Flexible AC interconnection device and control method

Abstract

The present application discloses a flexible AC interconnection device, which includes a three-phase series converter valve connecting two AC systems; the series converter valve includes N rectifier inverter modules, M flow blocking modules, and K reactive modules; the rectifier inverter module includes a rectifier full-bridge circuit and an inverter full-bridge circuit connected in parallel on the DC side; the AC port of the inverter full-bridge circuit and the AC port of the inverter full-bridge circuit of other rectifier inverter modules are cascaded in sequence; the AC port of the rectifier full-bridge circuit is connected to different secondary windings of a multi-winding transformer or a power supply with energy supply capability; the flow blocking module includes at least one diode full-bridge rectifier circuit and a blocking capacitor connected in parallel to its DC end; the flow blocking module also includes a flow loop. According to the embodiments of the present application, the device provided by the present application has a flexible operation mode, high efficiency and high reliability.

Description

Technical Field

[0001] The present application belongs to the technical field of high voltage direct current transmission, and in particular, relates to a flexible alternating current interconnection device and a control method. Background Art

[0002] At present, with the increasing requirements of users for electricity demand, power quality and power supply reliability, the traditional power supply network is increasingly unable to meet the power supply needs of users. In the existing power supply and distribution network, when one of the lines is overloaded or fails, it often causes a large-scale power outage. The flexible interconnection device based on power electronic conversion technology can connect power supplies in different supply areas or different bus power supplies to achieve closed-loop operation. At the same time, the flexible interconnection device can also play a role in mutual support between supply areas and balancing the flow.

[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 the problems of high cost, low transmission efficiency and large space.

[0004] The patent (CN115483683A) discloses a series-type flexible AC closing ring device and system, which has the advantages of bidirectional power control, fault isolation, and high efficiency. Since the commutation chain of the device is composed of a large number of power modules, when the amplitude difference and phase difference of the AC power sources on both sides of the device are small, the number of modules that actually play a regulating role is very small. When a low voltage fault occurs on one side of the two connected AC power sources, the voltage difference applied to the two ends of the device will suddenly increase, and then be applied to the power module, causing a DC overvoltage on the power module. Therefore, in order to solve the above-mentioned fault conditions, the number of power modules will increase to share the overvoltage generated on the AC side under the fault condition, resulting in a significant increase in the cost of the device.

[0005] The inventor of the present application has found 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 and has 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, wherein the three-phase series converter valve comprises:

[0008] 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;

[0009] 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;

[0010] 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;

[0011] 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.

[0012] According to some embodiments, the current blocking module further includes a mechanical switch, and the mechanical switch is connected in series to an 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 an on-state working state; when the current loop is turned off and the voltage of the blocking capacitor is increased, the current blocking module is in a blocking working state; and / or when the current loop is turned off, the voltage of the blocking capacitor is increased, and the mechanical switch is disconnected, the current blocking module is in a 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 circuit 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 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. 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 at both ends of the discrete capacitor.

[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 and short-circuited at the end, the wire passes through a series CT, and the output of the series CT is rectified;

[0021] 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.

[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 both ends of the blocking capacitor of the current blocking module, or the DC capacitor of an adjacent rectifier inverter module, or the module control unit of an adjacent rectifier inverter module, or the secondary winding of a 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 includes a rectifier inverter module, a reactive module and a flow blocking module connected in series, the rectifier inverter module is arranged in an n*N matrix, wherein n is the parallel number, n is greater than or equal to 1, and N is the series number, N is greater than or equal to 1; the reactive module is arranged in a k*K matrix, wherein k is the parallel number, n is greater than or equal to 0, K is the series number, K is greater than or equal to 0; the flow blocking module is arranged in an m*M matrix, wherein m is the parallel number, m is greater than or equal to 1, and M is the series number, M is greater than or equal to 1.

[0027] According to some embodiments, the rectifier-inverter module, the reactive power 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, the system comprising a flexible AC interconnection device as described in any of the foregoing, a control protection device and at least one valve control unit, the at least one valve control unit comprising 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 above is provided, comprising:

[0032] 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;

[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 circuit 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 working 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 degree of the rectifier and inverter modules, and controlling the bypass switches of the remaining rectifier / inverter modules to be closed; 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 the embodiment of the present application, the series-connected converter valve in the flexible AC interconnection device proposed in the present application is composed of a rectifier inverter module and a flow blocking module connected in series; wherein the rectifier inverter module is responsible for compensating the voltage difference at both ends of the output voltage, and adjusts the current flowing through the device by changing the amplitude and phase of the output voltage; the flow blocking module is usually bypassed, and its own loss is very low, and provides voltage to block the current flowing through the device in the event of a fault. The device has a flexible operation mode and high efficiency.

