Flexible DC line fault ride-through control method and system
By judging the capacitance voltage of the DC line and the output power of the wind turbine, and controlling the input and exit of the energy-consuming device, the problem of low operating efficiency of the energy-consuming device during DC line failure in the flexible DC power transmission system is solved, and the timely consumption of surplus power is achieved and the security and stability of the system.
Patent Information
- Application Number
- CN202411212433.3
- 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
When the existing flexible DC power transmission system fails in the DC line, the operating efficiency of the energy-consuming device is inefficient and cannot consume surplus power in time, which may cause the system to trip.
By determining whether the capacitance voltage of the power device of the transmitting inverter exceeds the upper voltage limit, decide whether to input energy-consuming devices into the wind farm, and input or exit the energy-consuming devices according to the output power of the wind turbine to control the DC line The voltage is within a reasonable range to ensure timely consumption of surplus power.
It improves the operating efficiency of the energy-consuming device, can consume surplus power in a timely and accurate manner, realizes reliable crossing of faults, and ensures the safety of the system.
Smart Images
Figure CN119134487A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a flexible DC line fault ride-through control method and system, belonging to the technical field of high-voltage DC 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 DC line fault occurs in the offshore wind power flexible DC transmission system, the insulation strength of the line is reduced, resulting in conductor-to-ground flashover, and the short-circuit point cannot extinguish the arc. Due to the discharge effect of the line capacitor, the fault current at the short-circuit point has a large overshoot, resulting in the generation of fault current. In addition, when a DC line fault occurs in the flexible DC system transmission system, the power flow in the system will be affected, the power imbalance will generate surplus power, and even cause the system to trip.
[0004] Existing strategies for DC line faults often absorb surplus power by adding energy-consuming resistors on the DC side of the receiving converter to maintain power balance and complete DC fault riding of the flexible DC transmission system. This strategy has a simple topological structure, but requires a large area and has high investment costs.
[0005] The Chinese invention patent with application publication number CN117498333A provides a method for calling a wind turbine energy consumption device and a technical solution of the device. When a DC fault occurs in an offshore wind power DC transmission system, the method obtains the DC operating power before the DC fault occurs, collects the current operating voltage value of each full-bridge submodule, calculates the average voltage value of the full-bridge submodule, performs closed-loop control and energy input calculation on the preset module voltage value and the average voltage value of the full-bridge submodule, and obtains the input amount. When the capacities of the energy consumption devices are the same, the input amount is divided by the capacity of a single energy consumption device, and the result is rounded up to determine the calling quantity. When the capacities of the energy consumption devices are different, the calling quantity is determined so that the total calling capacity is greater than the input amount and less than the sum of the input amount and the maximum capacity of a single unit; then, according to the obtained input amount of the wind turbine energy consumption device, the offshore wind power DC transmission system is called. The wind turbine energy consumption device in the wind turbine in the wind power direct current transmission system is called; the wind turbine energy consumption device in the offshore wind power direct current transmission system can participate in the processing of direct current faults to offset the surplus power generated by short circuit, thereby avoiding system tripping. The method saves land resources and reduces investment costs by utilizing the energy consumption device in the wind turbine set. However, the method needs to obtain the direct current operating power before the direct current fault occurs, collect the current operating voltage value of each full-bridge submodule, calculate the average voltage value of the full-bridge submodule, perform closed-loop control and energy consumption input calculation on the preset module voltage value and the average voltage value of the full-bridge submodule, and a series of calculation steps to obtain the input amount of the energy consumption device. After the input amount is obtained, the input of the energy consumption device can be triggered. The calculation is complex and inefficient, and the surplus power cannot be consumed in time, which may cause the system to trip. Summary of the invention
[0006] The purpose of the present invention is to provide a flexible DC line fault ride-through control method and system to solve the problem that when a DC line fault occurs in the existing strategy for a flexible DC transmission system, the operating efficiency of the energy-consuming device is low and the surplus power cannot be consumed in time, which may cause the system to trip.
