CN216699846U - Hybrid converter topological structure with active phase commutation - Google Patents
Hybrid converter topological structure with active phase commutation Download PDFInfo
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- CN216699846U CN216699846U CN202123059502.6U CN202123059502U CN216699846U CN 216699846 U CN216699846 U CN 216699846U CN 202123059502 U CN202123059502 U CN 202123059502U CN 216699846 U CN216699846 U CN 216699846U
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Abstract
The utility model discloses a hybrid converter topological structure with active phase commutation, which comprises: the three-phase six-bridge arm circuit comprises a three-phase six-bridge arm circuit, an upper bridge arm auxiliary valve, a lower bridge arm auxiliary valve and a controllable switch unit, wherein first ends of the upper bridge arm auxiliary valve and the lower bridge arm auxiliary valve are respectively connected with a cathode end of a thyristor valve of an upper bridge arm of each phase and an anode end of a thyristor valve of a lower bridge arm of each phase; the controllable switch unit comprises a selection module and a controllable turn-off module, wherein a first connecting end of the selection module is connected with the output end of the converter transformer, a second connecting end of the selection module is connected with a first end of the controllable turn-off module, the first selecting end is connected with an anode end of a thyristor valve of an upper bridge arm, the second selecting end is connected with a cathode end of the thyristor valve of a lower bridge arm, and a second end of the controllable turn-off module is connected with an anode end of an upper bridge arm auxiliary valve and a cathode end of the lower bridge arm auxiliary valve. By implementing the method, the occurrence of commutation failure is avoided, and the stability and the safety of the operation of the power grid are ensured.
Description
Technical Field
The utility model relates to the technical field of current conversion in power electronics, in particular to a hybrid current converter topological structure with active phase conversion.
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 an active phase-change hybrid converter topology structure, so as to solve the problem that a phase change failure affects stable and safe operation of a power grid.
According to a first aspect, the present embodiment provides an active phase-change hybrid converter topology, where the topology is connected to an ac power grid through a converter transformer, and the topology includes: each phase of bridge arm circuit of the three-phase six-bridge arm circuit comprises an upper bridge arm and a lower bridge arm, and a thyristor valve is arranged on each of the upper bridge arm and the lower bridge arm; the first end of the upper bridge arm auxiliary valve is connected with the cathode end of the thyristor valve of each phase of upper bridge arm; the first end of the lower bridge arm auxiliary valve is connected with the anode end of the thyristor valve of each phase of lower bridge arm; the controllable switch units are respectively arranged in three phases corresponding to the three-phase six-bridge arm circuit; the controllable switch unit comprises a selection module and a controllable turn-off module, wherein the selection module comprises two connection ends and two selection ends, the first connection end is connected with the output end of the converter transformer, and the second connection end is connected with the first end of the controllable turn-off module; the first selection end is connected with the anode end of the thyristor valve of the upper bridge arm, and the second selection end is connected with the cathode end of the thyristor valve of the lower bridge arm; and the second end of the controllable turn-off module is respectively connected with the anode end of the upper bridge arm auxiliary valve and the cathode end of the lower bridge arm auxiliary valve.
With reference to the first aspect, in a first implementation form of the first aspect, the selection module is a two-way valve.
With reference to the first embodiment of the first aspect, in a second embodiment of the first aspect, the two-way valve includes: the at least one thyristor is connected in parallel in the forward direction and the reverse direction; the first thyristor is a unidirectional thyristor or a bidirectional thyristor.
With reference to the first embodiment of the first aspect, in a third embodiment of the first aspect, the two-way valve includes: a first selection branch comprising at least one third power device, the at least one third power device being arranged in series; the third power device is a fully-controlled power electronic device; and the second selection branch is connected with the first selection branch in an inverse parallel mode, and the structure of the second selection branch is the same as that of the first selection branch.
With reference to the first embodiment of the first aspect, in a fourth embodiment of the first aspect, the two-way valve includes: the third selection branch is provided with a plurality of first diodes which are connected in series; the fourth selection branch is consistent with the structure of the third selection branch; the fifth selection branch is connected between the third selection branch and the fourth selection branch in parallel, and a plurality of fourth power devices connected in series are arranged on the fifth selection branch; the fourth power device is a fully-controlled power electronic device.
