A converter protection circuit, a protection method and a device

Abstract

The present invention discloses a converter protection circuit, which is used to protect a voltage source converter in a converter with DC fault ride-through capability, which is composed of a diode valve group or a current source type valve group unit and a voltage source type valve group unit connected in series. A bypass thyristor valve group is connected in parallel at both ends of the converter with DC fault ride-through capability, and the anode and cathode of the bypass thyristor valve group are respectively connected to the positive and negative electrodes of the converter with DC fault ride-through capability. The present invention also discloses a converter protection method, in which the voltage source converter detects that an AC or DC system fails, causing the voltage or current of the voltage source converter to exceed a threshold value, and the bypass thyristor valve group is put into operation, and the fault information is transmitted to a rectifier station, and the rectifier station reduces the DC voltage, reduces the DC current to zero, and the bypass thyristor valve group current passes through zero and is shut down. The above-mentioned voltage source converter protection circuit effectively solves the overvoltage and overcurrent problems of the voltage source converter caused by DC charging, and ensures the reliable operation of the voltage source converter.

Description

Technical Field

[0001] The present invention belongs to the field of flexible direct current power transmission and high voltage direct current power transmission, and in particular relates to a converter protection circuit and a protection method and device. Background Art

[0002] The advantages of current source HVDC transmission based on thyristors are low converter losses, and the DC system can be restarted by phase shifting when a DC line fault occurs; the disadvantages are that the inverter side converter works in active inverter and cannot be connected to the passive system; the inverter side is connected to the weak AC system and is prone to phase change failure after disturbance; the reactive power consumption is large, and the voltage and current harmonic content is high, so it is necessary to install a filter device to provide reactive power and filtering. The advantages of DC transmission based on voltage source converters are high controllability, can be connected to passive systems, and do not require reactive compensation devices; the disadvantages are large converter switch losses, and the modular multilevel converter with a half-bridge structure cannot control the fault current when the DC side fails. After the fault occurs, the fault can only be removed by disconnecting the AC side circuit breaker.

[0003] For DC side faults, ABB solves the problem by adding a circuit breaker to the DC line; Siemens solves the problem by using a full-bridge circuit structure; Alstom solves the problem by using a full-bridge circuit and connecting power electronic switching devices in series with the bridge arm; Zhejiang University solves the problem by connecting a diode in series with the main circuit. The above solutions will still cause serious overvoltage and overcurrent in the voltage source converter when an extreme fault occurs in the DC transmission system, such as grounding between the voltage source converter and the transformer, or a three-phase short circuit in the AC system. In order to ensure the reliable operation of the above converter, a new protection circuit, protection method and device are proposed based on this structure. Summary of the invention

[0004] The purpose of the present invention is to provide a converter protection circuit to prevent serious overvoltage or overcurrent in a voltage source converter, and to control the rectifier side converter to make the DC current reach zero, thereby achieving fault restart and protecting the voltage source valve group unit for reliable operation; at the same time, a converter protection method and device are provided for controlling this converter protection circuit.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: a converter protection circuit for protecting a voltage source converter in a voltage source valve group unit, adopting one of the following three solutions:

[0006] Solution 1: at least one bypass thyristor valve group and one diode valve group are included, the diode valve group is connected in series with a voltage source type valve group unit without DC fault ride-through capability to form a converter with DC fault ride-through capability, the bypass thyristor valve group is connected in parallel at both ends of the converter with DC fault ride-through capability, the anode of the bypass thyristor valve group is connected to the positive electrode of the converter, and the cathode of the bypass thyristor valve group is connected to the negative electrode of the converter;

[0007] Solution 2: at least one bypass thyristor valve group and one current source valve group unit; the connection method is that the current source valve group unit is connected in series with the voltage source valve group unit without DC fault ride-through capability to form a converter with DC fault ride-through capability; the bypass thyristor valve group is connected in parallel at both ends of the converter with DC fault ride-through capability, the anode of the bypass thyristor valve group is connected to the positive electrode of the converter, and the cathode of the bypass thyristor valve group is connected to the negative electrode of the converter;

[0008] Solution three: at least one bypass thyristor valve group is included, the anode of the bypass thyristor valve group is connected to the positive electrode of the voltage source type valve group unit with DC fault ride-through capability, and the cathode of the bypass thyristor valve group is connected to the negative electrode of the voltage source type valve group unit with DC fault ride-through capability.

