A series distributed DC power dissipation device and a flexible DC system for offshore wind power

Abstract

This application discloses a series distributed DC energy dissipation device and an offshore wind power flexible DC system. The series distributed DC energy dissipation device provided in this application has a main circuit switch module and an energy dissipation valve module located between the submarine cable port and the overhead line port, connected in parallel. The energy dissipation valve module contains multiple energy dissipation valve units connected in series. Each energy dissipation valve unit includes an energy dissipation resistor and a switching element for controlling the switching on or off of the energy dissipation resistor. A control module is used to control the on / off state of the switching elements in the main circuit switch module and the energy dissipation valve module. When an overhead line fault occurs, the device controls the main circuit switch module to disconnect via the control module, allowing DC current to flow through the circuit containing the energy dissipation valve module. By controlling the number of energy dissipation resistors switched on and off in each energy dissipation valve unit, the total energy consumed by the energy dissipation circuit is controlled, achieving system surplus power balance.

Description

Technical Field

[0001] This application relates to the field of offshore wind power technology, and in particular to a series distributed DC energy dissipation device and an offshore wind power system. Background Technology

[0002] Offshore wind power, with its high utilization rate and abundant resource reserves, is rapidly becoming one of the key areas for current and future new energy development. As the scale of offshore wind power continues to expand and transmission distances increase, intensive and centralized unified development and utilization will be the main approach to utilizing offshore wind power in the future. Currently, offshore wind power is generally transmitted to onshore converter stations via submarine DC cables, and then converted from DC to AC by converters and integrated into the coastal power grid. However, with the rapid growth of offshore wind power development, this near-shore grid connection method is no longer suitable for future ultra-large-scale offshore wind power development scenarios. To further compress transmission corridors, reduce transmission costs, and avoid increasing short-circuit currents in near-shore power grids, direct transmission of offshore wind power to load centers via a hybrid submarine cable-overhead line DC transmission line will become one of the main methods for future ultra-large-scale offshore wind power development.

[0003] In existing offshore wind power flexible DC transmission projects, only DC submarine cables are generally used for power transmission, and parallel DC energy dissipation devices are used to achieve fault voltage regulation. The specific principle is: after a fault occurs in the receiving end of the power grid, the DC voltage rises, the parallel DC energy dissipation device starts, consumes the surplus power and maintains the DC voltage. However, this device is not suitable for offshore wind power flexible DC systems that combine submarine cables and overhead lines, which leads to the technical problem of low reliability in existing offshore wind power flexible DC systems that combine submarine cables and overhead lines. Summary of the Invention

[0004] This application provides a series distributed DC energy dissipation device and a flexible DC system for offshore wind power, which solves the technical problem of low reliability in existing flexible DC systems for offshore wind power that combine submarine cables and overhead lines.

[0005] To address the aforementioned technical problems, the first aspect of this application provides a series distributed DC energy dissipation device, comprising: a submarine cable port, an overhead line port, a main circuit switch module, an energy dissipation valve module, and a control module;

[0006] The main circuit switch module and the energy dissipation valve module are disposed between the submarine cable port and the overhead line port, and the main circuit switch module and the energy dissipation valve module are connected in parallel.

[0007] The energy-consuming valve module has multiple energy-consuming valve units connected in series. Each energy-consuming valve unit includes an energy-consuming resistor and a switching element for controlling the energy-consuming resistor to be switched on or off.

[0008] The control module is used to control the on / off state of the switching elements in the main circuit switch module and the energy-consuming valve module.

[0009] Preferably, the main circuit switch module specifically includes: a main circuit mechanical switch and a power electronic switch connected in series.

[0010] Preferably, the power electronic switch is a switch array composed of multiple SM sub-modules.

[0011] Preferably, the SM submodule is a full-bridge submodule.

[0012] Preferably, the energy dissipation valve unit specifically includes: a first diode, a first switching transistor, a dynamic voltage equalization resistor, an energy storage capacitor, a second diode, a second switching transistor, and an energy dissipation resistor;

[0013] The cathode of the first diode is connected to the first port of the energy dissipation valve unit, and the anode is connected to the second port of the energy dissipation valve unit;

[0014] The first switching transistor is connected in parallel with the first diode, and the anode of the first switching transistor is connected to the first port of the energy dissipation valve unit, and the cathode is connected to the second port of the energy dissipation valve unit.

