New energy island flexible direct delivery system and black start method thereof

Abstract

The invention provides a new energy island flexible direct output system and a black start method thereof, and the system comprises a transmitting end connection transformer, a transmitting end converter valve, a direct current line, a receiving end converter valve, a starting resistor, a bypass isolation knife, a receiving end connection transformer, and an energy storage device. The energy storage equipment is connected in parallel to the low-voltage winding side of the receiving end connection transformer, and the receiving end connection transformer is configured to be a multi-winding connection transformer. According to some embodiments, the energy storage equipment is configured in the receiving end converter station and is directly connected in parallel to the low-voltage winding side of the multi-winding connection transformer, so that a multi-stage boosting transformer is omitted, and the energy storage access mode is effectively simplified. When the new energy island is isolated from the receiving end alternating current power grid through the flexible direct output system, the energy storage device can control and maintain the alternating current side voltage of the receiving end converter station. After black start of the system is completed, voltage and frequency support can be provided for a receiving end alternating current power grid.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage and flexible direct current transmission, and in particular to a new energy island flexible direct current transmission system and a black start method thereof. Background Art

[0002] As offshore wind power enters deep sea areas, there is an urgent need for a transmission solution that is suitable for medium and long-distance offshore wind power transmission. Due to the capacitive effect, the power of long-distance AC submarine cable transmission solutions is limited, while flexible DC has become the main solution for offshore wind power transmission at home and abroad due to its large transmission capacity, good economy, friendly access to the grid and small sea area.

[0003] Unlike conventional flexible direct current transmission projects, the flexible direct current transmission system for isolated new energy islands has great differences due to its special scenarios. For example, the system starting method, fault crossing strategy, energy consumption configuration plan, and unmanned operation and maintenance requirements. Taking the starting method as an example, the new energy side lacks an independent power supply, and the sending-end converter station needs to take power from the receiving-end converter station through the DC side line to unlock, and then provide the grid-connected voltage for the new energy station. In addition, due to the volatility of the transmitted power, the problem of wind and solar abandonment caused by the increase in the scale of new energy development has become more prominent. At present, in order to smooth out the fluctuations in the output of new energy, energy storage equipment with power storage and release characteristics has begun to be applied to new energy stations. By using energy storage equipment to balance the power generated by new energy in real time, the impact of new energy power fluctuations on the power grid can be reduced, and the power quality of the grid connection point can be effectively improved.

[0004] Compared with the receiving-end converter station, the construction and operation and maintenance costs of energy storage are higher because the sending-end stations are mostly located in remote areas and have inconvenient transportation. When the receiving-end AC power grid loses power or needs to be isolated from the converter station, the converter valve lacks voltage support and cannot complete the black start of the new energy island through the flexible direct current transmission system according to the existing plan. If energy storage is configured on the sending side to provide grid-connected voltage for new energy units, taking offshore wind power as an example, the installation cost is high and the maintenance is complex. At the same time, the existing starting strategy needs to be greatly adjusted to complete the black start. If energy storage is configured at the receiving-end converter station, such as the patent with publication number CN112736977A, which discloses a multi-terminal offshore wind power flexible direct current and energy storage coordinated grid-connected system and its control method, the patent connects the energy storage to the AC busbar on the side of the transformer valve connected to the onshore station through a multi-stage step-up transformer to smooth the wind power output, but the patent does not consider the black start problem of the system when the onshore AC power grid loses power.

[0005] The inventors of the present application discovered that the new energy island flexible direct current transmission system lacks a black start strategy that is independent of the receiving end AC power grid. Summary of the invention

[0006] The present application aims to propose a new energy island flexible direct current transmission system and a black start method thereof, so as to solve the problem that the new energy island flexible direct current transmission system needs to rely on the receiving end AC power grid during black start.