[0009] In the above scheme, there are two topological structures: the diode valve group is connected in series with the voltage source type valve group unit without DC fault ride-through capability:

[0010] (1) The cathode of the diode valve group is connected to the positive electrode of the voltage source type valve group unit; or

[0011] (2) The anode of the diode valve group is connected to the cathode of the voltage source type valve group unit;

[0012] For the first structure, the positive electrode of the converter with DC fault ride-through capability is the anode of the diode valve group, and the negative electrode of the converter with DC fault ride-through capability is the negative electrode of the voltage source type valve group unit; for the second structure, the positive electrode of the converter with DC fault ride-through capability is the positive electrode of the voltage source type valve group unit, and the negative electrode of the converter with DC fault ride-through capability is the cathode of the diode valve group.

[0013] The above-mentioned voltage source valve group unit without DC fault ride-through capability is unable to realize DC side fault ride-through of the DC transmission system by itself. The voltage source converter without DC fault ride-through capability by itself is any one or more of the following: a two-level converter, a diode clamped multi-level converter, a modular multi-level converter MMC composed of half-bridge structure sub-modules, a two-level cascade converter CSL or a stacked two-level converter CTL; the diode valve group is composed of multiple diodes connected in series.

[0014] The above-mentioned voltage source valve group unit with DC fault ride-through capability can realize DC side fault ride-through of the DC transmission system by itself, and is realized by adding auxiliary power electronic devices to suppress reverse current on the basis of a voltage source converter without DC fault ride-through capability. The voltage source converter with DC fault ride-through capability is any one or more of the following: a modular multilevel converter MMC composed of full-bridge structure submodules, a two-level cascade converter CSL, a stacked two-level converter CTL, a hybrid modular multilevel converter HMC composed of half-bridge and full-bridge structure submodules, or a diode clamped modular multilevel converter.

[0015] In the above scheme, there are two topological structures in which the current source valve group unit is connected in series with the voltage source valve group unit without DC fault ride-through capability:

[0016] (1) The cathode of the current source type valve group unit is connected to the positive electrode of the voltage source type valve group unit; or

[0017] (2) The anode of the current source type valve group unit is connected to the cathode of the voltage source type valve group unit;

[0018] For the first structure, the positive electrode of the converter with DC fault ride-through capability is the anode of the current source valve group unit; the negative electrode of the converter with DC fault ride-through capability is the negative electrode of the voltage source valve group unit; for the second structure, the positive electrode of the converter with DC fault ride-through capability is the positive electrode of the voltage source valve group unit; the negative electrode of the converter with DC fault ride-through capability is the cathode of the current source valve group unit.

[0019] The above-mentioned current source valve group unit includes a grid-commutating converter; or includes a grid-commutating converter and a bypass switch, which are connected in parallel; or includes a grid-commutating converter, a bypass switch and a knife switch assembly, the grid-commutating converter is connected in parallel with the bypass switch, and the two ends of the parallel-connected unit are respectively connected to one end of the knife switch, and the other end of the knife switch is connected in parallel with the bypass knife switch.

[0020] The grid-commutated converter is a six-pulse bridge circuit or a twelve-pulse bridge circuit, which is composed of non-shutdown half-controlled power semiconductors.

[0021] The above-mentioned voltage source valve group unit includes a voltage source converter; or a voltage source converter and its bypass circuit; or includes a voltage source converter and its bypass circuit and a knife switch assembly, and the two ends of the voltage source converter and its bypass circuit are respectively connected to one end of the knife switch, and the other end of the knife switch is connected in parallel with the bypass knife switch.

[0022] The voltage source converter and its bypass circuit are a circuit in which the voltage source converter is connected in parallel with a bypass switch; or a circuit in which the bypass switch is connected to an inductor and then connected in parallel with the voltage source converter; or a circuit in which the voltage source converter is connected to an inductor and then connected in parallel with the bypass switch. The bypass switch is any one or more of the following: a mechanical switch, a power electronic switch or a knife switch.

[0023] The above-mentioned voltage source converter is composed of fully-controlled power semiconductors that can be turned off; the fully-controlled power semiconductors that can be turned off are any one or more of the following: insulated gate bipolar transistor IGBT, integrated gate-commutated thyristor IGCT, turn-off thyristor GTO, power field effect transistor Power MOSFET, electron injection enhanced gate transistor IEGT, gate-commutated thyristor GCT or silicon carbide enhancement junction field effect transistor SiC-JFET.

[0024] The bypass thyristor valve group includes only one bridge arm, which is composed of multiple thyristors connected in series and includes a corresponding control protection circuit; or the bypass thyristor valve group is a bypass pair of parallel grid-commutated converters or is realized by fast phase shifting of the parallel grid-commutated converters.

[0025] In order to ensure reliable shut-off of the thyristor, a DC conversion switch or an isolating switch is connected in series at the beginning or end of the plurality of thyristors connected in series.