[0007] In order to solve the above technical problems, the present invention provides a flexible DC line fault ride-through control method, comprising: when a DC line has a transient fault, if the average value of the capacitor voltage of the power device in the sending-end converter of the DC line is greater than the voltage upper limit, then an energy-consuming device for consuming the surplus power at the sending end is started to be put into the wind turbine group running in the wind farm at the sending end of the DC line until the average value of the capacitor voltage of the power device in the sending-end converter is less than the voltage lower limit; otherwise, the energy-consuming device is not put into use.
[0008] Furthermore, the method of investing energy-consuming devices for absorbing surplus power at the sending end into the wind turbines in operation in the wind farm at the sending end of the DC line includes: investing energy-consuming devices for absorbing surplus power at the sending end into the wind turbines in operation in the wind farm at the sending end in order from large to small output powers of the wind turbines in operation in the wind farm at the sending end.
[0009] Furthermore, the method of investing energy-consuming devices for absorbing surplus power at the sending end into the wind turbines in operation in the sending-end wind farm also includes: when there is a wind turbine without energy-consuming devices invested, whose output power is greater than the energy-consuming devices of the wind turbines with energy-consuming devices invested, energy-consuming devices are started to be invested in the wind turbines without energy-consuming devices and whose current output power is the largest, and the energy-consuming devices of the wind turbines with energy-consuming devices invested and whose current output power is the smallest are withdrawn each time energy-consuming devices are invested.
[0010] Furthermore, it also includes: when a transient fault occurs in the DC line, stopping the control of the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter according to the DC voltage rated value, controlling the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter according to the DC voltage bias amount determined by the control amount of the DC current PI control by the sending end and the receiving end, and the sending-end converter and the receiving-end converter respectively control the number of negative inputs of their own full-bridge power modules according to the corresponding reference voltage to perform DC negative voltage control; the control amount of the DC current PI control is determined according to the difference between the actual current of the DC line and the set current reference value, and the set current reference value is a negative value.
[0011] Furthermore, it also includes: when the instantaneous fault of the DC line ends, stopping the DC negative voltage control and resuming the control of the reference voltage according to the DC voltage rated value; after the voltage of the DC line is increased to the DC voltage rated value by controlling the reference voltage according to the DC voltage rated value, exiting the energy consuming device in the wind turbine group that has been put into use.
[0012] Furthermore, the method of withdrawing the energy consuming devices in the wind turbines that have been put into use includes: withdrawing the energy consuming devices in the wind turbines in order from small to large output powers of the wind turbines that have been put into use in the wind farm.
[0013] Beneficial effect: The present invention provides a new flexible DC line fault ride-through control method. The method determines whether to start putting energy-consuming devices for consuming surplus power at the sending end into the wind turbines running in the wind farm by judging whether the average value of the capacitor voltage of the power device in the sending-end converter of the DC line is greater than the voltage upper limit, until the average voltage of the capacitor of the power device of the sending-end converter is less than the voltage lower limit. Therefore, it is only necessary to timely decide whether to put energy-consuming devices for consuming surplus power at the sending end into the wind turbines running in the wind farm based on simple judgment conditions, and ensure that the investment can be stopped in time when the invested energy-consuming devices are sufficient to consume the surplus power, avoiding the complex and tedious calculation of the number and distribution method of the energy-consuming devices invested in the wind turbines before the energy-consuming devices are invested, effectively improving the operating efficiency of the invested energy-consuming devices, being able to consume the surplus power in a timely and accurate manner, realizing reliable fault ride-through, and ensuring the safety of the system.
[0014] The present invention also provides a flexible DC line fault ride-through control system, comprising a first controller for controlling the sending-end converter of the DC line and a wind turbine controller for controlling the activation and deactivation of an energy-consuming device in a wind turbine in a wind farm at the sending end of the DC line, wherein the energy-consuming device is used to consume surplus power at the sending end when activated, and the first controller is used to trigger the wind turbine controller to activate the energy-consuming device in the wind turbine running in the sending-end wind farm when a transient fault occurs in the DC line, if the average value of the capacitor voltage of the power device in the activated state in the sending-end converter is greater than the upper voltage limit, until the average value of the capacitor voltage of the power device in the activated state in the sending-end converter is less than the lower voltage limit; otherwise, the wind turbine controller is not triggered to activate the energy-consuming device.
