Active commutation unit, hybrid converter topology and commutation control method

Abstract

The present invention discloses an active commutation unit, a hybrid converter topology structure and a commutation control method. The active commutation unit is arranged in the bridge arm circuit of the converter, one end of which is connected to the output end of the converter transformer, and the other end is connected to the DC bus. The active commutation unit includes: a main branch, an auxiliary branch and a bypass branch. A thyristor valve and a first control valve are arranged on the main branch. The auxiliary branch is connected in parallel with the main branch, and a second control valve is arranged thereon. The first control valve has a forward current controllable shutoff function, and the second control valve has a forward current controllable shutoff function and a forward and reverse voltage blocking function. The bypass branch is connected in parallel with the first control valve to protect the first control valve or replace the first control valve for normal flow of the main branch. By implementing the present invention, it is ensured that the hybrid converter can work in a conventional commutation mode, the probability of commutation failure is reduced, and the reliability and availability of the hybrid converter are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic commutation, and in particular to an active commutation unit, a hybrid converter topology structure and a commutation control method. Background Art

[0002] Traditional line commutated converter high voltage direct current (LCC-HVDC) transmission systems are widely used worldwide due to their advantages, including long-distance, large-capacity transmission and controllable active power. As the core equipment for DC transmission, converters are the core functional unit for converting AC and DC power. Their operational reliability largely determines the operational reliability of the ultra-high voltage direct current (UHVDC) grid. Because traditional converters often use half-controlled thyristors as core components to form a six-pulse bridge commutation topology, each bridge arm consists of multiple thyristors and their buffer components connected in series. Since thyristors lack self-shutoff capability, commutation failures are prone to occur in situations such as AC system faults, leading to a surge in DC current and a rapid and substantial loss of DC transmission power, impacting the stable and safe operation of the grid.

[0003] Currently, there is a hybrid converter with a shutoff capability. This hybrid converter has both a controllable commutation mode and a conventional commutation mode. The converter uses a thyristor valve connected in series with a small number of fully-controlled devices as the main branch, and a fully-controlled valve composed of multiple stages of turnable devices with reverse blocking capability as the auxiliary branch. The two branches are connected in parallel. The fully-controlled valve in the main branch has at least unidirectional shutoff capability. The thyristor valve current is shut off by a small number of turnable devices, transferring the current to the auxiliary branch. The auxiliary branch then replaces the main branch to perform phase change between the bridge arms, thus avoiding phase change failure. Although the converter can enter the controllable commutation mode to achieve phase change between the bridge arms in the event of a fault, if the conventional commutation mode can operate stably, there is no need to trigger the controllable shutoff mode. The stability of the conventional commutation mode depends on the stable operation of the fully-controlled valve in the main branch. When the fully-controlled valve in the main branch fails or the current exceeds the limit, it is difficult to ensure the reliable operation of the hybrid converter in the conventional commutation mode. Summary of the Invention

[0004] In view of this, an embodiment of the present invention provides an active commutation unit, a hybrid converter topology structure and a commutation control method to solve the problem that it is difficult to ensure the reliable operation of the hybrid converter in the conventional commutation mode when the main branch fully controlled valve fails or the current exceeds the limit.

[0005] According to the first aspect, an embodiment of the present invention provides an active commutation unit, which is arranged in the bridge arm circuit of the converter, one end of which is connected to the output end of the converter transformer, and the other end is connected to the DC bus. The active commutation unit includes: a main branch, on which a thyristor valve and a first control valve are provided, and the first control valve is used for controllable shutdown of the forward current; an auxiliary branch, which is arranged in parallel with the main branch, and a second control valve is provided on the auxiliary branch, and the second control valve has a controllable shutdown function of the forward current and a forward and reverse voltage blocking function; a bypass branch, which is arranged in parallel with the first control valve, and the bypass branch is used to protect the first control valve or replace the first control valve to allow the main branch to pass through.

