CN214256147U

CN214256147U - Hybrid converter topology structure with active phase change unit and forced phase change

Info

Publication number: CN214256147U
Application number: CN202120295957.9U
Authority: CN
Inventors: 高冲; 贺之渊; 张娟娟; 王治翔; 李婷婷
Original assignee: Global Energy Interconnection Research Institute
Current assignee: Global Energy Interconnection Research Institute
Priority date: 2021-02-01
Filing date: 2021-02-01
Publication date: 2021-09-21
Anticipated expiration: 2031-02-01

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 is connected to its one end, and direct current bus is connected to the other end, include: a main branch provided with a thyristor valve; and the auxiliary branch circuit is connected with the main branch circuit in parallel, a first control valve and a second control valve are sequentially arranged on the auxiliary branch circuit, the first control valve has a one-way voltage output controllable turn-off function, and the second control valve has a forward current controllable turn-off function and a forward and reverse voltage blocking function. The hybrid converter topological structure for forced phase change is connected to an alternating current power grid through a converter transformer, the topological structure comprises a three-phase six-bridge arm circuit, 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 an active phase change unit. Through implementing the utility model discloses, realized the reliable turn-off of main branch road and the initiative commutation of whole bridge arm.

Description

Hybrid converter topology structure with active phase change unit and forced phase change

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.

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 structure with active commutation unit and forced commutation to solve the problem that commutation failure affects the stable and safe operation of the power grid.

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 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; and the auxiliary branch circuit is arranged in parallel with the main branch circuit, a first control valve and a second control valve are sequentially arranged on the auxiliary branch circuit along the direction from the converter transformer to the direct current bus, the first control valve has a one-way voltage output controllable turn-off function, and the second control valve has a forward current controllable turn-off function and a forward and reverse voltage blocking function.

With reference to the first aspect, in a first implementation manner of the first aspect, the thyristor valve includes: at least one thyristor, the at least one thyristor arranged in series; at least one first snubber block connected in parallel or in series with the at least one thyristor.

With reference to the first aspect, in a second embodiment of the first aspect, the first control valve includes: at least one first power cell, the at least one first power cell arranged in series; at least one second buffer member connected in parallel with the at least one first power cell.

With reference to the second implementation manner of the first aspect, in a third implementation manner of the first aspect, the first power unit includes: the power supply comprises a first branch circuit, a second branch circuit and a control circuit, wherein the first branch circuit is provided with a first power device and a diode, and the first power device is a fully-controlled power electronic device; and the second branch circuit is connected with the first branch circuit in parallel, a first capacitor element and the first power device are arranged on the second branch circuit, and the first power device and the first capacitor element are connected in series.

With reference to the second implementation manner of the first aspect, in a fourth implementation manner of the first aspect, the first power unit includes: the third branch circuit is a full-bridge circuit formed by connecting four second power devices; the second power device is a fully-controlled power electronic device; and the fourth branch is provided with a second capacitance element, and the second capacitance element is connected between the upper half bridge and the lower half bridge of the full-bridge circuit in parallel.

With reference to the first aspect, in a fifth embodiment of the first aspect, the second control valve includes: at least one second power cell, the at least one second power cell arranged in series; at least one third damping member connected in parallel with the at least one second power cell.

With reference to the fifth implementation manner of the first aspect, in a sixth implementation manner of the first aspect, the second power unit includes: a fifth branch, wherein a third power device and a first diode are arranged on the fifth branch, and the third power device is connected with the first diode in series; or, a sixth branch, where at least one third power device is arranged on the sixth branch, and the at least one third power device is arranged in series; the third power device is a power electronic device without a reverse blocking function; a seventh branch in series with the sixth branch; and at least one second diode is arranged on the seventh branch and is arranged in series.

With reference to the fifth implementation manner of the first aspect, in a seventh implementation manner of the first aspect, the second power unit includes: the eighth branch circuit is a full-bridge circuit formed by connecting a plurality of fourth power devices; the fourth power device is a fully-controlled power electronic device.