[0015] Furthermore, the manner of triggering the wind turbine controller to put the energy consumption device into the wind turbine in operation in the sending-end wind farm includes:
[0016] The first controller triggers the wind turbine controllers in sequence according to the order of output power of each wind turbine being operated in the sending-end wind farm from large to small to put the energy consumption device into the wind turbine being operated in the sending-end wind farm.
[0017] Furthermore, the method of triggering the wind turbine controller to put energy-consuming devices for absorbing surplus power at the sending end into the wind turbines currently in operation in the sending-end wind farm also includes: when there is a wind turbine without energy-consuming devices whose output power is greater than the energy-consuming devices of the wind turbines with energy-consuming devices, the first controller starts to trigger the wind turbine controller to put energy-consuming devices into the wind turbine without energy-consuming devices and whose current output power is the largest, and at the same time, exits the energy-consuming devices of the wind turbine with energy-consuming devices and whose current output power is the smallest.
[0018] Furthermore, it also includes a second controller for controlling the receiving-end converter, and the first controller and the second controller are respectively used to stop the control of the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter according to the rated value of the DC voltage when a transient fault occurs in the DC line; the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter is respectively controlled according to the DC voltage bias amount determined by the control amount of the DC current PI controller, and the number of negative inputs of its own full-bridge power module is controlled according to the corresponding reference voltage to perform DC negative voltage control; the control amount of the DC current PI controller is determined according to the difference between the actual current of the DC line and the set current reference value, and the set current reference value is a negative value. Further, when the transient fault of the DC line ends, the first controller and the second controller respectively stop the DC negative voltage control and resume the control of the reference voltage according to the rated value of the DC voltage. After the voltage of the DC line is raised to the rated value of the DC voltage by controlling the reference voltage according to the rated value of the DC voltage, the first controller triggers the wind turbine controller to control the exit of the energy-consuming device in the wind turbine that has been put into the energy-consuming device.
[0019] Furthermore, the method of exiting the energy consuming devices in the wind turbines that have been put into use includes: the first controller triggers the wind turbine controllers in sequence according to the order of output power of each wind turbine that has been put into use in the wind farm from small to large, to control the exit of the energy consuming devices in the wind turbines.
[0020] Furthermore, the communication method between the first controller and each wind turbine controller includes: the first controller establishes two-way primary and backup communications with the wind turbine controller of the first wind turbine on the feeder and the wind turbine controller of the last wind turbine, and the wind turbine controllers of the remaining wind turbines establish two-way primary and backup communications with the wind turbine controllers of adjacent wind turbines.
[0021] The flexible DC line fault ride-through control system can achieve the same beneficial effects as the above-mentioned flexible DC line fault ride-through control method. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1It is a topological structure diagram of an offshore wind power flexible DC transmission system in an embodiment of a flexible DC line fault ride-through control method of the present invention;
[0023] Figure 2 It is a topological structure block diagram of an offshore wind turbine system in an embodiment of a flexible DC line fault ride-through control method of the present invention;
[0024] Figure 3 It is a topological structure diagram of power devices of a converter in an embodiment of a flexible DC line fault ride-through control method of the present invention;
[0025] Figure 4 is a flow chart of a flexible DC line fault ride-through control method in an embodiment of the flexible DC line fault ride-through control method of the present invention;
[0026] Figure 5 It is a DC negative voltage control logic diagram in an embodiment of a flexible DC line fault ride-through control method of the present invention;
[0027] Figure 6 It is a schematic diagram of communication between an offshore converter control system and an offshore wind turbine control system in an embodiment of a flexible DC line fault ride-through control system of the present invention. DETAILED DESCRIPTION
[0028] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.
[0029] Embodiment of a flexible DC line fault ride-through control method
[0030] This embodiment provides a technical solution for a flexible DC line fault ride-through control method, the method comprising: when a DC line has an instantaneous fault, if the average value of the capacitor voltage of the power device in the power device in the power device state in the DC line's sending-end converter is greater than the upper voltage limit, then start to put the energy-consuming device for consuming the surplus power at the sending end into the wind turbine set in operation in the wind farm at the DC line's sending end, until the average value of the capacitor voltage of the power device in the power device in the power device in the power device state in the sending-end converter is less than the lower voltage limit; otherwise, the energy-consuming device for consuming the surplus power at the sending end is not put into operation. The method only needs to be based on simple judgment conditions to determine whether to put the energy-consuming device for consuming the surplus power at the sending end into the wind turbine set in operation in the wind farm, thus avoiding complex and tedious calculations, being able to consume the surplus power in a timely manner, achieving reliable fault ride-through, and ensuring the safety of the system.