[0006] In combination with the first aspect, in a first implementation of the first aspect, the first control valve includes: a plurality of control submodules, the plurality of control submodules are arranged in series, and the control submodules are used to shut off the forward current.

[0007] In combination with the first embodiment of the first aspect, in the second embodiment of the first aspect, the bypass branch includes: a plurality of first bypass sub-branches, and the first bypass sub-branches are respectively arranged in parallel at both ends of the control sub-module.

[0008] In combination with the first embodiment of the first aspect, in the third embodiment of the first aspect, the bypass branch also includes: a second bypass sub-branch, the first end of the second bypass sub-branch is connected to the first end of the first control sub-module, and the second end of the second bypass sub-branch is connected to the first end of the last control sub-module.

[0009] In combination with the third embodiment of the first aspect, in the fourth embodiment of the first aspect, the first bypass sub-branch and / or the second bypass sub-branch includes: at least one first switch unit, and the at least one first switch unit is arranged in series.

[0010] In combination with the third embodiment of the first aspect, in a fifth embodiment of the first aspect, the first bypass sub-branch and / or the second bypass sub-branch includes: at least one first thyristor, and the at least one first thyristor is arranged in series.

[0011] According to the second aspect, the technical solution of the present invention provides a hybrid converter topology structure, which is connected to the AC power grid through a converter transformer. The topology structure includes a three-phase six-bridge arm circuit, and each phase bridge arm includes an upper bridge arm and a lower bridge arm. It is characterized in that at least one upper bridge arm or lower bridge arm is provided with the active commutation unit described in the first aspect or any embodiment of the first aspect.

[0012] According to the third aspect, the technical solution of the present invention provides a commutation control method for a hybrid converter topology structure, which is used for the hybrid converter topology structure as described in the second aspect. The method includes: obtaining the working status of a first control valve set on the main branch; judging whether the working status is abnormal; when the working status is abnormal, turning on the bypass branch.

[0013] In combination with the third aspect, in the first embodiment of the third aspect, before obtaining the working status of the first control valve set on the main branch, it also includes: obtaining the commutation mode of the hybrid converter, the commutation mode including the conventional commutation mode and the controllable commutation mode; judging whether the commutation mode of the hybrid converter is the conventional commutation mode; when the commutation mode of the hybrid converter is the conventional commutation mode, obtaining the working status of the first control valve set on the main branch.

[0014] In combination with the first embodiment of the third aspect, in the second embodiment of the third aspect, the method also includes: when the commutation mode of the hybrid converter is a controllable commutation mode, controlling the bypass branch to be in an off state, and performing controllable commutation between the main branch and the auxiliary branch.

[0015] The technical solution of the present invention has the following advantages:

[0016] 1. The active commutation unit provided in an embodiment of the present invention includes a main branch, an auxiliary branch, and a bypass branch. The main branch is provided with a thyristor valve and a first control valve. The auxiliary branch is connected in parallel with the main branch and is provided with a second control valve. The first control valve has a controllable forward current shutoff function, while the second control valve has both a forward current shutoff function and forward and reverse voltage blocking functions. The two branches are connected in parallel to enable controllable commutation mode in the event of an AC system fault. The auxiliary branch completes commutation between the bridge arms, preventing commutation failures. By setting up bypass branches in parallel at both ends of the first control valve, when the first control valve fails, the bypass branch can be opened to maintain the normal flow process of the main branch. When a current fault occurs, the first control valve of the main branch can be effectively protected from damage by opening the bypass branch, so that it can continue to be used in the event of a current fault, thereby ensuring the reliable operation of the hybrid converter in the conventional commutation mode, and thus ensuring to the greatest extent that the hybrid converter can cope with various faults, thereby ensuring the operating stability of the hybrid converter and ensuring the safe operation of the power grid.

