A direct current fault ride through method, a direct current fault ride through device, equipment and a medium

Abstract

The present application relates to a kind of direct current fault ride through method, direct current fault ride through device, equipment and medium, when the direct current sending line occurs temporary pole-to-ground fault, by active voltage reduction control strategy or direct current current control strategy, the control mode of network configuration type energy storage is switched to alternating voltage control mode or direct current current control strategy, the device in the multi-terminal direct current collection and sending system is coordinated control, realize the removal of fault current, simultaneously, using active voltage reduction control strategy or direct current current control strategy removes fault current, without additional increase direct current circuit breaker and other measures, control flexible and easy to realize, and by determining the operating state of the multi-terminal direct current collection and sending system, control the recovery of the multi-terminal direct current collection and sending system after fault removal, it is conducive to the safe and stable operation of the multi-terminal direct current collection and sending system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of direct current (DC) collection and sending, and in particular to a DC fault ride-through method, a DC fault ride-through device, equipment and a medium. BACKGROUND

[0002] At present, developing new energy will become one of the important directions for future development of power grids. The resource potential of new energy development in some regions is nearly 2 billion kilowatts, and the annual average growth rate in some regions is more than 50%, which has great development prospects. At the same time, the installed capacity in the new energy intensive areas in these regions far exceeds the load, the grid framework in these areas is weak and far away from the load center, and the external sending demand is urgent.

[0003] The current island large-scale new energy collection and external sending scheme generally adopts an alternating current (AC) transmission or a flexible DC transmission mode to be connected to a grid. A traditional power frequency high-voltage AC transmission scheme is transmitted through AC collection and step-by-step voltage boosting. This scheme is mature, is suitable for a new energy consumption scene with a relatively short transmission distance and a relatively small transmission capacity, however, with the large-scale access of new energy, the transmission distance of this scheme is difficult to further improve due to the limitation of the synchronous stability operation limit of the AC system, which may lead to a decrease in system strength and deterioration of stability, and requires expansion of the transmission and transformation facilities, occupies the resources of the city surrounding corridors, and thus is difficult to support the demand for island operation of the new energy grid. A flexible DC transmission scheme, i.e., new energy is sent out through AC collection and flexible DC rectification, does not depend on the AC grid, and can be operated in an island mode. This scheme has high technical maturity, flexible control, and the ability to build a grid, and can provide frequency and voltage support for the grid. However, this scheme needs to build a converter station based on full-controlled devices, and has a high investment cost.

[0004] In order to solve the deficiencies of the existing schemes, some documents propose that the AC power generated by new energy is rectified and sent out through a diode rectifier (DR) station. Since the DR station adopts uncontrollable power electronic elements, the AC voltage of the offshore AC system cannot be established, and therefore a network-constructing wind turbine or other auxiliary network-constructing equipment needs to be used to provide the voltage and frequency support of the AC system. Further, when the DC transmission line in the system adopts an overhead line, the probability of temporary fault is high, the DC fault current is large and develops fast, and in a serious case, the system will be shut down, power supply will be interrupted, and the stability and reliability of the power system will be affected.

[0005] In order to deal with the DC fault of the DC sending system, the existing technology configures a DC circuit breaker at the receiving end, cooperates with the AC circuit breaker at the sending end station to complete the DC short-circuit fault ride-through, and realizes the clearing of the DC short-circuit fault, but the use of the DC circuit breaker configured at the receiving end for the DC fault ride-through of the system increases the cost of the system. SUMMARY

[0006] In order to solve the problem of increasing the cost of the system by using the fault of the receiving end configured DC circuit breaker to cross the system in the prior art, the application provides a DC fault crossing method, a DC fault crossing device, equipment and a medium.

[0007] In the first aspect of the application, a DC fault crossing method is provided, which is suitable for a new energy multi-terminal DC collection and sending system based on diode rectification, and the method comprises:

[0008] When a pole-to-ground fault occurs in a DC sending line in a multi-terminal DC collection and sending system, the control mode of a network-type energy storage in the multi-terminal DC collection and sending system is switched to a fault control mode according to a preset fault control strategy, the devices in the multi-terminal DC collection and sending system are coordinately controlled, and the DC fault clearing of the multi-terminal DC collection and sending system is realized; the fault control mode comprises an AC voltage control mode or a DC current control strategy, and the preset fault control strategy comprises an active voltage reduction control strategy or a DC current control strategy;

[0009] Based on the DC voltage in the multi-terminal DC collection and sending system after the fault is cleared, it is determined whether the fault of the multi-terminal DC collection and sending system disappears;

[0010] If the fault of the multi-terminal DC collection and sending system disappears, the multi-terminal DC collection and sending system is controlled to recover by using the network-type energy storage.

[0011] Optionally, the DC fault clearing of the multi-terminal DC collection and sending system by switching the control mode of the network-type energy storage to the fault control mode according to the preset fault control strategy and coordinately controlling the devices in the multi-terminal DC collection and sending system comprises:

[0012] According to the active voltage reduction control strategy, the control mode of the network-type energy storage is switched to the AC voltage control mode, the reference AC voltage value is reduced by using the AC voltage control mode, and the active reduction of the system sending end AC voltage is realized to avoid the fault current from being fed into the fault point;

[0013] When the grid-connected point voltage of the new energy station is less than a first preset voltage threshold, the control mode of the new energy station is switched to a low-voltage fault crossing mode;

[0014] Based on the AC voltage control mode and the low-voltage fault crossing mode, the new energy station and the network-type energy storage are coordinately controlled, and the DC fault clearing of the multi-terminal DC collection and sending system is realized.

[0015] Optionally, the new energy plant and the grid-connected energy storage are coordinately controlled based on the alternating current voltage control mode and the low-voltage fault ride-through mode to realize DC fault clearing of the multi-terminal DC collection and transmission system, including:

[0016] In the alternating current voltage control mode, a preset alternating current voltage less than a voltage threshold is taken as a first reference alternating current voltage;

[0017] In the low-voltage fault ride-through mode, an adjustment current is calculated based on a reference alternating current and an actual grid-connected point voltage of the new energy plant, and an adjustment active power is calculated based on the actual grid-connected point voltage and a reference grid-connected point voltage of the new energy plant and a reference active power of the new energy plant;

[0018] Based on the first reference alternating current voltage, an active power and a reactive power of the grid-connected energy storage, a driving signal of a bridge valve in the grid-connected energy storage is generated by using outer loop control and inner loop voltage and current control of the grid-connected energy storage;

[0019] Based on the adjustment current, the adjustment active power, an active power and a reactive power of the new energy plant, a driving signal of a bridge valve in the new energy plant is generated by using inner loop current control of the new energy plant;

[0020] The new energy plant and the grid-connected energy storage are coordinately controlled based on the driving signal of the bridge valve in the grid-connected energy storage and the driving signal of the bridge valve in the new energy plant to realize DC fault clearing of the multi-terminal DC collection and transmission system.

[0021] Optionally, the control mode of the grid-connected energy storage in the multi-terminal DC collection and transmission system is switched to a fault control mode according to a preset fault control strategy, and devices in the multi-terminal DC collection and transmission system are coordinately controlled to realize DC fault clearing of the multi-terminal DC collection and transmission system, including:

[0022] According to a DC current control strategy, the control mode of the grid-connected energy storage and the control mode of a faulty converter station of a controllable commutation converter station at a receiving end are switched to a DC current control mode respectively, and a current reference value is equal;

[0023] When a grid-connected point voltage of the new energy plant is less than a first preset voltage threshold, the control mode of the new energy plant is switched to a low-voltage fault ride-through mode;

[0024] The new energy plant, the grid-connected energy storage and the controllable commutation converter station at the receiving end are coordinately controlled based on the DC current control mode and the low-voltage fault ride-through mode to realize DC fault clearing of the multi-terminal DC collection and transmission system.

[0025] Optionally, based on the direct current control mode and the low-voltage fault ride-through mode, the new energy plant, the grid-forming energy storage and the receiving end controllable commutation converter station are coordinated and controlled to realize direct current fault clearing of the multi-terminal direct current collection and transmission system, comprising:

[0026] In the direct current control mode, based on the direct current pole line current of the fault pole in the diode rectifier station and the reference current, a second reference alternating current voltage and the minimum trigger angle of the commutation station where the fault pole in the receiving end controllable commutation converter station is located are respectively generated;

[0027] In the low-voltage fault ride-through mode, an adjustment current is calculated based on the reference alternating current and the actual grid connection point voltage of the new energy plant, and an adjustment active power is calculated based on the actual grid connection point voltage and the reference grid connection point voltage of the new energy plant and the reference active power of the new energy plant;

[0028] Based on the second reference alternating current voltage, the actual active power and the actual reactive power of the grid-forming energy storage, the drive signal of the bridge valve in the grid-forming energy storage is generated by using the outer ring control and the inner ring voltage and current control of the grid-forming energy storage;

[0029] Based on the minimum trigger angle and the direct current voltage in the multi-terminal direct current collection and transmission system, the drive signal of the bridge valve in the diode rectifier station where the fault pole is located is generated;

[0030] Based on the adjustment current, the adjustment active power, the active power and the reactive power of the new energy plant, the drive signal of the bridge valve in the new energy plant is generated by using the inner ring current control of the new energy plant;

[0031] Based on the drive signal of the bridge valve in the grid-forming energy storage, the drive signal of the bridge valve in the diode rectifier station where the fault pole is located and the drive signal of the bridge valve in the new energy plant, the new energy plant, the grid-forming energy storage and the receiving end controllable commutation converter station are coordinated and controlled to realize direct current fault clearing of the multi-terminal direct current collection and transmission system.

