CN116316785A - Offshore Wind Power DC Sending System and Control Method Based on Onshore Cross Switch - Google Patents

Abstract

The invention provides a offshore wind power direct current sending-out system based on an onshore crossbar and a control method, wherein the system comprises the following components: the shore cross switch comprises a first switch, a second switch, a third switch and a fourth switch, wherein the first switch and the second switch are connected with the third switch and the fourth switch in a cross manner and then are connected with a submarine cable, and the first switch and the second switch are interlocked with the third switch and the fourth switch in a switch state so as to realize the positive-negative conversion of the voltage at the direct current side; the power grid is connected with the onshore converter valve through a low-voltage winding and a fifth switch of a transformer in the three-winding transformer, and is connected with the onshore converter valve through a high-voltage winding and a sixth switch of the transformer in the three-winding transformer; the on-shore converter valve adopts a half-bridge modularized multi-level converter, and the direct current side of the on-shore converter valve is connected with the direct current side of the on-shore converter valve through an on-shore cross switch and a sea cable; the alternating current side of the offshore converter valve is connected with an offshore wind farm. The system reduces the cost and ensures the stable operation of the offshore wind power direct current delivery system.

Description

Offshore Wind Power DC Transmission System and Control Method Based on Onshore Cross Switch

technical field

The invention relates to the technical field of offshore wind power, in particular to an offshore wind power direct current transmission system and a control method based on an onshore cross switch.

Background technique

Long-distance offshore wind power transmission generally adopts high-voltage DC transmission technology. After the power generation of offshore wind turbines is collected through AC cables, the offshore converter station converts AC power into DC power, and then transmits the power to the onshore converter station through the DC submarine cable. At present, the converter valves of the offshore converter stations in the offshore wind power DC transmission project all adopt the MMC structure, but the MMC converter valves are expensive and have a large volume and weight. For this reason, the prior art has proposed a variety of offshore converter valve topology schemes in which diode valves (DR) and MMC valves are connected in series. However, in practical applications, DR-MMC series valves have the problem that offshore wind farms are difficult to black-start.

Aiming at the problem of black start of offshore wind power DR-MMC series valve, the existing solution is to lead an AC line from the shore to the offshore converter station to supply the energy required for black start of the offshore wind farm, but this method will increase the Additional costs and losses. In addition, the black start of offshore wind farms can also be realized by using the MMC part of the offshore DR-MMC series valve. In this scheme, a bypass switch is connected in parallel with the DC side of the diode valve in the offshore DR-MMC series valve. Black start is required in offshore wind farms , first close the bypass switch, so that the onshore converter station can directly transmit power to the MMC part of the DR-MMC series valve, and then the MMC provides AC power for the offshore wind farm to achieve black start. In another DR-MMC series valve scheme for offshore wind power, the MMC converter valve of the onshore converter station adopts a full-bridge module topology, so that the onshore converter valve can output negative voltage, so that the diodes of the offshore DR-MMC series valve conduct forward. At this time, the MMC part of the offshore DR-MMC series valve can transmit electric energy to the offshore wind farm to realize black start.

Contents of the invention

Therefore, the technical solution of the present invention mainly solves the defect of high cost of the existing offshore wind power direct current transmission system, thereby providing an offshore wind power direct current transmission system and a control method based on an onshore cross switch.

In the first aspect, the embodiment of the present invention provides an offshore wind power direct current transmission system based on an onshore cross switch, including: a power grid, an onshore converter valve, an onshore cross switch, a submarine cable, an offshore converter valve, and an offshore wind farm; wherein,

The onshore cross switch includes a first switch, a second switch, a third switch and a fourth switch, and after cross-connection between the first switch and the second switch and the third switch and the fourth switch , connected to the submarine cable, the switch states of the first switch and the second switch are interlocked with the third switch and the fourth switch, so as to realize the positive and negative conversion of the DC side voltage;

The power grid is connected to the on-shore converter valve through the transformer low-voltage winding and the fifth switch in the three-winding transformer, and is connected to the on-shore converter valve through the transformer high-voltage winding and the sixth switch in the three-winding transformer; The converter valve adopts a half-bridge modular multilevel converter, and the DC side of the onshore converter valve is connected to the DC side of the offshore converter valve through the onshore cross switch and the submarine cable; The AC side of the converter valve is connected to the offshore wind farm.

The offshore wind power direct current transmission system and control method based on the onshore cross switch provided by the embodiment of the present invention can perform positive and negative pole conversion through the onshore cross switch. The cost of the diverter valve, and the interaction between the offshore converter valve, the onshore converter valve and the onshore cross switch and the offshore wind farm can realize the start-up and stable operation of the offshore wind power DC transmission system with low cost and high reliability.

With reference to the first aspect, in a possible implementation manner, the offshore converter valve includes: a first diode valve, a second diode valve and a full-bridge modular multilevel converter, wherein,

The AC sides of the first diode valve and the second diode valve are respectively connected in parallel with the AC side of the full-bridge modular multilevel converter, and the DC side of the first diode valve is side, the DC side of the second diode valve, and the DC side of the full-bridge modular multilevel converter are connected in series, and the first diode valve is connected to the offshore via the seventh switch and the first transformer. The second diode valve is connected to the offshore wind farm through the eighth switch and the second transformer, and the full-bridge modular multilevel converter is connected to the offshore wind farm through the ninth switch and the third transformer. connection of offshore wind farms.