[0017] 2. The hybrid converter topology provided in an embodiment of the present invention includes a three-phase six-bridge arm circuit, wherein each phase bridge arm includes an upper bridge arm and a lower bridge arm, and at least one upper bridge arm or a lower bridge arm is provided with an active commutation unit. This ensures that the hybrid converter can operate in a conventional commutation mode to reduce the probability of commutation failure and eliminate the need to resist commutation failure. It also ensures a controllable commutation mode that does not affect the hybrid converter topology, thereby maximizing the reliability and availability of the hybrid converter.

[0018] 3. The commutation control method for the hybrid converter topology structure provided in an embodiment of the present invention obtains the working status of the first control valve set on the main branch. When the working status of the first control valve is abnormal, the bypass branch is turned on to protect the first control valve or replace the first control valve to ensure normal flow of the main branch, thereby ensuring that the hybrid converter topology structure can operate in a conventional commutation mode.

[0019] 4. The commutation control method for a hybrid converter topology structure provided in an embodiment of the present invention places the bypass branch in an off state when the commutation mode of the hybrid converter is a controllable commutation mode to achieve controllable commutation between the main branch and the auxiliary branch. The bypass branch can also be turned on to switch the hybrid converter from the controllable commutation mode to the conventional commutation mode, thereby completing the functions of the hybrid converter and further improving the operational reliability of the hybrid converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. 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 any creative work.

[0021] Figure 1 is a structural block diagram of the active commutation unit of this embodiment;

[0022] Figure 2 is a structural block diagram of the first control valve and the bypass branch of this embodiment;

[0023] Figure 3 is another structural block diagram of the first control valve and the bypass branch of this embodiment;

[0024] Figure 4 is a topological diagram of the first / second bypass sub-branch of this embodiment;

[0025] Figure 5 is another topological structure diagram of the first / second bypass sub-branch of this embodiment;

[0026] Figure 6 is a topological structure diagram of the first control valve of this embodiment;

[0027] Figure 7 is a schematic diagram of the topological structure of the hybrid converter of this embodiment;

[0028] Figure 8 is a flow chart of a commutation control method for a hybrid converter topology structure of this embodiment;

[0029] Figure 9 This is another flow chart of the commutation control method of the hybrid converter topology structure of this embodiment. DETAILED DESCRIPTION

[0030] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying 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 those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0031] Currently, hybrid converters with switchable switching capabilities generally have both a controlled commutation mode and a conventional commutation mode. These use a thyristor valve in series with a small number of fully controlled devices as the main branch, and a fully controlled valve composed of multiple stages of switchable devices with reverse blocking capability as the auxiliary branch. The two branches are connected in parallel. The fully controlled valve in the main branch has at least unidirectional switchable capability. A small number of switchable devices shut off the thyristor valve current, transferring the current to the auxiliary branch. The auxiliary branch then replaces the main branch to perform phase change between the bridge arms, preventing commutation failure. Although the hybrid converter can enter the controlled commutation mode to achieve phase change between the bridge arms in the event of a fault, if the conventional commutation mode can operate stably, there is no need to trigger the controlled shutdown mode. The stability of the conventional commutation mode depends on the stable operation of the fully controlled valve in the main branch. When the fully controlled valve in the main branch fails or there is a current fault, it is difficult to ensure the reliable operation of the hybrid converter in the conventional commutation mode.

[0032] Based on this, this technical solution connects a bypass path in parallel to the first control valve set on the main branch, so that when a fault occurs in the first control valve or a current fault occurs, the bypass branch is opened to maintain an effective and normal commutation process, avoid damage to the first control valve, and ensure the reliable operation of the hybrid converter.