With reference to the first aspect, in a fifth implementation of the first aspect, the controllable turn-off module includes: the at least one shutoff valve is connected in series and used for bidirectional voltage output, and current in the thyristor valve of each bridge arm in the three-phase six-bridge arm circuit is transferred to the upper bridge arm auxiliary valve or the lower bridge arm auxiliary valve.
With reference to the fifth embodiment of the first aspect, in a sixth embodiment of the first aspect, the shutoff valve 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 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.
With reference to the fifth embodiment of the first aspect, in a seventh embodiment of the first aspect, the shutoff valve 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 or any one of the first to seventh embodiments of the first aspect, in an eighth embodiment of the first aspect, the controllable switch unit further includes: a buffer component disposed in the selection module and/or the controllable shutdown module, the buffer component to limit voltage/current stress.
With reference to the eighth embodiment of the first aspect, in the ninth embodiment of the first aspect, the buffer member includes: a first buffer branch composed of a third capacitive element; or, a second buffer branch circuit with a resistor connected in series with the third capacitive element; or, the third capacitor element and the third buffer branch of the resistor are connected in parallel; or, the resistor is connected in parallel with a fifth diode and then connected in series with the third capacitance element to form a fourth buffer branch circuit; or, the resistor is connected in parallel with the third capacitive element and then connected in series with the fifth diode to form a fifth buffer branch; or, a sixth buffer branch consisting 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.
The technical scheme of the utility model has the following advantages:
1. according to the topology structure of the active phase-change hybrid converter provided by the embodiment of the utility model, the controllable switch unit is introduced into the hybrid converter, the controllable switch unit comprises the selection module and the controllable turn-off module, and is arranged in three phases corresponding to a three-phase six-bridge arm circuit, when the bridge arm phase change fails or fails, the controllable switch unit is used for realizing the advanced transfer of bridge arm current, and meanwhile, reverse voltage is provided for the bridge arm, so that the phase change time area of the thyristor is increased, and the reliable turn-off of the thyristor is ensured. The controllable switch module is used for realizing current transfer, and the selection unit bears voltage stress, so that the upper bridge arm auxiliary valve and the lower bridge arm auxiliary valve participate in phase change, the occurrence of phase change failure is avoided, and the stability and the safety of the operation of a power grid are further ensured.
2. The active phase-change hybrid converter topological structure provided by the embodiment of the utility model 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 each upper bridge arm or lower bridge arm is provided with an upper bridge arm auxiliary valve or a lower bridge arm auxiliary valve corresponding to the upper bridge arm or lower bridge arm. The hybrid converter topological structure with active phase change can conduct the upper bridge arm auxiliary valve or the lower bridge arm auxiliary valve at any time, and effectively reduces the loss of each phase of bridge arm.
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 description of the embodiments or 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 other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a structural diagram of a hybrid converter topology for active phase commutation according to the present embodiment;
FIG. 2 is a block diagram showing the structure of the two-way valve of the present embodiment;
FIG. 3 is another block diagram of the two-way valve of the present embodiment;
FIG. 4 is another block diagram of the two-way valve of the present embodiment;
FIG. 5 is a block diagram of the construction of the shutoff valve of the present embodiment;
FIG. 6 is another block diagram of the shutoff valve of the present embodiment;
FIG. 7 is a block diagram showing the structure of a buffer member according to the present embodiment;
fig. 8 is a block diagram showing the structure of the thyristor valve of the present embodiment;
fig. 9 is a block diagram showing the structure of the upper/lower arm assist valve of the present embodiment;
fig. 10 is another structural block diagram of the upper/lower arm assist valve of the present embodiment;
fig. 11 is a flowchart of a control method of the hybrid converter topology of the present embodiment;
FIG. 12 is a schematic diagram of the trigger signal of the present embodiment;
FIG. 13 is a trigger control sequence in the first operation mode of the present embodiment;
FIG. 14 is a trigger control sequence in the second operation mode of the present embodiment;
FIG. 15 is a current flow path of the present embodiment in which the thyristor valve is periodically triggered during normal operation;
fig. 16 is a current flow path through which the thyristor valve is turned off and the upper arm auxiliary valve is passed in the present embodiment;
fig. 17 shows the current flow paths of the thyristor valve off and the upper arm assist valve off according to the present embodiment.