With reference to the first aspect, in another possible implementation manner, the full-bridge modular multilevel converter is formed by cascading multiple full-bridge sub-modules.

With reference to the first aspect, in another possible implementation manner, it further includes: an energy storage device;

The energy storage device is connected to the offshore wind farm through a tenth switch and a step-up transformer.

With reference to the first aspect, in another possible implementation manner, the first switch, the second switch, the third switch, and the fourth switch use high-voltage direct current circuit breakers.

In the second aspect, the embodiment of the present invention also provides a control method for an offshore wind power direct current transmission system based on an onshore cross switch, which is applied to an offshore wind power direct current transmission system based on an onshore cross switch. The method includes:

Obtain a start-up instruction, based on the start-up instruction, use the on-shore converter valve and the on-shore cross switch to establish a negative voltage, and the negative voltage supplies power to the offshore wind farm through the offshore converter valve, so as to complete the operation of the offshore wind farm. black start;

Disconnecting the onshore cross switch by limiting the wind turbine output of the offshore wind farm, so as to disconnect the connection between the onshore converter valve and the offshore converter valve;

Raise the DC side voltage of the onshore converter valve until the DC side voltage of the onshore converter valve is higher than the rated DC voltage, control the onshore cross switch to close, and establish a connection between the offshore converter valve and the onshore converter valve. connection to complete the start-up of the offshore wind power DC transmission system.

With reference to the second aspect, in another possible implementation manner, based on the startup instruction, the onshore converter valve and the onshore cross switch are used to establish a negative voltage, and the negative voltage is directed to The offshore wind farm provides power to complete the black start of the offshore wind farm, including:

Based on the starting instruction, a first opening instruction is sent to the first switch, the second switch and the fifth switch, and a first closing instruction is sent to the third switch, the fourth switch and the sixth switch, and the first opening instruction is used For controlling the opening of the first switch, the second switch and the fifth switch, the first closing instruction is used for controlling the closing of the third switch, the fourth switch and the sixth switch, Wherein, after the third switch, the fourth switch and the sixth switch are closed, the first working voltage output by the power grid is charged to the onshore converter valve through the low-voltage winding of the transformer;

Obtain the DC side voltage of the onshore converter valve, and when the DC side voltage of the onshore converter valve meets a preset voltage, send an unlock command to the onshore converter valve, wherein the onshore converter valve is based on the unlocking After the instruction is unlocked, the DC side voltage of the onshore converter valve establishes the negative voltage through the onshore cross switch, and uses the negative voltage to charge the offshore converter valve;

Obtain the DC side voltage of the offshore converter valve, and when the DC side voltage of the offshore converter valve meets a preset voltage, send a second closing command to the ninth switch, and the second closing command is used to control the ninth switch. The switch is closed, wherein, after the ninth switch is closed, the offshore converter valve adopts a zero-start method to establish the voltage of the offshore wind farm, so as to complete the black start of the offshore wind farm.

With reference to the second aspect, in another possible implementation manner, the onshore cross switch is disconnected by limiting the wind turbine output of the offshore wind farm, so as to disconnect the onshore converter valve from the offshore converter. Connections between valves, including:

Acquiring the AC integrated voltage of the offshore wind farm, and sending a first control instruction to the offshore wind farm based on the AC integrated voltage of the offshore wind farm, the first control instruction is used to limit the wind turbine output of the offshore wind turbine;

Acquiring the current of the third switch and the current of the fourth switch, when the current of the third switch and the current of the fourth switch cross zero, sending a second disconnection signal to the third switch and the fourth switch instruction, the second disconnection instruction is used to control the disconnection of the third switch and the fourth switch, so as to disconnect the connection between the onshore converter valve and the offshore converter valve.

With reference to the second aspect, in another possible implementation manner, the DC side voltage of the onshore converter valve is raised until the DC side voltage of the onshore converter valve is higher than the rated DC voltage, and the onshore cross switch is controlled to close , establishing a connection between the offshore converter valve and the onshore converter valve to complete the start-up of the offshore wind power DC transmission system, including:

After acquiring the off state of the third switch and the fourth switch, send a second control instruction to the full-bridge modular multilevel converter, the second control instruction is used to control the full-bridge modular The DC side voltage of the multilevel converter is converted into a forward rated voltage;

When it is obtained that the DC side voltage of the full-bridge modular multilevel converter is the forward rated voltage, a third disconnection command is sent to the sixth switch, and a second disconnection command is sent to the fifth switch. A closing command, wherein, when the fifth switch is closed based on the second closing command, the second working voltage output by the power grid charges the onshore converter valve through the high voltage winding of the transformer;

When the DC side voltage of the on-shore converter valve is higher than the rated DC voltage, a third closing command is sent to the first switch, the second switch, the seventh switch and the eighth switch, wherein, when After the first switch, the second switch, the seventh switch and the eighth switch are closed, the offshore wind farm operates in the maximum power point tracking mode, and the first diode valve, the second diode valve Pipe valves and full-bridge modular multilevel converters are put into offshore wind power transmission, and the offshore wind power DC transmission system is started.