[0033] According to an embodiment of the present invention, an embodiment of an active commutation unit is provided, wherein the active commutation unit is arranged in a bridge arm circuit of a converter. One end of the active commutation unit is connected to the output end of the converter transformer, and the other end is connected to the DC bus. Figure 1As shown, the active commutation unit includes: a main branch 1, an auxiliary branch 2, and a bypass branch 3. A thyristor valve 11 and a first control valve 12 are sequentially arranged on the main branch 1 along the direction from the converter transformer to the DC bus. The bypass branch 3 is arranged in parallel at both ends of the first control valve 12. When the first control valve 12 fails and it is difficult to maintain normal flow in the main branch, the bypass branch 3 can be opened and replaced by the first control valve 12 to perform normal flow in the main branch. That is, the bypass branch 3 assists the thyristor valve 11 in transferring current from the main branch to the auxiliary branch. The auxiliary branch 2 is arranged in parallel with the main branch 1 and is provided with a second control valve 13. The first control valve 12 has the function of controllable shutoff of forward current and controllable shutoff of forward and reverse voltages, and the second control valve 13 has the function of controllable shutoff of forward current and blocking of forward and reverse voltages.

[0034] Specifically, the first control valve 12 is a low-pressure fully controlled valve, which can be one or more turn-off devices such as IGBT, IGCT, IEGT, GTO, or MOSFET. The bypass branch 3 can be composed of components that can perform switching functions. When the first control valve 12 fails, the bypass branch 3 is opened, and when the first control valve 12 returns to normal, it is closed. In this way, it can serve as a backup branch for the first control valve 12 to complete the commutation operation of the main branch. It can also effectively protect the first control valve 12 from damage by opening the bypass branch 3 in the event of a fault current, a false triggering of the thyristor valve V11, or a failure or false shutdown of the first control valve 12. In the normal commutation mode, when the first control valve 12 fails, the bypass branch 3 is closed, the first control valve 12 on the main branch is short-circuited, and the second control valve 13 on the auxiliary branch is closed. At this time, the thyristor valve of the main branch is responsible for performing the commutation operation.

[0035] The active commutation unit provided in this embodiment, by setting a bypass branch in parallel at both ends of the first control valve, can maintain the normal flow process of the main branch by opening the bypass branch when the first control valve fails; in the event of a current fault, the first control valve of the main branch can be effectively protected from damage by opening the bypass branch, so that it can continue to be used in the event of a current fault, thereby ensuring the reliable operation of the hybrid converter in the conventional commutation mode, and further ensuring to the greatest extent that the hybrid converter can cope with various faults, thereby ensuring the operational reliability of the hybrid converter and ensuring the safe operation of the power grid.

[0036] Alternatively, as Figure 2 As shown, the first control valve 12 may include a plurality of control submodules 121, and the plurality of control submodules 121 are arranged in series to realize the function of forward current shutoff. Specifically, as Figure 6As shown, the control submodule 121 can be a power electronic unit consisting of two parallel branches, one of which is provided with a power device W, and the other branch is provided with a capacitor element C and a power device W in series, wherein the power device W is a fully controlled power electronic device, which is one or more turn-off devices such as IGBT, IGCT, IEGT, GTO, or MOSFET. Of course, the control submodule 121 can also have other topological forms, which are not specifically limited here.

[0037] like Figure 2 As shown, when the first control valve 12 includes multiple control sub-modules 121, the bypass branch 3 may include multiple first bypass sub-branches 31, and each first bypass sub-branch 31 is arranged in parallel at both ends of each control sub-module 121, thereby providing protection for each control sub-module of the first control valve 12. When a control sub-module fails, the first bypass sub-branch connected in parallel with it is closed, and the entire first control valve 12 can still operate normally.

[0038] Alternatively, as Figure 3 As shown, when the first control valve 12 includes multiple control submodules 121, the bypass branch 3 may further include a second bypass sub-branch 32. The second bypass sub-branch 32 may be connected in parallel at both ends of the first control valve 12 formed by the multiple control submodules 121. Specifically, the control submodules 121 include a first end and a second end. The first end of the first control submodule 121 is connected to one end of the thyristor valve, the second end of the first control submodule 121 is connected to the first end of the second control submodule 121, the second end of the second control submodule 121 is connected to the first end of the third control submodule 121, and so on. The first control valve 12 obtained by connecting the control submodules 121 in series, i.e., the second bypass sub-branch 32 has one end connected to the first end of the first control submodule 121, and the other end of the second bypass sub-branch 32 is connected to the second end of the last control submodule 121. Therefore, on the basis of providing protection for each control submodule of the first control valve 12, when each control submodule 121 fails, the second bypass sub-branch 31 connected in parallel with the first control valve 12 is closed, and each control module 121 of the first control valve 12 is short-circuited at the same time. At this time, the thyristor valve of the main branch is responsible for realizing the commutation operation.

