed; if a mechanical switch does not return to the closed state within the preset time, the DC circuit breaker is disconnected according to the opening sequence and returns to the open state.

[0027] Furthermore, the preset timing time is set according to the time it takes for the overcurrent set value to be reached after the DC line has a ground fault.

[0028] Furthermore, the preset time is set according to the longest closing time of the mechanical switch.

[0029] Furthermore, the overcurrent setting is greater than the rated operating current of the DC system and less than the maximum withstand current of the transfer branch.

[0030] The technical solution of the present invention has the following advantages:

[0031] 1. The hybrid DC circuit breaker provided by the present invention adopts a segmented design for the transfer branch and the energy consumption branch to reduce the type test capacity requirement, and distinguishes between fast and slow separation by setting two groups of energy storage capacitors with different energies, namely, slow separation capacitors and fast separation capacitors. The discharge of capacitors with higher energy storage is used to drive the mechanical switch to quickly separate in the event of a system failure, and the discharge of capacitors with lower energy storage is used to separate the mechanical switch at a slower speed when there is no fault in the DC system and the operator issues a separation operation instruction, so as to increase the service life of the mechanical switch; by setting three sets of position sensors, the cooperation between the mechanical switch and the transfer branch module is closer; and the redundant setting of the controller can improve the reliability of the switch control.

[0032] 2. The control and protection device of the hybrid DC circuit breaker provided by the present invention integrates the control, protection and three-out-of-two judgment functions into the control and protection host, which reduces the equipment links, reduces the communication delay, improves the protection response speed, and obtains a higher accuracy judgment result. At the same time, the reliability is improved by setting the control and protection host redundantly and cross-communicating with the interface unit and the merging unit.

[0033] 3. The control and protection method of the hybrid DC circuit breaker provided by the present invention shortens the state judgment time in the disconnection process by using a fast disconnection control method. During the circuit breaker disconnection process, the commutation detection and waiting time are shortened by prejudging the zero point of the main branch current. Since the damage of the semiconductor devices of the main branch and the transfer branch is considered in the zero-crossing prejudgment, it has a wider applicability. By adding an intermediate position sensor, it is possible to quickly judge whether the mechanical switch has reached the opening distance that meets the insulation requirements during the mechanical switch disconnection process, thereby shortening the disconnection time while ensuring the safety of the equipment. By specially setting the main branch commutation component and transfer branch state of the DC circuit breaker in the closed state and the split state, the module fault can be quickly discovered and the mechanical switch breakdown can be avoided to cause damage to the main branch commutation component module; the fast and slow control logics are set to improve the life of the mechanical switch. The super-redundant valve section delays the shutdown of the transfer branch fault to avoid overvoltage breakdown of a large number of devices. By grouping the arrester current, the rapid detection of the arrester breakdown fault is achieved. In the closed state, the line current is detected and overcurrent protection is implemented to prevent the circuit breaker from breaking currents that exceed its breaking capacity, thereby avoiding damage to the equipment. During the closing process, the DC system current and circuit breaker equipment faults are judged in real time to prevent the DC circuit breaker from being put into operation with a fault, or the fault current from impacting primary equipment such as the converter valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 A schematic diagram of the structure of a hybrid DC circuit breaker provided in an embodiment of the present invention;

[0036] Figure 2 A schematic diagram of the structure of a mechanical switch provided by an embodiment of the present invention;

[0037] Figure 3 A schematic diagram of the structure of a hybrid DC circuit breaker control and protection device provided in an embodiment of the present invention;

[0038] Figure 4 A schematic diagram of a transformer configuration provided by an embodiment of the present invention;

[0039] Figure 5 A schematic diagram of communication connection between the hybrid DC circuit breaker control protection device provided in an embodiment of the present invention and other devices after redundant configuration;

[0040] Figure 6 A flowchart of an example of a control and protection process of a hybrid DC circuit breaker in a closed state provided by an embodiment of the present invention;

[0041] Figure 7 A flowchart of a specific example of a hybrid DC circuit breaker in a closed state provided by an embodiment of the present invention;

[0042] Figure 8 A flowchart of an example of a control and protection process during the opening process of a hybrid DC circuit breaker provided in an embodiment of the present invention;

[0043] Fig. 9 The module provided in the embodiment of the present invention in which the transfer branch has no semiconductor device failure and is open-circuited, is a commutation equivalent circuit of the main branch and the transfer branch;