In combination with the second aspect, in another possible implementation manner, it also includes:

Obtaining the total voltage of the DC side of the multiple full-bridge sub-modules, and controlling the energy storage device to charge when the total voltage of the DC side of the multiple full-bridge sub-modules rises, and when the total voltage of the DC side of the multiple full-bridge sub-modules When the voltage drops, the energy storage device is controlled to discharge.

Description of drawings

In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that need to be used in the specific implementation or description of the prior art. Obviously, the accompanying drawings in the following description The drawings show some implementations of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

Fig. 1 is a circuit diagram of an offshore wind power direct current transmission system based on an onshore cross switch provided by an embodiment of the present invention;

Fig. 2 is a flow chart of a control method for an offshore wind power direct current transmission system based on an onshore cross switch provided by an embodiment of the present invention;

FIG. 3 is a flowchart of S201 provided by an embodiment of the present invention;

FIG. 4 is a flowchart of S202 provided by an embodiment of the present invention;

FIG. 5 is a flowchart of S203 provided by an embodiment of the present invention;

Fig. 6 is a diagram of a specific example of an electronic device in an embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Apparently, the described embodiments are part of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "first", "second", and "third" are used for description purposes only, and should not be understood as indicating or implying relative importance. In addition, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be interpreted in a broad sense, for example, it may be a fixed connection, a mechanical connection, or an electrical connection; or it may be a direct connection, It can also be connected indirectly through an intermediary, or it can be an internal connection between two components, and it can be a wireless connection or a wired connection. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention in specific situations.

The embodiment of the present invention provides an offshore wind power DC transmission system based on an onshore cross switch, as shown in Figure 1, including: a power grid 1, an onshore converter valve 2, an onshore cross switch 3, a submarine cable 4, an offshore converter valve 5 and an offshore Wind farm 6; among them,

The above-mentioned shore crossing switch 3 includes a first switch 7, a second switch 8, a third switch 9 and a fourth switch 10, the first switch 7 and the second switch 8 and the third switch 9 and the fourth switch 10 After being cross-connected, it is connected to the above-mentioned submarine cable 4, and the switch states of the above-mentioned first switch 7 and the above-mentioned second switch 8 are interlocked with the above-mentioned third switch 9 and the above-mentioned fourth switch 10, so as to realize the positive and negative of the DC side voltage pole conversion.

The power grid 1 is connected to the above-mentioned onshore converter valve 2 through the transformer low-voltage winding 11 and the fifth switch 12 in the three-winding transformer, and connected to the above-mentioned onshore converter valve 2 through the transformer high-voltage winding 13 and the sixth switch 14 in the three-winding transformer ; The above-mentioned onshore converter valve 2 adopts a half-bridge modular multilevel converter (referred to as a half-bridge MMC), and the DC side of the above-mentioned onshore converter valve 2 is connected to the above-mentioned offshore converter via the above-mentioned on-shore cross switch 3 and the above-mentioned submarine cable 4 The DC side of the valve 5 is connected; the AC side of the above-mentioned offshore converter valve 5 is connected to the above-mentioned offshore wind farm 6 .

Specifically, the first switch 7 , the second switch 8 , the third switch 9 and the fourth switch 10 are high-voltage direct current circuit breakers.

Further, the switching states of the above-mentioned first switch 7 and the above-mentioned second switch 8 are interlocked with the above-mentioned third switch 9 and the above-mentioned fourth switch 10, that is, the first switch 7 and the second switch 8 are opened or closed at the same time, and the second switch The three switches 9 and the fourth switch 10 are opened or closed at the same time, and the onshore cross switch 3 can realize positive and negative conversion of the output voltage of the onshore converter valve 2 .

The offshore wind power DC transmission system based on the on-shore cross-switch proposed in this embodiment uses the on-shore cross-switch to perform positive and negative conversion, and the on-shore converter valve does not need to output negative pressure and does not need to use a full-bridge sub-module, which saves the cost of the on-shore converter valve , and the offshore converter valve, the onshore converter valve cooperate with the onshore cross switch and the interaction between the offshore wind farm, which realizes the start-up and stable operation of the offshore wind power DC transmission system with low cost and high reliability.

As an optional embodiment of the present invention, the above-mentioned offshore converter valve 5 includes: a first diode valve 15, a second diode valve 16, and a full-bridge modular multilevel converter 17 (full-bridge MMC for short). ),in,

The AC sides of the above-mentioned first diode valve 15 and the above-mentioned second diode valve 16 are respectively connected in parallel with the AC side of the above-mentioned full-bridge modular multilevel converter 17, and the DC side of the above-mentioned first diode valve 15 side, the DC side of the above-mentioned second diode valve 16 and the DC side of the above-mentioned full-bridge modular multilevel converter 17 are connected in series, and the above-mentioned first diode valve 15 is connected in series through the seventh switch 18 and the first transformer 19 Connected to the offshore wind farm 6, the above-mentioned second diode valve 16 is connected to the above-mentioned offshore wind farm 6 via the eighth switch 20 and the second transformer 21, and the above-mentioned full-bridge modular multilevel converter 17 is connected to the ninth switch 22 And the third transformer 23 is connected to the above-mentioned offshore wind farm 6 .

