CN217087780U - Active commutation unit and hybrid converter topology structure for forced commutation - Google Patents
Active commutation unit and hybrid converter topology structure for forced commutation Download PDFInfo
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- CN217087780U CN217087780U CN202123430974.8U CN202123430974U CN217087780U CN 217087780 U CN217087780 U CN 217087780U CN 202123430974 U CN202123430974 U CN 202123430974U CN 217087780 U CN217087780 U CN 217087780U
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Abstract
The utility model discloses a hybrid transverter topological structure of initiative commutation unit and forced commutation, wherein, initiative commutation unit sets up in the bridge arm circuit of transverter, and converter transformer's output is connected to its one end, and direct current generating line is connected to the other end, and this initiative commutation unit includes: a main branch, on which a thyristor valve is arranged; the auxiliary branch is connected with the main branch in parallel, a first control valve is arranged on the auxiliary branch, and the first control valve has the functions of controllable turn-off of forward current and blocking of forward and reverse voltage; and the second control valve is connected with the thyristor valve or the first control valve, is used for transferring the current from the main branch to the auxiliary branch, comprises at least one power unit, and is used for controllably cutting off the forward current and controllably blocking the forward voltage and the reverse voltage. Through implementing the utility model discloses, realize the initiative commutation of each bridge arm, avoid the commutation failure, ensured the stable safe operation of electric wire netting.
Description
Technical Field
The utility model relates to a current conversion technical field among the power electronics, concretely relates to hybrid transverter topological structure of initiative commutation unit and forced commutation.
Background
The traditional power grid phase-change high voltage direct current (LCC-HVDC) power transmission system has the advantages of long-distance large-capacity power transmission, controllable active power and the like, and is widely applied in the world. The converter is used as core equipment of direct current transmission, is a core function unit for realizing alternating current and direct current electric energy conversion, and the operation reliability of the converter determines the operation reliability of an extra-high voltage direct current power grid to a great extent.
At present, a capacitor commutation converter or a turn-off device is generally connected in series with a thyristor to form a hybrid converter to realize alternating current and direct current electric energy conversion. The capacitor phase-change converter increases the valve phase-change voltage time area through the capacitor voltage to ensure the reliable turn-off of the converter, but realizes the controllable capacitor input and the controllable voltage direction through a controllable capacitor module formed by combining a power electronic switch and a capacitor, and needs a single-stage capacitor with a larger value to ensure the reliable phase change, thereby increasing the voltage and current stress of a core component thyristor, and the topological structure engineering has higher difficulty in realizing; the turn-off device and the thyristor are connected in series to form the hybrid converter, so that each bridge arm of the converter has turn-off capability, and the occurrence of phase commutation failure is avoided. Because the traditional converter mostly adopts a thyristor of a semi-controlled device as a core component to form a six-pulse bridge conversion topology, each bridge arm is formed by serially connecting a multi-stage thyristor and a buffer component thereof, and the thyristor does not have self-turn-off capability, phase change failure is easy to occur under the conditions of AC system failure and the like, so that the direct current is increased rapidly, a large amount of direct current transmission power is lost rapidly, and the stable and safe operation of a power grid is influenced.
SUMMERY OF THE UTILITY MODEL
In view of this, the embodiment of the present invention provides a hybrid converter topology with active commutation unit and forced commutation to solve the problem that the stable operation of the power grid is affected by the failed commutation.
According to a first aspect, the embodiment of the utility model provides an initiative commutation unit sets up in the bridge arm circuit of transverter, and converter transformer's output is connected to its one end, and direct current bus is connected to the other end, include: the main branch is provided with a thyristor valve; the auxiliary branch circuit is connected with the main branch circuit in parallel, a first control valve is arranged on the auxiliary branch circuit, and the first control valve has a forward current controllable turn-off function and a forward and reverse voltage blocking function; and the second control valve is connected with the thyristor valve of the main branch or connected with the first control valve of the auxiliary branch, the second control valve is used for transferring current from the main branch to the auxiliary branch, and the second control valve comprises at least one power unit which is used for controllable turn-off of forward current and controllable blocking of forward and reverse voltages.
With reference to the first aspect, in a first implementation manner of the first aspect, the power unit includes: the first branch circuit is provided with a first power device and a first diode, and the first power device is connected with the first diode in series; the second branch circuit is connected with the first branch circuit in parallel and comprises at least one first capacitor, and the at least one first capacitor is connected in series; the third branch circuit is respectively connected with the first branch circuit and the second branch circuit in parallel, a second power device and a first resistor are arranged on the third branch circuit, and the second power device is connected with the first resistor in series; the first power device and the second power device are both power electronic devices with a turn-off function.
With reference to the first aspect, in a second implementation manner of the first aspect, the power unit includes: a fourth branch, on which a first inductance element or a transformer is arranged; a fifth branch, the fifth branch being arranged in parallel with the fourth branch; the fifth branch circuit comprises a discharge switch, a second capacitor and a first charging circuit, wherein the discharge switch is connected with the second capacitor in series, and the charging circuit is connected with the second capacitor in parallel.
With reference to the first aspect, in a third implementation manner of the first aspect, the power unit includes: a sixth branch comprising at least one third power device, the at least one third power device being arranged in series; the seventh branch and the sixth branch have the same structure, and are arranged in parallel; the third power device is a power electronic device with a turn-off function.