[0026] The present invention also provides a converter protection method, which is used for the above-mentioned converter protection circuit, and is characterized in that: when a voltage source type valve group unit detects a fault, a bypass thyristor valve group is put into operation, and the fault information is transmitted to the rectifier station. For a fault that can be self-recovered or isolated instantaneously, the rectifier side reduces the DC voltage and the DC current, controls the bypass thyristor valve group current to zero and shuts it down. After the fault disappears, the DC transmission system is restarted through coordinated control of the rectifier side and the inverter side; for a fault that cannot be self-recovered or isolated instantaneously, the voltage source type valve group unit or the DC transmission system is locked through coordinated control of the rectifier side and the inverter side.

[0027] The faults detected by the above-mentioned voltage source valve group unit include control system faults, valve area faults, main transformer area faults and AC system faults; the specific method of fault detection is: by detecting that the total DC voltage, DC current or bridge arm current of the voltage source valve group unit exceeds the threshold; or by detecting that the sub-module voltage or current exceeds the threshold; or by detecting the AC voltage or AC current to indirectly predict or assist in judgment; or by the appearance of a shutdown signal of the voltage source valve group unit, a protection action signal, a locking signal or the disappearance of an operation signal.

[0028] The above-mentioned control of the bypass thyristor valve group current to zero and shutting down is achieved by the local station taking the lead in controlling the bypass thyristor valve group current to zero, or transmitting the fault information to the opposite station, the opposite station taking the lead in controlling the bypass thyristor valve group current to zero, or the two stations coordinating to control the bypass thyristor valve group current to zero; the method of controlling the bypass thyristor valve group current to zero is to apply zero pressure or reverse pressure to the bypass thyristor valve group, or to disconnect the DC conversion switch in the current loop of the DC transmission system.

[0029] The above-mentioned fault information is transmitted to the rectifier station when the inter-station communication is normal. The rectifier station receives the fault information sent by the inverter station or the rectifier station detects the DC voltage and DC current to identify the fault information. In the case of an inter-station communication failure, the rectifier station detects the DC voltage and DC current to identify the fault information. The fault that can be self-recovered or isolated instantly is a fault that can extinguish the arc instantly or can be quickly isolated by a switch or a knife switch; the fault that cannot be self-recovered or isolated instantly is a permanent fault that cannot extinguish the arc instantly or cannot be isolated by a switch or a knife switch.

[0030] The present invention also provides a converter protection device, which is used for the above converter protection circuit, characterized in that the device comprises a detection unit, a protection unit and a control unit, wherein:

[0031] The detection unit detects the DC voltage, DC current, bridge arm current of the voltage source valve group unit, the voltage and current of the submodule, the current flowing through the bypass thyristor valve group, the AC voltage and AC current connected to the AC system, the shutdown signal, protection action signal, locking signal, and operation signal of the voltage source valve group unit; determines whether there is a fault in the voltage source valve group unit, and triggers the protection unit if there is a fault;

[0032] The protection unit, when it is determined that the voltage source type valve group unit fails, puts the bypass thyristor valve group into operation, transmits the fault information to the rectifier station, and triggers the control unit;

[0033] The control unit reduces the DC voltage and the DC current on the rectifier side. If the voltage source type valve group unit can be self-recovered or isolated instantly after the fault occurs, the bypass thyristor valve group current is controlled to zero and shut down. After the fault disappears, the DC power transmission system is restarted. If the voltage source type valve group unit cannot be self-recovered or isolated instantly after the fault occurs, the voltage source type valve group unit or the DC power transmission system is locked.

[0034] The beneficial effects of the present invention are: a converter protection circuit, a protection method and a device are proposed, which releases DC energy by putting into bypass thyristors to prevent overvoltage or overcurrent in the voltage source converter in the converter with DC fault ride-through capability, and controls the current on the rectifier side to zero to achieve fault restart. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1A converter protection circuit structure of the present invention;

[0036] Among them, (a) is the cathode of the diode valve group connected to the positive electrode of the voltage source type valve group unit without DC fault ride-through capability, (b) is the anode of the diode valve group connected to the negative electrode of the voltage source type valve group unit without DC fault ride-through capability, (c) is the voltage source type valve group unit with DC fault ride-through capability, (d) is the cathode of the current source type valve group unit connected to the positive electrode of the voltage source type valve group unit, (e) is the anode of the current source type valve group unit connected to the negative electrode of the voltage source type valve group unit;

[0037] Figure 2 These are two typical submodule structures used in modular multilevel converters;

