GB2566123A - Method for performing a trip when the number of times for a flexible DC control system is temporarily locked and then unlocked again exceeds a threshold. - Google Patents
Method for performing a trip when the number of times for a flexible DC control system is temporarily locked and then unlocked again exceeds a threshold. Download PDFInfo
- Publication number
- GB2566123A GB2566123A GB1719220.4A GB201719220A GB2566123A GB 2566123 A GB2566123 A GB 2566123A GB 201719220 A GB201719220 A GB 201719220A GB 2566123 A GB2566123 A GB 2566123A
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- control system
- valve
- flexible
- bridge arm
- converter valve
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- 238000000034 method Methods 0.000 title claims abstract description 33
- 230000001960 triggered effect Effects 0.000 claims abstract description 6
- 230000008569 process Effects 0.000 claims abstract description 3
- 230000005540 biological transmission Effects 0.000 claims description 14
- 230000008859 change Effects 0.000 claims description 12
- 230000002238 attenuated effect Effects 0.000 abstract 1
- 238000005516 engineering process Methods 0.000 description 4
- 238000012544 monitoring process Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 239000013307 optical fiber Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 230000007257 malfunction Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000006855 networking Effects 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/02—Details
- H02H3/06—Details with automatic reconnection
- H02H3/07—Details with automatic reconnection and with permanent disconnection after a predetermined number of reconnection cycles
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
- H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
- H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
- H02H7/122—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for inverters, i.e. DC/AC converters
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Inverter Devices (AREA)
- Rectifiers (AREA)
Abstract
A method for performing a trip, when the number of times that a flexible DC control system is temporarily locked and then unlocked again exceeds a threshold. When a short-time fault occurs to the grid side AC system of an interconnection transformer, after a valve control system determines that the current of a bridge arm is in an over-current state, the valve control system is triggered to be locked temporarily, and a pole control system is notified to be locked. When the current of the bridge arm is gradually attenuated, the temporary lock state disappears, and the pole control system is unlocked again after a fixed time. When a serious fault occurs to the grid side of the interconnection transformer, the valve control system and the pole control system may repeat the process of temporarily locking and unlocking. When the number of times for locking and unlocking exceeds a threshold, the pole control system implements the locking and tripping operation. The method not only improves the traversal success rate of the flexible DC control system during an AC fault, but also protects the flexible DC converter valve which is primary equipment.
Description
DESCRIPTION
Tripping method applicable to situation that number of unlocking times exceeds limit since flexible DC control system has been temporarily locked
TECHNICAL FIELD
The present invention belongs to the technical field of electric and electronic control, particularly relates to a tripping method applicable to the situation that the number of unlocking times exceeds a limit after a flexible DC control system is temporarily locked.
BACKGROUND
A flexible DC converter valve technology based on a modular multilevel converter (MMC, hereafter referred to MMC) is mainly applied to new energy power generation system networking, asynchronous power grid connection, and the like, with the advantages that it can be independently adjusted with active power and reactive power, with no need of large-capacity reactive compensation and filter, commutation failure will not occur, and a receiving end can be connected to a passive system, etc.
A flexible DC power transmission system generally adopts the modular multilevel converter as its primary device. The MMC consists of 6 arms (hereinafter referred to as converter valve arms in the present application), and each arm is formed by connecting one reactor L and N submodules (SM) in series. With high modularization, MMC circuits can meet different requirements for power and voltage levels by increasing and decreasing the number of submodules connected to the converter, which is beneficial to fulfilling the integrated design, shortening the project cycle and saving the cost.
When an AC fault occurs in the flexible DC power transmission system at a connected transformer grid side, because a control system is delayed in sampling and communication and an internal link of a control device has delay, under the rated power operation, the fault occurs at the connected transformer grid side, which is easy to cause the overcurrent of the converter valve arms. At present, the industry generally tends to make the converter valve locked and carry out a tripping operation directly after the overcurrent of arms, to isolate the converter valve from the
AC system to protect converter valve equipment. By this method, the ride-through rate that the flexible DC transmission technology deals with the AC system fault is decreased, and the flexible DC transmission technology based on MMC cannot be fully brought into play.
