Multi-port flexible interconnection device, ac-dc hybrid power transmission system and ac substation

Abstract

The application provides a multi-port flexible interconnection device, an AC-DC hybrid power transmission system and an AC substation. The multi-port flexible AC interconnection device comprises a common AC bus and a plurality of three-phase series units. One end of each three-phase series unit is electrically connected to the common AC bus, and the other end of each three-phase series unit is connected to an AC port. Each three-phase series unit comprises a plurality of split-phase series units. Each split-phase series unit comprises a series-connected reactor and a converter chain. According to some embodiments, the first type of AC feeder and / or the second type of AC feeder comprises a load and / or a new energy power source. The new energy power source comprises photovoltaic power, wind power and / or energy storage. According to the embodiments of the application, the converter chain is connected between the common AC bus and an AC power source, and the common AC bus is used as a center point, so that the multi-port AC interconnection is facilitated.

Description

[0001] This application claims priority to Chinese Patent Application No. 202410114545.9, filed on January 26, 2024, entitled "Multi-port Flexible Interconnection Device, AC / DC Hybrid Transmission System and AC Substation", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of flexible AC conversion technology, and more specifically, to a multi-port flexible interconnection device, an AC / DC hybrid power transmission system, and an AC substation. Background Technology

[0003] Flexible interconnection solutions enable interconnection and mutual support between power sources in different areas of the power system, allowing the power supply network to operate in a closed loop and improving the reliability of power supply for users.

[0004] Traditional power systems operate in a closed-loop manner based on dual power sources, 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, to further improve the reliability of power supply to users and better integrate renewable energy sources locally, the complexity of power supply networks, power source types, and load characteristics has increased. Dual-source interconnection can no longer meet application demands, and the need for multi-terminal interconnection between more than two power sources is gradually increasing.

[0005] Multi-terminal flexible interconnection can fully allocate energy between regions, offering better flexibility and reliability. However, existing flexible interconnection solutions have the following drawbacks:

[0006] (1) The AC-DC-AC converter connects the AC buses of the two power sources. The two converters back to back are isolated by a DC bus. The AC voltage amplitude and phase are adjusted on the AC side respectively, which can realize flexible loop connection. Since there is a common DC bus, the number of interconnection terminals can be increased by adding AC-DC converters. Although this scheme can realize multi-terminal interconnection in principle, the converter must withstand full voltage and full current when regulating power flow, and the cost, loss and footprint are relatively high.

[0007] (2) "CN115483683A Flexible AC Loop Device and System" is a series-parallel flexible interconnection scheme proposed by the applicant. Compared with the AC-DC-AC converter scheme, this scheme has significant advantages in cost, footprint, and efficiency when the amplitude and phase angle differences between the two connected power supply points are small, since the converter only carries a portion of the power. However, this scheme also has many drawbacks when extended to multi-terminal interconnection applications. For example, this scheme connects and regulates power in pairs for AC ports. When there are 2, 3, 4, or 5 AC ports, the required interconnection devices are 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 scheme is in a state of independent control, without unified power regulation measures, which can easily cause scheduling problems. For yet another example, this scheme is not conducive to capacity expansion. With N existing AC ports and the requirement that all ports have power regulation, each additional port requires N new interconnection devices, which is not economically efficient.

[0008] Therefore, in the existing technology, there is a lack of a multi-terminal interconnected device solution that simultaneously meets the requirements of flexibility and economy. Summary of the Invention

[0009] This application aims to provide 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-mentioned problems.

[0010] According to one aspect of this application, a multi-port flexible AC interconnection device is proposed, comprising a common AC bus and multiple three-phase series units, wherein one end of each three-phase series unit is electrically connected to the common AC bus and the other end leads out to an AC port, wherein each of the three-phase series units includes multiple phase-separated series units, and each phase-separated series unit includes a reactor and a converter chain connected in series.

[0011] According to some embodiments, the voltage vector frequencies of the AC port and / or common bus are the same; or the integral of the frequency change of the voltage vector of the AC port and / or common bus within the tolerance period is 0.

[0012] According to some embodiments, the voltage amplitude and phase of the common bus are established by adjusting the output voltage of the converter chain of any of the three-phase series units.

[0013] According to some embodiments, the converter chain includes multiple power modules connected in series, and the length of the tolerance period is proportional to the number of power modules.

[0014] According to some embodiments, the voltage amplitude of the common AC bus is the average value of the voltage amplitudes of the AC ports of the plurality of three-phase series units; the voltage phase angle of the common AC bus is the median value of the voltage phase angles of the AC ports of the plurality of three-phase series units.

