WO2022160929A1 - Active commutation unit, forced commutation hybrid converter topological structure, and method - Google Patents

Abstract

Disclosed in the present invention are an active commutation unit, a forced commutation hybrid converter topological structure, and a method. The active commutation unit is disposed in a bridge arm circuit of a converter, has one end connected to a converter transformer and the other end connected to a direct-current bus, and comprises: a main branch provided with a thyristor valve, and an auxiliary branch arranged in parallel with the main branch; a first control valve and a second control valve are successively provided on the auxiliary branch, the first control valve has a unidirectional voltage output controllable turn-off function, and the second control valve has a forward current controllable turn-off function and a forward/reverse voltage blocking function. The forced commutation hybrid converter topological structure is connected to an alternating-current power grid by means of the converter transformer; the topological structure 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 lower bridge arm is provided with the active commutation unit.

Description

Active commutation unit and forced commutation hybrid converter topology and method

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is based on a Chinese patent application with an application number of 202110137729.3 and an application date of February 1, 2021, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is incorporated herein by reference.

technical field

The invention relates to the technical field of commutation in power electronics, in particular to an active commutation unit, a hybrid converter topology structure and a forced commutation method.

Background technique

The traditional line commutated converter high voltage direct current (LCC-HVDC) transmission system has the advantages of long-distance large-capacity power transmission and controllable active power, and is widely used in the world. As the core equipment of DC transmission, the converter is the core functional unit to realize the conversion of AC and DC power, and its operational reliability largely determines the operational reliability of the UHV DC power grid.

Since traditional converters mostly use half-controlled thyristors as the core components to form a six-pulse bridge commutation topology, each bridge arm is composed of multi-stage thyristors and their buffer components in series. Commutation failure is prone to occur in the case of faults, resulting in a surge of DC current and a rapid and large loss of DC transmission power, which affects the stable and safe operation of the power grid.

SUMMARY OF THE INVENTION

The embodiments of the present invention provide an active commutation unit and a forced commutation hybrid converter topology structure and method, so as to solve the problem that commutation failure affects the stable and safe operation of the power grid.

According to a first aspect, an embodiment of the present invention provides an active commutation unit, which is arranged in a bridge arm circuit of a converter, one end of which is connected to a converter transformer, and the other end is connected to a DC bus, including: a main branch, the A thyristor valve is arranged on the main branch; an auxiliary branch is arranged in parallel with the main branch, and a first control valve and a second control valve are sequentially arranged on the auxiliary branch along the direction from the converter transformer to the DC bus. The first control valve has a unidirectional voltage output controllable shutdown function, and the second control valve has a forward current controllable shutdown function and a forward and reverse voltage blocking function.

With reference to the first aspect, in a first embodiment of the first aspect, the thyristor valve includes: at least one thyristor, the at least one thyristor is arranged in series; at least one first buffer component, 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 unit, the at least one first power unit is arranged in series; at least one second buffer component, connected to The at least one first power unit is connected in parallel.

With reference to the second embodiment of the first aspect, in a third embodiment of the first aspect, the first power unit includes: a first branch, a first power device and a diode are arranged on the first branch, and the first branch is provided with a first power device and a diode. The first power device is a fully-controlled power electronic device; the second branch is connected in parallel with the first branch, and the second branch is provided with a first capacitive element and the first power device, and the first A power device is connected in series with the first capacitive element.

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

With reference to the first aspect, in a fifth embodiment of the first aspect, the second control valve includes: at least one second power unit, the at least one second power unit is arranged in series; at least one third buffer component, connected to The at least one second power unit is connected in parallel.

With reference to the fifth embodiment of the first aspect, in the sixth embodiment of the first aspect, the second power unit includes: a fifth branch, and the fifth branch is provided with a third power device and a first diode tube, the third power device is connected in series with the first diode; or, a sixth 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 third power device is a power electronic device without reverse blocking function; the seventh branch is connected in series with the sixth branch; the seventh branch is provided with at least one second diode, The at least one second diode is arranged in series.

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

With reference to the fifth embodiment of the first aspect, in the eighth embodiment of the first aspect, the second power unit includes: at least one ninth branch, the ninth branch includes a first sub-branch, a second branch sub-branch and third sub-branch; the first sub-branch, the second sub-branch, the third sub-branch and the third buffer component constitute an H-bridge circuit; the first sub-branch The branch is provided with a plurality of third diodes connected in series; the second sub-branch is connected in parallel between the first sub-branch and the third sub-branch, and the second sub-branch is connected in parallel A plurality of fifth power devices connected in series are provided, and the fifth power devices are fully-controlled power electronic devices; the third sub-branch is provided with a plurality of fourth diodes connected in series.