[0007] According to one aspect of the present application, a new energy island flexible direct current transmission system is proposed, including a receiving-end converter station, the receiving-end converter station including: a receiving-end connection transformer; and an energy storage device, wherein the energy storage device is connected in parallel to the low-voltage winding side of the receiving-end connection transformer, the receiving-end connection transformer is configured as a multi-winding connection transformer, and the number of windings of the multi-winding connection transformer is greater than 2.

[0008] According to some embodiments, the energy storage device adopts a grid-type control strategy to meet the voltage amplitude and frequency requirements of the AC side of the receiving-end converter station.

[0009] According to some embodiments, the energy storage device is configured with an energy storage module, and the energy storage module includes an energy storage element or a combination of an energy element and a power element.

[0010] According to some embodiments, the energy storage device adopts a series high-voltage topology structure or a parallel low-voltage topology structure.

[0011] According to some embodiments, the total capacity of the energy storage device is determined according to the energy required for a system black start.

[0012] According to some embodiments, the new energy island flexible direct current transmission system also includes: a sending-end converter valve and a receiving-end converter valve, and the bridge arm sub-modules of the sending-end converter valve and the receiving-end converter valve both adopt half-bridge sub-modules, full-bridge sub-modules or a mixed sub-module of half-bridge sub-modules and full-bridge sub-modules.

[0013] According to some embodiments, the new energy island flexible direct current transmission system further includes a sending-end connecting transformer, wherein the sending-end connecting transformer and the receiving-end connecting transformer are a single unit or multiple units.

[0014] According to some embodiments, the sending-end connection transformer is configured as a double-winding or multi-winding transformer.

[0015] According to one aspect of the present application, a black start method for a new energy island flexible direct current transmission system as described in any of the previous embodiments is proposed, the black start method comprising isolating a receiving-end converter station from an AC power grid; closing a low-voltage winding branch switch of a receiving-end connection transformer of the receiving-end converter station to connect an energy storage device to the receiving-end connection transformer; closing a bypass isolator of a starting resistor to bypass the starting resistor; using the energy storage device to control the branch bus voltage on the low-voltage winding side of the receiving-end connection transformer to rise to its rated value, the receiving-end converter valve enters an uncontrolled charging stage, and the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve rises; when the capacitor of the bridge arm submodule of the receiving-end converter valve is averaged, the voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve increases; When the average voltage reaches a preset first threshold, the receiving-end converter valve is controlled to enter the active charging stage; when the DC side voltage of the new energy island through the flexible direct current transmission system rises to a preset second threshold, the sending-end converter valve is controlled to enter the active charging stage; when the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve rises to its rated value, the receiving-end converter station is unlocked and the DC side voltage is controlled to rise to its rated value; when the average voltage of the capacitor of the bridge arm submodule of the sending-end converter valve rises to its rated value, the sending-end converter station is unlocked; the amplitude and frequency of the valve-side AC voltage of the sending-end converter station are controlled to their rated values ​​to achieve a black start of the new energy island through the flexible direct current transmission system.

[0016] According to one aspect of the present application, a black start method for a new energy island flexible direct current transmission system as described in any of the previous embodiments is proposed, the black start method comprising isolating a receiving-end converter station from an AC power grid; closing a low-voltage winding branch switch of a receiving-end connection transformer of the receiving-end converter station to connect an energy storage device to the receiving-end connection transformer; using the energy storage device to control the branch bus voltage on the low-voltage winding side of the receiving-end connection transformer to rise to its rated value, the receiving-end converter valve enters an uncontrolled charging stage, and the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve rises; when the valve-side current of the receiving-end converter station decreases to a preset receiving-end converter station valve-side current threshold, closing the bypass isolation knife of the starting resistor to bypass the starting resistor; when the When the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve reaches a preset first threshold value, the receiving-end converter valve is controlled to enter the active charging stage; when the DC side voltage of the new energy island through the flexible direct current transmission system rises to a preset second threshold value, the sending-end converter valve is controlled to enter the active charging stage; when the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve rises to its rated value, the receiving-end converter station is unlocked and the DC side voltage is controlled to rise to its rated value; when the average voltage of the capacitor of the bridge arm submodule of the sending-end converter valve rises to its rated value, the sending-end converter station is unlocked; the amplitude and frequency of the valve-side AC voltage of the sending-end converter station are controlled to rise to their rated values ​​respectively, so as to realize the black start of the new energy island through the flexible direct current transmission system.