[0032] Optionally, based on the direct current voltage in the multi-terminal direct current collection and transmission system after fault clearing, it is determined whether the fault of the multi-terminal direct current collection and transmission system disappears, comprising:

[0033] After the fault of the multi-terminal direct current collection and transmission system is cleared, the control mode of the grid-forming energy storage is switched to a power outer ring control mode;

[0034] In the power outer ring control mode, based on the actual active power and the reference active power output by the diode rectifier station, a standby reference alternating current voltage is generated by using proportional integral control;

[0035] based on the to-be-used reference alternating voltage, the reference angular frequency, and the active power and the reactive power of the grid-forming energy storage, power droop control is used to realize proportional sharing of internal power of the multi-unit energy storage, and target phase and direct-axis voltage are generated;

[0036] based on the target phase, the direct-axis voltage, and a preset quadrature-axis voltage, inner loop control of the grid-forming energy storage is used to control the bridge valve in the grid-forming energy storage;

[0037] In a first preset time period, if the direct-current voltage in the multi-terminal direct-current collection and transmission system after fault removal is greater than or equal to a second preset voltage threshold, it is determined that the multi-terminal direct-current collection and transmission system is fault-free.

[0038] Optionally, the use of the grid-forming energy storage to control the recovery of the multi-terminal direct-current collection and transmission system comprises:

[0039] The power of the grid-forming energy storage is used to adjust the power of the multi-terminal direct-current collection and transmission system;

[0040] When the new energy station is in a low-voltage fault ride-through mode, if the current grid-connected point voltage of the new energy station is greater than or equal to a first preset voltage threshold and the duration is greater than or equal to a second preset time period, the control mode of the new energy station is exited from the low-voltage fault ride-through mode;

[0041] When the sending-end alternating voltage is greater than or equal to a third preset voltage threshold, based on the direct-current voltage in the multi-terminal direct-current collection and transmission system after fault removal, the active power and the reactive power of the new energy station, inner loop current control of the new energy station is used to control the new energy station to restore normal power transmission, and recovery control of the multi-terminal direct-current collection and transmission system is realized.

[0042] Optionally, the determination of whether the multi-terminal direct-current collection and transmission system is fault-free based on the direct-current voltage in the multi-terminal direct-current collection and transmission system after fault removal comprises:

[0043] After the fault of the multi-terminal direct-current collection and transmission system is removed, the control mode of the commutation station in the faulty pole of the receiving-end controllable commutation converter station is switched to a current margin control mode;

[0044] Under the current margin control, based on the actual pole line current and the margin current in the receiving-end controllable commutation converter station, the direct-current voltage in the multi-terminal direct-current collection and transmission system after fault removal, maximum trigger angle control and proportional integral control are used to generate the current trigger angle of the receiving-end controllable commutation converter station;

[0045] control bridge valves in the receiving controllable commutation converter station based on a current trigger angle of the receiving controllable commutation converter station;

[0046] If the DC voltage in the multi-terminal DC collection and sending system after fault clearing is greater than or equal to a second preset voltage threshold for a first preset time period, it is determined that the multi-terminal DC collection and sending system is fault-free.

[0047] Optionally, the recovery control of the multi-terminal DC collection and sending system by using the grid-forming energy storage comprises:

[0048] switching the control mode of the grid-forming energy storage to a power outer loop control mode;

[0049] In the power outer loop control mode, a standby reference AC voltage is generated by using proportional integral control based on actual active power and reference active power output by the diode rectifier station;

[0050] Based on the standby reference AC voltage, a reference angle frequency, active power and reactive power of the grid-forming energy storage, power droop control is used to realize proportional sharing of internal power of the multi-unit energy storage, to generate a target phase and a direct-axis voltage;

[0051] Based on the target phase, the direct-axis voltage and a preset quadrature-axis voltage, inner loop control of the grid-forming energy storage is used to control bridge valves in the grid-forming energy storage;

[0052] When the new energy station is in a low-voltage fault ride-through mode, if the current grid connection point voltage of the new energy station is greater than or equal to a first preset voltage threshold and the duration is greater than or equal to a second preset time period, the control mode of the new energy station is exited from the low-voltage fault ride-through mode.

[0053] When the sending end AC voltage is greater than or equal to a third preset voltage threshold, based on the DC voltage in the multi-terminal DC collection and sending system after fault clearing, active power and reactive power of the new energy station, inner loop current control of the new energy station is used to control the new energy station to restore normal power transmission, to realize recovery control of the multi-terminal DC collection and sending system.

[0054] In a second aspect, the present application provides a direct current fault ride-through device suitable for a new energy multi-terminal direct current collection and transmission system based on diode rectification, the device comprising: a direct current fault clearing unit configured to switch a control mode of a grid-forming energy storage in the multi-terminal direct current collection and transmission system to a fault control mode according to a preset fault control strategy when a pole-to-ground fault occurs in a direct current transmission line in the multi-terminal direct current collection and transmission system, to coordinate control of devices in the multi-terminal direct current collection and transmission system, and to realize direct current fault clearing of the multi-terminal direct current collection and transmission system; the fault control mode comprises an alternating current voltage control mode or a direct current current control strategy, and the preset fault control strategy comprises an active voltage reduction control strategy or a direct current current control strategy; a fault disappearance judging unit configured to judge whether the fault of the multi-terminal direct current collection and transmission system disappears based on a direct current voltage in the multi-terminal direct current collection and transmission system after the fault is cleared; and a transmission system recovery unit configured to perform recovery control on the multi-terminal direct current collection and transmission system by using the grid-forming energy storage if the fault of the multi-terminal direct current collection and transmission system disappears.

[0055] Optionally, the direct current fault clearing unit comprises: a first control mode switching module configured to switch the control mode of the grid-forming energy storage to an alternating current voltage control mode according to an active voltage reduction control strategy, to reduce a reference alternating current voltage value by using the alternating current voltage control mode, and to realize active reduction of a system sending end alternating current voltage to avoid fault current feeding into a fault point; a second control mode switching module configured to switch a control mode of a new energy station to a low-voltage fault ride-through mode when a grid-connected point voltage of the new energy station is less than a first preset voltage threshold; and a first direct current fault clearing module configured to coordinate control of the new energy station and the grid-forming energy storage based on the alternating current voltage control mode and the low-voltage fault ride-through mode, and to realize direct current fault clearing of the multi-terminal direct current collection and transmission system.

[0056] Optionally, the first DC fault clearing module is specifically configured to: in the AC voltage control mode, take a preset AC voltage smaller than a voltage threshold as a first reference AC voltage; in the low-voltage fault ride-through mode, calculate an adjustment current based on a reference AC current and an actual grid connection point voltage of the new energy station, and calculate an adjustment active power based on the actual grid connection point voltage and a reference grid connection point voltage of the new energy station and a reference active power of the new energy station; generate a driving signal of a bridge valve in the grid-forming energy storage by using inner loop control of the grid-forming energy storage based on the first reference AC voltage, the active power and the reactive power of the grid-forming energy storage, generate a driving signal of a bridge valve in the new energy station by using inner loop current control of the new energy station based on the adjustment current, the adjustment active power, the active power and the reactive power of the new energy station, and perform coordinated control on the new energy station and the grid-forming energy storage based on the driving signal of the bridge valve in the grid-forming energy storage and the driving signal of the bridge valve in the new energy station, so as to realize DC fault clearing of the multi-terminal DC collection and transmission system.

[0057] Optionally, the DC fault clearing unit comprises: a third control mode switching module configured to switch control modes of the grid-forming energy storage and a fault pole of a converter station in a controllable commutation converter station at a receiving end to a DC current control mode according to a DC current control strategy, and the current reference values are equal; a fourth control mode switching module configured to switch the control mode of the new energy station to a low-voltage fault ride-through mode when a grid connection point voltage of the new energy station is smaller than a first preset voltage threshold; and a second DC fault clearing module configured to perform coordinated control on the new energy station, the grid-forming energy storage and the controllable commutation converter station at the receiving end based on the DC current control mode and the low-voltage fault ride-through mode, so as to realize DC fault clearing of the multi-terminal DC collection and transmission system.

[0058] Optionally, the second DC fault clearing module is specifically configured to: in the DC current control mode, based on the DC pole line current of the fault pole in the diode rectifier station and a reference current, generate a second reference AC voltage and a minimum trigger angle of the commutation station where the fault pole in the receiving end controllable commutation converter station is located, respectively; in the low-voltage fault ride-through mode, based on a reference AC current and an actual grid connection point voltage of the new energy station, calculate an adjustment current, and based on the actual grid connection point voltage and a reference grid connection point voltage of the new energy station and a reference active power of the new energy station, calculate an adjustment active power; based on the second reference AC voltage, an actual active power and an actual reactive power of the grid-forming energy storage, using outer loop control and inner loop voltage and current control of the grid-forming energy storage, generate a driving signal of a bridge valve in the grid-forming energy storage; based on the minimum trigger angle and a DC voltage in the multi-terminal DC collection and transmission system, generate a driving signal of a bridge valve where the fault pole in the diode rectifier station is located; based on the adjustment current, the adjustment active power, an active power and a reactive power of the new energy station, using inner loop current control of the new energy station, generate a driving signal of a bridge valve in the new energy station; based on the driving signal of the bridge valve in the grid-forming energy storage, the driving signal of the bridge valve where the fault pole in the diode rectifier station is located and the driving signal of the bridge valve in the new energy station, coordinate control of the new energy station, the grid-forming energy storage and the receiving end controllable commutation converter station to realize DC fault clearing of the multi-terminal DC collection and transmission system.

