Direct current transmission converter valve active turn-off method and system based on fault prediction
Through the fault prediction system, abnormal phase commutation is detected in the HCC converter, fault prediction signals are sent, and active shutdown is performed in the shutdown window, which solves the problem of phase commutation failure and improves shutdown efficiency and stability.
Patent Information
- Application Number
- CN202311282058.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-28
- Publication Date
- 2025-03-28
AI Technical Summary
In HCC converter, voltage drop during abnormal phase commutation causes the shutdown angle to be too small and the recovery cannot be completed, resulting in phase commutation failure.
The fault prediction system detects the zero-sequence voltage of the three-phase voltage, sends a fault prediction signal to the commutation valve control system, and performs active shutdown within the shutdown window to avoid phase commutation failure.
By performing active shutdown in advance, phase commutation failure caused by too small shutdown angle is avoided, shutdown efficiency is improved, and the stable operation of the converter valve in abnormal situations is ensured.
Smart Images
Figure CN119726884A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of direct current transmission, and in particular relates to a method and system for actively shutting down a direct current transmission converter valve based on fault prediction. Background Art
[0002] In order to solve the problem of commutation failure, Tsinghua University proposed a new converter topology based on reverse-resistance IGCT (Hybrid Commutated Converter). The basic principle of this topology is to replace the thyristor in the traditional LCC (Line-Commutated Converter) converter valve with a high-power reverse-resistance IGCT device, and use the high withstand voltage and high current capacity of the reverse-resistance IGCT to complete the work of the original thyristor under normal operation, and use the reverse-resistance IGCT's almost negligible reverse recovery period to achieve resistance to commutation failure under minor faults, and use the reverse-resistance IGCT's high current shutoff capability to achieve forced commutation under severe faults. Since the new HCC converter valve based on reverse-resistance IGCT has more functions, the original LCC control logic can no longer match the needs of the HCC converter valve, so a new control logic needs to be proposed for the HCC converter valve.
[0003] First, we need to briefly introduce the commutation failure. In the LCC system, the trigger angle is α, the commutation angle is μ, and the turn-off angle is γ. The sum of the three angles is π. In the normal commutation process, if Figure 1 As shown, when the next bridge arm reaches the trigger angle α0, the current bridge arm has been opened 120°, triggering the next bridge arm to start switching. L Refers to the AC line voltage on the current valve arm (T4), i T4 Refers to the current passing through the current bridge arm, and ωt refers to the phase of the AC voltage;
[0004] u LN Represents the rated value of the AC line voltage, the dotted line represents the voltage drop under fault, α0 represents the rated trigger angle of the next bridge arm (T6), μ0 refers to the rated value of the commutation angle, and γ0 refers to the rated value of the turn-off angle. 120° is the fixed time between the triggering moment of the current bridge arm and the triggering moment of the next bridge arm, ensuring the current flow of 1 / 3 cycle. The relationship between the current bridge arm and the next bridge arm is adjacent conduction. For example, if the current bridge arm is T4, then the next bridge arm is T6. The commutation duration is μ, and the current bridge arm current i after the commutation is completed is T4 The time from this point to the voltage crossing zero is called the turn-off angle. The thyristor valve needs a larger turn-off angle from the current crossing zero to being able to withstand positive pressure. For abnormal commutation process, such as Figure 2As shown in the figure, when the AC voltage drops (as shown by the dotted line), the problem is that the voltage is too low, which increases the commutation time. At the same time, the voltage crosses zero in advance, resulting in a very small turn-off angle. The thyristor cannot complete recovery, commutation failure occurs, and the current bridge arm is turned on again. The problem of abnormal commutation also needs to be solved in the HCC system.
[0005] Therefore, how to prevent commutation failure in the HCC converter valve when an abnormality occurs is a technical problem that needs to be solved urgently. Summary of the invention
[0006] In view of the above problems, the present invention provides a method for actively shutting down a DC power transmission converter valve based on fault prediction. The DC power transmission system where the converter valve is located includes a three-phase six-bridge arm, and each bridge arm is provided with the converter valve. The converter valve is an HCC converter valve, which can be actively shut down, and includes:
[0007] The commutation fault of the converter valve is predicted, and when a specified fault is predicted, active shutdown is performed within the shutdown window.
[0008] Furthermore, predicting the commutation fault of the converter valve includes:
[0009] Detect voltage drop or detect zero-sequence voltage of three-phase voltage.