SUMMARY
This invention aims to provide a tripping method applicable to the situation that the number of unlocking times exceeds a limit after a flexible DC control system is temporarily locked, which not only can improve the fault ride-through function of the flexible DC transmission technology based on MMC, but also can reliably protect converter valve equipment.
The present invention specifically adopts the following technical solution:
A tripping method applicable to the situation that the number of unlocking times exceeds a limit after a flexible DC control system is temporarily locked, a flexible DC power transmission system implementing the method based on a modular multilevel converter, wherein after a pole control system determines that a short-time fault occurs in an AC system at a connected transformer grid side, a valve control system determines whether bridge arm current is greater than a set protection value of converter valve equipment or not; if the bridge arm current is greater than the set protection value, the valve control system is triggered to lock temporarily and the pole control system is notified to lock; after the valve control system and the pole control system are locked, the temporary locking state of the valve control system disappears when the bridge arm current gradually weakens to be lower than the set protection value of the converter valve equipment; after the valve control system is unlocked, the pole control system is allowed to unlock again after a set delay and provide reactive power for the AC system through a converter valve; and when the valve control system and the pole control system repeat the process of temporary locking and unlocking and the number of unlocking and locking times exceeds the limit because a fault occurs in the AC system at the connected transformer grid side, the pole control system fulfills the locking and tripping function.
A tripping method applicable to the situation that the number of unlocking times exceeds a limit after a flexible DC control system is temporarily locked, a flexible DC power transmission system implementing the method based on a modular multilevel converter, wherein, when a fault occurs in an AC system at a connected transformer grid side, and bridge arm current of a converter valve is greater than a set overcurrent threshold, i.e. a set protection value of converter valve equipment, a valve control system is triggered to lock temporarily and the pole control system is notified to lock after the valve control system is locked; and when the fault at the connected transformer grid side disappears or the bridge arm current is lower than the set overcurrent threshold, the valve control system and the pole control system are unlocked successively; wherein, the tripping method applicable to the situation that the number of unlocking times exceeds the limit after the flexible DC control system is temporarily locked comprises the following steps:
Step 1: determining whether the converter valve is in an unlocked state or not, if the converter valve is in the unlocked state, proceeding to Step 2, or otherwise repeating Step 1;
Step 2: collecting AC voltage at the connected transformer grid side;
Step 3: determining whether the change of the AC voltage at the connected transformer grid side exceeds a set AC voltage threshold range or the change rate is higher than a set change rate threshold or not; if so, proceeding to Step 4, or otherwise returning to Step 2;
Step 4: collecting, by the valve control system, the bridge arm current of the converter valve in real time and determining whether the bridge arm current of the converter valve is greater than the set protection value of the converter valve equipment or not; if so, allowing the valve control system to lock and notifying the pole control system to lock, then proceeding to Step 5, or otherwise returning to Step 2;
Step 5: collecting, by the valve control system, the current bridge arm current of the converter valve in real time and determining whether the bridge arm current of the converter valve weakens to the set protection value of the converter valve equipment or not; if so, proceeding to Step 6, or otherwise repeating Step 5;
Step 6: if a temporary locking signal of the valve control system disappears, unlocking the valve control system and notifying the pole control system to unlock after a set delay T;
Step 7: counting up the number of times the flexible DC control system completes temporary locking and unlocking circles during the fault occurring at the connected transformer grid side; if the number exceeds a set limit, proceeding to Step 8, or otherwise returning to step 1; and
Step 8: fulfilling the locking and tripping function by the pole control system, so as to open circuit breakers at both sides connected to the transformer.
The present invention further comprises the following preferred solutions:
in Step 3, the AC voltage threshold range is 0.8Upu-1.2Upu; and the AC voltage change threshold is 0.01Upu/5ms-0.05Upu/5ms, where lUpu indicates a rated AC voltage.
4. The tripping method applicable to the situation that the number of unlocking times exceeds the limit after the flexible DC control system is temporarily locked according to claim 2, wherein in Step 4, the range of the set overcurrent protection value of the bridge arm current of converter valve equipment, i.e. an overcurrent threshold, is 1.15Ipu-1.5Ipu, where llpu indicates IGBT rated operating current.
5. The tripping method applicable to the situation that the number of unlocking times exceeds the limit after the flexible DC control system is temporarily locked according to claim 2, wherein in Step 5, the range of a defined reset value of the bridge arm current of converter valve equipment, i.e. reset threshold, is 30A-60A.
