Direct current fault ride-through method of offshore wind power sea-land integrated direct current system based on rapid communication link

Abstract

The invention discloses a DC fault ride-through method for an offshore wind power sea-land integrated DC system based on a rapid communication link, and the method comprises the steps: obtaining the voltage drop speed and voltage drop amplitude of a land converter station when a DC fault occurs; when the voltage drop speed is lower than a voltage drop speed threshold value and the voltage drop amplitude is lower than a voltage drop amplitude threshold value, a fan energy consumption input instruction is sent to an offshore converter station, so that the offshore converter station transmits the fan energy consumption input instruction to each communication forwarding device step by step through a bidirectional ring network optical fiber channel; each communication forwarding device transmits the fan energy consumption input instruction to a corresponding fan energy consumption device, so that the fan energy consumption device absorbs fault surplus power according to the fan energy consumption input instruction; wherein the time from the sending of the fan energy consumption input instruction from the flexible straight side to the starting of the fan energy consumption device is not greater than the maximum allowable delay duration.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a direct current fault ride-through method of an offshore wind power land-sea integrated direct current system based on a fast communication link. Background Art

[0002] my country has abundant offshore wind energy resources and great development potential. Existing offshore wind power uses direct current landing and then sends it to the load center through AC overhead lines. In response to the national development needs of tens of millions of kilowatts of offshore wind power bases, the existing model requires the construction of multiple AC channels to send them to the load center, which occupies a large amount of land resources and overall increases the cost of offshore wind power development. In terms of technology, because the existing offshore wind power direct current submarine cable is immediately converted to AC after landing, the problem of direct current fault crossing is generally not considered, because once a direct current submarine cable fails, it is a permanent fault and requires power outage for maintenance.

[0003] The large-scale offshore wind power integrated land and sea, submarine cable overhead hybrid direct transmission load consumption can realize the intensive development of offshore wind power, save land space, and reduce development costs. However, because there are DC overhead lines in the offshore wind power DC transmission system, it is necessary to overcome the DC fault crossing problem of the offshore wind power integrated land and sea DC transmission system. Summary of the invention

[0004] The embodiment of the present invention provides a DC fault riding method for an offshore wind power land-sea integrated DC system based on a fast communication link. The wind turbine energy consumption input command is transmitted through a bidirectional ring network optical fiber channel between an offshore converter station and several wind turbine energy consumption devices in an offshore wind farm. The speed of sending the wind turbine energy consumption input command to each wind turbine energy consumption device can be improved, the intervention of the wind turbine energy consumption device can be accelerated, the DC fault can be responded to and processed more quickly, and the stable operation of the offshore wind power land-sea integrated DC system can be ensured.

[0005] An embodiment of the present invention provides a DC fault ride-through method for an offshore wind power onshore integrated DC system based on a fast communication link, which is applied to the offshore wind power onshore integrated DC system. The offshore wind power onshore integrated DC system comprises: an offshore wind farm, an offshore converter station and an onshore converter station.

[0006] The offshore wind farm includes a plurality of wind power converters and a plurality of communication forwarding devices; each wind power converter is connected to a communication forwarding device, and each wind power converter includes a wind turbine energy consumption device; the offshore converter station and each communication forwarding device are connected in sequence through a bidirectional ring network optical fiber channel;

[0007] The DC fault ride-through method comprises:

[0008] When a DC fault occurs, obtain the voltage drop speed and voltage drop amplitude of the onshore converter station;

[0009] When the voltage drop speed is lower than the voltage drop speed threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, a wind turbine energy consumption input command is sent to the offshore converter station, so that the offshore converter station transmits the wind turbine energy consumption input command to each communication forwarding device step by step through the bidirectional ring network optical fiber channel, and each communication forwarding device transmits the wind turbine energy consumption input command to the corresponding wind turbine energy consumption device, so that each wind turbine energy consumption device absorbs the fault surplus power according to the wind turbine energy consumption input command; wherein, the time from the issuance of the wind turbine energy consumption input command from the flexible direct current side to the start-up of the wind turbine energy consumption device is not greater than the maximum allowable delay time.

[0010] Furthermore, the offshore wind power integrated sea-land DC system further includes: a terminal conversion station, a switch collection station and a receiving-end power grid, the terminal converter station includes a plurality of first DC high-speed switches, the switch collection station includes a plurality of second DC high-speed switches and a plurality of third DC high-speed switches, and the onshore converter station includes a plurality of fourth DC high-speed switches;

[0011] The offshore converter station is connected to the terminal converter station via a DC submarine cable;

[0012] Each of the first DC high-speed switches is connected to each of the second DC high-speed switches in a one-to-one correspondence via a first DC overhead line;

[0013] Each of the second DC high-speed switches is connected in parallel with each of the third DC high-speed switches;

[0014] Each third DC high-speed switch is connected to each fourth DC high-speed switch in a one-to-one correspondence through the second DC overhead line;

[0015] The onshore converter station is connected to the receiving-end power grid via a third DC overhead line.

[0016] Furthermore, the onshore converter station includes a first DC control and protection system, and the offshore converter station includes a second DC control and protection system;

[0017] The first DC control and protection system and the second DC control and protection system communicate through a direct communication channel.

