Flexible DC-AC fault ride-through control method and system
By judging the energy-consuming device based on the power ratio and voltage ratio when the AC system is faulty at the receiving end, the surplus power is timely absorbed, and the problem of low operating efficiency in the existing technology is solved, and reliable crossing and safety guarantee of AC faults is achieved.
Patent Information
- Application Number
- CN202411212437.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-30
- Publication Date
- 2024-12-13
AI Technical Summary
The existing fault control method of receiving AC system is low in operation efficiency when the fault occurs, and it cannot absorb the surplus power in time, which poses safety hazards.
When an instantaneous failure occurs in the AC system at the receiving end, it is determined whether the energy-consuming device is put into operation based on the ratio of the generated power to the rated power of the wind farm and the ratio of the AC voltage to the rated voltage, until the ratio of the generated power to the rated power is less than or equal to the AC voltage and The ratio of the rated voltage is not inputted, otherwise it will not be input; after the fault is completed, the energy-consuming device will be withdrawn, and the active current and reactive current will be limited according to the amplitude of the AC voltage.
It realizes timely processing of surplus power, improves the investment speed and control efficiency of energy-consuming devices, ensures reliable crossing of AC faults, and reduces the safety hazards of the system.
Smart Images
Figure CN119134488A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a flexible direct current (DC) and alternating current (AC) fault ride-through control method and system, belonging to the technical field of high-voltage direct current (HVDC) power transmission. Background Art
[0002] With the continuous advancement of the construction of new power systems, flexible DC transmission technology has ushered in new development opportunities in the fields of large-scale clean energy, cross-regional large-capacity transmission, flexible grid zoning, efficient transmission of deep and offshore wind power, massive distributed new energy consumption and DC load access. In terms of large-scale clean energy economical and efficient transmission and flexible interconnection, flexible DC transmission has been widely used for its advantages such as fast control regulation performance and large-capacity long-distance power transmission.
[0003] In terms of deep-sea wind power DC grid connection, when a fault occurs in the receiving-end AC system of the offshore wind power flexible DC transmission system, the AC voltage at the grid connection point will drop sharply, and the output power of the receiving-end converter station will be reduced. In the event of a serious fault, power transmission may be interrupted. Due to the sudden drop in the AC voltage at the grid connection point, the offshore sending-end converter station still inputs the original power before the fault to the receiving-end converter station, which will generate a large amount of surplus power. The surplus power will cause the DC side voltage to rise rapidly, endangering the safety of DC equipment and insulation safety, and may cause consequences such as DC line tripping and wind turbine disconnection.
[0004] In the existing control strategy for receiving-end AC system faults, the surplus power of wind turbines is often absorbed by DC energy-consuming devices configured in onshore converter stations to maintain power balance during faults. This method is simple, fast, effective and highly reliable. However, this method requires energy-consuming resistors to consume a large amount of power in a short period of time, so its resistance parameters are required to be high, requiring high investment costs and large land requirements, and is not very economical. At the same time, when a serious fault occurs, the configuration of this DC energy-consuming device will also increase the probability of system failure, which is not conducive to the stable operation of the offshore wind power DC grid-connected system. There is also a method of using wind turbines to reduce power operation. The control strategy uses the offshore converter station control system to reduce the voltage of the offshore AC system or increase the frequency of the offshore AC system. It uses the fault ride-through capability and frequency regulation capability of the offshore wind turbine to reduce the power of the wind turbine and reduce the power injected into the DC system. It can balance the power to a certain extent, but its essence is to use the low voltage ride-through capability of the offshore wind turbine. It has little effect on serious faults and can easily cause the wind turbine to be disconnected from the grid. In summary, these two control strategies can only absorb surplus power within a certain range. When a serious fault occurs and causes the output power of the onshore converter station to drop significantly, they cannot absorb a large amount of surplus power.