6. The tripping method applicable to the situation that the number of unlocking times exceeds the limit after the flexible DC control system is temporarily locked according to claim 2, wherein in Step 6, the set time T is 15ms.
7. The tripping method applicable to the situation that the number of unlocking times exceeds the limit after the flexible DC control system is temporarily locked according to claim 2, wherein
In Step 7, the set limit of times the flexible DC control system completes temporary locking and unlocking circles during the fault occurring at the connected transformer grid side is 2-5.
The present invention has the following beneficial effects:
The fault ride-through success rate of the converter valve based on MMC in the case that the AC system connected to the transformer malfunctions can be improved, and the availability of the converter valve can also be enhanced.
DESCRIPTION OF DRAWINGS
FIG. 1 is the structural schematic diagram of the flexible DC power transmission system apparatus according to the present invention;
FIG. 2 is the flow diagram of the tripping method applicable to the situation that the number of unlocking times exceeds a limit after a flexible DC control system is temporarily locked according to the present invention; and
FIG. 3 is the corresponding connection relationship diagram of a monitoring system, a pole control system, a protection system and a valve control system.
DETAILED DESCRIPTION
The technical solution and the control advantages of the present invention will be more clear from the following detailed description of the present invention in combination with the drawings.
In order to facilitate readers to understand the technical solution of the present invention, the technical terms related to the solution of this application are explained as follows:
In the flexible DC transmission system, a DC control protection system and a converter valve are the core equipment for implementing AC/DC conversion. Similar to the traditional DC, the DC control protection system controls the converter valve through a valve control system.
The flexible DC power transmission system is a complex multiple-input and multiple-output system. In order to improve its operation reliability, the control protection system is divided into three layers according to the principle of hierarchical design, which are a monitoring layer, a pole control system and pole protection layer, and an I/O layer (including a valve control system, see FIG.3). The pole control system and the protection system adopt the method of point-to-point connection via an optical fiber, the pole control system and the valve control system also adopt the method of point-to-point connection via an optical fiber, and the valve control system drives the SM of a converter valve to actuate. The tripping function in the situation that temporary locking exceeds the limit, described in this document, is mainly applicable to the pole control system and the valve control system.
Monitoring layer, fulfilling the functions of: starting and stopping control, sequence control for DC units within a station; and control, monitoring, measurement, alarm, recording, remote transmission, setting of parameters/fixed values for all the circuit breakers, isolation switches and other devices throughout the station; and connecting control and protection devices at different levels together via a redundant computer network.
Pole control system, i.e. converter control, which mainly fulfills such the functions as active power control, reactive power control, DC voltage control, inner current circuit control, modulation voltage production, etc.
Valve control system, which mainly fulfils the functions of bridge arm current circuit suppressing and control, MMC module triggering, lowest level approximation control, etc.
MMC: Modular Multilevel Converter
The introduction made in the embodiments of the present invention is based on the topological structure that the main circuit which adopts a connecting transformer and a modular multilevel converter (see FIG.1). The flexible DC transmission system includes a connected transformer 1, a charging resistance 2, a bridge arm reactor 3, and a cascaded MMC submodule 4, which are connected via an A/B/C three-phase cable to form an electrical connection system.
Operating parameters include voltage of connected transformer grid side 5, current of connected transformer valve side 6, current of start circuit 7, upper bridge arm current of converter valve 8, lower bridge arm current of converter valve 9, positive current 10, and negative current 11.
