Multi-port flexible interconnection apparatus, alternating-current and direct-current hybrid power transmission system and alternating-current transformer substation

Abstract

A multi-port flexible alternating-current interconnection apparatus, an alternating-current and direct-current hybrid power transmission system and an alternating-current transformer substation. The multi-port flexible alternating-current interconnection apparatus comprises a common alternating-current bus and a plurality of three-phase series-connection units. One end of a three-phase series-connection unit is electrically connected to the common alternating-current bus, and the other end thereof leads out an alternating-current port. Each three-phase series-connection unit comprises a plurality of split-phase series-connection units, each split-phase series-connection unit comprising a reactor and a converter chain which are connected in series. By connecting the converter chains between the common alternating-current bus and an alternating-current power supply and using the common alternating-current bus as a center point, multi-port alternating-current interconnection can be conveniently achieved.

Description

Multi-port flexible interconnection device, AC / DC hybrid transmission system and AC substation Technical Field

[0001] The present application relates to the field of flexible AC conversion technology, and in particular to a multi-port flexible interconnection device, an AC / DC hybrid power transmission system, and an AC substation. Background Art

[0002] The flexible interconnection solution can achieve mutual connection and support between power sources in different areas of the power system, enable closed operation of the power supply network, and improve the power supply reliability of users.

[0003] Traditional power systems operate in a closed-loop mode, relying on dual power sources. This involves connecting lines, transformers, or circuit breakers to form a closed network, similar to a "hand-in-hand" power supply network. With the development of new power systems, the complexity of power supply networks, power source types, and load characteristics has increased to further improve user power supply reliability and better accommodate renewable energy. Dual-source interconnection is no longer sufficient for these applications, and the demand for multi-terminal interconnection between more than two sources is growing.

[0004] Multi-terminal flexible interconnection can fully allocate energy between regions, with better flexibility and reliability. However, existing flexible interconnection solutions have the following drawbacks:

[0005] (1) The AC-DC-AC converter connects the AC buses of the two power supplies. The two back-to-back converters are isolated by a DC bus. The AC side adjusts the AC voltage amplitude and phase separately to achieve flexible loop closing. Since there is a common DC bus, the number of interconnected terminals can be increased by adding AC-DC converters. Although this solution can achieve multi-terminal interconnection in principle, when regulating the current, the converter must withstand full voltage and full current, which results in high cost, loss and space occupation.

[0006] (2) "CN115483683A Flexible AC Loop Closing Device and System" is a series-parallel flexible interconnection solution proposed by the applicant. Compared with the AC-DC converter solution, this solution has significant advantages in cost, space and efficiency when the amplitude difference and phase angle difference between the two connected power points are small, because the converter only flows through part of the power. However, this solution also has many disadvantages when it is expanded to multi-terminal interconnection applications. For example, this solution connects and regulates the power of AC ports in pairs. When the number of AC ports is 2, 3, 4 or 5, the number of interconnection devices required is 2, 3, 6 or 9 respectively. Therefore, as the number of connected AC ports increases, the number of interconnection devices increases significantly. For another example, this solution is in a state of independent control in terms of control, and there is no unified power control measure, which easily causes scheduling problems. For another example, this solution is not conducive to capacity expansion and access. If there are N AC ports and all ports are required to have power control, each additional port requires N new interconnection devices, which is less economical.

[0007] Therefore, in the prior art, there is a lack of a multi-terminal interconnection device solution that meets the requirements of flexibility and economy at the same time. Summary of the Invention

[0008] The present application aims to propose a multi-port flexible interconnection device, an AC / DC hybrid power transmission system and an AC substation to solve at least one of the above problems.

[0009] According to one aspect of the present application, a multi-port flexible AC interconnection device is proposed, comprising a common AC bus and a plurality of three-phase series units, wherein one end of the three-phase series unit is electrically connected to the common AC bus and the other end leads to an AC port, wherein: each of the three-phase series units comprises a plurality of split-phase series units, and each of the split-phase series units comprises a reactor and a commutation chain connected in series.

[0010] According to some embodiments, the voltage vectors of the AC ports and / or the common bus have the same frequency; or the integral of the frequency change of the voltage vectors of the AC ports and / or the common bus within a tolerance period is zero.

[0011] According to some embodiments, the voltage amplitude and phase of the common bus are established by adjusting the output voltage of a commutation chain of any one of the three-phase series units.

[0012] According to some embodiments, the commutation chain includes a plurality of power modules connected in series, and the length of the tolerance period is proportional to the number of the power modules.

[0013] According to some embodiments, the voltage amplitude of the common AC bus is the average voltage amplitude of the AC ports of the multiple three-phase series units; the voltage phase angle of the common AC bus is the middle value of the voltage phase angles of the AC ports of the multiple three-phase series units.

[0014] According to some embodiments, the power module includes an AC-DC-AC power submodule or an AC-DC power module, wherein the AC-DC-AC power module includes a first bridge circuit and / or a second bridge circuit; the AC-DC power module includes a third bridge circuit, and the third bridge circuit includes a power semiconductor device and a DC capacitor.

[0015] According to some embodiments, DC ends of the first bridge circuit and the second bridge circuit are connected in parallel, wherein the first bridge circuit and / or the second bridge circuit include power semiconductor devices and DC capacitors.

[0016] According to some embodiments, the AC end of the second bridge circuit is electrically connected to an external isolated power supply device, and the external isolated power supply device provides mutually isolated AC power for the AC-DC-AC power sub-modules.

[0017] According to some embodiments, the isolated energy supply unit includes a multi-winding transformer, the primary side of the multi-winding transformer is connected to the AC port of the three-phase series unit or an external AC power supply, and the secondary side is electrically connected to the AC end of the second bridge circuit.

