A flexible direct current transmission converter valve and a sub-module bypass switch state judgment method and a sub-module controller thereof

Abstract

The present application belongs to the technical field of flexible HVDC power transmission, and particularly relates to a flexible HVDC power transmission converter valve, a sub-module bypass switch state judgment method and a sub-module controller. The bypass switch trigger signal is sent to the sub-module bypass switch, and the IGBT off signal is sent to the IGBT of the sub-module. When the current is in the charging direction of the sub-module, after the IGBT of the sub-module is turned off, whether the bypass switch is correctly operated is judged based on the fluctuation trend of the sub-module capacitor voltage, which avoids the situation that the bypass switch state is misjudged when the bypass switch state feedback contact or hard contact connection is abnormal, and improves the safety and reliability of the converter valve.

Description

Technical Field

[0001] This invention belongs to the field of flexible DC transmission technology in power systems, specifically relating to a flexible DC transmission converter valve and its submodule bypass switch status judgment method, and a submodule controller. Background Technology

[0002] Flexible DC converter valves typically consist of hundreds of submodules and are widely used in flexible DC transmission systems and power electronic equipment. Each submodule of a flexible DC converter valve is equipped with a bypass switch. When a fault is detected in a submodule, a trigger signal is sent to the bypass switch, closing the bypass switch to take the submodule out of operation without affecting the normal operation of other submodules. For example, Chinese invention patent application CN106849016A discloses a method and device for fault protection of MMC submodules. When a submodule detects any fault, the submodule is locked and the bypass switch is closed, thus enabling the submodule to protect itself without the need for a protection command from the valve control system. Therefore, accurately and reliably determining the status of the bypass switch is crucial to ensuring the safe and stable operation of flexible DC transmission systems.

[0003] Currently, in addition to the main contacts, bypass switches are also equipped with status feedback contacts that are mechanically linked to the main contacts. When the main contacts are closed, the status feedback contact changes its state accordingly. The status signal of the status feedback contact is directly transmitted to the submodule controller via hard contacts to determine whether the bypass switch is closed. However, in actual engineering projects, problems with the wiring of the status feedback contact or hard contacts can lead to misjudgments of the bypass switch status. When the bypass switch is actually closed but is mistakenly judged as not closed, it will be considered that the bypass switch has failed to operate, causing the flexible DC transmission system to shut down and resulting in unplanned tripping. Summary of the Invention

[0004] The purpose of this invention is to provide a method for judging the status of a flexible DC transmission converter valve and its sub-module bypass switch, as well as a sub-module controller, to solve the problem of misjudgment that may occur when judging the status of the bypass switch through status feedback contacts and hard contacts.

[0005] To address the aforementioned technical problems, the first aspect of this invention provides a method for determining the status of a bypass switch in a flexible DC transmission converter valve submodule, comprising: A bypass switch trigger signal is sent to the submodule bypass switch, and an IGBT turn-off signal is sent to the submodule IGBT. If the current is in the direction of charging the submodule, then after the IGBT of the submodule is turned off, the bypass switch is judged to operate correctly based on the fluctuation trend of the submodule capacitor voltage.

[0006] In one possible implementation, if the current is in the direction of charging the submodule and the submodule's IGBT is turned off, and the submodule's capacitor voltage shows an upward trend, then it is determined that the bypass switch is not closed correctly.

[0007] In one possible implementation, if the current is in the direction of charging the submodule and the capacitor voltage of the submodule does not show an upward trend after the IGBT of the submodule is turned off, then it is determined that the bypass switch has been correctly closed.

[0008] In one possible implementation, the bypass switch trigger signal and the IGBT turn-off signal are issued when the flexible DC transmission converter valve submodule fails.

[0009] To address the aforementioned technical problems, a second aspect of this invention provides a flexible DC transmission converter valve submodule controller. The submodule controller is used to send a bypass switch trigger signal to the submodule bypass switch and simultaneously send an IGBT turn-off signal to the IGBT of the submodule. When the current is in the direction of charging the submodule, after the IGBT of the submodule is turned off, the controller determines whether the bypass switch has operated correctly based on the fluctuation trend of the submodule capacitor voltage.

[0010] In one possible implementation, if the current is in the direction of charging the submodule and the submodule's IGBT is turned off, and the submodule's capacitor voltage shows an upward trend, then it is determined that the bypass switch is not closed correctly.