A tripping method applicable to the situation that the number of unlocking times exceeds a limit after a flexible DC control system is temporarily locked, as shown in FIG. 2, includes the following steps:
Step 1: determining whether a converter valve is in an unlocked state or not, if so, proceeding to Step 2, or otherwise repeating Step 1;
Step 2: collecting AC voltage at the connected transformer grid side;
Step 3: determining whether the change of the AC voltage at the connected transformer grid side exceeds the set AC voltage threshold range or the change rate is higher than the set change rate threshold or not; if so, proceeding to Step 4, or otherwise returning to Step 2, wherein the AC voltage threshold range is 0.8Upu-1.2pUu; and the AC voltage change threshold is 0.01Upu/5ms-0.05Upu/5ms, where lUpu indicates a rated AC voltage;
Step 4: collecting, by the valve control system, the bridge arm current of a converter valve in real time and determining whether the bridge arm current of the converter valve is greater than the set protection value of converter valve equipment or not; if so, allowing the valve control system to temporarily lock and notifying the pole control system to lock, then proceeding to Step 5, or otherwise returning to Step 2, wherein the range of the set overcurrent protection value of the bridge arm current of converter valve equipment, i.e. an overcurrent threshold, is 1.15Ipu-1.5Ipu, where llpu indicates IGBT rated operating current; if it is beyond the range, the valve control system will determine to start temporary locking;
Step 5: collecting, by the valve control system, the bridge arm current of the converter valve in real time and determining whether the bridge arm current of the converter valve weakens to a defined reset value of the converter valve equipment or not; if so, proceeding to Step 6, or otherwise returning to Step 5, wherein the range of a defined reset value of the bridge arm current of converter valve equipment,
i.e. reset threshold of current, is 30A-60A;
Step 6: recording, by the pole control system, the number of times of transmitting a temporary locking signal by the valve control system, and locking the converter valve; and moreover, transmitting an unlocking command again after a T delay and proceeding to Step 7, wherein the set time T is 15ms;
Step 7: If the pole control system determines that the number of times of temporary locking triggered by the valve control system in a continuous AC system fault exceeds n, proceeding to Step 8, or otherwise returning to Step 1, wherein the set limit of temporary locking and unlocking circles the flexible DC control system completes during a fault occurring at the connected transformer grid side is 2-5; and
Step 8: allowing the pole control system to open circuit breakers to isolate the AC system from the MMC.
Although the embodiments of the present invention are illustrated and described in detail in combination with the drawings of description, those skilled in the art should understand that the above embodiments are only the preferred embodiments of the present invention. The detailed description is intended to help readers better understand the spirit of the present invention, rather than limiting the protection scope of the present invention. On the contrary, any improvement or modification made based on the inventive spirit of the present invention should fall within the protection scope of the present invention.
Claims (7)
1. A tripping method applicable to a situation that the number of unlocking times exceeds a limit since a flexible DC control system has been temporarily locked, a flexible DC power transmission system implementing the method based on a modular multilevel converter, wherein after a pole control system determines that a short-time fault occurs in an AC system at a connected transformer grid side, a valve control system determines whether bridge arm current is greater than a set protection value of converter valve equipment or not; if the bridge arm current is greater than the set protection value, the valve control system is triggered to lock temporarily and the pole control system is notified to lock; after the valve control system and the pole control system are locked, the temporary locking state of the valve control system disappears when the bridge arm current gradually weakens to be lower than the set protection value of the converter valve equipment; after the valve control system is unlocked, the pole control system is allowed to unlock again after a set delay and provide reactive power for the AC system through a converter valve; and when the valve control system and the pole control system repeat the process of temporary locking and unlocking due to a fault occurring in the AC system at the connected transformer grid side and the number of unlocking and locking times exceeds the limit, the pole control system fulfills locking and tripping function.
2. A tripping method applicable to a situation that the number of unlocking times exceeds a limit since a flexible DC control system has been temporarily locked, a flexible DC power transmission system implementing the method based on a modular multilevel converter, wherein, when a fault occurs in an AC system at a connected transformer grid side, and bridge arm current of a converter valve is greater than a set overcurrent threshold, i.e. a set protection value of converter valve equipment, a valve control system is triggered to lock temporarily and the pole control system is notified to lock after the valve control system is locked; and when the fault at the connected transformer grid side disappears or the bridge arm current is lower than the set overcurrent threshold, the valve control system and the pole control system are unlocked successively; wherein, the tripping method comprises the following steps:
step 1: determining whether the converter valve is in an unlocked state or not, if the converter valve is in the unlocked state, proceeding to step 2, or otherwise repeating step 1;
step 2: collecting AC voltage at the connected transformer grid side;
step 3: determining whether the change of the AC voltage exceeds a set AC voltage threshold range or the change rate is higher than a set change rate threshold or not; if so, proceeding to step 4, or otherwise returning to step 2;
step 4: collecting, by the valve control system, the bridge arm current of the converter valve in real time and determining whether the bridge arm current of the converter valve is greater than the set protection value of the converter valve equipment or not; if so, making the valve control system locked temporarily and notifying the pole control system to lock, then proceeding to step 5, or otherwise returning to step 2;
step 5: collecting, by the valve control system, the current bridge arm current of the converter valve in real time and determining whether the bridge arm current of the converter valve weakens to the set protection value of the converter valve equipment or not; if so, proceeding to step 6, or otherwise repeating step 5;
step 6: if a temporary locking signal of the valve control system disappears, unlocking the valve control system and notifying the pole control system to unlock after a set delay T;
step 7: counting up the number of times the flexible DC control system completes temporary locking and unlocking circles during the fault occurring at the connected transformer grid side; if the number exceeds a set limit, proceeding to step 8, or otherwise returning to step 1; and step 8: fulfilling the locking and tripping function by the pole control system, so as to open circuit breakers at both sides of the connected transformer.