In combination with the first embodiment or the second embodiment or the fifth embodiment of the first aspect, in the ninth embodiment of the first aspect, the first buffer part, the second buffer part and the third buffer part all include: composed of capacitors The first buffer branch; or, the second buffer branch of the resistor and the capacitor in series; or, the third buffer branch of the capacitor and the resistor in parallel; or, the resistor and the fifth diode connected in parallel, and then connected in series with the capacitor to form a fourth buffer branch; or, the resistor and the capacitor connected in parallel, and then connected in series with the fifth buffer to form a fifth buffer branch; or, a lightning arrester formed by the sixth buffer branch; or, the first buffer branch, the second buffer branch, the third buffer branch, the fourth buffer branch, the fifth buffer branch and the A seventh buffer branch formed by a plurality of parallel connection in the sixth buffer branch.

According to a second aspect, an embodiment of the present invention provides a forced commutation hybrid converter topology structure, the topology structure is connected to an AC power grid through a converter transformer, and the topology structure includes a three-phase six-arm circuit, Each phase bridge arm includes an upper bridge arm and a lower bridge arm respectively, and at least one of the upper bridge arm or the lower bridge arm is provided with the active commutation unit according to the first aspect or any embodiment of the first aspect.

According to a third aspect, an embodiment of the present invention provides a control method for forced commutation, which is used for the forced commutation hybrid converter topology structure described in the second aspect, including the following steps: turning on the forced commutation The thyristor valve of the main branch of the ith bridge arm of the hybrid converter topology structure; the first auxiliary branch of the ith bridge arm of the forced commutation hybrid converter topology is turned on a control valve and a second control valve; the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the forced commutation hybrid converter topology structure are turned off; after one control cycle, The thyristor valve that turns on the main branch of the ith bridge arm of the forced commutation hybrid converter topology structure is returned, where i∈[1,6].

With reference to the third aspect, in the first embodiment of the third aspect, the method further includes: when it is detected that a commutation failure or a short-circuit fault occurs in the i-th bridge arm of the hybrid converter topology, acquiring the commutation failure or the duration of the short-circuit fault; when the duration reaches the first preset duration, the second control valve of the auxiliary branch of the ith bridge arm is turned on, and when the duration reaches the second preset duration, the second control valve is turned on The first control valve of the auxiliary branch of the i-th bridge arm performs commutation from the main branch to the auxiliary branch, wherein the second preset duration is greater than or equal to the first preset duration; when the hybrid commutation is performed When the current of the main branch of the ith bridge arm of the ith bridge arm is reduced to zero, and the duration reaches the third preset time length, the second control valve of the auxiliary branch of the ith bridge arm is turned off, The third preset duration is longer than the second preset duration; when the thyristor valve of the main branch of the i-th bridge arm is turned on in the next control cycle, the first control valve of the auxiliary branch of the i-th bridge arm is turned off .

With reference to the first embodiment of the third aspect, in the second embodiment of the third aspect, the method further includes: the main branch and the auxiliary circuit of the ith bridge arm of the forced commutation hybrid converter topology structure The branches run alternately periodically.

The technical scheme of the present invention has the following advantages:

1. The active commutation unit provided by the embodiment of the present invention includes a main branch and an auxiliary branch connected in parallel, and the main branch is provided with a thyristor valve, which has a large current capacity and carries a normal operating current; the first branch of the auxiliary branch is The control valve has a forward current controllable shutdown function, and the second control valve has forward and reverse voltage blocking capabilities. The active commutation unit takes advantage of the thyristor and the advantages that the first control valve can be turned off and the second control valve can be turned off, adopts two branches in parallel, and realizes current transfer through the first control valve in the auxiliary branch. The second control valve is used to withstand a large turn-off voltage stress in the event of a fault, and does not need to withstand the current stress for a long time, thereby avoiding the increase of device loss and improving the utilization rate of the first control valve and the second control valve. On the basis of the thyristor valve, the auxiliary branch with reverse voltage and self-shutoff capability can be provided in parallel, so as to realize the reliable shutdown of the main branch and the active commutation of the entire bridge arm. When the active commutation unit is in normal operation, the auxiliary branch can be kept off and only needs to bear the voltage stress; when the active commutation unit fails to commutate, the auxiliary branch is immediately turned on, and the first control valve can transfer the current to the auxiliary branch The second control valve can replace the main branch to complete the commutation, so as to realize the auxiliary commutation function in a short time and avoid the occurrence of commutation failure.

2. The forced commutation hybrid converter topology structure provided by the embodiment of the present invention includes a three-phase six-arm circuit, and each phase arm includes an upper arm and a lower arm respectively, and at least one upper arm or a lower arm. The arm is provided with an active commutation unit. The first control valve of the auxiliary branch of the active commutation unit can cut off the current of the main branch in advance, and at the same time provide a reverse voltage, which increases the commutation voltage-time area of the thyristor valve of the main branch, ensures its reliable shutdown, and avoids The problem of commutation failure occurs, so as to ensure the stable and safe operation of the power grid.