[0015] 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, the third bridge circuit including power semiconductor devices and DC capacitors.

[0016] According to some embodiments, the DC terminals 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.

[0017] According to some embodiments, the AC terminal of the second bridge circuit is electrically connected to an external isolation power supply device, which provides mutually isolated AC power to the AC-DC-AC power submodule.

[0018] According to some embodiments, the isolated power supply unit includes a multi-winding transformer, the primary side of which 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.

[0019] 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. The DC side of the high-frequency full-bridge module is connected in parallel, and the AC side is electrically connected to the AC terminal of the AC-DC-AC power module through the high-frequency transformer.

[0020] According to some embodiments, the high-frequency full-bridge module includes power semiconductors and DC capacitors connected in a single-phase full-bridge configuration.

[0021] According to some embodiments, the converter chain includes a current 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 terminal of the diode rectifier bridge, wherein 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.

[0022] According to some embodiments, the commutation chain includes a current blocking module, which includes a diode rectifier bridge, and anti-parallel IGBTs are added to both ends of each diode in the upper or lower arm of the diode rectifier bridge.

[0023] According to some embodiments, the current blocking module further includes a mechanical switch connected in series with the AC terminal of the diode rectifier bridge.

[0024] According to some embodiments, the two ends of the DC capacitor of the current blocking module are connected in parallel with a discharge circuit. 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 isolating switch.

[0025] 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 circuit.

[0026] According to some embodiments, when the power semiconductor branch is turned on, the current blocking module is in the on-state; when the power semiconductor branch is turned off and the DC capacitor voltage rises, the current blocking module is in the blocking state; when the power semiconductor branch is turned off, and after the DC capacitor voltage rises and the mechanical switch is turned off, the current blocking module is in the off-state.

[0027] According to some embodiments, the multi-port flexible interconnect device further includes a startup unit connected in parallel to the common AC bus, wherein the startup unit includes a switch connected in a star configuration.

[0028] According to some embodiments, the converter chain is a series connection of multiple AC / DC power modules, each AC / DC power module consisting of four sets of power semiconductor devices and DC capacitors; the multi-port flexible interconnect device further includes a balance compensation unit, wherein the AC side of the balance compensation unit is directly connected to or electrically connected to the common AC bus via a transformer.

[0029] According to some embodiments, the balancing 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, wherein the chain structure includes a three-phase converter chain, and each phase converter 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.

[0030] According to some embodiments, 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 also 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 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 power generator.

[0031] According to some embodiments, the common AC busbar is connected to an external overvoltage protection device to ground, and the overvoltage protection device is connected across both ends of the converter chain.

[0032] According to some embodiments, the reactor is arranged on the AC port side, and the multi-port flexible interconnect device generates active power control commands and / or reactive power control commands based on the product of the reactor current and the voltage vector of the common AC bus.

[0033] According to some embodiments, the multi-port flexible interconnect device further includes a control module, which includes multiple subsystem controllers and a coordination controller. Each subsystem controller corresponds to one of the converter links. The subsystem controller generates active power commands and / or reactive power commands based on the voltage amplitude and phase of the common AC bus. The coordination controller controls the corresponding converter link based on the active power commands and / or the reactive power commands.

[0034] According to some embodiments, the coordination controller includes a current-source active power flow control mode, an impedance-source 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 converter chain. In the impedance-source active power flow control mode, the coordination controller indirectly controls the current flowing through the multi-port flexible interconnect device by modulating the output voltage of the converter chain to influence impedance distribution. 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.

[0035] According to some embodiments, in the current-source active power flow control mode, the coordinating controller is further configured to: set a control target and issue it to the subsystem controller, the control target including the active power command and / or reactive power command 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 converter chain; select any one of the three-phase series units, and control the output voltage of the selected three-phase series unit with the voltage vector of the common bus as the control target to establish the common bus voltage; control other subsystem controllers to control the current of the corresponding reactor according to the relationship between the voltage vector of the corresponding AC port and the voltage vector of the common bus, and according to the active power command and reactive power command.

[0036] According to one aspect of this application, an AC / DC hybrid power transmission system is proposed, comprising a multi-port flexible AC interconnection device as described above, and further comprising an AC-DC converter and / or a DC-AC converter, wherein the DC terminal of the AC-DC converter is led out and connected to a DC load and / or the DC terminal of the DC-AC converter; the AC terminal of the DC-AC converter is connected to another AC / DC hybrid power transmission system.

[0037] According to one aspect of this 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 serve as 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 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.