[0005] The Chinese invention patent with application publication number CN117498460A discloses a technical solution for an offshore wind power DC transmission system and control method. The technical solution cancels the DC energy consumption device centrally configured on the DC side of the onshore converter station, determines the number and capacity of the wind turbine energy consumption device to be triggered by calculating the estimated value of surplus power and the DC voltage fluctuation, and then puts the energy consumption device into operation according to the number and capacity of the wind turbine energy consumption device, thereby reducing the overall volume, weight and cost of the receiving-end AC system. Compared with the above two control strategies, the energy consumption device in the offshore wind turbine group is adopted, and a large amount of surplus power can be consumed when a serious fault occurs in the receiving-end AC system. However, when an AC fault occurs in the receiving-end AC system, the technical solution needs to wait until the number and capacity of the energy consumption devices to be put into operation are calculated according to the surplus power before triggering the operation of putting the energy consumption device into operation, which is inefficient and cannot consume the surplus power in time, posing a safety hazard. Summary of the invention
[0006] The object of the present invention is to provide a flexible DC AC fault ride-through control method and system to solve the problem of low operating efficiency of energy-consuming devices in existing control methods for receiving-end AC system faults when an AC fault occurs in the receiving-end AC system.
[0007] In order to solve the above technical problems, the present invention provides a flexible DC-AC fault ride-through control method, the method comprising: when a transient fault occurs in the AC system at the receiving end, if the ratio of the power generated by the wind farm at the sending end to the rated power is greater than the amplitude ratio of the AC voltage to the rated voltage of the AC system, then energy consumption devices for consuming the surplus power at the sending end are put into the wind turbines of the wind farm until the energy consumption devices put into use make the ratio of the power generated by the wind farm to the rated power less than or equal to the amplitude ratio of the AC voltage to the rated voltage of the AC system; otherwise, the energy consumption devices are not put into use.
[0008] Furthermore, it also includes: when the instantaneous fault of the AC system at the receiving end ends, the energy consumption device in the wind turbine set is exited.
[0009] Furthermore, it also includes: when a transient fault occurs in the AC system at the receiving end, the active current and the reactive current are limited according to the amplitude of the AC voltage of the AC system; when the transient fault of the AC system ends, the limitation of the active current and the reactive current is stopped.
[0010] Furthermore, the method of limiting active current and reactive current according to the amplitude of the AC voltage of the AC system includes: determining a reference value of inner loop current control corresponding to the active current and reactive current according to the amplitude of the AC voltage of the AC system to limit the active current and reactive current.
[0011] Beneficial effects: As a pioneering invention, the present invention determines whether to put energy-consuming devices into the wind turbines in the wind farm at the sending end by comparing the ratio of the power generated by the wind farm at the sending end to the rated power when the AC system at the receiving end has a transient fault with the ratio of the AC voltage of the AC system at the receiving end to the rated voltage; until the energy-consuming devices put into use make the ratio of the power generated by the wind farm at the sending end to the rated power less than or equal to the ratio of the AC voltage of the AC system at the receiving end to the rated voltage; this scheme is equivalent to setting the judgment conditions for putting energy-consuming devices into use, comprehensively considering the different actual situations of surplus power caused by the influence of the fault at the receiving end on the power consumption at the receiving end and the size of the power to be consumed generated at the sending end, that is, the transmission power of the sending end itself is low and the power reduction caused by the fault at the receiving end is slight, so that there is basically no surplus power, and the sending end itself Although the transmission power is high, the power reduction caused by the fault at the receiving end is relatively slight, which means that there is basically no surplus power; the transmission power of the sending end itself is low, while the power reduction caused by the fault at the receiving end is relatively serious, which means there is a large surplus power; and the transmission power of the sending end itself is high, while the power reduction caused by the fault at the receiving end is relatively serious, which means that there is a large surplus power. When it is determined that there is a large surplus power, the energy-consuming device can be directly controlled to be put into operation, and the energy-consuming device put into operation can ensure that the current situation is adjusted to a situation where there is basically no surplus power, thereby ensuring that the existence of a large surplus power can be judged in time, and the surplus power that is difficult to be absorbed during the AC fault at the receiving end can be absorbed in time, thereby ensuring that the AC fault at the receiving end is reliably traversed, and the speed of triggering the energy-consuming device to be put into operation is faster, and the logic of controlling the energy-consuming device to be put into operation is simple and more efficient.