3. The forced commutation hybrid converter topology provided by the embodiment of the present invention includes a three-phase six-arm circuit, and each phase arm includes an upper arm and a lower arm respectively, and at least one upper arm or a lower arm. The arm is provided with an active commutation unit. The second control valve of the auxiliary branch of the active commutation unit can quickly transfer the commutation current and flexibly control the commutation time. When the commutation fails, the current of the main branch is transferred to the auxiliary branch, and the commutation between the two bridge arms is completed through the second control valve, which speeds up the recovery time of the converter after the commutation failure.

4. The forced commutation hybrid converter topology structure provided by the embodiment of the present invention includes a three-phase six-arm circuit, and each phase arm includes an upper arm and a lower arm respectively, and at least one upper arm or a lower arm. The arm is provided with an active commutation unit. The forced commutation hybrid converter topology structure can turn on the auxiliary branch at any time, effectively reducing the loss of the main branch, and at the same time, it can realize low voltage and low turn-off angle operation, thereby reducing the reactive power on the inverter side .

5. The control method for forced commutation provided by the embodiment of the present invention, the first control valve and the second control valve of the auxiliary branch of the i-th bridge arm of the hybrid converter topology are kept in a closed state and turned on. The thyristor valve of the main branch of the ith bridge arm of the hybrid converter topology structure, thus realizing the forced commutation hybrid converter topology structure can work in the normal commutation operation mode, that is, in the temporary commutation In the normal operation mode of the hybrid converter, the auxiliary branch is in the off state and only bears the voltage stress, which reduces the increase of the converter loss under long-term operation. When a commutation failure or an AC short-circuit fault occurs, the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topology are turned on; the current of the main branch is forcibly transferred to The auxiliary branch, when the current transfer is completed, closes the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topology to realize the forced commutation of the hybrid converter . After a control cycle, the step of turning on the thyristor valve of the main branch of the i-th bridge arm of the hybrid converter topology structure is returned, and the main branch continues to operate independently and normally, so as to ensure that the auxiliary branch is only Turn-off voltage stress during faults reduces device losses, thereby extending device life.

6. The control method for forced commutation provided by the embodiment of the present invention controls the hybrid converter topology to turn on the forced commutation operation mode when commutation fails or a short-circuit fault occurs, so as to avoid the occurrence of commutation failure, and in the event of a commutation failure. When the commutation process of the hybrid converter returns to normal, the operation mode of forced commutation is exited, and the auxiliary branch continues to remain in the off state, and the main branch operates independently and normally, thus ensuring that the auxiliary branch can only be turned off in the event of a fault. The voltage stress reduces the loss of the device, thereby extending the service life of the device.

7. The control method for forced commutation provided by the embodiment of the present invention can not only resist the commutation failure, but also does not need to predict the commutation failure through the periodic alternate operation of the main branch and the auxiliary branch. At the same time, it is ensured that the hybrid inverter works in an operation mode with a small turn-off angle, and the reactive power consumption of the hybrid inverter is reduced.

Description of drawings

1 is a structural block diagram of an active commutation unit according to an embodiment of the present invention;

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

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

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

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

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

FIG. 7 is another structural block diagram of the second control valve according to an embodiment of the present invention;

8 is another structural block diagram of a second control valve according to an embodiment of the present invention;

9 is a structural block diagram of a buffer component according to an embodiment of the present invention;

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

11 is a flowchart of a control method for forced commutation according to an embodiment of the present invention;

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

13a is a trigger control sequence of a normal operation state according to an embodiment of the present invention;

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

Fig. 14a is a current flow path for commutation from the main branch to the auxiliary branch according to an embodiment of the present invention;

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

FIG. 14c is a current flow path in an auxiliary branch off stage according to an embodiment of the present invention;

FIG. 15 is the periodic triggering control sequence of the main branch and the auxiliary branch according to an embodiment of the present invention.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in 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. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

As the core equipment of DC transmission, the converter is the core functional unit to realize the conversion of AC and DC power, and its operational reliability largely determines the operational reliability of the UHV DC power grid. However, since traditional converters mostly use half-controlled thyristors as the core components to form a six-pulse bridge commutation topology, each bridge arm is composed of multi-stage thyristors and their buffer components in series. In the case of AC system failure, commutation failure is prone to occur, resulting in a surge in DC current and a rapid and large loss of DC transmission power, which affects the stable and safe operation of the power grid.

Based on this, the technical solution of the present invention utilizes the advantages of a thyristor and a control valve that can be turned off, and by shutting off the control valve in advance to ensure that the thyristor valve has a sufficient turn-off time to restore the turn-off capability, and realize the reliable turn-off of the converter. , to avoid commutation failure and affect the stable and safe operation of the power grid.