Detailed Description
In order to make the objects, 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 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. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within 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 the technical scheme, the control valve capable of being turned off is introduced into the alternating current side, so that the thyristor valve is guaranteed to have enough reverse recovery time to be turned off reliably, and meanwhile, the auxiliary valve branch is used for assisting phase commutation, so that the problem of phase commutation failure of a direct current system is solved fundamentally, and stable and safe operation of a power grid is guaranteed.
According to an embodiment of the present invention, an embodiment of an active phase-commutated hybrid converter topology is provided, where the active phase-commutated hybrid converter topology is connected to an ac power grid through a converter transformer, as shown in fig. 1, and the active phase-commutated hybrid converter topology includes: the device comprises a three-phase six-bridge arm circuit, an upper bridge arm auxiliary valve, a lower bridge arm auxiliary valve and a controllable switch unit. Each phase of bridge arm circuit of the three-phase six-bridge arm circuit comprises an upper bridge arm and a lower bridge arm, and thyristor valves are arranged on the upper bridge arm or the lower bridge arm. The first end of the upper bridge arm auxiliary valve is connected with the cathode end of the thyristor valve of each phase of upper bridge arm, and the first end of the lower bridge arm auxiliary valve is connected with the anode end of the thyristor valve of each phase of lower bridge arm; the controllable switch unit is arranged in each phase corresponding to the three-phase six-bridge arm circuit and comprises a selection module and a controllable turn-off module, the selection module comprises two connecting ends and two selection ends, the first connecting end of the selection module is connected with the output end of the converter transformer, the second connecting end of the selection module is connected with the first end of the controllable turn-off module, the first selection end is connected with the anode end of the thyristor valve of the upper bridge arm, and the second selection end of the selection module is connected with the cathode end of the thyristor valve of the lower bridge arm; and the second end of the controllable turn-off module is respectively connected with the anode end of the upper bridge arm auxiliary valve and the cathode end of the lower bridge arm auxiliary valve. For a three-phase six-bridge arm circuit, a first connecting end and a second connecting end of a selection module arranged on an a phase are respectively connected with an output end of a corresponding phase of a converter transformer and a first end of a controllable turn-off module, and a first selecting end and a second selecting end of the selection module are respectively connected with an anode end of an upper bridge arm thyristor valve and a cathode end of a lower bridge arm thyristor valve; in the same way, for the phase b and the phase c of the three-phase six-bridge arm circuit, the connection modes of the selection module and the controllable turn-off module are the same as the phase a.
As shown in fig. 1, one end of the three-phase six-leg circuit is connected to the positive electrode of the dc bus, and the other end is connected to the negative electrode of the dc bus. The selection unit may be a two-way valve, and two-way valves DVa, DVb and DVc are respectively provided on each ac bus of the three-phase six-leg. The three-phase six-leg circuit includes a V1 valve, a V2 valve, a V3 valve, a V4 valve, a V5 valve, and a V6 valve. The V1 valve, the V3 valve and the V5 valve are upper bridge arms, and each upper bridge arm is provided with a thyristor valve; the V2 valve, the V4 valve and the V6 valve are lower bridge arms, and each lower bridge arm is provided with a thyristor valve.
Vp is an upper bridge arm auxiliary valve, and the first end of Vp is respectively connected with the cathode end of a thyristor valve in the V1 valve, the V3 valve and the V5 valve; a first end of the Vn is connected with anode ends of thyristor valves of the V2 valve, the V4 valve and the V6 valve respectively; DVM is a controllable switch module, whose first end is connected to the first connection ends of the two-way valves DVa, DVb and DVc, respectively, and whose second end is connected to the second end of Vp and the second end of Vn, respectively.
Second connecting ends of the two-way valves DVa, DVb and DVc are respectively connected with an a-phase output end, a b-phase output end and a c-phase output end of the converter transformer; the first selection end of the bidirectional valve DVa is connected with the anode end of a thyristor valve in the V1 valve; the second selection end of the two-way valve DVa is connected with the cathode end of the thyristor valve in the V4 valve; the first selection end of the two-way valve DVb is connected with the anode end of a thyristor valve in the V3 valve; the second selection end of the two-way valve DVb is connected with the cathode end of the thyristor valve in the V6 valve; the first selection end of the two-way valve DVc is connected with the anode end of a thyristor valve in the V5 valve; the second selection terminal of the two-way valve DVc is connected to the cathode terminal of the thyristor valve in the V2 valve.