[0018] Furthermore, the offshore wind farm also includes a plurality of wind turbines; each wind turbine is connected to a wind power converter;

[0019] The bidirectional ring network optical fiber channel comprises: a first transmitting optical fiber, a second transmitting optical fiber, a first receiving optical fiber and a second receiving optical fiber;

[0020] The first transmitting end of the offshore converter station is connected to the first receiving end of the first communication forwarding device through the first transmitting optical fiber, the first transmitting ends of the remaining communication forwarding devices except the first communication forwarding device and the terminal communication forwarding device are sequentially connected to the first receiving end of the next communication forwarding device through the first transmitting optical fiber, and the first transmitting end of the terminal communication forwarding device is connected to the first receiving end of the offshore converter station through the first receiving optical fiber;

[0021] The second transmitting end of the offshore converter station is connected to the second receiving end of the terminal communication forwarding device through the second transmitting optical fiber. The second transmitting ends of the remaining communication forwarding devices except the first communication forwarding device and the terminal communication forwarding device are connected to the second receiving end of the previous communication forwarding device in sequence through the second receiving optical fiber. The second transmitting end of the first communication forwarding device is connected to the second receiving end of the offshore converter station through the second receiving optical fiber.

[0022] Furthermore, the capacity of each of the fan energy consumption devices is determined according to the following formula:

[0023] W0=P0*t0;

[0024] Wherein, W0 represents the capacity of the fan energy consumption device; P0 represents the rated output power of the fan; t0 represents the time margin, which is determined according to the DC fault ride-through time.

[0025] Furthermore, the maximum allowable delay duration is determined by the following formula:

[0026]

[0027] Among them, t allow is the maximum allowable delay time; C is the capacitance of the offshore converter station; V max The maximum permissible module voltage of the offshore converter station; is the rated module voltage of the offshore converter station; N full is the number of full-bridge modules in the offshore converter station; P max is the maximum active power of the offshore converter station.

[0028] Furthermore, when the voltage drop speed is lower than the voltage drop speed threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, the method further includes:

[0029] A DC fault ride-through instruction is sent to the onshore converter station and the offshore converter station, so that the offshore converter station and the onshore converter station establish a negative pressure according to the DC fault ride-through instruction, absorb the fault current, and complete a DC fault clearing.

[0030] Furthermore, each wind turbine energy consumption device absorbs the fault surplus power according to the wind turbine energy consumption input instruction, including:

[0031] The real-time power of each wind turbine energy-consuming device at the previous moment is obtained according to the wind turbine energy-consuming instruction, and each wind turbine energy-consuming device is controlled to absorb the surplus power of the fault according to the real-time power of each wind turbine energy-consuming device at the previous moment, until the offshore wind power sea-land integrated DC system achieves surplus power balance.

[0032] Furthermore, after the completion of clearing a fault of the offshore wind power land-sea integrated DC transmission system, it also includes:

[0033] Perform the first original pressure restart of the offshore wind power land-sea integrated DC system, control the offshore converter station to restore the first DC current, and control the onshore converter station to establish the first DC voltage;

[0034] If the first DC voltage is successfully established at the onshore converter station, the DC fault is completely cleared;

[0035] If the onshore converter station fails to establish the first DC voltage, the offshore wind power onshore integrated DC system is restarted at the original pressure for the second time, the offshore converter station is controlled to restore the second DC current, and the onshore converter station is controlled to establish the second DC voltage;

[0036] If the second DC voltage of the onshore converter station is successfully established, the DC fault is completely cleared.

[0037] Furthermore, after the offshore wind power land-sea integrated DC system is restarted at the original pressure for the second time, the offshore converter station is controlled to restore the second DC current, and the onshore converter station is controlled to establish the second DC voltage, the method further includes:

[0038] If the second DC voltage at the onshore converter station fails to be established, the wind turbine will be cut off and the energy-consuming devices of each wind turbine will be controlled to stop operation.

[0039] The following beneficial effects are achieved by implementing the present invention:

[0040] The present invention provides a DC fault crossing method of an offshore wind power sea-land integrated DC system based on a fast communication link. The offshore wind power sea-land integrated DC system includes: an offshore wind farm, an offshore converter station and an onshore converter station. The offshore wind farm includes a plurality of wind power converters and a plurality of communication forwarding devices; each wind power converter is connected to a communication forwarding device, and each wind power converter includes a wind turbine energy consumption device; the offshore converter station and each communication forwarding device are connected in sequence through a bidirectional ring network optical fiber channel. When a DC fault occurs, by obtaining the voltage drop speed and voltage drop amplitude of the onshore converter station; when the voltage drop speed is lower than the voltage drop speed threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, a wind turbine energy consumption input instruction is sent to the offshore converter station, so that the offshore converter station transmits the wind turbine energy consumption input instruction to each communication forwarding device step by step through the bidirectional ring network optical fiber channel, and each communication forwarding device transmits the wind turbine energy consumption input instruction to the corresponding wind turbine energy consumption device, so that the wind turbine energy consumption device can absorb the fault surplus power according to the wind turbine energy consumption input instruction within the maximum allowable delay time. Transmitting wind turbine energy consumption input commands through a bidirectional ring network optical fiber channel can increase the speed at which wind turbine energy consumption input commands are sent to each wind turbine energy consumption device, speed up the intervention of wind turbine energy consumption devices, respond to and handle DC faults more quickly, and ensure the stable operation of the offshore wind power sea-land integrated DC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a flow chart of a DC fault ride-through method of an offshore wind power land-sea integrated DC system based on a fast communication link provided by an embodiment of the present invention.

[0042] Figure 2 It is a structural schematic diagram of an offshore wind power sea-land integrated DC system provided by an embodiment of the present invention.

[0043] Figure 3 The present invention is a schematic diagram of communication between a land converter station and an offshore converter station through a direct communication channel provided by an embodiment of the present invention.