[0031] The sending end of the wind power flexible DC transmission system to which the flexible DC line 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 following takes the offshore wind power flexible DC transmission system as an example to specifically illustrate the flexible DC line fault ride-through control method:
[0032] The topological structure of the offshore wind power flexible DC transmission system to which the flexible DC line fault ride-through 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 (the offshore converter at the sending end may be referred to as the sending end converter or offshore converter hereinafter), an offshore wind farm at the sending end, an onshore converter at the receiving end (the onshore converter at the receiving end may be referred to as the receiving end converter or onshore converter hereinafter), a DC line between the offshore converter at the sending end and the 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.
[0033] Among them, the offshore wind farm includes multiple wind turbines. The topological structure diagram of the offshore wind turbine system is as follows: Figure 2 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 this embodiment, the topological structures of the offshore sending-end converter and the onshore receiving-end converter both adopt modular multilevel converters (MMC). The MMC adopts voltage source power devices (such as IGBT, IGCT, etc.). The offshore MMC (offshore sending-end converter) establishes the AC voltage required for the offshore wind turbine to be connected to the grid, and the onshore MMC (onshore receiving-end converter) transmits power to the onshore load. The topological structure diagram of the power devices of the converter is shown in FIG. Figure 3 As shown, the power devices of the converter all adopt a "full-bridge + half-bridge hybrid topology structure", and the full-bridge topology power devices account for more than 50%.
[0035] The flow chart of the flexible DC line fault ride-through control method is as follows: Figure 4 As shown, including:
[0036] When a transient fault occurs in a DC line, if the average value of the capacitor voltage of the power devices in the power device in the sending-end converter of the DC line is greater than the voltage upper limit, energy-consuming devices for consuming the surplus power at the sending end will be put into operation in the wind turbines in operation in the wind farm at the sending end of the DC line until the average value of the capacitor voltage of the power devices in the power device in the sending-end converter is less than the voltage lower limit; otherwise, the energy-consuming devices for consuming the surplus power at the sending end will not be put into operation.
[0037] The above-mentioned DC line fault includes a fault in the submarine cable portion of the DC line and a fault in the overhead line portion of the DC line, but usually the DC line fault is a fault in the overhead line.
[0038] Among them, the calculation formula of the average value of the capacitor voltage of the power device of the sending-end converter is:
[0039]
[0040] Where U sm is the average voltage of the capacitor of the power device of the sending-end converter; N is the number of power devices in the input state, U n is the capacitor voltage of the nth power device (1≤n≤N).
[0041] The flexible DC line fault ride-through control method also includes: when a transient fault occurs in the DC line, stopping the control of the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter according to the DC voltage rated value, controlling the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter according to the DC voltage bias determined by the control amount of the DC current PI control of the sending end and the receiving end, and the sending-end converter and the receiving-end converter respectively control the number of negative inputs of their own full-bridge power modules according to the corresponding reference voltages of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter to perform DC negative voltage control; the control amount of the DC current PI control is determined according to the difference between the actual current of the DC line and the set current reference value, and the set current reference value is a negative value; wherein, the number of negative inputs of the full-bridge power module refers to the number of full-bridge power sub-modules in the negative input state, and the number of negative inputs of the full-bridge power module is greater than the number of half-bridge sub-modules input at this time.
[0042] Specifically, the DC negative voltage control logic diagram is as follows: Figure 5 As shown, when a DC line instantaneous fault occurs, in order to effectively achieve fast discharge of the DC line fault, the current reference value I of the DC current controller is set dc_refIt is a negative value, with a range of [-0.1pu, -0.3pu]. The current feedback value I of the DC current controller dc is the DC line current. In this embodiment, the DC current controller adopts a DC current PI controller. The offshore sending-end converter controller and the onshore receiving-end converter controller enable the DC current PI controller. The DC current PI controller outputs a value I pi As the DC voltage bias used to calculate the reference voltage of the six bridge arms of the converter, calculate the reference voltage V arm1-6 When the DC voltage bias k value is set, the DC voltage rating Switch to DC current controller output value I pi .