According to the topology structure of the active phase-change hybrid converter provided by the embodiment of the utility model, the controllable switch unit is introduced into the hybrid converter, the controllable switch unit comprises the selection module and the controllable turn-off module, and is arranged in three phases corresponding to a three-phase six-bridge arm circuit, when the bridge arm phase change fails or fails, the controllable switch unit is used for realizing the advanced transfer of bridge arm current, and meanwhile, reverse voltage is provided for the bridge arm, so that the phase change time area of the thyristor is increased, and the reliable turn-off of the thyristor is ensured. The controllable switch module is used for realizing current transfer, and the selection module bears voltage stress, so that the upper bridge arm auxiliary valve and the lower bridge arm auxiliary valve participate in phase change, the occurrence of phase change failure is avoided, and the stability and the safety of the operation of a power grid are further ensured.
Optionally, the selection module is a two-way valve and has two-way opening and two-way pressure resistance capabilities, the three two-way valves are respectively arranged in each phase of the three-phase six-bridge arm circuit, and an upper bridge arm and a lower bridge arm of each phase share one two-way valve. Specifically, taking the two-way valve DVa as an example, as shown in fig. 2, the two-way valve DVa may include: at least one first thyristor J1, where a buffer component may be provided in parallel or in series with the first thyristor J1 in order to limit the voltage/current stress through the first thyristor J1. At least one thyristor J1 is divided into two paths to be connected in parallel in forward and reverse directions so as to ensure bidirectional conduction and bidirectional voltage resistance. The first thyristor J1 may be a unidirectional thyristor or a bidirectional thyristor, and is not limited herein.
Specifically, taking the two-way valve DVa as an example, as shown in fig. 3, the two-way valve DVa may include: a first selection branch and a second selection branch.
Wherein, the first selection branch comprises at least one third power device W3, and the at least one third power device W3 is arranged in series. Here, the third power device W3 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. It should be noted that, if the fully-controlled power electronic device does not have the reverse voltage blocking function, a diode needs to be connected in parallel to the fully-controlled power electronic device in the reverse direction to implement the unidirectional voltage blocking function. The structure of the second selection branch is the same as that of the first selection branch, and the second selection branch is connected with the first selection branch in an inverse parallel mode to ensure that the second selection branch can be conducted in two directions and withstand voltage in two directions.
Specifically, taking the two-way valve DVa as an example, as shown in fig. 4, the two-way valve DVa may include: a third selection branch, a fourth selection branch and a fifth selection branch.
The third selection branch is provided with a plurality of first diodes D1 connected in series; the structure of the fourth selection branch is consistent with that of the third selection branch; the fifth selection branch is connected between the third selection branch and the fourth selection branch in parallel. The fifth selection branch is provided with a plurality of fourth power devices W4 connected in series, the fourth power device W4 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.
Optionally, the controllable turn-off module is used for bidirectional voltage output, and can forcibly transfer the current in the thyristor valve of each bridge arm of the three-phase six-bridge arm circuit to the upper bridge arm auxiliary valve or the lower bridge arm auxiliary valve, and no thyristor valve provides a reverse recovery voltage.
In particular, the controllable shut-off module comprises at least one shut-off valve arranged in series. As shown in fig. 5, the shut-off valve may include a first branch and a second branch, wherein the first branch is provided with a first power device W1; the second branch is connected with the first branch in parallel, a first capacitance element C1 and a first power device W1 are arranged on the second branch, and the first power device W1 is connected with the first capacitance element C1 in series. The first power device W1 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. It should be noted that, if the fully-controlled power electronic device does not have the reverse voltage blocking function, a diode needs to be connected in parallel to the fully-controlled power electronic device in the reverse direction.
Specifically, as shown in fig. 6, the shutoff valve may also be formed by a third branch and a fourth branch, where the third branch is a full-bridge circuit formed by connecting four second power devices W2; the fourth branch is provided with a second capacitive element C2, and the second capacitive element C2 is connected in parallel between the upper half bridge and the lower half bridge of the full bridge circuit. The second power device W2 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, and a MOSFET. It should be noted that, if the fully-controlled power electronic device does not have the reverse voltage blocking function, a diode needs to be connected in parallel to the fully-controlled power electronic device in the reverse direction.
Optionally, the controllable switch unit further comprises a buffer component arranged in the selection module and/or the controllable shutdown module to limit the voltage/current stress of the selection module and the controllable shutdown module. The buffer member may be formed of one or more of a capacitor, a rc, a diode, an inductor, or a surge arrester.