[0038] Among them, (a) is a half-bridge structure submodule, and (b) is a full-bridge structure submodule;

[0039] Figure 3 It is a structural diagram of a current source type valve group unit;

[0040] Figure 4 It is a structural diagram of a voltage source type valve group unit;

[0041] Figure 5 is a voltage source converter and its bypass circuit;

[0042] Figure 6 It is a hybrid DC transmission circuit structure in which the sending end is based on a grid-commutated converter and the receiving end is based on a voltage source converter;

[0043] Figure 7 The sending end is based on a grid-commutated converter series structure, and the receiving end is based on a hybrid DC transmission circuit structure based on a grid-commutated converter and a voltage source converter series structure;

[0044] Figure 8 A converter protection method of the present invention;

[0045] Fig. 9 The invention relates to a converter protection device. DETAILED DESCRIPTION

[0046] Exemplary embodiments of the invention are described with reference to the following drawings, wherein identical components are provided with the same reference numerals. Figure 1 A converter protection circuit proposed in the present invention is used to protect a converter with DC fault ride-through capability, and includes at least one bypass thyristor valve group 1. The bypass thyristor valve group 1 is connected in parallel at both ends of the converter with DC fault ride-through capability, the anode of the bypass thyristor valve group 1 is connected to the positive electrode of the converter with DC fault ride-through capability, and the cathode of the bypass thyristor valve group 1 is connected to the negative electrode of the converter with DC fault ride-through capability.

[0047] Figure 1 (a) and Figure 1 (b) is a topological structure in which a diode valve group 2 is connected in series with a voltage source type valve group unit that does not have a DC fault ride-through capability: Figure 1 (a) The cathode of the diode valve group is connected to the positive electrode X1 of the voltage source type valve group unit without DC fault ride-through capability, the positive electrode of the converter is the anode of the diode valve group 2, the negative electrode of the converter is the negative electrode X2 of the voltage source type valve group unit, and the two ends of the converter are connected in parallel to bypass the thyristor valve group 1; Figure 1 (b) The anode of the diode valve group is connected to the negative electrode X2 of the voltage source type valve group unit without DC fault ride-through capability, the positive electrode of the converter is the positive electrode X1 of the voltage source type valve group unit, the negative electrode of the converter is the cathode of the diode valve group 2, and the two ends of the converter are connected in parallel to the bypass thyristor valve group 1; Figure 1 (c) is a bypass thyristor valve group 1 connected in parallel at both ends of a voltage source type valve group unit with DC fault ride-through capability; Figure 1 (d) and Figure 1 (e) Two hybrid DC converter topologies consisting of a current source valve group unit and a voltage source valve group unit connected in series: Figure 1 (d) The cathode X3 of the current source valve group unit and the positive electrode X1 of the voltage source valve group unit are connected, the positive electrode of the converter with DC fault ride-through capability is the anode X4 of the current source valve group unit, and the negative electrode of the converter with DC fault ride-through capability is the negative electrode X2 of the voltage source valve group unit; Figure 1 (e) The anode X4 of the current source type valve group unit and the cathode X2 of the voltage source type valve group unit are connected, the positive electrode of the converter with DC fault ride-through capability is the positive electrode X1 of the voltage source type valve group unit, and the negative electrode of the converter with DC fault ride-through capability is the cathode X3 of the current source type valve group unit.

[0048] Figure 2 These are two typical submodule structures used in modular multilevel converters. Figure 2 (a) is a submodule of a half-bridge structure, which consists of two IGBT switching devices and a capacitor, with port A being its positive terminal and port B being its negative terminal. The submodules of the half-bridge structure are connected in series to form a voltage source converter without DC fault ride-through capability; Figure 2 (b) is a full-bridge submodule, which consists of four IGBT switching devices and a capacitor. Port A is its positive terminal and port B is its negative terminal. The full-bridge submodules are connected in series to form a voltage source converter with DC fault ride-through capability. Figure 2 (a) and Figure 2 The sub-modules in (b) are mixed in series to form a voltage source converter with DC fault ride-through capability.

[0049] Figure 3It is a structural diagram of a current source type valve group unit, which has three structural forms: including a grid-commutated converter 3, such as Figure 3 (a); including a grid-commutated converter 3 connected in parallel with a bypass switch 4, such as Figure 3 (b) as shown; including a grid phase-commutating converter 3 and a bypass mechanical switch 4 connected in parallel, the two ends of the unit after parallel connection are respectively connected to one end of the connection switch 5, and the other end of the connection switch 5 is connected in parallel with the bypass switch 6, as Figure 3 (c) as shown.

