Flexible alternating-current interconnection apparatus and control method

Abstract

A flexible alternating-current interconnection apparatus and a control method therefor. The flexible alternating-current interconnection apparatus comprises a three-phase series-connected converter valve connecting two alternating-current systems, the series-connected converter valve comprising N rectifier-inverter modules, M conducting-current blocking modules and K reactive modules. Each of the rectifier-inverter module comprises a rectifier full-bridge circuit and an inverter full-bridge circuit which are connected in parallel on a direct-current side, an alternating-current port of the inverter full-bridge circuit of each of the rectifier-inverter modules and alternating-current ports of the inverter full-bridge circuits of the other rectifier-inverter modules being successively cascaded, and an alternating-current port of the rectifier full-bridge circuit of each of the rectifier-inverter modules being connected to different secondary windings of a multi-winding transformer or a power supply capable of supplying energy. Each of the conducting-current blocking modules at least comprises a diode full-bridge rectifier circuit and a blocking capacitor connected to a direct-current end of the diode full-bridge rectifier circuit in parallel, and the conducting-current blocking module further comprises a conducting-current loop. The flexible alternating-current interconnection apparatus has the following advantages of flexible operation mode, high efficiency, and high reliability.

Description

Flexible AC interconnection device and control method Technical Field

[0001] The present application relates to the field of high-voltage direct current (HVDC) transmission technology, and more specifically, to a flexible AC interconnection device and a control method. Background Art

[0002] As users' demands for electricity, power quality, and reliability continue to rise, traditional power supply networks are increasingly struggling to meet these needs. In existing power distribution networks, overload or faults in a single line often lead to widespread power outages. Flexible interconnection devices based on power electronic conversion technology can connect power sources from different supply zones or busbars, achieving closed-loop operation. Furthermore, flexible interconnection devices can provide mutual support and power balance between supply zones.

[0003] Traditional interconnection devices use the MMC back-to-back solution, which has the functions of double-end reactive power compensation and fault isolation, but has problems such as high cost, low transmission efficiency and large space occupation.

[0004] Patent (CN115483683A) discloses a series-connected flexible AC loop device and system with advantages such as bidirectional power control, fault isolation, and high efficiency. Because the device's commutation chain is composed of numerous power modules, when the amplitude and phase angle differences between the two AC power sources connected to the device are small, the number of modules actually performing the regulation function is small. When a low-voltage fault occurs on one of the two connected AC power sources, the voltage differential applied across the device suddenly increases, which in turn applies to the power modules, causing a DC overvoltage on the power modules. Therefore, to address these fault conditions, the number of power modules increases to share the overvoltage generated on the AC side during fault conditions, significantly increasing the cost of the device.

[0005] The inventors of the present application have discovered that there is currently a lack of a low-cost solution that can withstand the overvoltage problem caused by AC faults. Summary of the Invention

[0006] The present application aims to propose a flexible AC interconnection device and control method that can withstand overvoltage problems caused by AC faults at a low cost.

[0007] According to one aspect of the present application, a flexible AC interconnection device is provided, comprising a three-phase series converter valve connecting two AC systems, the three-phase series converter valve comprising:

[0008] N rectifier and inverter modules, where N ≥ 0, each of the rectifier and inverter modules includes a rectifier full-bridge circuit and an inverter full-bridge circuit connected in parallel on the DC side, wherein the AC port of the inverter full-bridge circuit of each rectifier and inverter module and the AC ports of the inverter full-bridge circuits of other rectifier and inverter modules are sequentially cascaded; the AC port of the rectifier full-bridge circuit of each rectifier and inverter module is connected to different secondary windings of a multi-winding transformer or a power supply with energy supply capability;

[0009] K reactive modules, where K ≥ 0, each of the reactive modules includes a reactive full-bridge circuit and a storage capacitor connected in parallel on the DC side, wherein the AC end of the reactive full-bridge circuit is connected in series with the AC end of the inverter full-bridge circuit of the rectifier inverter module, and N + K ≥ 1;

[0010] M flow blocking modules, where M ≥ 1, each of the flow blocking modules comprises a first diode full-bridge rectifier circuit and a blocking capacitor connected in parallel to the DC end thereof, and an AC end of the first diode full-bridge rectifier circuit is connected in series with the AC end of the inverter full-bridge circuit of the rectifier inverter module;

[0011] The through-current blocking module further includes a through-current loop, which is connected in parallel with the DC end or the AC end of the first diode full-bridge rectifier circuit.

[0012] According to some embodiments, the current blocking module further includes a mechanical switch, which is connected in series to the AC end of the first diode full-bridge rectifier circuit.

[0013] According to some embodiments, when the current loop is turned on, the current blocking module is in the on-state working state; when the current loop is closed and the voltage of the blocking capacitor is increased, the current blocking module is in the blocking working state; and / or when the current loop is closed, the voltage of the blocking capacitor is increased, and the mechanical switch is disconnected, the current blocking module is in the disconnected working state.

[0014] According to some embodiments, the AC ends of the at least two first diode full-bridge rectifier circuits are connected in series, and the current-passing loop is connected in parallel to the series branches of the AC ends of the at least two first diode full-bridge rectifier circuits.

[0015] According to some embodiments, the current-passing loop of the current-passing blocking module includes a bidirectional blocking unit, which is connected in parallel to the AC port of the first diode full-bridge rectifier circuit, wherein the bidirectional blocking unit includes a combination of one or more IGBTs, MOSFETs, IGCTs, GTOs, bidirectional thyristors or mechanical switches connected in reverse series.