[0059] Optionally, the fault disappearance determination unit is specifically configured to: after the fault clearing of the multi-terminal DC collection and transmission system, switch the control mode of the grid-forming energy storage to a power outer loop control mode; in the power outer loop control mode, based on an actual active power and a reference active power output by the diode rectifier station, generate a standby reference AC voltage using proportional integral control; based on the standby reference AC voltage, a reference angular frequency and an active power and a reactive power of the grid-forming energy storage, generate a target phase and a direct axis voltage using power droop control; based on the target phase, the direct axis voltage and a preset quadrature axis voltage, control the bridge valve in the grid-forming energy storage using outer loop control and inner loop voltage and current control of the grid-forming energy storage; in a first preset time period, if the DC voltage in the multi-terminal DC collection and transmission system after the fault clearing is greater than or equal to a second preset voltage threshold for a continuous time, it is determined that the multi-terminal DC collection and transmission system is fault-free.

[0060] Optionally, the sending system recovery unit is specifically configured to: utilize a power outer loop control mode of the network-constructed energy storage to perform power adjustment on the multi-terminal DC collection sending system; when the new energy station is in a low-voltage fault ride-through mode, if a current grid connection point voltage of the new energy station is greater than or equal to a first preset voltage threshold and a duration is greater than or equal to a second preset time period, the control mode of the new energy station is exited from the low-voltage fault ride-through mode; when an AC voltage at a sending end is greater than or equal to a third preset voltage threshold, based on a DC voltage in the multi-terminal DC collection sending system after fault clearing, active power and reactive power of the new energy station, the new energy station is controlled to restore normal power transmission by utilizing inner loop current control of the new energy station, so as to realize recovery control of the multi-terminal DC collection sending system.

[0061] Optionally, the fault disappearance determination unit is specifically configured to: after the multi-terminal DC collection sending system is cleared of fault, a control mode of a commutation station in a fault pole in the receiving terminal controllable commutation converter station is switched to a current margin control mode; under the current margin control, based on an actual pole line current and a margin current in the receiving terminal controllable commutation converter station and a DC voltage in the multi-terminal DC collection sending system after fault clearing, a current trigger angle of the receiving terminal controllable commutation converter station is generated by utilizing maximum trigger angle control and proportional integral control; based on the current trigger angle of the receiving terminal controllable commutation converter station, a bridge valve in the receiving terminal controllable commutation converter station is controlled; if the DC voltage in the multi-terminal DC collection sending system after fault clearing is greater than or equal to a second preset voltage threshold for a first preset time period, it is determined that the multi-terminal DC collection sending system is cleared of fault.

[0062] Optionally, the sending system recovery unit is specifically configured to: switch the control mode of the grid-forming energy storage to a power outer loop control mode; in the power outer loop control mode, based on actual active power and reference active power output by the diode rectifier station, generate a standby reference alternating current voltage by using proportional integral control; based on the standby reference alternating current voltage, a reference angular frequency, and active power and reactive power of the grid-forming energy storage, generate a target phase and a direct-axis voltage by using power droop control; based on the target phase, the direct-axis voltage, and a preset quadrature-axis voltage, control the bridge valve in the grid-forming energy storage by using outer loop control and inner loop voltage and current control of the grid-forming energy storage; when the new energy station is in a low-voltage fault ride-through mode, if a current grid-connected point voltage of the new energy station is greater than or equal to a first preset voltage threshold and a duration is greater than or equal to a second preset time period, exit the control mode of the new energy station from the low-voltage fault ride-through mode; when a sending-end alternating current voltage is greater than or equal to a third preset voltage threshold, based on a direct-current voltage in the multi-terminal direct-current collection and sending system after fault clearing, active power and reactive power of the new energy station, control the new energy station to restore normal power transmission by using inner loop current control of the new energy station, and realize recovery control of the multi-terminal direct-current collection and sending system.

[0063] In a third aspect, the present application provides a computer device, comprising: one or more processors;

[0064] The processor is configured to store one or more programs, and when the one or more programs are executed by the one or more processors, the direct-current fault ride-through method according to the first aspect is implemented.

[0065] In a fourth aspect, the present application provides a computer readable storage medium, which has a computer program stored thereon, and when the computer program is executed, the direct-current fault ride-through method according to the first aspect is implemented.

[0066] Compared with the prior art, the present application has the following beneficial effects:

[0067] The application provides a DC fault ride-through method, a DC fault ride-through device, equipment and a medium. BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1 A flowchart of a DC fault ride-through method provided by the application;

[0069] Figure 2 A schematic diagram of a diode rectification new energy multi-terminal DC collection and sending system topology structure provided by the application;

[0070] Figure 3 A schematic diagram of a diode rectification station topology structure provided by the application;

[0071] Figure 4 A schematic diagram of a CLCC inverter station topology structure provided by the application;

[0072] Figure 5 A schematic diagram of a CLCC inverter station single valve electrical topology structure provided by the application;

[0073] Figure 6 A schematic diagram of a low-voltage fault ride-through mode provided by the application;

[0074] Figure 7 A schematic diagram of a network-type energy storage control switching provided by the application;

[0075] Figure 8 A distribution diagram of a multi-terminal DC collection and sending system fault current provided by the application;

[0076] Figure 9 A schematic diagram of a network-type energy storage control switching provided by the application;

[0077] Figure 10 A schematic diagram of a receiving end controllable commutation converter station control switching provided by the application;

[0078] Figure 11 A schematic diagram of a multi-terminal DC collection and sending system steady-state control strategy provided by the application;

[0079] Figure 12 A schematic diagram of a "active voltage reduction control" simulation verification waveform is provided for the present application.

[0080] Figure 13 A schematic diagram of a "direct current control" simulation verification waveform is provided for the present application.

[0081] Figure 14 A flow chart of a "active voltage reduction control" DC fault ride-through control strategy is provided for the present application.

[0082] Figure 15 A flow chart of a "direct current control" DC fault ride-through control strategy is provided for the present application.

[0083] Figure 16 A schematic diagram of a DC fault ride-through device is provided for the present application.

[0084] Figure 17 A block diagram of a computer device is provided for the present application. DETAILED DESCRIPTION

[0085] Embodiment 1:

[0086] Figure 1 A flow chart of a DC fault ride-through method is provided for the present application, which is suitable for a new energy multi-terminal DC collection and transmission system based on diode rectification, such as Figure 1 As shown, the method can include the following steps 101-103:

[0087] In step 101, when a pole-to-ground fault occurs in a DC transmission line in a multi-terminal DC collection and transmission system, the control mode of a network-forming energy storage in the multi-terminal DC collection and transmission system is switched to a fault control mode according to a preset fault control strategy, the devices in the multi-terminal DC collection and transmission system are coordinated and controlled, and the DC fault clearance of the multi-terminal DC collection and transmission system is realized.

[0088] The fault control mode includes an AC voltage control mode or a DC current control strategy, and the preset fault control strategy includes an active voltage reduction control strategy or a DC current control strategy.

[0089] In step 102, based on the DC voltage in the multi-terminal DC collection and transmission system after fault clearance, it is determined whether the fault of the multi-terminal DC collection and transmission system disappears.

[0090] In step 103, if the fault of the multi-terminal DC collection and transmission system disappears, the multi-terminal DC collection and transmission system is controlled for recovery by the network-forming energy storage.

[0091] It should be noted that the application proposes two direct current fault ride-through control methods suitable for diode rectification new energy multi-terminal direct current collection and sending out system. One is the "active voltage reduction type" control (i.e. active voltage reduction control strategy), which mainly relies on the coordination of new energy station and network-forming energy storage to realize fault ride-through; and the other is "direct current control" (i.e. direct current control strategy), which mainly relies on the coordination among new energy station, network-forming energy storage and controlled line commutated converter (CLCC) at the receiving end to realize fault ride-through.

[0092] The application is directed to a new energy island multi-terminal direct current collection and sending out system based on network-forming energy storage and diode rectification, and studies the fault current rapid clearing and system recovery control strategy under temporary direct current sending out line fault.

[0093] In view of the problem of temporary fault on the direct current outgoing line of the island new energy direct current collection and sending out system, the application aims to propose a direct current fault ride-through control method for the diode rectification based new energy multi-terminal direct current collection and sending out system, consider the differences in uncontrolled diode converter station and controllable off characteristics of the receiving end converter station, study the coordinated control among the new energy station with power control capability, the network-forming energy storage with power compensation and voltage support capability, and the receiving end converter station with direct current voltage control capability, and solve the problems of device electrical impact out-of-limit and system shutdown caused by protection triggering in the temporary fault ride-through process. There is no related literature research and engineering application case for reference at present, and then a monopolar-to-ground fault ride-through control method for the direct current sending out line of the system is provided, the fault current is cleared, the system is recovered after the fault, and the safe and stable operation of the device and the system is realized, which is suitable for island or weak network new energy collection and grid connection and long distance sending out scene, has wide use scene and outstanding advantages and effects.