According to an embodiment of the present invention, an embodiment of an active commutation unit is provided, and the active commutation unit is provided in a bridge arm circuit of a converter. One end of the active commutation unit is connected to the output end of the converter transformer, and the other end is connected to the DC bus. As shown in FIG. 1 , the active commutation unit includes: a main branch 1 and an auxiliary branch 2 . The main branch 1 is provided with a thyristor valve 11; the auxiliary branch 2 is arranged in parallel with the main branch 1, and a first control valve 21 and a first control valve 21 and a second control valve are arranged on the auxiliary branch 2 in sequence along the direction from the converter transformer to the DC bus. The second control valve 22 is not specifically limited here for the arrangement sequence of the first control valve 21 and the second control valve 22 . The first control valve 21 has a unidirectional voltage output controllable shutdown function, and the second control valve 22 has a forward current controllable shutdown function and a forward and reverse voltage blocking function.

The active commutation unit provided by the embodiment of the present invention utilizes the advantages of a thyristor and that the first control valve can be turned off and the second control valve can be turned off, adopts two branches in parallel, and realizes the current through the first control valve in the auxiliary branch. The transfer of the second control valve is used to withstand a large turn-off voltage stress in the event of a fault, and it does not need to withstand the current stress for a long time, which avoids the increase of device loss and improves the utilization rate of the first control valve and the second control valve. On the basis of the thyristor valve, the auxiliary branch with reverse voltage and self-shutoff capability can be provided in parallel, so as to realize the reliable shutdown of the main branch and the active commutation of the entire bridge arm. When the active commutation unit is in normal operation, the auxiliary branch can be kept off and only needs to bear the voltage stress; when the active commutation unit fails to commutate, the auxiliary branch is immediately turned on, and the first control valve can transfer the current to the auxiliary branch The second control valve can replace the main branch to complete the commutation, so as to realize the auxiliary commutation function in a short time and avoid the occurrence of commutation failure.

In some embodiments of the present invention, the thyristor valve 11 includes at least one thyristor 111 and a first buffer part 112 respectively connected in parallel or in series with the thyristor 111, wherein the at least one thyristor is arranged in series, and the first buffer part 112 is used for the thyristor device to avoid suffering Damaged by high voltage and high 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.

In some embodiments of the present invention, the first control valve 21 includes at least one first power unit 211 and a second buffer component respectively connected in parallel with the first power unit 211 (those skilled in the art can know the parallel connection method, not shown in the figure). shown), wherein at least one first power unit is arranged in series, and a second buffer component is used to limit the voltage and current stress.

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

A first power device is arranged on the first branch; the second branch is connected in parallel with the first branch, a first capacitive element and a first power device are arranged on the second branch, and the first power device and the first capacitive element are connected in series. Wherein, the first power device is a fully-controlled power electronic device, and the fully-controlled power electronic device is one or more of IGBT, IGCT, IEGT, GTO, or MOSFET that can be turned off.

Exemplarily, 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.

The third branch is a full-bridge circuit formed by connecting four second power devices; the fourth branch is provided with a second capacitive element, and the second capacitive element is 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 IGBT, IGCT, IEGT, GTO, or MOSFET, which is not limited in the embodiment of the present invention.

The above-mentioned first control valve 21 is a low-pressure shut-off valve with a one-way voltage controllable output capability. It is mainly used to shut off the current of the main branch and provide it with a reverse voltage, so as to ensure that the thyristor valve of the main branch has sufficient capacity. The turn-off time can be reliably turned off, and the number of series stages of the first control valve 21 is required to be less, resulting in a lower total loss. The embodiment of the present invention does not limit the topological form of the first control valve 21, as long as it is a topological form with the function of unidirectional voltage controllable output.

In some embodiments of the present invention, the second control valve 22 includes at least one second power unit 221 and third buffer components 222 connected in parallel with the second power units 221 respectively, wherein the at least one second power unit 221 is arranged in series, the third The buffer member 222 is used to limit the voltage and current stress.

Exemplarily, as shown in FIG. 5 , the second power unit 221 may be a power electronic unit composed of a fifth branch.

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. Wherein, the third power device is a power electronic device without reverse blocking function, and the power electronic device without reverse blocking function is one or more of IGBT, IGCT, IEGT, GTO or MOSFET. The embodiment is not limited. The power electronic device without reverse blocking function is combined with the first diode in series to form a power electronic unit with reverse blocking and forward turn-off capabilities.

Exemplarily, 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 at least one third power device is arranged in series; the seventh branch is connected in series with the sixth branch, and at least one second diode is arranged on the seventh branch, and at least one second diode is arranged on the seventh branch. A second diode is placed in series. Wherein, the third power device is a power electronic device without reverse blocking function, and the power electronic device without reverse blocking function is one or more of IGBT, IGCT, IEGT, GTO or MOSFET. The embodiment is not limited.