[0050] Figure 4 It is a structural diagram of a voltage source valve group unit. There are two structural forms: including voltage source converters, such as Figure 4 (a); including a voltage source converter and its bypass circuit, such as Figure 4 (b) as shown; including a voltage source converter and its bypass circuit, and the two ends X5, X6 are respectively connected to one end of the connection switch 5, and the other end of the connection switch 5 is connected in parallel with the bypass switch 6, as shown Figure 4 (c) As shown. Among them, the voltage source converter and its bypass circuit have three structural forms: bypass mechanical switch or power electronic switch 8 and voltage source converter 7 in parallel circuit, such as Figure 5 (a); the bypass mechanical switch or power electronic switch 8 is connected to the inductor 9 and then connected in parallel with the voltage source converter 7, as shown in FIG. Figure 5 (b); the voltage source converter 7 is connected to the inductor 9 and then connected in parallel with the bypass mechanical switch or power electronic switch 8, as shown in FIG. Figure 5 (c) as shown.

[0051] The grid commutated converter 3 is a six-pulse or twelve-pulse three-phase bridge circuit, and the twelve-pulse three-phase bridge circuit includes two six-pulse three-phase bridge circuits connected in series. The voltage source converter 7 is any one or more of the following: a two-level converter, a diode clamped multilevel converter, a modular multilevel converter MMC, a hybrid multilevel converter HMC, a two-level cascade converter CSL or a stacked two-level converter CTL.

[0052] Figure 6An embodiment of a converter composed of a current source valve group unit on the rectifier side of a high-voltage direct current transmission device and a converter composed of a diode valve group 2 and a voltage source valve group unit without a DC fault ride-through capability connected in series on the inverter side is shown. The rectifier station 24 of the high-voltage direct current transmission device is composed of a current source valve group unit 23, and the inverter station 25 is composed of a positive converter and a negative converter respectively composed of voltage source valve group units 21 and 22 without a DC fault ride-through capability. The valve group 3 is a grid commutation converter, which is connected to the secondary winding of the high-voltage direct current transmission transformer 16 based on the grid commutation, and the valve group 7 is a voltage source converter, which is connected to the secondary winding of the high-voltage direct current transmission transformer 17 based on the voltage source converter. The rectifier station 24 is equipped with an AC filter 20, which is connected to the AC grid 10 through an AC switch 19 to filter out harmonics and provide reactive power. It is separated and connected with the AC grid 10 through an AC switch 11. In order to suppress the bridge arm circulation of the voltage source type valve group and the surge current under fault, a bridge arm reactor 12 is provided; in order to smooth the DC voltage of the DC circuit and suppress the DC fault current, a smoothing reactor 13 is provided. Figure 6 The grounding electrode conductor 18 is shown in the figure, which is used to connect the converter to the grounding electrode. A DC filter 14 is configured between the rectifier station DC line 15 and the grounding electrode conductor 18. The positive electrode of the inverter station voltage source type valve group unit 21 is connected to the cathode of the diode valve group 2, and its two ends are connected in parallel to bypass the thyristor valve group 1. The negative electrode of the inverter station voltage source type valve group unit 22 is connected to the anode of the diode valve group 2, and its two ends are connected in parallel to bypass the thyristor valve group 1.

[0053] Figure 7 An embodiment of a hybrid DC converter is shown, in which the rectifier side of a high-voltage direct current transmission device is composed of a converter composed of a current source type valve group unit connected in series, and the inverter side is composed of a current source type valve group unit and a voltage source type valve group unit connected in series. The rectifier station 24 of the high-voltage direct current transmission device is composed of a topological structure 28 in which current source type valve group units are connected in series, and the inverter station 25 is composed of hybrid DC converters 26 and 27, which respectively form its positive converter and negative converter. The valve group 3 is a grid commutation converter, which is connected to the secondary winding of the high-voltage direct current transmission transformer 16 based on the grid commutation, and the valve group 7 is a voltage source converter, which is connected to the secondary winding of the high-voltage direct current transmission transformer 17 based on the voltage source converter. The rectifier station 24 is equipped with an AC filter 20, which is connected to the AC grid 10 through an AC switch 19 to filter out harmonics and provide reactive power. It is separated and combined with the AC grid 10 through an AC switch 11. In order to suppress the bridge arm circulation of the voltage source type valve group and the surge current under fault, a bridge arm reactor 12 is provided; in order to smooth the DC voltage of the DC circuit and suppress the DC fault current, a smoothing reactor 13 is provided. Figure 7The grounding electrode conductor 18 is shown in the figure, which is used to connect the converter to the grounding electrode. A DC filter 14 is arranged between the DC line 15 of the rectifier station and the grounding electrode conductor 18. The two ends of the hybrid DC converters 26 and 27 of the inverter station are respectively connected in parallel with the bypass thyristor valve group 1.

