Hybrid converter topology with controllable shutdown on AC side and control method thereof

Abstract

The present invention discloses a hybrid converter topology structure with controllable shutdown on the AC side and a control method thereof. The topology structure includes: at least one phase commutation circuit, including a parallel thyristor valve branch and a first control valve or a second control valve branch; the thyristor valve branch is provided with a thyristor valve; the first control valve or the second control valve branch includes a first control valve and a second control valve, and the first control valve and the second control valve both have a forward current controllable shutdown function and a forward and reverse voltage blocking function; the connection end of the first control valve and the second control valve is connected to the output end of the converter transformer through a third control valve; the third control valve has a unidirectional voltage output controllable shutdown function; the connection end of the series thyristor valve is connected to the output end of the converter transformer. By implementing the present invention, the commutation failure problem of the DC system is fundamentally solved, thereby ensuring the stability and safety of the power grid operation.

Description

Technical Field

[0001] The present invention relates to the technical field of commutation in power electronics, and in particular to a hybrid converter topology structure with controllable shutdown on the AC side and a control method thereof. Background Art

[0002] The traditional line commutated converter high voltage direct current (LCC-HVDC) transmission system has the advantages of long-distance large-capacity transmission and controllable active power, and is widely used around the world. As the core equipment of DC transmission, the converter is the core functional unit for realizing AC and DC power conversion. Its operating reliability largely determines the operating reliability of the UHV DC grid.

[0003] Since traditional converters mostly use semi-controlled devices thyristors as core components to form a six-pulse bridge commutation topology, each bridge arm is composed of multiple stages of thyristors and their buffer components in series. Since thyristors do not have self-shutoff capabilities, commutation failures are prone to occur in situations such as AC system failures, resulting in a surge in DC current and a rapid and large loss of DC transmission power, affecting the stable and safe operation of the power grid. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides a hybrid converter topology structure with controllable shutdown on the AC side and a control method thereof, so as to solve the problem that commutation failure affects the stable and safe operation of the power grid.

[0005] According to the first aspect, an embodiment of the present invention provides a hybrid converter topology structure with controllable shutdown on the AC side, and the topology structure is connected to the AC power grid through a converter transformer, and the topology structure includes: at least one phase commutation circuit, including a parallel thyristor valve branch and a first control valve or a second control valve branch; a thyristor valve is arranged on the thyristor valve branch; the first control valve or the second control valve branch includes a first control valve and a second control valve, and the first control valve and the second control valve both have a forward current controllable shutdown function and a forward and reverse voltage blocking function; the connection end of the first control valve and the second control valve is connected to the output end of the converter transformer through a third control valve; the third control valve has a unidirectional voltage output controllable shutdown function; the connection end of the thyristor valve is connected to the output end of the converter transformer.

[0006] In combination with the first aspect, in a first implementation of the first aspect, the topology structure includes: a three-phase commutation circuit; the commutation circuits of each phase are arranged in parallel.

[0007] In combination with the first aspect, in a second implementation of the first aspect, the third control valve includes: at least one first power unit, the at least one first power unit is arranged in series; and a first buffer component is connected in parallel with the first power unit.

[0008] In combination with the second embodiment of the first aspect, in the third embodiment of the first aspect, the first power unit includes: a first branch, on which a first power device is arranged, and the first power device is a fully controlled power electronic device; a second branch, connected in parallel with the first branch, on which a first capacitor element and the first power device are arranged, and the first power device and the first capacitor element are connected in series.

[0009] In combination with the second embodiment of the first aspect, in the fourth embodiment of the first aspect, the first power unit includes: a third branch, the third branch is a full-bridge circuit composed of four second power devices connected; the second power device is a fully controlled power electronic device; a fourth branch, the fourth branch is provided with a second capacitor element, and the second capacitor element is connected in parallel between the upper half bridge and the lower half bridge of the full-bridge circuit.

[0010] In combination with the first aspect, in a fifth implementation of the first aspect, the first control valve and the second control valve have the same structure.

[0011] In combination with the fifth embodiment of the first aspect, in the third embodiment of the first aspect, the first control valve includes: at least one second power unit, the at least one second power unit is arranged in series; and a second buffer component, connected in parallel with the second power unit.

[0012] In combination with the sixth embodiment of the first aspect, in the seventh embodiment of the first aspect, the second power unit includes: at least one fifth branch, the at least one fifth branch is arranged in series; 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 is a power electronic device that does not have a reverse blocking function; 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; a seventh branch, 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.

[0013] In combination with the sixth implementation of the first aspect, in the eighth implementation of the first aspect, the second power unit includes: at least one eighth branch, the at least one eighth branch is arranged in series; the eighth branch is a full-bridge circuit composed of multiple fourth power devices connected; the fourth power device is a fully controlled power electronic device.