[0044] Figure 4 It is a schematic diagram of the internal structure of a wind power converter provided by an embodiment of the present invention.

[0045] Figure 5 It is a schematic diagram of a bidirectional ring network optical fiber channel provided by an embodiment of the present invention.

[0046] Figure 6 It is a schematic diagram of a DC fault ride-through stage provided by an embodiment of the present invention.

[0047] Figure 7 It is a schematic diagram of the communication delay of calling a wind turbine energy consumption device provided by an embodiment of the present invention.

[0048] Figure 8It is a schematic diagram of calculation results of a fault current situation generated in a DC fault situation caused by a DC overhead line between a terminal conversion station and a switch collection station provided by an embodiment of the present invention.

[0049] Fig. 9 It is a schematic diagram of calculation results of a fault current situation generated by a DC fault caused by a DC overhead line between a switch collection station and an onshore converter station provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0053] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0054] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0055] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0056] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0057] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0058] like Figure 1 As shown, a DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link is provided in an embodiment of the present invention, which is applied to Figure 2 The offshore wind power integrated land and sea DC system shown.

[0059] The offshore wind power integrated sea and land DC system includes: an offshore wind farm, an offshore converter station and an onshore converter station. The offshore wind farm includes a plurality of wind power converters and a plurality of communication forwarding devices; each wind power converter is connected to a communication forwarding device, and each wind power converter includes a wind turbine energy consumption device; the offshore converter station and each communication forwarding device are connected in sequence through a bidirectional ring network optical fiber channel.

[0060] In a preferred embodiment, the offshore wind power sea-land integrated DC system also includes: the offshore wind power sea-land integrated DC system also includes: a terminal conversion station, a switch collection station and a receiving-end power grid, the terminal converter station includes a number of first DC high-speed switches, the switch collection station includes a number of second DC high-speed switches and a number of third DC high-speed switches, and the onshore converter station includes a number of fourth DC high-speed switches; the offshore converter station is connected to the terminal converter station through a DC submarine cable; each of the first DC high-speed switches is connected one-to-one with each of the second DC high-speed switches of the switch collection station through a first DC overhead line; each of the second DC high-speed switches is connected in parallel with each of the third DC high-speed switches; each of the third DC high-speed switches is connected one-to-one with each of the fourth DC high-speed switches through a second DC overhead line; the onshore converter station is connected to the receiving-end power grid through a third DC overhead line.

[0061] Specifically, the offshore wind power sea-land integrated DC system proposed in the present invention is formed by connecting an offshore wind farm, an offshore converter station, a terminal conversion station, a switch collection station, an onshore converter station and a receiving power grid in sequence. Among them, both the offshore converter station and the onshore converter station are provided with a DC control and protection system, the first DC control and protection system refers to the DC control and protection system corresponding to the onshore converter station, and the second DC control and protection system refers to the DC control and protection system corresponding to the offshore converter station. In order to realize DC fault crossing in the DC transmission system of the present invention, the offshore converter station and the onshore converter station of the present invention both adopt a full half-bridge hybrid topology. When a DC line fault occurs, the full half-bridge hybrid topology converter can make the bridge arm current flow through the capacitor in both directions, effectively clamping the fault current, thereby inhibiting the further development of the fault current. Preferably, the present invention takes into account the situation where the MMC submodule of the offshore converter station is over-voltage due to the inability to transmit power. When constructing the offshore wind power sea-land integrated DC system, the present invention cancels the centralized energy consumption device and uses the wind turbine's own energy consumption device of the offshore wind farm to achieve the balance of the fault surplus power.

[0062] In order to realize DC fault ride-through in the offshore wind power land-sea integrated DC system of the present invention, a DC high-speed switch is configured at both ends of each DC overhead line. Figure 1 The HSS identifier in the terminal converter station, the switch collection station and the onshore converter station all include multiple DC high-speed switches. The terminal converter station is connected to multiple second DC high-speed switches of the switch collection station through multiple first DC high-speed switches in a one-to-one correspondence, and is collected into multiple third DC high-speed switches through the switch collection station, and each third DC high-speed switch is connected to each fourth DC high-speed switch in a one-to-one correspondence. It should be noted that the function of the switch collection station is to collect multiple second DC overhead lines passing through the second DC high-speed switches, thereby reducing the laying length of the second DC overhead lines. Therefore, the number of third DC high-speed switches in the switch collection station is less than the number of second DC high-speed switches, thereby realizing the collection of each second DC overhead line in the switch collection station, and further reducing the required DC overhead line laying length between the switch collection station and the onshore converter station.

[0063] In a preferred embodiment, the onshore converter station includes a first DC control and protection system, and the offshore converter station includes a second DC control and protection system; the first DC control and protection system and the second DC control and protection system communicate through a direct communication channel.

[0064] Specifically, the specific communication mode of the system under DC fault is as follows: Figure 3As shown, the present invention establishes a direct communication channel between the first DC control and protection system and the second DC control and protection system, and the DC communication channel is a 100M inter-station communication channel. Based on the construction of the communication channel, when a fault is detected in the first DC control and protection system of the onshore converter station, the fault signal can be transmitted to the second DC control and protection system of the offshore converter station through the 100M inter-station communication channel between the onshore converter station and the offshore converter station. The second DC control and protection system of the offshore converter station issues a wind turbine energy consumption input instruction for calling the wind turbine energy consumption device, which is transmitted to the wind turbine energy consumption device corresponding to each wind turbine through the optical fiber channel of the collector submarine cable.