[0015] The dynamic voltage equalizing resistor is connected in parallel with the second diode, and one end of the dynamic voltage equalizing resistor is connected in series with the anode of the second diode and the first port of the energy dissipation valve unit, and the other end of the dynamic voltage equalizing resistor is connected in series with the cathode of the second diode and the energy storage capacitor, and then connected to the second port of the energy dissipation valve unit to form an RCD buffer circuit.

[0016] The energy-consuming resistor and the second switching transistor are connected in series to form an energy-consuming resistor circuit, and the energy-consuming resistor circuit is connected in parallel with the RCD buffer circuit.

[0017] Preferably, the energy-consuming valve unit further includes: an energy-consuming valve bypass switch;

[0018] The energy-consuming valve bypass switch is used to control the activation or deactivation of the energy-consuming valve unit.

[0019] The second aspect of this application provides an offshore wind power flexible DC system, including: an offshore converter station, a terminal conversion station and an onshore converter station, wherein the terminal conversion station is equipped with a series distributed DC energy dissipation device as described in the first aspect of this application;

[0020] The offshore converter station is connected to the submarine cable port in the series distributed DC power dissipation device via a submarine cable.

[0021] The onshore converter station is connected to the overhead line port of the series distributed DC power dissipation device via an overhead line.

[0022] Preferably, the offshore converter station is a half-bridge MMC converter station.

[0023] Preferably, the onshore converter station is a hybrid MMC converter station consisting of a full-bridge and a half-bridge.

[0024] Preferably, the proportion of full-bridge submodules in the full-bridge / half-bridge hybrid MMC converter station is greater than 50%.

[0025] As can be seen from the above technical solutions, this application has the following advantages:

[0026] This application provides a series distributed DC energy dissipation device applicable to offshore wind power flexible DC systems with a hybrid submarine cable-overhead line configuration. The device includes: a submarine cable port, an overhead line port, a main circuit switch module, an energy dissipation valve module, and a control module. The main circuit switch module and the energy dissipation valve module are located between the submarine cable port and the overhead line port, and are connected in parallel. The energy dissipation valve module contains multiple energy dissipation valve units connected in series. Each energy dissipation valve unit includes an energy dissipation resistor and a switching element for controlling the switching on or off of the energy dissipation resistor. The control module controls the on / off state of the switching elements in the main circuit switch module and the energy dissipation valve module. When an overhead line fault occurs, the voltage at the overhead line port of the series distributed DC energy dissipation device is controlled to zero according to the constant DC voltage control commonly used in onshore converter stations. Considering the voltage drop of the overhead line, the DC voltage at the onshore converter station port is negative at this time. At this time, the device controls the main circuit switch module to disconnect through the control module, so that the DC current flows through the circuit where the energy dissipation valve module is located. Then, by controlling the number of energy dissipation resistors switched on and off in each energy dissipation valve unit, the total energy consumed by the energy dissipation circuit is controlled, thereby achieving the balance of surplus power in the system.

[0027] The proposed solution addresses the issues of fault crossing and surplus power balancing in hybrid submarine-overhead line DC systems. Offshore converter stations can adopt a half-bridge topology, reducing investment costs and construction complexity. By controlling the switching on and off of distributed energy-consuming resistors, surplus power can be accurately consumed with minimal power fluctuations. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This application provides a schematic diagram of the architecture of an offshore wind power flexible DC system that includes a hybrid submarine cable-overhead line.

[0030] Figure 2This is a schematic diagram of an embodiment of a series distributed DC energy dissipation device provided in this application.

[0031] Figure 3 A schematic diagram of the circuit structure of the SM submodule in the series distributed DC energy dissipation device provided in this application.

[0032] Figure 4 A schematic diagram of the circuit structure of the energy dissipation valve unit in the series distributed DC energy dissipation device provided in this application.