With reference to the first aspect, in a fourth implementation manner of the first aspect, the power unit includes: an eighth branch comprising at least one first sub-branch, the at least one first sub-branch being arranged in series; the first sub-branch comprises a fourth power device and a third capacitor or a second resistor which are arranged in parallel; the fourth power device is a power electronic device with a turn-off function.
With reference to the first aspect, in a fifth implementation of the first aspect, the power unit includes: the ninth branch comprises at least one branch consisting of a second sub-branch, a third sub-branch and a fourth capacitor or a third resistor, and at least one branch is arranged in series; the second sub-branch comprises a fifth power device and a sixth power device which are arranged in series, and a first end of the fifth power device is connected with a first end of the sixth power device; the third sub-branch comprises a seventh power device and an eighth power device which are arranged in series, and the second end of the seventh power device is connected with the second end of the eighth power device; one end of the fourth capacitor or the third resistor is connected between the fifth power device and the sixth power device, and the other end of the fourth capacitor or the third resistor is connected between the seventh power device and the eighth power device; the fifth power device, the sixth power device, the seventh power device, and the eighth power device are power electronic devices having a turn-off function.
With reference to the first aspect, in a sixth implementation manner of the first aspect, the power unit includes: a tenth branch, on which a ninth power device is arranged; an eleventh branch arranged in parallel with the tenth branch; the eleventh branch comprises a tenth power device, a second inductor, a fifth capacitor and a second charging circuit, wherein the tenth power device, the second inductor and the fifth capacitor are arranged in series, and the second charging circuit is arranged in parallel with the fifth capacitor; the ninth power device and the tenth power device are power electronic devices having a turn-off function.
With reference to the first aspect or any one of the first to sixth embodiments of the first aspect, in a seventh embodiment of the first aspect, the second control valve further comprises: at least one buffer member disposed in parallel in the power device; the buffer member includes: the first buffer branch circuit consists of a sixth capacitor; or, the fourth resistor and the seventh capacitor are connected in series to form a second buffer branch circuit; or, the fourth resistor and the seventh capacitor are connected in parallel by a third buffer branch; or, the fifth resistor is connected with the third diode in parallel and then connected with the eighth capacitor in series to form a fourth buffer branch circuit; or, the sixth resistor is connected in parallel with the ninth capacitor and then connected in series with the fourth diode to form a fifth buffer branch circuit; or, a sixth buffering branch composed of the lightning arrester; or, a plurality of the first buffering branch, the second buffering branch, the third buffering branch, the fourth buffering branch, the fifth buffering branch and the sixth buffering branch are connected in parallel to form a seventh buffering branch.
According to a second aspect, the embodiment of the present invention provides a hybrid converter topology structure for forced commutation, the topology structure is connected to an ac power grid through a converter transformer, the topology structure includes a three-phase six-leg circuit, each phase of leg includes an upper leg and a lower leg, and at least one upper leg or one lower leg is provided with an active commutation unit according to the first aspect or any one of the embodiments of the first aspect.
The utility model discloses technical scheme has following advantage:
1. the embodiment of the utility model provides an initiative commutation unit is including parallelly connected main tributary way and supplementary branch road, and set up the second control valve in main tributary way or supplementary branch road, wherein main tributary way is provided with the thyristor valve, be provided with the first control valve that possesses forward and reverse voltage blocking ability on the supplementary branch road, the second control valve is connected with thyristor valve or is connected with first control valve, it includes at least one power unit, this power unit is used for the controllable shutoff of forward current and the blocking of forward and reverse voltage, make the second control valve possess the ability that one-way voltage output or one-way controllable shutoff, guarantee that the second control valve has great through-flow capacity, bear normal operating current, so that transfer the electric current to the supplementary branch road from the main tributary way through the second control valve. The active phase change unit controls the forward turn-off voltage through the second control valve to prolong the reverse recovery time of the main branch thyristor valve, so that the reliable turn-off of the main branch thyristor valve is ensured, the active phase change of each bridge arm is realized, the phase change failure is avoided, and the stable and safe operation of a power grid is ensured.