[0014] In combination with the sixth embodiment of the first aspect, in the ninth embodiment of the first aspect, the second power unit includes: at least one ninth branch, the at least one ninth branch is arranged in series to form an H-bridge circuit; the ninth branch includes a first sub-branch, a second sub-branch and a third sub-branch; 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 the second sub-branch is provided with a plurality of fifth power devices connected in series, and the fifth power device is a fully controlled power electronic device; the third sub-branch is provided with a plurality of fourth diodes connected in series.

[0015] In combination with the first aspect, in a tenth implementation of the first aspect, the thyristor valve includes: at least one thyristor, the at least one thyristor is arranged in series; and a third buffer component, connected in parallel or in series with the thyristor.

[0016] In combination with the second embodiment or the sixth embodiment or the tenth embodiment of the first aspect, in the eleventh embodiment of the first aspect, the first buffer component, the second buffer component and the third buffer component all include: a first buffer branch composed of a capacitor; or, a second buffer branch in which a resistor and the capacitor are connected in series; or, a third buffer branch in which the capacitor and the resistor are connected in parallel; or, a fourth buffer branch formed by connecting the resistor and a fifth diode in parallel and then connecting them in series with the capacitor; or, a fifth buffer branch formed by connecting the resistor and the capacitor in parallel and then connecting them in series with the fifth diode; or, a sixth buffer branch composed of a lightning arrester; or, a seventh buffer branch formed by connecting multiple 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.

[0017] According to a second aspect, an embodiment of the present invention provides a control method for a hybrid converter topology structure with controllable shutdown on the AC side, which is used for the hybrid converter topology structure with controllable shutdown on the AC side described in the first aspect or any embodiment of the first aspect, and the method includes: turning on a third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm; turning on the thyristor valve of the i-th bridge arm; after a control cycle, turning off the thyristor valve of the i-th bridge arm; turning on a thyristor valve different from the i-th bridge arm, wherein, .

[0018] In combination with the second aspect, in the first implementation manner of the second aspect, the method further includes: when a commutation failure or a short-circuit fault is detected in the thyristor valve of the i-th bridge arm, obtaining the duration of the commutation failure or the short-circuit fault; when the duration reaches a first preset duration, turning on the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm, and when the duration reaches a second preset duration, turning off the third control valve connected to the thyristor valve of the i-th bridge arm; the second preset duration is greater than the first preset duration; when the thyristor valve of the i-th bridge arm is in a forward blocking state, turning off the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm; when the control cycle in which the commutation failure or the short-circuit fault is located ends, turning on the thyristor valve of the i-th bridge arm, turning on the third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the third control valve connected to the thyristor valve of the i-th bridge arm. the first control valve or the second control valve of the thyristor valve of the i-th bridge arm; after a third preset time, the third control valve connected to the thyristor valve of the i-th bridge arm is turned off, and the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned on; when the thyristor valve of the i-th bridge arm is in a forward blocking state, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned off, and after a fourth preset time, the step of turning on the thyristor valve of the i-th bridge arm, turning on the third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is returned to execution; when the voltage of the hybrid converter topology structure with controllable shutdown on the AC side returns to stability, the third control valve connected to the thyristor valve of the i-th bridge arm is turned on, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned off, and the thyristor valve of the i-th bridge arm is turned on.

[0019] According to a third aspect, an embodiment of the present invention provides a control method for a hybrid converter topology structure with controllable shutdown on the AC side, which is used for the hybrid converter topology structure with controllable shutdown on the AC side described in the first aspect or any embodiment of the first aspect, and the method includes: turning on the thyristor valve of the i-th bridge arm, turning on the third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the first control valve or the second control valve connected to the i-th thyristor valve; after a third preset time, turning off the third control valve connected to the thyristor valve of the i-th bridge arm, and turning on the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm; when the i-th thyristor valve is in a forward blocking state, turning off the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm; after a fourth preset time, returning to the steps of turning on the thyristor valve of the i-th bridge arm, turning on the third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the first control valve or the second control valve connected to the i-th thyristor valve.

[0020] The technical solution of the present invention has the following advantages:

[0021] 1. An embodiment of the present invention provides a hybrid converter topology structure with controllable shutdown on the AC side and a control method thereof, the topology structure includes at least one phase commutation circuit, each phase commutation circuit includes a parallel thyristor valve branch and an auxiliary valve branch, the thyristor valve branch is provided with a thyristor valve, the auxiliary valve branch includes a first control valve and a second control valve, and the first control valve and the second control valve both have a forward current controllable shutdown function and a forward and reverse voltage blocking function; the connection end of the first control valve and the second control valve is connected to the converter transformer through a third control valve; the third control valve has a unidirectional voltage output controllable shutdown function; the connection end of the thyristor valve is connected to the converter transformer. The hybrid converter topology structure with controllable shutdown on the AC side ensures that the thyristor valve has sufficient reverse recovery time to be reliably shut down by providing a third control valve on the AC side, and at the same time, the auxiliary valve branch is used to fundamentally solve the commutation failure problem of the DC system, thereby ensuring the stability and safety of the power grid operation.