[0017] According to some embodiments of the present application, by configuring an energy storage device at the receiving-end converter station and directly connecting it in parallel to the low-voltage winding side of the multi-winding connection transformer, the multi-stage step-up transformer is omitted, thereby effectively simplifying the energy storage access method.

[0018] According to other embodiments, by adopting a grid-type control strategy for energy storage equipment and improving the existing starting strategy, a system black start is achieved when the receiving-end power grid is isolated from the converter station, new energy units are connected to the grid, and voltage and frequency support is provided for the receiving-end power grid.

[0019] It should be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments. By describing the exemplary embodiments in detail with reference to the drawings, the above and other objectives, features and advantages of the present application will become more apparent.

[0021] Figure 1 A device block diagram of a new energy island flexible direct current transmission system according to an exemplary embodiment of the present application is shown.

[0022] Figure 2 A topological structure diagram of a series high-voltage energy storage system according to an exemplary embodiment of the present application is shown.

[0023] Figure 3 A topological structure diagram of a parallel low-voltage energy storage system according to an exemplary embodiment of the present application is shown.

[0024] Figure 4 A topological structure diagram of a half-bridge power module according to an exemplary embodiment of the present application is shown.

[0025] Figure 5 A topological structure diagram of a full-bridge power module according to an exemplary embodiment of the present application is shown.

[0026] Figure 6 A schematic diagram of an offshore wind power flexible direct current transmission system according to an example embodiment of the present application is shown.

[0027] Figure 7 A flow chart of a black start method for an offshore wind power island via a flexible direct current transmission system according to an example embodiment of the present application is shown.

[0028] Figure 8 A flow chart of a black start method for another offshore wind power island via a flexible direct current transmission system according to an example embodiment of the present application is shown.

[0029] Fig. 9A schematic diagram of a wind power flexible direct current transmission system according to an example embodiment of the present application is shown.

[0030] Description of reference numerals:

[0031] 1: Switch Q0.

[0032] 2: Switch Q1.

[0033] 3: Onshore connection transformer,

[0034] 4: Startup resistor

[0035] 5: Bypass knife,

[0036] 6: Onshore converter valve,

[0037] 7: DC submarine cable,

[0038] 8: Offshore converter valve

[0039] 9: Offshore connection transformer,

[0040] 10: Offshore wind farm;

[0041] 11: Switch Q3.

[0042] 12: Switch Q4.

[0043] 13: Switch Q2.

[0044] 14: Energy storage equipment. DETAILED DESCRIPTION

[0045] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this application will be comprehensive and complete and will fully convey the concepts of the example embodiments to those skilled in the art. In the figures, the same figures show the same or similar parts, and thus their repeated description will be omitted.

[0046] The described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of these specific details, or other modes, components, materials, devices or operations may be adopted. In these cases, known structures, methods, devices, implementations, materials or operations will not be shown or described in detail.

[0047] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0048] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0049] As mentioned above, since the sending-end stations are mostly located in remote areas with inconvenient transportation, the cost of energy storage construction and operation and maintenance is higher. When the receiving-end AC grid loses power or needs to be isolated from the converter station, the converter valve lacks voltage support and cannot complete the black start of the new energy island through flexible direct current transmission system according to the existing plan.