[0044] Fig.10 An equivalent circuit for commutation between the main branch and the transfer branch when the transfer branch has a module with a semiconductor device failure and an open circuit and the breakdown voltage of the transfer branch failure is still higher than the breakdown voltage of the main branch commutation module provided by the embodiment of the present invention;

[0045] Fig.11 A flowchart of an example of a control and protection process of a hybrid DC circuit breaker under split states provided by an embodiment of the present invention;

[0046] Fig.12 The present invention provides a flowchart of an example of a control and protection process during the closing process of a hybrid DC circuit breaker provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0050] Example 1

[0051] The embodiment of the present invention provides a hybrid DC circuit breaker, such as Figure 1 As shown, it includes: main branch, transfer branch and energy consumption branch, among which:

[0052] The main branch is used for normal current flow, which includes a mechanical switch and a commutation component capable of high-speed operation. The commutation component realizes the current transfer from the main branch to the transfer branch. It can be composed of a combination of fully controlled semiconductor devices and RC buffer and voltage limiting circuits. By turning off the semiconductor devices, a voltage can be connected in series to the main branch, forcing the current to flow to the transfer branch. The main branch commutation component adopts a modular design and can be composed of multiple modules.

[0053] The transfer branch is used to disconnect the current and is composed of multiple valve sections in series, each valve section includes multiple semiconductor devices connected in series; in the embodiment of the present invention, the transfer branch is composed of semiconductor devices such as IGBT and diode or IGCT and diode connected in series and parallel, which can disconnect the fault current and withstand transient overvoltage, and is composed of multiple modules in series.

[0054] The energy consumption branch is used to dissipate energy, and is composed of multiple valve sections connected in series. Each valve section includes multiple parallel lightning arresters. All parallel lightning arresters in each valve section are evenly divided into two groups, and each group is a branch. The lightning arrester in the embodiment of the present invention is a metal oxide lightning arrester. The transfer branch and the energy consumption branch adopt a segmented design. Each transfer branch is composed of multiple modules in series and is connected in parallel with a lightning arrester. The segmented design can reduce the type test capacity requirements.

[0055] In the embodiment of the present invention, the mechanical switch includes: a mechanical switch control module 1, a switch body 2, an opening repulsion mechanism 3, a closing repulsion mechanism 4 and a switch state sensor module 5. Figure 2 As shown:

[0056] The mechanical switch control module 1 includes two mechanical switch controllers: a mechanical switch controller A and a mechanical switch controller B. The two mechanical switch controllers are mutually redundant. By setting the controllers redundantly, the reliability of the switch control can be improved. The switch body 2 includes: a vacuum interrupter 21, a static contact 22 and a moving contact 23. The opening repulsion mechanism 3 includes: an opening discharge coil 31, a fast opening capacitor 32, a slow opening capacitor 33, a fast opening trigger thyristor 34 and a slow opening trigger thyristor 35; the slow opening capacitor 33 has a smaller capacitance or a lower charging voltage than the fast opening capacitor 32, so the stored energy is smaller, and when the discharge is triggered, the moving contact can be pushed to open with less energy. The mechanical switch is driven by electromagnetic repulsion, and the fast opening and slow opening are distinguished by these two groups of energy storage capacitors with different energies. The discharge of the capacitor with higher energy storage is used to drive the mechanical switch to open quickly in the case of system failure, and the discharge of the capacitor with lower energy storage is used when there is no fault in the DC system and the operator issues an opening operation instruction. The mechanical switch opens at a slower speed to improve the life of the mechanical switch. The closing repulsion mechanism 4 comprises: a closing discharge coil 41 , a closing capacitor 42 and a closing trigger thyristor 43 .

[0057] In order to make the cooperation between the mechanical switch and the transfer branch module closer during the opening process, and to shut down the transfer branch as early as possible to complete the opening operation under the premise of ensuring the safety of the equipment, each mechanical switch is equipped with 3 sets of position sensors. In the embodiment of the present invention, the switch state sensor module 5 adopts a non-contact sensor, including: an open position sensor, a closed position sensor and a withstand voltage position sensor. The use of a non-contact sensor can avoid the sensor from affecting the movement of the contact, and prevent the sensor and the lead from being shortened due to mechanical fatigue caused by frequent movement. In this embodiment, if Figure 2 As shown, each sensor includes a transmitting unit and a receiving unit, which are respectively a partial position sensor transmitting unit 51, a partial position sensor receiving unit 52, a combined position sensor transmitting unit 61, a combined position sensor receiving unit 62, a pressure resistance position sensor transmitting unit 71 and a pressure resistance position sensor receiving unit 72. This is only an example and is not limited to this. In other embodiments, other non-contact sensors, such as metal sensing sensors, may be used.