[0022] 2. The hybrid converter topology structure with controllable shutdown on the AC side and the control method thereof provided by the embodiment of the present invention, the auxiliary valve branch can quickly transfer the phase current and flexibly control the switching time area of ​​the thyristor valve. When the switching fails or the short circuit fails, the current of the thyristor valve branch can be quickly transferred to the auxiliary valve branch. Through the current shutdown characteristics of the auxiliary valve branch, the switching between the two bridge arms can be quickly restored, thereby speeding up the recovery time of the converter when the switching fails or the short circuit fails.

[0023] 3. The hybrid converter topology structure with controllable shutdown on the AC side and the control method thereof provided by the embodiment of the present invention, the third control valve can shut down the current of the thyristor valve branch in advance, and provide a reverse voltage for the thyristor valve at the same time, thereby increasing the thyristor valve switching time area and ensuring the reliable shutdown of the thyristor valve. The third control valve only needs to be arranged on each phase of the three-phase AC bus, with a small number of series stages, thereby improving the utilization rate of the device and reducing the total loss of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a structural diagram of a hybrid converter topology structure with controllable shutdown on the AC side according to an embodiment of the present invention;

[0026] Figure 2is a structural block diagram of a thyristor valve according to an embodiment of the present invention;

[0027] Figure 3 is a structural block diagram of a third control valve according to an embodiment of the present invention;

[0028] Figure 4 is another structural block diagram of a third control valve according to an embodiment of the present invention;

[0029] Figure 5 is a structural block diagram of a first / second control valve according to an embodiment of the present invention;

[0030] Figure 6 is a structural block diagram of a second power unit according to an embodiment of the present invention;

[0031] Figure 7 is another structural block diagram of a first / second control valve according to an embodiment of the present invention;

[0032] Figure 8 is another structural block diagram of a first / second control valve according to an embodiment of the present invention;

[0033] Fig. 9 is a structural block diagram of a buffer component according to an embodiment of the present invention;

[0034] Fig.10 is a flow chart of a control method of a hybrid converter topology structure with controllable shutdown of the AC side according to an embodiment of the present invention;

[0035] Fig.11 is a current flow path in a normal operating state according to an embodiment of the present invention;

[0036] Fig.12 is a trigger control timing according to an embodiment of the present invention;

[0037] FIG13( a ) is a current flow path during the commutation phase from the thyristor valve branch to the auxiliary valve branch according to an embodiment of the present invention;

[0038] FIG13( b ) is a current flow path of the thyristor valve branch when the auxiliary valve branch is turned off and the current is passed through the auxiliary valve branch according to an embodiment of the present invention;

[0039] FIG13( c ) is a diagram showing the current flow path of the thyristor valve branch and the auxiliary valve branch during the turn-off phase according to an embodiment of the present invention;

[0040] Fig.14 is the control timing of each valve when a commutation failure or a short circuit fault is detected according to an embodiment of the present invention;

[0041] Fig.15 This is another control method of a hybrid converter topology structure with controllable shutdown of the AC side according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0043] As the core equipment of DC power transmission, the converter is the core functional unit for realizing AC-DC power conversion. Its operating reliability largely determines the operating reliability of the UHV DC power grid. However, since traditional converters mostly use semi-controlled devices, thyristors, as core components to form a six-pulse bridge commutation topology, each bridge arm is composed of multiple thyristors and their buffer components in series, and since thyristors do not have self-shutoff capabilities, commutation failures are prone to occur in the event of AC system failures, resulting in a surge in DC current and a rapid and large loss of DC transmission power, affecting the stable and safe operation of the power grid.

[0044] Based on this, the technical solution of the present invention introduces a shutoff control valve on the AC side to ensure that the thyristor valve has sufficient reverse recovery time for reliable shutdown, and at the same time uses the auxiliary valve branch to assist in commutation, fundamentally solving the commutation failure problem of the DC system, thereby ensuring the stable and safe operation of the power grid.

[0045] According to an embodiment of the present invention, an embodiment of a hybrid converter topology structure with controllable shutdown on the AC side is provided, and the hybrid converter topology structure with controllable shutdown on the AC side is connected to the AC power grid through a converter transformer. Figure 1 As shown, the hybrid converter topology structure with controllable shutdown on the AC side includes: at least one phase commutation circuit, each phase commutation circuit includes a parallel thyristor valve branch and an auxiliary valve branch. The thyristor valve branch is provided with a thyristor valve, such as Figure 1 The V11, V21, V31, V41, V51 and V61 shown are thyristor valves; the auxiliary valve branch includes a first control valve and a second control valve, and the first control valve and the second control valve both have a forward current controllable shutoff function and a forward and reverse voltage blocking function, such as Figure 1 The V13, V33 and V53 shown are first control valves, and V23, V43 and V63 are second control valves. Specifically, V11 and V41 are connected in series, V31 and V61 are connected in series, and V51 and V21 are connected in series, which are thyristor valve branches of each phase commutation circuit respectively; V13 and V43 are connected in series, V33 and V63 are connected in series, and V53 and V23 are connected in series, which are auxiliary valve branches in each phase commutation circuit respectively.