[0016] According to some embodiments, the current-passing loop of the current-passing blocking module includes at least one power semiconductor device, wherein the power semiconductor device is connected in parallel at both ends of the DC of the first diode full-bridge rectifier circuit; or the power semiconductor device is connected in parallel at both ends of each diode of the upper bridge arm or the lower bridge arm of the first diode full-bridge rectifier circuit; the semiconductor device includes a combination of one or more of IGBT, MOSFET, IGCT, GTO, and thyristor; the AC end of the first diode full-bridge rectifier circuit includes the midpoint of the two half-bridges constituting the full-bridge structure, the midpoint of any one half-bridge constituting the full-bridge structure, and the positive or negative pole of the DC capacitor; the upper bridge arm includes the part of the positive pole of the DC capacitor and the midpoint of the half bridge; the lower bridge arm includes the part of the negative pole of the DC capacitor and the midpoint of the half bridge. According to some embodiments, an overvoltage protection device, and / or a bypass switch and / or a bidirectional thyristor are connected in parallel at both ends of the inverter full-bridge circuit of the rectifier inverter module and / or the current blocking module's current loop, wherein the bypass switch is electrically open and closed and has a power-off closing retention function.

[0017] According to some embodiments, the blocking capacitor of the current blocking module includes at least two discrete capacitors connected in series, wherein a voltage grading resistor is connected in parallel across the discrete capacitors.

[0018] According to some embodiments, the current blocking module further includes a drive isolation circuit for receiving an external drive signal and controlling the on and off of the power semiconductor device after potential isolation.

[0019] According to some embodiments, the primary side of the drive isolation circuit is connected to a DC power supply; the DC power supply is obtained by at least one of the following methods:

[0020] 1) A low voltage AC power source at ground potential is connected to a wire short-circuited at the end, and the wire passes through a series CT, the output of which is rectified;

[0021] 2) Any secondary winding of a multi-winding transformer is connected to a wire and short-circuited at the end. The wire passes through a series CT, and the output of the series CT is rectified.

[0022] According to some embodiments, the current blocking module also includes a rectifier unit and at least one isolated power supply, the rectifier unit having a second diode full-bridge rectifier circuit connected in parallel with the blocking capacitor at the DC end, wherein the AC end of the second diode full-bridge rectifier circuit is connected to the secondary winding of the power supply transformer; the input of the isolated power supply is connected to the blocking capacitor, and the output of the isolated power supply is connected to the drive isolation circuit.

[0023] According to some embodiments, the current blocking module also includes an isolated power supply, wherein the input of the isolated power supply is connected to the two ends of the blocking capacitor of the current blocking module, or the DC capacitor of the adjacent rectifier inverter module, or the module control unit of the adjacent rectifier inverter module, or the secondary winding of the multi-winding transformer; the output of the isolated power supply is connected to the drive isolation circuit.

[0024] According to some embodiments, a discharge circuit is connected in parallel at both ends of the blocking capacitor of the current blocking module, and after the blocking capacitor and the discharge circuit are connected in parallel, they are connected in series with an isolation switch.

[0025] According to some embodiments, at least one power semiconductor device in the current-passing loop is connected in series with a current-limiting loop.

[0026] According to one aspect of the present application, a modular flexible AC interconnection device is proposed, including a phase-split series converter valve, the phase-split series converter valve including a rectifier inverter module, a reactive module and a flow blocking module connected in series, the rectifier inverter module being arranged in an n*N matrix, wherein n is the number of parallel connections, n is greater than or equal to 1, and N is the number of series connections, and N is greater than or equal to 1; the reactive module is arranged in a k*K matrix, wherein k is the number of parallel connections, n is greater than or equal to 0, and K is the number of series connections, and K is greater than or equal to 0; the flow blocking module is arranged in an m*M matrix, wherein m is the number of parallel connections, m is greater than or equal to 1, and M is the number of series connections, and M is greater than or equal to 1.

[0027] According to some embodiments, the rectifier and inverter modules, the reactive module, and the current blocking module are respectively designed as a preset number of series-connected units.

[0028] According to some embodiments, the AC ports of the rectifier-inverter module, the reactive module and / or the current blocking module are connected in parallel with bypass switches, wherein the number of the bypass switches put into operation is adjusted to adjust the scale of the corresponding matrix.

[0029] According to one aspect of the present application, a flexible AC interconnection system is proposed, which includes a flexible AC interconnection device as described in any of the above, a control and protection device, and at least one valve control unit, wherein the at least one valve control unit includes a first valve control unit and a second valve control unit, wherein the first valve control unit communicates with the module control units of the rectifier inverter module and the reactive module respectively; the second valve control unit communicates with the flow blocking module; the first valve control unit and the second valve control unit communicate with each other, or are integrated in the same chassis.

[0030] According to some embodiments, the flexible AC interconnection system further includes at least three single-phase reactors, wherein the single-phase reactors are connected in series with the series converter valves of the flexible AC interconnection device, and the single-phase reactors are located at one end or both ends of the series converter valves.

[0031] According to one aspect of the present application, a control method for a flexible AC interconnection device as described in any one of the preceding items is provided, comprising:

[0032] When the flexible AC interconnection device operates normally, in response to the difference between the phase voltages of the two AC systems being within a preset threshold range, the rectifier and inverter modules are responsible for compensating for the phase voltage vector difference between the two AC systems and turning on the current loop of the current blocking module;

[0033] When the flexible AC interconnection device has an overvoltage fault, in response to the difference between the phase voltages of the two AC systems exceeding a preset threshold range, the rectifier inverter module is locked, and the current loop of the current blocking module is locked to block the phase voltage vector difference between the two AC systems.