[0043] The converter controllers at the sending end and the receiving end send the six bridge wall reference voltages to their respective valve control systems. The valve control systems of the converters at the sending end and the receiving end respectively calculate the number of switching on and off of the full-bridge and half-bridge power modules of their respective converters to control the DC negative voltage. The reference voltages of the abc three-phase upper bridge arms of the converter controllers at the sending end and the receiving end are as follows:
[0044]
[0045] The reference voltage of the lower bridge arm of the abc three-phase converter is as follows:
[0046]
[0047] Converter DC voltage U dc The larger of equation 1 and equation 2 is obtained by summing them phase by phase.
[0048] U dc =v arm_xp +v arm_xn =k(x=a,b,c)
[0049] From the above formula, we can see that when k is less than zero, the DC voltage U dc Less than zero. The offshore valve control system and the onshore converter valve control system respectively adjust the number of negative inputs of the full-bridge power modules in real time according to the reference voltage of their six bridge arms to achieve DC negative voltage control. The DC negative voltage control strategy can quickly absorb the fault current on the DC line and reduce the impact of the fault current on the sending and receiving AC systems.
[0050] The method of putting energy-consuming devices for absorbing surplus power at the sending end into the wind turbines in operation in the wind farm at the sending end of the DC line includes: putting energy-consuming devices for absorbing surplus power at the sending end into the wind turbines in operation in the wind farm at the sending end in order from large to small output powers of the wind turbines in operation in the wind farm at the sending end. Thus, it is equivalent to choosing to put energy-consuming devices into the wind turbines with larger output powers as much as possible, and putting energy-consuming devices into the wind turbines with larger output powers can make the efficiency of absorbing surplus power faster.
[0051] In this embodiment, the time interval for sequentially adding energy consumption devices to each wind turbine generator set is 50 us.
[0052] The method of adding energy-consuming devices for absorbing surplus power at the sending end to the wind turbine sets currently in operation in the sending-end wind farm also includes: when the output power of a wind turbine set that does not have energy-consuming devices for absorbing surplus power at the sending end is greater than the energy-consuming devices of the wind turbine sets that have energy-consuming devices added, energy-consuming devices are added to the wind turbine sets that have not had energy-consuming devices added and that currently have the largest output power, and energy-consuming devices of the wind turbine sets that have had energy-consuming devices added and that currently have the smallest output power are withdrawn each time energy-consuming devices are added. For example, if energy-consuming devices have been put into use in wind turbine sets A and B, but not in wind turbine set C, and the output power of wind turbine set C is greater than the output power of wind turbine set A, and the output power of wind turbine set A is greater than the output power of wind turbine set B, then the energy-consuming devices will be put into use in wind turbine set C, and the energy-consuming devices in wind turbine set B will be withdrawn. The purpose of putting energy-consuming devices into the wind turbine set that has not been put into use and currently has the largest output power is to put energy-consuming devices into the wind turbine set with the larger output power as much as possible, so as to make the efficiency of absorbing surplus power faster. At the same time, the purpose of withdrawing the energy-consuming devices of the wind turbine set that has been put into use and currently has the smallest output power is to prevent excessive absorption of surplus power, which may cause power transmission interruption.
[0053] The flexible DC line fault ride-through control method also includes: when the DC line instantaneous fault ends, stopping the DC negative voltage control and resuming the control of the reference voltage according to the DC voltage rated value, after the DC line voltage is increased to the DC voltage rated value by controlling the reference voltage according to the DC voltage rated value, exiting the energy consuming devices in the wind turbine set that have been put into use; after analysis, it is found that the system will not be stable until the DC line voltage is increased to the DC voltage rated value, so choosing to exit the energy consuming devices in the wind turbine set that have been put into use at this time can ensure that the sub-modules of the sending-end converter do not experience overvoltage.
[0054] Among them, the rate at which the voltage of the DC line is increased to the DC voltage rated value by controlling the reference voltage according to the DC voltage rated value is determined by the DC current PI controller, and the rate at which the voltage of the DC line is reduced to the negative voltage value corresponding to the DC negative voltage control according to the negative voltage control can be freely set.
