Controllable commutator protection methods and devices

Abstract

This application provides a protection method and device for a controllable commutated converter. The controllable commutated converter has at least one arm comprising a main branch and an auxiliary commutation branch connected in parallel. The auxiliary commutation branch includes a full control valve. The method includes: when the auxiliary commutation branch fails, controlling the auxiliary commutation branch to lock out; when the main branch is turned off and the auxiliary commutation branch is turned on, if the current in the auxiliary commutation branch exceeds a first current threshold, or if the auxiliary commutation branch fails, controlling the main branch to turn on; when the main branch is turned off and the auxiliary commutation branch is turned off, if the voltage of the full control valve in the auxiliary commutation branch exceeds a first voltage threshold, controlling the main branch to turn on.

Description

Technical Field

[0001] This application relates to the field of high voltage direct current transmission technology, specifically to a protection method and device for a controllable commutated converter. Background Technology

[0002] High voltage and ultra-high voltage direct current transmission have large capacities. Existing technology uses a twelve-pulse circuit, with each twelve-pulse circuit consisting of two three-phase six-arm circuits connected in series. Each arm uses a single high-capacity thyristor connected in series. Since the thyristors cannot be controlled to turn off, the existing converter structure has a commutation failure problem.

[0003] With the increasing number of high-voltage and ultra-high-voltage direct current (HVDC) transmission systems connected to the grid, multi-infeed HVDC transmission systems have formed in many regional power grids. When multiple HVDC lines experience simultaneous commutation failures, it can threaten the safe operation of the AC power grid in those regions. As the proportion of renewable energy generation increases, the AC voltage support capacity decreases, placing higher demands on the stable operation of HVDC transmission systems and their ability to suppress commutation failures. Existing HVDC, flexible HVDC, and hybrid HVDC transmission technologies struggle to meet the stringent cost and performance requirements. While HVDC transmission systems based on controllable commutation converters offer certain advantages in terms of overall cost and performance, the technology remains immature, particularly regarding the protection methods for controllable commutation converters, which require further research. Summary of the Invention

[0004] This application provides a protection method for a controllable commutated converter. The controllable commutated converter has at least one arm comprising a main branch and an auxiliary commutated branch connected in parallel. The auxiliary commutated branch includes a full control valve. The method includes: when the auxiliary commutated branch fails, controlling the auxiliary commutated branch to lock out; when the main branch is turned off and the auxiliary commutated branch is turned on, controlling the main branch to turn on if the current in the auxiliary commutated branch exceeds a first current threshold or if the auxiliary commutated branch fails; when the main branch is turned off and the auxiliary commutated branch is turned off, controlling the main branch to turn on if the voltage of the full control valve in the auxiliary commutated branch exceeds a first voltage threshold.

[0005] According to some embodiments, the first current threshold is greater than the rated current of the auxiliary commutation branch and less than or equal to the maximum allowable current of the auxiliary commutation branch.

[0006] According to some embodiments, the first voltage threshold is greater than the rated voltage of the full control valve of the auxiliary commutation branch, and less than or equal to the maximum shut-off voltage of the full control valve of the auxiliary commutation branch.

[0007] According to some embodiments, the auxiliary commutation branch fault includes at least one of grounding fault, power device fault, drive circuit fault, buffer circuit fault, and control circuit fault.

[0008] According to some embodiments, the control of the auxiliary commutation branch blocking includes: controlling the cessation of the auxiliary commutation branch pulse.

[0009] According to some embodiments, the bridge arm further includes a disconnecting switch for separating the auxiliary commutation branch from the main branch, and the protection method further includes: when the auxiliary commutation branch fails, controlling the auxiliary commutation branch to be blocked or / and isolated.

[0010] This application embodiment also provides a controllable commutator protection device, which applies the controllable commutator protection method described above. The protection device includes a detection unit and a protection unit. The detection unit is used to detect the operating parameters and faults of the controllable commutator. Based on the operating parameters of the controllable commutator, the protection unit determines that when the auxiliary commutator branch is faulty, it controls the auxiliary commutator branch to be blocked. When the main branch is turned off and the auxiliary commutator branch is turned on, if the current of the auxiliary commutator branch exceeds a first current threshold or if the auxiliary commutator branch is faulty, it controls the main branch to be turned on. When the main branch is turned off and the auxiliary commutator branch is turned off, if the voltage of the full control valve of the auxiliary commutator branch exceeds a first voltage threshold, it controls the main branch to be turned on.