2. The embodiment of the utility model provides a hybrid transverter topological structure of forced commutation, including six bridge arm circuits of three-phase, every looks bridge arm includes bridge arm and lower bridge arm respectively, is provided with initiative commutation unit on at least one bridge arm or the lower bridge arm. The second control valve in the active phase change unit can turn off the main branch current in advance and provide reverse voltage at the same time, so that the phase change voltage-time area of the main branch thyristor valve is increased, the reliable turn-off of the main branch thyristor valve is ensured, the problem of phase change failure is avoided, and the stable and safe operation of a power grid is ensured.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the technical solutions in the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a block diagram of an active commutation unit according to an embodiment of the present invention;
fig. 2 is another block diagram of the second control valve according to the embodiment of the present invention;
fig. 3 is another block diagram of the second control valve according to the embodiment of the present invention;
fig. 4 is another block diagram of the second control valve according to the embodiment of the present invention;
fig. 5 is another block diagram of the second control valve according to the embodiment of the present invention;
fig. 6 is another block diagram of the second control valve according to the embodiment of the present invention;
fig. 7 is another block diagram of the second control valve according to the embodiment of the present invention;
fig. 8 is another block diagram of a second control valve according to an embodiment of the present invention;
fig. 9 is another block diagram of the second control valve according to the embodiment of the present invention;
fig. 10 is another block diagram of the second control valve according to the embodiment of the present invention;
fig. 11 is a block diagram of a buffer member according to an embodiment of the present invention;
fig. 12 is a block diagram of a thyristor valve according to an embodiment of the present invention;
fig. 13 is a block diagram of a first control valve according to an embodiment of the present invention;
fig. 14 is a hybrid converter topology diagram of forced commutation according to an embodiment of the present invention;
fig. 15 is another topology of a forced commutated hybrid converter according to an embodiment of the present invention;
fig. 16 is another topology of a forced commutated hybrid converter according to an embodiment of the present invention;
fig. 17 is a current flow path in a normal operation state according to an embodiment of the present invention;
fig. 18 is a trigger control sequence for a normal operating state of an embodiment of the present invention;
fig. 19 is a schematic diagram of the current path for the main branch to flow to the auxiliary branch according to the embodiment of the present invention;
fig. 20 is a timing diagram of the trigger control of commutation failure or short circuit fault in an embodiment of the present invention;
fig. 21 is a control trigger sequence for detecting a commutation failure or a short-circuit fault in advance.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by the skilled in the art without creative work belong to the protection scope of the present invention.
The converter is used as core equipment of direct current transmission, is a core function unit for realizing alternating current and direct current electric energy conversion, and the operation reliability of the converter determines the operation reliability of an extra-high voltage direct current power grid to a great extent. However, in the conventional converter, a thyristor which is a half-controlled device is mostly adopted as a core component to form a six-pulse bridge conversion topology, each bridge arm is formed by serially connecting a multi-stage thyristor and a buffer component thereof, and the thyristor does not have self-turn-off capability, so that phase change failure is easy to occur under the conditions of AC system faults and the like, so that the direct current is increased rapidly, a large amount of direct current transmission power is lost rapidly, and the stable and safe operation of a power grid is influenced.
Based on this, the utility model discloses technical scheme has utilized thyristor and first control valve to turn-off and the advantage that the second control valve can turn-off, has adopted two branches parallelly connected, through parallelly connected auxiliary branch road that can provide reverse voltage and possess the ability of turn-offs certainly on the basis of main branch road, realizes the reliable turn-offs of main branch road and the initiative commutation of whole bridge arm to realize supplementary commutation function in short time, avoid the emergence of commutation failure, the stable safe operation of guarantee electric wire netting.
According to the embodiment of the utility model provides an embodiment of initiative commutation unit is provided, this initiative commutation unit sets up in the bridge arm circuit of transverter. 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, as shown in fig. 1, the active commutation unit includes: a main branch and an auxiliary branch. As shown in fig. 12, the thyristor valve V11 includes at least one thyristor and a buffer component connected in parallel or in series with the thyristor, where the at least one thyristor is connected in series, and the buffer component is used for protecting the thyristor device from being damaged by high voltage and large current.
The auxiliary branch circuit is connected with the main branch circuit in parallel, a first control valve V13 is arranged on the auxiliary branch circuit along the direction from the output end of the converter transformer to the direct current bus, and the first control valve V13 has a forward current controllable turn-off function and a forward and reverse voltage blocking function. As shown in fig. 13, the first control valve V13 includes a power device and a thyristor, which are arranged in series, wherein the thyristor has a reverse blocking function, the power device has a controllable turn-off of a forward current and a blocking function of a forward and a reverse voltage, and the power device is a power electronic device having a turn-off function, and the power electronic device is one or more of turn-off devices such as an IGBT, an IGCT, an IEGT, a GTO, or a MOSFET.
The first control valve V13 is a high-voltage shutoff valve, but of course, the first control valve V13 may also be a series connection of a plurality of power devices and thyristors, as long as it is a topology that can realize the functions of forward current controllable shutoff and forward and reverse voltage blocking capability, and the topology of the first control valve V13 is not limited in this application.
The second control valve V12 may be connected to the thyristor valve V11 of the main branch, or may be connected to the first control valve V13 of the auxiliary branch, and the second control valve V12 includes: and the power unit 11 is used for controllably switching off the forward current and blocking the forward voltage and the reverse voltage, so that the first control valve V12 has a function of controllably switching off the unidirectional voltage output. The second control valve V12 may be a low-voltage shutoff valve with a unidirectional voltage controllable output capability or a unidirectional controllable shutoff function, and is used to shut off the main branch current and provide a reverse voltage for the main branch current, so as to ensure that the thyristor valve of the main branch has sufficient shutoff time to perform reliable shutoff.
The active phase-changing unit provided by this embodiment includes a main branch and an auxiliary branch connected in parallel, and a second control valve disposed in the main branch or the auxiliary branch, where the main branch is provided with a thyristor valve, the auxiliary branch is provided with a first control valve having forward and reverse voltage blocking capabilities, and the second control valve is connected with the thyristor valve of the main branch or connected with the first control valve of the auxiliary branch, and includes at least one power unit, and the power unit is used for controllable turn-off of forward current and blocking of forward and reverse voltage, so that the second control valve has a capability of unidirectional voltage output or unidirectional controllable turn-off, ensures that the second control valve has a larger current capacity, and carries normal operating current, so as to transfer current from the main branch to the auxiliary branch through the second control valve. The active phase change unit controls the forward turn-off voltage through the second control valve to prolong the reverse recovery time of the main branch thyristor valve, so that the reliable turn-off of the main branch thyristor valve is ensured, the active phase change of each bridge arm is realized, the phase change failure is avoided, and the stable and safe operation of a power grid is ensured.