[0010] Furthermore, the prediction system sends a fault prediction signal to the converter valve control system, and the converter valve control system shuts off the converter valve according to the fault prediction signal.
[0011] Further, performing active shutdown within the shutdown window range includes:
[0012] The shutdown process is executed immediately after the current bridge arm enters the shutdown window.
[0013] Furthermore, performing active shutdown includes determining whether a shutdown condition is met before shutting down the converter valve, and performing active shutdown when the shutdown condition is met.
[0014] Further, determining whether the shutdown condition is met includes:
[0015] It is determined whether the current exceeds the maximum switchable current of the bridge arm at this time. If the current exceeds the maximum switchable current, active shutdown is not performed.
[0016] Further, determining whether the shutdown condition is met includes:
[0017] It is determined whether the voltage of the lightning arrester connected in parallel with the converter valve meets the shutdown energy requirement. If the energy overflows, active shutdown is not performed.
[0018] Further, determining whether the shutdown condition is met includes:
[0019] It is determined whether the next bridge arm meets the trigger opening conditions. If not, active shutdown is not performed.
[0020] The present invention provides a DC power transmission converter valve active shutdown system based on fault prediction. The DC power transmission system where the converter valve is located includes three-phase six bridge arms, each bridge arm is provided with the converter valve, and the converter valve is an HCC converter valve, which can be actively shut down.
[0021] Prediction system and converter valve control system,
[0022] The prediction system is used to predict the shut-off valve commutation failure fault and send a fault prediction signal to the converter valve control system;
[0023] The converter valve control system is used to control the converter valve to perform active shutdown within the shutdown window range according to the fault prediction signal.
[0024] Further,
[0025] The converter valve control system includes a shut-off logic judgment unit and a shut-off execution unit;
[0026] The shutdown logic judgment unit is used to judge whether the following shutdown conditions are met:
[0027] Determine whether the current exceeds the maximum current that can be turned off in the bridge arm at this time; determine whether the voltage of the lightning arrester connected in parallel with the converter valve meets the shutdown energy requirement; determine whether the next bridge arm has the conditions for triggering opening;
[0028] When all the shutdown conditions are met, the shutdown execution unit is used to send a shutdown instruction to the corresponding converter valve on the current bridge arm to execute shutdown.
[0029] The method and system for actively shutting down a DC power transmission converter valve based on fault prediction of the present invention fully utilize existing fault detection or fault prediction means to advance the shut-down operation, thereby solving the problem of commutation failure of an HCC converter valve.
[0030] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0032] Figure 1 shows an electrical signal curve diagram of normal commutation of an LCC system according to the prior art;
[0033] Figure 2 An electrical signal curve diagram of a commutation failure of an LCC system according to the prior art is shown;
[0034] Figure 3 An electrical signal curve diagram of active shutdown of HCC based on fault prediction according to an embodiment of the present invention is shown;
[0035] Figure 4 A flow chart of a method for actively shutting down a DC power transmission converter valve based on fault prediction according to an embodiment of the present invention is shown;
[0036] Figure 5 A schematic structural diagram of a DC transmission converter valve active shutdown system based on fault prediction according to an embodiment of the present invention is shown. DETAILED DESCRIPTION
[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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.
[0038] The embodiment of the present invention proposes a method for actively shutting down a DC transmission converter valve based on fault prediction. The DC transmission converter valve is an HCC converter valve, which is used to set up a DC transmission system (i.e., an HCC system). The HCC system includes three-phase six bridge arms. Each bridge arm includes a series of turnable valve strings and thyristor valve strings. The turnable valve string includes a series-connected converter valve (i.e., an HCC converter valve), and the converter valve adopts an active shut-off device to achieve active shut-off. The converter valve can adopt an insulated gate bipolar transistor IGBT, a gate turn-off thyristor GTO, an integrated gate commutated thyristor IGCT, an injection enhanced gate transistor IEGT, etc. In the three-phase six bridge arms of the DC transmission system, the connection points of the upper bridge arm and the lower bridge arm of each phase are connected to the AC system. The endpoints of the upper bridge arm and the lower bridge arm are connected to the DC system.
[0039] The method comprises: predicting a commutation fault of a converter valve, and when a specified fault is predicted, performing active shutdown within a shutdown window range.