[0011] According to some embodiments, the bridge arm further includes a disconnecting switch for separating the auxiliary commutation branch from the main branch, and the protection unit controls the auxiliary commutation branch to be blocked or / and isolated when the auxiliary commutation branch fails.

[0012] According to some embodiments, the first current threshold is greater than the rated current of the auxiliary commutation branch and less than or equal to the maximum allowable current of the auxiliary commutation branch; the first voltage threshold is greater than the rated voltage of the full control valve of the auxiliary commutation branch and less than or equal to the maximum shut-off voltage of the full control valve of the auxiliary commutation branch.

[0013] According to some embodiments, the auxiliary commutation branch fault includes at least one of grounding fault, power device fault, drive circuit fault, buffer circuit fault, and control circuit fault.

[0014] The technical solution provided in this application embodiment detects the current and voltage of the auxiliary commutation branch. If a fault, overcurrent or overvoltage problem occurs, the auxiliary commutation branch is blocked or / and isolated, or the main branch is turned on, so as to protect the power devices of the auxiliary commutation branch and improve the reliability of the controllable commutation converter. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of a controllable commutation converter provided in an embodiment of this application.

[0017] Figure 2 This is a schematic diagram of another controllable commutator provided in the embodiments of this application.

[0018] Figures 3a-3i This is a schematic diagram of the semi-controlled valve and the fully controlled valve provided in the embodiments of this application.

[0019] Figure 4 This is a schematic flowchart of a controllable commutator control method provided in an embodiment of this application.

[0020] Figure 5 This is a schematic diagram of a control device for a controllable commutator provided in an embodiment of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] It should be understood that the terms "comprising" and "including" used in the specification and claims of this application indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0023] Figure 1 This is a schematic diagram of a controllable commutation converter provided in an embodiment of this application. The controllable commutation converter has at least one bridge arm, which includes a main branch and an auxiliary commutation branch connected in parallel. The auxiliary commutation branch includes a full control valve.

[0024] According to some embodiments, such as Figure 1 As shown, the controllable commutator has three phases and six arms. Each arm includes a main branch and an auxiliary commutator branch connected in parallel. The main branch includes a semi-controlled valve and a fully controlled valve connected in series, and the auxiliary commutator branch includes a fully controlled valve and a semi-controlled valve connected in series.

[0025] like Figure 1 As shown, the main branch of the upper arm of phase A consists of a semi-controlled valve V41 and a fully controlled valve V42 connected in series, and the auxiliary commutation branch consists of a fully controlled valve V43 and a semi-controlled valve V44 connected in series. The main branch of the upper arm of phase B consists of a semi-controlled valve V61 and a fully controlled valve V62 connected in series, and the auxiliary commutation branch consists of a fully controlled valve V63 and a semi-controlled valve V64 connected in series. The main branch of the upper arm of phase C consists of a semi-controlled valve V21 and a fully controlled valve V22 connected in series, and the auxiliary commutation branch consists of a fully controlled valve V23 and a semi-controlled valve V24 connected in series. The main branch of the lower arm of phase A consists of a semi-controlled valve V11 and a fully controlled valve V12 connected in series, and the auxiliary commutation branch consists of a fully controlled valve V13 and a semi-controlled valve V14 connected in series. The main branch of the lower arm of phase B consists of a semi-controlled valve V31 and a fully controlled valve V32 connected in series, and the auxiliary commutation branch consists of a fully controlled valve V33 and a semi-controlled valve V34 connected in series. The main branch of the C-phase lower arm consists of a semi-controlled valve V51 and a fully controlled valve V52 connected in series, while the auxiliary phase-switching branch consists of a fully controlled valve V53 and a semi-controlled valve V54 connected in series.