[0065] In a preferred embodiment, the offshore wind farm further comprises a plurality of wind turbines; each wind turbine is connected to a wind power converter;

[0066] The bidirectional ring network optical fiber channel includes: a first optical fiber, a second optical fiber, a third optical fiber and a fourth optical fiber;

[0067] The first transmitting end of the offshore converter station is connected to the first receiving end of the first communication forwarding device through the first optical fiber, the first transmitting ends of the remaining communication forwarding devices except the first communication forwarding device and the terminal communication forwarding device are sequentially connected to the first receiving end of the next communication forwarding device through the first optical fiber, and the first transmitting end of the terminal communication forwarding device is connected to the first receiving end of the offshore converter station through the first optical fiber;

[0068] The second transmitting end of the offshore converter station is connected to the second receiving end of the terminal communication forwarding device through the second optical fiber, and the second transmitting ends of the remaining communication forwarding devices except the first communication forwarding device and the terminal communication forwarding device are sequentially connected to the second receiving end of the previous communication forwarding device through the second optical fiber, and the second transmitting end of the first communication forwarding device is connected to the second receiving end of the offshore converter station through the second optical fiber;

[0069] The third transmitting end of the offshore converter station is connected to the third receiving end of the first communication forwarding device through the third optical fiber, the third transmitting ends of the remaining communication forwarding devices except the first communication forwarding device and the terminal communication forwarding device are sequentially connected to the third receiving end of the next communication forwarding device through the third optical fiber, and the third transmitting end of the terminal communication forwarding device is connected to the third receiving end of the offshore converter station through the third optical fiber;

[0070] The fourth transmitting end of the offshore converter station is connected to the fourth receiving end of the terminal communication forwarding device through a fourth optical fiber. The fourth transmitting ends of the remaining communication forwarding devices except the first communication forwarding device and the terminal communication forwarding device are connected to the fourth receiving end of the previous communication forwarding device in sequence through the fourth optical fiber. The fourth transmitting end of the first communication forwarding device is connected to the fourth receiving end of the offshore converter station through the fourth optical fiber.

[0071] Specifically, Figure 4The figure is a schematic diagram of the internal structure of a wind power converter provided by the present invention, wherein the wind power converter comprises a machine-side converter, a wind turbine energy consumption device and a grid-side converter. An offshore wind farm comprises a plurality of wind turbines, a plurality of wind power converters and a plurality of communication forwarding devices.

[0072] like Figure 5 As shown, the present invention provides a schematic diagram of communication between an offshore converter station and a communication forwarding device of each wind turbine through a bidirectional ring network optical fiber channel.

[0073] Taking n wind turbines as an example, the offshore converter station sends the wind turbine energy consumption input instruction from the first transmitting end TX1 of the offshore converter station to the first receiving end RX1 of the communication forwarding device 1 through the first optical fiber. After receiving the signal, the first receiving end RX1 transmits it through the internal signal, and then sends it to the first receiving end RX1 of the communication forwarding device 2 through the first transmitting end TX1 of the communication forwarding device 1 through the first optical fiber. After being sent to the first receiving end RX1 of the communication forwarding device n in turn, after the internal signal transmission of the communication forwarding device n, the response signal of each communication forwarding device to the wind turbine energy consumption input instruction is sent to the first receiving end RX1 of the offshore converter station through the first transmitting end of the communication forwarding device n through the first optical fiber.

[0074] At the same time, the offshore converter station sends the wind turbine energy consumption input instruction from the second transmitting end TX2 to the second receiving end RX2 of the communication forwarding device n through the second optical fiber, and after the internal signal transmission of the communication forwarding device n, it is sent from the second transmitting end TX1 of the communication forwarding device n to the second receiving end RX2 of the communication forwarding device n-1 through the second optical fiber, and then sent to the second receiving end RX2 of the communication forwarding device 1 in turn. After the internal signal transmission of the communication forwarding device 1, the response signal of each communication forwarding device to the wind turbine energy consumption input instruction is transmitted to the second receiving end RX2 of the offshore converter station through the second transmitting end TX2 of the communication forwarding device 1 through the second optical fiber.

[0075] At the same time, the offshore converter station sends the wind turbine energy consumption input instruction from the third transmitting end TX3 of the offshore converter station to the third receiving end RX3 of the communication forwarding device 1 through the third optical fiber. After receiving the signal, the third receiving end RX3 transmits it through the internal signal, and again sends it to the third receiving end RX3 of the communication forwarding device 2 through the third transmitting end TX3 of the communication forwarding device 1 through the first transmitting optical fiber. After being sent to the third receiving end RX3 of the communication forwarding device n in turn, after the internal signal transmission of the communication forwarding device n, the response signal of each communication forwarding device to the wind turbine energy consumption input instruction is sent to the third receiving end RX3 of the offshore converter station through the first transmitting end of the communication forwarding device n through the third optical fiber.

[0076] At the same time, the offshore converter station sends the wind turbine energy consumption input instruction from the fourth transmitting end TX4 to the fourth receiving end RX4 of the communication forwarding device n through the fourth optical fiber, and after the internal signal transmission of the communication forwarding device n, it is sent from the fourth transmitting end TX4 of the communication forwarding device n to the fourth receiving end RX4 of the communication forwarding device n-1 through the fourth optical fiber, and then sent to the fourth receiving end RX4 of the communication forwarding device 1 in turn, and after the internal signal transmission of the communication forwarding device 1, the response signal of each communication forwarding device to the wind turbine energy consumption input instruction is transmitted to the fourth receiving end RX4 of the offshore converter station through the fourth optical fiber through the fourth transmitting end TX4 of the communication forwarding device 1.