[0034] According to some embodiments, the control method also includes: when the flexible AC interconnection device is operating normally, calculating the difference between the phase voltages of the two AC systems, and determining the number of rectifier and inverter modules to be put into use based on the DC voltage and modulation index of the rectifier and inverter modules, and controlling the bypass switches of the remaining rectifier / inverter modules to close; when redundancy is lost or the difference between the phase voltages of the two AC systems increases, the bypass switches of the bypassed rectifier and inverter modules are disconnected.

[0035] According to an embodiment of the present application, the series-connected converter valve in the flexible AC interconnect device proposed herein consists of a rectifier-inverter module and a flow-blocking module connected in series. The rectifier-inverter module compensates for the voltage differential across its output voltage, regulating the current through the device by changing the amplitude and phase of the output voltage. The flow-blocking module, normally bypassed and with very low losses, provides voltage to block the current in the event of a fault. This device offers flexible operation and high efficiency.

[0036] According to some embodiments, the current blocking module adopts a high-voltage design. By properly allocating the number of current blocking modules to the rectifier and inverter modules, the voltage stress of the rectifier and inverter modules can be shared, effectively protecting the rectifier and inverter modules. Due to the simple structure, low cost, and small footprint of the current blocking module, the overall cost and footprint of the device are reduced.

[0037] According to other embodiments, the current blocking module draws energy from the adjacent rectifier inverter module, avoiding the design difficulty of the energy-drawing power supply at high voltage, and the design is simple and reliable; the rectifier inverter module adopts bypass control with voltage difference feedback at both ends to further reduce losses.

[0038] It should be understood that the foregoing general description and the following detailed description are merely illustrative and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments. By describing the exemplary embodiments in detail with reference to the accompanying drawings, the above and other objects, features and advantages of the present application will become more apparent.

[0040] FIG1 shows a device block diagram of a flexible AC interconnect device according to an exemplary embodiment of the present application.

[0041] FIG2 shows a circuit diagram of a flexible AC interconnect device according to an exemplary embodiment of the present application.

[0042] FIG3A shows a circuit diagram of a current-carrying loop formed by IGBTs according to an exemplary embodiment of the present application.

[0043] FIG3B shows a circuit diagram of a flow loop consisting of an IGBT and an anti-parallel thyristor connected in series according to an exemplary embodiment of the present application.

[0044] FIG3C shows a circuit diagram of another current-carrying loop formed by IGBTs according to an exemplary embodiment of the present application.

[0045] FIG3D shows a circuit diagram of another current-carrying loop formed by IGBTs according to an exemplary embodiment of the present application.

[0046] FIG3E shows a circuit diagram of another current-passing circuit connected in series with a current-limiting circuit according to an exemplary embodiment of the present application.

[0047] FIG4A shows a circuit diagram of a parallel discharge loop of blocking capacitors according to an exemplary embodiment of the present application.

[0048] FIG4B shows a circuit diagram of a blocking capacitor connected in series with a diode according to an exemplary embodiment of the present application.

[0049] FIG5 shows a circuit diagram of a driving isolation circuit for an external driving signal according to an exemplary embodiment of the present application.

[0050] FIG6 shows a circuit diagram of a DC power supply obtained from any secondary winding of a power supply transformer according to an exemplary embodiment of the present application.

[0051] FIG7 shows a circuit diagram of a DC power supply obtained from the output of a power supply board of an adjacent rectifier / inverter module according to an exemplary embodiment of the present application.

[0052] FIG8 shows a circuit diagram of another flexible AC interconnect device according to an exemplary embodiment of the present application.

[0053] FIG9 shows a circuit diagram of a through-current loop connected in parallel with a bidirectional blocking unit according to an exemplary embodiment of the present application.

[0054] FIG10 shows a schematic diagram of a flow blocking module connected in series with a mechanical switch according to an exemplary embodiment of the present application.

[0055] FIG11 shows a circuit diagram of another flexible AC interconnect device according to an exemplary embodiment of the present application.

[0056] FIG12 shows a circuit diagram of another flexible AC interconnect device according to an exemplary embodiment of the present application.

[0057] FIG13 shows a flow chart of a control method for a flexible AC interconnect device according to an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0058] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be embodied in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. Identical figures in the drawings represent identical or similar parts, and thus repeated description thereof will be omitted.

[0059] The described features, structures or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of these specific details, or other modes, components, materials, devices or operations may be employed. In these cases, well-known structures, methods, devices, implementations, materials or operations will not be shown or described in detail.

[0060] The flowcharts shown in the accompanying drawings are for illustrative purposes only and do not necessarily include all contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps may be decomposed, while others may be combined or partially combined. Therefore, the actual execution order may vary depending on the actual situation.

[0061] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0062] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0063] FIG1 shows a block diagram of a flexible AC interconnection device according to an exemplary embodiment of the present application. The flexible AC interconnection device shown in FIG1 includes N rectifier and inverter modules 101, K reactive modules 103, and M current blocking modules 105. Where N ≥ 0, M ≥ 1, K ≥ 0, and N + K ≥ 1.

[0064] According to an embodiment of the present application, each of the rectifier inverter modules includes a rectifier full-bridge circuit and an inverter full-bridge circuit connected in parallel on the DC side, wherein the AC port of the inverter full-bridge circuit of each of the rectifier inverter modules and the AC ports of the inverter full-bridge circuits of other rectifier inverter modules are cascaded in sequence; the AC port of the rectifier full-bridge circuit of each of the rectifier inverter modules is connected to different secondary windings of a multi-winding transformer or a power supply with energy supply capability.