[0039] Alternatively, as Figure 4 As shown, the first bypass sub-branch 31 and / or the second bypass sub-branch 32 may include: at least a first first switch unit K1, and each first switch unit K1 is arranged in series, and the first switch unit K1 is a switch component.

[0040] Alternatively, as Figure 5As shown, the first bypass sub-branch 31 and / or the second bypass sub-branch 32 may include at least one first thyristor J1, with each first thyristor J1 connected in series. In normal commutation mode, the first control valve 12 and the second control valve 13 are both closed, and the thyristor valve 1 of the main branch and the first thyristor J1 in the second bypass sub-branch 31 are synchronously triggered. At this time, the first thyristor J1 in the second bypass sub-branch 31 cooperates with the thyristor valve 1 of the main branch to achieve commutation operation.

[0041] According to an embodiment of the present invention, a forced commutation hybrid converter topology is provided, which is connected to the AC power grid via a converter transformer. Figure 7 As shown, the forced commutation hybrid converter topology includes a three-phase six-bridge arm circuit, each phase bridge arm includes an upper bridge arm and a lower bridge arm, and at least one of the upper bridge arm or the lower bridge arm is provided with the active commutation unit described in the above embodiment.

[0042] Specifically, if Figure 7 The forced commutation hybrid converter topology structure includes three upper bridge arms and three lower bridge arms. Each active commutation unit acts as a commutation valve. Figure 7 The forced-commutation hybrid converter topology comprises a converter valve V1, a converter valve V2, a converter valve V3, a converter valve V4, a converter valve V5, and a converter valve V6. The main branches of the three upper bridge arms comprise thyristor valves V11, V31, and V51, respectively, and also include first control valves V12, V32, and V52 connected in series with the thyristor valves; the auxiliary branches of the three upper bridge arms comprise first control valves V13, V33, and V53, respectively; the main branches of the three lower bridge arms comprise thyristor valves V21, V41, and V61, respectively, and also include first control valves V22, V42, and V62 connected in series with the thyristor valves; the auxiliary branches of the three lower bridge arms comprise first control valves V23, V43, and V63, respectively, and a bypass branch 3 is connected in parallel at both ends of each of the first control valves V12, V32, V52, V22, V42, and V62. The thyristor valve, the first control valve, the second control valve and the bypass branch are controlled to be turned on and off by triggering the control system to realize the commutation operation of the hybrid converter topology structure.

[0043] The forced-commutation hybrid converter topology provided in this embodiment includes a three-phase six-bridge arm circuit, where each phase bridge arm includes an upper bridge arm and a lower bridge arm, and at least one upper bridge arm or a lower bridge arm is provided with an active commutation unit. This ensures that the hybrid converter can operate in a conventional commutation mode to reduce the probability of commutation failure and eliminates the need to resist commutation failure. It also ensures a controllable commutation mode that does not affect the hybrid converter topology, thereby maximizing the operational stability of the hybrid converter.

[0044] According to an embodiment of the present invention, an embodiment of a commutation control method for a hybrid converter topology structure is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0045] In this embodiment, a commutation control method for a hybrid converter topology is provided, which can be used for the above-mentioned forced commutation hybrid converter topology. Figure 8 FIG. 1 is a flow chart of a commutation control method according to a hybrid converter topology structure according to an embodiment of the present invention. Figure 8 As shown, the process includes the following steps:

[0046] S21, obtaining the working status of the first control valve provided on the main branch.