[0040] Among them, for the prediction means of fault, a DC transmission system fault detection method is adopted, including detecting voltage drop, detecting zero-sequence voltage of three-phase voltage or some other prediction means. When the prediction system predicts that the converter valve is about to have a commutation fault, for example, when a fault occurs in the AC system causing voltage fluctuations, the prediction system sends a fault prediction signal to the converter valve control system, but the converter valve control system does not immediately execute the shutdown after receiving the fault prediction signal, but waits until the shutdown window opens before executing the shutdown process. Among them, the shutdown window is relative to the conduction window. The bridge arm is opened within 120°, which is the conduction window, and the rest is the shutdown window (greater than 120°, for example, 120°-180°). Further, in an embodiment of the present invention, after judging that the converter valve enters the shutdown window, the converter valve control system immediately shuts down the process.
[0041] like Figure 3 As shown, the coordinate axis u L Refers to the AC line voltage on the current valve arm (T4), i T4 refers to the current passing through the bridge arm, ωt refers to the phase of the AC voltage; u LN Represents the rated value of the AC line voltage, the dotted line represents the voltage drop under fault, α0 represents the rated trigger angle of the next bridge arm (T6), μ0 refers to the rated value of the commutation angle, γ0 refers to the rated value of the turn-off angle, and the sum of the three angles is π. 120° is the fixed time between the triggering moment of the current bridge arm and the triggering moment of the next bridge arm, ensuring the flow of 1 / 3 cycle.
[0042] For voltage u L Detection is performed. When an AC fault is predicted before the shutdown window, the voltage will drop. The fault prediction signal is sent to the shutdown valve control system. When the shutdown valve control system enters the shutdown window, the current bridge arm is opened 120°, and the AC voltage reaches the next bridge arm trigger angle α0, and it is immediately shut down. At this time, phase switching begins and phase switching is completed within the phase switching angle μ0. The current i T4 becomes 0. The remaining turn-off angle γ0 is large enough to restore to the tolerable positive pressure. Among them, the fault prediction starts after the conduction trigger of the converter valve. For example, the trigger signal is sent again 100us after the trigger signal is sent (re-triggering) to ensure that the converter valve can be reliably triggered to conduct.
[0043] The embodiment of the present invention predicts possible commutation faults and uses the HCC converter valve to actively shut down, thereby avoiding commutation failures caused by too small a shut-off angle. By shutting down at the boundary of the shut-off window, the shut-off efficiency is further improved.
[0044] like Figure 4As shown, the shutdown process includes active shutdown logic judgment, which needs to judge whether the current at this time exceeds the maximum switchable current of the bridge arm. If the current exceeds the maximum switchable current, active shutdown will not be performed; judge whether the voltage of the lightning arrester (in parallel with the converter valve) at this time meets the shutdown energy requirement. If the energy overflows, active shutdown will not be performed; judge whether the next bridge arm has the trigger opening condition (the state of the next converter valve is already turned on or has the trigger opening condition when it is positive pressure). If not, active shutdown will not be performed. Only when all the above conditions are met will active shutdown be performed. After the active shutdown is performed, the current will quickly switch to the next bridge arm, thereby avoiding commutation failure. The embodiment of the present invention protects the HCC converter valve and the lightning arrester by judging the shutdown conditions, so as to avoid the current from being unable to transfer to the next bridge arm during shutdown, resulting in all the current passing through the lightning arrester, and the lightning arrester will fail.
[0045] In the embodiment of the present invention, the prediction signal is sent to the converter valve control system (valve control), and the valve control uses the prediction signal to make a shutdown control judgment, thereby improving the control accuracy. The valve control enters the judgment logic after the shutdown control judgment, and the shutdown time can be executed after entering the shutdown window, or it can be executed after a certain delay.
[0046] The active shutdown method of the embodiment of the present invention makes full use of existing fault detection or fault prediction means to advance the shutdown operation, thereby solving the problem of HCC converter valve commutation failure.
[0047] Based on the same inventive concept, the embodiment of the present invention also includes a DC transmission converter valve active shutdown system based on fault prediction, such as Figure 5 As shown, it includes the following subsystems:
[0048] Prediction system and converter valve control system,
[0049] The prediction system is used to predict the shut-off valve commutation failure fault and send a fault prediction signal to the converter valve control system;
[0050] The converter valve control system is used to control the converter valve to perform active shutdown within the shutdown window range according to the fault prediction signal.