Specifically, the above-mentioned full-bridge modular multilevel converter 17 is formed by cascading multiple full-bridge sub-modules.

Furthermore, the offshore wind turbines in the offshore wind farm 6 are collected to the offshore converter valve 5 through the medium-voltage AC cable, and the medium-voltage AC submarine cable passes through the transformer (including the first transformer 19, the second transformer 21 and the third transformer 23) and the switch (including the seventh switch 18, the eighth switch 20 and the ninth switch 22) respectively connected to the first diode valve 15, the second diode valve 16 of the offshore converter valve 5 and the full-bridge modular multilevel converter Streamer 17.

Further, the ratio of the DC rated voltage of the first diode valve 15 and the second diode valve 16 to the DC side rated voltage of the full-bridge modular multilevel converter 17 is 3:1.

In this optional embodiment, the offshore converter valve adopts a structure in which the DC side of the first diode valve, the DC side of the second diode valve, and the DC side of the full-bridge modular multilevel converter are connected in series, The onshore converter valve adopts the form of ordinary half-bridge MMC, cooperates with the onshore cross switch and the energy storage on the offshore wind power collection side, reduces the volume and cost of the offshore converter valve, and realizes the stable operation of the low-cost and high-reliability offshore wind power DC transmission system, and The AC voltage on the converging side of the offshore wind turbine is continuously stable to ensure that the offshore wind turbine can operate stably in the grid-following mode.

As an optional embodiment of the present invention, it also includes: an energy storage device 24;

The energy storage device 24 is connected to the offshore wind farm 6 through a tenth switch 25 and a step-up transformer 26 .

The embodiment of the present invention also discloses a control method for an offshore wind power direct current transmission system based on an onshore cross switch, which is applied to the above-mentioned offshore wind power direct current transmission system based on an onshore cross switch. As shown in FIG. 2 , the above method includes:

S201. Obtain a starting instruction, and based on the above starting instruction, use the onshore converter valve and the onshore cross switch to establish a negative voltage, and the above negative voltage supplies power to the offshore wind farm through the offshore converter valve, so as to complete the blackout of the above offshore wind farm. start up.

S202. Disconnect the above-mentioned onshore cross switch by limiting the wind turbine output of the above-mentioned offshore wind farm, so as to disconnect the connection between the above-mentioned onshore converter valve and the above-mentioned offshore converter valve.

S203. Raise the voltage on the DC side of the onshore converter valve until the voltage on the DC side of the above-mentioned onshore converter valve is higher than the rated DC voltage, control the above-mentioned on-shore cross switch to close, and establish a connection between the above-mentioned offshore converter valve and the above-mentioned on-shore converter valve, In order to complete the start-up of the offshore wind power DC transmission system.

The control method of the offshore wind power direct current transmission system based on the onshore cross switch provided by the present invention performs positive and negative pole conversion through the onshore cross switch, and the onshore converter valve does not need to output negative pressure, and does not need to use a full bridge sub-module, saving onshore converter valves The cost, and the interaction between the offshore converter valve and the onshore converter valve, the onshore cross switch and the offshore wind farm can realize the start-up and stable operation of the offshore wind power DC transmission system with low cost and high reliability.

As an optional implementation of the present invention, as shown in Fig. 3, the above-mentioned S201, based on the above-mentioned starting command, uses the on-shore converter valve and the on-shore cross switch to establish a negative voltage, and the above-mentioned negative voltage is sent to the sea through the above-mentioned offshore converter valve. Wind farms provide power to complete the black start of the above-mentioned offshore wind farms, including:

S2011. Send a first opening instruction to the first switch, the second switch, and the fifth switch based on the above-mentioned starting instruction, and send a first closing instruction to the third switch, the fourth switch, and the sixth switch. The above-mentioned first opening instruction is used In order to control the opening of the first switch, the second switch and the fifth switch, the first closing instruction is used to control the closing of the third switch, the fourth switch and the sixth switch, wherein the third switch, After the fourth switch and the sixth switch are closed, the first working voltage output by the power grid charges the onshore converter valve through the low-voltage winding of the transformer.

S2012. Acquire the DC side voltage of the onshore converter valve, and when the DC side voltage of the onshore converter valve meets the preset voltage, send an unlocking command to the onshore converter valve, wherein the onshore converter valve is unlocked based on the unlocking command Afterwards, the DC side voltage of the above-mentioned onshore converter valve establishes the above-mentioned negative voltage through the on-shore cross switch, and the above-mentioned offshore converter valve is charged by using the above-mentioned negative voltage.

Specifically, the power grid charges the DC side capacitor of the onshore converter valve through soft start. When the voltage of the DC side capacitor of the onshore converter valve reaches 80% of the rated voltage, the charging is completed, and the onshore converter valve is unlocked.