[0050] Therefore, a wind power flexible DC transmission system is proposed. Fig. 9 As shown, the wind power flexible direct current transmission system includes a sending-end connection transformer, a sending-end converter valve, a receiving-end converter valve, a starting resistor and its bypass isolator, a receiving-end connection transformer and an energy storage device. Among them, the receiving-end connection transformer is configured as a multi-winding connection transformer, and the energy storage device is connected in parallel to its low-voltage winding side. According to an embodiment of the present application, by configuring an energy storage device at the receiving-end converter station and directly connecting it in parallel to the low-voltage winding side of the receiving-end connection transformer, a multi-stage step-up transformer is omitted, and the energy storage access method is effectively simplified. According to other embodiments, by adopting a grid-type control strategy for the energy storage device and optimizing the system starting strategy, it is possible to achieve a system black start when the receiving-end power grid is isolated from the converter station, connect new energy units to the grid, and provide voltage and frequency support for the receiving-end power grid.

[0051] The specific embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0052] Figure 1 A device block diagram of a new energy island flexible direct current transmission system according to an exemplary embodiment of the present application is shown below. Figure 1 Taking the example, a receiving-end converter station of a new energy island flexible direct current transmission system according to an exemplary embodiment of the present application is described in detail.

[0053] like Figure 1The shown new energy island flexible direct current transmission system includes a sending-end converter station 101 and a receiving-end converter station 103, wherein the receiving-end converter station 103 includes a receiving-end connection transformer 1031 and an energy storage device 1033. The energy storage device 1033 is configured at the receiving-end converter station of the new energy island flexible direct current transmission system, and is connected in parallel to the low-voltage winding side of the receiving-end connection transformer 1031. In some embodiments, the receiving-end connection transformer 1031 is configured as a multi-winding connection transformer, and the number of windings of the multi-winding connection transformer is greater than 2.

[0054] According to an embodiment of the present application, the energy storage device 1033 adopts a grid-type control strategy to meet the voltage amplitude and frequency requirements of the AC side of the receiving-end converter station.

[0055] In a specific embodiment, the energy storage device 1033 is configured with an energy storage module, wherein the energy storage module includes an energy storage element or a combination of an energy element and a power element.

[0056] In some embodiments, the energy storage device 1033 is implemented as follows: Figure 2 The series high voltage topology shown or the Figure 3 The parallel low-voltage topology shown in the figure realizes the overall expansion of the energy storage device 1033 by grouping small-capacity energy storage modules in series and parallel on the AC or DC side.

[0057] According to an embodiment of the present application, the total capacity of the energy storage device is determined according to the energy required for black start of the new energy island through the flexible direct current transmission system. In some embodiments, the energy storage devices are grouped according to the number of transformers 1031 connected to the receiving station, for example, according to the number of transformers 1031 connected to the receiving station, the energy storage devices are grouped in a manner that the energy storage capacity of each group is equal.

[0058] according to Figure 1 In the embodiment shown, by configuring an energy storage device at the receiving-end converter station and directly connecting the energy storage device to the low-voltage winding side of the multi-winding connection transformer, a multi-stage step-up transformer is omitted, effectively simplifying the access method of the energy storage device. According to other embodiments, a grid-type control strategy is adopted for the energy storage device to meet the voltage amplitude and frequency requirements of the AC side of the receiving-end converter station.

[0059] According to other embodiments of the present application, Figure 1 The new energy island flexible direct current transmission system shown in the figure also includes a sending-end converter valve and a receiving-end converter valve. The bridge arm submodules of the sending-end converter valve and the receiving-end converter valve are both as follows: Figure 4 The half-bridge submodule shown in Figure 5 The full-bridge submodule shown is a submodule that is a mixture of a half-bridge submodule and a full-bridge submodule.

[0060] According to some embodiments, Figure 1 The shown new energy island flexible direct current transmission system also includes a sending-end connection transformer, wherein the new energy island flexible direct current transmission system sending-end connection transformer and receiving-end connection transformer 1031 are single or multiple.

[0061] In a specific embodiment, the sending-end connection transformer is configured as a double-winding or multi-winding transformer.

[0062] Figure 6 A schematic diagram of a new energy island flexible direct current transmission system according to an exemplary embodiment of the present application is shown. Figure 6 The new energy island flexible direct current transmission system shown includes an onshore connection transformer 3, an energy storage device 14, a starting resistor 4 and its bypass isolator 5, an onshore converter valve (receiving end converter valve) 6, a DC submarine cable 7, an offshore converter valve (sending end converter valve) 8 and an offshore connection transformer 9.