[0038] According to some embodiments, the first type of AC feeder and / or the second type of AC feeder include loads and / or renewable energy sources, wherein the renewable energy sources include photovoltaic, wind power, and / or energy storage. According to embodiments of this application, by connecting the converter chain between the common AC bus and the AC power source, with the AC bus as the central point, multi-port AC interconnection can be easily achieved.

[0039] According to other embodiments, by selecting one of the converter chains as the control execution unit, the voltage amplitude and phase of the common AC bus are controllable, greatly increasing the flexibility of the device's control. Furthermore, when the voltage amplitude and phase of the common AC bus are adjusted to the median values ​​of each AC port, the device achieves its optimal operating point, resulting in optimal economic efficiency.

[0040] According to other embodiments, by proposing the technical feature that the voltage vector frequencies of the AC ports and / or common buses are the same or that 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 during use, as well as the influencing factors of the tolerance period, are given so as to better exert the control effect of the device.

[0041] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this application. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. The above and other objectives, features, and advantages of this application will become more apparent by referring to the accompanying drawings and describing exemplary embodiments in detail.

[0043] Figure 1 A block diagram of a multi-port flexible AC interconnection device according to an example embodiment of this application is shown.

[0044] Figure 2 A device block diagram of an AC / DC hybrid power transmission system according to an example embodiment of this application is shown.

[0045] Figure 3 A block diagram of an AC substation according to an example embodiment of this application is shown.

[0046] Figure 4 A schematic diagram of a multi-port flexible AC interconnection device according to an example embodiment of this application is shown.

[0047] Figure 5 A schematic diagram of the structure of an AC-DC-AC power submodule according to an example embodiment of this application is shown.

[0048] Figure 6 A schematic diagram of an externally isolated power supply unit according to an example embodiment of this application is shown.

[0049] Figure 7 A schematic diagram of another AC-DC-AC power submodule according to an example embodiment of this application is shown.

[0050] Figure 8A A schematic diagram of a flow blocking module according to an example embodiment of this application is shown.

[0051] Figure 8B A schematic diagram of another flow-blocking module according to an example embodiment of this application is shown.

[0052] Figure 8C A schematic diagram of another flow-blocking module according to an example embodiment of this application is shown.

[0053] Figure 8D A schematic diagram of another flow-blocking module according to an example embodiment of this application is shown.

[0054] Figure 8E A schematic diagram of another flow-blocking module according to an example embodiment of this application is shown.

[0055] Figure 8F A schematic diagram of another flow-blocking module according to an example embodiment of this application is shown.

[0056] Figure 9 A schematic diagram of the structure of a startup unit according to an example embodiment of this application is shown.

[0057] Figure 10A A schematic diagram of the structure of a balance compensation unit according to an example embodiment of this application is shown.

[0058] Figure 10B A schematic diagram of another balance compensation unit according to an example embodiment of this application is shown.

[0059] Figure 11 A schematic diagram of another balance compensation unit according to an example embodiment of this application is shown.

[0060] Figure 12 A flowchart of a method for a current-source type active power flow control mode according to an example embodiment of this application is shown.

[0061] Figure 13 A schematic diagram of the structure of an AC substation according to an example embodiment of this application is shown. Detailed Implementation

[0062] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same drawings in the figures show the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0063] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, apparatus, or operations may be employed. In these cases, well-known structures, methods, apparatuses, implementations, materials, or operations will not be shown or described in detail.

[0064] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0065] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0066] The specific embodiments according to this application will now be described in detail with reference to the accompanying drawings.

[0067] Figure 1 A block diagram of a multi-port flexible AC interconnection device according to an example embodiment of this application is shown, such as Figure 1 The multi-port flexible AC interconnection device shown 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 out to an AC port.

[0068] According to some embodiments, the common AC busbar is connected to an external overvoltage protection device to ground, and the overvoltage protection device is connected across both ends of the converter chain.

[0069] According to embodiments of this application, each of the three-phase series units includes multiple phase-separated series units, and each phase-separated series unit includes a reactor and a converter chain connected in series.

[0070] In a specific embodiment, the reactor is arranged on the AC port side, and the multi-port flexible interconnection device generates active power control commands and / or reactive power control commands based on the product of the reactor current and the voltage vector of the common AC bus.

[0071] In some embodiments, the voltage vector frequencies of the AC port and / or common bus are the same; or the integral of the frequency change of the voltage vector of the AC port and / or common bus within the tolerance period is 0, as shown in Equation (1).

[0072]

[0073] Wherein, Δf(t) is a function of the frequency change over time, and the frequency change is the frequency difference between AC ports or the frequency difference between AC ports and the common bus.