[0046] The connection end of the first control valve and the second control valve is connected to the converter transformer through the third control valve, and the third control valve has a unidirectional voltage output controllable shut-off function, such as Figure 1 As shown, V14, V36 and V52 are the third control valves. Among them, the connection end of V13 and V43 is connected to the a-phase output end of the converter transformer through V14; the connection end of V33 and V63 is connected to the b-phase output end of the converter transformer through V36; and the connection end of V53 and V23 is connected to the c-phase output end of the converter transformer through V52.

[0047] The connection end of the thyristor valve on the thyristor valve branch is also connected to the output end of the converter transformer, thereby realizing the third control valve that can be controlled to shut down by introducing a unidirectional voltage on the AC side. Figure 1 As shown, the connection ends of V11 and V41 are connected to the a-phase output end of the converter transformer; the connection ends of V31 and V61 are connected to the b-phase output end of the converter transformer; and the connection ends of V51 and V21 are connected to the c-phase output end of the converter transformer.

[0048] The hybrid converter topology structure with controllable shutdown on the AC side provided by the embodiment of the present invention includes at least one phase commutation circuit, each phase commutation circuit includes a parallel thyristor valve branch and an auxiliary valve branch, a thyristor valve is arranged on the thyristor valve branch, the auxiliary valve branch includes a first control valve and a second control valve, and the first control valve and the second control valve both have a forward current controllable shutdown function and a forward and reverse voltage blocking function, and the connection end of the first control valve and the second control valve is connected to the converter transformer through a third control valve; the third control valve has a unidirectional voltage output controllable shutdown function, and the connection end of the thyristor valve on the thyristor valve branch is connected to the converter transformer. The hybrid converter topology structure ensures that the thyristor valve has sufficient reverse recovery time for reliable shutdown by arranging the third control valve on the AC side, and at the same time, the auxiliary valve branch is used to fundamentally solve the commutation failure problem of the DC system, thereby ensuring the stability and safety of the power grid operation.

[0049] Optionally, the hybrid converter topology structure with controllable shutdown on the AC side includes a three-phase commutation circuit, and each phase commutation circuit is arranged in parallel. One end of the three-phase commutation circuit is connected to the positive pole of the DC bus, and the other end is connected to the negative pole of the DC bus, such as Figure 1 shown.

[0050] Optionally, the thyristor valve includes at least one thyristor and a third buffer component connected in parallel or in series with the thyristor, wherein at least one thyristor is arranged in series, and the first buffer component is used to prevent the thyristor device from being damaged by high voltage and high current. Figure 2 As shown, the thyristor valve includes at least one thyristor and third buffer components respectively connected in parallel with the thyristors.

[0051] Optionally, taking the third control valve V14 as an example, the third control valve V14 includes at least one first power unit and first buffer components connected in parallel with the first power units respectively (a person skilled in the art may know the parallel connection method, which is not shown in the figure), wherein at least one first power unit is arranged in series, and the second buffer component is used to limit voltage and current stress.

[0052] Specifically, Figure 3 As shown, the first power unit may be a power electronic unit consisting of a first branch and a second branch.

[0053] The first branch is provided with a first power device; the second branch is connected in parallel with the first branch, and the second branch is provided with a first capacitor element and a first power device, and the first power device and the first capacitor element are connected in series. The first power device is a fully controlled power electronic device, and the fully controlled power electronic device is one or more turn-off devices such as IGBT, IGCT, IEGT, GTO or MOSFET. It should be noted that if the fully controlled power electronic device does not have a reverse voltage blocking function, a diode needs to be reversely connected in parallel with the fully controlled power electronic device.

[0054] Specifically, Figure 4 As shown, the first power unit may also be a power electronic unit composed of a third branch and a fourth branch.

[0055] The third branch is a full-bridge circuit composed of four second power devices connected; the fourth branch is provided with a second capacitor element, which is connected in parallel between the upper half bridge and the lower half bridge of the full-bridge circuit. Among them, 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. It should be noted that if the fully controlled power electronic device does not have a reverse voltage blocking function, a diode needs to be connected in reverse parallel to the fully controlled power electronic device.

[0056] The third control valve is a low-voltage fully controlled shutoff valve with a unidirectional voltage controllable output capability, and is mainly used to shut off the current of the thyristor valve branch and provide a reverse voltage therefor, to ensure that the thyristor valve of the thyristor valve branch has sufficient shutoff time for reliable shutoff. This application does not limit the topology of the third control valve, as long as it is a topology with the function of unidirectional voltage controllable output.