[0011] In one possible implementation, if the current is in the direction of charging the submodule and the capacitor voltage of the submodule does not show an upward trend after the IGBT of the submodule is turned off, then it is determined that the bypass switch has been correctly closed.

[0012] In one possible implementation, the bypass switch trigger signal and the IGBT turn-off signal are issued when the flexible DC transmission converter valve submodule fails.

[0013] To address the aforementioned technical problems, a third aspect of the present invention provides a flexible DC transmission converter valve, comprising a submodule and a submodule controller. The submodule controller employs the steps of a method for determining the state of a submodule bypass switch in a flexible DC transmission converter valve to determine the state of the submodule bypass switch. This method includes: A bypass switch trigger signal is sent to the submodule bypass switch, and an IGBT turn-off signal is sent to the submodule IGBT. If the current is in the direction of charging the submodule, then after the IGBT of the submodule is turned off, the bypass switch is judged to operate correctly based on the fluctuation trend of the submodule capacitor voltage.

[0014] In one possible implementation, if the current is in the direction of charging the submodule and the submodule's IGBT is turned off, and the submodule's capacitor voltage shows an upward trend, then it is determined that the bypass switch is not closed correctly.

[0015] In one possible implementation, if the current is in the direction of charging the submodule and the capacitor voltage of the submodule does not show an upward trend after the IGBT of the submodule is turned off, then it is determined that the bypass switch has been correctly closed.

[0016] In one possible implementation, the bypass switch trigger signal and the IGBT turn-off signal are issued when the flexible DC transmission converter valve submodule fails.

[0017] In one possible implementation, the submodule controller is a central control board.

[0018] The beneficial effects of this invention are as follows: By analyzing the current flow direction when the bypass switch is closed and open under charging and discharging scenarios and after the submodule IGBT is locked, this invention reveals that when the current is in the charging direction of the submodule, the fluctuation trend of the capacitor is significantly inconsistent when the bypass switch is closed and open. Therefore, this invention determines whether the bypass switch is truly closed by turning off the submodule IGBT and then using the fluctuation trend of the submodule capacitor voltage when the current is in the charging direction. This avoids the situation where the bypass switch status is misjudged due to abnormal wiring of the bypass switch status feedback contact or hard contact, thus improving the safety and reliability of the converter valve. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the current flow direction in the charging direction when the bypass switch of the present invention is closed; Figure 2 This is a schematic diagram of the current flow direction when the bypass switch of the present invention is closed; Figure 3 This is a schematic diagram of the current flow direction in the charging direction when the bypass switch of the present invention is not closed; Figure 4 This is a schematic diagram of the current flow direction when the bypass switch of the present invention is not closed; Figure 5 This is a flowchart of the bypass switch status judgment process for the flexible DC power transmission converter valve submodule of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0021] This invention shuts off the upper and lower IGBTs of the submodule at the same time as issuing the bypass switch closing command. Then, when the current is in the charging direction, it uses the fluctuation trend of the submodule capacitor voltage to determine whether the bypass switch is actually closed, avoiding misjudgment when the bypass switch feedback contact is abnormal, and improving the safety of the converter valve.

[0022] Implementation Method for Determining the Status of Bypass Switch in Flexible DC Transmission Converter Valve Submodule The present invention provides a method for determining the status of a bypass switch in a flexible DC transmission converter valve submodule. By combining the actual fluctuations in the capacitor voltage of the flexible DC transmission converter valve submodule, the true status of the bypass switch is determined.

[0023] A typical flexible DC-DC converter valve submodule includes a bypass switch, a power submodule, and capacitors. In the event of a fault in the flexible DC-DC converter valve submodule, the submodule controller sends a bypass switch trigger signal (i.e., a bypass switch closing signal) to the bypass switch to drive the electrical structure and close the bypass switch. The power submodule can be a half-bridge or full-bridge submodule composed of IGBTs. The submodule controller is a central control board.

[0024] The principle of this invention will be explained below using the flexible DC-DC transmission converter valve submodule with a half-bridge structure as an example.

[0025] The flexible DC-DC power transmission converter valve submodule includes a bypass switch K, an upper IGBT (T1), a lower IGBT (T2), and a capacitor C.

[0026] After a failure of the flexible DC-DC converter valve submodule, the central control board sends a bypass switch closing signal to the bypass switch K, and simultaneously shuts down the upper and lower IGBTs of the submodule.