[0065] According to some embodiments, each of the reactive modules includes a reactive full-bridge circuit and an energy storage capacitor connected in parallel on the DC side, wherein the AC end of the reactive full-bridge circuit is connected in series with the AC end of the inverter full-bridge circuit of the rectifier inverter module.

[0066] According to other embodiments, each of the current blocking modules includes a first diode full-bridge rectifier circuit and a blocking capacitor connected in parallel to its DC end, and the AC end of the first diode full-bridge rectifier circuit is connected in series with the AC end of the inverter full-bridge circuit of the rectifier inverter module.

[0067] According to an embodiment of the present application, the flow blocking module further includes a mechanical switch connected in series with the AC end of the first diode full-bridge rectifier circuit. When the flow loop is on, the flow blocking module is in an on-state operating state; when the flow loop is off and the voltage of the blocking capacitor is raised, the flow blocking module is in a blocking state; and / or when the flow loop is off, the voltage of the blocking capacitor is raised, and the mechanical switch is off, the flow blocking module is in an off-state operating state.

[0068] In some embodiments, the rectifier / inverter module and the reactive power module each include a module control unit; the rectifier / inverter module and the reactive power module are controlled by their module control units, or by a superior control unit, for example, a superior valve control unit of the flexible AC interconnect device.

[0069] In some specific embodiments, each of the current blocking modules includes a first diode full-bridge rectifier circuit and a blocking capacitor connected in parallel to its DC end, and the AC end of the first diode full-bridge rectifier circuit is connected in series with the AC end of the inverter full-bridge circuit of the rectifier inverter module.

[0070] In other embodiments, the current blocking module's current-passing loop includes at least one power semiconductor device, wherein the power semiconductor device is connected in parallel across the DC terminals of the first diode full-bridge rectifier circuit; or the power semiconductor device is connected in parallel across the diodes of the upper arm or the lower arm of the first diode full-bridge rectifier circuit; the semiconductor device includes a combination of one or more of an IGBT, a MOSFET, an IGCT, a GTO, and a thyristor. The AC terminals of the first diode full-bridge rectifier circuit include the midpoints of the two half-bridges forming the full-bridge structure, the midpoint of any one of the half-bridges forming the full-bridge structure, and the positive or negative electrode of a DC capacitor; the upper arm includes the portion between the positive electrode of the DC capacitor and the midpoint of the half-bridge; and the lower arm includes the portion between the negative electrode of the DC capacitor and the midpoint of the half-bridge.

[0071] According to the embodiment shown in Figure 1, the rectifier-inverter module is responsible for compensating the voltage differential across the output voltage and regulating the current flowing through the flexible AC interconnection device by changing the amplitude and phase of the output voltage. The current blocking module is normally bypassed and has very low losses. However, in the event of an overvoltage fault in the flexible AC interconnection device, the current blocking module provides voltage to block the current flowing through the current blocking module, thereby sharing the voltage stress with the rectifier-inverter module and effectively protecting it. Due to the simple structure, low cost, and small footprint of the current blocking module, the overall cost and footprint of the flexible AC interconnection device are reduced.

[0072] Figure 2 shows a circuit diagram of a flexible AC interconnection device according to an exemplary embodiment of the present application. The flexible AC interconnection device shown in Figure 2 includes a three-phase series converter valve connecting two AC systems S1 and S2. As shown in Figure 2, the three-phase series converter valve 1 includes N rectifier-inverter modules 2, M flow-blocking modules 3, and K reactive power modules 4. Where N ≥ 1, M ≥ 1, and K ≥ 0.

[0073] The rectifier-inverter module 2 includes a rectifier full-bridge circuit 5 and an inverter full-bridge circuit 6 connected in parallel on the DC side. The AC ports of the inverter full-bridge circuit 6 and the AC ports of the inverter full-bridge circuits of other rectifier-inverter modules are sequentially connected in cascade. The AC ports of the rectifier full-bridge circuit 5 are connected to different secondary windings X2 of a multi-winding transformer 7. The primary winding X1 of the multi-winding transformer is connected to any AC system.

[0074] The reactive module 4 includes a reactive full-bridge circuit and a storage capacitor connected in parallel on the DC side, wherein the AC end of the reactive full-bridge circuit is connected in series with the AC end of the inverter full-bridge circuit 6 of the rectifier inverter module 2 .

[0075] The rectifier and inverter modules and the reactive module include a module control unit.

[0076] In some embodiments, at least two sampling resistors are connected in parallel to both ends of the blocking capacitor 9 of the current blocking module 3; the voltage on the blocking capacitor is divided by the sampling resistors and isolated before being sent to the module control unit of the rectifier inverter module 2.

[0077] The current blocking module 3 includes at least a first diode full-bridge rectifier circuit 8 and a blocking capacitor 9 connected in parallel to its DC end, and the AC end of the first diode full-bridge rectifier circuit 8 is connected in series with the AC end of the inverter full-bridge circuit 3 of the rectifier inverter module 2.

[0078] According to some embodiments, the blocking capacitor of the current blocking module includes at least two discrete capacitors connected in series, wherein a voltage grading resistor is connected in parallel across the discrete capacitors.

[0079] As shown in FIG2 , the through-current blocking module 3 further includes a through-current loop 10 , which is connected in parallel with the DC end or the AC end of the diode full-bridge rectifier circuit.