[0057] Optionally, the first control valve has the same structure as the second control valve. Taking the first control valve V13 as an example, the first control valve V13 includes at least one second power unit and second buffer components respectively connected in parallel with the second power units, wherein at least one second power unit is arranged in series, and the third buffer component is used to limit voltage and current stress.

[0058] Specifically, Figure 5 As shown, the second power unit may be a power electronic unit composed of at least one fifth branch, and the at least one fifth branch is arranged in series.

[0059] The fifth branch is provided with a third power device and a first diode, and the third power device is provided in series with the first diode. The third 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. It should be noted that if the fully controlled power electronic device does not have a reverse voltage blocking function, a diode needs to be reversely connected in parallel with the fully controlled power electronic device to achieve the reverse voltage blocking function.

[0060] Specifically, Figure 6 As shown, the second power unit may also be a power electronic unit composed of a sixth branch and a seventh branch.

[0061] 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 in series. Among them, the third 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. It should be noted that if the fully controlled power electronic device does not have a reverse voltage blocking function, a diode needs to be reversely connected in parallel with the fully controlled power electronic device to achieve the reverse voltage blocking function.

[0062] Specifically, Figure 7 As shown, the second power unit can also be a power electronic unit composed of an eighth branch. The eighth branch is a full-bridge circuit composed of a plurality of fourth power devices connected, wherein the fourth 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. It should be noted that if the fully controlled power electronic device does not have a reverse voltage blocking function, a diode needs to be reversely connected in parallel to the fully controlled power electronic device to achieve the reverse voltage blocking function.

[0063] The full-bridge circuits are connected in series in sequence to realize forward and reverse current control, complete the transfer of the thyristor valve branch current to the auxiliary valve branch at any time, and the auxiliary valve branch bears the forward and reverse voltages. Each bridge arm in the full-bridge circuit is a single-stage structure or a multi-stage series structure composed of a fully controlled power electronic device and a diode. Of course, it can also be other topological forms, which are not specifically limited here, and technical personnel in this field can determine according to actual needs.

[0064] Specifically, Figure 8As shown, the second power unit may also be a power electronic unit composed of at least one ninth branch, and the at least one ninth branch is connected in series to form an H-bridge circuit.

[0065] The ninth branch includes: a first sub-branch, a second sub-branch and a third sub-branch. Among them, a plurality of third diodes connected in series are arranged on the first sub-branch; the second sub-branch is connected in parallel between the first sub-branch and the third sub-branch, and a plurality of fifth power devices connected in series are arranged on the second sub-branch, wherein the fifth power 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. It should be noted that if the fully controlled power electronic device does not have a reverse voltage blocking function, a diode needs to be reversely connected in parallel to the fully controlled power electronic device to realize the reverse voltage blocking function; 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 a single-stage structure or a multi-stage series structure. The H-bridge circuits are connected in series in sequence to realize bidirectional flow and bidirectional shutdown functions.

[0066] The above-mentioned first control valve and second control valve are both auxiliary valves, which have the ability of controllable shutdown of forward current and forward and reverse voltage blocking. The present application does not limit the topological form of the first control valve and the second control valve, as long as the topological form has the function of controllable shutdown of forward current and forward and reverse voltage blocking.

[0067] Optionally, the first buffer component, the second buffer component and the third buffer component are all composed of one or more forms of components such as capacitors, resistor-capacitor circuits, diodes, inductors or lightning arresters.

[0068] Specifically, Fig. 9 As shown, the first buffer component, the second buffer component and the third buffer component can be a first buffer branch composed of a capacitor; can be a second buffer branch composed of a resistor and a capacitor in series; can be a third buffer branch composed of a capacitor and a resistor in parallel; can be a fourth buffer branch RCD1 composed of a resistor and a fifth diode in parallel and then in series with a capacitor; can be a fifth buffer branch RCD2 composed of a resistor and a capacitor in parallel and then in series with a fifth diode; can also be a sixth buffer branch composed of a lightning arrester; can also be a seventh buffer branch composed of multiple of the above-mentioned first buffer branch, second buffer branch, third buffer branch, fourth buffer branch, fifth buffer branch and sixth buffer branch in parallel.

[0069] According to an embodiment of the present invention, an embodiment of a control method for a hybrid converter topology structure with controllable shutdown on the AC side is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0070] In this embodiment, a control method for a hybrid converter topology structure with controllable shutdown on the AC side is provided, which can be used for the hybrid converter topology structure with controllable shutdown on the AC side. Fig.10 is a flow chart of forced commutation according to an embodiment of the present invention, such as Fig.10 As shown, the process includes the following steps:

[0071] S21, turning on the third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm.

[0072] S22, turning on the thyristor valve of the i-th bridge arm.

[0073] S23, after one control cycle, the thyristor valve of the i-th bridge arm is turned on, wherein, .