Alternatively, as shown in fig. 2, the power unit 11 may be a power electronic unit composed of a first branch, a second branch and a third branch.
The first branch is provided with a first power device W1 and a first diode D1, and the first power device W1 and the first diode D1 are arranged in series. The first power device W1 is a power electronic device with a turn-off function, and the power electronic device is one or more of turn-off devices such as an IGBT, an IGCT, an IEGT, a GTO, or a MOSFET. The second branch is connected in parallel with the third branch, and at least one first capacitor C1 is arranged on the second branch, wherein at least one first capacitor C1 is arranged in series. And the third branch circuit is respectively connected with the first branch circuit and the second branch circuit in parallel, a second power device W2 and a first resistor R1 are arranged on the third branch circuit, and the second power device W2 and the first resistor R1 are connected in series. The second power device W2 is a power electronic device with a turn-off function, and the power electronic device is one or more of turn-off devices such as an IGBT, an IGCT, an IEGT, a GTO, or a MOSFET.
Alternatively, as shown in fig. 3, the power unit 11 may be a power electronic unit composed of a fourth branch and a fifth branch.
Wherein, a first inductance element L1 is arranged on the fourth branch; the fifth branch and the fourth branch are arranged in parallel, a discharging switch K1, a second capacitor C2 and a first charging circuit P1 are arranged on the fifth branch, a discharging switch K1 and a second capacitor C2 are arranged in series, and a charging circuit P1 and the second capacitor C2 are arranged in parallel. As shown in fig. 3, the discharge switch K1 is composed of a thyristor and a diode, one end of the first inductance element L1 is connected to the positive electrode of the thyristor and the negative electrode of the diode, the other end of the first inductance element L1 is connected to one end of the second capacitance C2, and the other end of the second capacitance C2 is connected to the negative electrode of the thyristor and the positive electrode of the diode.
Alternatively, as shown in fig. 4, the power unit 11 may be a power electronic unit composed of a fourth branch and a fifth branch.
Wherein, a transformer B1 is arranged on the fourth branch; the fifth branch and the fourth branch are arranged in parallel, a discharging switch K1, a second capacitor C2 and a first charging circuit P1 are arranged on the fifth branch, a discharging switch K1 and a second capacitor C2 are arranged in series, and a charging circuit P1 and the second capacitor C2 are arranged in parallel. As shown in fig. 4, the discharge switch K1 is composed of a thyristor and a diode, one end of the transformer B1 is connected to the positive electrode of the thyristor and the negative electrode of the diode, the other end of the transformer B1 is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the negative electrode of the thyristor and the positive electrode of the diode.
Alternatively, as shown in fig. 5, the power unit 11 may be a power electronic unit composed of a sixth branch and a seventh branch.
The sixth branch is provided with at least one third power device W3, the at least one third power device W3 is arranged in series, the third power device W3 is a power electronic device with a turn-off function, and the power electronic device is one or more of turn-off devices such as an IGBT, an IGCT, an IEGT, a GTO, or a MOSFET. The seventh branch and the sixth branch have the same structure, and are arranged in parallel.
Alternatively, as shown in fig. 6, the power unit 11 may be a power electronic unit composed of an eighth branch. The eighth branch is formed by at least one first sub-branch, the at least one first sub-branch is arranged in series, the first sub-branch is formed by a fourth power device W4 and a third capacitor C3 which are arranged in parallel, wherein the fourth power device W4 is a power electronic device with a turn-off function, and the power electronic device is one or more of an IGBT, an IGCT, an IEGT, a GTO or a MOSFET.
Alternatively, as shown in fig. 8, the power unit 11 may be a power electronic unit composed of an eighth branch. The eighth branch is formed by at least one first sub-branch, the at least one first sub-branch is arranged in series, the first sub-branch is formed by a fourth power device W4 and a second resistor R2 which are arranged in parallel, wherein the second resistor R2 is a nonlinear resistor, the fourth power device W4 is a power electronic device with a turn-off function, and the power electronic device is one or more of turn-off devices such as an IGBT, an IGCT, an IEGT, a GTO or a MOSFET.
Alternatively, as shown in fig. 7, the power unit 11 may be a power electronic unit composed of a ninth branch, where the ninth branch includes at least one branch formed by a second sub-branch, a third sub-branch and a fourth capacitor C4, and at least one branch is arranged in series.
The second sub-branch comprises a fifth power device W5 and a sixth power device W6 which are arranged in series, the fifth power device W5 and the sixth power device W6 both have a first end and a second end, and the first end of the fifth power device W5 is connected with the first end of the sixth power device W6; the third sub-branch comprises a seventh power device W7 and an eighth power device W8 which are arranged in series, the seventh power device W7 and the eighth power device W8 both have a first end and a second end, and the second end of the seventh power device W7 is connected with the second end of the eighth power device W8; one end of the fourth capacitor C4 is connected between the fifth power device W5 and the sixth power device W6, and the other end is connected between the seventh power device W7 and the eighth power device W8. The fifth power device W5, the sixth power device W6, the seventh power device W7 and the eighth power device W8 are all power electronic devices with a turn-off function, and the power electronic devices are one or more of turn-off devices such as IGBTs, IGCTs, IEGTs, GTOs or MOSFETs.