[0018] According to some embodiments, the isolated power supply unit includes multiple high-frequency isolated power supply modules, each of which includes a high-frequency transformer and a high-frequency full-bridge module, wherein the DC side of the high-frequency full-bridge module is connected in parallel, and the AC side is electrically connected to the AC end of the AC-DC power module through the high-frequency transformer.

[0019] According to some embodiments, the high-frequency full-bridge module includes power semiconductors and DC capacitors connected in a single-phase full-bridge connection.

[0020] According to some embodiments, the commutation chain includes a current blocking module, which includes a power semiconductor branch, a diode rectifier bridge and a DC capacitor, and the DC capacitor is connected in parallel to the DC end of the diode rectifier bridge, wherein the power semiconductor branch is connected in parallel to the AC end of the diode rectifier bridge; or the power semiconductor branch is connected in parallel to the DC end of the diode rectifier bridge.

[0021] According to some embodiments, the commutation chain includes a flow blocking module, the flow blocking module includes a diode rectifier bridge, and anti-parallel IGBTs are added at both ends of each diode in the upper arm or the lower arm of the diode rectifier bridge.

[0022] According to some embodiments, the current blocking module further includes a mechanical switch, and the mechanical switch is connected in series with the AC end of the diode rectifier bridge.

[0023] According to some embodiments, a discharge circuit is connected in parallel at both ends of the DC capacitor of the current blocking module. The discharge circuit includes a discharge resistor and a discharge switch connected in series. The DC capacitor and the discharge circuit are connected in parallel and then connected in series with the isolation switch.

[0024] According to some embodiments, the power semiconductor branch includes at least one power semiconductor device, and the at least one power semiconductor device is connected in series with a current limiting loop.

[0025] According to some embodiments, when the power semiconductor branch is turned on, the current blocking module is in the on-state working state; when the power semiconductor branch is turned off and the DC capacitor voltage is raised, the current blocking module is in the blocking working state; when the power semiconductor branch is turned off and the DC capacitor voltage is raised and the mechanical switch is disconnected, the current blocking module is in the disconnecting working state.

[0026] According to some embodiments, the multi-port flexible interconnection device further includes a starting unit connected in parallel to the common AC bus, wherein the starting unit includes switches connected in a star manner.

[0027] According to some embodiments, the commutation chain is a series connection of multiple AC and DC power modules, and the AC and DC power modules are composed of four groups of power semiconductor devices and DC capacitors; the multi-port flexible interconnection device also includes a balancing compensation unit, wherein the AC side of the balancing compensation unit is directly connected to or electrically connected to the common AC bus via a transformer.

[0028] According to some embodiments, the balancing compensation unit includes a reactive generator and / or an AC-DC converter, wherein the reactive generator includes a star-connected or delta-connected chain structure, wherein the chain structure includes a three-phase commutation chain, and each phase commutation chain in the reactive generator is formed by cascading AC-DC power modules; the AC-DC converter includes a modular multilevel converter, a two-level converter and / or a three-level converter.

[0029] According to some embodiments, the AC / DC power module in the reactive generator includes a DC capacitor, and the DC capacitor in the AC / DC power module in the reactive generator is also connected to a power supply unit or an energy storage unit, wherein: the power supply unit includes a multi-winding transformer and a rectifier bridge, and the secondary side of the multi-winding transformer is connected to the DC capacitor of the AC / DC power module via the rectifier bridge; or the energy storage unit is electrically connected to the DC capacitor in the AC / DC power module in the reactive generator.

[0030] According to some embodiments, the common AC bus is connected to an external overvoltage protection device relative to the ground, and the overvoltage protection device is connected across both ends of the commutation chain.

[0031] According to some embodiments, the reactor is arranged on the AC port side, and the multi-port flexible interconnection device generates an active power control instruction and / or a reactive power control instruction according to the product of the reactor current and the voltage vector of the common AC bus.

[0032] According to some embodiments, the multi-port flexible interconnection device further includes a control module, which includes multiple subsystem controllers and a coordination controller, wherein the subsystem controllers correspond one-to-one to the commutation chains, the subsystem controllers generate active power instructions and / or reactive power instructions based on the voltage amplitude and phase of the common AC bus, and the coordination controller controls the corresponding commutation chain based on the active power instructions and / or the reactive power instructions.

[0033] According to some embodiments, the coordinated controller includes a current source type active power flow control mode, an impedance type active power flow control mode, a reactive power control mode and / or a voltage control mode, wherein, in the current source type active power flow control mode, the coordinated controller directly controls the reactor current by modulating the output voltage of the commutation chain; in the impedance type active power flow control mode, the coordinated controller modulates the output voltage of the commutation chain to affect the impedance distribution, thereby indirectly controlling the current flowing through the multi-port flexible interconnection device; in the reactive power control mode, the coordinated controller modulates the output voltage of the commutation chain with the reactive power of the AC port as the target; in the voltage control mode, the coordinated controller modulates the output voltage of the commutation chain with the voltage of the common AC bus or the voltage of any AC port as the target.

[0034] According to some embodiments, in the current source type active power flow control mode, the coordination controller is further configured to: set a control target and send it to the subsystem controller, the control target including the active power instruction and / or reactive power instruction of the AC port, and the amplitude and phase angle of the common bus voltage; execute a startup step and charge the DC capacitor of the bridge circuit in the commutation chain; select any one of the three-phase series units, use the voltage vector of the common bus as the control target, control the output voltage of the selected three-phase series unit to establish the common bus voltage; control other subsystem controllers to control the current of the corresponding inductor according to the relationship between the voltage vector of the corresponding AC port and the common bus voltage vector, and according to the active power instruction and reactive power instruction.