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

[0037] According to other embodiments, the current blocking module obtains energy from the adjacent rectifier inverter module, thereby avoiding the design difficulty of the energy-drawing power supply under 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 exemplary only 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 drawings, the above and other objectives, features and advantages of the present application will become more apparent.

[0040] Figure 1 A device block diagram of a flexible AC interconnect device according to an exemplary embodiment of the present application is shown.

[0041] Figure 2 A circuit diagram of a flexible AC interconnect device according to an exemplary embodiment of the present application is shown.

[0042] Figure 3A A circuit schematic diagram of a current-carrying loop formed by IGBTs according to an exemplary embodiment of the present application is shown.

[0043] Figure 3B A circuit schematic diagram of a current-carrying loop consisting of an IGBT and an anti-parallel thyristor connected in series according to an exemplary embodiment of the present application is shown.

[0044] Figure 3C A circuit schematic diagram of another current-carrying loop formed by IGBTs according to an exemplary embodiment of the present application is shown.

[0045] Figure 3D A circuit schematic diagram of another current-carrying loop formed by IGBTs according to an exemplary embodiment of the present application is shown.

[0046] Figure 3E 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 is shown.

[0047] Figure 4A A circuit diagram of a parallel discharge loop of a blocking capacitor according to an exemplary embodiment of the present application is shown.

[0048] Figure 4B A circuit diagram of a blocking capacitor connected in series with a diode according to an exemplary embodiment of the present application is shown.

[0049] Figure 5 A circuit diagram of a driving isolation circuit for an external driving signal according to an exemplary embodiment of the present application is shown.

[0050] Figure 6 A circuit diagram showing a direct current power supply obtained from any secondary winding of a power supply transformer according to an exemplary embodiment of the present application is shown.

[0051] Figure 7 A circuit diagram showing a direct current power supply obtained from the output of a power board of a rectifier / inverter module of an adjacent rectifier / inverter module according to an exemplary embodiment of the present application is shown.

[0052] Figure 8 A circuit diagram of another flexible AC interconnect device according to an exemplary embodiment of the present application is shown.

[0053] Fig. 9 A circuit schematic diagram of a through-current loop connected in parallel with a bidirectional blocking unit according to an exemplary embodiment of the present application is shown.

[0054] Fig.10 A schematic diagram of a flow blocking module connected in series with a mechanical switch according to an exemplary embodiment of the present application is shown.

[0055] Fig.11 A circuit diagram of another flexible AC interconnect device according to an exemplary embodiment of the present application is shown.

[0056] Fig.12 A circuit diagram of another flexible AC interconnect device according to an exemplary embodiment of the present application is shown.

[0057] Fig.13 A flow chart of a control method for a flexible AC interconnect device according to an exemplary embodiment of the present application is shown. DETAILED DESCRIPTION

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

[0059] The described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. 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 adopted. In these cases, 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 only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0061] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

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

[0063] Figure 1 A device block diagram of a flexible AC interconnection device according to an exemplary embodiment of the present application is shown. Figure 1 The flexible AC interconnection device shown includes N rectifier-inverter modules 101, K reactive modules 103, and M current blocking modules 105. Wherein, 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 some 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 through-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. When the through-current loop is turned on, the through-current blocking module is in an on-state working state; when the through-current loop is turned off and the voltage of the blocking capacitor is raised, the through-current blocking module is in a blocking working state; and / or when the through-current loop is turned off, the voltage of the blocking capacitor is raised, and the mechanical switch is disconnected, the through-current blocking module is in a disconnected working state.

[0068] In some embodiments, the rectifier inverter module and the reactive module both include a module control unit; the rectifier inverter module and the reactive module are both controlled by their module control units, or by a superior control unit, for example, by a superior valve control unit of a flexible AC interconnection 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-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 the 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 half-bridge constituting the full-bridge structure, and the positive or negative electrode of the DC capacitor; the upper bridge arm includes the portion of the positive electrode of the DC capacitor and the midpoint of the half bridge; the lower bridge arm includes the portion of the negative electrode of the DC capacitor and the midpoint of the half bridge.