[0012] The present invention also provides a flexible DC-AC fault ride-through control system, comprising a first controller for controlling the converter of the wind farm at the sending end and an energy consuming device controller for controlling the investment and withdrawal of energy consuming devices of the wind turbines in the wind farm, wherein the energy consuming devices are used to consume surplus power at the sending end when invested; the first controller is used to trigger the energy consuming device controller to control the investment of the energy consuming devices into the wind turbines in the wind farm when a transient fault occurs in the AC system at the receiving end, if the ratio of the power generated by the wind farm to the rated power is greater than the amplitude ratio of the AC voltage to the rated voltage of the AC system, until the invested energy consuming devices make the ratio of the power generated by the wind farm to the rated power less than or equal to the amplitude ratio of the AC voltage to the rated voltage of the AC system; otherwise, the energy consuming device controller is not triggered to invest the energy consuming devices.
[0013] Furthermore, the energy consuming device controller is also used to control the exit of the energy consuming device after the fault ends.
[0014] Furthermore, it also includes a second controller corresponding to the converter of the AC system at the receiving end; the second controller is also used to limit the active current and reactive current according to the amplitude of the AC voltage of the AC system when a momentary fault occurs in the AC system; when the momentary fault of the AC system ends, stop limiting the active current and reactive current.
[0015] Furthermore, the method of limiting active current and reactive current according to the amplitude of the AC voltage of the AC system includes: a second controller determines a reference value of inner loop current control corresponding to the active current and reactive current according to the amplitude of the AC voltage of the AC system to limit the active current and reactive current.
[0016] Furthermore, the communication method among the first controller, the second controller and the energy consuming device controller includes: the first controller, the second controller and the energy consuming device controller communicate with each other through optical fiber communication via the goose protocol.
[0017] Furthermore, the second controller is also used to generate a receiving-end AC fault signal when a transient fault is detected in the AC system; the first controller determines whether a transient fault occurs in the AC system including: when the receiving-end AC fault signal is detected, it is determined that a transient fault occurs in the AC system.
[0018] The flexible DC AC fault ride-through control system can achieve the same beneficial effects as the above-mentioned flexible DC AC fault ride-through control method. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 It is a topological structure diagram of an offshore wind power flexible DC transmission system in an embodiment of the flexible DC AC fault ride-through control method of the present invention;
[0020] Figure 2 It is a flow chart of a flexible DC AC fault ride-through control method in an embodiment of the flexible DC AC fault ride-through control method of the present invention;
[0021] Figure 3 It is a topological structure diagram of an offshore wind turbine in an embodiment of the flexible DC / AC fault ride-through control method of the present invention;
[0022] Figure 4 It is a logic block diagram of limiting active current and reactive current in an embodiment of the flexible DC / AC fault ride-through control method of the present invention;
[0023] Figure 5 It is a schematic diagram of onshore AC fault signal transmission in an embodiment of a flexible DC AC fault ride-through control system of the present invention. DETAILED DESCRIPTION
[0024] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.
[0025] Flexible DC / AC Fault Ride-Through Control Method Embodiment
[0026] The present embodiment provides a technical solution for a flexible DC-AC fault ride-through control method, the method comprising: when a transient fault occurs in the AC system at the receiving end, if the ratio of the power generated by the wind farm at the sending end to the rated power is greater than the amplitude ratio of the AC voltage to the rated voltage of the AC system, energy consumption devices for consuming the surplus power at the sending end are started to be put into the wind turbines of the wind farm until the energy consumption devices put into use make the ratio of the power generated by the wind farm to the rated power less than or equal to the amplitude ratio of the AC voltage to the rated voltage of the AC system; otherwise, the energy consumption devices are not put into use.
[0027] The method determines whether to put energy-consuming devices into the wind turbines in the wind farm by comparing the ratio of the power generated by the wind farm at the sending end to the rated power with the amplitude ratio of the AC voltage of the AC system at the receiving end to the rated voltage, so that the energy-consuming devices in the wind turbines can absorb the surplus power during the fault of the AC system at the receiving end. The use of this control method can ensure the timely processing of the surplus power.