[0074] Specifically, Fig.11 The figure shows the valve current flow path of the hybrid converter topology under normal operating conditions. The thyristor valve branch is subjected to voltage and current stress periodically, and the auxiliary valve branch is always in the off state and is subjected to voltage stress only when the thyristor valve of the thyristor valve branch is turned off.

[0075] Fig.12 The trigger control timing of each valve under normal operating conditions is given, where Sg1 is the control timing of the thyristor valve, Sg12 is the control timing of the third control valve, and Sg13 is the control timing of the first control valve or the second control valve. t 0 is the initial trigger time, is the conduction time of the thyristor valve, is the turn-off time of the thyristor valve, is the forward blocking time of the thyristor valve, and the control period T is 2π.

[0076] When commutation fails or a short circuit occurs, a forced commutation operation of a hybrid converter topology structure with a controllable shutdown on the AC side is triggered. The control method of the hybrid converter topology structure with controllable shutdown on the AC side includes: when a commutation failure or a short-circuit fault is detected in the thyristor valve of the i-th bridge arm, the duration of the commutation failure or the short-circuit fault is obtained; when the duration reaches a first preset duration, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned on, and when the duration reaches a second preset duration, the third control valve connected to the thyristor valve of the i-th bridge arm is turned off; the second preset duration is greater than the first preset duration; when the thyristor valve of the i-th bridge arm is in a forward blocking state, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned off; when the control cycle in which the commutation failure or the short-circuit fault is located ends, the thyristor valve of the i-th bridge arm is turned on, the third control valve connected to the thyristor valve of the i-th bridge arm is turned on, and the third control valve connected to the thyristor valve of the i-th bridge arm is turned off. the first control valve or the second control valve of the thyristor valve of the i-th bridge arm; after a third preset time, the third control valve connected to the thyristor valve of the i-th bridge arm is turned off, and the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned on; when the thyristor valve of the i-th bridge arm is in a forward blocking state, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned off, and after a fourth preset time, the step of turning on the thyristor valve of the i-th bridge arm, turning on the third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is returned to execution; when the voltage of the hybrid converter topology structure with controllable shutdown on the AC side returns to stability, the third control valve connected to the thyristor valve of the i-th bridge arm is turned on, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned off, and the thyristor valve of the i-th bridge arm is turned on.

[0077] Specifically, the first preset time length is the set time length for turning on the first control valve or the second control valve, and the second preset time length is the set time length for turning off the third control valve. The first preset time length and the second preset time length can be determined according to the properties of the electronic device used and the empirical value, and are not specifically limited here. The third preset time length is the turn-on time length of the third control valve.

[0078] As shown in Figure 13 (a), Figure 13 (b), Figure 13 (c) and Fig.14 As shown, when tf When the thyristor valve i is detected to have a commutation failure or a short circuit fault, At the moment, the first control valve or the second control valve connected to the i-th thyristor valve is turned on, and at the moment The third control valve connected to the i-th thyristor valve is always turned off, and when the i-th thyristor valve is in a forward blocking state, the first control valve or the second control valve connected to the i-th thyristor valve is turned off. Taking V11, V13 and V14 as examples, as shown in Figures 13(a), 13(b) and 13(c), the process is divided into three stages. Figure 13(a) shows the commutation stage from the thyristor valve branch to the auxiliary valve branch. In this stage, the V13 valve on the auxiliary valve branch receives a trigger signal and turns on, and then the V14 valve receives a signal and turns off, completing the commutation process from the thyristor valve branch to the auxiliary valve branch; Figure 13(b) shows the thyristor valve branch off and the auxiliary valve branch through-current stage. In this stage, the thyristor valve branch has been completely turned off and all the current has been transferred to the auxiliary valve branch; Figure 13(c) shows the thyristor valve branch and the auxiliary valve branch off stage. In this stage, the V13 valve of the auxiliary valve branch is turned off after receiving the turn-off signal. At this time, the thyristor valve V11 is in a forward blocking state to withstand the forward voltage.

[0079] in, is the delay time of turning on the first control valve or the second control valve of the i-th thyristor, is the delay time for turning off the third control valve connected to the i-th thyristor, .

[0080] Fig.14 The figure shows the control timing of each valve when a commutation failure or a short circuit fault is detected. Sg1 is the control timing of the thyristor valve, Sg12 is the control timing of the third control valve, and Sg13 is the control timing of the first control valve or the second control valve. t 1 is the initial triggering moment, and the control period T is 2π. It should be noted that the time from the thyristor valve branch current passing through zero to the auxiliary valve branch being turned off is the thyristor valve turn-off time. , here Greater than the minimum preset off time of the thyristor valve.

[0081] when tf After the control cycle ends, step S1 is executed until the voltage of the hybrid converter topology structure returns to stability, the third control valve connected to the i-th thyristor valve is turned on, the first control valve or the second control valve connected to the i-th thyristor valve is turned off, and the step of turning on the thyristor valve of the i-th bridge arm is executed.