[0063] It should be noted here that Figure 8 The offshore end of Figure 1 The new energy island shown in the figure is sent out through the flexible direct current transmission system, and the onshore end is Figure 1 The new energy island shown is sent to the receiving end of the flexible direct current transmission system. The number of connecting transformers in the sending and receiving end converter stations (onshore connecting transformer 3 and offshore connecting transformer 9) can be selected as a single unit or multiple units according to the system capacity.

[0064] like Figure 6 As shown, the onshore station energy storage device 14 is connected in parallel to the 35kV low-voltage winding side of the onshore connection transformer 3. The low-voltage winding connection mode of the onshore connection transformer can be selected as an angle type to isolate the zero-sequence component. The energy storage module used in the energy storage device 14 is composed of energy-type energy storage elements or a mixture of energy-type elements and power-type elements.

[0065] In a specific embodiment, the topology of the energy storage device 14 is as follows: Figure 2 The series high voltage structure shown or Figure 3 The parallel low-voltage structure shown in the figure can achieve overall capacity expansion by connecting energy storage modules in groups and in series.

[0066] In some embodiments, the energy storage device 14 uses a grid-type control technology to control the voltage amplitude and frequency on the AC side of the onshore converter station.

[0067] When the new energy island is black-started through the flexible direct current transmission system, the bridge arm submodule capacitors of the onshore converter valve 6 and the offshore converter valve 8, the AC / DC submarine cable, and the onshore connection transformer 3 and the offshore connection transformer 9 and other components need to absorb energy. The total capacity of the energy storage device 14 should meet the energy demand of the system black-start, and it is grouped according to the number of onshore station connection transformers 3, and the number of groups is equal to the number of onshore station connection transformers 3, and the capacity of each group is equal.

[0068] In some embodiments, the offshore connection transformer 9 is a double-winding transformer, and a multi-winding transformer may also be used according to actual transmission capacity requirements. For example, the use of a multi-winding transformer in an offshore wind power flexible direct current transmission system can reduce the weight of the offshore platform.

[0069] Figure 7 A flowchart of a black start method for an offshore wind power island through a flexible direct current transmission system according to an exemplary embodiment of the present application is shown. Figure 6 As an example, the offshore wind power island flexible direct current transmission system shown in the figure is used to Figure 7 A black start method for an offshore wind power island through a flexible direct current transmission system is shown in detail.

[0070] like Figure 7 As shown, in step S701, the receiving-end converter station is isolated from the AC power grid. Figure 6 As described above, disconnect the tie switch Q0 between the grid-side busbar of the onshore converter station and the grid.

[0071] In step S703, the low-voltage winding branch switch of the receiving-end connection transformer of the receiving-end converter station is closed to connect the energy storage device to the receiving-end connection transformer. Figure 6 As shown, the branch switches Q1 to Q3 of each winding of each connection transformer of the land station are closed, so that each group of energy storage equipment of the land station is connected to the receiving-end connection transformer.

[0072] In step S705, the bypass isolation switch of the starting resistor is closed to bypass the starting resistor. Figure 6 As described above, the starting resistor bypass isolation knife 5 is closed to bypass the starting resistor 4.

[0073] In step S707, the energy storage device is used to control the branch bus voltage on the low-voltage winding side of the receiving-end connection transformer to rise to its rated value, the receiving-end converter valve enters the uncontrolled charging stage, and the average voltage of the capacitor of the receiving-end converter valve bridge arm submodule rises. Figure 6 As described above, the energy storage device controls the branch bus voltage on the low-voltage winding side of the land station connection transformer to rise to the rated value, the land station converter valve 6 enters the uncontrolled charging stage, and the average voltage of the capacitor of the land station converter valve bridge arm submodule rises.