[0028] The sending end of the wind power flexible DC transmission system to which the flexible DC AC fault ride-through control method is applicable can be on land or at sea, while the receiving end of the wind power flexible DC transmission system is generally on land, for example, an offshore wind power flexible DC transmission system, a large desert wind power flexible DC transmission system, etc. The flexible DC AC fault ride-through control method is specifically described below by taking an offshore wind power flexible DC transmission system as an example:
[0029] The topological structure of the offshore wind power flexible DC transmission system to which this control method is applicable is shown in the figure below: Figure 1 As shown, the offshore wind power flexible DC transmission system includes: an offshore converter at the sending end and an offshore wind farm, a DC line between the offshore converter at the sending end and an onshore converter at the receiving end, an onshore converter at the receiving end, and an onshore AC system (onshore load), wherein the DC line adopts a combination of submarine cables and overhead lines. Compared with the existing offshore wind power flexible DC transmission system, a part of the DC line of this system uses overhead lines, the location of the onshore converter is not limited to the seaside, and the setting of the location of the onshore converter is more free; the offshore wind farm at the sending end replenishes energy to the onshore AC system (onshore load) at the receiving end through the offshore converter at the sending end, the DC line between the offshore converter at the sending end and the onshore converter at the receiving end, and the onshore converter at the receiving end.
[0030] The flow chart of the flexible DC / AC fault ride-through control method is as follows: Figure 2 As shown, the method includes:
[0031] When a transient fault occurs in the onshore AC system at the receiving end, if the ratio of the generated power to the rated power of the offshore wind farm at the sending end is greater than the amplitude ratio of the AC voltage to the rated voltage of the onshore AC system, energy consumption devices for consuming the surplus power at the sending end will be put into the wind turbines of the offshore wind farm until the energy consumption devices put into use make the ratio of the generated power to the rated power of the offshore wind farm less than or equal to the amplitude ratio of the AC voltage to the rated voltage of the onshore AC system; otherwise, the energy consumption devices will not be put into use. Specifically, the amplitude ratio of the AC voltage to the rated voltage of the onshore AC system is represented by a normalized value.
[0032] This scheme is equivalent to setting the judgment conditions for putting the energy-consuming device into operation, comprehensively considering the different actual situations of surplus power caused by the influence of the fault at the receiving end on the power consumption at the receiving end and the size of the power to be consumed at the sending end, that is, the transmission power of the sending end itself is low and the power reduction caused by the fault at the receiving end is relatively slight, so that there is basically no surplus power; although the transmission power of the sending end itself is high, the power reduction caused by the fault at the receiving end is relatively slight, so that there is basically no surplus power; the transmission power of the sending end itself is low and the power reduction caused by the fault at the receiving end is relatively serious, so that there is a large surplus power; and the transmission power of the sending end itself is high and the power reduction caused by the fault at the receiving end is relatively serious, so that there is a large surplus power. When it is judged that there is a large surplus power, the energy-consuming device can be directly controlled to be put into operation, and the put-in energy-consuming device can ensure that the current situation is adjusted to a situation where there is basically no surplus power, thereby ensuring that the situation of the existence of a large surplus power can be judged in time, and the surplus power that is difficult to be absorbed during the AC fault at the receiving end can be absorbed in time, so as to ensure that the AC fault at the receiving end is reliably traversed, and the speed of triggering the energy-consuming device to be put into operation is faster, and the logic of controlling the energy-consuming device to be put into operation is simple and efficient.
[0033] Among them, the offshore wind farm includes multiple wind turbines. The topological structure of the offshore wind turbine is shown in the figure below: Figure 3 As shown, the offshore wind turbine includes blades, a wind turbine, a machine-side converter, a grid-side converter, a step-up transformer, an offshore AC system and an energy-consuming device; the machine-side converter realizes the conversion of AC into DC, the grid-side converter realizes the conversion of DC into AC, and the energy-consuming device is connected in parallel between the machine-side converter and the grid-side converter of the wind turbine, so that the energy-consuming device can be flexibly put into and out of operation.