[0080] In some embodiments, a bypass switch and / or a bidirectional thyristor is connected in parallel to the AC port of the inverter full-bridge circuit 6 of the rectifier-inverter module 2 and / or the first diode full-bridge rectifier circuit 8 of the current blocking module 3. The bypass switch is electrically openable and has a power-off hold function.

[0081] In a specific embodiment, the through-current circuit 10 of the through-current blocking module 3 includes at least one power semiconductor device, wherein the semiconductor device includes one or more combinations of IGBT, MOSFET, IGCT, GTO, and thyristor.

[0082] In some embodiments, the two ends of the DC current of the first diode full-bridge rectifier circuit 8 are connected in parallel. As shown in Figures 3A and 3B .

[0083] In other embodiments, the power semiconductor devices in the current-passing loop are connected in parallel at both ends of the diode of the upper bridge arm or the lower bridge arm of the diode full-bridge rectifier circuit, as shown in Figures 3C and 3D. The AC end of the diode full-bridge rectifier circuit includes the midpoints of the two half-bridges that make up the full-bridge structure, the midpoint of any half-bridge that makes up the full-bridge structure, and the positive or negative electrode of the DC capacitor; the upper bridge arm includes the portion between the positive electrode of the DC capacitor and the midpoint of the half-bridge; and the lower bridge arm includes the portion between the negative electrode of the DC capacitor and the midpoint of the half-bridge.

[0084] In a specific embodiment, at least one power semiconductor device in the current-passing loop is further connected in series with a current-limiting loop, which includes a current-limiting resistor 35 and a current-limiting bypass switch 34 connected in parallel, as shown in FIG3E .

[0085] In a specific embodiment, a discharge circuit is connected in parallel across the blocking capacitor 9 of the current blocking module 3, as shown in FIG4A . The discharge circuit comprises a series connection of a discharge resistor 33 and a discharge switch 32. After the blocking capacitor and the discharge circuit are connected in parallel, they are also connected in series with an isolation switch 31, as shown in FIG3C .

[0086] In some other embodiments, the blocking capacitor 9 of the current blocking module 3 is further connected in series with a diode and / or a resistive-inductive element, wherein the cathode of the diode is connected to the positive electrode of the blocking capacitor, as shown in FIG4B .

[0087] In some embodiments, the through-current blocking module 3's through-current loop 10 includes at least one bidirectional blocking power semiconductor unit. In a specific embodiment, the through-current loop 10 is connected in parallel to the AC port of the first diode full-bridge rectifier circuit 8; the bidirectional blocking power semiconductor unit comprises a combination of one or more of an IGBT, MOSFET, IGCT, GTO, or bidirectional thyristor connected in reverse series. As shown in FIG2 , the through-current blocking module 3's through-current loop 10 is connected in parallel to the AC port of the first diode full-bridge rectifier circuit 8; the bidirectional blocking power semiconductor unit comprises an IGBT connected in reverse series.

[0088] In a specific embodiment, the IGBT in the current blocking module 3 further includes an anti-parallel diode.

[0089] In some embodiments, the number of diodes in the first diode full-bridge rectifier circuit is greater than or equal to 1. When the number of diodes in the first diode full-bridge rectifier circuit is greater than 1, the diodes are connected in series and / or in parallel to the rectifier circuit.

[0090] According to an embodiment of the present application, the flexible AC interconnection device shown in FIG2 further includes at least one valve control unit, and the rectifier-inverter module and the reactive power module include a module control unit. The valve control unit communicates with the module control units of the rectifier-inverter module and the reactive power module.

[0091] In some embodiments, as shown in FIG5 , the through-current blocking module 3 further includes a drive isolation circuit 11 for receiving an external drive signal and controlling the on and off of the power semiconductor devices in the through-current blocking module 3 after potential isolation. The external drive signal comes from a module control unit 12 of a valve control unit or a rectifier-inverter module of the flexible AC interconnect device.

[0092] In a specific embodiment, the primary side of the drive isolation circuit is connected to a DC power supply; the DC power supply is obtained by at least one of the following methods:

[0093] 1) A low-voltage AC power source at ground potential is connected to a conductor, short-circuited at one end; the conductor passes through a series CT, and the output of the series CT is rectified. A series CT is a current transformer connected together with the output ends of two or more current transformers, where the output current signal is the algebraic sum of the output current signals of the series current transformers.

[0094] 2) Connect any secondary winding of a multi-winding transformer with a wire connected to it and short-circuited at the end. The wire passes through a series CT, and the output of the series CT is rectified, as shown in Figure 6.

[0095] 3) Obtained from the output of the power board of the adjacent rectifier inverter module, as shown in Figure 7.

[0096] According to the embodiment shown in FIG2 , the rectifier inverter module is responsible for compensating the voltage difference at both ends of the output voltage and regulating the current flowing through the device by changing the amplitude and phase of the output voltage; the current blocking module is normally bypassed and has very low losses itself. In the event of a fault, it provides voltage to block the current flowing through the device, making the device flexible and efficient in operation.

[0097] In other embodiments, the AC ends of at least two first diode full-bridge rectifier circuits are connected in series, and the pass-through loop is connected in parallel to the series branches of the AC ends of the at least two first diode full-bridge rectifier circuits. As shown in FIG8 , the AC ends of the two first diode full-bridge rectifier circuits are connected in series, and the pass-through loop is connected in parallel to the series branches of the AC ends of the two first diode full-bridge rectifier circuits.