The topological form of the above-mentioned second power unit is that a power electronic device without a reverse blocking function cooperates with the first diode, and a single-stage power electronic device without a reverse blocking function can be matched with a single-stage diode and a buffer component. A multi-stage series structure is formed, which can be composed of multi-stage power electronic devices without reverse blocking function and their buffer components in series with multi-stage diodes and their buffer components, or multi-stage power electronics without reverse blocking function. The electronic devices and the multi-stage diodes are alternately connected in series, and of course other topological forms are also possible, which are not specifically limited here, and can be determined by those skilled in the art according to actual needs.

Exemplarily, 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 is a full-bridge circuit formed by connecting a plurality of fourth power devices, wherein the fourth power device is a fully-controlled power electronic device, and the fully-controlled power electronic device is one of IGBT, IGCT, IEGT, GTO or MOSFET. One or more of the embodiments of the present invention are not limited.

The full-bridge circuits can be connected in series to realize the forward and reverse current control, and the transfer of the current from the main branch to the auxiliary branch can be completed at any time, and at the same time, it can withstand the forward and reverse voltages. Of course, the single-stage structure or multi-stage series structure composed of diodes can also be other topological forms, which are not specifically limited here, and can be determined by those skilled in the art according to actual needs.

Exemplarily, as shown in FIG. 8 , the second power unit 221 may also be a power electronic unit composed of a ninth branch, and the nine branches include 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 part constitute an H-bridge circuit.

The first sub-branch is provided with a plurality of third diodes 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 series-connected diodes are arranged on the second sub-branch The fifth power device, wherein the fifth power device is a fully-controlled power electronic device, and the fully-controlled power electronic device is one or more of IGBT, IGCT, IEGT, GTO or MOSFET. Definition; a plurality of fourth diodes connected in series are arranged on the third sub-branch. The fully-controlled power electronic devices and diodes in the H-bridge circuit can be either a single-stage structure or a multi-stage series structure, and the H-bridge circuit can be connected in series to realize bidirectional current flow and bidirectional shutdown functions.

The above-mentioned second control valve 22 is a high-pressure shut-off valve, with forward current controllable shut-off and forward and reverse voltage blocking capabilities. The application does not limit the topology of the second control valve 212, as long as it has a forward current control valve 212. Topological forms of the function of current-controlled turn-off and forward and reverse voltage blocking are sufficient.

In some embodiments of the present invention, the auxiliary branch may be constituted by the first control valve 21 and the second control valve 22 in series, or may be constituted by the units in the first control valve 21 and the second control valve 22 in alternate series.

In some embodiments of the present invention, the first buffer component 112 , the second buffer component 212 , and the third buffer component 222 are all composed of one or more forms of components such as capacitors, RC loops, diodes, inductors, or arresters.

Exemplarily, as shown in FIG. 9 , the first buffer component 112 , the second buffer component and the third buffer component 222 may be a first buffer branch composed of capacitors; may be a second buffer branch composed of a resistor and a capacitor in series. It can be a third buffering branch consisting of a capacitor and a resistor in parallel; it can be a fourth buffering branch RCD1 consisting of a resistor and a fifth diode in parallel, and then a capacitor in series; it can be a resistor and a capacitor in parallel, and then The fifth buffer branch RCD2 formed in series with the fifth diode; it can also be the sixth buffer branch formed by the arrester; it can also be the above-mentioned first buffer branch, second buffer branch, and third buffer branch , a seventh buffer branch formed in parallel among the fourth buffer branch, the fifth buffer branch and the sixth buffer branch.

According to an embodiment of the present invention, a forced commutation hybrid converter topology structure is provided, and the topology structure is connected to an AC power grid through a converter transformer. As shown in FIG. 10 , the forced commutation hybrid converter topology includes a three-phase six-arm circuit, each phase arm includes an upper arm and a lower arm, and at least one upper arm or lower arm thereof The arm is provided with the active commutation unit described in the above embodiment.

Exemplarily, the forced commutation hybrid converter topology shown in FIG. 10 includes 3 upper bridge arms and 3 lower bridge arms. Each active commutation unit is used as a converter valve, and the topology of the hybrid converter with forced commutation described in FIG. 10 includes a converter valve V1, a converter valve V2, a converter valve V3, and a converter valve. V4, converter valve V5 and converter valve V6. The main branches of the three upper arms respectively include thyristor valves V11, V31 and V51; the auxiliary branches of the three upper arms respectively include the first control valves V13, V33 and V53; the auxiliary branches of the 3 upper bridge arms respectively include the second control valves V12, V32 and V52, the main branches of the 3 lower bridge arms respectively include the thyristor valves V21, V41 and V6; the auxiliary branches of the 3 lower bridge arms The auxiliary branches of the three lower bridge arms respectively include the second control valves V22, V42 and V62, and the thyristor valve, the first control valve and the second control valve are controlled by the control trigger control system. Control valve off and on.