[0058] The hybrid DC circuit breaker provided by the present invention adopts a segmented design through the transfer branch and the energy consumption branch to reduce the type test capacity requirement, and distinguishes between fast and slow separation by setting two groups of energy storage capacitors with different energies, namely slow separation capacitors and fast separation capacitors. The discharge of the capacitor with higher energy storage is used to drive the mechanical switch to quickly separate in the event of a system failure, and the discharge of the capacitor with lower energy storage is used to separate the mechanical switch at a slower speed when there is no fault in the DC system and the operator issues a separation operation instruction, so as to increase the service life of the mechanical switch; by setting three sets of position sensors, the cooperation between the mechanical switch and the transfer branch module is closer; and the redundant setting of the controller can improve the reliability of the switch control.

[0059] Example 2

[0060] The embodiment of the present invention provides a hybrid DC circuit breaker control and protection device, such as Figure 3 As shown, it includes: three independent merging units (merging unit A, merging unit B, merging unit C) control protection host and interface unit, the three independent merging units are used to collect the line current of the total outgoing line at one end of the hybrid DC circuit breaker, the main branch current, the transfer branch current, the total current of the energy-consuming branch and the branch current of the energy-consuming branch; the control protection host includes: a communication module, a control module, a protection judgment module, and a three-out-of-two logic module, wherein the communication module is used to realize communication with the main branch, the transfer branch, the converter station control equipment, and the converter station protection equipment; the protection judgment module performs overcurrent judgment of the hybrid DC circuit breaker according to the current of the three independent merging units; the three-out-of-two logic module is used to perform overcurrent three-out-of-two logic judgment according to the judgment result of the protection judgment module; the control module realizes the hybrid DC circuit breaker opening and closing timing and DC circuit breaker equipment fault judgment; the control module sends the control protection instruction to the main branch commutation component and the transfer branch semiconductor component of the hybrid DC circuit breaker through the communication module and the interface unit.

[0061] The transformer configuration method in the embodiment of the present invention is as follows Figure 4 As shown, three sets of current transformers are respectively configured for the main outgoing line, main branch, and transfer branch at one end of the circuit breaker. The parallel lightning arresters of each energy-consuming branch are evenly divided into two groups, each group is a branch, and three sets of current transformers are respectively installed in the main circuit of the energy-consuming branch and one branch. The three sets of current sensors at each position are respectively connected to the merging unit A, merging unit B, and merging unit C, and the three merging units are all connected to the circuit breaker control protection A and the circuit breaker control protection B.

[0062] In the embodiment of the present invention, Figure 5 As shown, the control and protection host is redundantly set, control and protection host A and control and protection host B, one set of devices is on duty, and the other set of devices is in standby state, and the control and protection host cross-communicates with the mechanical switch controller. The communication module of each set of control and protection devices receives data from three sets of merging units, and communicates bidirectionally with the converter station control and protection A and converter station control and protection B, mechanical switch controller A, mechanical switch controller B and interface device, and the interface module communicates bidirectionally with the main branch commutation component submodule and the transfer branch submodule. The interface module forwards the on-duty circuit breaker control and protection device instructions to the main branch commutation component submodule and the transfer branch submodule, and does not forward the standby circuit breaker control and protection device instructions. The mechanical switch controller only executes the on-duty circuit breaker control and protection device instructions, and does not execute the standby circuit breaker control and protection device instructions.

[0063] Each set of control and protection device receives current sampling from three sets of merging units. Each set of merging pairs has independent current sensors to sample the total current of the circuit breaker, the main branch current, the transfer branch current, the total loop current of the energy-consuming branch, and the branch current of the energy-consuming branch. The circuit breaker control and protection device determines whether the total current of the circuit breaker, the main branch current, and the transfer branch current are overcurrent, and uses the three-out-of-two logic to draw the final conclusion as the basis for overcurrent protection.

[0064] The control device of the hybrid DC circuit breaker provided in the embodiment of the present invention samples the current respectively through three sets of independent current merging units, integrates the protection judgment and three-out-of-two functions into the control device, reduces the equipment links, reduces the communication delay, improves the protection response speed, and obtains a higher accuracy of the judgment result. At the same time, cross-communication is performed by redundantly setting the control device, thereby improving reliability.