[0098] According to some other embodiments, the current-passing circuit of the current-passing blocking module includes at least one bidirectional blocking unit, and the bidirectional blocking unit is connected in parallel to the AC port of the first diode full-bridge rectifier circuit, wherein the bidirectional blocking unit includes a combination of one or more IGBTs, MOSFETs, IGCTs, GTOs, bidirectional thyristors or mechanical switches connected in reverse series, as shown in Figure 9.

[0099] According to some other embodiments, the flow blocking module further includes a mechanical switch 20, which is connected in series to the AC end of a diode full-bridge rectifier circuit. As shown in Figure 10, the bidirectional blocking power semiconductor unit in the flow loop 10 includes a controllable semiconductor device, and the blocking capacitor 9 includes a DC capacitor. The flow blocking module includes three working states: on, blocking, and disconnected. Among them, the on working state is achieved by controlling the controllable semiconductor device to turn on; the blocking working state is achieved by controlling the controllable semiconductor device to turn off and the DC capacitor voltage to rise; the disconnecting working state is achieved by controlling the controllable semiconductor device to turn off and the DC capacitor voltage to rise and the mechanical switch to disconnect.

[0100] According to some embodiments of the present application, the current blocking module further includes a drive isolation circuit for receiving an external drive signal and controlling the on and off of the power semiconductor device after potential isolation.

[0101] In a specific embodiment, the input of the isolated power supply is connected to the two ends of the blocking capacitor of the flow blocking module, or the DC capacitor of the adjacent rectifier inverter module, or the module control unit of the adjacent rectifier inverter module, or the secondary winding of the multi-winding transformer; the output of the isolated power supply is connected to the drive isolation circuit. The flow blocking module and the rectifier inverter module are in the same series converter valve. As shown in Figure 11, in this embodiment, the flow blocking module draws energy from the adjacent rectifier inverter module, avoiding the design difficulties of the energy-drawing power supply at high voltage, and the design is simple and reliable; the rectifier inverter module adopts bypass control with voltage difference feedback at both ends to further reduce losses.

[0102] In other embodiments, the current blocking module further includes a rectifier unit and at least one isolated power supply. The rectifier unit includes a second diode full-bridge rectifier circuit connected in parallel with the blocking capacitor at the DC end, wherein the AC end of the second diode full-bridge rectifier circuit is connected to the secondary winding of the power supply transformer; the input of the isolated power supply is connected to the blocking capacitor, and the output of the isolated power supply is connected to the drive isolation circuit. As shown in Figure 12.

[0103] According to an embodiment of the present application, a modular flexible AC interconnection device is also proposed, comprising a phase-series converter valve, wherein the phase-series converter valve comprises a rectifier-inverter module, a reactive module, and a flow-blocking module connected in series. The rectifier-inverter modules are arranged in an n*N matrix, where n is the number of parallel connections, n is greater than or equal to 1, and N is the number of series connections, N is greater than or equal to 1; the reactive modules are arranged in a k*K matrix, where k is the number of parallel connections, n is greater than or equal to 0, and K is the number of series connections, K is greater than or equal to 0; and the flow-blocking modules are arranged in an m*M matrix, where m is the number of parallel connections, m is greater than or equal to 1, and M is the number of series connections, M is greater than or equal to 1.

[0104] According to some embodiments, the rectifier-inverter module, the reactive power module, and the flow-blocking module are each designed as a preset number of series units. In a specific embodiment, the modular flexible AC interconnect device includes a preset number of series units, wherein the series units include a rectifier-inverter module, a reactive power module, and a flow-blocking module.

[0105] According to some embodiments, bypass switches are connected in parallel to the AC ports of the rectifier-inverter module, reactive power module, and / or current-blocking module. The number of bypass switches enabled is adjusted to adjust the size of the corresponding matrix. That is, when a bypass switch is closed, the rectifier-inverter module, reactive power module, or current-blocking module connected in parallel with the bypass switch is bypassed.

[0106] According to some embodiments of the present application, a flexible AC interconnection system is provided, wherein the flexible AC interconnection system includes any of the above-mentioned flexible AC interconnection devices, a control and protection device, and at least one valve control unit.

[0107] According to some embodiments, the at least one valve control unit includes a first valve control unit and a second valve control unit, wherein the first valve control unit communicates with the module control units of the rectifier inverter module and the reactive module respectively; the second valve control unit communicates with the flow blocking module; the first valve control unit and the second valve control unit communicate with each other, or are integrated in the same chassis.

[0108] According to some embodiments, the flexible AC interconnection system further includes at least three single-phase reactors, wherein the single-phase reactors are connected in series with the series converter valves of the flexible AC interconnection device, and the single-phase reactors are located at one or both ends of the series converter valves. In other words, the single-phase reactors are connected in series at one end of the flexible AC interconnection device or at both ends of the flexible AC interconnection device.

[0109] FIG13 shows a flow chart of a control method for a flexible AC interconnect device according to an exemplary embodiment of the present application. The method shown in FIG13 includes the following steps.

[0110] In step S1201, the working state of the flexible AC interconnection device is first determined to determine whether the flexible AC interconnection device is in normal working state. If the flexible AC interconnection device is working normally, step S1203 is executed; if the flexible AC interconnection device has an overvoltage fault, step S1205 is executed.

[0111] In step S1203, when the flexible AC interconnection device operates normally, in response to the difference between the phase voltages of the two AC systems being within a preset threshold range, the rectifier inverter module is responsible for compensating for the phase voltage vector difference between the two AC systems and turning on the current loop of the current blocking module.