[0035] According to one aspect of the present application, an AC / DC hybrid power transmission system is proposed, comprising a multi-port flexible AC interconnection device as described in any of the foregoing, and further comprising an AC / DC converter and / or a DC / AC converter, wherein the DC end of the AC / DC converter is connected to a DC load and / or the DC end of the DC / AC converter; and the AC end of the DC / AC converter is connected to another AC / DC hybrid power transmission system.

[0036] According to one aspect of the present application, an AC substation is proposed, comprising a multi-port flexible AC interconnection device as described above, a first type of AC feeder, and a second type of AC feeder, wherein any three-phase series unit in the multi-port flexible AC interconnection device serves as a main series unit, and the other three-phase series units are slave series units, one end of the main series unit is connected to the incoming line of the AC substation, and the other end is connected to a public AC bus serving as the AC bus of the AC substation; one end of the slave series unit is connected to the AC bus of the AC substation, and the other end is connected to the first type of AC feeder; and the second type of AC feeder is connected to the AC bus of the AC substation.

[0037] According to some embodiments, the first-class AC feeder and / or the second-class AC feeder include loads and / or new energy sources, wherein the new energy sources include photovoltaic power, wind power, and / or energy storage. According to embodiments of the present application, by connecting the commutation chain between the common AC bus and the AC power source, with the AC bus as the center point, multi-port AC interconnection is facilitated.

[0038] According to other embodiments, by selecting one of the commutation chains as the control execution unit, the voltage amplitude and phase of the common AC bus can be controlled, greatly increasing the control flexibility of the device. Furthermore, when the voltage amplitude and phase of the common AC bus are adjusted to the intermediate values ​​of each AC port, the device achieves the optimal operating point and achieves optimal economic efficiency.

[0039] According to other embodiments, by proposing the technical feature that the voltage vector frequency of the AC port and / or the common bus is the same or the integral of the frequency change within the tolerance period T is 0, the frequency requirements that the multi-port flexible AC interconnection device needs to meet when in use and the influencing factors of the tolerance period are given, so as to better exert the control effect of the device.

[0040] 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

[0041] 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.

[0042] FIG1 shows a block diagram of a multi-port flexible AC interconnect device according to an exemplary embodiment of the present application.

[0043] FIG2 shows a device block diagram of an AC / DC hybrid power transmission system according to an exemplary embodiment of the present application.

[0044] FIG3 shows a device block diagram of an AC substation according to an exemplary embodiment of the present application.

[0045] FIG4 shows a schematic structural diagram of a multi-port flexible AC interconnect device according to an exemplary embodiment of the present application.

[0046] FIG5 shows a schematic structural diagram of an AC-DC-AC power submodule according to an exemplary embodiment of the present application.

[0047] FIG6 shows a schematic structural diagram of an external isolation energy supply unit according to an exemplary embodiment of the present application.

[0048] FIG7 shows a schematic structural diagram of another AC-DC-AC power submodule according to an exemplary embodiment of the present application.

[0049] FIG8A shows a schematic structural diagram of a flow blocking module according to an exemplary embodiment of the present application.

[0050] FIG8B shows a schematic structural diagram of another flow blocking module according to an exemplary embodiment of the present application.

[0051] FIG8C shows a schematic structural diagram of another flow blocking module according to an exemplary embodiment of the present application.

[0052] FIG8D shows a schematic structural diagram of another flow blocking module according to an exemplary embodiment of the present application.

[0053] FIG8E shows a schematic structural diagram of another flow blocking module according to an exemplary embodiment of the present application.

[0054] FIG8F shows a schematic structural diagram of another flow blocking module according to an exemplary embodiment of the present application.

[0055] FIG9 shows a schematic structural diagram of a starting unit according to an exemplary embodiment of the present application.

[0056] FIG10A shows a schematic structural diagram of a balance compensation unit according to an exemplary embodiment of the present application.

[0057] FIG10B shows a schematic structural diagram of another balance compensation unit according to an exemplary embodiment of the present application.

[0058] FIG11 shows a schematic structural diagram of another balance compensation unit according to an exemplary embodiment of the present application.

[0059] FIG12 shows a flow chart of a method for a current source type active power flow control mode according to an exemplary embodiment of the present application.

[0060] FIG13 shows a schematic structural diagram of an AC substation according to an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0066] Figure 1 shows a block diagram of a multi-port flexible AC interconnection device according to an exemplary embodiment of the present application. The multi-port flexible AC interconnection device shown in Figure 1 includes a common AC bus 101 and multiple three-phase series units 103. One end of each three-phase series unit is electrically connected to the common AC bus, and the other end leads to an AC port.

[0067] According to some embodiments, the common AC bus is connected to an external overvoltage protection device relative to the ground, and the overvoltage protection device is connected across both ends of the commutation chain.

[0068] According to an embodiment of the present application, each of the three-phase series units includes a plurality of split-phase series units, and each of the split-phase series units includes a reactor and a commutation chain connected in series.

[0069] In a specific embodiment, the reactor is arranged on the AC port side, and the multi-port flexible interconnection device generates an active power control instruction and / or a reactive power control instruction according to the product of the reactor current and the voltage vector of the common AC bus.

[0070] In some embodiments, the voltage vector frequencies of the AC port and / or the common bus are the same; or the integral of the frequency change of the voltage vector of the AC port and / or the common bus within the tolerance period is 0, as shown in formula (1).

[0071] Wherein, Δf(t) is a function of the frequency variation over time, and the frequency variation is the frequency difference between the AC ports or the frequency difference between the AC ports and the common bus.

[0072] According to an embodiment of the present application, the commutation chain includes multiple power modules connected in series, and the length of the tolerance period is proportional to the number of the power modules. For example, the length of the tolerance period is the product of the total number of power modules and 2ms.