[0027] After the central control board shuts off the upper and lower IGBTs of the submodule, if the bypass switch is actually closed, in a charging scenario, when the current is in the charging direction (towards the submodule), such as... Figure 1 As shown, the current flows directly out of the submodule after passing through the bypass switch K, and no longer charges the capacitor C through the power submodule. Figure 1 The red arrows indicate the direction of current flow.

[0028] After the central control board shuts off the upper and lower IGBTs of the submodule, if the bypass switch is actually closed, in a discharge scenario, when the current is in the discharge direction (submodule discharge output), such as... Figure 2 As shown, the current flows directly out of the submodule after passing through the bypass switch K, and the capacitor C no longer discharges rapidly through the power submodule. Figure 2 The red arrows indicate the direction of current flow.

[0029] As can be seen, once the bypass switch is actually closed, regardless of whether it is in a charging or discharging scenario, the current flows directly out of the submodule after passing through the bypass switch, and no longer charges or discharges the capacitor through the power submodule. The capacitor voltage of the submodule only decreases at a certain rate due to its own losses.

[0030] After the central control board shuts off the upper and lower IGBTs of the submodule, if the bypass switch is not closed and the current is in the charging direction, such as... Figure 3 As shown, the current flows through the diode connected in anti-parallel to the upper IGBT in the power submodule to charge the submodule capacitor, causing the voltage of the submodule capacitor to rise. Figure 3 The red arrows indicate the direction of current flow.

[0031] After the central control board shuts off the upper and lower IGBTs of the submodule, if the bypass switch is not closed and the current is in the discharge direction, such as... Figure 4 As shown, the current flows directly out of the submodule after passing through the diode connected in anti-parallel to the lower IGBT in the power submodule, and the voltage of the submodule capacitor decreases at a certain rate due to its own losses. Figure 4 The red arrows indicate the direction of current flow.

[0032] Based on the above principles, the actual state of the bypass switch can be determined by the actual fluctuation of the submodule capacitor voltage. When the central control board sends a bypass switch closing signal and simultaneously turns off the upper and lower IGBTs of the submodule, if the voltage of the submodule capacitor shows a decreasing trend when the current is in the charging direction, the current does not flow through the capacitor, but flows directly out after passing through the bypass switch. At this time, it is determined that the bypass switch has been correctly closed.

[0033] When the central control board sends a bypass switch closing signal and simultaneously turns off the upper and lower IGBTs of the submodule, if the current is in the charging direction, it is determined that the voltage of the submodule capacitor is rising. If the current flows through the capacitor but not through the bypass switch, it is determined that the bypass switch is not closed correctly.

[0034] Based on the above specific implementation process, such as Figure 5 As shown, the method for determining the status of the bypass switch of the flexible DC transmission converter valve submodule of the present invention includes the following steps: sending a bypass switch trigger signal to the submodule bypass switch and simultaneously sending an IGBT turn-off signal to the IGBT of the submodule; if the current is in the direction of charging the submodule, then after the IGBT of the submodule is turned off, the bypass switch is judged to be operating correctly based on the fluctuation trend of the capacitor voltage of the submodule.

[0035] If the current is in the direction of charging the submodule and the voltage of the submodule capacitor rises after the submodule's IGBT is turned off, then the bypass switch is not closed correctly.

[0036] If the current is in the direction of charging the submodule and the capacitor voltage of the submodule does not show an upward trend after the IGBT of the submodule is turned off, then it is determined that the bypass switch has been closed correctly.

[0037] Bypass switch trigger signal and IGBT turn-off signal can be issued when the flexible DC transmission converter valve submodule fails.

[0038] Implementation of Flexible DC Transmission Converter Valve Submodule Controller This invention discloses a controller for a flexible DC-DC converter valve submodule, used to implement a method for determining the status of a bypass switch in a flexible DC-DC converter valve submodule. The method includes the following steps: sending a bypass switch trigger signal to the submodule bypass switch and simultaneously sending an IGBT turn-off signal to the submodule's IGBT; if the current is in the charging direction of the submodule, then after the submodule's IGBT is turned off, determining whether the bypass switch has operated correctly based on the fluctuation trend of the submodule's capacitor voltage. The bypass switch trigger signal and the IGBT turn-off signal are sent when the flexible DC-DC converter valve submodule malfunctions.

[0039] The submodule controller can be a central control board.

[0040] After a failure of the flexible DC-DC converter valve submodule, the central control board sends a bypass switch closing signal to the bypass switch, and at the same time shuts down the upper IGBT and lower IGBT of the submodule.