[0112] In step S2105, when the flexible AC interconnection device has an overvoltage fault, in response to the difference between the phase voltages of the two AC systems exceeding a preset threshold range, the rectifier inverter module is locked, and the current blocking module's current loop is locked. The capacitor voltages of the two types of modules increase to form a voltage source to block the phase voltage vector difference between the two AC systems.

[0113] According to an embodiment of the present application, in order to further improve efficiency, the method shown in Figure 13 also includes: when the flexible AC interconnection device is operating normally, the number of rectifier inverter modules to be put into use is determined based on the calculated difference in phase voltages of the two AC systems and the DC voltage and modulation index of the rectifier inverter modules, and the remaining rectifier inverter modules are controlled to close the bypass switches or turn on the bidirectional thyristors; when redundancy is lost or the difference in phase voltages of the two AC systems increases, the bypass switches of the bypassed rectifier inverter modules are disconnected or the bidirectional thyristors are turned off. According to some embodiments, the flow blocking module adopts a high-voltage design. In this embodiment, by reasonably allocating the number ratio of the flow blocking modules to the rectifier inverter modules, the voltage stress can be shared for the rectifier inverter modules, effectively protecting the rectifier inverter modules. Since the flow blocking module has a simple structure, low cost, and small footprint, the overall cost and footprint of the device are reduced.

[0114] The embodiments of the present application are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only intended to help understand the method and core ideas of the present application. At the same time, changes or modifications made by those skilled in the art based on the ideas of the present application, the specific implementation methods, and the scope of application of the present application, all fall within the scope of protection of the present application. In summary, the contents of this specification should not be construed as limiting the present application.

Claims

1. A flexible AC interconnection device, comprising a three-phase series converter valve connecting two AC systems, characterized in that: The three-phase series converter valve comprises: N rectifier inverter modules, wherein N≥0, each of the rectifier inverter modules comprises a rectifier full-bridge circuit and an inverter full-bridge circuit connected in parallel on the DC side, wherein the AC port of the inverter full-bridge circuit of each rectifier inverter module and the AC port of the inverter full-bridge circuit of other rectifier inverter modules are sequentially cascaded; the AC port of the rectifier full-bridge circuit of each rectifier inverter module is connected to different secondary windings of a multi-winding transformer or a power supply with energy supply capability; K reactive modules, where K≥0, each of the reactive modules comprises a reactive full-bridge circuit and an energy storage capacitor connected in parallel on the DC side, wherein the AC end of the reactive full-bridge circuit is connected in series with the AC end of the inverter full-bridge circuit of the rectifier inverter module, and N+K≥1; M through-current blocking modules, where M≥1, each of the through-current blocking modules comprises a first diode full-bridge rectifier circuit and a blocking capacitor connected in parallel to its DC end, and an AC end of the first diode full-bridge rectifier circuit is connected in series with an AC end of the inverter full-bridge circuit of the rectifier inverter module; The current blocking module further includes a current loop, and the current loop is connected in parallel with the DC end or the AC end of the first diode full-bridge rectifier circuit.

2. The flexible AC interconnection device according to claim 1, characterized in that: The current blocking module further includes a mechanical switch, which is connected in series to the AC end of the first diode full-bridge rectifier circuit.

3. The flexible AC interconnection device according to claim 2, characterized in that: When the through-current loop is turned on, the through-current blocking module is in a through-state working state; When the current-passing loop is closed and the voltage of the blocking capacitor is raised, the current-passing blocking module is in a blocking working state; and / or When the current-carrying loop is closed, the voltage of the blocking capacitor rises, and after the mechanical switch is disconnected, the current-carrying blocking module is in a disconnected working state.

4. The flexible AC interconnection device according to claim 1, characterized in that: The rectifier inverter module and the reactive power module both include a module control unit; The rectifier and inverter modules and the reactive power modules are controlled by their module control units or by a superior control unit.

5. The flexible AC interconnect device according to claim 1, characterized in that: The AC ends of the at least two first diode full-bridge rectifier circuits are connected in series, and the current-carrying loop is connected in parallel to the series branches of the AC ends of the at least two first diode full-bridge rectifier circuits.

6. The flexible AC interconnect device according to claim 1, characterized in that: The current-passing circuit of the current-passing blocking module includes a bidirectional blocking unit connected in parallel to the AC port of the first diode full-bridge rectifier circuit, wherein: The bidirectional blocking unit includes a combination of one or more of IGBTs, MOSFETs, IGCTs, GTOs, bidirectional thyristors or mechanical switches connected in reverse series.

7. The flexible AC interconnect device according to claim 1, characterized in that: The through-current circuit of the through-current blocking module includes at least one power semiconductor device, wherein: The power semiconductor device is connected in parallel at both ends of the DC of the first diode full-bridge rectifier circuit; or The power semiconductor device is connected in parallel to both ends of each diode of the upper bridge arm or both ends of the diode of the lower bridge arm of the first diode full-bridge rectifier circuit; The semiconductor device includes one or more combinations of IGBT, MOSFET, IGCT, GTO and thyristor; The AC end of the first diode full-bridge rectifier circuit includes the midpoint of the two half-bridges constituting the full-bridge structure, the midpoint of any one half-bridge constituting the full-bridge structure, and the positive or negative electrode of the DC capacitor; the upper bridge arm includes the part of the positive electrode of the DC capacitor and the midpoint of the half-bridge; the lower bridge arm includes the part of the negative electrode of the DC capacitor and the midpoint of the half-bridge.