With reference to the fifth implementation manner of the first aspect, in an eighth implementation manner of the first aspect, the second power unit includes: at least one ninth branch comprising a first sub-branch, a second sub-branch, and a third sub-branch; the first sub-branch, the second sub-branch, the third sub-branch and the third buffer component form an H-bridge circuit; the first sub-branch is provided with a plurality of third diodes which are connected in series; the second sub-branch is connected in parallel between the first sub-branch and the third sub-branch, a plurality of fifth power devices connected in series are arranged on the second sub-branch, and the fifth power devices are full-control power electronic devices; and the third sub-branch is provided with a plurality of fourth diodes which are connected in series.

With reference to the first embodiment or the second embodiment or the fifth embodiment of the first aspect, in a ninth embodiment of the first aspect, the first cushioning member, the second cushioning member and the third cushioning member each include: the first buffer branch circuit consists of a capacitor; or, a second buffer branch circuit with a resistor and the capacitor connected in series; or, the capacitor and the resistor are connected in parallel by a third buffer branch; or the resistor is connected with the fifth diode in parallel and then connected with the capacitor in series to form a fourth buffer branch circuit; or, the resistor is connected in parallel with the capacitor and then connected in series with the fifth 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 active commutation unit provided by the embodiment of the utility model comprises a main branch and an auxiliary branch which are connected in parallel, wherein the main branch is provided with a thyristor valve, has larger through-current capacity and bears normal running current; the first control valve of the auxiliary branch has a forward current controllable turn-off function, and the second control valve has a forward and reverse voltage blocking capability. This initiative commutation unit has utilized thyristor and the advantage that first control valve can be turn-offed and the second control valve can be turn-offed, adopts two branch roads to connect in parallel, realizes the transfer of electric current through the first control valve in the auxiliary branch road, and the second control valve bears great shutoff voltage stress when being used for the trouble, need not to bear current stress for a long time to avoid the increase of device loss, improved the utilization ratio of first control valve and second control valve. The auxiliary branch circuit which can provide reverse voltage and has self-turn-off capability is connected in parallel on the basis of the thyristor valve, so that the reliable turn-off of the main branch circuit and the active phase change of the whole bridge arm are realized. When the active commutation unit normally operates, the auxiliary branch can keep a turn-off state and only needs to bear voltage stress; the auxiliary branch is immediately conducted when the active phase change unit fails in phase change, the first control valve can transfer current to the auxiliary branch and provide reverse voltage for a thyristor valve of the main branch, and the second control valve can replace the main branch to complete phase change, so that an auxiliary phase change function is realized in a short time, and the occurrence of phase change failure is avoided.

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 first control valve of the auxiliary branch of the active phase change unit can turn off the current of the main branch in advance and provide reverse voltage at the same time, so that the phase change voltage-time area of the thyristor valve of the main branch is increased, the reliable turn-off of the thyristor valve is ensured, the problem of phase change failure is avoided, and the stable and safe operation of a power grid is ensured.

3. 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 of the auxiliary branch of the active phase change unit can quickly transfer phase change current and flexibly control phase change time. When the phase change fails, the current of the main branch is transferred to the auxiliary branch, the phase change between the two bridge arms is completed through the second control valve, and the recovery time of the converter after the phase change fails is shortened.

4. 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 hybrid converter topological structure with forced phase change can conduct the auxiliary branch at any time, effectively reduces the loss of the main branch, and can realize low-voltage and low-turn-off angle operation, thereby reducing the reactive power of the inverter side.