[0074] According to an embodiment of this application, the converter chain includes multiple power modules connected in series, and the length of the tolerance period is proportional to the number of power modules. For example, the length of the tolerance period is the product of the total number of power modules and 2ms.

[0075] According to some embodiments, the voltage amplitude and phase of the common bus are established by adjusting the output voltage of the converter chain of any of the three-phase series units.

[0076] In a specific embodiment, the voltage amplitude of the common AC bus is the average value of the voltage amplitudes of the AC ports of the plurality of three-phase series units, and the voltage phase angle of the common AC bus is the median value of the voltage phase angles of the AC ports of the plurality of three-phase series units.

[0077] 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. The first bridge circuit and / or the second bridge circuit includes power semiconductor devices and DC capacitors.

[0078] In a specific embodiment, the DC terminals of the first bridge circuit and the second bridge circuit are connected in parallel, and the AC terminal of the second bridge circuit is electrically connected to an external isolation power supply device, which provides mutually isolated AC power to the AC-DC-AC power submodule.

[0079] In some embodiments, the isolated power supply unit includes a multi-winding transformer, the primary side of which 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.

[0080] In other embodiments, the isolated power supply unit includes multiple high-frequency isolated power supply modules. Each high-frequency isolated power supply module includes a high-frequency transformer and a high-frequency full-bridge module. The DC side of the high-frequency full-bridge module is connected in parallel, and the AC side is electrically connected to the AC terminal of the AC-DC-AC power module through the high-frequency transformer. The high-frequency full-bridge module includes power semiconductors and DC capacitors connected in a single-phase full-bridge configuration.

[0081] According to embodiments of this application, in some embodiments, the converter chain includes a current 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 terminal of the diode rectifier bridge, wherein 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.

[0082] According to some embodiments, the commutation chain includes a current blocking module, which includes a diode rectifier bridge, and anti-parallel IGBTs are added to both ends of each diode in the upper or lower arm of the diode rectifier bridge.

[0083] According to some embodiments, the current blocking module further includes a mechanical switch connected in series with the AC terminal of the diode rectifier bridge.

[0084] In other embodiments, a discharge circuit is connected in parallel across the two ends of the DC capacitor of the current blocking module. The discharge circuit includes a discharge resistor and a discharge switch connected in series, and the DC capacitor and the discharge circuit are connected in parallel and then connected in series with the isolating switch.

[0085] 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 circuit.

[0086] In a specific embodiment, when the power semiconductor branch is turned on, the current blocking module is in the on-state; when the power semiconductor branch is turned off and the DC capacitor voltage rises, the current blocking module is in the blocking state; when the power semiconductor branch is turned off, and after the DC capacitor voltage rises and the mechanical switch is disconnected, the current blocking module is in the disconnected state.

[0087] According to an embodiment of this application, the multi-port flexible interconnect device further includes a start-up unit connected in parallel to the common AC bus, wherein the start-up unit includes a switch connected in a star configuration.

[0088] According to other embodiments, the multi-port flexible interconnect device further 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.

[0089] In a specific embodiment, the balancing 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; and the AC-DC converter includes a modular multilevel converter, a two-level converter, and / or a three-level converter.

[0090] According to an embodiment of this application, the multi-port flexible interconnect device further includes a control module, which includes multiple subsystem controllers and a coordination controller. Each subsystem controller corresponds to a converter chain. The subsystem controller generates active power commands and / or reactive power commands based on the voltage amplitude and phase of the common AC bus. The coordination controller controls the corresponding converter chain based on the active power commands and / or the reactive power commands.

[0091] In some embodiments, the coordination controller includes a current-source active power flow control mode, an impedance-source 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 converter chain. In the impedance-source active power flow control mode, the coordination controller indirectly controls the current flowing through the multi-port flexible interconnect device by modulating the output voltage of the converter chain to influence impedance distribution. 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.

[0092] In a specific embodiment, under the current-source active power flow control mode, the coordinating controller first sets a control target and sends it to the subsystem controller. The control target includes the active power command and / or reactive power command of the AC port, as well as the amplitude and phase angle of the common bus voltage. Then, a startup step is executed, and the DC capacitor of the bridge circuit in the converter chain is charged. Next, any one of the three-phase series units is selected, and the output voltage of the selected three-phase series unit is controlled with the voltage vector of the common bus as the control target to establish the common bus voltage. Finally, other subsystem controllers are controlled to control the current of the corresponding reactors according to the relationship between the voltage vector of the corresponding AC port and the voltage vector of the common bus, based on the active power command and reactive power command.