[0065] Example 3

[0066] An embodiment of the present invention provides a control and protection method for a hybrid DC circuit breaker. Based on the hybrid DC circuit breaker control and protection device in Example 2, the hybrid DC circuit breaker is controlled and protected in the closing state, the opening state, the opening process and the closing process.

[0067] The control and protection process of the hybrid DC circuit breaker in the closed state according to the embodiment of the present invention is as follows: Figure 6 As shown, the following steps are included:

[0068] Step S11: The control module controls the main branch and the transfer branch to be in a conducting state through the communication module;

[0069] Step S12: The control module detects in real time whether there are faults in the components of the transfer branch and the main branch;

[0070] Step S13: when it is detected that there is a fault in the components of the transfer branch and the main branch, the circuit breaker is prohibited from opening;

[0071] Step S14: when it is detected that there is no fault in the components of the transfer branch and the main branch and the opening operation cannot be completed, the circuit breaker is prohibited from opening, otherwise it is determined according to the three-out-of-two logic module whether the line current is greater than the preset current;

[0072] Step S15: When the line current is not greater than the preset current, the circuit breaker is allowed to close;

[0073] Step S16: According to the fast or slow trip instruction issued by the converter station control protection, the circuit breaker is subjected to a fast trip process or a slow trip process.

[0074] In a specific embodiment, if Figure 7As shown, the mechanical switch and commutation components of the main branch are both in the on state. After the transfer branch is in the on state, firstly detect whether the semiconductor devices of the transfer branch and the commutation component have faults such as abnormal opening and detect whether the mechanical switch has the conditions for opening. When there is no fault, the three-out-of-two logic module determines whether the line current is greater than the preset current I 3 Specifically, the protection judgment module judges whether the sampling values ​​of the three sets of line current sensors are greater than I 3 , and then the three-out-of-two logic module uses three-out-of-two logic for the three judgment results, that is, if two or more sampling values ​​are greater than I 3 If it is greater than I 3 The switch is allowed to open only when the device fails or is less than I 3 When the switch is closed, it is forbidden to close the switch. Under the conditions of permission and closing, the fast or slow opening process is entered according to the fast or slow opening instruction issued by the converter station control protection.

[0075] In the embodiment of the present invention, in order to prevent the DC circuit breaker from breaking the current exceeding its breaking capacity and causing damage to the equipment, the current I is preset 3 Set according to the breaking capacity of the transfer branch, I 3 The calculation method is as follows:

[0076]

[0077] Among them, I 4 is the maximum current that the circuit breaker transfer branch can break, t open is the breaking time of the circuit breaker, is the maximum fault current rise rate of the DC system, I mar is the current margin (which may be 1.5 kA, but this is only an example and is not intended to be limiting).

[0078] In the embodiment of the present invention, when the DC circuit breaker is in the closed state, when the communication module of the circuit breaker control and protection device receives the circuit breaker slow opening instruction (non-emergency stop operation from the operator) from the converter station control and protection device and the circuit breaker is not prohibited from opening, the control module of the circuit breaker control and protection device executes the circuit breaker slow opening process; when the communication module of the circuit breaker control and protection device receives the circuit breaker fast opening instruction (non-emergency stop operation from the operator) from the converter station control and protection device and the circuit breaker is not prohibited from opening, the control module of the circuit breaker control and protection device executes the circuit breaker fast opening process. The circuit breaker fast opening process and the circuit breaker slow opening process both belong to the devices in the opening process of the circuit breaker, the difference is that in the slow opening process, the opening instruction sent by the circuit breaker control and protection device to the mechanical switch is a slow opening instruction, and in the fast opening process, the opening instruction sent by the circuit breaker control and protection device to the mechanical switch is a fast opening instruction.

[0079] The control protection process of the hybrid DC circuit breaker during the opening process of the embodiment of the present invention is as follows: Figure 8 As shown, the following steps are included: when the control module executes a fast or slow separation process on the circuit breaker, the communication module sends an instruction to shut down the main branch commutation component; after a preset waiting time, the mechanical switch slow or fast separation instruction is sent; when the communication module detects that the displacement of the mechanical switch reaches a withstand voltage position or the transfer branch is overcurrent, the control module sends an instruction to shut down the transfer branch and turn on the main branch commutation component; it is determined whether the uneven flow between the two groups of lightning arresters of each valve section of the energy-consuming branch exceeds a preset threshold; when the threshold is exceeded, it is considered that the lightning arrester of the valve section is broken down and closing is prohibited; when the preset threshold is not exceeded, the opening is completed.