[0026] Figure 1 The working principle of the controllable commutation converter shown includes: when a fault may cause commutation failure, the current in the main branch of the commutation arm is transferred to the auxiliary commutation branch, and then controllable commutation is achieved by shutting down the auxiliary commutation branch. Taking the upper arm of phase A as an example, when the semi-control valve V41 of the main branch of the upper arm of phase A may cause commutation failure due to a fault, the fully control valve V42 is shut off, transferring the current in the main branch to the auxiliary commutation branch. After the semi-control valve V41 of the main branch of the upper arm of phase A is shut off, the fully control valve V43 of the auxiliary commutation branch is shut off, and the current is commutated from the upper arm of phase A to the upper arm of phase B, thus achieving controllable commutation.

[0027] According to some embodiments, such as Figure 2 As shown, the controllable commutator has three phases and six arms. Each arm includes a main branch and an auxiliary commutator branch connected in parallel. The main branch of the arm includes a semi-controlled valve, and the auxiliary commutator branch includes a fully controlled valve and a capacitor connected in series.

[0028] like Figure 2 As shown, the main branch of the upper arm of phase A consists of a semi-controlled valve V41, and the auxiliary commutation branch consists of a fully controlled valve V43 and a capacitor C43 connected in series. The main branch of the upper arm of phase B consists of a semi-controlled valve V61, and the auxiliary commutation branch consists of a fully controlled valve V63 and a capacitor C63 connected in series. The main branch of the upper arm of phase C consists of a semi-controlled valve V21, and the auxiliary commutation branch consists of a fully controlled valve V23 and a capacitor C23 connected in series. The main branch of the lower arm of phase A consists of a semi-controlled valve V11, and the auxiliary commutation branch consists of a fully controlled valve V13 and a capacitor C13 connected in series. The main branch of the lower arm of phase B consists of a semi-controlled valve V31, and the auxiliary commutation branch consists of a fully controlled valve V33 and a capacitor C33 connected in series. The main branch of the lower arm of phase C consists of a semi-controlled valve V51, and the auxiliary commutation branch consists of a fully controlled valve V53 and a capacitor C53 connected in series.

[0029] Figure 2 The working principle of the controllable commutation converter shown includes: During normal operation, the capacitor controlling the auxiliary commutation branch is under negative voltage. When a fault may occur and commutation failure is possible, the current in the main branch of the commutation arm is transferred to the auxiliary commutation branch, and then controllable commutation is achieved by shutting down the auxiliary commutation branch. Taking the upper arm of phase A as an example, when the upper arm of phase A is shut down, the full control valve V43 is reverse-biased, and capacitor C43 is reverse-charged, resulting in a negative voltage. When the half control valve V41 of the main branch of the upper arm of phase A may fail to commutate due to a fault, the full control valve V43 is forward-biased, transferring the current in the main branch to the auxiliary commutation branch. After the half control valve V41 of the main branch of the upper arm of phase A is shut down, the full control valve V43 is shut down, and the current is commutated from the upper arm of phase A to the upper arm of phase B, thus achieving auxiliary commutation.

[0030] According to some embodiments, surge arresters are connected in parallel at both ends of the semi-controlled valve and the fully controlled valve.

[0031] A semi-controlled valve is composed of semi-controlled devices, including but not limited to thyristors. Each semi-controlled device is configured with a corresponding trigger circuit. Optionally, a semi-controlled valve may consist of thyristors and diodes connected in series or parallel.

[0032] According to some embodiments, the semi-controlled valve includes thyristors 4 connected in series, such as... Figure 3a As shown, it can only control the on-state, not the off-state, and has unidirectional current-carrying capability and bidirectional voltage-blocking capability.

[0033] A fully controlled valve consists of fully controlled devices, including but not limited to at least one of the following: IGCT (Integrated Gate Commutated Thyristors), IGBT (Insulated Gate Bipolar Transistor), GTO (Gate Turn-Off Thyristor), and MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Each fully controlled device is configured with corresponding drive circuits and / or buffer circuits. Fully controlled valves are classified into unidirectional fully controlled valves, bidirectional fully controlled valves, and MMC (Modular Multilevel Converter) single valves.