[0047] The operating status of the first control valve indicates whether the first control valve has experienced any abnormal operation, such as erroneous triggering of the main branch thyristor valve, non-triggering or erroneous shutdown of the main branch first control valve, etc. The hybrid converter monitors the commutation process through its corresponding trigger control system to obtain the operating status of the first control valve.

[0048] S22, determining whether the working status is abnormal.

[0049] The hybrid converter determines whether the operating state of the first control valve, detected by the trigger control system, has experienced a fault such as a fault current, erroneous triggering of the main branch thyristor valve, or failure to trigger or erroneous shutdown of the main branch first control valve. If an abnormality is detected in the operating state, step S23 is executed. Otherwise, other operations are performed, which may include maintaining the current commutation operation or continuing to detect abnormalities in the operating state. These other operations are not specifically limited herein and can be determined by those skilled in the art based on actual needs.

[0050] S23, turns on the bypass branch.

[0051] When an abnormality occurs in the operating state, indicating that the first control valve has experienced an operational anomaly, the bypass branch can be opened to short-circuit the first control valve, allowing the bypass branch to protect the first control valve or replace the first control valve to ensure normal flow through the main branch, thereby preventing the abnormal operation of the first control valve from affecting the flow through the main branch. For example, when a current fault occurs, the bypass branch can be opened to effectively protect the first control valve and prevent damage to the first control valve.

[0052] The commutation control method for the hybrid converter topology structure provided in this embodiment obtains the working status of the first control valve set on the main branch. When the working status of the first control valve is abnormal, the bypass branch is opened to protect the first control valve or replace the first control valve to ensure normal flow of the main branch, thereby ensuring that the hybrid converter topology structure can operate in the conventional commutation mode.

[0053] In this embodiment, a commutation control method for a hybrid converter topology is provided, which can be used for the above-mentioned forced commutation hybrid converter topology. Figure 9 FIG. 1 is a flow chart of a commutation control method according to a hybrid converter topology structure according to an embodiment of the present invention. Figure 9 As shown, the process includes the following steps:

[0054] S31, obtaining a commutation mode of the hybrid converter, where the commutation mode includes a conventional commutation mode and a controllable commutation mode.

[0055] The hybrid converter can detect in real time the commutation mode it is using, which includes conventional and controlled commutation modes. In conventional commutation mode, the converter valve is in rectification operation (power reverse), without the need to protect against commutation failure. In this state, the converter valve closes the bypass branch and controls the closing of the second control valve in the auxiliary branch. This allows the converter valve to achieve normal commutation operation through the action of the thyristor valve, just like a traditional converter valve.

[0056] The controllable commutation mode includes normal operation and forced commutation operation due to AC fault. During normal operation, the main branch is periodically turned on and DC current flows through it. After the main branch is turned on for 120°, the first control valve of the main branch is turned off at low current, and the auxiliary branch is turned on. The first control valve of the main branch establishes a forward voltage, and the thyristor valve of the main branch withstands the reverse pressure and is reliably turned off. When an AC fault occurs on the inverter side, the commutation valve operates in forced commutation. After the commutation of the commutation valve begins, the auxiliary branch is turned on, the first control valve of the main branch is turned off, and the current is transferred to the auxiliary branch. At the same time, the thyristor valve of the main branch establishes a reverse pressure. After the thyristor valve of the main branch is turned off, the second control valve of the auxiliary branch is turned off, and the current is transferred to the auxiliary branch, thereby successfully completing the commutation between the bridge arms.

[0057] S32, determining whether the commutation mode of the hybrid converter is a conventional commutation mode.

[0058] The hybrid converter can determine whether its current commutation mode is the conventional commutation mode based on the difference between the conventional commutation mode and the controllable commutation mode. If the commutation mode is the conventional commutation mode, step S33 is executed; if the commutation mode is the controllable commutation mode, step S36 is executed.

[0059] S33, obtaining the working status of the first control valve provided on the main branch.

[0060] When the commutation mode of the hybrid converter is the normal commutation mode, the operating state of the first control valve is obtained to determine whether the operating state of the first control valve is normal. Detailed description of obtaining the operating state of the first control valve is provided in the description of step S21 in the above embodiment and is not repeated here.