[0033] Figure 5 This application provides a schematic diagram of the control logic flow for a series distributed DC energy dissipation device and an offshore wind power flexible DC system. Detailed Implementation

[0034] To address the problems of existing technologies, research has revealed that current offshore wind power flexible DC transmission projects generally only use DC submarine cables, eliminating the need to consider DC fault ride-through issues. However, overhead lines have a high failure rate, and DC faults cannot be ignored. After an overhead line fault occurs, the system needs to not only clear the DC fault but also consume surplus power to prevent excessive DC voltage from triggering system protection and causing shutdowns, or even endangering equipment safety. Therefore, energy dissipation devices need to be added to the system. However, offshore wind power flexible DC transmission systems using a hybrid submarine cable-overhead line DC line system need to consider DC fault ride-through issues, but based on a full-half-bridge hybrid... When clearing DC faults, the MMC (Multi-Mechanical Control Unit) needs to reduce the DC voltage to zero or negative, which conflicts with the need to maintain a stable DC voltage when the parallel DC power dissipation device is working. Therefore, the parallel DC power dissipation device is incompatible with the hybrid submarine cable-overhead line flexible DC system and cannot effectively dissipate the surplus power of the hybrid submarine cable-overhead line system. This results in the current technical status of low reliability of the existing hybrid submarine cable-overhead line offshore wind power flexible DC system. Therefore, finding a surplus power dissipation scheme that is compatible with the hybrid submarine cable-overhead line system has become one of the key research objectives for those skilled in the art.

[0035] This application provides a series distributed DC energy dissipation device and a flexible DC system for offshore wind power, which solves the technical problem of low reliability in existing flexible DC systems for offshore wind power that combine submarine cables and overhead lines.

[0036] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0037] First, this application provides a detailed description of an embodiment of an offshore wind power flexible DC transmission system comprising a hybrid submarine cable-overhead line, as follows:

[0038] This embodiment proposes a hybrid submarine cable-overhead line offshore wind power flexible DC system based on a series distributed DC energy dissipation device, such as... Figure 1 As shown, the submarine cable-overhead line hybrid offshore wind power flexible DC system includes an offshore converter station, submarine cable, terminal conversion station, overhead line, and onshore converter station. The offshore converter station adopts a half-bridge MMC, and the onshore converter station adopts a full-half-bridge hybrid MMC. The proportion of full-bridge MMC needs to be greater than 50%, and is generally 60%.

[0039] Figure 1 The terminal conversion station is a node connecting submarine cables and overhead lines. The station is equipped with a series distributed DC power dissipation device as provided in this application, the device structure of which is as follows: Figure 2 As shown, it includes: submarine cable port, overhead line port, main circuit switch module, energy dissipation valve module and control module (not shown in the figure).

[0040] The main circuit switch module and the energy dissipation valve module are disposed between the submarine cable port and the overhead line port, and the main circuit switch module and the energy dissipation valve module are connected in parallel.

[0041] More specifically, the main circuit switch module includes: a main circuit mechanical switch and a power electronic switch array connected in series.

[0042] More specifically, the power electronic switch is a switch array composed of multiple SM submodules. The SM submodules are preferably full-bridge submodules, with one feasible topology being as follows: Figure 3 As shown, the topology consists of a full-bridge module composed of power devices, anti-parallel diodes, and capacitors. When the power devices are in the on state, the capacitor voltage is zero. When the power devices are in the off state, the DC current charges the capacitor, causing the capacitor voltage to rise.

[0043] It should be noted that the power electronic switch array is used to control the current switching. Since the current carrying capacity of IGBT devices is limited, a single SM cannot handle the rated DC current. Therefore, the power electronic switch array in this embodiment can improve the current carrying capacity of the main circuit by connecting multiple SMs in parallel to shunt the current.

[0044] The energy-consuming valve module has multiple energy-consuming valve units connected in series. Each energy-consuming valve unit includes an energy-consuming resistor and a switching element for controlling the energy-consuming resistor to be switched on or off.

[0045] The control module is used to control the on / off state of the switching elements in the main circuit switch module and the energy-consuming valve module.