[0051] The prediction system uses voltage drop detection, zero-sequence voltage detection of three-phase voltage or some other prediction means to predict faults. When the prediction system predicts that a switching fault is about to occur in the converter valve, for example, when a fault occurs in the AC system causing voltage fluctuations, the prediction system sends a fault prediction signal to the converter valve control system.
[0052] The converter valve control system includes a shut-off logic judgment unit and a shut-off execution unit.
[0053] The shutdown logic judgment unit is used to judge whether the following shutdown conditions are met:
[0054] Determine whether the current at this time exceeds the maximum switchable current of the bridge arm; determine whether the arrester voltage at this time meets the switch-off energy requirement; determine whether the next bridge arm (the next bridge arm relative to the current bridge arm where the current converter valve is located) has the trigger opening conditions.
[0055] When all the shutdown conditions are met, the shutdown execution unit is used to send a shutdown instruction to the corresponding converter valve on the current bridge arm to execute shutdown.
[0056] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for actively shutting down a DC power transmission converter valve based on fault prediction, wherein the DC power transmission system where the converter valve is located includes a three-phase six-bridge arm, each bridge arm is provided with the converter valve, and the converter valve is an HCC converter valve capable of active shutdown, characterized in that: include: The commutation fault of the converter valve is predicted, and when a specified fault is predicted, active shutdown is performed within the shutdown window.
2. The method for actively shutting down a DC power transmission converter valve based on fault prediction according to claim 1, characterized in that: Prediction of converter valve commutation fault includes: Detect voltage drop or detect zero-sequence voltage of three-phase voltage.
3. The method for actively shutting down a DC power transmission converter valve based on fault prediction according to claim 1, characterized in that: The prediction system sends a fault prediction signal to the converter valve control system, and the converter valve control system shuts off the converter valve according to the fault prediction signal.
4. The method for actively shutting down a DC power transmission converter valve based on fault prediction according to claim 1, characterized in that: Active shutdown within the shutdown window includes: The shutdown process is executed immediately after the current bridge arm enters the shutdown window.
5. The method for actively shutting down a DC power transmission converter valve based on fault prediction according to any one of claims 1 to 4, characterized in that: Executing active shutdown includes determining whether a shutdown condition is met before shutting down the converter valve, and executing active shutdown when the shutdown condition is met.
6. The method for actively shutting down a DC power transmission converter valve based on fault prediction according to claim 5, characterized in that: Determining whether the shutdown conditions are met includes: It is determined whether the current exceeds the maximum switchable current of the bridge arm at this time. If the current exceeds the maximum switchable current, active shutdown is not performed.
7. The method for actively shutting down a DC power transmission converter valve based on fault prediction according to claim 5, characterized in that: Determining whether the shutdown conditions are met includes: It is determined whether the voltage of the lightning arrester connected in parallel with the converter valve meets the shutdown energy requirement. If the energy overflows, active shutdown is not performed.
8. The method for actively shutting down a DC power transmission converter valve based on fault prediction according to claim 5, characterized in that: Determining whether the shutdown conditions are met includes: It is determined whether the next bridge arm meets the trigger opening conditions. If not, active shutdown is not performed.
9. A DC power transmission converter valve active shutdown system based on fault prediction, wherein the DC power transmission system where the converter valve is located includes three-phase six bridge arms, each bridge arm is provided with the converter valve, and the converter valve is an HCC converter valve capable of active shutdown, characterized in that: Prediction system and converter valve control system, The prediction system is used to predict the shut-off valve commutation failure fault and send a fault prediction signal to the converter valve control system; The converter valve control system is used to control the converter valve to perform active shutdown within the shutdown window range according to the fault prediction signal.
10. The DC transmission converter valve active shutdown system based on fault prediction according to claim 9, characterized in that: The converter valve control system includes a shut-off logic judgment unit and a shut-off execution unit; The shutdown logic judgment unit is used to judge whether the following shutdown conditions are met: Determine whether the current exceeds the maximum current that can be turned off in the bridge arm at this time; determine whether the voltage of the lightning arrester connected in parallel with the converter valve meets the shutdown energy requirement; determine whether the next bridge arm has the conditions for triggering opening; When all the shutdown conditions are met, the shutdown execution unit is used to send a shutdown instruction to the corresponding converter valve on the current bridge arm to execute shutdown.