[0061] S34, determining whether the working state is abnormal. Detailed descriptions refer to the corresponding step S22 of the above embodiment, which will not be repeated here.

[0062] S35, when the working state is abnormal, the bypass branch is turned on. Detailed descriptions refer to the corresponding step S23 in the above embodiment, which will not be repeated here.

[0063] S36, controlling the bypass branch to be in an off state, and performing controllable commutation between the main branch and the auxiliary branch.

[0064] When the commutation mode of the hybrid converter is the controllable commutation mode, the bypass branch is controlled to be in the off state, so that controllable commutation can be performed between the main branch and the auxiliary branch without being affected by the bypass branch.

[0065] The commutation control method for the hybrid converter topology structure provided in this embodiment places the bypass branch in a shut-off state when the commutation mode of the hybrid converter is a controllable commutation mode to achieve controllable commutation between the main branch and the auxiliary branch. The bypass branch can also be turned on to switch the hybrid converter from the controllable commutation mode to the conventional commutation mode, thereby completing the functions of the hybrid converter and further improving the operational reliability of the hybrid converter.

[0066] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. An active commutation unit, arranged in the bridge arm circuit of the converter, one end of which is connected to the output end of the converter transformer and the other end is connected to the DC bus, characterized in that: include: A main branch, wherein a thyristor valve and a first control valve are arranged on the main branch, and the first control valve is used for controllably shutting off a forward current; An auxiliary branch is arranged in parallel with the main branch, and a second control valve is arranged on the auxiliary branch, and the second control valve has a forward current controllable shutoff function and a forward and reverse voltage blocking function; a bypass branch, arranged in parallel with the first control valve, the bypass branch being used to protect the first control valve or replace the first control valve to pass the main branch; Wherein, the first control valve comprises: a plurality of control submodules, the plurality of control submodules are arranged in series, and the control submodules are used for forward current shutoff; The bypass branch comprises: a plurality of first bypass sub-branches, wherein the first bypass sub-branches are respectively arranged in parallel at two ends of the control sub-module; The hybrid converter topology is connected to the AC power grid through a converter transformer, and the topology includes a three-phase six-bridge arm circuit, each phase bridge arm includes an upper bridge arm and a lower bridge arm, and the active commutation unit is provided on at least one upper bridge arm or a lower bridge arm; The commutation control method for the hybrid converter topology structure comprises: Obtaining the working status of the first control valve provided on the main branch; Determining whether the working state is abnormal; When the working state is abnormal, the bypass branch is turned on.

2. The active commutation unit according to claim 1, characterized in that: The bypass branch also includes: A second bypass sub-branch, wherein a first end of the second bypass sub-branch is connected to a first end of the first control sub-module, and a second end of the second bypass sub-branch is connected to a first end of the last control sub-module.

3. The active commutation unit according to claim 2, characterized in that: The first bypass sub-branch and / or the second bypass sub-branch comprises: At least one first switch unit is provided, and the at least one first switch unit is arranged in series.

4. The active commutation unit according to claim 2, characterized in that: The first bypass sub-branch and / or the second bypass sub-branch comprises: At least one first thyristor is provided, and the at least one first thyristor is arranged in series.

5. The active commutation unit according to claim 1, characterized in that: Before obtaining the working state of the first control valve arranged on the main branch, the method further includes: Acquire a commutation mode of the hybrid converter, wherein the commutation mode includes a conventional commutation mode and a controllable commutation mode; Determining whether the commutation mode of the hybrid converter is a conventional commutation mode; When the commutation mode of the hybrid converter is the conventional commutation mode, the working state of the first control valve provided on the main branch is obtained.

6. The active commutation unit according to claim 5, characterized in that: Also includes: When the commutation mode of the hybrid converter is a controllable commutation mode, the bypass branch is controlled to be in an off state, and controllable commutation is performed between the main branch and the auxiliary branch.

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