[0041] After the central control board turns off the upper and lower IGBTs of the submodule, if the bypass switch is actually closed, in the charging scenario, when the current is in the charging direction, the current flows directly out of the submodule after passing through the bypass switch, and no longer charges the capacitor through the power submodule.

[0042] After the central control board turns off the upper and lower IGBTs of the submodule, if the bypass switch is actually closed, in the discharge scenario, when the current is in the discharge direction, the current flows directly out of the submodule after passing through the bypass switch, and the capacitor no longer discharges quickly through the power submodule.

[0043] As can be seen, once the bypass switch is actually closed, regardless of whether it is in a charging or discharging scenario, the current flows directly out of the submodule after passing through the bypass switch, and no longer charges or discharges the capacitor through the power submodule. The capacitor voltage of the submodule only decreases at a certain rate due to its own losses.

[0044] After the central control board turns off the upper and lower IGBTs of the submodule, if the bypass switch is not closed and the current is in the charging direction, the current charges the submodule capacitor through the diode connected in anti-parallel to the upper IGBT in the power submodule, causing the submodule capacitor voltage to rise.

[0045] After the central control board turns off the upper and lower IGBTs of the submodule, if the bypass switch is not closed and the current is in the discharge direction, the current flows directly out of the submodule after passing through the diode connected in anti-parallel to the lower IGBT in the power submodule. The voltage of the submodule capacitor decreases at a certain rate due to its own losses.

[0046] Based on the above principles, the actual state of the bypass switch can be determined by the actual fluctuation of the submodule capacitor voltage. If the current is in the charging direction and the submodule's IGBT is turned off, and the submodule's capacitor voltage shows a non-rising trend, then the bypass switch is considered to have closed correctly. That is, after the central control board sends a bypass switch closing signal and simultaneously turns off the submodule's upper and lower IGBTs, if the submodule's capacitor voltage shows a non-rising trend when the current is in the charging direction, then the current does not flow through the capacitor but flows directly out through the bypass switch; in this case, the bypass switch is considered to have closed correctly.

[0047] If the current is in the charging direction and the submodule's IGBT is turned off, and the submodule's capacitor voltage shows an upward trend, then the bypass switch is determined not to be closed correctly. That is, after the central control board sends a bypass switch closing signal and simultaneously turns off the submodule's upper and lower IGBTs, if the current is in the charging direction and the submodule's capacitor voltage shows an upward trend, then the current flows through the capacitor and not through the bypass switch, indicating that the bypass switch is not closed correctly.

[0048] Implementation of Flexible DC Transmission Converter Valve This invention discloses a flexible DC-DC converter valve, comprising a submodule and a submodule controller. The submodule typically includes a bypass switch, a power submodule, and a capacitor. In the event of a submodule failure, the submodule controller sends a bypass switch trigger signal to the bypass switch to drive the electrical structure and close the bypass switch. The power submodule can be a half-bridge or full-bridge submodule composed of IGBTs.

[0049] The submodule controller can be a central control board.

[0050] After a failure of the flexible DC-DC converter valve submodule, the central control board sends a bypass switch closing signal to the bypass switch, and at the same time shuts down the upper IGBT and lower IGBT of the submodule.

[0051] After the central control board turns off the upper and lower IGBTs of the submodule, if the bypass switch is actually closed, in the charging scenario, when the current is in the charging direction, the current flows directly out of the submodule after passing through the bypass switch, and no longer charges the capacitor through the power submodule.

[0052] After the central control board turns off the upper and lower IGBTs of the submodule, if the bypass switch is actually closed, in the discharge scenario, when the current is in the discharge direction, the current flows directly out of the submodule after passing through the bypass switch, and the capacitor no longer discharges quickly through the power submodule.

[0053] As can be seen, once the bypass switch is actually closed, regardless of whether it is in a charging or discharging scenario, the current flows directly out of the submodule after passing through the bypass switch, and no longer charges or discharges the capacitor through the power submodule. The capacitor voltage of the submodule only decreases at a certain rate due to its own losses.

[0054] After the central control board turns off the upper and lower IGBTs of the submodule, if the bypass switch is not closed and the current is in the charging direction, the current charges the submodule capacitor through the diode connected in anti-parallel to the upper IGBT in the power submodule, causing the submodule capacitor voltage to rise.