[0055] The method of withdrawing the energy consuming devices in the wind turbines that have been put into use includes: withdrawing the energy consuming devices in the wind turbines in order from small to large output powers of the wind turbines that have been put into use in the wind farm.
[0056] In this embodiment, the time interval for sequentially exiting the energy-consuming devices in each wind turbine generator set is 50 us.
[0057] In other embodiments, the flexible DC line fault ride-through control method can also be applied to other flexible DC transmission systems including a sending-end converter, a sending-end wind farm, and energy-consuming devices corresponding to wind turbines for consuming surplus power at the sending end. The specific application method is basically consistent with the principle of the above-mentioned flexible DC line fault ride-through control method being applicable to the offshore wind power flexible DC transmission system, and will not be repeated here.
[0058] Implementation example of a flexible DC line fault ride-through control system
[0059] The present embodiment provides a technical solution for a flexible DC line fault ride-through control system, the system comprising a first controller for controlling a sending-end converter of the DC line (the first controller of the sending-end converter may be referred to as an offshore converter station control system hereinafter) and a wind turbine controller for controlling the activation and deactivation of an energy-consuming device in a wind turbine in a wind farm at the sending end of the DC line (the wind turbine controller may be referred to as a wind turbine control system hereinafter), the energy-consuming device being used to consume surplus power at the sending end when activated, the first controller being used to trigger the wind turbine controller to activate the energy-consuming device in the wind turbine running in the sending-end wind farm when a transient fault occurs in the DC line, if the average value of the capacitor voltage of the power device in the activated state in the sending-end converter is greater than the upper voltage limit; otherwise, the wind turbine controller is not triggered to activate the energy-consuming device.
[0060] The method of triggering the wind turbine controller to put the energy consumption device into the wind turbine running in the sending-end wind farm includes:
[0061] The first controller triggers the wind turbine controllers to input energy consumption devices into the wind turbines in operation in the sending-end wind farm in sequence according to the output power of each wind turbine in operation in the sending-end wind farm from large to small.
[0062] The method of triggering the wind turbine controller to put energy-consuming devices for absorbing surplus power at the sending end into the wind turbines currently in operation in the sending-end wind farm also includes: when the output power of a wind turbine without energy-consuming devices is greater than the energy-consuming devices of the wind turbines with energy-consuming devices, the first controller starts to trigger the wind turbine controller to put energy-consuming devices into the wind turbine without energy-consuming devices and with the largest current output power, and at the same time, exits the energy-consuming devices of the wind turbine with energy-consuming devices and with the smallest current output power each time energy-consuming devices are put into operation.
[0063] The flexible DC line fault ride-through control system also includes a second controller for controlling the receiving-end converter (the second controller may also be referred to as the onshore converter station control system hereinafter). The first controller and the second controller are respectively used to stop controlling the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter according to the DC voltage rated value when a transient fault occurs in the DC line; control the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter according to the DC voltage bias amount determined by the control amount of the DC current PI controller, and control the number of negative inputs of its own full-bridge power modules according to the corresponding reference voltage to perform DC negative voltage control; the control amount of the DC current PI controller is determined according to the difference between the actual current of the DC line and the set current reference value, and the set current reference value is a negative value; wherein, the number of negative inputs of the full-bridge power module refers to the number of full-bridge power sub-modules in the negative input state, and the negative input number is greater than the number of half-bridge sub-modules input at this time.
[0064] The specific process of using negative voltage to control fault current has been described in detail in the embodiment of the flexible DC line fault ride-through control method, and will not be described in detail here.
[0065] When the instantaneous fault of the DC line ends, the first controller and the second controller respectively stop the DC negative voltage control and resume the control of the reference voltage according to the DC voltage rated value. After the voltage of the DC line is increased to the DC voltage rated value by controlling the reference voltage according to the DC voltage rated value, the first controller triggers the wind turbine controller to control the exit of the energy consuming devices in the wind turbine that have been put into use. After analysis, it is found that the system will not be stable until the voltage of the DC line is increased to the DC voltage rated value. Therefore, choosing to exit the energy consuming devices in the wind turbine that have been put into use at this time can ensure that the sub-modules of the sending-end converter do not experience overvoltage.