The above-mentioned forced commutation hybrid converter topology can provide reverse voltage and auxiliary branches with self-shut-off capability by connecting thyristor valves in parallel, so as to achieve reliable shutdown of the main branch and active active switching of the entire bridge arm. commutation. The auxiliary branch is composed of a first control valve capable of providing reverse voltage and a second control valve having bidirectional pressure bearing capability in series, that is, a shut-off valve is introduced for each bridge arm.

The forced commutation hybrid converter topology provided by the embodiment of the present invention includes a three-phase six-arm circuit, and each phase arm includes an upper arm and a lower arm respectively, and at least one upper arm or a lower arm An active commutation unit is provided. The first control valve of the auxiliary branch of the active commutation unit can cut off the current of the main branch in advance, and at the same time provide a reverse voltage to realize the active commutation of the entire bridge arm. The forced commutation hybrid converter topology increases the commutation voltage-time area of the thyristor valve of the main branch to ensure its reliable shutdown, avoid the problem of commutation failure, and ensure the stable and safe operation of the power grid.

According to an embodiment of the present invention, an embodiment of a control method for forced commutation is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings may be executed in a computer system such as a set of computer-executable instructions, Also, although a logical order is shown in the flowcharts, in some cases the steps shown or described may be performed in an order different from that herein.

An embodiment of the present invention provides a control method for forced commutation, which can be used for the above-mentioned forced commutation hybrid converter topology. FIG. 11 is a flow chart of a control method for forced commutation according to an embodiment of the present invention. Figure, as shown in Figure 11, the process includes the following steps:

S21. Turn on the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topology structure.

S22. Turn on the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topology.

S23. Turn off the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topology.

S24. After one control cycle, turn on the thyristor valve of the main branch of the ith bridge arm of the hybrid converter topology, where i∈[1,6].

Exemplarily, Figure 12 shows the valve current flow path of the hybrid converter topology under normal operating conditions. The main branch is periodically subjected to voltage and current stress, and the auxiliary branch is always in the off state. The thyristor valve of the main branch is subjected to voltage stress when it is turned off.

In the control method for forced commutation provided by the embodiment of the present invention, 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 a closed state, and the hybrid converter is turned on. The thyristor valve of the main branch of the i-th bridge arm of the converter topology, thereby realizing the forced commutation hybrid converter topology can work in the normal commutation operation mode, that is, in the temporary commutation operation mode When the hybrid converter is in normal operation, the auxiliary branch is in the off state and only bears the voltage stress, which reduces the increase of the converter loss under long-term operation.

When a commutation failure or an AC short-circuit fault occurs, the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topology are turned on; the current of the main branch is forcibly transferred to The auxiliary branch, when the current transfer is completed, closes the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the hybrid converter topology to realize the forced commutation of the hybrid converter . After a control cycle, the step of turning on the thyristor valve of the main branch of the i-th bridge arm of the hybrid converter topology structure is returned, and the main branch continues to operate independently and normally, so as to ensure that the auxiliary branch is only Turn-off voltage stress during faults reduces device losses, thereby extending device life.

Figure 13a shows the trigger control sequence in the normal operation mode, and t0 in the figure represents the initial trigger moment.

Figure 14a, Figure 14b and Figure 14c close the V1 valve when the main branch is commutating to the auxiliary branch, and the auxiliary branch begins to bear the voltage stress. This process is divided into three stages. Figure 14a converts the main branch to the auxiliary branch. At this stage, the auxiliary branch receives the trigger signal and turns on, and then the auxiliary branch V12 valve and V13 valve receive the conduction signal, transfer the current of the main branch to the auxiliary branch, and apply a reverse voltage to the main branch. ; Figure 14b is the auxiliary branch flow-through stage, the main branch has been completely turned off at this stage, and the main branch current has been fully transferred to the auxiliary branch; Figure 14c is the auxiliary branch off stage, this stage receives the turn-off signal At this time, the V13 valve of the auxiliary branch is closed first, and the V1 valve is in the closed state to withstand the forward voltage, and then the V12 valve is closed before the V11 valve of the main branch is opened or at the same time in the next control cycle. The above operation process can be put into operation when a commutation failure or a commutation failure is predicted.