[0093] according to Figure 1 The multi-port flexible interconnection device shown connects the converter chain between the common AC bus and the AC power source, with the AC bus as the central point, to facilitate multi-port AC interconnection. By selecting one of the converter chains as the control execution unit, the voltage amplitude and phase of the common AC bus are controllable, greatly increasing the device's control flexibility. Furthermore, when the voltage amplitude and phase of the common AC bus are adjusted to the median values ​​of each AC port, the device achieves its optimal operating point, resulting in optimal economic efficiency.

[0094] Figure 2 A block diagram of an AC / DC hybrid power transmission system according to an example embodiment of this application is shown, such as Figure 2 The AC / DC hybrid power transmission system includes the multi-port flexible AC interconnection device 201, AC / DC converter 203 and / or DC / AC converter 205 as described above.

[0095] According to an embodiment of this application, the DC terminal of the AC-DC converter is led out and connected to a DC load and / or the DC terminal of the DC-AC converter; the AC terminal of the DC-AC converter is connected to another AC-DC hybrid power transmission system.

[0096] Figure 3 A block diagram of an AC substation according to an example embodiment of this application is shown, such as... Figure 3 The AC substation includes the multi-port flexible AC interconnection device 301, the first type of AC feeder 303, and the second type of AC feeder 305 as described above.

[0097] According to the example in this application, any three-phase series unit in the multi-port flexible AC interconnection device serves as the main series unit, and the other three-phase series units serve as 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.

[0098] In a specific embodiment, the first type of AC feeder and / or the second type of AC feeder include loads and / or new energy sources, wherein the new energy sources include photovoltaic, wind power and / or energy storage.

[0099] Figure 4 A schematic diagram of a multi-port flexible AC interconnection device structure according to an example embodiment of this application is shown, such as... Figure 4 The multi-port flexible AC interconnection device shown includes a common AC bus L0, which connects one end of N three-phase series units 1, where N is an integer greater than or equal to 2; the other end of each three-phase series unit leads out an AC port.

[0100] The three-phase series unit includes three separate-phase series units 2; each separate-phase series unit includes a reactor 3 and a converter chain connected in series; the converter chain is composed of multiple power modules 4 connected in series to achieve stepless regulation of voltage or current.

[0101] In some embodiments, the voltage vector frequencies of the AC ports and / or the common bus are the same, or the integral of the frequency change of the voltage vector within the tolerance period T is 0.

[0102] 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 converter chain. 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).

[0103] Preferably, the voltage amplitude of the common bus is the average value of the voltage amplitude of the AC port of each three-phase series unit; the voltage phase angle of the common bus is the median value of the voltage phase angle of the AC port of each three-phase series unit.

[0104] In this implementation, such as Figure 4 As shown, the voltage U0 of the common bus satisfies formula (2).

[0105]

[0106] The power module includes AC-DC-AC power submodules, such as in some embodiments. Figure 5 As shown, the AC-DC-AC power submodule includes a first bridge circuit H1 and a second bridge circuit H2. The AC terminal of the first bridge circuit is defined as the primary side of the AC-DC-AC power module, and the AC terminal of the second bridge circuit is defined as the secondary side of the AC-DC-AC power module.

[0107] The DC terminals of the first bridge circuit H1 and the second bridge circuit H2 are connected in parallel; the AC terminal of the AC-DC-AC power module is connected to an external isolation power supply unit, which provides mutually isolated AC power to each AC-DC-AC power module.

[0108] In a specific embodiment, the first bridge circuit H1 and the second bridge circuit H2 are bridge circuits composed of power semiconductor devices and DC capacitors.

[0109] like Figure 5 As shown, the external isolation power 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 connected to the AC terminals of the second bridge circuit respectively.

[0110] In other embodiments, the external isolated power supply unit includes M high-frequency isolated power supply modules, such as... Figure 6 As shown, the high-frequency isolated power supply module consists of a high-frequency transformer T2 and a high-frequency full-bridge module H4. The DC side of the high-frequency full-bridge module is connected in parallel, and the AC side is connected to the AC terminal of the second bridge circuit via the high-frequency transformer. Figure 6 As shown, the high-frequency full-bridge module consists of four groups of power semiconductors and DC capacitors forming a single-phase full-bridge connection.

[0111] In other embodiments, such as Figure 7 As shown, 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.

[0112] According to an embodiment of this application, the converter chain in the multi-port flexible interconnect device further includes a current-blocking module, which comprises 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.

[0113] In some embodiments, the power semiconductor branch is connected in parallel to the AC terminal of the diode rectifier bridge, such as... Figure 8A As shown.

[0114] In other embodiments, the power semiconductor branch of the current-blocking module can also be connected in parallel to the DC terminal of the diode full-bridge rectifier bridge, such as... Figure 8B As shown.