[0066] Among them, the first controller and the second controller respectively control the reference voltage according to the DC voltage rated value, and the rate at which the DC line voltage is increased to the DC voltage rated value is determined by the DC current PI controller, and the rate at which the DC line voltage is reduced to the negative voltage value corresponding to the DC negative voltage control according to the negative voltage control can be freely set.
[0067] The method of exiting the energy consuming devices in the wind turbines that have been put into use includes: the first controller triggers the wind turbine controllers in sequence according to the output power of each wind turbine in the wind farm that has been put into use in order from small to large to control the exit of the energy consuming devices in the wind turbines.
[0068] The communication diagram between the offshore converter control system and the offshore wind turbine control system is shown in the figure. Figure 6 As shown, the communication method between the first controller and each wind turbine controller includes:
[0069] The first controller establishes two-way active-standby communication with the wind turbine controller of the first wind turbine and the wind turbine controller of the last wind turbine on the feeder, and the wind turbine controllers of the remaining wind turbines establish two-way active-standby communication with the wind turbine controllers of adjacent wind turbines.
[0070] In this embodiment, the offshore converter controller uses gigabit optical fiber communication with the first offshore wind turbine controller and the last offshore wind turbine controller on each 66KV AC submarine cable feeder of the offshore wind power, respectively, to achieve one-master-one-standby communication, which is used to transmit the operating status of the offshore wind turbine, the input and exit instructions of the energy-consuming device, etc. The offshore converter controller (offshore MMC control system) detects the operating status of the offshore wind turbine in real time, such as the number and number of wind turbines in operation on each feeder, the output power of each operating wind turbine, etc. The offshore MMC control system establishes two-way communication with the first wind turbine on the feeder, the first wind turbine establishes two-way communication with the second wind turbine, and so on, the last wind turbine at the end of the feeder establishes two-way communication with the offshore MMC control system. If there are several wind turbines out of operation in the feeder, the entire optical fiber communication channel should still operate normally to ensure the normal communication of other operating wind turbines.
Claims
1. A method for controlling fault ride-through of a flexible DC line, characterized in that: include: When a transient fault occurs in a DC line, if the average value of the capacitor voltage of the power device in the power device in the sending-end converter of the DC line is greater than the voltage upper limit, energy-consuming devices for consuming the surplus power at the sending end will be put into operation in the wind turbines in operation in the wind farm at the sending end of the DC line until the average value of the capacitor voltage of the power device in the power device in the sending-end converter is less than the voltage lower limit; otherwise, the energy-consuming devices will not be put into operation.
2. The flexible DC line fault ride-through control method according to claim 1, characterized in that: The method of investing energy-consuming devices for absorbing surplus power at the sending end into the wind turbines currently operating in the wind farm at the sending end of the DC line comprises: investing energy-consuming devices for absorbing surplus power at the sending end into the wind turbines currently operating in the wind farm at the sending end in order from large to small output powers of the wind turbines currently operating in the wind farm at the sending end.
3. The flexible DC line fault ride-through control method according to claim 2, characterized in that: The method of putting energy-consuming devices for absorbing surplus power at the sending end into the wind turbine sets in operation in the sending-end wind farm also includes: when there is a wind turbine set without energy-consuming devices put into operation with a greater output power than the energy-consuming devices of the wind turbine sets with energy-consuming devices put into operation, energy-consuming devices are started to be put into the wind turbine sets without energy-consuming devices put into operation and with the largest current output power, and energy-consuming devices of the wind turbine sets with energy-consuming devices put into operation and with the smallest current output power are withdrawn each time energy-consuming devices are put into operation.
4. The method for controlling fault ride-through of a flexible DC line according to any one of claims 1 to 3, characterized in that: Also includes: When a transient fault occurs in the DC line, the control of the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter according to the DC voltage rated value is stopped, and the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter is controlled according to the DC voltage bias amount determined by the control amount of the DC current PI control by the sending end and the receiving end. The sending-end converter and the receiving-end converter respectively control the number of negative inputs of their own full-bridge power modules according to the corresponding reference voltage to perform DC negative voltage control; the control amount of the DC current PI control is determined according to the difference between the actual current of the DC line and the set current reference value, and the set current reference value is a negative value.