Specifically, as shown in fig. 7, the buffer member may be a first buffer branch composed of a third capacitive element C3; a second snubber branch consisting of a resistor R and a third capacitive element C3 connected in series; a third buffer branch which can be connected in parallel by a third capacitance element C3 and a resistor R; the fourth buffer branch RCD1 may be formed by connecting the resistor R in parallel with the third diode D3, and then connecting the third capacitor C3 in series; the third buffer branch RCD2 may be formed by connecting a resistor R and a third capacitive element C3 in parallel, and then connecting the third diode D3 in series; the third buffer branch may also be a sixth buffer branch composed of the lightning arrester, and may also be a seventh buffer branch formed by connecting one or more 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.
The shutoff valve has bidirectional voltage controllable output capability, is mainly used for shutting off the current of the thyristor branch circuit and providing reverse voltage for the thyristor branch circuit, and ensures that the thyristor valve of the thyristor branch circuit has enough shutoff time to carry out reliable shutoff. The topological form of the shutoff valve is not limited in the application, and the shutoff valve can be in the topological form with the function of bidirectional voltage controllable output.
Optionally, the thyristor valve comprises at least one thyristor and a buffer member connected in parallel or in series with the thyristor, respectively, wherein the at least one thyristor is arranged in series, and the buffer member is used for the thyristor device to protect against high voltage and high current. As shown in fig. 8, the thyristor valve includes at least one thyristor and a buffer member connected in parallel with the thyristor, respectively.
Optionally, the upper bridge arm auxiliary valve and the lower bridge arm auxiliary valve have the same structure. As shown in fig. 9, taking the upper arm assist valve as an example, the upper arm assist valve includes: a first auxiliary branch and a buffer member. The first auxiliary branch may be formed by at least one fifth power device W5 connected in series; the power device can also be formed by connecting at least two fifth power devices W5 in series in the forward and reverse directions; may also be constituted by at least one fifth power device W5 and at least one second diode D2 connected in series with the at least one fifth power device W5; can also be formed by at least one fifth power device W5 and at least one second thyristor J2 connected in series with the at least one fifth power device W5. The fifth power device W5 is a fully-controlled power electronic device, which is one or more of an IGBT, an IGCT, an IEGT, a GTO, and a MOSFET, and it should be noted that the fully-controlled power electronic device may be a device with bidirectional voltage blocking capability, and may also be a device with unidirectional voltage blocking capability. The form of the auxiliary branch is not limited herein.
As shown in fig. 10, the upper arm assist valve may further include a second assist branch and a third assist branch, where the second assist branch is provided with at least one sixth power device W6, and the at least one sixth power device W6 is connected in series. The sixth power device W6 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 third auxiliary branch is arranged in parallel with the second auxiliary branch, at least one seventh power device W7 and a third capacitance element C3 are arranged on the third auxiliary branch, at least one seventh power device W7 is arranged in series with the third capacitance element C3, and at least one seventh power device W7 is arranged in series, the seventh power device W7 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 topological form of the upper bridge arm auxiliary valve or the lower bridge arm auxiliary valve is not limited, and the topological form can be any topological form which can realize the function of auxiliary phase change of the main branch to the auxiliary branch.
It should be noted that, although a logical order is shown in the flow chart, in some cases, the steps shown or described may be performed in an order different from the order shown or described herein.
In this embodiment, a method for controlling an active phase-change hybrid converter topology is provided, which may be used in the active phase-change hybrid converter topology described above, and fig. 11 is a flowchart according to an embodiment of the present invention, as shown in fig. 11, where the flowchart includes the following steps:
and S11, turning off the controllable switch unit connected with the ith bridge arm of the active phase-changing hybrid converter topological structure and the upper bridge arm auxiliary valve or the lower bridge arm auxiliary valve.
And S12, switching on the thyristor valve of the ith bridge arm.
S13, after a control period, returning to the step of conducting the thyristor valve of the ith bridge arm; wherein i ∈ [1,6 ].
Specifically, in the hybrid converter topology, under a normal operation condition, the thyristor valve periodically bears voltage and current stress, the upper bridge arm auxiliary valve and the lower bridge arm auxiliary valve are always in a turn-off state, and the thyristor valve of the bridge arm bears the voltage stress only when the thyristor valve is turned off.