[0077] In a preferred embodiment, the capacity of each of the fan energy consumption devices is determined according to the following formula:

[0078] W0=P0*t0;

[0079] Wherein, W0 represents the capacity of the fan energy consumption device; P0 represents the rated output power of the fan; t0 represents the time margin, the unit is s, and the value is determined according to the DC fault ride-through time.

[0080] Specifically, since the present invention eliminates the centralized energy-consuming device and only realizes the balance of surplus power during DC fault riding through the wind turbine energy-consuming device, when designing the offshore wind power sea-land integrated DC system, it is necessary to reset the capacity requirements of the wind turbine energy-consuming device so that the wind turbine energy-consuming device can meet the energy dissipation requirements during DC fault riding.

[0081] When designing fan energy consumption devices, it is necessary to focus on the capacity requirements of fan energy consumption devices, such as Figure 6 As shown, the DC fault ride-through takes 600-700ms. Considering the working conditions of two restarts, the fan energy consumption device needs to absorb a maximum surplus power of "rated power*2.1s". Considering a certain power margin, the present invention sets the capacity requirement of each fan energy consumption device as:

[0082] W0=P0*2.5s;

[0083] Among them, W0 represents the capacity of the wind turbine energy consumption device; P0 represents the rated output power of the offshore wind turbine; t0 is taken based on the time required for DC fault ride-through, with redundancy added and a value of 2.5s.

[0084] Existing wind turbines do not have the ability to absorb surplus power accordingly, and are usually designed according to "rated power * 1.5s" in engineering. However, by resetting the capacity of the wind turbine energy consumption device as mentioned above, 2.5s zero voltage ride-through can be achieved, and there is little impact on the wind turbine inverter, the structure of the offshore wind farm itself and temperature control.

[0085] In a preferred embodiment, the maximum allowable delay duration is determined by the following formula:

[0086]

[0087] Among them, t allow is the maximum allowable delay time; C is the capacitance of the offshore converter station; V max is the maximum allowable module voltage of the offshore converter station; V norm is the rated module voltage of the offshore converter station; N full is the number of full-bridge modules in the offshore converter station; P max is the maximum active power of the offshore converter station.

[0088] For example, as shown in the following table, the present invention refers to the actual requirements of the project and takes typical values ​​for t allow Calculate and get t according to the typical values ​​in the table below allow =9.22ms, that is, after a fault occurs in the DC overhead line, the maximum allowable delay time from the issuance of the wind turbine energy consumption input command from the flexible DC side to the start-up of the wind turbine energy consumption device is 9.22ms. During the period when the DC overhead line fails and the wind turbine energy consumption device is not put into operation, the surplus power is absorbed by the offshore converter station.

[0089] category Numeric Capacitor C 11mF <![CDATA[Maximum allowable module voltage V max > 2.6kV <![CDATA[Rated module voltage V norm > 2.1kV <![CDATA[Number N of full-bridge modules full > 1428 <![CDATA[Maximum active power P max > 2000MW

[0090] Specifically, the existing system has not established direct communication between the second DC control and protection system of the offshore converter station and the wind turbine converter of the offshore wind farm. It needs to be forwarded through the offshore wind farm SCADA system. The current communication time is about hundreds of milliseconds to several seconds. Therefore, the large communication delay seriously affects the stability of the DC transmission system. The communication device of the system needs to be redesigned to make the communication time meet t allow The indicator requires that the bidirectional ring network fiber optic channel constructed under the constraint of meeting the maximum allowable delay time can enable the wind turbine energy-consuming devices to be put into use in a timely and rapid manner to absorb the surplus power of the fault, achieve rapid clearing of the DC fault and restore the stable operation of the system.

[0091] Based on the above analysis, it can be seen that in the offshore wind power integrated land-sea DC system, the communication delay from the occurrence of a fault to the commissioning of the wind turbine energy consumption device mainly includes the following links: fault feature transmission delay, line fault detection and communication delay, communication delay between the offshore converter station and each wind turbine converter, and wind turbine energy consumption device commissioning delay. Figure 7As shown in the figure, combined with the existing DC engineering construction and operation conditions, it can be calculated that when a fault occurs in the remote DC overhead line, the transmission delay from the fault occurrence to the second DC control and protection system forwarded to the offshore converter station is about 5ms. The communication delay from the fault occurrence to the second DC control and protection system forwarded to the offshore converter station specifically includes: fault feature transmission delay of 1.5ms; line fault detection delay of 3ms; protection host forwarding control host delay of 0.5ms. Through the bidirectional ring network optical fiber channel for communication and signal transmission, it can be achieved from the offshore converter station issuing the wind turbine energy consumption input command to the wind turbine energy consumption device input control within 1ms. The communication delay between the offshore converter station and each wind turbine energy consumption device specifically includes: the optical fiber fast communication delay between the flexible direct current and the wind turbine converter is 100~200us; the communication data packet length is 100~200us; the wind turbine converter receives the control command, and the DSP processes the information, 500us within 2 cycles. Taking the above communication delays into consideration, after a DC fault occurs, the fault information is transmitted to the wind turbine energy consumption device and the fault delay of the remote DC overhead line is about 6ms, which can realize fast communication of the DC transmission system.