[0071] according to Figure 1 In the embodiment shown, the rectifier-inverter module is responsible for compensating the voltage difference between the two ends of the output voltage, and adjusting the current flowing through the flexible AC interconnection device by changing the amplitude and phase of the output voltage. The through-current blocking module is usually bypassed, and its own loss is very low. When the flexible AC interconnection device has an overvoltage fault, the through-current blocking module provides voltage to block the current flowing through the through-current blocking module device, thereby sharing the voltage stress for the rectifier-inverter module and effectively protecting the rectifier-inverter module. Since the through-current blocking module has a simple structure, low cost, and small footprint, the overall cost and footprint of the flexible AC interconnection device are reduced.

[0072] Figure 2 A circuit diagram of a flexible AC interconnection device according to an exemplary embodiment of the present application is shown. Figure 2 The flexible AC interconnection device shown includes a three-phase series converter valve connecting two AC systems S1 and S2. Figure 2 As shown, the three-phase series converter valve 1 includes N rectifier inverter modules 2, M flow blocking modules 3, and K reactive modules 4. Wherein N≥1, M≥1, 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 port of the inverter full-bridge circuit 6 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 5 is connected to different secondary windings X2 of the 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 is isolated and then 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] like Figure 2 As shown, the current blocking module 3 further includes a current-passing loop 10, and the current-passing loop is connected in parallel with the DC end or the AC end of the diode full-bridge rectifier circuit.

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

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

[0082] In some embodiments, the first diode full-bridge rectifier circuit 8 is connected in parallel to both ends of the DC current. Figure 3A and Figure 3Bshown.

[0083] In other embodiments, the power semiconductor device in the current-carrying loop is connected in parallel to both ends of the diode of the upper bridge arm or the lower bridge arm of the diode full-bridge rectifier circuit. Figure 3C and Figure 3D The AC end of the diode full-bridge rectifier circuit includes the midpoints of the two half-bridges constituting the full-bridge structure, the midpoint of any half-bridge constituting 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 also connected in series with a current-limiting loop, and the current-limiting loop includes a current-limiting resistor 35 and a current-limiting bypass switch 34 connected in parallel. Figure 3E shown.

[0085] In a specific embodiment, the two ends of the blocking capacitor 9 of the through-current blocking module 3 are also connected in parallel with a discharge circuit, such as Figure 4A The discharge circuit includes a series connection of a discharge resistor 33 and a discharge switch 32, and the two ends of the blocking capacitor are connected in parallel with the discharge circuit and are also connected in series with the isolation switch 31. Figure 3C shown.

[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. The cathode of the diode is connected to the positive electrode of the blocking capacitor, such as Figure 4B shown.

[0087] In some embodiments, the current-passing loop 10 of the current-passing blocking module 3 includes at least one bidirectional blocking power semiconductor unit. In a specific embodiment, the current-passing 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 includes a combination of one or more of IGBT, MOSFET, IGCT, GTO or bidirectional thyristor connected in reverse series. Figure 2 As shown, the current-carrying loop 10 is connected in parallel to the AC port of the first diode full-bridge rectifier circuit 8, and the bidirectional blocking power semiconductor unit includes IGBTs 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 rectifier circuit is connected in series and / or in parallel.

[0090] According to an embodiment of the present application, Figure 2 The flexible AC interconnection device shown further includes at least one valve control unit, and the rectifier inverter module and the reactive module include a module control unit. The valve control unit communicates with the module control units of the rectifier inverter module and the reactive module.

[0091] In some embodiments, Figure 5 As shown, the through-current blocking module 3 further includes a driving isolation circuit 11, which is used to receive an external driving signal and control the on and off of the power semiconductor device in the through-current blocking module 3 after potential isolation. The external driving signal comes from the valve control unit of the flexible AC interconnection device or the module control unit 12 of the rectifier inverter module.

[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 supply at ground potential is connected to a conductor and short-circuited at the end; the conductor passes through a series CT, and the output of the series CT is rectified; wherein the series CT refers to connecting the output ends of two or more current transformers together, and the current signal output after the series connection is the algebraic sum of the output current signals of each current transformer after the series connection.

[0094] 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. Figure 6 shown.