Alternatively, as shown in fig. 9, the power unit 11 may be a power electronic unit formed by the ninth branch. The ninth branch comprises at least one branch composed of a second sub-branch, a third sub-branch and a third resistor R3, and at least one branch is arranged in series.
The second sub-branch comprises a fifth power device W5 and a sixth power device W6 which are arranged in series, the fifth power device W5 and the sixth power device W6 both have a first end and a second end, and the first end of the fifth power device W5 is connected with the first end of the sixth power device W6; the third sub-branch comprises a seventh power device W7 and an eighth power device W8 which are arranged in series, the seventh power device W7 and the eighth power device W8 both have a first end and a second end, and the second end of the seventh power device W7 is connected with the second end of the eighth power device W8; one end of the third resistor R3 is connected between the fifth power device W5 and the sixth power device W6, and the other end is connected between the seventh power device W7 and the eighth power device W8. The fifth power device W5, the sixth power device W6, the seventh power device W7 and the eighth power device W8 are all power electronic devices with a turn-off function, and the power electronic devices are one or more of turn-off devices such as IGBTs, IGCTs, IEGTs, GTOs or MOSFETs.
Alternatively, as shown in fig. 10, the power unit 11 may be a power electronic unit composed of a tenth branch and an eleventh branch.
The tenth branch is provided with a ninth power device W9, the eleventh branch is arranged in parallel with the tenth branch, the eleventh branch comprises a tenth power device W10, a second inductor L2, a fifth capacitor C5 and a second charging circuit P2, the tenth power device W10, the second inductor L2 and the fifth capacitor C5 are arranged in series, and the second charging circuit P2 is arranged in parallel with the fifth capacitor C5. The ninth power device W9 and the tenth power device W10 are power electronic devices having a turn-off function, and the power electronic devices are one or more of turn-off devices such as IGBTs, IGCTs, IEGTs, GTOs, or MOSFETs.
The second control valve V12 is a low-voltage shutoff valve, has a unidirectional voltage controllable output capability or a unidirectional controllable shutoff function, and is mainly used for shutting off the main branch current and providing a reverse voltage for the main branch current, so as to ensure that the thyristor valve of the main branch has enough shutoff time to perform reliable shutoff. The topological form of the second control valve V12 is not limited in the present application, and may be any topological form that has a one-way voltage-controllable output or a one-way controllable shut-off function. The topological form of the power unit may also be the cooperation of a power electronic device without a reverse blocking function and a diode, a multistage series structure form may be formed by the cooperation of a single-stage power electronic device without a reverse blocking function, a single-stage diode and a buffer component, a multistage combination of a power electronic device without a reverse blocking function and a buffer component may be connected in series with a multistage combination of a diode and a buffer component, a multistage combination of a power electronic device without a reverse blocking function and a multistage diode may also be connected in series alternately, and of course, other topological forms may also be possible, which are not specifically limited herein, and those skilled in the art may determine the topological form according to actual needs.
Optionally, the second control valve V12 may further include: at least one buffer member, which is disposed in parallel in the power unit 11. The parallel connection of the damping member and the power unit 11 is known to those skilled in the art, and is not limited to this. Alternatively, as shown in fig. 11, the above-mentioned buffer components are formed by one or more of capacitors, rc circuits, diodes, inductors, or lightning arresters, and the at least one power unit 11 may form a full-bridge circuit with the at least one buffer component to stabilize the operation of the second control valve V12.
Specifically, as shown in fig. 11, the buffer member may be a first buffer branch composed of a sixth capacitor; the second buffer branch can be formed by connecting a fourth resistor and a seventh capacitor in series; the third buffer branch can be formed by connecting a fourth resistor and a seventh capacitor in parallel; a fourth buffering branch RCD1 formed by a fifth resistor connected in parallel with a third diode and then connected in series with an eighth capacitor; a fifth buffer branch RCD2 formed by a sixth resistor, a ninth capacitor, and a fourth diode connected in series; the sixth buffering branch circuit can also be composed of lightning arresters; the buffer circuit can also be a seventh buffer branch formed by connecting a plurality of the first buffer branch, the second buffer branch, the third buffer branch, the fourth buffer branch, the fifth buffer branch and the sixth buffer branch in parallel.
According to the embodiment of the utility model provides a hybrid transverter topological structure of forced commutation is provided, and this topological structure passes through converter transformer and inserts alternating current electric wire netting. The hybrid converter topological structure for forced phase change comprises a three-phase six-bridge arm circuit, wherein each phase of bridge arm comprises an upper bridge arm and a lower bridge arm respectively, and at least one upper bridge arm or one lower bridge arm is provided with the active phase change unit.