[0115] In other embodiments, the current-pass blocking module includes a diode rectifier bridge, and anti-parallel IGBTs are added across each diode in the upper or lower arm of the diode rectifier bridge. For example... Figure 8C and Figure 8D As shown.

[0116] In other embodiments, the power semiconductor branch includes at least one power semiconductor device. In this embodiment, the at least one power semiconductor device is further connected in series with a current-limiting loop. For example... Figure 8E As shown, the current limiting circuit includes a current limiting resistor 35 and a current limiting bypass switch 34 connected in parallel.

[0117] In some embodiments, the current-blocking module further includes a mechanical switch, wherein the mechanical switch is connected in series with the AC terminal of the diode rectifier bridge, such as... Figure 8A As shown.

[0118] In some other specific embodiments, a discharge circuit is also connected in parallel across the DC capacitor of the current-pass blocking module. For example... Figure 8F As shown, the discharge circuit includes a discharge resistor 33 and a discharge switch 32 connected in series. The DC capacitor is connected in parallel with the discharge circuit and then connected in series with the isolating switch 31.

[0119] In a specific embodiment, the current blocking module includes three working states: on, blocking, and disconnection. The on state is achieved by controlling the power semiconductor branch to conduct; the blocking state is achieved by controlling the power semiconductor branch to close and then raising the DC capacitor voltage; and the disconnection state is achieved by controlling the power semiconductor branch to close, raising the DC capacitor voltage, and then disconnecting the mechanical switch.

[0120] According to embodiments of this application, the multi-port flexible interconnect device further includes a startup unit, such as... Figure 9 As shown, the starting unit 5 is connected in parallel to the common AC bus, and the starting unit 5 includes a switch connected in a star configuration.

[0121] According to other embodiments of this application, the converter chain is a series connection of multiple AC / DC power modules, each AC / DC power module consisting of four sets of power semiconductor devices and a DC capacitor. The multi-port flexible interconnect device further 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.

[0122] In some embodiments, the balancing 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, wherein the chain structure includes a three-phase converter chain, and each phase converter 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. Figure 10A The diagram shown is a star-connected chain structure of the reactive power generator 6.

[0123] In other embodiments, the DC capacitor in the AC / DC power module of the reactive power generator is also connected to the power supply unit or the energy storage unit.

[0124] For example, 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;

[0125] For example, the energy storage unit is electrically connected to the DC capacitor in the AC / DC power module of the reactive power generator.

[0126] Figure 10B A schematic diagram of another balance compensation unit according to an example embodiment of this application is shown, as follows: Figure 10B This embodiment uses an external multi-winding transformer 61, with the secondary side of the multi-winding transformer 61 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.

[0127] In some embodiments, the AC-DC converter includes a modular multilevel converter, a two-level converter, and / or a three-level converter. For example... Figure 11 The AC-DC converter 7 shown is a schematic diagram of a three-level converter.

[0128] In a specific embodiment, the common AC bus is connected to ground via an overvoltage protection device, the two ends of the converter chain are connected to an external overvoltage protection device, the reactor is arranged on the AC port side, and the active power and reactive power control commands of the device are corresponding to the vector product of the reactor current and the three-phase common AC bus voltage.

[0129] According to an embodiment of this application, the multi-port flexible interconnect device includes a control module, which comprises N subsystem controllers and a coordination controller. The coordination controller communicates with the N subsystem controllers, providing the voltage amplitude and phase of a common AC bus, and issuing active power and / or reactive power commands for the N AC ports. Each of the N subsystem controllers corresponds one-to-one with one of the N converter links, and controls the corresponding converter link according to the received commands.

[0130] In a specific embodiment, the control module includes a current-source active power flow control mode, an impedance-type active power flow control mode, a reactive power control mode, and a voltage control mode. Specifically, the current-source active power flow control mode directly controls the reactor current by modulating the converter chain output voltage; the impedance-type active power flow control mode indirectly controls the current flowing through the device by modulating the converter chain output voltage to influence the system impedance distribution; the reactive power control mode modulates the converter chain output voltage with the reactive power at the AC port as the target; and the voltage control mode modulates the converter chain output voltage with the common AC bus voltage or the voltage at any AC port as the target.

[0131] Figure 12 A flowchart illustrating a method for a current-source type active power flow control mode according to an example embodiment of this application is shown, as follows: Figure 12 As shown, in step S1201, the coordinating controller sets the control target and sends it to each subsystem controller.

[0132] In some embodiments, the control targets include the active power and / or reactive power of one or more ports, and the magnitude and phase angle of the common bus voltage.