[0034] According to some embodiments, the one-way fully controlled valve includes an IGBT module connected in series, the IGBT module including an IGBT5 and a diode 7 connected in parallel therewith, such as... Figure 3b As shown, it can control the on and off states in only one direction, and has the ability to conduct current in both directions and block voltage in one direction.

[0035] According to some embodiments, the one-way fully controllable valve includes IGCT6 connected in series, such as Figure 3c As shown, it can control the on and off in only one direction, and has the ability to carry current in one direction and block voltage in both directions.

[0036] According to some embodiments, the one-way fully controlled valve includes an IGBT module and a diode 7 connected in series, such as... Figure 3d As shown, it can control the on and off in only one direction, and has the ability to carry current in one direction and block voltage in both directions.

[0037] According to some embodiments, the one-way fully controlled valve includes a sub-module connected in series, the sub-module including an IGCT6 and a thyristor 4 connected in anti-parallel, such as Figure 3e As shown, it can only control the on and off in one direction, and has the ability to conduct current in both directions and block voltage in both directions.

[0038] According to some embodiments, the bidirectional fully controlled valve includes a forward IGBT module and a reverse IGBT module connected in series, such as... Figure 3f As shown, it can be controlled to turn on and off in both directions, and has the ability to conduct current in both directions and block voltage in both directions.

[0039] According to some embodiments, the bidirectional fully controlled valve includes sub-modules connected in series, and the sub-modules include forward IGCT6 and reverse IGCT6 connected in parallel, such as... Figure 3g As shown, it can be controlled to turn on and off in both directions, and has the ability to conduct current in both directions and block voltage in both directions.

[0040] According to some embodiments, the MMC single valve includes sub-modules connected in series. Each sub-module includes two IGBT modules and a capacitor 8. The connection point of the two IGBT modules serves as the positive terminal of the sub-module, and the other end of one of the IGBT modules serves as the negative terminal. The sub-modules are connected in series, as shown below. Figure 3h As shown, it can only control the opening and closing in one direction, and has bidirectional current carrying capacity and unidirectional voltage blocking capacity.

[0041] According to some embodiments, the MMC single valve includes a sub-module connected in series. Each sub-module includes four IGBT modules and a capacitor 8. The IGBT modules are connected in series in pairs and then in parallel, and are also connected in parallel with the capacitor 7. The connection points where the IGBT modules are connected in series in pairs serve as the positive and negative terminals of the sub-module, respectively. Figure 3i As shown, it can be controlled to turn on and off in both directions, and has bidirectional current carrying capacity and bidirectional voltage blocking capacity.

[0042] Figure 4 This is a schematic flowchart of a control method for a controllable commutated converter provided in an embodiment of this application. It is applicable to the controllable commutated converter described above, and the method includes the following steps.

[0043] In S110, when the auxiliary commutation branch fails, the auxiliary commutation branch is locked.

[0044] Auxiliary commutation branch faults include, but are not limited to, at least one of the following: grounding fault, power device fault, drive circuit fault, buffer circuit fault, and control circuit fault.

[0045] by Figure 1 Taking the upper arm of phase A as an example, determine whether the full control valve V43 and the partial control valve V44 of the auxiliary commutation branch are faulty. If the full control valve V43 or the partial control valve V44 of the auxiliary commutation branch is faulty, control the full control valve V43 or the partial control valve V44 of the auxiliary commutation branch to be locked. The auxiliary commutation branch is locked by controlling the cessation of pulses from the full control valve V43 or the partial control valve V44 of the auxiliary commutation branch.

[0046] by Figure 2 Taking the upper arm of phase A as an example, it is determined whether the full control valve V43 and capacitor C43 of the auxiliary commutation branch are faulty. If the full control valve V43 or capacitor C43 of the auxiliary commutation branch is faulty, the full control valve V43 of the auxiliary commutation branch is locked. The locking of the auxiliary commutation branch is to control the cessation of the pulse of the full control valve V43 of the auxiliary commutation branch.

[0047] According to some embodiments, the bridge arm circuit also includes a disconnecting switch to separate the auxiliary commutation branch from the main branch. In the event of a fault in the auxiliary commutation branch, the auxiliary commutation branch is controlled to be blocked or / and isolated.