[0080] In the embodiment of the present invention, the first stage of the opening is from shutting off the main branch to issuing the mechanical switch opening command, and the second stage of the opening is from issuing the mechanical switch opening command to shutting off the transfer command. In the first stage of the opening, if the mechanical switch fault is detected to be super redundant, the main branch commutation component is turned on and the closing state is returned.

[0081] In the embodiment of the present invention, the preset waiting time t 1 The control module of the circuit breaker control protection device calculates the current in the main branch and the equivalent circuit parameters of the main branch and the transfer branch in real time. Depending on whether there is a module with a semiconductor device failure and an open circuit in the transfer branch, two situations are handled:

[0082] The first case: If there is no module in the transfer branch that cannot pass current due to a fault at this stage, the semiconductor devices of the main branch and the transfer branch are equivalent to a voltage source and a resistor in series. The equivalent circuit of the main branch and the transfer branch is as follows: Fig. 9 As shown, according to the circuit principle:

[0083]

[0084] Among them, i line ,i m ,i t are the line, main branch and transfer branch currents respectively. m It is the overall equivalent resistance of the main branch after the commutation component is turned off, including the overall equivalent resistance of the semiconductor devices in the commutation component and the on-resistance of the mechanical switch. m The equivalent inductance of the main branch is mainly the stray inductance of the main branch wiring. m is the overall equivalent voltage source of the semiconductor components in the commutation component. C m It is the equivalent capacitance of the main branch after the commutation component is turned off. Its capacitance is calculated based on the capacitance of the main branch submodule and the series-parallel relationship of the main branch submodule, and the submodule of the fault bypass is removed. t is the total equivalent resistance of the transfer branch semiconductor components. t It is the equivalent inductance of the transfer branch, mainly the stray inductance of the transfer branch wiring.t is the overall equivalent voltage source of the semiconductor components of the transfer branch. To simplify the calculation, the line current i is ignored during the commutation process. line Change, according to the constant value I line Calculation can solve the main branch current i m The time t required to become 0 0 .

[0085] Main branch current i m The time t required to become 0 0 The calculation method can also be simplified as:

[0086]

[0087] Waiting time t 1 Use the following formula to calculate:

[0088] t 1 =t 0 -t sam -t swd -t comm +t mar

[0089] Among them, t sam is the sampling delay (including sampling communication delay), t swd It is the delay from the switch receiving the command to the break opening, t comm is the communication delay from the circuit breaker control protection to the mechanical switch command, t mar is the waiting time margin (e.g. 100μs). 1 If it is less than or equal to 0, the mechanical switch opening command is directly issued.

[0090] The second case: If there is a module in the transfer branch that cannot flow due to a fault and the breakdown voltage of the transfer branch fault is still lower than the breakdown voltage of the main branch commutation module, the equivalent circuit of the main branch and transfer branch commutation is as follows: Fig.10 As shown, according to the circuit principle:

[0091]

[0092] Among them, C t is the series equivalent capacitance of the fault open module of the transfer branch semiconductor device. Ignore the line current change during the commutation process. The transfer branch current is 0 at the beginning of commutation. Solve for the voltage V of the fault open module of the transfer branch. ct The time required to reach the device breakdown voltage is t z The device breakdown voltage can be obtained from the semiconductor device data sheet and the number of failed modules.

[0093] Transfer branch fault open circuit module total voltage vct Reaching the breakdown voltage V z The time required t z The calculation method can also be simplified as:

[0094]

[0095] Waiting time t 1 Use the following formula to calculate:

[0096]

[0097] After the control module issues a mechanical switch opening command through the communication module, the control module determines the switch position signal in real time, and disconnects the transfer branch through the communication module when the mechanical switch displacement meets the insulation withstand voltage requirements or the transfer branch is overcurrent. When disconnecting the transfer branch, the communication module detects that the mechanical switch displacement reaches the withstand voltage position or the transfer branch is overcurrent. If the transfer branch has a valve section with redundant fault modules, all modules in the valve section are delayed to shut down, and the delay time should be greater than the falling time of the DC system fault current after the DC circuit breaker is disconnected. (For example, 100ms) to avoid the overall overvoltage breakdown of the redundant fault valve section.