Furthermore, after the onshore converter valve is unlocked, the half-bridge modular multilevel converter in the onshore converter valve adopts the voltage derating operation mode, and the half bridge of each bridge arm of the half bridge modular multilevel converter The DC side voltage of the bridge module adopts the step-down operation mode, the DC side voltage of the onshore converter valve establishes a negative voltage through the onshore cross switch, and uses the negative voltage to charge the offshore converter valve, and then the full bridge in the offshore converter valve The DC side of the modular multi-level converter establishes a stable negative voltage, and the DC side of the full-bridge modular multi-level converter of the offshore converter valve will also be charged at the same time. The DC sides of the pole tube valve and the second diode valve are short-circuited.

S2013. Obtain the DC side voltage of the offshore converter valve, and when the DC side voltage of the offshore converter valve meets the preset voltage, send a second closing command to the ninth switch, and the second closing command is used to control the ninth switch closed, wherein, after the ninth switch is closed, the above-mentioned offshore converter valve adopts a zero-start method to establish the voltage of the offshore wind farm, so as to complete the black start of the above-mentioned offshore wind farm.

Specifically, the full-bridge modular multilevel converter in the offshore converter valve adopts the V/F voltage source operation mode (a mode that ensures that the output voltage is proportional to the frequency) and completes the start-up unlocking to establish an AC voltage for the offshore wind farm. , in order to prevent the start-up inrush current of the transformer on the AC side of the offshore converter valve, the full-bridge modular multilevel converter of the offshore converter valve adopts a zero-start method to establish the voltage of the offshore wind farm.

As an optional implementation of the present invention, as shown in Figure 4, the above S202 is to disconnect the above-mentioned onshore cross switch by limiting the output of the wind turbines of the above-mentioned offshore wind farm, so as to disconnect the above-mentioned onshore converter valve and the above-mentioned offshore converter valve. connections, including:

S2021. Acquire the AC collection voltage of the offshore wind farm, and send a first control command to the offshore wind farm based on the AC collection voltage of the offshore wind farm, where the first control command is used to limit the output of the offshore wind turbine.

Specifically, the offshore wind turbines are started sequentially and run in the grid-following mode. At the same time, based on the first control command, the output of the wind turbines is close to zero through power limitation such as adjustment of the blades of the wind turbines, ensuring that the third switch and the fourth switch flow through The current direction is from the onshore converter valve to the offshore converter valve, and then gradually increase the output of the wind turbine, so that the current flowing through the third switch and the fourth switch can appear at zero point, ensuring the normal disconnection of the third switch and the fourth switch.

S2022. Obtain the current of the third switch and the current of the fourth switch, and when the current of the third switch and the current of the fourth switch cross zero, send a second disconnection instruction to the third switch and the fourth switch, The second disconnection command is used to control the disconnection of the third switch and the fourth switch, so as to disconnect the connection between the onshore converter valve and the offshore converter valve.

Specifically, the wind turbine output limit of the offshore wind farm is gradually raised until the current flowing through the third and fourth switches drops to 0. At this time, the third switch and the fourth switch are turned off, and the onshore converter valve and the offshore converter valve Disconnect between valves.

As an optional implementation of the present invention, as shown in Figure 5, the above S203 is to increase the DC side voltage of the onshore converter valve until the DC side voltage of the above-mentioned onshore converter valve is higher than the rated DC voltage, and control the above-mentioned onshore cross switch to close , to establish a connection between the above-mentioned offshore converter valve and the above-mentioned onshore converter valve to complete the start-up of the offshore wind power DC transmission system, including:

S2031. After obtaining the off state of the third switch and the fourth switch, send a second control instruction to the full-bridge modular multilevel converter, where the second control instruction is used to control the full-bridge modular multilevel converter. The DC side voltage of the level converter is converted to a forward rated voltage.

Specifically, the DC-side voltage control function of the full-bridge modular multi-level converter is used to raise the total DC-side voltage of the full-bridge modular multi-level converter, and adjust from the negative voltage to the positive rated voltage. At this time The AC voltage of the offshore wind farm is provided by a full-bridge modular multilevel converter.

S2032. When the DC side voltage of the above-mentioned full-bridge modular multilevel converter is obtained as the above-mentioned forward rated voltage, send a third opening instruction to the above-mentioned sixth switch, and send a second closing instruction to the above-mentioned fifth switch , wherein, when the fifth switch is closed based on the second closing command, the second working voltage output by the power grid charges the onshore converter valve through the high voltage winding of the transformer.

S2033. When the DC side voltage of the above-mentioned onshore converter valve is higher than the above-mentioned rated DC voltage, send a third closing command to the above-mentioned first switch, the above-mentioned second switch, the seventh switch and the eighth switch, wherein, when the above-mentioned first switch After the first switch, the above-mentioned second switch, the above-mentioned seventh switch and the above-mentioned eighth switch are closed, the above-mentioned offshore wind farm operates in the maximum power point tracking mode (ie MPPT mode), and the first diode valve and the second diode valve And the full-bridge modular multilevel converter is put into offshore wind power transmission (that is, the offshore converter valve works in the full power transmission operation mode), and the offshore wind power DC transmission system is started.