8. The flexible AC interconnect device according to claim 1, characterized in that: The inverter full-bridge circuit of the rectifier inverter module and / or the current blocking module are / is connected in parallel with overvoltage protection devices at both ends of the current loop, and / or bypass switches and / or bidirectional thyristors, wherein the bypass switch is electrically open and closed and has a power-off closing retention function.

9. The flexible AC interconnect device according to claim 5, characterized in that: The blocking capacitor of the current blocking module includes at least two discrete capacitors connected in series, wherein a voltage-equalizing resistor is connected in parallel at both ends of the discrete capacitor.

10. The flexible AC interconnect device according to claim 7, characterized in that: The current blocking module also includes a drive isolation circuit for receiving an external drive signal and controlling the on and off of the power semiconductor device after potential isolation.

11. The flexible AC interconnect device according to claim 10, characterized in that: The primary side of the drive isolation circuit is connected to a DC power supply; the DC power supply is obtained by at least one of the following methods: 1) A low voltage AC power source at ground potential is connected to a wire and short-circuited at the end, the wire passes through a series CT, and the output of the series CT is rectified; 2) Any secondary winding of the multi-winding transformer is connected to a wire and short-circuited at the end. The wire passes through a series CT, and the output of the series CT is rectified.

12. The flexible AC interconnect device according to claim 10, characterized in that: The current blocking module further includes a rectifier unit and at least one isolated power supply, wherein the rectifier unit is connected at the DC end to a second diode full-bridge rectifier circuit in parallel with the blocking capacitor, wherein: The AC end of the second diode full-bridge rectifier circuit is connected to the secondary winding of the energy supply transformer; The input of the isolated power supply is connected to the blocking capacitor, and the output of the isolated power supply is connected to the driving isolation circuit.

13. The flexible AC interconnect device according to claim 10, characterized in that: The through-current blocking module also includes an isolated power supply, wherein: The input of the isolated power supply is connected to the two ends of the blocking capacitor of the current blocking module, or the DC capacitor of the adjacent rectifier inverter module, or the module control unit of the adjacent rectifier inverter module, or the secondary winding of the multi-winding transformer; The output of the isolated power supply is connected to the drive isolation circuit.

14. The flexible AC interconnect device according to claim 1, characterized in that: A discharge circuit is connected in parallel at both ends of the blocking capacitor of the through-current blocking module, and after the blocking capacitor and the discharge circuit are connected in parallel, they are connected in series with an isolating switch.

15. The flexible AC interconnect device according to claim 7, characterized in that: At least one power semiconductor device in the current-passing loop is connected in series with the current-limiting loop.

16. A modular flexible AC interconnection device, characterized in that: It includes a phase-separated series converter valve, which includes a rectifier inverter module, a reactive module and a flow blocking module connected in series. The rectifier and inverter modules are arranged in an n*N matrix, wherein n is the number of parallel connections, n is greater than or equal to 1, and N is the number of series connections, N is greater than or equal to 1; The reactive modules are arranged in a k*K matrix, wherein k is the number of parallel connections, n is greater than or equal to 0, and K is the number of series connections, K is greater than or equal to 0; The flow blocking modules are arranged in an m*M matrix, wherein m is the number of parallel connections, which is greater than or equal to 1, and M is the number of series connections, which is greater than or equal to 1.

17. The modular flexible AC interconnection device according to claim 16, characterized in that: The rectifying and inverting module, the reactive module and the current blocking module are respectively designed to be a preset number of series-connected units.

18. The modular flexible AC interconnection device according to any one of claims 16 to 17, characterized in that: The AC ports of the rectifier inverter module, reactive power module and / or current blocking module are connected in parallel with bypass switches, wherein: The bypass switch adjusts the number of inputs to adjust the scale of the corresponding matrix.

19. A flexible AC interconnection system, characterized in that: The system comprises the flexible AC interconnection device according to any one of claims 1 to 11, a control protection device and at least one valve control unit, wherein the at least one valve control unit comprises a first valve control unit and a second valve control unit, wherein: The first valve control unit communicates with the module control units of the rectifier inverter module and the reactive module respectively; The second valve control unit communicates with the flow blocking module; The first valve control unit and the second valve control unit communicate with each other, or are integrated in the same chassis.

20. The flexible AC interconnection system according to claim 19, characterized in that: It also includes at least three single-phase reactors, wherein the single-phase reactors are connected in series with the series converter valves of the flexible AC interconnection device, and the single-phase reactors are located at one end or both ends of the series converter valves.

21. A control method for a flexible AC interconnection device according to any one of claims 1 to 15, characterized in that: include: When the flexible AC interconnection device works normally, in response to the difference between the phase voltages of the two AC systems being within a preset threshold range, the rectifier inverter module is responsible for compensating the phase voltage vector difference of the two AC systems and conducting the current circuit of the current blocking module; When the flexible AC interconnection device has an overvoltage fault, in response to the difference between the phase voltages of the two AC systems exceeding a preset threshold range, the rectifier inverter module is locked, and the current circuit of the current blocking module is locked to block the phase voltage vector difference between the two AC systems.

22. The control method according to claim 21, characterized in that: The control method further comprises: When the flexible AC interconnection device works normally, the difference between the phase voltages of the two AC systems is calculated, and the number of rectifier / inverter modules to be put into use is determined according to the DC voltage and modulation degree of the rectifier / inverter modules, and the bypass switches of the remaining rectifier / inverter modules are controlled to be closed; When redundancy is lost or the difference between the phase voltages of the two AC systems increases, the bypass switch of the bypassed rectifier inverter module is disconnected.

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