[0098] After the control module locks the transfer branch, the protection judgment module uses the sampling values ​​of the three sets of sensors to calculate the current deviation ratio of the energy-consuming branch:

[0099] The current deviation proportion P of the xth energy-consuming branch calculated by the A set of sensors xa =|i dxa / i da -0.5|;

[0100] The current deviation proportion P of the xth energy-consuming branch calculated by the B set of sensors xb =|i dxb / i db -0.5|;

[0101] The current deviation proportion P of the xth energy-consuming branch calculated by the B set of sensors xc =|i dxc / i dc -0.5|;(x=1,2...n)

[0102] The protection judgment module judges P xa , P xb , P xc Whether it exceeds the fixed value m, the three-out-of-two logic module is xa , P xb , P xcPerform two-out-of-three logical judgment, that is, if two or more judgment results are exceeded, it is considered that the lightning arrester of the valve section of the x-th energy-consuming branch is broken down, and further closing operations are prohibited; if all valve sections of the circuit breaker energy-consuming branch do not exceed the threshold, the disconnection process ends, and the constant m is set according to the normal current sharing of the lightning arrester product, for example, it can be 0.3.

[0103] In the embodiment of the present invention, the control and protection process of the hybrid DC circuit breaker under the split state includes: Fig.11 Follow these steps:

[0104] Step S31: The control module uses the communication module to make the mechanical switch of the main branch in the disconnected state, the commutation component in the on state, and the transfer branch in the disconnected state;

[0105] Step S32: The control module detects the component status of the main branch and the transfer branch in real time. When the main branch or the transfer branch fails and causes the circuit breaker to be unable to complete the closing operation, or can complete the closing operation but can no longer be opened after closing, the circuit breaker is prohibited from closing.

[0106] When the communication module of the circuit breaker control protection device in the embodiment of the present invention receives the circuit breaker closing instruction of the converter station control protection device and the circuit breaker is not prohibited from closing, the control module of the circuit breaker control protection device executes the circuit breaker closing process. When executing the closing process, the circuit breaker state is in the closing process.

[0107] The control protection process of the hybrid DC circuit breaker during the closing process of the embodiment of the present invention is as follows: Fig.12 As shown, the method comprises the following steps: when executing the closing process, the control module sends an instruction through the communication module to open the transfer branch and start timing; when the preset timing time T is reached, 5 Previously, if the circuit breaker device fails, or the line current collected by the current acquisition module is judged by the protection judgment module and processed by the three-out-of-two logic module, it is determined that it exceeds the overcurrent setting value I 5 , the transfer branch is shut down through the communication module, the closing process is terminated, and the switch returns to the open state; if there is no equipment failure or line overcurrent when the preset timing time is reached, the mechanical switch closing command is issued through the communication module, and all mechanical switches are disconnected within the preset time T 6 After all the reports are closed, the closing is completed; within the preset time T 6 If the internal mechanical switch has not returned to the closed state, the DC circuit breaker will be disconnected according to the opening sequence and return to the open state.

[0108] In the embodiment of the present invention, the timing time T 5 After the DC line ground fault, the overcurrent setting value I 5 The maximum time setting of overcurrent setting is 1ms. 5It should be greater than the rated operating current of the DC system and less than the maximum withstand current of the converted DC. To reduce the stress of the equipment under DC fault conditions, this value can be set to be slightly higher than the rated operating current. Waiting time T 6 It is set according to the longest closing time of the mechanical switch and a certain margin (e.g. 2ms) is taken into account. The overcurrent setting is greater than the rated operating current of the DC system and less than the maximum withstand current of the transfer branch.

[0109] In the embodiment of the present invention, during the closing process, the transfer branch is first turned on in order to utilize the flexible on-off characteristics of semiconductor devices to test whether there are faults in the DC system and the circuit breaker equipment. If there is a fault, it can immediately return to the open state to avoid the DC circuit breaker being put into operation with a fault, or the fault current causing an impact on primary equipment such as the converter valve.

[0110] The control and protection logic of the hybrid DC circuit breaker in the split state and the closed state, as well as the closing and opening operation processes are all implemented in the circuit breaker control and protection device. The main branch current i m The time t required to become 0 0 and the transfer branch fault open circuit module voltage v ct The time required to reach the device breakdown voltage is t z Can be completed offline to simplify the procedure and shorten the program running time.