[0073] According to some embodiments, the voltage amplitude and phase of the common bus are established by adjusting the output voltage of a commutation chain of any one of the three-phase series units.

[0074] In a specific embodiment, the voltage amplitude of the common AC bus is the average voltage amplitude of the AC ports of the multiple three-phase series units, and the voltage phase angle of the common AC bus is the middle value of the voltage phase angles of the AC ports of the multiple three-phase series units.

[0075] In some embodiments, the power module includes an AC-DC-AC power submodule, and the AC-DC-AC power module includes a first bridge circuit and / or a second bridge circuit, wherein the first bridge circuit and / or the second bridge circuit include power semiconductor devices and DC capacitors.

[0076] In a specific embodiment, the DC ends of the first bridge circuit and the second bridge circuit are connected in parallel, and the AC end of the second bridge circuit is electrically connected to an external isolation power supply device, which provides mutually isolated AC power for the AC-DC-AC power sub-modules.

[0077] In some embodiments, the isolated energy supply unit includes a multi-winding transformer, the primary side of the multi-winding transformer is connected to the AC port of the three-phase series unit or an external AC power supply, and the secondary side is electrically connected to the AC end of the second bridge circuit.

[0078] In other embodiments, the isolated power supply unit includes multiple high-frequency isolated power supply modules, each of which includes a high-frequency transformer and a high-frequency full-bridge module. The DC sides of the high-frequency full-bridge modules are connected in parallel, and the AC sides are electrically connected to the AC terminals of the AC-DC-AC power modules via the high-frequency transformer. The high-frequency full-bridge modules include power semiconductors and DC capacitors connected in a single-phase full-bridge configuration.

[0079] According to an embodiment of the present application, according to some embodiments, the commutation chain includes a current blocking module, the current blocking module includes a power semiconductor branch, a diode rectifier bridge and a DC capacitor, the DC capacitor is connected in parallel to the DC end of the diode rectifier bridge, wherein the power semiconductor branch is connected in parallel to the AC end of the diode rectifier bridge; or the power semiconductor branch is connected in parallel to the DC end of the diode rectifier bridge.

[0080] According to some embodiments, the commutation chain includes a flow blocking module, the flow blocking module includes a diode rectifier bridge, and anti-parallel IGBTs are added at both ends of each diode in the upper arm or the lower arm of the diode rectifier bridge.

[0081] According to some embodiments, the current blocking module further includes a mechanical switch, and the mechanical switch is connected in series with the AC end of the diode rectifier bridge.

[0082] In other embodiments, a discharge circuit is connected in parallel at both ends of the DC capacitor of the current blocking module, and the discharge circuit includes a discharge resistor and a discharge switch connected in series. The DC capacitor and the discharge circuit are connected in parallel and then connected in series with the isolation switch.

[0083] According to some embodiments, the power semiconductor branch includes at least one power semiconductor device, and the at least one power semiconductor device is connected in series with a current limiting loop.

[0084] In a specific embodiment, when the power semiconductor branch is turned on, the current blocking module is in the on-state working state; when the power semiconductor branch is turned off and the DC capacitor voltage is raised, the current blocking module is in the blocking working state; when the power semiconductor branch is turned off and the DC capacitor voltage is raised and the mechanical switch is disconnected, the current blocking module is in the disconnecting working state.

[0085] According to an embodiment of the present application, the multi-port flexible interconnection device further includes a starting unit, which is connected in parallel to the common AC bus, wherein the starting unit includes switches connected in a star manner.

[0086] According to some other embodiments, the multi-port flexible interconnection device further includes a balancing compensation unit, wherein an AC side of the balancing compensation unit is directly connected to the common AC bus or electrically connected to the common AC bus via a transformer.

[0087] In a specific embodiment, the balancing compensation unit includes a reactive generator and / or an AC-DC converter, wherein the reactive generator includes a star-connected or delta-connected chain structure; and the AC-DC converter includes a modular multilevel converter, a two-level converter and / or a three-level converter.

[0088] According to an embodiment of the present application, the multi-port flexible interconnection device also includes a control module, which includes multiple subsystem controllers and a coordination controller, wherein the subsystem controllers correspond one-to-one to the commutation chains, and the subsystem controllers generate active power instructions and / or reactive power instructions based on the voltage amplitude and phase of the common AC bus, and the coordination controller controls the corresponding commutation chain according to the active power instructions and / or the reactive power instructions.

[0089] In some embodiments, the coordination controller includes a current source active power flow control mode, an impedance active power flow control mode, a reactive power control mode, and / or a voltage control mode. In the current source active power flow control mode, the coordination controller directly controls the reactor current by modulating the output voltage of the commutation chain. In the impedance active power flow control mode, the coordination controller modulates the output voltage of the commutation chain to affect the impedance distribution, thereby indirectly controlling the current flowing through the multi-port flexible interconnection device. In the reactive power control mode, the coordination controller modulates the output voltage of the commutation chain based on the reactive power of the AC port. In the voltage control mode, the coordination controller modulates the output voltage of the commutation chain based on the voltage of the common AC bus or the voltage of any AC port.

[0090] In a specific embodiment, in the current source type active power flow control mode, the coordination controller first sets a control target and sends it to the subsystem controller, wherein the control target includes the active power instruction and / or reactive power instruction of the AC port, and the amplitude and phase angle of the common bus voltage; then, a startup step is performed, and the DC capacitor of the bridge circuit in the commutation chain is charged; then, any one of the three-phase series units is selected, and the voltage vector of the common bus is used as the control target to control the output voltage of the selected three-phase series unit to establish the common bus voltage; finally, other subsystem controllers are controlled to control the current of the corresponding inductor according to the relationship between the voltage vector of the corresponding AC port and the common bus voltage vector, and according to the active power instruction and the reactive power instruction.