[0074] In step S709, when the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve reaches a preset first threshold, the receiving-end converter valve is controlled to enter the active charging stage. Figure 6 When the average voltage of the capacitor of the bridge arm submodule of the land station converter valve reaches the first threshold, it is made to enter the active charging stage to further increase the average voltage of the capacitor of the bridge arm submodule.

[0075] In step S711, when the DC side voltage of the new energy island through the flexible DC transmission system rises to a preset second threshold, the sending-end converter valve is controlled to enter the active charging stage. Figure 6 As described above, when the onshore station converter valve bridge arm submodule is charged, the DC submarine cable 7 will be energized, and the capacitor of the offshore station converter valve 8 bridge arm submodule will be charged through the DC submarine cable; when the DC side voltage rises to the second threshold, the offshore station converter valve bridge arm submodule will enter active charging to further increase the average voltage of its bridge arm submodule capacitor.

[0076] In step S713, when the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve rises to its rated value, the receiving-end converter station is unlocked and controls the DC side voltage to rise to its rated value. Figure 6 As described above, when the average voltage of the capacitor of the converter valve bridge arm submodule of the onshore station rises to its rated value, the onshore station is unlocked and the DC side voltage is controlled to rise to the rated value; at the same time, the average voltage of the capacitor of the converter valve bridge arm submodule of the offshore platform also rises further, and the offshore station is unlocked when it rises to its rated value.

[0077] In step S715, when the average voltage of the capacitor of the bridge arm submodule of the sending-end converter valve rises to its rated value, the sending-end converter station is unlocked, and the amplitude and frequency of the valve-side AC voltage of the sending-end converter station are controlled to rise to their rated values, so as to realize the black start of the new energy island through the flexible direct current transmission system. Figure 6 As described above, after the offshore station valve is unlocked, the amplitude and frequency of the AC voltage on the offshore station valve side are controlled to the rated value, and the black start of the offshore wind power flexible direct current transmission system is completed.

[0078] According to the embodiment of the present application, when the offshore wind turbines are connected to the grid one by one to generate electricity, it is also necessary to control the output of the new energy units to be less than or equal to the energy absorbed by the energy storage of the receiving end converter station.

[0079] According to other embodiments of the present application, before executing step S703, it is also necessary to confirm whether the status of the primary equipment and the secondary equipment of the transmitting and receiving end converter station are normal, and whether the status of the primary equipment and the secondary equipment meet the black start conditions. Step S703 is executed only when the status of the primary equipment and the secondary equipment meet the black start conditions.

[0080] Figure 8 A flowchart of a black start method of another offshore wind power island through a flexible direct current transmission system according to an exemplary embodiment of the present application is shown. Figure 6 As an example, the offshore wind power island flexible direct current transmission system shown in the figure is used to Figure 8 A black start method for an offshore wind power island through a flexible direct current transmission system is shown in detail.

[0081] like Figure 8As shown, in step S801, the receiving-end converter station is isolated from the AC power grid. Figure 6 As described above, disconnect the tie switch Q0 between the grid-side busbar of the onshore converter station and the grid.

[0082] In step S803, the low-voltage winding branch switch of the receiving-end connection transformer of the receiving-end converter station is closed to connect the energy storage device to the receiving-end connection transformer. Figure 6 As shown, the branch switches Q1 to Q3 of each winding of each connection transformer of the land station are closed, so that each group of energy storage equipment of the land station is connected to the receiving-end connection transformer.

[0083] In step S805, the energy storage device is used to control the branch bus voltage on the low-voltage winding side of the receiving-end connection transformer to rise to its rated value, the receiving-end converter valve enters the uncontrolled charging stage, and the average voltage of the capacitor of the receiving-end converter valve bridge arm submodule rises. Figure 6 As described above, the energy storage device controls the branch bus voltage on the low-voltage winding side of the land station connection transformer to rise to the rated value, the land station converter valve 6 enters the uncontrolled charging stage, and the average voltage of the capacitor of the land station converter valve bridge arm submodule rises.