[0111] The control and protection method of the hybrid DC circuit breaker provided by the embodiment of the present invention shortens the state judgment time in the breaking process by using the fast breaking control method. During the breaking process of the circuit breaker, the commutation detection and waiting time are shortened by prejudging the zero point of the main branch current. Since the damage of the semiconductor devices of the main branch and the transfer branch is considered in the zero-crossing prejudgment, it has a wider applicability. By adding an intermediate position sensor, it is quickly judged whether the mechanical switch has reached the opening distance that meets the insulation requirements during the mechanical switch breaking process, and the opening time is shortened under the premise of ensuring the safety of the equipment. By specially setting the main branch commutation component and the transfer branch state of the DC circuit breaker in the closed state and the split state, the module fault can be quickly discovered and the mechanical switch breakdown can be avoided to cause the damage of the main branch commutation component module; the fast and slow separation control logics are set to improve the life of the mechanical switch. The valve section of the transfer branch fault is delayed to close, avoiding the overvoltage breakdown of a large number of devices. By grouping the arrester current, the rapid detection of the arrester breakdown fault is realized. In the closed state, the line current is detected and overcurrent protection is implemented to prevent the circuit breaker from breaking currents that exceed its breaking capacity, thereby avoiding damage to the equipment. During the closing process, the DC system current and circuit breaker equipment faults are judged in real time to prevent the DC circuit breaker from being put into operation with a fault, or the fault current from impacting primary equipment such as the converter valve.

[0112] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A control and protection method for a hybrid DC circuit breaker, characterized in that: Based on the hybrid DC circuit breaker control and protection device, the hybrid DC circuit breaker is controlled and protected in the closing state, the opening state, the opening process and the closing process. The hybrid DC circuit breaker control and protection device includes: three independent merging units, a control and protection host and an interface unit. Three independent merging units are used to collect the line current, main branch current, transfer branch current, energy consumption branch total current and energy consumption branch current of the total outgoing line at one end of the hybrid DC circuit breaker; The control and protection host is a redundant setting, one set of devices is on duty and the other set of devices is in standby state. The control and protection host cross-communicates with the mechanical switch controller, which includes: a communication module, a control module, a protection judgment module, and a three-out-of-two logic module, wherein: The communication module is used to realize communication with the main branch, transfer branch, converter station control equipment, and converter station protection equipment; the protection judgment module performs overcurrent judgment of the hybrid DC circuit breaker according to the current of the three independent merging units; the three-out-of-two logic module is used to perform three-out-of-two logic judgment of overcurrent according to the judgment result of the protection judgment module; the control module realizes the hybrid DC circuit breaker opening and closing timing and DC circuit breaker equipment fault judgment; the control module sends the control protection instruction to the main branch commutation component and the transfer branch semiconductor component of the hybrid DC circuit breaker through the communication module and the interface unit; The control and protection process of the hybrid DC circuit breaker in the closed state includes the following steps: The control module controls the main branch and the transfer branch through the communication module to be in the on state. The control module detects in real time whether there are faults in the components of the transfer branch and the main branch; When it is detected that the components of the transfer branch and the main branch are faulty and the opening operation cannot be completed, the circuit breaker is prohibited from opening. Otherwise, the three-out-of-two logic module determines whether the line current is greater than the preset current; When the line current is not greater than the preset current, the circuit breaker is allowed to close; According to the fast or slow opening instructions issued by the converter station control protection, the circuit breaker is subjected to the fast opening process or the slow opening process.

2. The control and protection method of the hybrid DC circuit breaker according to claim 1, characterized in that: The preset current is set according to the breaking capacity of the transfer branch and is calculated by the following formula: Among them, I3 is the preset current, I4 is the maximum current that the circuit breaker transfer branch can break, t open is the breaking time of the circuit breaker, is the maximum fault current rise rate of the DC system, I mar is the current margin.

3. The control and protection method of a hybrid DC circuit breaker according to claim 1, characterized in that: The control and protection process during the hybrid DC circuit breaker opening process includes the following steps: When the control module executes the fast or slow separation process on the circuit breaker, it sends instructions through the communication module to shut down the main branch commutation component; After a preset waiting time, a slow or fast opening instruction of the mechanical switch is issued; When the communication module detects that the displacement of the mechanical switch reaches the withstand voltage position or the transfer branch is overcurrent, the control module sends a command to shut down the transfer branch and turn on the main branch commutation component; Determine whether the degree of uneven current between two groups of lightning arresters in each valve section of the energy consumption branch exceeds a preset threshold; When the threshold is exceeded, the arrester of the valve section is considered to be broken down and closing is prohibited; When the preset threshold is not exceeded, the circuit breaker is opened.