[0034] In order to reduce the impact of the energy-consuming devices on the offshore wind power flexible DC transmission system when the receiving end is operating normally, and the waste of power on the sending end caused by the energy-consuming devices when the receiving end is operating normally, the flexible DC AC fault ride-through control method of this embodiment also includes: when the instantaneous fault of the onshore AC system ends, exit the energy-consuming devices in the wind turbine group.
[0035] In order to reduce the impact of the fault current of the AC system at the receiving end on the wind power flexible DC transmission system, the flexible DC AC fault ride-through control method of this embodiment also includes: when a transient fault occurs in the onshore AC system at the receiving end, the active current and reactive current are limited according to the amplitude of the AC voltage of the onshore AC system; when the transient fault of the onshore AC system ends, the limitation of the active current and reactive current is stopped. The logic block diagram of limiting the active current and reactive current is shown in FIG. Figure 4 As shown, the method of limiting the active current and reactive current according to the amplitude of the AC voltage of the AC system at the receiving end includes: determining the reference value of the inner loop current control corresponding to the active current and reactive current according to the amplitude of the AC voltage of the AC system at the receiving end, so as to limit the active current and reactive current. Specifically, according to the amplitude of the AC voltage U of the onshore AC system at the receiving end ac_avg (Per unit value) to obtain the corresponding current reference value i of the d-axis and q-axis respectively d_ref with i q_ref , U ac_avg is i d_ref with i q_ref The upper limit value is based on the current reference value i d_ref (per unit value) and i q_ref (per unit value) to perform inner loop current control on active current and reactive current respectively, i d_ref (per unit value) and i q_ref (per unit value) greater than U ac_avg It will be limited to U ac_avg Specifically, inner loop current control is a prior art and will not be elaborated here.
[0036] Flexible DC / AC Fault Ride-Through Control System Embodiment
[0037] This embodiment provides a technical solution for a flexible DC-AC fault ride-through control system, the system includes a first controller for controlling the converter of the wind farm at the sending end and an energy consuming device controller for controlling the investment and withdrawal of energy consuming devices of the wind turbines in the wind farm, the energy consuming devices being used to consume surplus power at the sending end when being invested; the first controller is used to trigger the energy consuming device controller to control the investment of energy consuming devices into the wind turbines in the wind farm when a transient fault occurs in the AC system at the receiving end, if the ratio of the power generated by the wind farm to the rated power is greater than the amplitude ratio of the AC voltage of the AC system to the rated voltage, until the invested energy consuming devices make the ratio of the power generated by the wind farm to the rated power less than or equal to the amplitude ratio of the AC voltage of the AC system to the rated voltage; otherwise, the energy consuming device controller is not triggered to invest the energy consuming devices. The flexible DC-AC fault ride-through control system is specifically described below, taking the offshore wind power flexible DC transmission system as an example:
[0038] The flexible DC AC fault ride-through control system is used to control the first controller of the offshore converter of the offshore wind farm at the sending end (the first controller can be called an offshore controller, or an offshore rectifier converter control system) and the energy consumption device controller (offshore wind turbine control system) for controlling the investment and withdrawal of the energy consumption device of the wind turbine group of the offshore wind farm. The energy consumption device is used to consume the surplus power of the sending end when it is invested; the offshore controller is used to trigger the energy consumption device controller (offshore wind turbine control system) to control the investment of the energy consumption device in the wind turbine group of the offshore wind farm when a transient fault occurs in the onshore AC system at the receiving end, if the ratio of the generated power of the offshore wind farm to the rated power is greater than the amplitude ratio of the AC voltage of the onshore AC system to the rated voltage, until the invested energy consumption device makes the ratio of the generated power of the offshore wind farm to the rated power less than or equal to the amplitude ratio of the AC voltage of the onshore AC system to the rated voltage; otherwise, the energy consumption device controller is not triggered to invest the energy consumption device. In this embodiment, the flexible DC AC fault ride-through control system is included in the above-mentioned offshore wind power flexible DC transmission system. In other embodiments, the control system can also be independent. The system is used to control the offshore wind power flexible DC transmission system according to the flexible DC AC fault ride-through control method when a fault occurs in the onshore AC system at the receiving end of the offshore wind power flexible DC transmission system to achieve reliable ride-through of the AC fault in the onshore AC system at the receiving end.