[0091] The multi-port flexible interconnection device shown in Figure 1 connects a commutation chain between a common AC bus and an AC power source, with the AC bus as the center point, to facilitate multi-port AC interconnection. By selecting one of the commutation chains as the control execution unit, the voltage amplitude and phase of the common AC bus can be controlled, greatly increasing the device's control flexibility. When the voltage amplitude and phase of the common AC bus are adjusted to the midpoint between the values ​​of each AC port, the device achieves the optimal operating point and achieves optimal economic efficiency.

[0092] Figure 2 shows a device block diagram of an AC / DC hybrid power transmission system according to an exemplary embodiment of the present application. The AC / DC hybrid power transmission system shown in Figure 2 includes a multi-port flexible AC interconnection device 201, an AC / DC converter 203 and / or a DC / AC converter 205 as described above.

[0093] According to an embodiment of the present application, the DC end of the AC-DC converter is connected to a DC load and / or the DC end of the DC-AC converter; the AC end of the DC-AC converter is connected to another AC-DC hybrid power transmission system.

[0094] Figure 3 shows a device block diagram of an AC substation according to an exemplary embodiment of the present application. The AC substation shown in Figure 3 includes any of the multi-port flexible AC interconnection devices 301 described above, a first type AC feeder 303 and a second type AC feeder 305.

[0095] According to an example of the present application, any three-phase series unit in the multi-port flexible AC interconnection device serves as a master series unit, and the other three-phase series units serve as slave series units. One end of the master series unit is connected to the incoming line of the AC substation, and the other end is connected to a public AC busbar serving as the AC busbar of the AC substation; one end of the slave series unit is connected to the AC busbar of the AC substation, and the other end is connected to the first type of AC feeder; and the second type of AC feeder is connected to the AC busbar of the AC substation.

[0096] In a specific embodiment, the first type AC feeder and / or the second type AC feeder include loads and / or new energy power sources, and the new energy power sources include photovoltaic power, wind power and / or energy storage.

[0097] FIG4 shows a schematic structural diagram of a multi-port flexible AC interconnection device according to an exemplary embodiment of the present application. The multi-port flexible AC interconnection device shown in FIG4 includes a common AC busbar L0, which is connected to one end of N three-phase series units 1, where N is an integer greater than or equal to 2; and the other end of the three-phase series units leads to an AC port;

[0098] The three-phase series unit includes three split-phase series units 2; the split-phase series unit includes a reactor 3 and a commutation chain in series; the commutation chain is composed of multiple power modules 4 connected in series to achieve stepless voltage or current regulation.

[0099] In some embodiments, the voltage vector frequencies of the AC port and / or the common bus are the same or within a tolerance period T, the integral of the frequency change of the voltage vector is 0.

[0100] In a specific embodiment, any three-phase series unit is selected, and the amplitude and phase of the common bus voltage U0 are established by adjusting the output voltage of the three-phase series unit commutation chain. The value of the tolerance period T is proportional to the number of power modules, and the integral of the frequency change is 0, as shown in formula (1).

[0101] Preferably, the voltage amplitude of the common bus is the average value of the voltage amplitudes of the AC ports of the three-phase series units; the voltage phase angle of the common bus is the middle value of the voltage phase angles of the AC ports of the three-phase series units.

[0102] In this embodiment, as shown in FIG4 , the voltage U0 of the common bus satisfies formula (2).

[0103] The power module includes an AC / DC / AC power submodule. In some embodiments, as shown in FIG5 , the AC / DC / AC power submodule includes a first bridge circuit H1 and a second bridge circuit H2. The AC end of the first bridge circuit is defined as the primary side of the AC / DC / AC power module, and the AC end of the second bridge circuit is defined as the secondary side of the AC / DC / AC power module.

[0104] The DC ends of the first bridge circuit H1 and the second bridge circuit H2 are connected in parallel; the AC ends of the AC-DC-AC power modules are connected to an external isolation power supply unit, which provides mutually isolated AC power for each AC-DC-AC power module.

[0105] In a specific embodiment, the first bridge circuit H1 and the second bridge circuit H2 are bridge circuits formed by power semiconductor devices and DC capacitors.

[0106] As shown in FIG5 , the external isolated energy supply unit is a multi-winding transformer T1 , the primary side of the multi-winding transformer is connected to the AC port of the three-phase series unit or an external AC power supply, and the M secondary sides are correspondingly connected to the AC end of the second bridge circuit.

[0107] In other embodiments, the external isolated energy supply unit includes M high-frequency isolated energy supply modules, as shown in Figure 6. The high-frequency isolated energy supply module is composed of a high-frequency transformer T2 and a high-frequency full-bridge module H4. The DC sides of the high-frequency full-bridge modules are connected in parallel, and the AC sides are connected to the AC ends of the second bridge circuit via a high-frequency transformer. As shown in Figure 6, the high-frequency full-bridge module is composed of four groups of power semiconductors and DC capacitors to form a single-phase full-bridge connection.

[0108] In some other embodiments, as shown in Figure 7, the AC / DC power module includes a third bridge circuit H3. In a specific embodiment, the third bridge circuit is a bridge circuit composed of power semiconductor devices and DC capacitors.

[0109] According to an embodiment of the present application, the commutation chain in the multi-port flexible interconnection device further includes a flow blocking module, which includes a power semiconductor branch, a diode rectifier bridge, and a DC capacitor. The DC capacitor is connected in parallel to the DC end of the diode rectifier bridge.

[0110] In some embodiments, the power semiconductor branch is connected in parallel to the AC end of the diode rectifier bridge, as shown in FIG8A .