[0055] After the central control board turns off the upper and lower IGBTs of the submodule, if the bypass switch is not closed and the current is in the discharge direction, the current flows directly out of the submodule after passing through the diode connected in anti-parallel to the lower IGBT in the power submodule. The voltage of the submodule capacitor decreases at a certain rate due to its own losses.

[0056] Based on the above principles, the actual state of the bypass switch can be determined by the actual fluctuation of the submodule capacitor voltage. If the current flows in the charging direction and the submodule's IGBT is turned off, and the submodule's capacitor voltage shows a non-rising trend, then the bypass switch is considered to have closed correctly. That is, after the central control board sends a bypass switch closing signal and simultaneously turns off the submodule's upper and lower IGBTs, if the submodule's capacitor voltage shows a falling trend when the current flows in the charging direction, then the current does not flow through the capacitor but instead flows directly out through the bypass switch; in this case, the bypass switch is considered to have closed correctly.

[0057] If the current is in the charging direction and the submodule's IGBT is turned off, and the submodule's capacitor voltage shows an upward trend, then the bypass switch is determined not to be closed correctly. That is, after the central control board sends a bypass switch closing signal and simultaneously turns off the submodule's upper and lower IGBTs, if the current is in the charging direction and the submodule's capacitor voltage shows an upward trend, then the current flows through the capacitor and not through the bypass switch, indicating that the bypass switch is not closed correctly.

[0058] This invention proposes that after a failure of the flexible DC converter valve submodule, a bypass switch trigger signal is sent from the central control board to isolate the submodule from the electrical circuit. At the same time, the upper and lower IGBTs of the submodule are turned off. Then, when the current is in the charging direction, the failure of the bypass switch is determined by whether the voltage fluctuation trend of the submodule capacitor decreases. This avoids misjudgment when the bypass switch feedback contact is abnormal, thus improving the safety of the converter valve.

Claims

1. A method for determining the status of a bypass switch in a flexible DC transmission converter valve submodule, characterized in that, include: A bypass switch trigger signal is sent to the submodule bypass switch, and an IGBT turn-off signal is sent to the submodule IGBT. If the current is in the direction of charging the submodule, then after the IGBT of the submodule is turned off, the bypass switch is judged to operate correctly based on the fluctuation trend of the submodule capacitor voltage.

2. The method for determining the status of the bypass switch of the flexible DC transmission converter valve submodule according to claim 1, characterized in that, If the current is in the direction of charging the submodule and the voltage of the submodule capacitor rises after the submodule's IGBT is turned off, then the bypass switch is not closed correctly.

3. The method for determining the status of the bypass switch of the flexible DC transmission converter valve submodule according to claim 1 or 2, characterized in that, If the current is in the direction of charging the submodule and the capacitor voltage of the submodule does not show an upward trend after the IGBT of the submodule is turned off, then it is determined that the bypass switch has been closed correctly.

4. The method for determining the status of the bypass switch of the flexible DC transmission converter valve submodule according to claim 1, characterized in that, The bypass switch trigger signal and IGBT turn-off signal are issued when the flexible DC transmission converter valve submodule fails.

5. A flexible DC transmission converter valve submodule controller, characterized in that, The submodule controller is used to send a bypass switch trigger signal to the submodule bypass switch and an IGBT turn-off signal to the submodule's IGBT. When the current is in the direction of charging the submodule, after the submodule's IGBT is turned off, the controller determines whether the bypass switch has operated correctly based on the fluctuation trend of the submodule's capacitor voltage.

6. The flexible DC transmission converter valve submodule controller according to claim 5, characterized in that, If the current is in the direction of charging the submodule and the voltage of the submodule capacitor rises after the submodule's IGBT is turned off, then the bypass switch is not closed correctly.

7. The flexible DC transmission converter valve submodule controller according to claim 5 or 6, characterized in that, If the current is in the direction of charging the submodule and the capacitor voltage of the submodule does not show an upward trend after the IGBT of the submodule is turned off, then it is determined that the bypass switch has been closed correctly.

8. The flexible DC transmission converter valve submodule controller according to claim 5, characterized in that, The bypass switch trigger signal and IGBT turn-off signal are issued when the flexible DC transmission converter valve submodule fails.

9. A flexible DC transmission converter valve, comprising a submodule and a submodule controller, characterized in that, The submodule controller uses the steps of the method described in any one of claims 1-4 to determine the state of the submodule bypass switch.

10. The flexible DC transmission converter valve according to claim 9, characterized in that, The submodule controller is a central control board.

Images