[0094] In some embodiments of the application, as shown in Figure 2 The diode rectification based new energy multi-terminal direct current collection and sending out system can include an alternating current bus, a new energy station, a network-forming energy storage, a diode rectification station (DR), a direct current sending out line and a receiving end station, the network-forming energy storage and the new energy station are connected with the alternating current bus respectively, the alternating current side of the diode rectification station is connected with the alternating current bus, the direct current side of the diode rectification station is connected with the direct current side of the receiving end station through the direct current sending out line, and the alternating current side of the receiving end station is connected with the alternating current grid.

[0095] The new energy station can be a wind power station, a photovoltaic station, a geothermal power station or a hybrid station (for example, a hybrid station composed of wind power and photovoltaic), etc., the receiving end station can be an inverter station based on a controlled line commutated converter (CLCC), and the direct current sending out line can be a direct current overhead line. In some scenarios, the new energy multi-terminal direct current collection and sending out system further includes a filtering device.

[0096] For example, a wind farm can consist of a cluster of multiple AC wind turbines connected in parallel. Each AC wind turbine can include a permanent magnet synchronous wind turbine generator, a turbine-side converter, a DC power dissipation device, and a grid-side converter. The AC power generated is connected to the offshore AC power grid via a local transformer.

[0097] The voltage is then further increased by a step-up substation, and the diode rectifier station, as follows: Figure 3 As shown, it includes a converter transformer, a converter valve, and a smoothing reactor. The converter valve can adopt a pseudo-bipolar structure with 6 pulses per pole to rectify the AC power and generate DC power for long-distance transmission. The reactive power consumed by the diode rectifier station can be provided by grid-type energy storage and new energy sources. No reactive power compensation device is configured in the station. The converter transformer of the diode rectifier station can adopt a positive Y / Y and negative Y / Δ connection method to form a 12-pulse rectifier bridge.

[0098] The filtering device uses BP (Band Pass) 11th / 13th order resonant filters, HP (High Pass) 24th / 36th order resonant filters, and HP 3rd order resonant filters.

[0099] The topology of a CLCC inverter station is similar to that of a traditional LCC, such as... Figure 4 As shown, a pseudo-bipolar structure with 6 pulses per pole and neutral point grounding is adopted. The converter transformer of the CLCC inverter station adopts a positive pole Y / Y and negative pole Y / Δ connection method to form a 12-pulse inverter bridge. Each pole consists of 6 converter valves.

[0100] The electrical topology diagram of a single valve is as follows: Figure 5 As shown, V11 and V12 form the main branch, and V13 and V14 form the auxiliary branch. The main branch and the auxiliary branch are connected in parallel. V11 and V14 are thyristor valves, V12 and V13 are fully controllable IGBT (Insulated Gate Bipolar Transistor) valves, V11 is a high-voltage thyristor valve, and V14 is a low-current thyristor valve. The thyristors are connected in parallel to an RC circuit, and the IGBTs are connected in parallel to an RCD circuit to achieve dynamic voltage equalization. Thyristor V11 is connected to resistor R... d1 and capacitor C d1 The series-connected RC circuit is connected in parallel, with thyristor V14 connected to resistor R. d4 and capacitor C d4 The two ends connected in series with resistor R dc4 The RC circuits formed by parallel connections are connected in parallel, with the main fully controllable valve V12 connected to the resistor R. d2 With capacitor C d2 Series connection, resistor R d2 With diode D d2 The parallel RCD circuit, which assists the fully controllable valve V13 and is connected to the resistor Rd3 with the capacitor C d3 in series, the resistance R d3 with the diode D d3 in parallel, the auxiliary fully controllable valve V13 is also connected in parallel with the arrester arr13, and the thyristor valve V11 can also be connected with the saturable reactor L SR in series, the auxiliary fully controllable IGBT valve V13 is connected with the thyristor valve V14 through the reactor L FSR the fully controllable IGBT valve is connected in reverse parallel with the diode.

[0101] The AC filter device adopts BP11 / 13 harmonic resonant filter, HP24 / 36 harmonic resonant filter and HP3 harmonic resonant filter, and the DC filter device adopts HP12 / 24 harmonic resonant filter.

[0102] The controllable commutation mode of the CLCC includes two states of natural commutation operation and forced commutation operation. When the natural commutation operation is performed, the valves V11 and V12 are turned on, and the current flows through the main branch. When the commutation current is less than a certain set value, the valve V12 is turned off, the auxiliary branch valves V13 and V14 are turned on, and the current flows through the main auxiliary branch. At this time, the valve V11 enters the blocking recovery period due to bearing reverse voltage. When the auxiliary branch current decays to zero under the action of external AC voltage, the natural commutation is completed. When the AC system fault occurs in the receiving end power grid, the valve V13 is turned off, so that the current commutation valve has the ability to actively turn off the current, and the CLCC enters the forced commutation operation. The turn-on sequence timing of each valve is consistent with that in normal operation, except that after the valve V13 is turned off, due to the AC system fault, the current cannot be reduced to 0, at this time the current is transferred to the arrester arr13, and the arrester action voltage is enhanced to complete the forced commutation process.

[0103] In order to deal with the DC fault of the DC transmission system, the wind farm through the diode rectification transmission grid-connected system and the control and protection system (CN114825431A) proposes a strategy of completing the DC short-circuit fault ride-through by the fault current limiting control ability of the wind turbine, cooperating with the receiving end station AC / DC circuit breaker and the sending end station AC circuit breaker, realizing the clearance of the DC short-circuit fault, and quickly recovering the wind farm power after the fault recovery. But the system still needs to configure a DC circuit breaker at the receiving end, which has high cost, and the sending and receiving end systems are completely disconnected during the fault, which cannot maintain the transmission of part of the active power.

[0104] The two DC current passing strategies suitable for the new energy DC collection and sending out system provided by the application can clear fault current without additional measures such as DC circuit breaker, and are flexible and easy to implement. In the process of using the DC current control, the non-fault DC line can still transmit 50% of the active power, the impact of the active power generated by the sending and receiving end AC system is significantly reduced, which is beneficial to the system recovery after temporary fault. From the equipment level, the number of switch device actions can be reduced, thereby reducing equipment wear and tear and operation and maintenance costs; from the system level, through rapid suppression of fault current and system recovery, the time delay and energy loss caused by system restart and power supply recovery after opening can be avoided, the disturbance of the fault to the system can be effectively reduced, and the tolerance of the new energy DC sending out system to temporary faults of the DC line can be improved, thereby ensuring reliable transmission and consumption of new energy power.

[0105] The above Figure 1 A possible implementation of the step 101 can include the following steps 1011-1013:

[0106] In the step 1011, according to the active voltage reduction control strategy, the control mode of the grid-forming energy storage is switched to an AC voltage control mode, the reference AC voltage value is reduced by using the AC voltage control mode, and the active reduction of the system sending end AC voltage is realized to avoid the fault current feeding into the fault point.

[0107] In the step 1012, when the grid-connected point voltage of the new energy station is less than a first preset voltage threshold, the control mode of the new energy station is switched to a low-voltage fault passing mode.

[0108] In the step 1013, based on the AC voltage control mode and the low-voltage fault passing mode, the new energy station and the grid-forming energy storage are coordinately controlled to realize DC fault clearing of the multi-terminal DC collection and sending out system.

[0109] It should be noted that the active voltage reduction control strategy reduces the AC voltage of the new energy grid-connected point by the grid-forming energy storage, realizes fault current clearing, and then uses the voltage control capability of the grid-forming energy storage and the inverter station, and cooperates with the coordinated control of the new energy unit to realize system recovery. In the fault current clearing stage, the new energy station and the grid-forming energy storage are mainly coordinated and cooperated, the grid-forming energy storage is actively reduced, and the new energy power is quickly dissipated to realize fast clearing of the fault current; in the fault disappearance judgment stage, the grid-forming energy storage switches the control to the normal control mode, and transmits a small current to the receiving end station, and whether the fault disappears is judged by judging whether the DC voltage can be successfully established; in the system recovery stage, the AC voltage establishment capability of the grid-forming energy storage is used, and the coordinated control of the new energy unit is used to realize system power recovery.

[0110] That is, in the fault current clearing phase, the control includes: a new energy side control switching link and a grid-forming energy storage control switching link. The new energy side control switching link is used to realize safe operation of the unit under low AC voltage conditions; and the grid-forming energy storage control switching link directly controls voltage reduction of the new energy AC grid-connected point, so that the DC voltage output by the DR station is lower than the voltage at the fault point port, the current is suppressed to feed into the fault point, and thus the fault current is cleared.

[0111] Possible implementation manners of the above step 1013 can include the following steps S1 to S5:

[0112] In step S1, in the AC voltage control mode, a preset AC voltage less than a voltage threshold is taken as a first reference AC voltage.

[0113] In step S2, in the low-voltage fault ride-through mode, an adjustment current is calculated based on a reference AC current and an actual grid-connected point voltage of the new energy station, and an adjustment active power is calculated based on the actual grid-connected point voltage and a reference grid-connected point voltage of the new energy station and a reference active power of the new energy station.

[0114] In step S3, a drive signal of a bridge valve in the grid-forming energy storage is generated by using inner loop control of the grid-forming energy storage based on the first reference AC voltage, the active power and the reactive power of the grid-forming energy storage.