Specifically, the DC side voltage of the onshore converter valve is higher than the above-mentioned rated DC voltage, which ensures that the first diode valve and the second diode valve will not be turned on after the offshore converter valve is activated.

In this optional embodiment, the offshore converter valve adopts a structure in which the DC side of the first diode valve, the DC side of the second diode valve, and the DC side of the full-bridge modular multilevel converter are connected in series, The onshore converter valve adopts the form of ordinary half-bridge MMC, cooperates with the onshore cross switch and the energy storage on the offshore wind power collection side, reduces the volume and cost of the offshore converter valve, and realizes the stable operation of the low-cost and high-reliability offshore wind power DC transmission system, and The AC voltage on the converging side of the offshore wind turbine is continuously stable to ensure that the offshore wind turbine can operate stably in the grid-following mode.

As an optional implementation of the present invention, it also includes:

S204. Obtain the total voltage of the DC side of the multiple full-bridge sub-modules, and control the energy storage device to charge when the total voltage of the DC side of the multiple full-bridge sub-modules increases. When the voltage drops, the energy storage device is controlled to discharge.

Specifically, after the integrated AC voltage of the offshore wind farm is established, the tenth switch is closed, the energy storage device is put into operation, the energy storage device operates in the current source mode, and the full-bridge modular multilevel converter in the offshore converter valve Charge the energy storage device until the SOC of the energy storage device reaches about 80%.

Further, when the wind turbine output of the offshore wind farm is close to zero, the energy storage control target is changed to keep the DC side voltage of the full-bridge sub-module unchanged, and the energy storage is charged if the DC-side voltage of the full-bridge sub-module rises. When the DC side voltage of the bridge sub-module decreases, the stored energy is discharged.

As shown in Fig. 1 , a control method of an offshore wind power direct current transmission system based on an onshore cross switch is described below through a specific embodiment.

Example 1:

Disconnect K1 and K2, and close K3 and K4 in the onshore cross switch.

Close the switch K6 connected to the low-voltage winding of the transformer in the three-winding transformer, and then charge the capacitor on the DC side of the onshore converter valve through the soft start circuit. At this time, the DC side of the full bridge MMC of the offshore converter valve will also be charged at the same time. At this time, the DC side of the diode valve of the offshore converter valve will be in a short circuit state.

The onshore converter valve is unlocked and a stable negative voltage is established on the DC side of the full-bridge MMC in the offshore converter valve. In this step, the control method of the half-bridge MMC converter valve in the onshore The DC side voltage of the half-bridge module of each bridge arm of the bridge MMC adopts a step-down operation mode.

Close the switch K9, then the full-bridge MMC in the offshore converter valve adopts the V/F voltage source operation mode and completes the start-up unlocking, and establishes an AC voltage for the offshore wind farm. The full-bridge MMC of the converter valve adopts the zero-start method to establish the voltage of the offshore wind farm.

After the collection of AC voltage in the offshore wind farm is established, the switch K10 is closed, the energy storage device is put into operation, the energy storage device operates in the current source mode, and charges the energy storage device until the energy storage device SOC (state of charge, that is, the remaining power) Reach about 80%.

Offshore wind turbines are started sequentially and run in the grid-following mode. At the same time, the output of the wind turbines is close to zero through power limitation such as adjustment of the blades of the wind turbines. After that, the energy storage control target is changed to keep the DC side voltage of the full-bridge sub-modules in the full-bridge MMC constant. If the DC side voltage of the full-bridge sub-module increases, the energy storage device will be charged, and if the DC-side voltage of the full-bridge MMC converter valve sub-module decreases, the energy storage device will be discharged.

Gradually increase the output limit of the fan until the current flowing through the switches K3 and K4 drops to 0, then turn off the switches K3 and K4; then increase the total voltage of the DC side of the full-bridge MMC, and adjust it from the negative rated voltage to the positive rated voltage, At this time, the AC voltage of the offshore wind farm is still provided by the full-bridge MMC, and the energy storage device is responsible for maintaining the power balance of the offshore wind farm.

Close the switch K5, activate the high-voltage winding of the land-connected transformer, start and unlock the onshore converter valve, and establish the rated voltage of the DC side. The rated voltage value of the DC side must ensure that the diode valve will not be turned on after the offshore diode valve is started.

Close K1 and K2, then close K7 and K8 in turn, and the offshore wind turbines run in MPPT mode in turn. When the switches K1 and K2 flow through the current, the control target of the energy storage device changes to control the SOC of the energy storage device to reach about 80%. The MMC works in the normal operation mode, and the entire offshore wind power DC transmission system completes the start-up control process.

In addition, the embodiment of the present invention also provides an electronic device. As shown in FIG. 6, the electronic device may include a processor 110 and a memory 120, wherein the processor 110 and the memory 120 may be connected through a bus or other methods. In FIG. 6 Take connection via bus as an example. In addition, the electronic device further includes at least one interface 130, and the at least one interface 130 may be a communication interface or other interfaces, which is not limited in this embodiment.