[0082] Step S1: Turn on the i-th thyristor valve, turn on the third control valve connected to the i-th thyristor valve, turn off the first control valve or the second control valve connected to the i-th thyristor valve, and Then, execute step S2;

[0083] Step S2: turning off the third control valve connected to the i-th thyristor valve, and turning on the first control valve or the second control valve connected to the i-th thyristor valve. When the i-th thyristor valve is in a forward blocking state, executing step S3;

[0084] Step S3: Turn off the first control valve or the second control valve connected to the i-th thyristor valve. Then, return to step S1;

[0085] in, is the time duration that the i-th thyristor valve is in the forward blocking state within a control cycle, is the delay time for turning on the first control valve or the second control valve connected to the i-th thyristor valve, is the delay time for turning off the third control valve connected to the i-th thyristor valve, is the conduction time of the third control valve connected to the i-th thyristor valve, 0< , T is a control cycle, , .

[0086] The control method of the hybrid converter topology structure with controllable shutdown on the AC side provided in this embodiment is that during normal operation, the first control valve and the second control valve are not put into operation, and only need to bear voltage stress, which will not have a negative impact on various operating conditions of the converter valve; after a commutation failure or a short circuit fault occurs, the first control valve or the second control valve is immediately put into operation to achieve the auxiliary commutation function in a relatively short time and quickly restore the commutation between the bridge arms. This control method makes full use of the advantages of thyristors, the first control valve that can be turned off, and the second control valve that can be turned off. The third control valve is introduced on the AC side to complete the current transfer from the thyristor valve branch to the auxiliary valve branch in advance. The first control valve and the second control valve only bear a large shutdown voltage stress when the commutation fails or the short circuit fails, and do not need to bear current stress for a long time, thereby avoiding the increase of device loss, improving the utilization rate of the device, and reducing the loss cost.

[0087] Based on the same inventive concept, the present invention also provides another control method for a hybrid converter topology structure with controllable shutdown on the AC side, such as Fig.15 As shown, the method includes:

[0088] Step T1: Turn on the i-th thyristor valve of the hybrid converter topology, turn on the third control valve connected to the i-th thyristor valve, turn off the first control valve and the second control valve connected to the i-th thyristor valve, and Then, execute step T2, 0 < ;

[0089] Step T2: turning off the third control valve connected to the i-th thyristor valve, turning on the first control valve and the second control valve connected to the i-th thyristor valve, and when the i-th thyristor valve is in a forward blocking state, executing step T3;

[0090] Step T3: Turn off the first control valve and the second control valve connected to the i-th thyristor valve. Then, return to step T1;

[0091] in, is the time duration that the i-th thyristor valve is in the forward blocking state within a control cycle, is the third control valve connected to the i-th thyristor valve, 0< , T is a control cycle, .

[0092] Fig.15 In the figure, Sg1 is the control timing of the thyristor valve, Sg12 is the control timing of the third control valve, and Sg13 is the control timing of the first control valve and the second control valve. is the conduction time of the thyristor valve, is the forward blocking time of the thyristor valve, the control period T is 2π, is the conduction time of the third control valve, 0< , Δ t 13 is the conduction time of the first control valve and the second control valve, and the time from the thyristor valve branch current passing through zero to the auxiliary valve branch being turned off is the thyristor valve turn-off time , here Greater than the minimum preset off time of the thyristor valve.

[0093] The control method of the hybrid converter topology structure with controllable shutdown on the AC side provided in an embodiment of the present invention avoids the occurrence of commutation failure or short-circuit failure by connecting the third control valve to the thyristor valve, the first control valve or the second control valve in an alternating operation mode, which is beneficial to improving the overall reliability of the hybrid converter.

[0094] 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 present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A hybrid converter topology with controllable shutdown on the AC side, wherein the topology is connected to the AC power grid through a converter transformer, characterized in that: The topology structure includes: At least one phase commutation circuit, comprising a thyristor valve branch and an auxiliary valve branch connected in parallel; The thyristor valve branch is provided with a thyristor valve; The auxiliary valve branch includes a first control valve and a second control valve, both of which have a forward current controllable shutoff function and a forward and reverse voltage blocking function; the first control valve and the second control valve have the same structure; The connecting end of the first control valve and the second control valve is connected to the output end of the converter transformer through a third control valve; the third control valve has a unidirectional voltage output controllable shutoff function; The connection end of the thyristor valve is connected to the output end of the converter transformer; The third control valve includes: at least one first power unit, which is arranged in series; and a first buffer component, which is connected in parallel with the first power unit.

2. The topological structure according to claim 1, characterized in that: The topology structure includes: Three-phase commutation circuit; the commutation circuits of each phase are arranged in parallel.

3. The topological structure according to claim 1, characterized in that: The first power unit comprises: A first branch, wherein 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 capacitor element and the first power device. The first power device and the first capacitor element are connected in series.