[0115] In step S4, a drive signal of a bridge valve in the new energy station is generated by using inner loop current control of the new energy station based on the adjustment current, the adjustment active power, the active power and the reactive power of the new energy station.

[0116] In step S5, the new energy station and the grid-forming energy storage are coordinately controlled based on the drive signal of the bridge valve in the grid-forming energy storage and the drive signal of the bridge valve in the new energy station, so as to realize DC fault clearing of the multi-terminal DC collection and transmission system.

[0117] The drive signal can be a PWM (Pulse Width Modulation) signal.

[0118] It should be noted that the fault causes the pole-to-ground voltage of the DC fault pole to be a near-zero value, and therefore the wind farm AC grid-connected point voltage will also drop, and when the threshold is lower than the threshold, the wind turbine enters the low-voltage fault ride-through control mode and uses a current limiting link to limit AC overcurrent. This process is a control switching link of the new energy, and the dynamic reactive power support implementation manner of the converter in the new energy station is as follows:

[0119]

[0120] In the above formula,i dref for a converter in a new energy station d axle current reference value, i qref for a converter in a new energy station q axle current reference value, k p for a proportionality coefficient, V s for an actual grid connection point voltage (or AC voltage reference value) of a new energy station, I N for an AC current reference value (i.e. reference AC current), I lim for an AC current limiting value (or reference value), i dmax for d axle current upper limit value, i dmin for d axle current lower limit value, Δ i q for an adjustment current, i q for q axle current.

[0121] The machine-side converter appropriately reduces load according to AC voltage drop, surplus power is absorbed by energy consumption devices in the new energy station, and the active power reference value is switched to P ref_frt The implementation is as follows:

[0122]

[0123] wherein, V sref for an AC voltage reference value of a new energy station, V s for an actual grid connection point voltage of a new energy station, k for a power regulation proportionality coefficient, P ref for an active power reference value under rated operating conditions, P ref_frt for an adjustment active power.

[0124] The grid-forming energy storage will control multi-active power when the AC voltage at the sending end grid connection point drops, support the AC voltage at the grid connection point through fast reactive power response capability, and ensure reactive power balance on the AC side of the system sending end under transient operating conditions.

[0125] For example, as Figure 6As shown, when the grid-connected point voltage of the new energy station is less than the first preset voltage threshold, an enable signal FRT_flag1 is generated, and the control system of the new energy station receives the enable signal FRT_flag1 to switch the control mode of the new energy station to a low-voltage fault ride-through mode.

[0126] The grid-side converter control receives the enable signal FRT_flag1, and calculates an adjustment current Δ based on a reference alternating current I N , an actual grid-connected point voltage V s and a proportional coefficient k p . i q , that is, as shown below:

[0127]

[0128] The actual reactive power of the grid-side converter Q m and the reference reactive power Q ref are subtracted to obtain a reactive power difference value, and the reactive power difference value is processed by PI (Proportional-Integral) control to obtain q axis current, the adjustment current and the q axis current i q are added to obtain a reference q axis current i qref . The direct current voltage U dc and the reference direct current voltage U dcref are subtracted to obtain a voltage difference value, and the voltage difference value, the alternating current amplitude limit value I lim and the reference q axis current i qref are used to calculate an upper limit value and a lower limit value of the generated d-axis current, and the voltage difference value, the upper limit value and the lower limit value of the d-axis current are used to generate a reference d-axis current i dref by PI control. Based on the reference q axis current i qref and the reference d-axis current i dref , inner loop current control is used to generate q axis voltage u q and d-axis voltage u d,based on q shaft voltage u q d-axis voltage u d The phase obtained from the PLL (Phase-Locked Loop) is transformed into coordinates using inverse Parker transform and inverse Clarke transform to generate the PWM signal for the grid-side converter.

[0129] When the generator-side converter receives the enable signal FRT_flag1, it controls the converter based on the actual grid connection point voltage. V s AC voltage reference value V sref Power regulation ratio coefficient k and reference active power under rated operating conditions P ref The adjusted active power was calculated. P ref_frt Adjusting active power P ref_frt and actual active power P m The difference is calculated to obtain the active power difference. Then, PI control is used to process this active power difference to obtain a reference value. q shaft current i qref Based on reference q shaft current i qref and reference d-axis current i dref By utilizing inner loop current control, generation q shaft voltage u q and d-axis voltage u d ,based on q shaft voltage u q d-axis voltage u d The phase obtained from the PLL is used to perform coordinate transformation through inverse Parker transform and inverse Clarke transform to generate the PWM signal for the machine-side converter.

[0130] The system control and protection device can generate a DC fault ride-through signal through the characteristic quantity identification method, triggering the grid-type energy storage to switch the control switch, switching the additional power outer loop to AC voltage control, and actively reducing the AC voltage so that the DC outlet voltage of the DR station is lower than the fault point port voltage, thereby suppressing the current feed into the fault point and realizing the rapid clearing of the fault current. At the same time, this process requires the cooperation of the new energy power station units to quickly dissipate the surplus power.

[0131] For example, such asFigure 7 As shown, when a pole-to-ground fault occurs in the DC transmission line in the multi-terminal DC collection and transmission system, the system control and protection device can generate a protection signal, process the protection signal using delay control, generate a DC fault ride-through signal FRT_flag2, and switch the control mode of the grid-forming energy storage from a power outer loop control mode to an AC voltage control mode through the DC fault ride-through signal FRT_flag2. In the AC voltage control mode, a preset AC voltage V acset As the first reference AC voltage V acref In the power outer loop control mode, the actual active power output by the DR station is calculated P drum and the difference between the reference active power P druref , to obtain the first reference AC voltage V acref .

[0132] The above Figure 1 Another possible implementation of step 101 can include the following steps 1014-1016:

[0133] In step 1014, according to the DC current control strategy, the control mode of the grid-forming energy storage and the faulty pole converter station of the receiving end controllable commutation converter station are switched to the DC current control mode, and the current reference value is equal.

[0134] In step 1015, when the grid-connected point voltage of the new energy station is less than a first preset voltage threshold, the control mode of the new energy station is switched to a low-voltage fault ride-through mode.

[0135] In step 1016, based on the DC current control mode and the low-voltage fault ride-through mode, the new energy station, the grid-forming energy storage, and the receiving end controllable commutation converter station are coordinated and controlled to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

[0136] It should be noted that the strategy utilizes the DC current regulation capability of the converter stations at both ends of the fault point to achieve fault current clearing, and then utilizes the voltage control capability of the grid-forming energy storage and the inverter station, supplemented by coordinated control on the new energy side to achieve system recovery. In the fault current clearing stage, the DC current regulation capability of the grid-forming energy storage and the receiving end converter station at both ends of the fault point is utilized to control the DC currents on both sides of the fault point to be consistent, thereby achieving fault current clearing and ensuring stable transmission of part of the active power through the non-fault pole; in the fault disappearance judgment stage, the control strategy of the receiving end station is switched, the minimum trigger angle limit value is adjusted, and whether the fault disappears is determined by judging whether the DC voltage can be successfully established; in the system recovery stage, the voltage control capability of the inverter station and the grid-forming energy storage is utilized, supplemented by coordinated control on the new energy side to achieve system recovery. It includes: a new energy side control switching link, a grid-forming energy storage control switching link and a receiving end converter station control switching link.

[0137] That is, in the fault current clearing stage, the control includes: a new energy side control switching link, a grid-forming energy storage control switching link and an inverter station control switching link. The new energy side control switching link is used to realize safe operation of the unit under low AC voltage conditions; the grid-forming energy storage control switching link is used to control the DC current of the diode rectifier station; and the inverter station control switching link is used to control the DC current of the pole line of the receiving end station where the fault is located, thereby achieving fault current clearing by controlling the currents on both sides of the fault point to be consistent.

[0138] Possible implementations of the above step 1016 can include the following steps S6-S11:

[0139] In step S6, in the DC current control mode, a second reference AC voltage and a minimum trigger angle of the fault pole of the receiving end controllable commutation converter station are respectively generated based on the DC pole line current of the fault pole in the diode rectifier station and the reference current.

[0140] In step S7, in the low voltage fault ride-through mode, an adjustment current is calculated based on the reference AC current and the actual grid connection point voltage of the new energy field station, and an adjustment active power is calculated based on the actual grid connection point voltage and the reference grid connection point voltage of the new energy field station and the reference active power of the new energy field station.

[0141] In step S8, based on the second reference AC voltage, the actual active power and the actual reactive power of the grid-forming energy storage, the drive signal of the bridge valve in the grid-forming energy storage is generated by using the inner loop control of the grid-forming energy storage.

[0142] In step S9, based on the minimum trigger angle and the DC voltage in the multi-terminal DC collection and sending out system, the drive signal of the bridge valve in the diode rectifier station where the fault pole is located is generated.

[0143] In step S10, based on the adjustment current, the adjustment active power, the active power and the reactive power of the new energy station, the drive signal of the bridge valve in the new energy station is generated by using the inner loop current control of the new energy station.

[0144] In step S11, based on the drive signal of the bridge valve in the grid-forming energy storage, the drive signal of the bridge valve in the fault pole of the diode rectifier station and the drive signal of the bridge valve in the new energy station, the new energy station, the grid-forming energy storage and the receiving end controllable commutation converter station are coordinately controlled to realize the DC fault clearing of the multi-terminal DC collection and transmission system.