[0084] In step S807, when the valve-side current of the receiving-end converter station drops to a preset valve-side current threshold of the receiving-end converter station, the bypass isolation switch of the starting resistor is closed to bypass the starting resistor. Figure 6 As described above, the starting resistor bypass isolation knife 5 is closed to bypass the starting resistor 4.

[0085] In step S809, when the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve reaches a preset first threshold, the receiving-end converter valve is controlled to enter the active charging stage. Figure 6 When the average voltage of the capacitor of the bridge arm submodule of the land station converter valve reaches the first threshold, it is made to enter the active charging stage to further increase the average voltage of the capacitor of the bridge arm submodule.

[0086] In step S811, when the DC side voltage of the new energy island through the flexible DC transmission system rises to a preset second threshold, the sending-end converter valve is controlled to enter the active charging stage. Figure 6 As described above, when the onshore station converter valve bridge arm submodule is charged, the DC submarine cable 7 will be energized, and the capacitor of the offshore station converter valve 8 bridge arm submodule will be charged through the DC submarine cable; when the DC side voltage rises to the second threshold, the offshore station converter valve bridge arm submodule will enter active charging to further increase the average voltage of its bridge arm submodule capacitor.

[0087] In step S813, when the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve rises to its rated value, the receiving-end converter station is unlocked and controls the DC side voltage to rise to its rated value. Figure 6As described above, when the average voltage of the capacitor of the converter valve bridge arm submodule of the onshore station rises to its rated value, the onshore station is unlocked and the DC side voltage is controlled to rise to the rated value; at the same time, the average voltage of the capacitor of the converter valve bridge arm submodule of the offshore platform also rises further, and the offshore station is unlocked when it rises to its rated value.

[0088] In step S815, when the average capacitor voltage of the sending-end converter valve bridge arm submodule rises to its rated value, the sending-end converter station is unlocked, and the amplitude and frequency of the valve-side AC voltage of the sending-end converter station are controlled to rise to their rated values, respectively, to achieve a black start of the new energy island through flexible direct current transmission system. Figure 6 As described above, after the offshore station valve is unlocked, the amplitude and frequency of the AC voltage on the offshore station valve side are controlled to the rated value, and the black start of the offshore wind power flexible direct current transmission system is completed.

[0089] According to the embodiment of the present application, when the offshore wind turbines are connected to the grid one by one to generate electricity, it is also necessary to control the output of the new energy units to be less than or equal to the energy absorbed by the energy storage of the receiving end converter station.

[0090] According to other embodiments of the present application, before executing step S803, it is also necessary to confirm whether the status of the primary equipment and the secondary equipment of the transmitting and receiving end converter station are normal, and whether the status of the primary equipment and the secondary equipment meet the black start conditions. Step S803 is executed only when the status of the primary equipment and the secondary equipment meet the black start conditions.

[0091] The embodiments of the present application are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and its core idea of ​​the present application. At the same time, changes or deformations made by those skilled in the art based on the ideas of the present application, the specific implementation methods and the scope of application of the present application, all belong to the scope of protection of the present application. In summary, the content of this specification should not be construed as a limitation on the present application.

Claims

1. A new energy island flexible direct current transmission system, characterized in that: The receiving end converter station includes: Receiving end connection transformer; and Energy storage device, wherein the energy storage device is connected in parallel to the low voltage winding side of the receiving end connection transformer; the receiving end connection transformer is configured as a multi-winding connection transformer, and The number of windings of the multi-winding connection transformer is greater than 2.

2. The new energy island flexible direct current transmission system as claimed in claim 1, characterized in that: The energy storage device adopts a grid-type control strategy to meet the voltage amplitude and frequency requirements of the AC side of the receiving-end converter station.

3. The new energy island flexible direct current transmission system as claimed in claim 1, characterized in that: The energy storage device is configured with an energy storage module, and the energy storage module includes an energy-type energy storage element or a combination of an energy-type element and a power-type element.