Fig. 13b is the trigger control sequence of the forced commutation hybrid converter topology when commutation failure or AC short circuit fault occurs. In Fig. 13b, after monitoring the failure of the commutation of the V1 valve to the V3 valve at time tf, the auxiliary branch V13 valve is turned on when the first preset time period Δt1 passes, and the auxiliary branch V12 valve is turned on when the second preset time period Δt2 passes. The commutation process from the main branch to the auxiliary branch is performed, and Δt2≥Δt1≥0. The main branch current I11 gradually decreases to zero, and the auxiliary branch current I12 gradually increases. After the third preset time period Δt3, the auxiliary branch V13 valve is turned off, and the time between the main branch current zero crossing and the V13 valve turning off is the turn-off time toff of the thyristor valve, and the toff here is greater than the minimum turn-off time of the thyristor valve 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 it reaches the DC current Id. At this point, the commutation of the V1 valve to the V3 valve is completed, successfully resisting the commutation failure fault, and then in the next control cycle. Close the auxiliary branch V12 valve before opening the V11 valve. This operation mode is started when commutation failure is predicted or detected, which can successfully avoid commutation failure. When the commutation process of the converter returns to normal, the operation mode is exited, and the auxiliary branch keeps In the off state, the main branch operates independently and normally.

The control method for forced commutation provided by the embodiment of the present invention controls the hybrid converter topology to enable the forced commutation operation mode when commutation fails or a short-circuit fault occurs, so as to avoid the occurrence of commutation failure, and in the hybrid converter When the commutation process of the converter returns to normal, the operation mode of forced commutation is exited, and the auxiliary branch continues to be turned off. , reducing the loss of the device, thereby extending the service life of the device.

Figure 15 shows the control trigger sequence when the forced commutation hybrid converter topology structure detects commutation failure or short-circuit fault in advance, and the control of each valve when the main branch and auxiliary branch of the V1 valve operate alternately periodically The trigger sequence, the specific operation process is shown in Figure 14a, Figure 14b and Figure 14c. At the beginning of the commutation between the V1 valve and the V3 valve, that is, the trigger pulse Sg1 of the V1 valve is delayed by 120°, or the auxiliary branch V13 valve is triggered near this moment, and the auxiliary branch V12 is opened after a short time (such as 1s, 5s, etc.) The valve realizes the commutation from the main branch to the auxiliary branch. After the main branch current crosses zero, the main branch V11 valve is turned off and bears the reverse voltage, and the time from the main branch current zero crossing to the auxiliary branch V13 valve turning off is the turn-off time toff of the thyristor valve, and toff The minimum turn-off time of the thyristor valve is greater than the minimum turn-off time of the thyristor valve to ensure its reliable turn-off. At this point, the V1 valve current is all transferred to the auxiliary branch. After Δt, the auxiliary branch V13 valve starts to turn off, and the V1 valve begins to bear the forward voltage, and then the next work The auxiliary branch V12 valve is closed before or at the same time as the period V11 valve is opened. In this operating mode, the main branch and the auxiliary branch in the bridge arm of the forced commutation hybrid converter topology operate alternately periodically. On the basis of the ability to resist commutation failure, there is no need to predict commutation failure. , at the same time, the hybrid inverter can be in a small turn-off angle operation mode, and the reactive power consumption of the hybrid inverter can be reduced.

The control method for forced commutation provided by the embodiment of the present invention can not only resist the commutation failure, but also does not need to predict the commutation failure through the periodic alternate operation of the main branch and the auxiliary branch. At the same time, it is ensured that the hybrid inverter works in an operation mode with a small turn-off angle, and the reactive power consumption of the hybrid inverter is reduced.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, various modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the present invention, and such modifications and variations fall within the scope of the appended claims within the limits of the requirements.

Industrial Applicability

The invention discloses an active commutation unit and a forced commutation hybrid converter topology structure and method, wherein the active commutation unit is arranged in the bridge arm circuit of the converter, one end of which is connected to the converter transformer, and the other is connected to the converter transformer. One end is connected to the DC bus, including: a main branch, which is provided with a thyristor valve; an auxiliary branch, which is arranged in parallel with the main branch, and a first control valve and a second control valve are arranged on the auxiliary branch in sequence, and the first control valve has a one-way voltage Output controllable shutdown function, the second control valve has forward current controllable shutdown function and forward and reverse voltage blocking function. The forced commutation hybrid converter topology structure is connected to the AC power grid through the converter transformer. The topology structure includes a three-phase six-bridge circuit, and each phase bridge includes an upper bridge arm and a lower bridge arm, and at least one upper bridge arm. Or an active commutation unit is arranged on the lower bridge arm. By implementing the present invention, the reliable shutdown of the main branch and the active commutation of the entire bridge arm are realized.