In the control method of the active phase-change hybrid converter topology structure provided in this embodiment, the controllable switch unit and the upper bridge arm auxiliary valve or the lower bridge arm auxiliary valve connected to the ith bridge arm of the active phase-change hybrid converter topology structure are turned off; conducting a thyristor valve of the ith bridge arm; after a control period, returning to the step of conducting the thyristor valve of the ith bridge arm; and i belongs to [1,6], so that the hybrid converter topological structure with active phase change works in a normal operation mode.
Fig. 12 to 17 collectively illustrate a phase commutation process of the hybrid converter. Taking the example that the V1 valve in the hybrid converter shown in fig. 1 changes phase to the V3 valve, and the bidirectional valve DVa adopts a thyristor anti-parallel structure, fig. 12 gives an explanation of trigger signals of related circuits, Sg1 and Sg3 respectively trigger signals of thyristor valves V1 and V3, Sga1 is a forward control signal of the bidirectional valve DVa, Sga2 is a reverse control signal of the bidirectional valve DVa, Sap is a control signal of the upper arm auxiliary valve Vp, and Sgm is an output control signal of the controllable switch module.
Fig. 13 is a trigger timing sequence of each valve in the first operation mode, in which the V1 thyristor valve is periodically triggered during normal operation, the upper arm auxiliary valve Vp, the bidirectional valve DVa, and the closable valve Vga are all in the off state, and the current is as shown in fig. 15. t is tfWhen the phase change failure or the short circuit failure occurs in the valve at the time V1, the bidirectional valve DVa and the upper arm auxiliary valve Vp are triggered to be turned on, and the shutoff valve Vga is triggered to output a reverse voltage to the arm at the position of V1, so that the current conversion is performed on the auxiliary arm at the position of the upper arm auxiliary valve, as shown in fig. 16. After the current of the bridge arm where the thyristor valve is located crosses zero, the thyristor valve of the bridge arm where the V1 valve is located is turned off and starts to bear reverse voltage, and the current of the V1 valve is completely transferred to the upper bridge arm auxiliary valve, as shown in fig. 17. At tfAt time + Δ t2, the upper arm auxiliary valve Vp starts to close, and the current is completely transferred to the V3 valve, thereby completing the phase change from the V1 valve to the V3 valve. Slave thyristorThe time of the zero crossing of the current of the bridge arm where the pipe valve is located to the turn-off of the upper bridge arm auxiliary valve Vp is the turn-off time t of the back pressure born by the thyristoroffThe time is controllable, and the reliable turn-off can be ensured only by being longer than the minimum turn-off time of the thyristor. Where Δ t2 is the delay time for turning off the upper arm assist valve.
Fig. 14 is a trigger timing sequence of each valve in the second operation mode, in each operation cycle, the phase change start time of the V1 valve and the V3 valve, that is, the trigger pulse Sg1 of the V1 valve delays by 120 ° to trigger the two-way valve DVa and the upper arm auxiliary valve Vp, and at the same time, the switchable valve Vga is triggered to apply a reverse voltage to the thyristor valve of the arm where the V1 valve is located, so as to realize the phase change of the arm where the V1 valve is located to the auxiliary arm where the upper arm auxiliary valve is located, as shown in fig. 16. After the current of the bridge arm where the V1 valve is located crosses zero, the thyristor valve of the bridge arm where the V1 valve is located is turned off and bears reverse voltage, and the V1 valve current is completely transferred to the upper bridge arm auxiliary valve Vp, as shown in fig. 17. The controllable switch module is turned off after the time of delta t1, and the time of delta t1 is not less than the minimum turn-off time t required by the thyristor valveoffAfter the time of delta t2, the upper bridge arm auxiliary valve Vp is closed, and the current is completely transferred to the V3 valve, so that the phase change is completed. The thyristor valve has controllable reverse bearing time, so that the thyristor valve can be ensured to have enough time to recover blocking capability, and the upper bridge arm auxiliary valve can be controlled to be turned off and bear high pressure, so that the active phase change process can be ensured to be completed smoothly, and the occurrence of phase change failure is avoided. And the delta t1 is the delay time for turning off the controllable switch module, and the delta t2 is the delay time for turning off the upper bridge arm auxiliary valve.