[0111] In other embodiments, the power semiconductor branch of the current blocking module may also be connected in parallel to the DC end of the diode full-bridge rectifier, as shown in FIG8B .

[0112] In other embodiments, the current blocking module includes a diode rectifier bridge, and anti-parallel IGBTs are added at both ends of each diode in the upper arm or lower arm of the diode rectifier bridge, as shown in FIG8C and FIG8D .

[0113] In other embodiments, the power semiconductor branch includes at least one power semiconductor device. The at least one power semiconductor device is further connected in series with a current limiting circuit. As shown in FIG8E , the current limiting circuit includes a current limiting resistor 35 and a current limiting bypass switch 34 connected in parallel.

[0114] In some embodiments, the current blocking module further includes a mechanical switch, wherein the mechanical switch is connected in series with the AC end of the diode rectifier bridge, as shown in FIG8A .

[0115] In other specific embodiments, a discharge circuit is further connected in parallel across the DC capacitor of the current blocking module. As shown in FIG8F , the discharge circuit includes a series connection of a discharge resistor 33 and a discharge switch 32 . The DC capacitor and the discharge circuit are connected in parallel and then connected in series with an isolation switch 31 .

[0116] In a specific embodiment, the current blocking module includes three working states: on, blocking and disconnecting; wherein, the on state is achieved by controlling the power semiconductor branch to be turned on; the blocking is achieved by controlling the power semiconductor branch to be turned off and the DC capacitor voltage to be raised; the disconnecting is achieved by controlling the power semiconductor branch to be turned off, the DC capacitor voltage to be raised, and the mechanical switch to be disconnected.

[0117] According to an embodiment of the present application, the multi-port flexible interconnection device further includes a starting unit. As shown in FIG9 , the starting unit 5 is connected in parallel to the common AC bus, and the starting unit 5 includes switches connected in a star manner.

[0118] According to other embodiments of the present application, the commutation chain comprises a series connection of multiple AC / DC power modules, each of which is composed of four groups of power semiconductor devices and DC capacitors. The multi-port flexible interconnect device further comprises a balancing and compensation unit, wherein the AC side of the balancing and compensation unit is electrically connected to the common AC bus directly or via a transformer.

[0119] In some embodiments, the balancing and compensation unit includes a reactive power generator and / or an AC / DC converter, wherein the reactive power generator comprises a star-connected or delta-connected chain structure, wherein the chain structure comprises a three-phase commutation chain, and each phase commutation chain in the reactive power generator is formed by cascading AC / DC power modules; the AC / DC converter comprises a modular multilevel converter, a two-level converter, and / or a three-level converter. The reactive power generator 6 shown in FIG10A is a schematic diagram of a star-connected chain structure.

[0120] In other embodiments, the DC capacitor in the AC / DC power module in the reactive generator is further connected to an energy supply unit or an energy storage unit.

[0121] For example, the energy supply unit includes a multi-winding transformer and a rectifier bridge, and the secondary side of the multi-winding transformer is connected to the DC capacitor of the AC / DC power module via the rectifier bridge;

[0122] For another example, the energy storage unit is electrically connected to the DC capacitor in the AC / DC power module in the reactive generator.

[0123] FIG10B shows a schematic diagram of the structure of another balance compensation unit according to an exemplary embodiment of the present application. FIG10B shows an embodiment in which an external multi-winding transformer 61 is connected, and the secondary side of the multi-winding transformer 61 is connected to a DC capacitor via a rectifier bridge 62. In practice, the primary side of the multi-winding transformer can be connected to an AC power source.

[0124] In some embodiments, the AC-DC converter includes a modular multi-level converter, a two-level converter and / or a three-level converter. The AC-DC converter 7 shown in FIG11 is a schematic diagram of connecting a three-level converter.

[0125] In a specific embodiment, the common AC bus is connected to the ground with an overvoltage protection device, external overvoltage protection devices are connected across both ends of the commutation chain, the reactor is arranged on the AC port side, and the active power and reactive power control instructions of the device corresponding to the vector product of the reactor current and the three-phase common AC bus voltage.

[0126] According to an embodiment of the present application, the multi-port flexible interconnect device includes a control module, which includes N subsystem controllers and a coordination controller. The coordination controller communicates with the N subsystem controllers, determines the voltage amplitude and phase of a common AC bus, and issues active power and / or reactive power commands for the N AC ports. The N subsystem controllers correspond one-to-one with the N commutation chains and control the corresponding commutation chains based on the received commands.

[0127] In a specific embodiment, the control module includes a current source active power flow control mode, an impedance active power flow control mode, a reactive power control mode, and a voltage control mode. The current source active power flow control mode directly controls the reactor current by modulating the commutation chain output voltage; the impedance active power flow control mode indirectly controls the current flowing through the device by modulating the commutation chain output voltage to affect the system impedance distribution; the reactive power control mode modulates the commutation chain output voltage with the AC port reactive power as the target; and the voltage control mode modulates the commutation chain output voltage with the common AC bus voltage or any AC port voltage as the target.

[0128] FIG12 shows a method flow chart of a current source type active power flow control mode according to an exemplary embodiment of the present application. As shown in FIG12 , in step S1201 , the coordination controller sets a control target and sends it to each subsystem controller.

[0129] In some embodiments, the control targets include active power and / or reactive power of one or more ports, and the amplitude and phase angle of the common bus voltage.

[0130] In step S1203 , the coordination controller executes a startup step to charge the DC capacitor of the bridge circuit in the commutation chain.

[0131] In step S1205 , any three-phase series unit is selected, and the voltage vector of the common bus voltage is used as a control target to control the output voltage of the selected three-phase series unit to establish the common bus voltage.