[0145] It should be noted that the fault causes the voltage of the grid connection point of the new energy station to drop below the threshold value, thereby triggering the new energy to enter the low-voltage fault ride-through control mode, and the DC fault ride-through signal is generated through characteristic quantity identification. On the one hand, the grid-forming energy storage control switching link is triggered to switch the additional power outer loop control to DC current control, and the current reference value is the rated current. The current control implementation of the grid-forming energy storage is as follows:

[0146]

[0147] Among them, V acref is the sending end AC voltage reference value (i.e. the second reference AC voltage), k p is the proportional coefficient, k i is the integral coefficient, i dcref is the DC current reference value (i.e. the reference current), i dc is the DR station DC pole line current measurement value (i.e. the DC pole line current of the fault pole in the diode rectifier station), and s is a complex variable.

[0148] On the other hand, the CLCC station fault pole converter control switching link is triggered, and the current margin value Δ i is adjusted to zero, so that the CLCC is switched from the actual DC voltage control mode to the DC current control, and the current reference value is the rated current. At the same time, the minimum trigger angle limit value α min is adjusted. The constant current control implementation of the CLCC station is as follows:

[0149]

[0150] Among them, α min is the minimum trigger angle of the bridge valve of the CLCC station (i.e. the minimum trigger angle of the fault pole in the receiving end controllable commutation converter station),k p is a proportional coefficient, k i is an integral coefficient, i dcref is a direct current reference value (i.e., a reference current), i dc is a CLCC station fault pole line current measurement value (i.e., a direct pole line current of a fault pole in a diode rectifier station), and s is a complex variable.

[0151] At this time, the system forms two current loops, as shown in Figure 8 , a fault loop 1 flows through a direct pole line on the right side of the fault point and a Y-bridge converter station of the CLCC, and a fault loop 2 flows through a 12-pulse diode rectifier station, a direct pole line on the left side of the fault point and a D-bridge converter station of the CLCC. The two currents can be offset at the fault point, achieving fault current clearing; at the same time, cooperating with the new energy low-voltage fault ride-through control and the power dynamic compensation capability of the grid-forming energy storage, the active power of loop 2 is stably transmitted and delivered through a non-fault pole.

[0152] For example, when a pole-to-ground fault occurs in a direct current transmission line in a multi-terminal direct current collection and transmission system, a system control and protection device can generate a protection signal, as shown in Figure 9 , and as shown in Figure 10 , the protection signal is processed by using delay control to generate a direct current fault ride-through signal FRT_flag2, as shown in Figure 9 , the control mode of the grid-forming energy storage is switched from a power outer loop control mode to a direct current control mode through the direct current fault ride-through signal FRT_flag2, and in the direct current control mode, based on a direct pole line current of a fault pole in a DR station i dc and a reference direct current i dcref , a second reference alternating current voltage V acref is obtained by using PI control. P drum In the power outer loop control mode, a difference between an actual active power P druref output by the DR station and a reference active power V acref is obtained to obtain the second reference alternating current voltage

[0153] As shown in Figure 10 , the control mode of the CLCC is switched to the direct current control mode through the direct current fault ride-through signal FRT_flag2, and based on the direct pole line current of the fault pole in the DR station i dc and the reference direct current idcref , obtaining the minimum trigger angle of the faulty pole in the controllable commutation converter station at the receiving end by using PI control α min , based on the actual pole-to-ground voltage of the faulty pole in the LCCC station U dc and the reference voltage U dcref , generating the maximum trigger angle of the faulty pole in the controllable commutation converter station by using PI control and maximum trigger angle control α max , based on the maximum trigger angle α max and the minimum trigger angle α min , generating the trigger angle of the faulty pole in the controllable commutation converter station α .

[0154] A possible implementation of the step 102 shown in the above Figure 1 may include the following steps 1021-1025:

[0155] In step 1021, after the fault clearing of the multi-terminal DC collection and transmission system, the control mode of the grid-forming energy storage is switched to a power outer loop control mode.

[0156] In step 1022, in the power outer loop control mode, based on the actual active power and the reference active power output by the diode rectifier station, a standby reference AC voltage is generated by using proportional integral control.

[0157] In step 1023, based on the standby reference AC voltage, the reference angle frequency, and the active power and the reactive power of the grid-forming energy storage, a target phase and a direct-axis voltage are generated by using power droop control.

[0158] In step 1024, based on the target phase, the direct-axis voltage and a preset quadrature-axis voltage, the bridge valve in the grid-forming energy storage is controlled by using the inner loop control of the grid-forming energy storage.

[0159] In step 1025, within a first preset time period, if the DC voltage in the multi-terminal DC collection and transmission system after fault clearing is greater than or equal to a second preset voltage threshold, it is determined that the fault of the multi-terminal DC collection and transmission system is eliminated.

[0160] It should be noted that after the deionization of the fault point is completed, the grid-forming energy storage will switch the control to the normal additional power outer loop control mode (i.e., the power outer loop control mode), as shown in Figure 7As shown, by controlling the power instruction of the "active power-alternating current voltage" outer ring to be a low power value, a certain small current is transmitted to the receiving end station. If the CLCC station can successfully establish a direct current voltage and lasts for a period of time, it is determined that the fault has disappeared, a direct current fault ride-through exit signal is generated, otherwise the fault clearing stage is continued. After two system restart failures, it is determined as a permanent fault, and the system is shut down. That is, in the fault disappearance judgment stage, the control includes: switching the network type energy storage control back to the "active power-alternating current voltage" outer ring control mode (i.e. power outer ring control mode), by controlling the power instruction to be a low power value, a certain small current is transmitted to the receiving end station. If the CLCC station can successfully establish a direct current voltage and lasts for a period of time, it is determined that the fault has disappeared, a direct current fault ride-through exit signal is generated, otherwise the fault clearing stage is continued. After two system restart failures, it is determined as a permanent fault, and the system is shut down.

[0161] The above Figure 1 Another possible implementation of step 102 can include the following steps 1021-1029:

[0162] In step 1026, after the fault clearing of the multi-terminal direct current collection and transmission system, the control mode of the converter station where the fault pole is located in the receiving end controllable commutation converter station is switched to the current margin control mode.

[0163] In step 1027, under the current margin control, based on the actual pole line current and the margin current in the receiving end controllable commutation converter station, and the direct current voltage in the multi-terminal direct current collection and transmission system after fault clearing, the current trigger angle of the receiving end controllable commutation converter station is generated by using maximum trigger angle control and proportional integral control.

[0164] In step 1028, based on the current trigger angle of the receiving end controllable commutation converter station, the bridge valve in the receiving end controllable commutation converter station is controlled.

[0165] In step 1029, within a first preset time period, if the direct current voltage in the multi-terminal direct current collection and transmission system after fault clearing is greater than or equal to a second preset voltage threshold, it is determined that the multi-terminal direct current collection and transmission system fault disappears.

[0166] It should be noted that after the deionization of the fault point, the current margin of the receiving end control strategy is increased, and the minimum trigger angle limit α min As shown in Figure 10 The current margin control implementation of the CLCC station is as follows:

[0167]

[0168] Wherein, α p is the trigger angle of the Y-bridge valve of the CLCC station, kp k is a proportional coefficient, i k is an integral coefficient, i dcref I ref is a DC current reference value, i dc I f is a CLCC station fault pole line current measurement value, i I lim is a CLCC station current margin value, s is a complex variable. If the DC voltage can be continuously established and the fault current is cleared to near zero, it is determined that the fault has disappeared, a DC fault ride-through exit signal is generated, otherwise the fault clearing stage is continued, after two system restart failures, it is determined as a permanent fault, the system is shut down. That is, in the fault disappearance judgment stage, the control includes: after completing the fault point deionization, increasing the current margin of the receiving end control strategy, adjusting the minimum trigger angle limit value a min , the trigger angle of the CLCC fault pole can be increased, if the DC voltage can be continuously established and the fault current is cleared to near zero, it is determined that the fault has disappeared, a DC fault ride-through exit signal is generated, otherwise the fault clearing stage is continued, after two system restart failures, it is determined as a permanent fault, the system is shut down.

[0169] The above Figure 1 A possible implementation of step 103 can include the following steps 1031-1033:

[0170] In step 1031, the power of the multi-terminal DC collection and sending system is adjusted by using the power outer loop control mode of the grid-forming energy storage.

[0171] In step 1032, when the new energy station is in a low-voltage fault ride-through mode, if the current grid-connected point voltage of the new energy station is greater than or equal to a first preset voltage threshold and the duration is greater than or equal to a second preset time period, the control mode of the new energy station is exited from the low-voltage fault ride-through mode.

[0172] In step 1033, when the sending end AC voltage is greater than or equal to a third preset voltage threshold, based on the DC voltage in the multi-terminal DC collection and sending system after fault clearing, the active power and the reactive power of the new energy station, the new energy station is controlled to restore normal power transmission by using the inner loop current control of the new energy station, and the recovery control of the multi-terminal DC collection and sending system is realized.