4. The control and protection method of the hybrid DC circuit breaker according to claim 3, characterized in that: The preset waiting time is calculated by the control module in real time according to the main branch current, the main branch and the transfer branch equivalent circuit parameters. When the transfer branch has no module that cannot pass current due to a fault, the preset time t1 is calculated by the following formula: t1=t0-t sam -t swd -t comm +t mar Among them, t0 is the time required for the main branch current to become 0, t sam is the sampling delay, t swd The delay from when the switch receives the command to when the break occurs, t comm is the communication delay from the circuit breaker control protection to the mechanical switch command, t mar is the waiting time margin; When there is a module in the transfer branch that cannot flow due to a fault and the breakdown voltage of the transfer branch fault is lower than the breakdown voltage of the main branch commutation module, the preset time t1 is calculated by the following formula: t1=t z -t sam -t swd -t comm +t mar Among them, t z The time required for the total voltage of the transfer branch fault open module to reach the breakdown voltage, t sam is the sampling delay, t swd It is the delay from the switch receiving the command to the break opening, t comm is the communication delay from the circuit breaker control protection to the mechanical switch command, t mar is the waiting time margin.

5. The control and protection method of the hybrid DC circuit breaker according to claim 3, characterized in that: When the communication module detects that the displacement of the mechanical switch reaches the withstand voltage position or the transfer branch is overcurrent, if the transfer branch has a valve section with an excess redundant number of faulty modules, all modules in the valve section will be delayed in shutting down. The delay time should be greater than the falling time of the DC system fault current after the DC circuit breaker is disconnected.

6. The control and protection method of a hybrid DC circuit breaker according to claim 3, characterized in that: The step of determining whether the degree of current inequality between the two groups of arresters exceeds a preset threshold comprises: The protection judgment module obtains the sampling values ​​of the three sets of sensors respectively to calculate the current deviation ratio of the energy-consuming branch, and judges whether the three calculated current deviation ratios exceed the preset threshold value. The three-out-of-two logic module performs a three-out-of-two logic judgment on it. If two or more judgment results are exceeded, it is determined that the lightning arrester of the valve section of the energy-consuming branch is broken down, and the closing operation is prohibited. If all valve sections of the energy-consuming branch of the circuit breaker do not exceed the preset threshold value, the disconnection process ends.

7. The control and protection method of a hybrid DC circuit breaker according to claim 1, characterized in that: The control and protection process of the hybrid DC circuit breaker under split state includes the following steps: The control module uses the communication module to make the mechanical switch of the main branch in the disconnected state, the commutation component in the on state, and the transfer branch in the disconnected state; The control module detects the component status of the main branch and the transfer branch in real time. When the main branch or the transfer branch fails and the circuit breaker cannot complete the closing operation, or the closing operation can be completed but the circuit breaker can no longer be opened after closing, the circuit breaker is prohibited from closing.

8. The control and protection method of a hybrid DC circuit breaker according to claim 1, characterized in that: The control and protection process during the hybrid DC circuit breaker closing process includes the following steps: When executing the closing process, the control module sends a command through the communication module to open the transfer branch and start timing; Before the preset timing time is reached, if the circuit breaker device fails, or the line current collected by the current acquisition module is judged by the protection judgment module and processed by the three-out-of-two logic module to exceed the overcurrent setting value, the transfer branch is shut down through the communication module, the closing process is terminated, and the circuit breaker returns to the opening state; If there is no equipment failure or line overcurrent when the preset timing time is reached, the communication module will send a command to close the mechanical switch. After all the breaks of the mechanical switch return to the closed state within the preset time, the closing is completed; If a mechanical switch does not return to the closed state within the preset time, the DC circuit breaker is disconnected according to the opening sequence and returns to the open state.

9. The control and protection method of the hybrid DC circuit breaker according to claim 8, characterized in that: The preset timing time is set according to the time it takes to reach the overcurrent set value after a DC line ground fault occurs.

10. The control and protection method of a hybrid DC circuit breaker according to claim 8, characterized in that: The preset time is set according to the longest closing time of the mechanical switch.

11. The control and protection method for a hybrid DC circuit breaker according to claim 8, wherein the overcurrent setting is greater than the rated operating current of the DC system and less than the maximum withstand current of the transfer branch.

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