[0046] More specifically, such as Figure 4 As shown, the energy-consuming valve unit specifically includes: a first diode D1, a first switching transistor T1, and a dynamic voltage equalization resistor R. d Energy storage capacitor C, second diode D2, second switch T2, and energy dissipation resistor R ch ;

[0047] The cathode of the first diode D1 is connected to the first port of the energy dissipation valve unit, and the anode is connected to the second port of the energy dissipation valve unit;

[0048] The first switching transistor is connected in parallel with the first diode D1, and the anode of the first switching transistor D1 is connected to the first port of the energy dissipation valve unit, and the cathode is connected to the second port of the energy dissipation valve unit.

[0049] The dynamic voltage equalization resistor R d It is connected in parallel with the second diode D2, and the dynamic voltage equalization resistor R d One end of the resistor is connected to the anode of the second diode D2 and the first port of the energy dissipation valve unit, and the dynamic voltage equalization resistor R d The other end is connected in series with the cathode of the second diode D2 and the energy storage capacitor C, and then connected to the second port of the energy dissipation valve unit to form an RCD buffer circuit;

[0050] The energy-consuming resistor R ch The second switch T2 is connected in series to form a power dissipation resistor circuit, and the power dissipation resistor circuit is connected in parallel with the RCD buffer circuit.

[0051] It should be noted that a single energy-consuming valve consists of a capacitor C and a dynamic voltage-equalizing resistor R. d Diode D2, power-consuming resistor R ch It consists of integrated gate commutated thyristors (IGCTs) T1 and T2, anti-parallel diode D1, and bypass switch K, R d D2 is connected in parallel with capacitor C and then in series with capacitor C to form an RCD buffer circuit. ch Together with T2, they form a power dissipation circuit. The RCD buffer circuit and the power dissipation circuit are then connected in parallel with T1, D1, and K. When T1 is on, the capacitor voltage is zero. When T1 is off, current flows through the RCD buffer circuit to charge the capacitor. The capacitor voltage can be controlled by controlling the on and off states of T1. When the capacitor voltage is maintained at the rated voltage, T2 is on to connect the power dissipation resistor, consuming the system's surplus power. T2 is off to disconnect the power dissipation resistor. The system's surplus power can be accurately consumed by controlling the on and off states of T2. The anti-parallel diode D1 is used to reverse the flow of DC current during the startup of the offshore converter station. The bypass switch K operates when the power dissipation valve voltage is too high, protecting the device from overvoltage damage.

[0052] The energy-consuming valve unit mentioned in this embodiment is not only Figure 5 The topology shown can be used as long as the power dissipation resistor R can be controlled. ch The energy-consuming circuit topologies with input and output functions can be used as alternative implementation methods.

[0053] More specifically, the energy-consuming valve unit also includes: an energy-consuming valve bypass switch K;

[0054] The bypass switch K for the energy-consuming valve is used to control the activation or deactivation of the energy-consuming valve unit. If the energy-consuming valve malfunctions, the bypass switch will close; under normal operating conditions, the switch will open.

[0055] It should be noted that, as Figure 5 As shown, during steady-state operation, the offshore converter station employs VF control to provide a stable AC-side voltage for wind turbine grid connection. The onshore converter station employs constant DC voltage control to maintain the rated DC voltage U. dc In the series-connected distributed DC energy dissipation device, both the main circuit mechanical switch and the main circuit power electronic switch array are in the ON state, providing a path for DC current. In the energy dissipation circuit, the bypass switch K of the energy dissipation valve remains in the OFF state, and the switch T1 is in the ON state, providing a path for the rated current. Moreover, because the DC current rises very quickly after a fault occurs in the DC line, if the switch T1 remains in the ON state, the increased DC current can be transferred to the energy dissipation circuit T1, and there is no delay in turning on T1. The switch T2 is in the OFF state, and the energy dissipation resistor is bypassed.

[0056] When an overhead line fault occurs, the offshore converter station continues to use VF control to maintain stable AC voltage. The onshore converter station continues to use constant DC voltage control, with the control objective being to bring the voltage at the overhead line port of the series distributed DC energy dissipation device to zero. Considering the voltage drop of the overhead line, the DC voltage at the onshore converter station port is negative at this time. Both the mechanical switch and the power electronic switch of the main circuit of the series distributed energy dissipation device are closed. DC current flows through the energy dissipation circuit, and the energy dissipation valve controls the voltage across it by controlling the conduction and closure of the T1 switch. The control objective is the rated voltage U. C And satisfy 2*N*U C =U dc Where N is the number of energy-consuming valves in a single series distributed energy-consuming device, U dc This is the rated voltage for the DC system.