[0132] In step S1207, the coordination controller controls the remaining subsystem controllers to control the reactor currents on their respective branches according to the relationship between their respective sampled AC port voltage vectors and the common bus voltage vector and according to the allocated active power and reactive power instructions.

[0133] The embodiment shown in Figure 12 proposes a variety of control modes based on the interconnection system control method of the device circuit structure, allowing for adjustment and tuning based on actual application requirements in specific engineering applications. By combining the topology system and method of a multi-port flexible AC interconnect device, flexible control of the multi-port flexible AC interconnect device is achieved.

[0134] FIG13 shows a schematic structural diagram of an AC substation according to an exemplary embodiment of the present application. The AC substation shown in FIG13 includes a multi-port flexible AC interconnection device, a first-class AC feeder, and a second-class AC feeder as described above. Among them, any three-phase series unit is selected from the multi-port flexible AC interconnection device as the main series unit 11, and the other three-phase series units are selected as slave series units 12. As shown in FIG13 , one end of the main series unit is connected to the incoming line of the AC substation, and the other end is connected to the public AC bus as the substation AC bus; one end of the slave series unit is connected to the substation AC bus, and the other end is connected to the first-class AC feeder 13; the second-class AC feeder 14 is connected to the substation AC bus.

[0135] In some embodiments, the first type AC feeder or the second type AC feeder includes a load and a new energy power source; the new energy power source includes photovoltaic power, wind power, and energy storage.

[0136] 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 multi-port flexible AC interconnection device, characterized in that It includes a common AC bus and multiple three-phase series units, one end of each three-phase series unit is electrically connected to the common AC bus, and the other end leads out an AC port, where: Each of the three-phase series units includes multiple phase-split series units, and each of the phase-split series units includes a reactor and a commutation chain connected in series.

2. The multi-port flexible AC interconnection device according to claim 1, wherein the voltage vector frequencies of the AC port and / or the common bus are the same; or the integral of the frequency change of the voltage vector of the AC port and / or the common bus within the tolerance period is 0.

3. The multi-port flexible AC interconnection device according to claim 2, wherein, The voltage amplitude and phase of the common bus are established by adjusting the output voltage of the commutation chain of any one of the three-phase series units.

4. The multi-port flexible AC interconnection device according to claim 2, characterized in that, The commutation chain includes multiple series-connected power modules, and the length of the tolerance period is proportional to the number of the power modules.

5. The multi-port flexible AC interconnection device according to claim 1, wherein the voltage amplitude of the common AC bus is the average value of the voltage amplitudes of the AC ports of the multiple three-phase series units; the voltage phase angle of the common AC bus is the intermediate value of the voltage phase angles of the AC ports of the multiple three-phase series units.

6. The multi-port flexible AC interconnection device according to claim 4, wherein, The power module includes an AC-DC-AC power sub-module or an AC-DC power module, where the AC-DC-AC power module includes a first bridge circuit and / or a second bridge circuit; the AC-DC power module includes a third bridge circuit, and the third bridge circuit includes power semiconductor devices and a DC capacitor.

7. The multi-port flexible interconnection device according to claim 6, wherein The DC terminals of the first bridge circuit and the second bridge circuit are connected in parallel, where the first bridge circuit and / or the second bridge circuit includes power semiconductor devices and a DC capacitor.

8. The multi-port flexible interconnection device according to claim 6, characterized in that, The AC terminal of the second bridge circuit is electrically connected to an external isolated power supply device, and the external isolated power supply device provides mutually isolated AC power supplies for the AC-DC-AC power sub-module.

9. The multi-port flexible interconnection device according to claim 8, wherein The isolation power supply unit includes a multi-winding transformer, the primary side of the multi-winding transformer is connected to the AC port of the three-phase series unit or an external AC power supply, and the secondary side is electrically connected to the AC terminal of the second bridge circuit.

10. The multi-port flexible interconnection device according to claim 8, wherein, The isolation power supply unit includes multiple high-frequency isolation power supply modules, and each of the high-frequency isolation power supply modules includes a high-frequency transformer and a high-frequency full-bridge module, where the DC sides of the high-frequency full-bridge modules are connected in parallel, and the AC sides are electrically connected to the AC terminals of the AC-DC-AC power modules through the high-frequency transformers.

11. The multi-port flexible interconnection device according to claim 10, wherein, The high-frequency full-bridge module includes power semiconductors and a DC capacitor connected in a single-phase full-bridge connection manner.

12. The multi-port flexible interconnection device according to claim 1, characterized in that, The commutation chain includes a current flow blocking module, the current flow blocking module includes a power semiconductor branch, a diode rectifier bridge, and a DC capacitor, the DC capacitor is connected in parallel to the DC terminal of the diode rectifier bridge, where the power semiconductor branch is connected in parallel to the AC terminal of the diode rectifier bridge; or the power semiconductor branch is connected in parallel to the DC terminal of the diode rectifier bridge.

13. The multi-port flexible interconnection device according to claim 1, wherein The commutation chain includes a current flow blocking module, the current flow blocking module includes a diode rectifier bridge, and anti-parallel IGBTs are added to both ends of each diode in the upper bridge arm or the lower bridge arm of the diode rectifier bridge.

14. The multi-port flexible interconnection device according to claim 12, wherein The current flow blocking module further includes a mechanical switch, and the mechanical switch is connected in series with the AC terminal of the diode rectifier bridge.

15. The multi-port flexible interconnection device according to claim 12, characterized in that Both ends of the DC capacitor of the current flow blocking module are connected in parallel with a discharge circuit. The discharge circuit includes a discharge resistor and a discharge switch connected in series, and after the DC capacitor and the discharge circuit are connected in parallel, they are connected in series with the disconnector.