[0133] In step S1203, the coordinating controller performs a startup step to charge the DC capacitor of the bridge circuit in the commutation chain.

[0134] In step S1205, any three-phase series unit is selected, and the output voltage of the selected three-phase series unit is controlled with the voltage vector of the common bus voltage as the control target to establish the common bus voltage.

[0135] In step S1207, the coordinating controller controls the other subsystem controllers to control the reactor current 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 and reactive power commands.

[0136] according to Figure 12The illustrated embodiment, based on the interconnection system control method of the device circuit structure, proposes multiple control modes to allow for adjustment and tuning according to actual application requirements in specific engineering applications. By combining the topology system and method of the multi-port flexible AC interconnection device, flexible control of the multi-port flexible AC interconnection device is achieved.

[0137] Figure 13 A schematic diagram of the structure of an AC substation according to an example embodiment of this application is shown, such as... Figure 13 The AC substation shown includes a multi-port flexible AC interconnection device, a first-type AC feeder, and a second-type AC feeder as described above. In the multi-port flexible AC interconnection device, any three-phase series unit is selected as the main series unit 11, and the other three-phase series units are selected as slave series units 12. Figure 13 As shown, 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 as the AC bus of the substation; one end of the secondary series unit is connected to the AC bus of the substation, and the other end is connected to the first type of AC feeder 13; the second type of AC feeder 14 is connected to the AC bus of the substation.

[0138] In some embodiments, the first type of AC feeder or the second type of AC feeder includes loads and new energy sources; the new energy sources include photovoltaic, wind power and energy storage.

[0139] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. Furthermore, any changes or modifications made by those skilled in the art based on the ideas of this application, and on the specific implementation methods and application scope of this application, are all within the scope of protection of this application. Therefore, the content of this specification should not be construed as a limitation of this 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 which is electrically connected to the common AC bus, and the other end of which leads out to an AC port, wherein: Each of the three-phase series units includes three separate-phase series units, and each separate-phase series unit includes a reactor and a converter chain connected in series. The converter chain includes multiple power modules connected in series. The power module includes an AC-DC-AC power submodule or an AC-DC power module, and The AC-DC-AC power submodule includes a first bridge circuit and / or a second bridge circuit, and the AC-DC power module includes a third bridge circuit, which includes power semiconductor devices and DC capacitors. The integral of the frequency change of the voltage vector of the AC port and / or common bus within the tolerance period is 0, and the length of the tolerance period is the product of the total number of power modules and 2ms. The voltage amplitude and phase of the common bus are established by adjusting the output voltage of the converter chain of any of the three-phase series units; The voltage amplitude of the common AC bus is the average value of the voltage amplitudes of the AC ports of the plurality of three-phase series units; The voltage phase angle of the common AC bus is the median value of the voltage phase angle of the AC ports of the multiple three-phase series units.

2. The multi-port flexible AC interconnection device as described in claim 1, characterized in that, The DC terminals 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.

3. The multi-port flexible AC interconnection device as described in claim 1, characterized in that, The AC terminal of the second bridge circuit is electrically connected to an external isolation power supply device, which provides mutually isolated AC power to the AC-DC-AC power submodule.

4. The multi-port flexible AC interconnection device as described in claim 3, characterized in that, The isolated power supply device 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.

5. The multi-port flexible AC interconnection device as described in claim 3, characterized in that, The isolated power supply device 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 side of the high-frequency full-bridge module is connected in parallel, and the AC side is electrically connected to the AC terminal of the AC-DC-AC power submodule through the high-frequency transformer.

6. The multi-port flexible AC interconnection device as described in claim 5, characterized in that, The high-frequency full-bridge module includes power semiconductors and DC capacitors connected in a single-phase full-bridge configuration.

7. The multi-port flexible AC interconnection device as described in claim 1, characterized in that, The converter chain includes a current-blocking module, which comprises 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, and 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.

8. The multi-port flexible AC interconnection device as described in claim 1, characterized in that, The converter chain includes a current blocking module, which includes a diode rectifier bridge, and anti-parallel IGBTs are added to both ends of each diode in the upper or lower arm of the diode rectifier bridge.

9. The multi-port flexible AC interconnection device as described in claim 7, characterized in that, The current-pass blocking module also includes a mechanical switch, which is connected in series with the AC terminal of the diode rectifier bridge.

10. The multi-port flexible AC interconnection device as described in claim 7, characterized in that, The DC capacitor of the current-passing blocking module is connected in parallel with a discharge circuit. 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 isolating switch.

11. The multi-port flexible AC interconnection device according to claim 7, 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.