[0057] To balance the system's surplus power, a series distributed energy consumption device is used to acquire the power P transmitted from the offshore converter station. w When the switching transistor of energy-consuming valve T2 is turned on, the energy consumed by the energy-consuming valve is P. ch =U C 2 / R chTherefore, by controlling the switching transistors of each energy-consuming valve T2, the total energy consumed by the energy-consuming circuit can be controlled, and P is satisfied. w =n ch *P ch , where n ch This represents the number of energy-consuming valves in the T2 switching state.

[0058] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0059] Unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0060] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A series distributed DC energy dissipation device, characterized in that, include: Submarine cable port, overhead line port, main circuit switch module, energy dissipation valve module and control module; The main circuit switch module and the energy dissipation valve module are disposed between the submarine cable port and the overhead line port, and the main circuit switch module and the energy dissipation valve module are connected in parallel. The energy-consuming valve module has multiple energy-consuming valve units connected in series. Each energy-consuming valve unit includes an energy-consuming resistor and a switching element for controlling the energy-consuming resistor to be switched on or off. The control module is used to control the on / off state of the switching elements in the main circuit switch module and the energy-consuming valve module; The energy dissipation valve unit specifically includes: a first diode, a first switching transistor, a dynamic voltage equalization resistor, an energy storage capacitor, a second diode, a second switching transistor, and an energy dissipation resistor; The cathode of the first diode is connected to the first port of the energy dissipation valve unit, and the anode is connected to the second port of the energy dissipation valve unit; The first switching transistor is connected in parallel with the first diode, and the anode of the first switching transistor is connected to the first port of the energy dissipation valve unit, and the cathode is connected to the second port of the energy dissipation valve unit. The dynamic voltage equalizing resistor is connected in parallel with the second diode, and one end of the dynamic voltage equalizing resistor is connected in series with the anode of the second diode and the first port of the energy dissipation valve unit, and the other end of the dynamic voltage equalizing resistor is connected in series with the cathode of the second diode and the energy storage capacitor, and then connected to the second port of the energy dissipation valve unit to form an RCD buffer circuit. The energy-consuming resistor and the second switching transistor are connected in series to form an energy-consuming resistor circuit, and the energy-consuming resistor circuit is connected in parallel with the RCD buffer circuit.

2. The series distributed DC energy dissipation device according to claim 1, characterized in that, The main circuit switch module specifically includes a main circuit mechanical switch and a power electronic switch connected in series.

3. The series distributed DC energy dissipation device according to claim 2, characterized in that, The power electronic switch is specifically a switch array composed of multiple SM sub-modules.

4. The series distributed DC energy dissipation device according to claim 3, characterized in that, The SM submodule is specifically the full-bridge submodule.

5. A series distributed DC energy dissipation device according to claim 1, characterized in that, The energy-consuming valve unit also includes: an energy-consuming valve bypass switch; The energy-consuming valve bypass switch is used to control the activation or deactivation of the energy-consuming valve unit.

6. A flexible DC-DC transmission system for offshore wind power, characterized in that, include: Offshore converter station, terminal conversion station and onshore converter station, wherein the terminal conversion station is equipped with a series distributed DC power dissipation device as described in any one of claims 1 to 5; The offshore converter station is connected to the submarine cable port in the series distributed DC power dissipation device via a submarine cable. The onshore converter station is connected to the overhead line port of the series distributed DC power dissipation device via an overhead line.

7. A flexible DC-DC transmission system for offshore wind power according to claim 6, characterized in that, The offshore converter station is specifically a half-bridge MMC converter station.

8. A flexible DC-DC transmission system for offshore wind power according to claim 6, characterized in that, The onshore converter station is specifically a hybrid MMC converter station consisting of a full-bridge and a half-bridge.

9. A flexible DC-DC transmission system for offshore wind power according to claim 8, characterized in that, The proportion of full-bridge submodules in the hybrid MMC converter station is greater than 50%.

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