[0173] It should be noted that the voltage reference value of the grid-forming energy storage is gradually increased to restore the sending end grid-connected point AC voltage, and when the wind power AC grid-connected point voltage is restored to a threshold value and lasts for a period of time, a wind turbine low-voltage ride-through exit signal is triggered, and the wind turbine exits the low-voltage control mode and enters the normal power control, such as Figure 6As shown, then the new energy unit slope increases the active power, while adjusting the grid type energy storage additional power outer loop reference value, to realize the active power transmission recovery after system fault. That is, in the system recovery stage, the control includes: confirming that the fault disappears, through the grid type energy storage control switching link to realize the re-establishment of the system alternating voltage, when the wind power alternating current grid connection point voltage recovers to the threshold value and lasts for a period of time, triggering the wind turbine low voltage ride through exit signal, the wind turbine exits the low penetration control mode and enters the normal power control, and then the wind turbine slope increases the active power, that is, through the new energy side control switching link to restore the new energy power regulation ability.

[0174] The above Figure 1 Another possible implementation of step 103 can include steps 1034-1039 as follows:

[0175] In step 1034, the control mode of the grid type energy storage is switched to a power outer loop control mode.

[0176] In step 1035, in the power outer loop control mode, based on the actual active power output by the diode rectifier station and the reference active power, a to-be-used reference alternating voltage is generated by using proportional integral control.

[0177] In step 1036, based on the to-be-used reference alternating voltage, the reference angular frequency, and the active power and the reactive power of the grid type energy storage, a target phase and a direct-axis voltage are generated by using power droop control.

[0178] In step 1037, based on the target phase, the direct-axis voltage, and a preset quadrature-axis voltage, the bridge valve in the grid type energy storage is controlled by using the inner loop control of the grid type energy storage.

[0179] In step 1038, when the new energy station is in a low voltage fault ride through mode, if the current grid connection point voltage of the new energy station is greater than or equal to a first preset voltage threshold value and the duration is greater than or equal to a second preset time period, the control mode of the new energy station is exited from the low voltage fault ride through mode.

[0180] In step 1039, when the sending end alternating voltage is greater than or equal to a third preset voltage threshold value, based on the DC voltage in the multi-terminal DC collection and sending system after fault clearing, the active power and the reactive power of the new energy station, the inner loop current control of the new energy station is used to control the new energy station to restore normal power transmission, and the recovery control of the multi-terminal DC collection and sending system is realized.

[0181] It should be noted that the grid type energy storage receives a DC fault ride through exit signal, and switches the DC current control to an additional power outer loop control, such as Figure 9As shown, the sending end grid-connected point AC voltage is restored to the rated value, when the wind power AC grid-connected point voltage is restored to the threshold value and lasts for a period of time, the low voltage ride-through exit signal of the wind turbine is triggered, the wind turbine exits the low penetration control mode and enters the normal power control, such as Figure 6 As shown, the wind turbine slope increase active power realizes the recovery after system fault. That is, in the system recovery stage, the control includes: new energy side control switching link, grid-forming energy storage control switching link and inverter station control switching link. After confirming the disappearance of the fault, the power regulation ability of the new energy is restored through the new energy side control protection switching link, the system AC voltage is re-established through the grid-forming energy storage control switching link, and the stability control ability of the system DC voltage is restored through the inverter station control switching link.

[0182] For example, in the embodiment of the application, the schematic diagram of the new energy multi-terminal DC collection and sending out system based on diode rectification is as shown in the figure Figure 11 As shown, it includes: AC wind turbine control system, grid-forming energy storage control system and CLCC station control.

[0183] The AC wind turbine control system includes: machine side converter, DC energy consumption device and grid side converter. The machine side converter adopts zero d axis double-loop vector control mode to realize power regulation, d The axis current reference value is zero, and the d axis reactive current is eliminated to reduce the loss, q The axis control active power, and the inner loop control reference value i dref , i qref The grid side converter controls the wind turbine DC side voltage U dc and reactive power Q m , and the inner loop control reference value i dref , i qref is generated by control.

[0184] The trigger signal of the wind turbine DC energy consumption device is the deviation of the wind turbine converter DC voltage amplitude and the threshold value, which is composed of controllable devices and resistors. The surplus power consumption is realized by the input resistance through hysteresis control, which avoids overvoltage on the DC side and overcurrent on the rotor side.

[0185] The grid-forming energy storage adopts double-loop voltage and current control based on the droop characteristics of active power-frequency and reactive power-alternating voltage to establish the alternating voltage and frequency. The additional power outer loop generates voltage deviation to correct the rated voltage of the grid connection point, so as to realize the DR station power regulation under the new energy output fluctuation. The reactive power of the system is borne by the new energy and the grid-forming energy storage, and is adjusted in real time according to the capacity of the two, so as to realize the reactive power balance under the transient and steady state conditions.

[0186] The implementation mode of the active power-frequency droop control (i.e. P-f droop control) is as follows:

[0187]

[0188] Wherein: θ is a phase value, m p is a droop coefficient, and ω is an angular frequency reference value, P ref is an active power reference value, P is a grid-forming energy storage active power measurement value, t is time.

[0189] The implementation mode of the reactive power-alternating voltage droop control (i.e. Q-f droop control) is as follows:

[0190]

[0191] Wherein: v ref is an alternating voltage d axis reference component, m Q is a droop coefficient, Q ref is a reactive power reference value, Q is a grid-forming energy storage reactive power measurement value.

[0192] The implementation mode of the power outer loop control is as follows:

[0193]

[0194] Wherein: V acref is a reference alternating voltage, k p is a proportional coefficient, k i is an integral coefficient, P druref is an active power reference value output by the DR station, P drum is an active power measurement value output by the DR station, and s is a complex variable.

[0195] The inner loop control can be inner loop voltage control and inner loop current control, wherein the inner loop current control is implemented as follows:

[0196]

[0197] wherein, v dref is an alternating voltage d axis component ，v qref is an alternating voltage q axis component, k p is a proportional coefficient, k i is an integral coefficient, i dref and i qref are inner loop current d axis reference values and inner loop current q axis reference values, V acref is a reference alternating voltage, v ref is an alternating voltage d axis reference component, V d is d axis alternating voltage ，V q is q axis alternating voltage, s is a complex variable.

[0198] The inner loop current d axis reference values generated by the inner loop current control on the inner loop voltage control are processed to obtain the control signal of the valve bridge in the grid-forming energy storage. q

[0199] The Y-bridge and D-bridge of the receiving end CLCC converter station both adopt fixed DC voltage control to stabilize the DC bus voltage. The implementation of the current margin control of the CLCC station is as follows:

[0200]

[0201] wherein, α p and α n are the valve firing angles of the Y-bridge and D-bridge of the CLCC station, k p is a proportional coefficient, k i is an integral coefficient, i dcref is a DC current reference value, s is a complex variable, i dcp and i ​dcn are positive and negative electrode current measurement values respectively, Δi is a CLCC station current margin value, generally 0.1 p.u. In steady state, i dc -i dcref +Δi is a positive value, so the trigger angle reaches the upper limit, the upper limit is the DC voltage control loop output value, determined by the following formula:

[0202]

[0203] wherein, α pmax and α nmax are upper limits of Y-bridge and D-bridge valve trigger angles of the CLCC station respectively, k p is a proportional coefficient, k i is an integral coefficient, U dcref is a DC voltage reference value, U dcp and U dcn are absolute values of positive and negative electrode voltages to ground respectively, and s is a complex variable.

[0204] In the embodiment of the application, the example analysis provided by the embodiment of the application is as shown in Figure 12 , 13. A new energy multi-terminal DC collection and transmission system simulation model based on diode rectification is established in PSCAD / EMTDC as shown in Figure 2 . The DC transmission line has a rated voltage of ±200kV and a rated power of 600MW. The inverter side adopts a neutral point grounded 12-pulse CLCC structure, that is, there are two 6-pulse converter valves, and the single valve group has a rated DC voltage of 200kV and a smoothing reactor of 150mH.

[0205] For the pole-to-ground fault on the DC transmission line of the system, two DC fault ride-through strategies are proposed. The specific process of the first control strategy is as shown in Figure 14 . Taking a fault duration of 100ms as an example, the specific steps are as follows:

[0206] Step T1, after the pole-to-ground short-circuit fault of the DC transmission line occurs, the traveling wave signal-based characteristic quantity identification generates a DC ride-through enabling signal FRT_sig2, and the grid-connected point of the sending end wind turbine drops in AC voltage.

[0207] Step T2, the grid-forming energy storage receives the DC ride-through enabling signal FRT_sig2, switches the “active power-AC voltage” outer ring to voltage control, and at the same time, the grid-forming energy storage sends out reactive power, as shown inFigure 7 As shown, the voltage reference value is given as 1.1 p.u., Figure 12 It can be seen that the system can clear the fault point current within 25 ms; when the voltage at the wind turbine grid connection point is lower than the threshold value 0.8 p.u., the low voltage ride through signal FRT_sig1 is triggered, and the wind turbine control is switched to the low voltage ride through control, as shown in the following formula: Figure 5 As shown, the wind turbine consumes energy to dissipate the surplus power quickly.

[0208] Step T3, after waiting for the first de-ionization time of 150 ms, the first restart is performed. The grid-forming energy storage restores the "active power-AC voltage" outer loop and gives a low power reference value of 0.1 p.u. If the DC voltage is restored to the rated value and lasts for a certain time of 50 ms, it is proved that the fault has been cleared, and step T5 is performed; otherwise, it is proved that the fault has not been cleared, and step T4 is performed. In this embodiment, the fault duration is 100 ms, so this restart is successful, and step T5 is performed; if the fault duration is 300 ms, this restart is not successful, and step T4 should be performed.