12. The multi-port flexible AC interconnection device as described in claim 9, characterized in that, When the power semiconductor branch is turned on, the current blocking module is in the on-state operation. When the power semiconductor branch is closed and the DC capacitor voltage rises, the current blocking module is in the blocking operation state. When the power semiconductor branch is closed, and after the DC capacitor voltage rises and the mechanical switch is disconnected, the current blocking module is in the disconnected working state.

13. The multi-port flexible AC interconnection device as described in claim 1, characterized in that, The multi-port flexible AC interconnection device also includes a start-up unit, which is connected in parallel to the common AC bus, wherein the start-up unit includes a switch connected in a star configuration.

14. The multi-port flexible AC interconnection device as described in claim 1, characterized in that, The converter chain is a series connection of multiple AC / DC power modules, each consisting of four sets of power semiconductor devices and a DC capacitor; the multi-port flexible AC 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.

15. The multi-port flexible AC interconnection device as described in claim 14, characterized in that, The balancing 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, wherein the chain structure includes a three-phase converter chain, and each phase converter chain in the reactive power generator is formed by cascading AC and DC power modules. The AC-DC converter includes a modular multilevel converter, a two-level converter, and / or a three-level converter.

16. The multi-port flexible AC interconnection device as described in claim 15, characterized in that, The AC / DC power module in the reactive power generator includes a DC capacitor, and the DC capacitor in the AC / DC power module of the reactive power 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. 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 of the reactive power generator.

17. The multi-port flexible AC interconnection device as described in claim 1, characterized in that, The common AC busbar is connected to an external overvoltage protection device, and the overvoltage protection device is connected across both ends of the converter chain.

18. The multi-port flexible AC interconnection device as described in claim 1, characterized in that, The reactor is arranged on the AC port side, and the multi-port flexible AC interconnection device generates active power control commands and / or reactive power control commands based on the product of the current of the reactor and the voltage vector of the common AC bus.

19. The multi-port flexible AC interconnection device as described in claim 1, characterized in that, The multi-port flexible AC interconnection device further includes a control module, which includes multiple subsystem controllers and a coordination controller. Each subsystem controller corresponds to one of the converter links. The subsystem controller generates active power commands and / or reactive power commands based on the voltage amplitude and phase of the common AC bus. The coordination controller controls the corresponding converter link based on the active power commands and / or the reactive power commands.

20. The multi-port flexible AC interconnection device as described in claim 19, characterized in that, The coordination controller includes current-source active power flow control mode, impedance-source active power flow control mode, reactive power control mode, and / or voltage control mode, wherein... In the current source type active power flow control mode, the coordination controller directly controls the current of the reactor by modulating the output voltage of the converter chain; In the impedance-type active power flow control mode, the coordination controller modulates the output voltage of the converter chain to affect the impedance distribution, thereby indirectly controlling the current flowing through the multi-port flexible AC interconnect 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.

21. The multi-port flexible AC interconnection device as described in claim 20, characterized in that, In the current-source type active power flow control mode, the coordination controller is further configured as follows: Set control targets and send them to the subsystem controller. The control targets include the active power command and / or reactive power command of the AC port, as well as the amplitude and phase angle of the common bus voltage. Perform the startup steps and charge the DC capacitor of the bridge circuit in the converter chain; Select any of the three-phase series units, and use the voltage vector of the common bus as the control target to control the output voltage of the selected three-phase series unit in order to establish the common bus voltage; The controllers of other subsystems control the current of the corresponding reactors based on the relationship between the voltage vector of the corresponding AC port and the voltage vector of the common bus, and based on the active power command and reactive power command.

22. A hybrid AC / DC power transmission system, characterized in that, The device includes the multi-port flexible AC interconnection device as described in any one of claims 1 to 21, and further includes an AC-DC converter and / or a DC-AC converter, wherein, The DC terminal of the AC-DC converter is led out and connected to the DC load and / or the DC terminal of the DC-AC converter; The AC terminal of the DC-AC converter is connected to another AC-DC hybrid power transmission system.

23. An AC substation, characterized in that, Includes the multi-port flexible AC interconnection device as described in any one of claims 1 to 21, 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 the master series unit, and the other three-phase series units serve as 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. The AC busbar of the AC substation is connected from one end of the series unit, and the other end is connected to the first type of AC feeder; The second type of AC feeder is connected to the AC busbar of the AC substation.

24. The AC substation as described in claim 23, characterized in that, The first type of AC feeder and / or the second type of AC feeder include loads and / or new energy sources, wherein the new energy sources include photovoltaic, wind power and / or energy storage.

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