[0092] After completing the construction of the above-mentioned offshore wind power integrated sea-land DC system and the fast communication design of the bidirectional ring network optical fiber channel, a DC fault ride-through method is implemented on the system, including:

[0093] Step S1: when a DC fault occurs, obtaining a voltage drop speed and a voltage drop amplitude of an onshore converter station;

[0094] Step S2: When the voltage drop speed is lower than the voltage drop speed threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, a wind turbine energy consumption input instruction is sent to the offshore converter station, so that the offshore converter station transmits the wind turbine energy consumption input instruction to each communication forwarding device step by step through the bidirectional ring network optical fiber channel, and each communication forwarding device transmits the wind turbine energy consumption input instruction to the corresponding wind turbine energy consumption device, so that the wind turbine energy consumption device absorbs the fault surplus power according to the wind turbine energy consumption input instruction; wherein, the time from the issuance of the wind turbine energy consumption input instruction from the flexible direct current side to the start-up of the wind turbine energy consumption device is not greater than the maximum allowable delay time.

[0095] For step S1, after the DC fault occurs, the voltage at the fault point will drop instantly and the DC current will rise. At this time, the fault of the offshore wind power sea-land integrated DC system is detected and located, and the DC voltage data of the onshore converter station at the fault point is obtained. When the DC voltage does not reach the preset control start standard, it means that the fault degree is low at this time, and unnecessary system intervention can be avoided at this time, thereby maintaining the stability and safety of the power grid; wherein, the preset control start standard is that the voltage drop speed is lower than the voltage drop speed threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold. In the present invention, the voltage drop speed threshold is a low voltage constant value, which is 0.45pu, and the voltage drop amplitude threshold is a voltage mutation constant value, which is -1.16pu / ms. When the DC voltage data reaches the preset control start condition, it is necessary to send a wind turbine energy consumption input instruction to the offshore converter station, so that the offshore converter station transmits the wind turbine energy consumption input instruction to each wind turbine energy consumption device through a bidirectional ring network optical fiber channel, so that each wind turbine energy consumption device absorbs the fault surplus power according to the wind turbine energy consumption input instruction.

[0096] For step S2, in a preferred embodiment, each wind turbine energy-consuming device absorbs the surplus power caused by the fault according to the wind turbine energy-consuming input instruction, including: obtaining the real-time power of each wind turbine energy-consuming device at the previous moment according to the wind turbine energy-consuming input instruction, and controlling each wind turbine energy-consuming device to absorb the surplus power caused by the fault according to the real-time power of each wind turbine energy-consuming device at the previous moment, until the offshore wind power sea-land integrated DC system achieves surplus power balance.

[0097] Specifically, after receiving the wind turbine energy consumption input instruction, the wind turbine energy consumption device needs to absorb the fault surplus power according to the instruction. Specifically, the real-time power of each wind turbine energy consumption device at the last moment is obtained, and each wind turbine energy consumption device is controlled to consume the fault surplus power according to the real-time power of each wind turbine energy consumption device at the last moment, until the offshore wind power land-sea integrated DC system achieves surplus power balance.

[0098] In a preferred embodiment, when the voltage drop speed is lower than the voltage drop speed threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, it also includes: sending a DC fault ride-through instruction to the onshore converter station and the offshore converter station, so that the offshore converter station and the onshore converter station establish a negative voltage according to the DC fault ride-through instruction, absorb the fault current, and complete a DC fault clearing.

[0099] Specifically, when the DC voltage data reaches the preset control start condition, it is also necessary to send a DC fault ride-through instruction to the offshore converter station and the onshore converter station. After receiving the DC fault ride-through instruction, the offshore converter station and the onshore converter station establish negative pressure and actively absorb the fault current.

[0100] At this time, the first fault clearing of the offshore wind power onshore and offshore integrated DC system is completed. Preferably, after the first fault clearing, the offshore wind power onshore and offshore integrated DC system enters the de-ionization stage, during which the flexible DC ensures that the DC current is 0, so that the fault line is completely de-ionized, ensuring that the flashover arc disappears and the insulation performance is restored to the original level. It is worth noting that the de-ionization time should not be too long, so as to avoid causing a long-term overpower of the sending-end power grid and a long-term underpower of the receiving-end power grid, thereby causing stable control actions such as load shedding.

[0101] In a preferred embodiment, after completing the clearing of one fault of the offshore wind power sea-land integrated DC system, it also includes: restarting the offshore wind power sea-land integrated DC system at the original pressure for the first time, controlling the offshore converter station to restore the first DC current, and controlling the onshore converter station to establish the first DC voltage; if the first DC voltage of the onshore converter station is successfully established, the DC fault is completely cleared; if the first DC voltage of the onshore converter station fails to be established, restarting the offshore wind power sea-land integrated DC system at the original pressure for the second time, controlling the offshore converter station to restore the second DC current, and controlling the onshore converter station to establish the second DC voltage; if the second DC voltage of the onshore converter station is successfully established, the DC fault is completely cleared.

[0102] In a preferred embodiment, after the offshore wind power sea-land integrated DC system is restarted at the original pressure for the second time, the offshore converter station is controlled to restore the second DC current, and the onshore converter station is controlled to establish the second DC voltage, it also includes: if the second DC voltage of the onshore converter station fails to be established, the wind turbine is cut off and the energy-consuming devices of each wind turbine are controlled to exit operation.