[0054] Figure 8 A converter protection method proposed by the present invention controls Figure 6 and Figure 7 Converter protection circuit. Figure 6 When the voltage source valve group unit 21 or 22 detects a fault, the bypass thyristor valve group 1 is put into operation, and the fault information is transmitted to the rectifier station 24. For a fault that can be self-recovered or isolated instantaneously, such as an instantaneous three-phase grounding fault in the AC system, the current source valve group unit 23 of the rectifier station 24 reduces the DC voltage and DC current, controls the current of the bypass thyristor valve group 1 to zero and shuts it down. After the fault disappears, the DC transmission system is restarted; for a fault that cannot be self-recovered or isolated instantaneously, such as a fault in the voltage source converter itself, the DC transmission system is locked. Figure 7 The voltage source type valve group unit in the rectifier station 24 detects a fault, puts the bypass thyristor valve group 1 into operation, and transmits the fault information to the rectifier station 24. For a fault that can be self-recovered or isolated instantaneously, such as an instantaneous three-phase grounding fault in the AC system, the current source type valve group unit 23 of the rectifier station 24 reduces the DC voltage and DC current, controls the current of the bypass thyristor valve group 1 to zero and shuts it off. After the fault disappears, the DC transmission system is restarted; for a fault that cannot be self-recovered instantaneously, such as a fault in the voltage source converter itself, the voltage source converter is locked and the fault is isolated, and other fault-free converters in the DC transmission system are reorganized and continue to operate; for a fault that cannot be isolated, such as a grounding fault in the valve group connecting line, the DC transmission system is locked.

[0055] Fig. 9 The present invention provides a converter protection device, which controls Figure 6 and Figure 7 A converter protection circuit with DC fault ride-through capability, comprising:

[0056] The detection unit 29 detects the DC voltage, DC current, bridge arm current of the voltage source valve group unit, the voltage and current of the submodule, the current flowing through the bypass thyristor valve group, the AC voltage and AC current connected to the AC system, the shutdown signal, protection action signal, locking signal, and operation signal of the voltage source valve group unit; determines whether there is a fault in the voltage source valve group unit, and triggers the protection unit 30 if there is a fault;

[0057] The protection unit 30 determines that a voltage source type valve group unit fault occurs, puts the bypass thyristor valve group into operation, transmits the fault information to the rectifier station, and triggers the control unit 31;

[0058] The control unit 31 reduces the DC voltage and the DC current on the rectifier side. If the voltage source type valve group unit can be self-recovered or isolated instantly after the fault occurs, the bypass thyristor valve group current is controlled to zero and shut down. After the fault disappears, the DC power transmission system is restarted. If the voltage source type valve group unit cannot be self-recovered or isolated instantly after the fault occurs, the voltage source type valve group unit or the DC power transmission system is locked.

[0059] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A converter protection circuit for protecting a voltage source converter in a voltage source valve group unit, characterized in that: Use one of the following three options: Solution 1: at least one bypass thyristor valve group and one diode valve group are included, and the connection mode is that the diode valve group is connected in series with a voltage source type valve group unit without DC fault ride-through capability to form a converter with DC fault ride-through capability, and the bypass thyristor valve group is connected in parallel at both ends of the converter with DC fault ride-through capability, the anode of the bypass thyristor valve group is connected to the positive electrode of the converter with DC fault ride-through capability, and the cathode of the bypass thyristor valve group is connected to the negative electrode of the converter with DC fault ride-through capability; Solution 2: at least one bypass thyristor valve group and one current source valve group unit; the connection method is that the current source valve group unit is connected in series with the voltage source valve group unit without DC fault ride-through capability to form a converter with DC fault ride-through capability; the bypass thyristor valve group is connected in parallel at both ends of the converter with DC fault ride-through capability, the anode of the bypass thyristor valve group is connected to the positive electrode of the converter with DC fault ride-through capability, and the cathode of the bypass thyristor valve group is connected to the negative electrode of the converter with DC fault ride-through capability; Solution 3: at least one bypass thyristor valve group is included, the anode of the bypass thyristor valve group is connected to the positive electrode of the voltage source type valve group unit with DC fault ride-through capability, and the cathode of the bypass thyristor valve group is connected to the negative electrode of the voltage source type valve group unit with DC fault ride-through capability; The voltage source valve group unit without DC fault ride-through capability is unable to achieve DC side fault ride-through of the DC power transmission system by itself; The voltage source valve group unit with DC fault ride-through capability can itself realize DC side fault ride-through of the DC power transmission system, and is realized by adding auxiliary power electronic devices to suppress reverse current on the basis of the voltage source converter included in the voltage source valve group unit without DC fault ride-through capability.