[0039] The energy consuming device controller is also used to control the exit of the energy consuming device after the AC failure of the onshore AC system ends.
[0040] The flexible DC-AC fault ride-through control system also includes a second controller corresponding to the converter of the onshore AC system at the receiving end (the second controller can be called an onshore controller or an onshore inverter control system); the onshore controller is also used to limit the active current and reactive current according to the amplitude of the AC voltage of the onshore AC system when a transient fault occurs in the onshore AC system; and stop limiting the active current and reactive current when the transient fault of the onshore AC system ends.
[0041] The onshore controller limits the active current and reactive current according to the amplitude of the AC voltage of the onshore AC system, including: the onshore controller determines the reference value of the inner loop current control corresponding to the active current and reactive current according to the amplitude of the AC voltage of the onshore AC system, so as to limit the active current and reactive current. The specific method of limiting the active current and reactive current has been described in detail in the embodiment of the flexible DC AC fault ride-through control method, and will not be repeated here.
[0042] The onshore controller is further used to generate an onshore AC fault signal when a transient fault is detected in the onshore AC system; the offshore controller determines whether a transient fault occurs in the onshore AC system in the following manners: when the onshore AC fault signal is detected, it is determined that a transient fault occurs in the onshore AC system. When the onshore AC fault signal is detected to be absent, it is determined that no transient fault occurs in the onshore AC system or the transient fault ends.
[0043] Schematic diagram of onshore AC fault signal transmission Figure 5 As shown, the communication method between the onshore controller, the offshore controller and the energy consuming device controller (offshore wind turbine control system) includes: the onshore controller, the offshore controller and the energy consuming device controller (offshore wind turbine control system) communicate with each other through optical fiber via the goose protocol. In this embodiment, the energy consuming device controller is an offshore wind turbine control system.
[0044] When a transient fault occurs in the onshore AC system, the onshore controller is used to send an onshore AC system fault signal and the amplitude ratio of the AC voltage of the onshore AC system to the rated voltage to the offshore controller; at the same time, the onshore controller limits the active current and reactive current according to the amplitude of the AC voltage of the onshore AC system. When the offshore controller detects the existence of the onshore AC fault signal, it determines that a transient fault occurs in the onshore AC system. At this time, the offshore controller sends an activation and deactivation instruction of the energy consuming device of the wind turbine to the energy consuming device controller (offshore wind turbine control system). If the ratio of the generated power to the rated power of the offshore wind farm is greater than the amplitude ratio of the AC voltage to the rated voltage of the AC system at the receiving end, the offshore controller sends an activation instruction of the energy consuming device of the wind turbine to the energy consuming device controller (offshore wind turbine control system), triggering the energy consuming device controller (offshore wind turbine control system) to control the activation of the energy consuming device in the wind turbine of the offshore wind farm, so that the ratio of the generated power to the rated power of the offshore wind farm after the activation of the energy consuming device is less than or equal to the amplitude ratio of the AC voltage of the onshore AC system to the rated voltage; otherwise, the offshore controller does not send an activation instruction of the energy consuming device. When the offshore controller detects that the onshore AC system fault signal does not exist, the onshore AC fault system is restored, and the offshore controller sends an exit instruction of the energy consuming device of the wind turbine to the energy consuming device controller (offshore wind turbine control system), and the energy consuming device controller (offshore wind turbine control system) controls the energy consuming device to exit the wind turbine; at the same time, the onshore controller stops limiting the active current and reactive current.