4. The topological structure according to claim 1, characterized in that: The first power unit comprises: A third branch, wherein the third branch is a full-bridge circuit formed by connecting four second power devices; the second power devices are fully controlled power electronic devices; A fourth branch is provided with a second capacitance element, and the second capacitance element is connected in parallel between the upper half bridge and the lower half bridge of the full-bridge circuit.

5. The topological structure according to claim 1, characterized in that: The first control valve comprises: at least one second power unit, the at least one second power unit being arranged in series; The second buffer component is connected in parallel with the second power unit.

6. The topological structure according to claim 5, characterized in that: The second power unit comprises: At least one fifth branch, the at least one fifth branch is arranged in series; a third power device and a first diode are arranged on the fifth branch, the third power device is connected in series with the first diode; the third power device is a power electronic device without a reverse blocking function; or, A sixth branch, wherein at least one of the third power devices is disposed on the sixth branch, and the at least one third power device is disposed in series; The seventh branch is connected in series with the sixth branch; the seventh branch is provided with at least one second diode, and the at least one second diode is arranged in series.

7. The topological structure according to claim 5, characterized in that: The second power unit comprises: At least one eighth branch, the at least one eighth branch is arranged in series; the eighth branch is a full-bridge circuit composed of a plurality of fourth power devices connected; the fourth power device is a fully controlled power electronic device.

8. The topological structure according to claim 5, characterized in that: The second power unit comprises: At least one ninth branch, wherein the at least one ninth branch is connected in series to form an H-bridge circuit; The ninth branch includes a first sub-branch, a second sub-branch and a third sub-branch; 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, 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.

9. The topological structure according to claim 1, characterized in that: The thyristor valve comprises: at least one thyristor, the at least one thyristor being arranged in series; A third buffer component is connected in parallel or in series with the thyristor.

10. The topological structure according to claim 1 or 5 or 9, characterized in that: The first buffer component, the second buffer component and the third buffer component each include: A first buffer branch composed of a capacitor; or, a second buffer branch in which a resistor and the capacitor are connected in series; or, a third buffer branch in which the capacitor and the resistor are connected in parallel; Or, the resistor and the fifth diode are connected in parallel, 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, a sixth buffer branch consisting of a lightning arrester; Or, a seventh buffer branch formed by connecting in parallel a plurality of the first buffer branch, the second buffer branch, the third buffer branch, the fourth buffer branch, the fifth buffer branch and the sixth buffer branch.

11. A control method for a hybrid converter topology structure with controllable shutdown on the AC side, used for the hybrid converter topology structure with controllable shutdown on the AC side as claimed in any one of claims 1 to 10, characterized in that: The method comprises: Turning on the third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm; Turn on the thyristor valve of the i-th bridge arm; After one control cycle, the thyristor valve of the i-th bridge arm is turned on, where: .

12. The method according to claim 11, characterized in that Also includes: When a commutation failure or a short circuit fault occurs in the thyristor valve of the i-th bridge arm, the duration of the commutation failure or the short circuit fault is obtained; When the duration reaches a first preset duration, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned on, and when the duration reaches a second preset duration, the third control valve connected to the thyristor valve of the i-th bridge arm is turned off; the second preset duration is greater than the first preset duration; When the thyristor valve of the i-th bridge arm is in a forward blocking state, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned off; When the control cycle of the commutation failure or short circuit fault ends, the thyristor valve of the i-th bridge arm is turned on, the third control valve connected to the thyristor valve of the i-th bridge arm is turned on, and the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned off; After a third preset time, the third control valve connected to the thyristor valve of the i-th bridge arm is turned off, and the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned on; When the thyristor valve of the i-th bridge arm is in a forward blocking state, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned off, and after a fourth preset time, the step of returning to the step of turning on the thyristor valve of the i-th bridge arm, turning on the third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm; When the voltage of the hybrid converter topology structure with controllable shutdown on the AC side returns to stability, the third control valve connected to the thyristor valve of the i-th bridge arm is turned on, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned off, and the thyristor valve of the i-th bridge arm is turned on.

13. A control method for a hybrid converter topology structure with controllable shutdown on the AC side, used for the hybrid converter topology structure with controllable shutdown on the AC side as claimed in any one of claims 1 to 10, characterized in that: The method comprises: Turning on the thyristor valve of the i-th bridge arm, turning on the third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the first control valve or the second control valve connected to the i-th thyristor valve; After a third preset time, the third control valve connected to the thyristor valve of the i-th bridge arm is turned off, and the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned on; When the i-th thyristor valve is in a forward blocking state, the first control valve or the second control valve connected to the thyristor valve of the i-th bridge arm is turned off; After the fourth preset time period, return to the step of turning on the thyristor valve of the i-th bridge arm, turning on the third control valve connected to the thyristor valve of the i-th bridge arm, and turning off the first control valve or the second control valve connected to the i-th thyristor valve.

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