3. The tripping method applicable to a situation that the number of unlocking times exceeds the limit since the flexible DC control system has been temporarily locked according to claim 2, wherein in step 3, the AC voltage threshold range is 0.8Upu-1.2Upu; and the AC voltage change threshold is 0.01Upu/5ms-0.05Upu/5ms, where lUpu represents a rated AC voltage.
4. The tripping method applicable to a situation that the number of unlocking times exceeds the limit since the flexible DC control system has been temporarily locked according to claim 2, wherein io in step 4, the range of the set overcurrent protection value of the bridge arm current of converter valve equipment, i.e. an overcurrent threshold, is 1.15Ipu-1.5Ipu, where llpu represents IGBT rated operating current.
5. The tripping method applicable to a situation that the number of unlocking times exceeds the limit since the flexible DC control system has been temporarily locked according to claim 2, wherein in step 5, the range of a defined reset value of the bridge arm current of converter valve equipment, i.e. reset threshold, is 30A-60A.
6. The tripping method applicable to a situation that the number of unlocking times exceeds the limit since the flexible DC control system has been temporarily locked according to claim 2, wherein in step 6, the set time T is 15ms.
7. The tripping method applicable to a situation that the number of unlocking times exceeds the limit since the flexible DC control system has been temporarily locked according to claim 2, wherein in step 7, the set limit of times the flexible DC control system completes temporary locking and unlocking circles during the fault occurring at the connected transformer grid side is 2-5.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201611114463.6A CN106505512B (en) | 2016-12-07 | 2016-12-07 | Number is unlocked after soft straight control system temporary blocking again to overflow trip method |
| PCT/CN2016/000717 WO2018102935A1 (en) | 2016-12-07 | 2016-12-28 | Method for performing a trip when the number of times for a flexible dc control system is temporarily locked and then unlocked again exceeds a threshold |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB201719220D0 GB201719220D0 (en) | 2018-01-03 |
| GB2566123A true GB2566123A (en) | 2019-03-06 |
| GB2566123B GB2566123B (en) | 2022-10-19 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1719220.4A Active GB2566123B (en) | 2016-12-07 | 2016-12-28 | Tripping method applicable to situation that number of unlocking times exceeds limit since flexible DC control system has been temporarily locked |
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| Country | Link |
|---|---|
| GB (1) | GB2566123B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN121035911A (en) * | 2025-10-30 | 2025-11-28 | 浙江晶科储能有限公司 | Fault protection methods for energy storage converters, energy storage converters and energy storage systems |
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| CN105680421A (en) * | 2014-11-17 | 2016-06-15 | 南京南瑞继保电气有限公司 | Protection method for modular multilevel converter |
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2016
- 2016-12-28 GB GB1719220.4A patent/GB2566123B/en active Active
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|---|---|---|---|---|
| WO2008157695A2 (en) * | 2007-06-20 | 2008-12-24 | S & C Electric Co. | Fault protection device with ground trip delay and method |
| CN102299506A (en) * | 2011-08-24 | 2011-12-28 | 中国电力科学研究院 | Protection system and method thereof for modular multi-level converter |
| CN104269890A (en) * | 2014-09-26 | 2015-01-07 | 华北电力大学 | Control method and system for extra-high-voltage direct current layering access mode |
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| Publication number | Publication date |
|---|---|
| GB201719220D0 (en) | 2018-01-03 |
| GB2566123B (en) | 2022-10-19 |
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