[0048] In S120, when the main branch is turned off and the auxiliary commutation branch is turned on, if the current of the auxiliary commutation branch exceeds the first current threshold or if the auxiliary commutation branch fails, the main branch is controlled to turn on.

[0049] by Figure 1 Taking the upper arm of phase A as an example, when the semi-control valve V41 and full control valve V42 of the main branch are closed and the full control valve V43 and semi-control valve V44 of the auxiliary commutation branch are open, if the current of the auxiliary commutation branch exceeds the first current threshold or if the auxiliary commutation branch fails, the semi-control valve V41 and full control valve V42 of the main branch will be opened.

[0050] by Figure 2 Taking the upper arm of phase A as an example, when the semi-controlled valve V41 of the main branch is closed and the full-controlled valve V43 of the auxiliary commutation branch is open, if the current of the auxiliary commutation branch exceeds the first current threshold or if the auxiliary commutation branch fails, the semi-controlled valve V41 of the main branch is controlled to open.

[0051] According to some embodiments, the first current threshold is greater than the rated current of the auxiliary commutation branch and less than or equal to the maximum allowable current of the auxiliary commutation branch, but is not limited thereto.

[0052] In S130, when the main branch is turned off and the auxiliary commutation branch is turned off, if the voltage of the full control valve of the auxiliary commutation branch exceeds the first voltage threshold, the main branch is controlled to turn on.

[0053] by Figure 1 Taking the upper arm of phase A as an example, when the semi-control valve V41 and full control valve V42 of the main branch are closed, and the full control valve V43 and semi-control valve V44 of the auxiliary commutation branch are closed, if the voltage of the full control valve V43 of the auxiliary commutation branch exceeds the first voltage threshold, the semi-control valve V41 and full control valve V42 of the main branch are controlled to be turned on.

[0054] by Figure 2 Taking the upper arm of phase A as an example, when the semi-controlled valve V41 of the main branch is closed and the full-controlled valve V43 of the auxiliary commutation branch is closed, if the voltage of the full-controlled valve V43 of the auxiliary commutation branch exceeds the first voltage threshold, the semi-controlled valve V41 of the main branch is controlled to open.

[0055] According to some embodiments, the first voltage threshold is greater than the rated voltage of the full control valve V43 of the auxiliary commutation branch and less than or equal to the maximum shut-off voltage of the full control valve V43 of the auxiliary commutation branch, but is not limited thereto.

[0056] The technical solution provided in this embodiment detects the current and voltage of the auxiliary commutation branch. If a fault, overcurrent or overvoltage problem occurs, the auxiliary commutation branch is blocked or / and isolated, or the main branch is controlled to conduct, so as to protect the power devices of the auxiliary commutation branch and improve the working reliability of the controllable commutation converter.

[0057] Figure 5 This is a schematic diagram of a controllable commutator control device provided in an embodiment of this application. The control device 300 includes a detection unit 310 and a protection unit 320.

[0058] The detection unit 310 is used to detect the operating parameters and faults of the controllable commutation converter, including but not limited to the AC voltage, DC voltage, DC current, operating status of the converter, and the operating status of the semi-controlled valve and the fully controlled valve.

[0059] The protection unit 320 determines whether the auxiliary commutation branch is faulty based on the operating parameters of the controllable commutation converter. If the auxiliary commutation branch is faulty, it controls the commutation branch to be blocked. When the main branch is turned off and the auxiliary commutation branch is turned on, if the current in the auxiliary commutation branch exceeds a first current threshold, or if the auxiliary commutation branch is faulty, it controls the main branch to be turned on. When the main branch is turned off and the auxiliary commutation branch is turned off, if the voltage of the full control valve of the auxiliary commutation branch exceeds a first voltage threshold, it controls the main branch to be turned on. According to some embodiments, the bridge arm also includes a disconnecting switch, which is used to separate the auxiliary commutation branch from the main branch. When the auxiliary commutation branch is faulty, the protection unit 320 controls the auxiliary commutation branch to be blocked or / and isolated.