2. A converter protection circuit as claimed in claim 1, characterized in that: There are two topological structures in which the diode valve group is connected in series with the voltage source type valve group unit without DC fault ride-through capability: (1) The cathode of the diode valve group is connected to the positive electrode of the voltage source type valve group unit; or (2) The anode of the diode valve group is connected to the cathode of the voltage source type valve group unit; For the first structure, the positive electrode of the converter with DC fault ride-through capability is the anode of the diode valve group, and the negative electrode of the converter with DC fault ride-through capability is the negative electrode of the voltage source type valve group unit; for the second structure, the positive electrode of the converter with DC fault ride-through capability is the positive electrode of the voltage source type valve group unit, and the negative electrode of the converter with DC fault ride-through capability is the cathode of the diode valve group.

3. The converter protection circuit according to claim 1, characterized in that: The voltage source converter included in the voltage source valve group unit without DC fault ride-through capability is any one or more of the following: a two-level converter, a diode clamped multilevel converter, a modular multilevel converter MMC composed of half-bridge structure sub-modules, a two-level cascade converter CSL or a stacked two-level converter CTL; the diode valve group is composed of multiple diodes connected in series.

4. The converter protection circuit according to claim 1, characterized in that: The voltage source converter included in the voltage source valve group unit with DC fault ride-through capability is any one or more of the following: a modular multilevel converter MMC composed of full-bridge structure submodules, a two-level cascade converter CSL, a stacked two-level converter CTL, a hybrid modular multilevel converter HMC composed of half-bridge and full-bridge structure submodules, or a diode clamped modular multilevel converter.

5. The converter protection circuit according to claim 1, characterized in that: There are two topological structures in which the current source valve group unit is connected in series with the voltage source valve group unit without DC fault ride-through capability: (1) The cathode of the current source valve unit is connected to the positive electrode of the voltage source valve unit; or (2) The anode of the current source type valve group unit is connected to the cathode of the voltage source type valve group unit; For the first structure, the positive electrode of the converter with DC fault ride-through capability is the anode of the current source valve group unit; the negative electrode of the converter with DC fault ride-through capability is the negative electrode of the voltage source valve group unit; for the second structure, the positive electrode of the converter with DC fault ride-through capability is the positive electrode of the voltage source valve group unit; the negative electrode of the converter with DC fault ride-through capability is the cathode of the current source valve group unit.

6. A converter protection circuit as claimed in claim 5, characterized in that: The current source valve group unit includes a grid phase-commutating converter; or includes a grid phase-commutating converter and a bypass switch, which are connected in parallel; or includes a grid phase-commutating converter, a bypass switch and a knife switch assembly, wherein the knife switch assembly includes a connecting knife switch and a bypass knife switch, the grid phase-commutating converter is connected in parallel with the bypass switch, and the two ends of the parallel-connected unit are respectively connected to one end of the connecting knife switch, and the other end of the connecting knife switch is connected in parallel with the bypass knife switch.

7. A converter protection circuit as claimed in claim 6, characterized in that: The grid phase-commutation converter is a six-pulse bridge circuit or a twelve-pulse bridge circuit, which is composed of non-shutdown half-controlled power semiconductors.

8. The converter protection circuit according to claim 1, characterized in that: The voltage source valve group unit includes a voltage source converter; or a voltage source converter and its bypass circuit; or includes a voltage source converter and its bypass circuit and a knife switch assembly, wherein the knife switch assembly includes a connecting knife switch and a bypass knife switch, and both ends of the voltage source converter and its bypass circuit are respectively connected to one end of the connecting knife switch, and the other end of the connecting knife switch is connected in parallel with the bypass knife switch.

9. A converter protection circuit as claimed in claim 8, characterized in that: The voltage source converter and its bypass circuit are a circuit in which the voltage source converter is connected in parallel with a bypass switch; or a circuit in which the bypass switch is connected in series with an inductor and then connected in parallel with the voltage source converter; or a circuit in which the voltage source converter is connected in series with an inductor and then connected in parallel with a bypass switch.

10. The converter protection circuit according to claim 1, characterized in that: The voltage source converter is composed of fully-controlled power semiconductors that can be turned off; the fully-controlled power semiconductors that can be turned off are any one or more of the following: insulated gate bipolar transistors IGBT, integrated gate-commutated thyristors IGCT, turn-off thyristors GTO, power field-effect transistors PowerMOSFET, electron injection enhanced gate transistors IEGT, gate-commutated thyristors GCT or silicon carbide enhancement junction field-effect transistors SiC-JFET.