16. The multi-port flexible interconnection device according to claim 12, characterized in that, The power semiconductor branch includes at least one power semiconductor device, and the at least one power semiconductor device is connected in series with a current limiting circuit.

17. The multi-port flexible interconnection device according to claim 14, wherein When the power semiconductor branch is turned on, the current flow blocking module is in a conducting operating state; When the power semiconductor branch is turned off and the voltage of the DC capacitor rises, the current flow blocking module is in a blocking operating state; When the power semiconductor branch is turned off, and after the voltage of the DC capacitor rises and the mechanical switch is opened, the current flow blocking module is in an open operating state.

18. The multi-port flexible interconnection device according to claim 1, wherein, The multi-port flexible interconnection device further includes a starting unit, and the starting unit is connected in parallel to the common AC bus. Among them, the starting unit includes switches connected in a star configuration.

19. The multi-port flexible interconnection device according to claim 1, characterized in that The commutation chain is a series connection of multiple AC-DC power modules. The AC-DC power module is composed of four groups of power semiconductor devices and a DC capacitor; the multi-port flexible interconnection device further includes a balance compensation unit. Among them, the AC side of the balance compensation unit is directly connected or electrically connected to the common AC bus through a transformer.

20. The multi-port flexible interconnection device according to claim 19, wherein The balance compensation unit includes a reactive power generator and / or an AC-DC converter, wherein The reactive power generator includes a star-connected or delta-connected chain structure. Among them, the chain structure includes a three-phase commutation chain, and each phase commutation chain in the reactive power generator is formed by cascading AC-DC power modules; The AC-DC converter includes a modular multilevel converter, a two-level converter, and / or a three-level converter.

21. The multi-port flexible interconnection device according to claim 20, wherein The AC-DC power module in the reactive power generator includes a DC capacitor, and the DC capacitor in the AC-DC power module in the reactive power generator is further connected to an energy supply unit or an energy storage unit, wherein: The energy supply unit includes a multi-winding transformer and a rectifier bridge, and the secondary side of the multi-winding transformer is connected to the DC capacitor of the AC-DC power module through the rectifier bridge; or The energy storage unit is electrically connected to the DC capacitor in the AC-DC power module in the reactive power generator.

22. The multi-port flexible interconnection device according to claim 1, characterized in that, The common AC bus is connected to an external overvoltage protection device to the ground, and the overvoltage protection device is connected across both ends of the commutation chain.

23. The multi-port flexible interconnection device according to claim 1, characterized in that, The reactor is arranged on the AC port side, and the multi-port flexible interconnection device generates an active power control instruction and / or a reactive power control instruction according to the product of the reactor current and the voltage vector of the common AC bus.

24. The multi-port flexible interconnection device according to claim 1, wherein The multi-port flexible interconnection device further includes a control module, which includes a plurality of subsystem controllers and a coordination controller. Among them, the subsystem controllers correspond to the converter chains one by one. The subsystem controllers generate active power commands and / or reactive power commands according to the voltage amplitude and phase of the common AC bus, and the coordination controller controls the corresponding converter chain according to the active power commands and / or the reactive power commands.

25. The multi-port flexible interconnection device according to claim 24, wherein The coordination controller includes a current-source active power flow control mode, an impedance-type active power flow control mode, a reactive power control mode, and / or a voltage control mode. Among them, In the current-source active power flow control mode, the coordination controller directly controls the reactor current by modulating the output voltage of the converter chain. In the impedance-type active power flow control mode, the coordination controller affects the impedance distribution by modulating the output voltage of the converter chain, thereby indirectly controlling the current flowing through the multi-port flexible interconnection device. In the reactive power control mode, the coordination controller modulates the output voltage of the converter chain with the reactive power of the AC port as the target. In the voltage control mode, the coordination controller modulates the output voltage of the converter chain with the voltage of the common AC bus or the voltage of any AC port as the target.

26. The multi-port flexible interconnection device according to claim 25, characterized in that, In the current-source active power flow control mode, the coordination controller is further configured to: Set control targets and send them to the subsystem controllers. The control targets include the active power commands and / or reactive power commands of the AC port, as well as the amplitude and phase angle of the common bus voltage. Execute the startup procedure and charge the DC capacitors of the bridge circuits in the converter chain. Select any one of the three-phase series units, use the voltage vector of the common bus as the control target, and control the output voltage of the selected three-phase series unit to establish the common bus voltage. Control other subsystem controllers to control the current of the corresponding reactors according to the relationship between the voltage vectors of the corresponding AC ports and the voltage vector of the common bus, and according to the active power commands and reactive power commands.

27. A hybrid AC / DC power transmission system, characterized in that, Comprising the multi-port flexible AC interconnection device according to any one of claims 1 to 26, further including an AC-DC converter and / or a DC-AC converter. Among them, The DC side of the AC-DC converter is led out and connected to the DC load and / or the DC side of the DC-AC converter. The AC side of the DC-AC converter is connected to another AC-DC hybrid power transmission system.

28. An AC substation, characterized in that, Comprising the multi-port flexible AC interconnection device according to any one of claims 1 to 26, a first type of AC feeder, and a second type of AC feeder. Among them, any one of the three-phase series units in the multi-port flexible AC interconnection device is used as the main series unit, and the other three-phase series units are slave series units. One end of the main series unit is connected to the incoming line of the AC substation, and the other end is connected to the common AC bus, which serves as the AC bus of the AC substation. One end of the slave series unit is connected to the AC bus of the AC substation, and the other end is connected to the first type of AC feeder. The second type of AC feeder is connected to the AC bus of the AC substation.

29. The AC substation according to claim 28, wherein, The first type of AC feeder and / or the second type of AC feeder includes loads and / or new energy power sources, and the new energy power sources include photovoltaic, wind power, and / or energy storage.

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