5. The flexible DC line fault ride-through control method according to claim 4, characterized in that: Also includes: When the instantaneous fault of the DC line ends, the DC negative voltage control is stopped and the control of the reference voltage according to the DC voltage rated value is restored. After the voltage of the DC line is increased to the DC voltage rated value by controlling the reference voltage according to the DC voltage rated value, the energy consuming devices in the wind turbine group that have been put into use are withdrawn.
6. The method for controlling the fault ride-through of a flexible DC line according to claim 5, characterized in that: The method of withdrawing the energy consuming devices in the wind turbines that have been put into use includes: withdrawing the energy consuming devices in the wind turbines in order from small to large output powers of the wind turbines that have been put into use in the wind farm.
7. A flexible DC line fault ride-through control system, comprising a first controller for controlling a converter at a sending end of the DC line and a wind turbine controller for controlling the energy consumption device in a wind turbine in a wind farm at the sending end of the DC line to be put into and out of operation, 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 wind turbine controller to put the energy consumption device into the wind turbines running in the sending-end wind farm when a transient fault occurs in the DC line, if the average value of the capacitor voltage of the power device in the sending-end converter is greater than the voltage upper limit, until the average value of the capacitor voltage of the power device in the sending-end converter is less than the voltage lower limit; otherwise, the wind turbine controller is not triggered to put the energy consumption device into operation.
8. The flexible DC line fault ride-through control system according to claim 7, characterized in that: The method of triggering the wind turbine controller to put the energy consumption device into the wind turbine in operation in the sending-end wind farm includes: The first controller triggers the wind turbine controllers in sequence according to the order of output power of each wind turbine being operated in the sending-end wind farm from large to small to put the energy consumption device into the wind turbine being operated in the sending-end wind farm.
9. The flexible DC line fault ride-through control system according to claim 8, characterized in that: The method of triggering the wind turbine controller to put energy-consuming devices for absorbing surplus power at the sending end into the wind turbines currently in operation in the sending-end wind farm also includes: when there is a wind turbine without energy-consuming devices whose output power is greater than the energy-consuming devices of the wind turbines with energy-consuming devices, the first controller starts to trigger the wind turbine controller to put energy-consuming devices into the wind turbine without energy-consuming devices and whose current output power is the largest, and at the same time, the energy-consuming devices of the wind turbine with energy-consuming devices and whose current output power is the smallest are withdrawn each time energy-consuming devices are put into operation.
10. The flexible DC line fault ride-through control system according to any one of claims 7 to 9, characterized in that: It also includes a second controller for controlling the receiving-end converter. The first controller and the second controller are respectively used to stop controlling the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter according to the DC voltage rated value when a transient fault occurs in the DC line; control the reference voltage of each bridge arm of the sending-end converter and each bridge arm of the receiving-end converter according to the DC voltage bias amount determined by the control amount of the DC current PI controller, and control the number of negative inputs of its own full-bridge power module according to the corresponding reference voltage to perform DC negative voltage control; the control amount of the DC current PI controller is determined according to the difference between the actual current of the DC line and the set current reference value, and the set current reference value is a negative value.
11. The flexible DC line fault ride-through control system according to claim 10, characterized in that: When the instantaneous fault of the DC line ends, the first controller and the second controller respectively stop the DC negative voltage control and resume the control of the reference voltage according to the DC voltage rated value. After the voltage of the DC line is increased to the DC voltage rated value by controlling the reference voltage according to the DC voltage rated value, the first controller triggers the wind turbine controller to control the exit of the energy consuming devices in the wind turbine that have been put into use.
12. The flexible DC line fault ride-through control system according to claim 11, characterized in that: The method of exiting the energy consuming devices in the wind turbine sets that have been put into use includes: the first controller triggers the wind turbine set controllers in sequence according to the output power of each wind turbine set that has been put into use in the wind farm from small to large, to control the exit of the energy consuming devices in the wind turbine sets.
13. The flexible DC line fault ride-through control system according to claim 12, characterized in that: The communication method between the first controller and each wind turbine controller includes: The first controller establishes two-way active-standby communication with the wind turbine controller of the first wind turbine and the wind turbine controller of the last wind turbine on the feeder, and the wind turbine controllers of the remaining wind turbines establish two-way active-standby communication with the wind turbine controllers of adjacent wind turbines.