11. The converter protection circuit according to claim 1, characterized in that: The bypass thyristor valve group includes only one bridge arm, which is composed of multiple thyristors connected in series and includes a corresponding control protection circuit; or the bypass thyristor valve group is a bypass pair of parallel grid-commutated converters or is achieved by fast phase shifting of the parallel grid-commutated converters.

12. A converter protection circuit according to claim 11, characterized in that: A DC conversion switch or an isolating knife switch is connected in series at the beginning or end of the plurality of thyristors connected in series.

13. A converter protection method applicable to the converter protection circuit according to any one of claims 1 to 12, wherein the inverter station is configured with a voltage source valve group unit without DC fault ride-through capability or the voltage source valve group unit with DC fault ride-through capability, and when the DC power transmission system is in operation, the inverter station is the inverter side of the DC power transmission system, and the rectifier station is the rectifier side of the DC power transmission system; characterized in that: When the voltage source valve group unit detects a fault, it puts the bypass thyristor valve group into operation and transmits the fault information to the rectifier station. For faults that can be self-recovered or isolated instantaneously, the rectifier side reduces the DC voltage and DC current, controls the bypass thyristor valve group current to zero and shuts it off. After the fault disappears, the DC transmission system is restarted through coordinated control of the rectifier side and the inverter side. For faults that cannot be self-recovered or isolated instantaneously, the voltage source valve group unit or the DC transmission system is locked through coordinated control of the rectifier side and the inverter side.

14. The converter protection method according to claim 13, characterized in that: The faults detected by the voltage source valve group unit include control system faults, valve area faults, main transformer area faults and AC system faults; the specific method of fault detection is: by detecting that the total DC voltage, DC current or bridge arm current of the voltage source valve group unit exceeds the threshold; or by detecting that the sub-module voltage or current of the voltage source valve group unit exceeds the threshold; or by detecting the AC voltage or AC current to indirectly predict or assist in judgment; or by judging through the appearance of a shutdown signal of the voltage source valve group unit, the appearance of a protection action signal, the appearance of a locking signal or the disappearance of an operation signal.

15. The converter protection method according to claim 13, characterized in that: The bypass thyristor valve group current is controlled to zero and turned off by the inverter station leading the control of the bypass thyristor valve group current to zero, or the fault information is transmitted to the rectifier station, and the rectifier station leads the control of the bypass thyristor valve group current to zero, or the two stations coordinate to control the bypass thyristor valve group current to zero; The method of controlling the bypass thyristor valve group current to zero is achieved by applying zero pressure or reverse pressure to the bypass thyristor valve group, or disconnecting the DC conversion switch in the current loop of the DC power transmission system.

16. The converter protection method according to claim 13, characterized in that: The fault information is transmitted to the rectifier station when the inter-station communication is normal, the rectifier station receives the fault information sent by the inverter station or the rectifier station detects the DC voltage and DC current to identify the fault information. In the case of inter-station communication failure, the rectifier station detects the DC voltage and DC current to identify the fault information; The instantaneous self-recoverable or isolable fault is a fault that can extinguish the arc instantly or can be quickly isolated by a switch or a knife switch; the instantaneous non-self-recoverable or non-isolated fault is a permanent fault that cannot extinguish the arc instantly or cannot be isolated by a switch or a knife switch.

17. A converter protection device applicable to the converter protection circuit according to any one of claims 1 to 12, characterized in that: The device comprises a detection unit, a protection unit and a control unit, wherein: A detection unit detects the DC voltage, DC current, bridge arm current of the voltage source valve group unit, the voltage and current of the submodule of the voltage source valve group unit, the current flowing through the bypass thyristor valve group, the AC voltage and AC current connected to the AC system, the shutdown signal, protection action signal, locking signal, and operation signal of the voltage source valve group unit, and determines whether there is a fault in the voltage source valve group unit, and triggers the protection unit if there is a fault; The protection unit, when it is determined that the voltage source type valve group unit fails, puts the bypass thyristor valve group into operation, transmits the fault information to the rectifier station, and triggers the control unit; The control unit reduces the DC voltage and the DC current on the rectifier side. If the voltage source type valve group unit can be self-recovered or isolated instantly after the fault occurs, the bypass thyristor valve group current is controlled to zero and shut down. After the fault disappears, the DC power transmission system is restarted. If the voltage source type valve group unit cannot be self-recovered or isolated instantly after the fault occurs, the voltage source type valve group unit or the DC power transmission system is locked.

Images