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 cell according to an embodiment of the present invention;

fig. 2 is a block diagram of a thyristor valve according to an embodiment of the present invention;

fig. 3 is a block diagram of a first control valve according to an embodiment of the present invention;

fig. 4 is another block diagram of the first control valve according to an embodiment of the present invention;

fig. 5 is a block diagram of a second control valve according to an embodiment of the present invention;

fig. 6 is a block diagram of a second power unit according to an embodiment of the present invention;

fig. 7 is another block diagram of a second control valve according to an 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 a block diagram of a buffer member according to an embodiment of the present invention;

fig. 10 is a block diagram of a forced commutated hybrid converter topology according to an embodiment of the present invention;

FIG. 11 is a flow chart of a method of controlling forced commutation according to an embodiment of the present invention;

fig. 12 is a normal operating condition V1 valve bridge arm current flow path according to an embodiment of the present invention;

fig. 13a is a trigger control sequence for a normal operating state according to an embodiment of the present invention;

fig. 13b is a trigger control sequence for a commutation failure or short circuit fault according to an embodiment of the present invention;

fig. 14a is a current flow path through which the primary leg commutates to the secondary leg in accordance with an embodiment of the present invention;

fig. 14b is a current flow path of the auxiliary branch current flow stage according to an embodiment of the invention;

fig. 14c is a current flow path during the auxiliary branch turn-off phase according to an embodiment of the present invention;

fig. 15 is a timing diagram of the periodic triggering control of the primary branch and the secondary branch according to an embodiment of the present invention.

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 utilizes the thyristor and has the advantage of the control valve of shutoff ability, through turn-off the control valve in advance in order to guarantee that thyristor valve possesses sufficient turn-off time and resume shutoff ability, realizes the reliable shutoff of transverter, avoids appearing commutation failure and influences the stable safe operation of 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 1 and an auxiliary branch 2. Wherein, a thyristor valve 11 is arranged on the main branch 1; the auxiliary branch 2 is arranged in parallel with the main branch 1, and a first control valve 21 and a second control valve 22 are sequentially arranged on the auxiliary branch 2 along the direction from the converter transformer to the direct current bus, where the arrangement order of the first control valve 21 and the second control valve 22 is not particularly limited. The first control valve 21 has a unidirectional voltage output controllable turn-off function, and the second control valve 22 has a forward current controllable turn-off function and a forward and reverse voltage blocking function.

The active commutation unit that this embodiment provided utilizes thyristor and the advantage that first control valve can be turn-offed and the second control valve can be turn-offed, adopts two branch roads parallelly connected, realizes the transfer of electric current through the first control valve in the auxiliary branch road, and the second control valve bears great shutoff voltage stress when being used for the trouble, need not to bear current stress for a long time, has avoided the increase of device loss, has improved the utilization ratio of first control valve and second control valve. The auxiliary branch circuit which can provide reverse voltage and has self-turn-off capability is connected in parallel on the basis of the thyristor valve, so that the reliable turn-off of the main branch circuit and the active phase change of the whole bridge arm are realized. When the active commutation unit normally operates, the auxiliary branch can keep a turn-off state and only needs to bear voltage stress; the auxiliary branch is immediately conducted when the active phase change unit fails in phase change, the first control valve can transfer current to the auxiliary branch and provide reverse voltage for a thyristor valve of the main branch, and the second control valve can replace the main branch to complete phase change, so that an auxiliary phase change function is realized in a short time, and the occurrence of phase change failure is avoided.

Optionally, the thyristor valve 11 comprises at least one thyristor 111 and a first buffer component 112 connected in parallel or in series with the thyristor 111, respectively, wherein the at least one thyristor is arranged in series, and the first buffer component 112 is used for the thyristor device to protect against high voltage and large current. As shown in fig. 2, the thyristor valve 11 includes at least one thyristor 111 and first buffer members 112 connected in parallel with the thyristors 111, respectively.

Optionally, the first control valve 21 includes at least one first power unit 211 and a second buffer component (a parallel connection manner is known to those skilled in the art and is not shown in the drawings) respectively connected in parallel with the first power unit 211, wherein the at least one first power unit is connected in series, and the second buffer component is used for limiting the voltage and current stress.

Specifically, as shown in fig. 3, the first power unit 211 may be a power electronic unit composed of a first branch and a second branch.