[0103] Specifically, after a sufficient de-ionization process, the original pressure restart is performed, the offshore converter station is controlled to restore the first DC current, and the onshore converter station is controlled to establish the first DC voltage. If the onshore converter station successfully establishes the first DC voltage, it means that the DC fault has been completely cleared, and each station will gradually restore the DC power. If the onshore converter station fails to establish the first DC voltage, it means that the DC fault still exists, and it is necessary to repeat the de-ionization process, and then perform the second original pressure restart, control the offshore converter station to restore the second DC current, and control the onshore converter station to establish the second DC voltage. If the onshore converter station successfully establishes the second DC voltage, it means that the DC fault has been completely cleared, and each station will gradually restore the DC power. If the onshore converter station fails to establish the second DC voltage, it means that the DC fault still exists and the fault is a permanent fault. After two restarts, the DC current of the DC transmission system is still outside the stable operating range, and a machine cut-off operation is required. It should be noted that, for the offshore wind power integrated sea-land DC system of the present invention, considering that the DC fault ride-through takes 600-700ms, the wind turbine energy consumption device absorbs a maximum of "rated power * 2.5s" surplus power. Considering that the DC fault ride-through takes 600-700ms and the machine disconnection delay takes at least 150ms, two restarts are used as the machine disconnection criterion for the offshore wind power integrated sea-land DC system. When the number of restarts of the DC transmission system is less than or equal to 2 times, the surplus power is absorbed by the offshore converter station, the onshore converter station and the wind turbine energy consumption device. When the number of restarts of the DC transmission system is greater than 2 times, the machine disconnection operation is performed, and the wind turbine energy consumption device exits operation.

[0104] For example, a simulation study on offshore wind power DC fault crossing is conducted in an integrated offshore wind power system. In steady state, there are three groups of flexible DC converter stations at sea to send out wind turbine power, and VF control is adopted in steady state, with the rated power of 2000MW; the receiving end converter station of the onshore converter station has two groups of converters, which are connected to the HSS through the DC bus, and the DC voltage and active power are controlled separately in steady state. Considering two scenarios, the DC fault caused by the DC overhead line between the terminal conversion station and the switch collection station, and the DC fault caused by the DC overhead line between the switch collection station and the onshore converter station, a simulation experiment is designed. The positive and negative bus voltages on the DC side of the onshore converter station receiving end voltage station are ±500kV, and the DC current is about 2.6kA. The fault occurs at 5.1s. After the fault, the onshore converter station is put into control 5ms, the offshore converter station is put into control 6ms, and the wind turbine energy consumption device is put into control 7ms. The specific results of the example are as follows Figure 8 and Fig. 9 As shown, Figure 8 The fault current generated by the DC overhead line between the terminal conversion station and the switch collection station under the DC fault condition (scenario 1) is: Fig. 9The fault current is generated by the DC fault (scenario 2) caused by the DC overhead line between the switch collection station and the onshore converter station. At the moment of the fault, the fault pole capacitor discharges through the fault point to form a large fault current. As the DC voltage and current are controlled to 0, the fault current drops rapidly. About 120ms (scenario 1) / 200ms (scenario 2) after the fault, the fault current presents an AC fluctuation with a peak value of less than 200A.

[0105] The following table gives a comparison of key electrical parameters under different fault conditions. It can be found that during the fault process, the maximum overvoltage of the submodule capacitor at the sending end (offshore converter station) does not exceed 1.30pu, and the current does not exceed 2.5kA; the maximum overvoltage of the submodule capacitor at the receiving end (onshore converter station) does not exceed 1.20pu, and the current does not exceed 3.5kA. The calculation results show that the offshore wind power integrated land-sea DC transmission system and offshore wind power DC fault crossing method proposed in this paper can use distributed wind turbine energy consumption devices to consume wind power surplus power, and at the same time, there is no risk of overvoltage and overcurrent in the converter valves at the sending and receiving ends.

[0106]

[0107] It should be noted that the system embodiment described above is merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. In addition, in the drawings of the system embodiment provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, which may be specifically implemented as one or more communication buses or signal lines. A person of ordinary skill in the art may understand and implement it without paying any creative effort.

[0108] Those skilled in the art can clearly understand that for the sake of convenience and brevity, the specific working process of the device described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0109] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link, characterized in that: Applicable to an offshore wind power sea-land integrated DC system, the offshore wind power sea-land integrated DC system comprises: an offshore wind farm, an offshore converter station and an onshore converter station, the offshore wind farm comprises a plurality of wind power converters and a plurality of communication forwarding devices; each wind power converter is connected to a communication forwarding device, and each wind power converter comprises a wind turbine energy consumption device; the offshore converter station and each communication forwarding device are sequentially connected via a bidirectional ring network optical fiber channel; The DC fault ride-through method comprises: When a DC fault occurs, obtain the voltage drop speed and voltage drop amplitude of the onshore converter station; When the voltage drop speed is lower than the voltage drop speed threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, a wind turbine energy consumption input instruction is sent to the offshore converter station, so that the offshore converter station transmits the wind turbine energy consumption input instruction to each communication forwarding device step by step through the bidirectional ring network optical fiber channel, and each communication forwarding device transmits the wind turbine energy consumption input instruction to the corresponding wind turbine energy consumption device, so that the wind turbine energy consumption device absorbs the fault surplus power according to the wind turbine energy consumption input instruction; wherein, the time from the issuance of the wind turbine energy consumption input instruction from the flexible direct current side to the start-up of the wind turbine energy consumption device is not greater than the maximum allowable delay time.

2. A DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link as claimed in claim 1, characterized in that: The offshore wind power integrated sea-land DC system also includes: a terminal conversion station, a switch collection station and a receiving-end power grid, the terminal converter station includes a plurality of first DC high-speed switches, the switch collection station includes a plurality of second DC high-speed switches and a plurality of third DC high-speed switches, and the onshore converter station includes a plurality of fourth DC high-speed switches; The offshore converter station is connected to the terminal converter station via a DC submarine cable; Each of the first DC high-speed switches is connected to each of the second DC high-speed switches in a one-to-one correspondence via a first DC overhead line; Each of the second DC high-speed switches is connected in parallel with each of the third DC high-speed switches; Each third DC high-speed switch is connected to each fourth DC high-speed switch in a one-to-one correspondence through the second DC overhead line; The onshore converter station is connected to the receiving-end power grid via a third DC overhead line.