In the control method of the active phase-change hybrid converter topology provided in this embodiment,
when the phase change fails or short-circuit faults occur, the topological structure of the hybrid converter triggers an active phase change operation mode to conduct a selection module connected with a current bridge arm and an upper bridge arm auxiliary valve or a lower bridge arm auxiliary valve connected with the current bridge arm, triggers a controllable turn-off module to output reverse voltage to a thyristor valve of the current bridge arm, carries out current conversion from the current bridge arm to the upper bridge arm or the lower bridge arm connected with the current bridge arm, avoids the occurrence of phase change failures, and closes the upper bridge arm auxiliary valve or the lower bridge arm auxiliary valve when the phase change process of the hybrid converter is recovered to be normal, and each phase bridge arm independently and normally operates, so that the selection unit and the upper bridge arm auxiliary valve or the lower bridge arm auxiliary valve are guaranteed to bear turn-off voltage stress only when the phase change fails or fails, the loss of devices is reduced, and the service life of the devices is prolonged.
Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the utility model, and such modifications and variations fall within the scope defined by the appended claims.
Claims (10)
1. An active commutation hybrid converter topology for accessing an ac power grid through a converter transformer, the topology comprising:
each phase of bridge arm circuit of the three-phase six-bridge arm circuit comprises an upper bridge arm and a lower bridge arm, and a thyristor valve is arranged on each of the upper bridge arm and the lower bridge arm;
the first end of the upper bridge arm auxiliary valve is connected with the cathode end of the thyristor valve of each phase of upper bridge arm;
the first end of the lower bridge arm auxiliary valve is connected with the anode end of the thyristor valve of each phase of lower bridge arm;
the controllable switch units are respectively arranged in three phases corresponding to the three-phase six-bridge arm circuit;
the controllable switch unit comprises a selection module and a controllable turn-off module, wherein the selection module comprises two connection ends and two selection ends, the first connection end is connected with the output end of the converter transformer, and the second connection end is connected with the first end of the controllable turn-off module; the first selection end is connected with the anode end of the thyristor valve of the upper bridge arm, and the second selection end is connected with the cathode end of the thyristor valve of the lower bridge arm; and the second end of the controllable turn-off module is respectively connected with the anode end of the upper bridge arm auxiliary valve and the cathode end of the lower bridge arm auxiliary valve.
2. The topology of claim 1, wherein the selection module is a two-way valve.
3. The topology of claim 2, wherein the two-way valve comprises:
the at least one thyristor is connected in parallel in the forward direction and the reverse direction; the first thyristor is a unidirectional thyristor or a bidirectional thyristor.
4. The topology of claim 2, wherein the two-way valve comprises:
a first selection branch comprising at least one third power device, the at least one third power device being arranged in series; the third power device is a fully-controlled power electronic device;
and the second selection branch is reversely connected with the first selection branch in parallel, and the second selection branch has the same structure as the first selection branch.
5. The topology of claim 2, wherein the two-way valve comprises:
the third selection branch is provided with a plurality of first diodes which are connected in series;
the fourth selection branch is consistent with the structure of the third selection branch;
the fifth selection branch is connected between the third selection branch and the fourth selection branch in parallel, and a plurality of fourth power devices connected in series are arranged on the fifth selection branch;
the fourth power device is a fully-controlled power electronic device.
6. The topology according to claim 1, wherein the controllable shutdown module comprises: the at least one shutoff valve is connected in series and used for bidirectional voltage output, and current in the thyristor valve of each bridge arm in the three-phase six-bridge arm circuit is transferred to the upper bridge arm auxiliary valve or the lower bridge arm auxiliary valve.
7. The topology of claim 6, wherein the shutoff valve 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.
8. The topology of claim 6, wherein the shutoff valve 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 circuit 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.
9. The topology according to any of claims 1-8, wherein the controllable switching unit further comprises:
a buffer component disposed in the selection module and/or the controllable shutdown module, the buffer component to limit voltage/current stress.
10. The topology of claim 9, wherein the buffer component comprises:
a first buffer branch composed of a third capacitive element;
or, a second buffer branch circuit with a resistor connected in series with the third capacitive element;
or, the third capacitor element and the third buffer branch of the resistor are connected in parallel;
or, the resistor is connected in parallel with a fifth diode and then connected in series with the third capacitance element to form a fourth buffer branch circuit;
or, the resistor is connected in parallel with the third capacitive element and then connected in series with the fifth diode to form a fifth buffer branch;
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.
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