Specifically, the forced commutated hybrid converter topology as depicted in fig. 14 comprises 3 upper legs and 3 lower legs. Each active commutation cell acts as a converter valve, and the hybrid converter topology for forced commutation described with respect to fig. 14 includes converter valve V1, converter valve V2, converter valve V3, converter valve V4, converter valve V5, and converter valve V6. The main branches of the 3 upper bridge arms respectively comprise thyristor valves V11, V31, V51 and second control valves V12, V32 and V52, and the auxiliary branches of the 3 upper bridge arms respectively comprise first control valves V13, V33 and V53. The main branches of the 3 lower arms respectively comprise thyristor valves V21, V41, V61 and second control valves V22, V42 and V62, and the auxiliary branches of the 3 lower arms respectively comprise first control valves V23, V43 and V63. The on-off and the on-off of the thyristor valve, the first control valve and the second control valve are controlled by a control trigger control system.
Specifically, the forced commutated hybrid converter topology as depicted in fig. 15 comprises 3 upper legs and 3 lower legs. Each active commutation cell acts as a converter valve, and the hybrid converter topology for forced commutation described with respect to fig. 15, i.e. comprises converter valves V1, V2, V3, V4, V5 and V6. The main branches of the 3 upper bridge arms respectively comprise thyristor valves V11, V31 and V51, and the auxiliary branches of the 3 upper bridge arms respectively comprise first control valves V13, V33 and V53 and second control valves V12, V32 and V52. The main branches of the 3 lower arms respectively comprise thyristor valves V21, V41 and V61, and the auxiliary branches of the 3 lower arms respectively comprise first control valves V23, V43 and V63 and second control valves V22, V42 and V62. The on-off and the on-off of the thyristor valve, the first control valve and the second control valve are controlled by a control trigger control system.
Specifically, the hybrid converter topology as shown in fig. 16 includes 3 upper legs and 3 lower legs. Each active commutation cell acts as a converter valve, and the hybrid converter topology for forced commutation described with respect to fig. 16 includes converter valve V1, converter valve V2, converter valve V3, converter valve V4, converter valve V5, and converter valve V6. The main branches of the 3 upper bridge arms respectively comprise thyristor valves V11, V31 and V51, and the auxiliary branches of the 3 upper bridge arms respectively comprise first control valves V13, V33 and V53. The main branches of the 3 lower bridge arms respectively comprise thyristor valves V21, V41 and V61, and the auxiliary branches of the 3 lower bridge arms respectively comprise first control valves V23, V43 and V63. One end of each of the phase change control valves Va2, Vb2, and Vc2 is connected between the upper bridge arm and the lower bridge arm, and the other end of each of the phase change control valves Va2, Vb2, and Vc2 are connected to the output end of the converter transformer, and the phase change control valves Va2, Vb2, and Vc2 may have a forward and reverse current turn-off function and a forward and reverse voltage output function at the same time. The thyristor valve, the first control valve and the second control valve are controlled to be switched off and on by controlling the trigger control system, so that the reliable switching off of the main branch and the active phase change of the whole bridge arm are realized.
The hybrid converter topological structure for forced commutation can provide reverse voltage and an auxiliary branch with self-turn-off capability by being connected in parallel on the basis of a thyristor valve, so that reliable turn-off of a main branch and active commutation of the whole bridge arm are realized. The auxiliary branch is formed by connecting second control valves with bidirectional pressure bearing capacity in series, namely, a shutoff valve is introduced for each bridge arm.
The hybrid converter topology structure for forced phase commutation provided by the embodiment comprises a three-phase six-bridge arm circuit, each phase bridge arm comprises an upper bridge arm and a lower bridge arm, and at least one upper bridge arm or one lower bridge arm is provided with an active phase commutation unit. The second control valve in the active phase change unit can turn off the main branch current in advance and provide reverse voltage at the same time, so that the phase change voltage-time area of the main branch thyristor valve is increased, the reliable turn-off of the main branch thyristor valve is ensured, the problem of phase change failure is avoided, and the stable and safe operation of a power grid is ensured.
In this embodiment, a forced commutation control method is provided, which can be used in the hybrid converter topology with forced commutation, and takes the example that the second control valve V12 is disposed in the auxiliary branch, and the forced commutation control method includes the following steps:
(1) and the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topological structure is conducted.
(2) And the first control valve and the second control valve are used for conducting the auxiliary branch of the ith bridge arm of the hybrid converter topological structure.
(3) And switching off the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topology.
(4) And after a control period, switching on a thyristor valve of a main branch of the ith bridge arm of the hybrid converter topological structure, wherein i belongs to [1,6 ].
Specifically, as shown in fig. 17, the valve current flow path of the hybrid converter topology under normal operating conditions is shown, the main branch is subjected to voltage and current stress periodically, the auxiliary branch is always in an off state, and the auxiliary branch is subjected to voltage stress only when the thyristor valve of the main branch is turned off. The first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topological structure are kept in a turn-off state, and the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topological structure is switched on, so that the hybrid converter topological structure with forced phase change can work in a normal phase change operation mode, namely in a temporary phase change operation mode, the auxiliary branch is in a turn-off state when the hybrid converter normally operates, only bears voltage stress, and the increase of converter loss under long-term operation is reduced.
When a phase change failure or an alternating current short circuit fault occurs, a first control valve and a second control valve of an auxiliary branch of the ith bridge arm of the hybrid converter topological structure are conducted; and forcibly transferring the current of the main branch to the auxiliary branch, and turning off the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topological structure when the current transfer is finished, so as to realize the forced phase change of the hybrid converter. After a control period, returning to the step of conducting the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topological structure, and continuing to independently and normally operate by the main branch, thereby ensuring that the auxiliary branch bears the turn-off voltage stress only when in fault, reducing the loss of the device and further prolonging the service life of the device.