[0060] Auxiliary commutation branch faults include, but are not limited to, at least one of the following: grounding fault, power device fault, drive circuit fault, buffer circuit fault, and control circuit fault.

[0061] According to some embodiments, the first current threshold is greater than the rated current of the auxiliary commutation branch and less than or equal to the maximum allowable current of the auxiliary commutation branch, but is not limited thereto.

[0062] According to some embodiments, the first voltage threshold is greater than the rated voltage of the full control valve V43 of the auxiliary commutation branch and less than or equal to the maximum shut-off voltage of the full control valve V43 of the auxiliary commutation branch, but is not limited thereto.

[0063] The above embodiments are only for illustrating the technical concept of this application and should not be used to limit the scope of protection of this application. Any modifications made to the technical solution based on the technical concept proposed in this application shall fall within the scope of protection of this application.

Claims

1. A protection method for a controllable commutated converter, wherein the controllable commutated converter has at least one arm comprising a main branch and an auxiliary commutation branch connected in parallel, the auxiliary commutation branch comprising a full control valve, the method comprising: When the auxiliary commutation branch fails, the auxiliary commutation branch is locked out. When the main branch is turned off and the auxiliary commutation branch is turned on, if the current of the auxiliary commutation branch exceeds the first current threshold or if the auxiliary commutation branch fails, the main branch is controlled to turn on. When the main branch is turned off and the auxiliary commutation branch is turned off, if the voltage of the full control valve of the auxiliary commutation branch exceeds the first voltage threshold, the main branch is controlled to be turned on.

2. The protection method as described in claim 1, wherein, The first current threshold is greater than the rated current of the auxiliary commutation branch and less than or equal to the maximum allowable current of the auxiliary commutation branch.

3. The protection method as described in claim 1, wherein, The first voltage threshold is greater than the rated voltage of the full control valve of the auxiliary commutation branch, and less than or equal to the maximum shut-off voltage of the full control valve of the auxiliary commutation branch.

4. The protection method as described in claim 1, wherein, The auxiliary commutation branch faults include at least one of the following: grounding fault, power device fault, drive circuit fault, buffer circuit fault, and control circuit fault.

5. The protection method as described in claim 1, wherein, The control of the auxiliary commutation branch blocking includes: controlling the cessation of the auxiliary commutation branch pulse.

6. The protection method as described in claim 1, wherein, The bridge arm also includes a disconnect switch for separating the auxiliary commutation branch from the main branch, and the protection method further includes: When the auxiliary commutation branch fails, the auxiliary commutation branch is controlled to be blocked or / and isolated.

7. A controllable commutator protection device, employing the controllable commutator protection method according to any one of claims 1 to 6, the protection device comprising: The detection unit is used to detect the operating parameters and faults of the controllable commutator. The protection unit, based on the operating parameters of the controllable commutator, determines that the auxiliary commutator branch is faulty and controls the auxiliary commutator branch to be locked out. When the main branch is turned off and the auxiliary commutation branch is turned on, if the current of the auxiliary commutation branch exceeds a first current threshold or if the auxiliary commutation branch fails, the main branch is controlled to turn on; when the main branch is turned off and the auxiliary commutation branch is turned off, if the voltage of the full control valve of the auxiliary commutation branch exceeds a first voltage threshold, the main branch is controlled to turn on.

8. The protection device as claimed in claim 7, wherein, The bridge arm also includes a disconnecting switch for separating the auxiliary commutation branch from the main branch. When the auxiliary commutation branch fails, the protection unit controls the auxiliary commutation branch to be blocked or / and isolated.

9. The protection device as claimed in claim 7, wherein, The first current threshold is greater than the rated current of the auxiliary commutation branch and less than or equal to the maximum allowable current of the auxiliary commutation branch; the first voltage threshold is greater than the rated voltage of the full control valve of the auxiliary commutation branch and less than or equal to the maximum shut-off voltage of the full control valve of the auxiliary commutation branch.

10. The protection device as claimed in claim 7, wherein, The auxiliary commutation branch faults include at least one of the following: grounding fault, power device fault, drive circuit fault, buffer circuit fault, and control circuit fault.

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