Wherein, the processor 110 may be a central processing unit (Central Processing Unit, CPU). The processor 110 may also be other general-purpose processors, digital signal processors (Digital Signal Processor, DSP), application specific integrated circuits (Application Specific Integrated Circuit, ASIC), field-programmable gate arrays (Field-Programmable Gate Array, FPGA) or Other chips such as programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or combinations of the above-mentioned types of chips.

As a non-transitory computer-readable storage medium, the memory 120 can be used to store non-transitory software programs, non-transitory computer-executable programs and modules, such as program instructions/modules corresponding to the video synthesis method in the embodiment of the present invention. The processor 110 executes various functional applications and data processing of the processor by running the non-transitory software programs, instructions and modules stored in the memory 120, that is, realizes the offshore wind power DC based on the onshore cross switch in the above method embodiment. Send the control method of the system.

The memory 120 may include a program storage area and a data storage area, wherein the program storage area may store an operating system and an application program required by at least one function; the data storage area may store data created by the processor 110 and the like. In addition, the memory 120 may include a high-speed random access memory, and may also include a non-transitory memory, such as at least one magnetic disk storage device, a flash memory device, or other non-transitory solid-state storage devices. In some embodiments, the memory 120 may optionally include a memory that is remotely located relative to the processor 110, and these remote memories may be connected to the processor 110 through a network. Examples of the aforementioned networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

In addition, at least one interface 130 is used for communication between the electronic device and external devices, such as communication with a server. Optionally, at least one interface 130 may also be used to connect peripheral input and output devices, such as keyboards and display screens.

The one or more modules are stored in the memory 120 , and when executed by the processor 110 , execute the control method of the offshore wind power direct current transmission system based on the onshore crossbar in the embodiment shown in FIG. 2 .

The specific details of the above-mentioned electronic device can be understood by correspondingly referring to the corresponding description and effects in the embodiment shown in FIG. 2 , which will not be repeated here.

Those skilled in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing related hardware through computer programs, and the programs can be stored in a computer-readable storage medium. During execution, it may include the processes of the embodiments of the above-mentioned methods. Wherein, the storage medium may be a magnetic disk, an optical disk, a read-only memory (Read-Only Memory, ROM), a random access memory (Random Access Memory, RAM), a flash memory (Flash Memory), a hard disk (Hard Disk Drive, HDD) or solid-state hard drive (Solid-State Drive, SSD), etc.; the storage medium may also include a combination of the above-mentioned types of memory.

Apparently, the above-mentioned embodiments are only examples for clear description, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims (10)

1. Offshore wind power direct current delivery system based on onshore crossbar switch, characterized by comprising: the system comprises a power grid, an onshore converter valve, an onshore cross switch, a submarine cable, an offshore converter valve and an offshore wind farm; wherein,,

the shore cross switch comprises a first switch, a second switch, a third switch and a fourth switch, wherein the first switch and the second switch are connected with the sea cable after being cross-connected with the third switch and the fourth switch, and the first switch and the second switch are interlocked with the switch states of the third switch and the fourth switch so as to realize the positive-negative conversion of the direct-current side voltage;

the power grid is connected with the onshore converter valve through a transformer low-voltage winding and a fifth switch in the three-winding transformer, and is connected with the onshore converter valve through a transformer high-voltage winding and a sixth switch in the three-winding transformer; the on-shore converter valve adopts a half-bridge modularized multi-level converter, and the direct current side of the on-shore converter valve is connected with the direct current side of the on-shore converter valve through the on-shore cross switch and the submarine cable; the alternating current side of the offshore converter valve is connected with the offshore wind farm.

2. Offshore wind power direct current delivery system based on an onshore crossbar according to claim 1, characterized in that the offshore converter valve comprises: a first diode valve, a second diode valve and a full-bridge modular multilevel converter, wherein,

the alternating current sides of the first diode valve and the second diode valve are respectively connected with the alternating current side of the full-bridge modularized multi-level converter in parallel, the direct current side of the first diode valve, the direct current side of the second diode valve and the direct current side of the full-bridge modularized multi-level converter are connected in series, the first diode valve is connected with an offshore wind farm through a seventh switch and a first transformer, the second diode valve is connected with the offshore wind farm through an eighth switch and a second transformer, and the full-bridge modularized multi-level converter is connected with the offshore wind farm through a ninth switch and a third transformer.

3. Offshore wind power direct current delivery system based on an onshore crossbar according to claim 2, characterized in that the full-bridge modular multilevel converter is composed of a cascade of a plurality of full-bridge sub-modules.

4. Offshore wind power direct current delivery system based on an onshore crossbar according to claim 1, further comprising: an energy storage device;

the energy storage device is connected with the offshore wind farm through a tenth switch and a step-up transformer.

5. Offshore wind power direct current delivery system based on an onshore crossbar according to claim 1, characterized in that the first switch, the second switch, the third switch and the fourth switch are high voltage direct current breakers.