A first power device is arranged on the first branch; the second branch circuit is connected with the first branch circuit in parallel, a first capacitor element and a first power device are arranged on the second branch circuit, and the first power device is connected with the first capacitor element in series. The first power device is a fully-controlled power electronic device, and the fully-controlled power electronic device is one or more of turn-off devices such as an IGBT, an IGCT, an IEGT, a GTO or a MOSFET.

Specifically, as shown in fig. 4, the first power unit 211 may also be a power electronic unit composed of a third branch and a fourth branch.

A full-bridge circuit is formed by connecting four second power devices of the third branch circuit; and a second capacitive element is arranged on the fourth branch and connected in parallel between the upper half bridge and the lower half bridge of the full-bridge circuit. The second power device is a fully-controlled power electronic device, and the fully-controlled power electronic device is one or more of an IGBT, an IGCT, an IEGT, a GTO or a MOSFET.

The first control valve 21 is a low-voltage shutoff valve, has a one-way voltage controllable output capability, and is mainly used for shutting off the main branch current and providing a reverse voltage for the main branch current, so that the thyristor valve of the main branch can be reliably shut off within enough shut-off time, and the required series number of the first control valve 21 is small, so that the total loss is low. The present application does not limit the topology of the first control valve 21, and any topology may be used as long as it has a function of outputting a unidirectional voltage.

Optionally, the second control valve 22 includes at least one second power unit 221 and third buffer components 222 respectively connected in parallel to the second power unit 221, wherein the at least one second power unit 221 is connected in series, and the third buffer components 222 are used for limiting voltage and current stress.

Specifically, as shown in fig. 5, the second power unit 221 may be a power electronic unit composed of a fifth branch circuit.

And a third power device and a first diode are arranged on the fifth branch, and the third power device and the first diode are arranged in series. The third power device is a power electronic device without a reverse blocking function, and the power electronic device without the reverse blocking function is one or more of an IGBT, an IGCT, an IEGT, a GTO or a MOSFET. The power electronics device without reverse blocking function and the first diode are combined in series to form a power electronics unit with reverse blocking and forward turn-off capability.

Specifically, as shown in fig. 6, the second power unit 221 may also be a power electronic unit composed of a sixth branch and a seventh branch.

At least one third power device is arranged on the sixth branch, and the at least one third power device is arranged in series; the seventh branch circuit is connected in series with the sixth branch circuit, at least one second diode is arranged on the seventh branch circuit, and the at least one second diode is arranged in series. The third power device is a power electronic device without a reverse blocking function, and the power electronic device without the reverse blocking function is one or more of an IGBT, an IGCT, an IEGT, a GTO or a MOSFET.

The topological form of the second power unit is a form in which a power electronic device without a reverse blocking function is matched with the first diode, a form in which a single-stage power electronic device without a reverse blocking function, a single-stage diode and a buffer component are matched to form a multistage series structure, a form in which a multistage power electronic device without a reverse blocking function and a buffer component combination thereof are combined with a multistage diode and a buffer component combination thereof are connected in series, a form in which a multistage power electronic device without a reverse blocking function and a multistage diode and a buffer component combination thereof are alternately connected in series, or a form in which a multistage power electronic device without a reverse blocking function and a multistage diode are alternately connected in series, or other topological forms, which is not specifically limited herein, and can be determined by those skilled in the art according to actual needs.

Specifically, as shown in fig. 7, the second power unit 221 may also be a power electronic unit composed of an eighth branch. The eighth branch circuit is a full-bridge circuit formed by connecting a plurality of fourth power devices, wherein the fourth power devices are fully-controlled power electronic devices, and the fully-controlled power electronic devices are one or more of IGBTs, IGCTs, IEGTs, GTOs or MOSFETs.

The full-bridge circuits are sequentially connected in series to realize forward and reverse control of current, transfer of current of the main branch circuit to the auxiliary branch circuit can be completed at any time, forward and reverse voltage can be borne, each bridge arm in the full-bridge circuit is of a single-stage structure or a multi-stage series structure formed by a fully-controlled power electronic device matched with a diode, and other topological forms can be adopted, and the full-bridge circuit is not particularly limited and can be determined by a person skilled in the art according to actual needs.