FIG. 18 shows the trigger control sequence in the normal operation mode, t 0 Indicating the initial trigger time.
Fig. 19 shows the main branch switching to the auxiliary branch by turning off the V1 valve and the auxiliary branch starting to bear voltage stress, the process is divided into three stages, fig. 19 (left) shows the main branch switching to the auxiliary branch by receiving a trigger signal, the auxiliary branch is turned on by receiving a turn-on signal by the V12 valve and the V13 valve of the auxiliary branch, the current of the main branch is transferred to the auxiliary branch, and a reverse voltage is applied to the main branch; FIG. 19 is a (middle) auxiliary branch current flow phase in which the main branch has been completely turned off and the main branch current has been fully diverted to the auxiliary branch; fig. 19 (right) shows the auxiliary branch off phase, in which the auxiliary branch V13 valve is turned off first when receiving the off signal, and the V1 valve is in the off state for receiving the forward voltage, and then the V12 valve is turned off before or at the same time as the main branch V11 valve is turned on in the next control cycle. The above-described operation can be put into operation when a commutation fault is detected or predicted.
Fig. 20 is a trigger control timing for a hybrid converter topology with forced commutation in the event of a commutation failure or ac short circuit fault. At t in FIG. 20 f When the phase change failure of the V1 valve to the V3 valve is monitored at the moment, the phase change failure of the V1 valve to the V3 valve is detectedFirst preset duration deltat 1 The auxiliary branch V13 valve is conducted for a second preset time period delta t 2 The V12 valve of the auxiliary branch is switched on, the commutation process of the main branch to the auxiliary branch is carried out, and delta t 2 ≥Δt 1 Is more than or equal to 0. The main branch current I11 is gradually reduced to zero, the auxiliary branch current I12 is gradually increased, and the current passes through a third preset time period delta t 3 The V13 valve of the auxiliary branch is closed, and the time from the zero crossing of the main branch current to the closing of the V13 valve is the closing time t of the thyristor valve off Here, t off Greater than the minimum turn-off time of the thyristor valve to ensure that the thyristor valve V11 has sufficient time to turn off. After the auxiliary branch V13 valve is turned off, the auxiliary branch current will commutate to the V3 valve until the direct current Id is reached, so that the phase change from the V1 valve to the V3 valve is completed, the failure of phase change is successfully resisted, and then the auxiliary branch V12 valve is turned off before the V11 valve of the next control period is turned on. The operation mode is started when the phase commutation failure is predicted to occur or detected to occur, the phase commutation failure can be successfully avoided, the operation mode is exited when the phase commutation process of the converter is recovered to be normal, the auxiliary branch keeps a turn-off state, and the main branch independently and normally operates.
When the phase change fails or short circuit faults occur, the hybrid converter topological structure is controlled to start the operation mode of forced phase change, the occurrence of the phase change failure is avoided, the operation mode of the forced phase change is quitted when the phase change process of the hybrid converter is recovered to be normal, the auxiliary branch circuit continues to be in a turn-off state, and the main branch circuit independently and normally operates, so that the auxiliary branch circuit is guaranteed to bear turn-off voltage stress only when the faults occur, the loss of devices is reduced, and the service life of the devices is prolonged.
Fig. 21 shows a control trigger timing when the hybrid converter topology for forced phase commutation detects a phase commutation failure or a short-circuit fault in advance, and a specific operation process of each valve control trigger timing when the main branch and the auxiliary branch of the V1 valve periodically and alternately operate is shown in fig. 19. At the beginning of the commutation of the V1 valve and the V3 valve, i.e. the time delay of 120 for the V1 valve activation pulse Sg1, or in the vicinity of this moment, the auxiliary branch V13 valve is activated and the auxiliary branch V12 valve is opened after a short time (e.g. 1s, 5s, etc.),and realizing the commutation of the main branch to the auxiliary branch. After the main branch current crosses zero, the main branch V11 valve is closed and bears reverse voltage, and the time from the main branch current crossing zero to the auxiliary branch V13 valve closing is the closing time t of the thyristor valve off And t is off The minimum turn-off time of the thyristor valve is longer than the minimum turn-off time of the thyristor valve, so that the reliable turn-off of the thyristor valve is guaranteed, the current of the V1 valve is completely transferred to the auxiliary branch, the V13 valve of the auxiliary branch starts to be turned off after delta t, the V1 valve starts to bear forward voltage, and then the V12 valve of the auxiliary branch is turned off before or at the same time of turning on the V11 valve in the next working period. In the operation mode, the main branch and the auxiliary branch in the bridge arm of the hybrid converter topological structure for forced commutation periodically and alternately operate, on the basis of resisting commutation failure, commutation failure does not need to be predicted, and meanwhile the hybrid converter can be in a small turn-off angle operation mode, so that reactive power consumption of the hybrid converter is reduced.
The forced commutation control method provided by this embodiment can not only resist commutation failure, but also does not need to predict commutation failure through the periodic alternate operation of the main branch and the auxiliary branch. Meanwhile, the hybrid converter is ensured to work in a small-cut-off-angle operation mode, and the reactive power consumption of the hybrid converter is reduced.