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

[0096] according to Figure 2 In the embodiment shown, the rectifier inverter module is responsible for compensating the voltage difference at both ends of the output voltage, and adjusts the current flowing through the device by changing the amplitude and phase of the output voltage; the current blocking module is usually bypassed and has very low loss itself. In the event of a fault, it provides voltage to block the current flowing through the device, and the device operates flexibly and efficiently.

[0097] In some other embodiments, the AC ends of at least two first diode full-bridge rectifier circuits are connected in series, and the current-passing loop is connected in parallel to the AC end series branches of the at least two first diode full-bridge rectifier circuits. Figure 8As shown, the AC ends of the two first diode full-bridge rectifier circuits are connected in series, and the current-passing loop is connected in parallel to the series branch of the AC ends of the two first diode full-bridge rectifier circuits.

[0098] According to some other embodiments, the through-current circuit of the through-current 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 of IGBT, MOSFET, IGCT, GTO, bidirectional thyristor or mechanical switch connected in reverse series, such as Fig. 9 shown.

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

[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 isolation 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 isolation power supply is connected to the drive isolation circuit. The current blocking module and the rectifier inverter module are in the same series converter valve. Fig.11 As shown, in this embodiment, the current blocking module takes energy from the adjacent rectifier inverter module, avoiding the design difficulty of the energy supply under 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, the current blocking module further includes a rectifier unit and at least one isolated power supply, the rectifier unit is connected to a second diode full-bridge rectifier circuit 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 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. Fig.12 shown.

[0103] According to an embodiment of the present application, a modular flexible AC interconnection device is also proposed, including a phase-series converter valve, wherein the phase-series converter valve includes a rectifier inverter module, a reactive module and a flow blocking module connected in series. The rectifier inverter module is 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 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, 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, M is greater than or equal to 1.

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

[0105] According to some embodiments, the AC ports of the rectifier inverter module, reactive module and / or current blocking module are connected in parallel with bypass switches, wherein the number of bypass switches put into operation is adjusted to adjust the scale of the corresponding matrix. That is, when the bypass switch is closed, the rectifier inverter module, reactive 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 comprises 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-controlled unit includes a first valve-controlled unit and a second valve-controlled unit, wherein the first valve-controlled unit communicates with the module control units of the rectifier inverter module and the reactive module respectively; the second valve-controlled unit communicates with the flow blocking module; the first valve-controlled unit and the second valve-controlled 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 end or both ends of the series converter valves. That is, 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] Fig.13 A flow chart of a control method of a flexible AC interconnection device according to an exemplary embodiment of the present application is shown. Fig.13 The method shown comprises the 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 a normal working state. When the flexible AC interconnection device is working normally, step S1203 is executed; when the flexible AC interconnection device has an overvoltage fault, step S1205 is executed.

[0111] In step S1203, 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 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 the embodiments of the present application, in order to further improve the efficiency, Fig.13 The method shown also includes: when the flexible AC interconnection device is working normally, according to the calculated difference between the phase voltages of the two AC systems, and according to the DC voltage and modulation degree of the rectifier inverter module, the number of rectifier inverter modules to be put into use is determined, and the remaining rectifier inverter modules are controlled to close the bypass switch or turn on the bidirectional thyristor; 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 or the bidirectional thyristor is turned off. According to some embodiments, the current blocking module adopts a high-voltage design. In this embodiment, by reasonably allocating the ratio of the number of current blocking modules to the rectifier inverter modules, the voltage stress can be shared for the rectifier inverter module, and the rectifier inverter module is effectively protected. Since the current blocking module has a simple structure, low cost, and small footprint, the overall cost and footprint of the device are reduced overall.

[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 used to help understand the method and its core idea of ​​the present application. At the same time, changes or deformations 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 belong to the scope of protection of the present application. In summary, the content of this specification should not be construed as a limitation on 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 at least two of the 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 a 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 through-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; 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, and 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 cascaded in sequence; 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; Each of the reactive modules comprises a reactive full-bridge circuit and an energy storage capacitor connected in parallel on the DC side, and 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; Each of the current blocking modules comprises a first diode full-bridge rectifier circuit and a blocking capacitor connected in parallel to the DC end thereof, 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; 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.

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 a control and protection device, at least one valve control unit and a flexible AC interconnection device as claimed in any one of claims 1 to 11, 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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