Specifically, as shown in fig. 8, the second power unit 221 may also be a power electronic unit formed by a ninth branch, where the ninth branch includes a first sub-branch, a second sub-branch, and a third sub-branch. The first sub-branch, the second sub-branch, the third sub-branch and the third buffer component form an H-bridge circuit.

The first sub-branch is provided with a plurality of third diodes which are connected in series; the second sub-branch is connected in parallel between the first sub-branch and the third sub-branch, and a plurality of fifth power devices connected in series are arranged on the second sub-branch, wherein the fifth power devices are fully-controlled power electronic devices, and the fully-controlled power electronic devices are one or more of IGBTs, IGCTs, IEGT, GTOs and MOSFETs; and a plurality of fourth diodes connected in series are arranged on the third sub-branch. The fully-controlled power electronic device and the diode in the H-bridge circuit can be of a single-stage structure or a multi-stage series structure, and the H-bridge circuit is sequentially connected in series to realize the functions of bidirectional through-current and bidirectional turn-off.

The second control valve 22 is a high-voltage shutoff valve, and has forward current controllable shutoff and forward and reverse voltage blocking capabilities, and the present application does not limit the topology of the second control valve 212, and the topology may be any topology having the functions of forward current controllable shutoff and forward and reverse voltage blocking.

Alternatively, the auxiliary branch may be formed by connecting the first control valve 21 and the second control valve 22 in series, or by connecting the units of the first control valve 21 and the second control valve 22 alternately in series.

Optionally, the first buffer member 112, the second buffer member 212 and the third buffer member 222 are all formed by one or more of a capacitor, a rc circuit, a diode, an inductor or an arrester.

Specifically, as shown in fig. 9, the first, second, and third buffer parts 112, 222 may be a first buffer branch composed of a capacitor; the second buffer branch can be formed by connecting a resistor and a capacitor in series; the third buffer branch can be formed by connecting a capacitor and a resistor in parallel; the fourth buffer branch RCD1 can be formed by connecting a resistor and a fifth diode in parallel and then connecting the resistor and a capacitor in series; a fifth buffer branch RCD2 formed by a resistor and a capacitor connected in parallel and then connected in series with a fifth diode; 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. As shown in fig. 10, the hybrid converter topology structure with forced phase commutation includes a three-phase six-leg circuit, each phase leg includes an upper leg and a lower leg, and at least one of the upper leg or the lower leg is provided with the active phase commutation unit according to the above embodiment.

Specifically, the forced commutated hybrid converter topology as depicted in fig. 10 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 in relation to fig. 10, 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; the auxiliary branches of the 3 upper bridge arms respectively comprise first control valves V13, V33 and V53; the auxiliary branches of the 3 upper bridge arms respectively comprise second control valves V12, V32 and V52, and the main branches of the 3 lower bridge arms respectively comprise thyristor valves V21, V41 and V6; the auxiliary branches of the 3 lower bridge arms respectively comprise first control valves V23, V43 and V63; the auxiliary branches of the 3 lower bridge arms respectively comprise second control valves V22, V42 and V62, and the on and off of the thyristor valve, the first control valve and the second control valve are controlled by a control trigger control system.

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 a first control valve with reverse voltage supply capacity and a second control valve 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 first control valve of the auxiliary branch of the active phase change unit can cut off the current of the main branch in advance, and provides reverse voltage at the same time, so that the active phase change of the whole bridge arm is realized. The hybrid converter topological structure for forced commutation increases the commutation voltage-time area of the main branch thyristor valve so as to ensure the reliable turn-off of the hybrid converter, avoid the problem of commutation failure and ensure the stable and safe operation of a power grid.

In accordance with an embodiment of the present invention, there is provided an embodiment of a forced commutation control method, it should be noted that the steps illustrated in the flowchart of the figure may be performed in a computer system such as a set of computer executable instructions, and that while a logical order is illustrated in the flowchart, in some cases the steps illustrated or described may be performed in an order different than here.