Claims (14)

1. An active commutation unit is arranged in a bridge arm circuit of a converter, one end of which is connected to a converter transformer, and the other end is connected to a DC bus, comprising:

   a main branch, which is provided with a thyristor valve;

   An auxiliary branch is arranged in parallel with the main branch, and a first control valve and a second control valve are sequentially arranged on the auxiliary branch along the direction from the converter transformer to the DC bus, and the first control valve It has a unidirectional voltage output controllable shutdown function, and the second control valve has a forward current controllable shutdown function and a forward and reverse voltage blocking function.
2. The active commutation unit of claim 1, wherein the thyristor valve comprises:

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

   At least one first buffer component is connected in parallel or in series with the at least one thyristor.
3. The active commutation unit of claim 1, wherein the first control valve comprises:

   at least one first power unit, the at least one first power unit is arranged in series;

   At least one second buffer component is connected in parallel with the at least one first power unit.
4. The active commutation unit of claim 3, wherein the first power unit comprises:

   A first branch, where a first power device is disposed on the first branch, and the first power device is a fully-controlled power electronic device;

   The second branch is connected in parallel with the first branch, the second branch is provided with a first capacitive element and the first power device, and the first power device and the first capacitive element are connected in series.
5. The active commutation unit of claim 3, wherein the first power unit comprises:

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

   The fourth branch is provided with a second capacitive element, and the second capacitive element is connected in parallel between the upper half-bridge and the lower half-bridge of the full-bridge circuit.
6. The active commutation unit of claim 1, wherein the second control valve comprises:

   at least one second power unit, the at least one second power unit is arranged in series;

   At least one third buffer component is connected in parallel with the at least one second power unit.
7. The active commutation unit of claim 6, wherein the second power unit comprises:

   A fifth branch, a third power device and a first diode are arranged on the fifth branch, and the third power device is connected in series with the first diode; the third power device has no inverter; Power electronics to blocking function;

   Or, a sixth branch, where at least one of the third power devices is arranged on the sixth branch, and the at least one of the third power devices is arranged in series;

   The seventh branch is connected in series with the sixth branch; at least one second diode is arranged on the seventh branch, and the at least one second diode is arranged in series.
8. The active commutation unit of claim 6, wherein the second power unit comprises:

   The eighth branch 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 unit of claim 6, wherein the second power unit comprises:

   Ninth branch, 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 The sub-branch and the third buffer component form an H-bridge circuit;

   the first sub-branch is provided with a plurality of third diodes 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. The power device is a fully controlled power electronic device;

   The third sub-branch is provided with a plurality of fourth diodes connected in series.
10. The active commutation unit according to claim 2 or 3 or 6, wherein the first buffer part, the second buffer part and the third buffer part all comprise:

    The first buffer branch composed of capacitors;

    Or, a second buffer branch in which a resistor is connected in series with the capacitor;

    Or, a third buffer branch in which the capacitor and the resistor are connected in parallel;

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

    Or, the resistor and the capacitor are connected in parallel, and then connected in series with the fifth diode to form a fifth buffer branch;

    Or, the sixth buffer branch composed of arresters;

    Or, among 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 The seventh buffer branch composed of multiple parallel connections.
11. 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-bridge circuit, and each phase bridge arm includes an upper bridge arm and a lower bridge arm respectively. The bridge arm, at least one of the upper bridge arm or the lower bridge arm is provided with the active commutation unit according to any one of claims 1-10.
12. A kind of control method of forced commutation, for the hybrid converter topology structure of forced commutation as claimed in claim 11, comprises the steps:

    Turn on the thyristor valve of the main branch of the i-th bridge arm of the hybrid converter topology with forced commutation;

    Conducting the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the forced commutation hybrid converter topology structure;

    shutting off the first control valve and the second control valve of the auxiliary branch of the ith bridge arm of the forced commutation hybrid converter topology;

    After one control cycle, the thyristor valve that conducts the main branch of the i-th bridge arm of the forced commutation hybrid converter topology structure is returned, where i∈[1,6].
13. The method of claim 12, further comprising:

    When it is detected that commutation failure or short-circuit fault occurs in the i-th bridge arm of the hybrid converter topology, obtain the duration of commutation failure or short-circuit fault;

    When the duration reaches the first preset duration, the second control valve of the auxiliary branch of the ith bridge arm is turned on, and when the duration reaches the second preset duration, the auxiliary branch of the ith bridge arm is turned on The first control valve of the branch circuit performs the commutation of the main branch circuit to the auxiliary branch circuit, wherein the second preset duration is greater than or equal to the first preset duration;

    When the current of the main branch of the ith bridge arm of the hybrid converter topology is reduced to zero, and the duration reaches the third preset time duration, the auxiliary branch of the ith bridge arm is turned off. a second control valve, wherein the third preset duration is greater than the second preset duration;

    When the thyristor valve of the main branch of the ith bridge arm is turned on in the next control cycle, the first control valve of the auxiliary branch of the ith bridge arm is turned off.
14. The method of claim 13, further comprising:

    The main branch and the auxiliary branch of the i-th bridge arm of the forced commutation hybrid converter topology structure operate alternately periodically.

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