4. The new energy island flexible direct current transmission system as claimed in claim 1, characterized in that: The energy storage device adopts a series high-voltage topology structure or a parallel low-voltage topology structure.

5. The new energy island flexible direct current transmission system as claimed in claim 1, characterized in that: The total capacity of the energy storage device is determined according to the energy required for the system black start.

6. The new energy island flexible direct current transmission system as claimed in claim 1, characterized in that: Also includes: The sending-end converter valve and the receiving-end converter valve, the bridge arm submodules of the sending-end converter valve and the receiving-end converter valve all adopt half-bridge submodules, or full-bridge submodules, or submodules mixed with half-bridge submodules and full-bridge submodules.

7. The new energy island flexible direct current transmission system as claimed in claim 1, characterized in that: It also includes a sending-end connection transformer, wherein the sending-end connection transformer and the receiving-end connection transformer are a single unit or multiple units.

8. The new energy island flexible direct current transmission system as claimed in claim 1, characterized in that: The sending-end connection transformer is configured as a double-winding or multi-winding transformer.

9. A black start method for a new energy isolated island flexible direct current transmission system as claimed in any one of claims 1 to 8, characterized in that: The black start method comprises: Isolate the receiving-end converter station from the AC power grid; Closing the low-voltage winding branch switch of the receiving-end connection transformer of the receiving-end converter station to connect the energy storage device to the receiving-end connection transformer; Close the bypass isolation knife of the starting resistor to bypass the starting resistor; The energy storage device is used to control the branch bus voltage on the low-voltage winding side of the receiving-end connection transformer to rise to its rated value, the receiving-end converter valve enters an uncontrolled charging stage, and the average voltage of the capacitor of the receiving-end converter valve bridge arm submodule rises; When the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve reaches a preset first threshold, controlling the receiving-end converter valve to enter an active charging stage; When the DC side voltage of the new energy island through the flexible DC transmission system rises to a preset second threshold, the sending-end converter valve is controlled to enter the active charging stage; When the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve rises to its rated value, the receiving-end converter station is unlocked and controls the DC side voltage to rise to its rated value; When the average voltage of the capacitor of the sending-end converter valve bridge arm submodule rises to its rated value, the sending-end converter station is unlocked, and the amplitude and frequency of the valve-side AC voltage of the sending-end converter station are controlled to rise to their rated values ​​respectively, so as to realize the black start of the new energy island flexible direct current transmission system.

10. A black start method for a new energy isolated island flexible direct current transmission system as claimed in any one of claims 1 to 8, characterized in that: The black start method comprises: Isolate the receiving-end converter station from the AC power grid; Closing the low-voltage winding branch switch of the receiving-end connection transformer of the receiving-end converter station to connect the energy storage device to the receiving-end connection transformer; The energy storage device is used to control the branch bus voltage on the low-voltage winding side of the receiving-end connection transformer to rise to its rated value, the receiving-end converter valve enters an uncontrolled charging stage, and the average voltage of the capacitor of the receiving-end converter valve bridge arm submodule rises; When the valve-side current of the receiving-end converter station drops to a preset valve-side current threshold of the receiving-end converter station, the bypass isolator of the starting resistor is closed to bypass the starting resistor; When the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve reaches a preset first threshold, controlling the receiving-end converter valve to enter an active charging stage; When the DC side voltage of the new energy island through the flexible DC transmission system rises to a preset second threshold, the sending-end converter valve is controlled to enter the active charging stage; When the average voltage of the capacitor of the bridge arm submodule of the receiving-end converter valve rises to its rated value, the receiving-end converter station is unlocked and controls the DC side voltage to rise to its rated value; When the average voltage of the capacitor of the sending-end converter valve bridge arm submodule rises to its rated value, the sending-end converter station is unlocked, and the amplitude and frequency of the valve-side AC voltage of the sending-end converter station are controlled to rise to their rated values ​​respectively, so as to realize the black start of the new energy island flexible direct current transmission system.

Images