In this embodiment, a method for controlling forced commutation is provided, which can be used in the above-mentioned hybrid converter topology for forced commutation, and fig. 11 is a flowchart of a method for controlling forced commutation according to an embodiment of the present invention, as shown in fig. 11, the flowchart includes the following steps:

and S21, switching on the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topology.

And S22, conducting the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topology.

And S23, 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.

And S24, conducting the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topological structure after a control period, wherein i belongs to [1,6 ].

Specifically, as shown in fig. 12, the valve current flow path of the hybrid converter topology under normal operating conditions is shown, the main branch is periodically subjected to voltage and current stresses, the auxiliary branch is always in an off state, and the auxiliary branch is subjected to voltage stresses only when the thyristor valve of the main branch is turned off.

In the control method for forced commutation provided by this embodiment, the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topology are kept in the off state, and the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topology is turned on, so that the hybrid converter topology for forced commutation can work in the normal commutation operation mode, that is, in the temporary commutation operation mode, the auxiliary branch is in the off state when the hybrid converter normally operates, and only bears voltage stress, thereby reducing the increase of converter loss in long-term operation.

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. 13a shows the trigger control sequence in the normal operation mode, t₀Indicating the initial trigger time.

Fig. 14a, 14b and 14c show the main branch switching off the V1 valve and the auxiliary branch starting to bear voltage stress, the process being divided into three phases, fig. 14a shows the main branch switching phase to the auxiliary branch, the auxiliary branch receiving a trigger signal to turn on, and the auxiliary branch V12 valve and the V13 valve receiving turn-on signals to transfer the current of the main branch to the auxiliary branch and apply a reverse voltage to the main branch; FIG. 14b is the 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. 14c shows the auxiliary branch off phase, in which the auxiliary branch V13 valve is turned off first when the off signal is received, 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 V11 valve of the main branch is turned on in the next control period. The above-described operation can be put into operation when a commutation fault is detected or predicted.

Fig. 13b is a trigger control sequence of the hybrid converter topology for forced commutation in the event of commutation failure or ac short circuit fault. At t in FIG. 13b_fWhen the phase change failure of the V1 valve to the V3 valve is monitored at the moment, the first preset time delta t is passed₁The auxiliary branch V13 valve is conducted for a second preset time period delta t₂The 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 t₂≥Δt₁Is 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 t₃The 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_offHere, t_offLarger than the thyristor valveThe off time is small to ensure that the thyristor valve V11 has enough 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 of the V1 valve to the V3 valve is completed, the failure fault 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.

According to the control method for forced commutation provided by the embodiment, when commutation fails or short-circuit faults occur, the hybrid converter topological structure is controlled to start the operation mode of forced commutation, the occurrence of commutation failure is avoided, the operation mode of forced commutation is quitted when the commutation process of the hybrid converter is recovered to be normal, the auxiliary branch is continuously kept in a turn-off state, and the main branch independently and normally operates, so that the auxiliary branch is guaranteed to bear turn-off voltage stress only when the fault occurs, the loss of a device is reduced, and the service life of the device is prolonged.

Fig. 15 shows a control trigger timing when the hybrid converter topology for forced phase commutation detects a commutation failure or a short-circuit fault in advance, and the 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. 14a, 14b and 14 c. At the beginning of the commutation of the V1 valve and the V3 valve, i.e., the V1 valve trigger pulse Sg1 is delayed by 120 °, or in the vicinity of this moment the auxiliary branch V13 valve is triggered and the auxiliary branch V12 valve is opened over a short period of time (e.g., 1s, 5s, etc.), effecting 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_offAnd t is_offThe 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 ensured, 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 the positive voltage, and then the thyristor valve is switched offThe auxiliary branch V12 valve is closed before or at the same time as the valve is opened in the next duty cycle V11. 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

1. An active phase change unit is arranged in a bridge arm circuit of a current converter, one end of the active phase change unit is connected with a converter transformer, and the other end of the active phase change unit is connected with a direct current bus

The main branch is provided with a thyristor valve;

and the auxiliary branch circuit is arranged in parallel with the main branch circuit, a first control valve and a second control valve are sequentially arranged on the auxiliary branch circuit along the direction from the converter transformer to the direct current bus, the first control valve has a one-way voltage output controllable turn-off function, and the second control valve has a forward current controllable turn-off function and a forward and reverse voltage blocking function.