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 invention, and such modifications and variations fall within the scope defined by the appended claims.
Claims (9)
1. An active commutation unit is arranged in a bridge arm circuit of a current converter, one end of the active commutation unit is connected with the output end of a converter transformer, and the other end of the active commutation unit is connected with a direct current bus, and the active commutation unit is characterized by comprising:
the main branch is provided with a thyristor valve;
the auxiliary branch circuit is connected with the main branch circuit in parallel, a first control valve is arranged on the auxiliary branch circuit, and the first control valve has a forward current controllable turn-off function and a forward and reverse voltage blocking function;
and the second control valve is connected with the thyristor valve of the main branch or connected with the first control valve of the auxiliary branch, the second control valve is used for transferring current from the main branch to the auxiliary branch, and the second control valve comprises at least one power unit which is used for controllable turn-off of forward current and controllable blocking of forward and reverse voltages.
2. The active commutation cell of claim 1, wherein the power cell comprises:
the circuit comprises a first branch circuit, a second branch circuit and a third branch circuit, wherein the first branch circuit is provided with a first power device and a first diode, and the first power device is connected with the first diode in series;
the second branch circuit is connected with the first branch circuit in parallel and comprises at least one first capacitor, and the at least one first capacitor is connected in series;
the third branch circuit is respectively connected with the first branch circuit and the second branch circuit in parallel, a second power device and a first resistor are arranged on the third branch circuit, and the second power device is connected with the first resistor in series;
the first power device and the second power device are both power electronic devices with a turn-off function.
3. The active commutation cell of claim 1, wherein the power cell comprises:
a fourth branch, on which a first inductance element or a transformer is arranged;
a fifth branch, the fifth branch being arranged in parallel with the fourth branch; the fifth branch circuit comprises a discharge switch, a second capacitance device and a first charging circuit, wherein the discharge switch is connected with the second capacitance in series, and the charging circuit is connected with the second capacitance in parallel.
4. The active commutation cell of claim 1, wherein the power cell comprises:
a sixth branch comprising at least one third power device, the at least one third power device being arranged in series;
the seventh branch and the sixth branch have the same structure, and are arranged in parallel;
the third power device is a power electronic device with a turn-off function.
5. The active commutation cell of claim 1, wherein the power cell comprises:
an eighth branch comprising at least one first sub-branch, the at least one first sub-branch being arranged in series;
the first sub-branch comprises a fourth power device and a third capacitor or a second resistor which are arranged in parallel;
the fourth power device is a power electronic device with a turn-off function.
6. The active commutation cell of claim 1, wherein the power cell comprises:
the ninth branch comprises at least one branch consisting of a second sub-branch, a third sub-branch and a fourth capacitor or a third resistor, and at least one branch is arranged in series;
the second sub-branch comprises a fifth power device and a sixth power device which are arranged in series, and a first end of the fifth power device is connected with a first end of the sixth power device;
the third sub-branch comprises a seventh power device and an eighth power device which are arranged in series, and the second end of the seventh power device is connected with the second end of the eighth power device;
one end of the fourth capacitor or the third resistor is connected between the fifth power device and the sixth power device, and the other end of the fourth capacitor or the third resistor is connected between the seventh power device and the eighth power device;
the fifth power device, the sixth power device, the seventh power device, and the eighth power device are power electronic devices having a turn-off function.
7. The active commutation cell of claim 1, wherein the power cell comprises:
a tenth branch, on which a ninth power device is arranged;
an eleventh branch arranged in parallel with the tenth branch; the eleventh branch comprises a tenth power device, a second inductor, a fifth capacitor and a second charging circuit, wherein the tenth power device, the second inductor and the fifth capacitor are arranged in series, and the second charging circuit is arranged in parallel with the fifth capacitor;
the ninth power device and the tenth power device are power electronic devices having a turn-off function.
8. The active commutation cell of any one of claims 1-7, wherein the second control valve further comprises:
at least one buffer member disposed in parallel in the power device;
the buffer member includes:
the first buffer branch circuit consists of a sixth capacitor;
or, the fourth resistor and the seventh capacitor are connected in series to form a second buffer branch circuit;
or, the fourth resistor and the seventh capacitor are connected in parallel by a third buffer branch;
or, the fifth resistor is connected with the third diode in parallel and then connected with the eighth capacitor in series to form a fourth buffer branch circuit;
or, the sixth resistor is connected in parallel with the ninth capacitor and then connected in series with the fourth diode to form a fifth buffer branch circuit;
or, a sixth buffering branch composed of the lightning arrester;
or, a plurality of the first buffering branch, the second buffering branch, the third buffering branch, the fourth buffering branch, the fifth buffering branch and the sixth buffering branch are connected in parallel to form a seventh buffering branch.
9. A hybrid converter topological structure for forced commutation, the topological structure is connected to an alternating current power grid through a converter transformer, the topological structure comprises a three-phase six-leg circuit, each phase of the bridge leg comprises an upper bridge leg and a lower bridge leg respectively, and the hybrid converter topological structure is characterized in that at least one upper bridge leg or one lower bridge leg is provided with an active commutation unit according to any one of claims 1 to 8.
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