[0045] The offshore wind farm includes multiple wind turbines, each of which has a set of energy consumption devices connected in parallel between the machine-side converter and the grid-side converter of the wind turbine. The energy consumption devices are controlled by the offshore wind farm controller (offshore wind turbine control system), which controls the input and output of the energy consumption devices. The structural composition of the wind turbine has been described in detail in the flexible DC / AC fault ride-through control method embodiment, so no further description is given here.
[0046] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, but do not constitute a limitation to the present invention.
Claims
1. A flexible DC / AC fault ride-through control method, characterized in that: include: When a transient fault occurs in the AC system at the receiving end, if the ratio of the power generated by the wind farm at the sending end to the rated power is greater than the amplitude ratio of the AC voltage to the rated voltage of the AC system, energy-consuming devices for consuming the surplus power at the sending end are put into use in the wind turbines of the wind farm until the energy-consuming devices put into use make the ratio of the power generated by the wind farm to the rated power less than or equal to the amplitude ratio of the AC voltage to the rated voltage of the AC system; otherwise, the energy-consuming devices are not put into use.
2. The flexible DC / AC fault ride-through control method according to claim 1, characterized in that: Also includes: When the instantaneous fault of the AC system at the receiving end ends, the energy-consuming devices in the wind turbine are shut down.
3. The flexible DC / AC fault ride-through control method according to claim 1 or 2, characterized in that: Also includes: When a transient fault occurs in the AC system at the receiving end, the active current and reactive current are limited according to the amplitude of the AC voltage of the AC system; when the transient fault of the AC system ends, the limitation of the active current and reactive current is stopped.
4. The flexible DC / AC fault ride-through control method according to claim 3 is characterized in that: The method of limiting active current and reactive current according to the amplitude of the AC voltage of the AC system includes: determining a reference value of inner loop current control corresponding to the active current and reactive current according to the amplitude of the AC voltage of the AC system to limit the active current and reactive current.
5. A flexible DC / AC fault ride-through control system, comprising a first controller for controlling a converter of a wind farm at a sending end and an energy consuming device controller for controlling the activation and deactivation of energy consuming devices of wind turbines in the wind farm, characterized in that: The energy consumption device is used to consume surplus power at the sending end when it is put into operation; the first controller is used to trigger the energy consumption device controller to control the input of the energy consumption device into the wind turbines of the wind farm when a transient fault occurs in the AC system at the receiving end, if the ratio of the power generated by the wind farm to the rated power is greater than the amplitude ratio of the AC voltage of the AC system to the rated voltage. The energy consumption device is put into operation until the ratio of the power generated by the wind farm to the rated power is less than or equal to the amplitude ratio of the AC voltage of the AC system to the rated voltage. Otherwise, the energy consumption device controller is not triggered to put the energy consumption device into operation.
6. The flexible DC / AC fault ride-through control system according to claim 5, characterized in that: The energy consumption device controller is also used to control the exit of the energy consumption device after the fault ends.
7. The flexible DC / AC fault ride-through control system according to claim 5, characterized in that: It also includes a second controller corresponding to the converter of the AC system at the receiving end; the second controller is also used to limit the active current and reactive current according to the amplitude of the AC voltage of the AC system when a momentary fault occurs in the AC system; when the momentary fault of the AC system ends, stop limiting the active current and reactive current.
8. The flexible DC / AC fault ride-through control system according to claim 7, characterized in that: The method of limiting active current and reactive current according to the amplitude of the AC voltage of the AC system includes: the second controller determines the reference value of the inner loop current control corresponding to the active current and reactive current according to the amplitude of the AC voltage of the AC system to limit the active current and reactive current.
9. The flexible DC / AC fault ride-through control system according to claim 7, characterized in that: The communication method among the first controller, the second controller and the energy consuming device controller includes: the first controller, the second controller and the energy consuming device controller communicate with each other through optical fiber communication via the goose protocol.
10. The flexible DC / AC fault ride-through control system according to any one of claims 7 to 9, characterized in that: The second controller is also used to generate a receiving-end AC fault signal when a transient fault is detected in the AC system; the first controller determines whether a transient fault occurs in the AC system by: when the receiving-end AC fault signal is detected, determining that a transient fault occurs in the AC system.