2. The active commutation cell of claim 1, wherein the thyristor valve comprises:

at least one thyristor, the at least one thyristor arranged in series;

at least one first snubber block connected in parallel or in series with the at least one thyristor.

3. The active commutation cell of claim 1, wherein the first control valve comprises:

at least one first power cell, the at least one first power cell arranged in series;

at least one second buffer member connected in parallel with the at least one first power cell.

4. The active commutation cell of claim 3, wherein the first power cell comprises:

the power supply comprises a first branch circuit, a second branch circuit and a control circuit, wherein the first branch circuit is provided with a first power device which is a fully-controlled power electronic device;

and the second branch circuit is connected with the first branch circuit in parallel, a first capacitor element and the first power device are arranged on the second branch circuit, and the first power device and the first capacitor element are connected in series.

5. The active commutation cell of claim 3, wherein the first power cell comprises:

the third branch circuit is a full-bridge circuit formed by connecting four second power devices; the second power device is a fully-controlled power electronic device;

and the fourth branch is provided with a second capacitance element, and the second capacitance element is connected between the upper half bridge and the lower half bridge of the full-bridge circuit in parallel.

6. The active commutation cell of claim 1, wherein the second control valve comprises:

at least one second power cell, the at least one second power cell arranged in series;

at least one third damping member connected in parallel with the at least one second power cell.

7. The active commutation cell of claim 6, wherein the second power cell comprises:

a fifth branch, wherein a third power device and a first diode are arranged on the fifth branch, and the third power device is connected with the first diode in series; the third power device is a power electronic device without a reverse blocking function;

or the like, or, alternatively,

a sixth branch, on which at least one third power device is arranged, the at least one third power device being arranged in series;

a seventh branch in series with the sixth branch; and at least one second diode is arranged on the seventh branch and is arranged in series.

8. The active commutation cell of claim 6, wherein the second power cell comprises:

the eighth branch circuit is a full-bridge circuit formed by connecting a plurality of fourth power devices; the fourth power device is a fully-controlled power electronic device.

9. The active commutation cell of claim 6, wherein the second power cell comprises:

a ninth branch comprising a first sub-branch, a second sub-branch, and a third sub-branch; the first sub-branch, the second sub-branch, the third sub-branch and the third buffer component form an H-bridge circuit;

the first sub-branch is provided with a plurality of third diodes which are connected in series;

the second sub-branch is connected in parallel between the first sub-branch and the third sub-branch, a plurality of fifth power devices connected in series are arranged on the second sub-branch, and the fifth power devices are full-control power electronic devices;

and the third sub-branch is provided with a plurality of fourth diodes which are connected in series.

10. The active commutation cell of claim 2, 3 or 6, wherein the first, second and third damping members each comprise:

the first buffer branch circuit consists of a capacitor;

or, a second buffer branch circuit with a resistor and the capacitor connected in series;

or, the capacitor and the resistor are connected in parallel by a third buffer branch;

or the resistor is connected with the fifth diode in parallel and then connected with the capacitor in series to form a fourth buffer branch circuit;

or, the resistor is connected in parallel with the capacitor and then connected in series with the fifth 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.

11. A hybrid converter topology for forced commutation, the topology being switched into an ac power grid through a converter transformer, the topology comprising a three-phase six-leg circuit, each leg of the phase comprising an upper leg and a lower leg, respectively, wherein at least one of the upper or lower legs is provided with an active commutation cell according to any one of claims 1 to 10.