6. Method for controlling an offshore wind power dc delivery system based on an onshore crossbar, applied to an offshore wind power dc delivery system based on an onshore crossbar according to any of claims 1 to 5, the method comprising:

acquiring a starting instruction, and based on the starting instruction, establishing negative voltage by using an on-shore converter valve and an on-shore cross switch, wherein the negative voltage supplies power to an offshore wind farm through the offshore converter valve so as to finish black starting of the offshore wind farm;

disconnecting the onshore cross switch by limiting fan output of the offshore wind farm to disconnect the connection between the onshore converter valve and the offshore converter valve;

and lifting the direct current side voltage of the on-shore converter valve, and controlling the on-shore cross switch to be closed until the direct current side voltage of the on-shore converter valve is higher than the rated direct current voltage, wherein connection is established between the on-shore converter valve and the on-shore converter valve so as to finish starting of the on-shore wind power direct current delivery system.

7. The method for controlling an offshore wind farm direct current delivery system based on an onshore crossbar according to claim 6, wherein the establishing a negative voltage using an onshore converter valve and an onshore crossbar based on the start command, the negative voltage supplying power to an offshore wind farm via the onshore converter valve to complete a black start of the offshore wind farm, comprises:

a first opening instruction is sent to a first switch, a second switch and a fifth switch based on the starting instruction, a first closing instruction is sent to a third switch, a fourth switch and a sixth switch Guan Fasong, the first opening instruction is used for controlling the first switch, the second switch and the fifth switch to be opened, the first closing instruction is used for controlling the third switch, the fourth switch and the sixth switch to be closed, and after the third switch, the fourth switch and the sixth switch are closed, a first working voltage output by a power grid is charged to an onshore converter valve through a transformer low-voltage winding;

acquiring direct-current side voltage of an on-shore converter valve, and sending an unlocking instruction to the on-shore converter valve when the direct-current side voltage of the on-shore converter valve accords with a preset voltage, wherein after the on-shore converter valve is unlocked based on the unlocking instruction, the direct-current side voltage of the on-shore converter valve establishes the negative voltage through an on-shore cross switch, and the negative voltage is used for charging the offshore converter valve;

and when the direct-current side voltage of the offshore converter valve accords with the preset voltage, sending a second closing instruction to a ninth switch, wherein the second closing instruction is used for controlling the closing of the ninth switch, and after the ninth switch is closed, the offshore converter valve establishes the voltage of the offshore wind farm in a zero-starting mode so as to finish black start of the offshore wind farm.

8. The method of controlling an offshore wind power direct current delivery system based on an onshore crossbar of claim 7, wherein the opening of the onshore crossbar by limiting a fan output of the offshore wind farm to disconnect the onshore converter valve from the offshore converter valve comprises:

acquiring alternating current collection voltage of an offshore wind farm, and sending a first control instruction to the offshore wind farm based on the alternating current collection voltage of the offshore wind farm, wherein the first control instruction is used for limiting fan output of an offshore fan;

and acquiring the current of a third switch and the current of a fourth switch, and when the current of the third switch and the current of the fourth switch pass through zero points, giving a second disconnection instruction to the third switch and the fourth switch Guan Fasong, wherein the second disconnection instruction is used for controlling the disconnection of the third switch and the fourth switch so as to disconnect the connection between the onshore converter valve and the offshore converter valve.

9. The method for controlling an offshore wind power direct current delivery system based on an onshore crossbar according to claim 8, wherein the step of raising the onshore converter valve direct current side voltage until the onshore converter valve direct current side voltage is higher than a rated direct current voltage, controlling the onshore crossbar to be closed, and establishing a connection between the onshore converter valve and the onshore converter valve to complete startup of the offshore wind power direct current delivery system comprises:

after the disconnection states of the third switch and the fourth switch are obtained, a second control instruction is sent to the full-bridge modularized multi-level converter, and the second control instruction is used for controlling the direct-current side voltage of the full-bridge modularized multi-level converter to be converted into a forward rated voltage;

when the direct-current side voltage of the full-bridge modularized multi-level converter is the forward rated voltage, a third opening instruction is sent to the sixth opening Guan Fasong, and a second closing instruction is sent to the fifth switch, wherein when the fifth switch is closed based on the second closing instruction, a second working voltage output by a power grid charges the onshore converter valve through a transformer high-voltage winding;

and when the direct-current side voltage of the shore-based converter valve is higher than the rated direct-current voltage, a third closing instruction is given to the first switch, the second switch, the seventh switch and the eighth switch Guan Fasong, wherein after the first switch, the second switch, the seventh switch and the eighth switch are closed, the offshore wind farm operates in a maximum power point tracking mode, and the first diode valve, the second diode valve and the full-bridge modularized multi-level converter are put into offshore wind power transmission, and an offshore wind power direct-current delivery system is started.

10. The method for controlling an offshore wind power direct current delivery system based on an onshore crossbar of claim 6, further comprising:

and the direct current side total voltage of the full-bridge sub-modules is obtained, the energy storage device is controlled to charge when the direct current side total voltage of the full-bridge sub-modules is increased, and the energy storage device is controlled to discharge when the direct current side total voltage of the full-bridge sub-modules is reduced.

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