3. A DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link as claimed in claim 2, characterized in that: The onshore converter station includes a first DC control and protection system, and the offshore converter station includes a second DC control and protection system; The first DC control and protection system and the second DC control and protection system communicate through a direct communication channel.

4. A DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link as claimed in claim 3, characterized in that: The offshore wind farm also includes a plurality of wind turbines; each wind turbine is connected to a wind power converter; The bidirectional ring network optical fiber channel includes: a first optical fiber, a second optical fiber, a third optical fiber and a fourth optical fiber; The first transmitting end of the offshore converter station is connected to the first receiving end of the first communication forwarding device through the first optical fiber, the first transmitting ends of the remaining communication forwarding devices except the first communication forwarding device and the terminal communication forwarding device are sequentially connected to the first receiving end of the next communication forwarding device through the first optical fiber, and the first transmitting end of the terminal communication forwarding device is connected to the first receiving end of the offshore converter station through the first optical fiber; The second transmitting end of the offshore converter station is connected to the second receiving end of the terminal communication forwarding device through the second optical fiber, and the second transmitting ends of the remaining communication forwarding devices except the first communication forwarding device and the terminal communication forwarding device are sequentially connected to the second receiving end of the previous communication forwarding device through the second optical fiber, and the second transmitting end of the first communication forwarding device is connected to the second receiving end of the offshore converter station through the second optical fiber; The third transmitting end of the offshore converter station is connected to the third receiving end of the first communication forwarding device through the third optical fiber, the third transmitting ends of the remaining communication forwarding devices except the first communication forwarding device and the terminal communication forwarding device are sequentially connected to the third receiving end of the next communication forwarding device through the third optical fiber, and the third transmitting end of the terminal communication forwarding device is connected to the third receiving end of the offshore converter station through the third optical fiber; The fourth transmitting end of the offshore converter station is connected to the fourth receiving end of the terminal communication forwarding device through a fourth optical fiber. The fourth transmitting ends of the remaining communication forwarding devices except the first communication forwarding device and the terminal communication forwarding device are connected to the fourth receiving end of the previous communication forwarding device in sequence through the fourth optical fiber. The fourth transmitting end of the first communication forwarding device is connected to the fourth receiving end of the offshore converter station through the fourth optical fiber.

5. A DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link as claimed in claim 4, characterized in that: The capacity of each of the fan energy consumption devices is determined according to the following formula: W0=P0*t0; Wherein, W0 represents the capacity of the fan energy consumption device; P0 represents the rated output power of the fan; t0 represents the time margin, which is determined according to the DC fault ride-through time.

6. A DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link as claimed in claim 5, characterized in that: The maximum allowable delay duration is determined by the following formula: Among them, t allow is the maximum allowable delay time; C is the capacitance of the offshore converter station; V max is the maximum allowable module voltage of the offshore converter station; V norm is the rated module voltage of the offshore converter station; N full is the number of full-bridge modules in the offshore converter station; P max is the maximum active power of the offshore converter station.

7. A DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link as claimed in claim 6, characterized in that: When the voltage drop speed is lower than the voltage drop speed threshold and the voltage drop amplitude is lower than the voltage drop amplitude threshold, the following also includes: A DC fault ride-through instruction is sent to the onshore converter station and the offshore converter station, so that the offshore converter station and the onshore converter station establish a negative pressure according to the DC fault ride-through instruction, absorb the fault current, and complete a DC fault clearing.

8. A DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link as claimed in claim 7, characterized in that: Each fan energy consumption device absorbs the fault surplus power according to the fan energy consumption input instruction, including: The real-time power of each wind turbine energy-consuming device at the previous moment is obtained according to the wind turbine energy-consuming instruction, and each wind turbine energy-consuming device is controlled to absorb the surplus power of the fault according to the real-time power of each wind turbine energy-consuming device at the previous moment, until the offshore wind power sea-land integrated DC system achieves surplus power balance.

9. A DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link as claimed in claim 8, characterized in that: After completing the first fault clearing of the offshore wind power land-sea integrated DC transmission system, it also includes: Perform the first original pressure restart of the offshore wind power land-sea integrated DC system, control the offshore converter station to restore the first DC current, and control the onshore converter station to establish the first DC voltage; If the first DC voltage is successfully established at the onshore converter station, the DC fault is completely cleared; If the onshore converter station fails to establish the first DC voltage, the offshore wind power onshore integrated DC system is restarted at the original pressure for the second time, the offshore converter station is controlled to restore the second DC current, and the onshore converter station is controlled to establish the second DC voltage; If the second DC voltage of the onshore converter station is successfully established, the DC fault is completely cleared.

10. A DC fault ride-through method for an offshore wind power land-sea integrated DC system based on a fast communication link as claimed in claim 9, characterized in that: After the offshore wind power land-sea integrated DC system is restarted at the original pressure for the second time, the offshore converter station is controlled to restore the second DC current, and the onshore converter station is controlled to establish the second DC voltage, the method further includes: If the second DC voltage at the onshore converter station fails to be established, the wind turbine will be cut off and the energy-consuming devices of each wind turbine will be controlled to stop operation.

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