[0209] Step T4, after the first restart is not successful, the second restart is performed after waiting for the second de-ionization time of 200 ms. The grid-forming energy storage receives the DC fault ride through exit signal, restores the "active power-AC voltage" outer loop, and gives a low power reference value of 0.1 p.u. If the DC voltage is restored to the rated value and lasts for a certain time of 50 ms, it is proved that the fault has been cleared, and step T5 is performed; otherwise, it is proved that the fault is a permanent fault, and the system should be gradually shut down.

[0210] Step T5, after the line restart is successful, the active power reference value of the grid-forming energy storage is increased to the rated value at a speed of 1 p.u. / 100 ms.

[0211] Step T6, when the voltage at the wind turbine grid connection point exceeds the threshold value 0.9 p.u. and lasts for a certain time of 100 ms, the low voltage ride through signal FRT_sig1 exits, the wind turbine exits the low voltage ride through mode, and is increased to the rated value at a speed of 1 p.u. / 100 ms, and the system enters the normal operation state, realizing the system recovery after fault.

[0212] The simulation waveforms are as follows: Figure 12As shown, after a fault occurs in the DC transmission line, considering the approximately 3ms delay for protection output and communication, the grid-connected energy storage will receive the DC fault ride-through enable signal and "actively" reduce the voltage at the new energy AC grid connection point to 1.1pu. The peak fault current is 2.8kA, which can gradually decay to near zero within 25ms, thus clearing the fault current. At this time, there is no active power transmission in the system. After the first deionization time of 150ms at the fault point ends, the grid-connected energy storage will switch control and send low power. The CLCC can establish a DC voltage, thus determining that the fault has disappeared. Finally, the system will be restored to normal operation without impact through control.

[0213] The second method mainly utilizes the DC current regulation capabilities of grid-type energy storage and the receiving-end CLCC station to control the DC current on both sides of the fault point to be equal, thereby clearing the fault current. The specific control process is as follows: Figure 15 As shown. Taking a fault duration of 100ms as an example, the specific steps are as follows:

[0214] Step T1: After a short-circuit fault occurs between pole and ground in the DC transmission line, a DC ride-through enable signal FRT_sig2 is generated based on the characteristic quantity identification of the traveling wave signal, causing the voltage at the AC grid connection point of the sending-end wind turbine to drop.

[0215] Step T2: Upon receiving the DC ride-through enable signal FRT_sig2, the grid-type energy storage switches the outer loop of "active power - AC voltage" to constant DC current control. Simultaneously, the grid-type energy storage generates reactive power, such as... Figure 10 As shown, a current reference value of 1 p.u. is given; the CLCC fault pole converter Y-bridge receives the DC ride-through enable signal FRT_sig2, sets the current margin to zero, and switches the constant DC voltage control to constant DC current control, giving a current reference value of 1 p.u., and adjusting the minimum output firing angle, that is, adjusting the lower limit of the current control output from 110° to 80°. At this time, the firing angle of the CLCC Y-bridge will be adjusted from 141° in steady state to about 88° at a rate of 3000° / s; when the voltage at the wind turbine grid connection point is lower than the threshold of 0.8 pu, the low voltage ride-through signal FRT_sig1 is triggered, and the wind turbine switches to low voltage ride-through control, as shown. Figure 6 As shown, the wind turbine consumes energy in conjunction with the rapid dissipation of surplus power.

[0216] Step T3, after waiting for the first de-ionization time of 150 ms, the first restart is performed. The control of the CLCC adds a current margin of 0.1 p.u., and adjusts the minimum trigger angle, that is, the lower limit of the output of the current control is adjusted from 80° to 110°. During the restart process, the trigger angle of the Y-bridge of the CLCC station is fast adjusted (at a rate of 6000° / s) before being adjusted to 110°, and is slow adjusted (at a rate of 1200° / s) after being adjusted to 110°. If the DC voltage is restored to the rated value and lasts for a certain time of 50 ms, and there is no current at the fault point in the line, it is proved that the fault is cleared, and step T5 is performed. Otherwise, it is proved that the fault has not been cleared, and step T2 is performed. In this embodiment, since the fault duration is 100 ms, the restart is successful this time, and step T5 should be performed. If the fault duration is 300 ms, the restart is not successful this time, and step T4 should be performed.

[0217] Step T4, after the first restart is not successful, the second restart is performed after waiting for the second de-ionization time of 200 ms. The control of the CLCC adds a current margin of 0.1 p.u., and adjusts the minimum trigger angle, that is, the lower limit of the output of the current control is adjusted from 80° to 110°, and the trigger angle is adjusted in a variable rate mode. If the DC voltage is restored to the rated value, and there is no current at the fault point in the line, it is proved that the fault is cleared, and step T5 is performed. Otherwise, it is proved that the fault is a permanent fault, and the system should be gradually shut down.

[0218] Step T5, when the DC voltage reaches 1 p.u., a DC fault ride-through exit enabling signal is sent to the grid-forming energy storage, the DC current control is switched to the "active power-AC voltage" outer ring, and the active power instruction is given as 1 p.u.

[0219] Step T6, when the voltage at the wind turbine grid connection point exceeds the threshold value of 0.9 p.u. and lasts for a certain time of 100 ms, the low-voltage ride-through signal FRT_sig1 exits, the wind turbine exits the low-voltage ride-through mode, and is raised to the rated value at a rate of 1 p.u. / 100 ms. The system enters a normal operating state, and the system fault recovery is realized.

[0220] The simulation waveforms are shown in Figure 13 After the DC transmission line fault, considering the protection exit and communication delay of about 3 ms, the grid-forming energy storage and the CLCC station will receive the DC fault ride-through enabling signal, and are switched to the DC current control mode with a current reference value of the rated value. The fault current can be cleared within 25 ms, and the system still has an active power transmission capacity of 300 MW at this time. When the first de-ionization time of 150 ms ends, since the system still has power transmission, the CLCC can establish the DC voltage, and thus it is determined that the fault is cleared. Finally, the system is recovered to the normal operating state without impact through control.

[0221] Embodiment 2:

[0222] Figure 16 A schematic diagram of a direct current fault ride-through device provided by the present application is suitable for a new energy multi-terminal direct current collection and sending-out system based on diode rectification, such as Figure 16 As shown in the figure, the device comprises: a direct current fault clearing unit, configured to, when a pole-to-ground fault occurs in a direct current sending-out line in a multi-terminal direct current collection and sending-out system, switch a control mode of a grid-connected energy storage in the multi-terminal direct current collection and sending-out system to a fault control mode according to a preset fault control strategy, and perform coordinated control on devices in the multi-terminal direct current collection and sending-out system to realize direct current fault clearing of the multi-terminal direct current collection and sending-out system; the fault control mode comprises an alternating current voltage control mode or a direct current current control strategy, and the preset fault control strategy comprises an active voltage reduction control strategy or a direct current current control strategy; a fault disappearance judging unit, configured to judge whether the multi-terminal direct current collection and sending-out system fault disappears based on a direct current voltage in the multi-terminal direct current collection and sending-out system after fault clearing; and a sending-out system recovery unit, configured to, if the multi-terminal direct current collection and sending-out system fault disappears, perform recovery control on the multi-terminal direct current collection and sending-out system by using the grid-connected energy storage.

[0223] Optionally, the direct current fault clearing unit comprises: a first control mode switching module, configured to switch the control mode of the grid-connected energy storage to an alternating current voltage control mode according to an active voltage reduction control strategy, and reduce a reference alternating current voltage value by using the alternating current voltage control mode to realize active reduction of a system sending end alternating current voltage to avoid fault current feeding into a fault point; a second control mode switching module, configured to switch a control mode of a new energy station to a low-voltage fault ride-through mode when a grid-connected point voltage of the new energy station is less than a first preset voltage threshold; and a first direct current fault clearing module, configured to perform coordinated control on the new energy station and the grid-connected energy storage based on the alternating current voltage control mode and the low-voltage fault ride-through mode to realize direct current fault clearing of the multi-terminal direct current collection and sending-out system.

[0224] Optionally, the first DC fault clearing module is specifically configured to: in the AC voltage control mode, take a preset AC voltage smaller than a voltage threshold as a first reference AC voltage; in the low-voltage fault ride-through mode, calculate an adjustment current based on a reference AC current and an actual grid connection point voltage of the new energy station, and calculate an adjustment active power based on the actual grid connection point voltage and a reference grid connection point voltage of the new energy station and a reference active power of the new energy station; generate a driving signal of a bridge valve in the grid-forming energy storage by using inner loop control of the grid-forming energy storage based on the first reference AC voltage, the active power and the reactive power of the grid-forming energy storage, generate a driving signal of a bridge valve in the new energy station by using inner loop current control of the new energy station based on the adjustment current, the adjustment active power, the active power and the reactive power of the new energy station, and perform coordinated control on the new energy station and the grid-forming energy storage based on the driving signal of the bridge valve in the grid-forming energy storage and the driving signal of the bridge valve in the new energy station, so as to realize DC fault clearing of the multi-terminal DC collection and transmission system.

[0225] Optionally, the DC fault clearing unit comprises: a third control mode switching module configured to switch control modes of the grid-forming energy storage and a fault pole of a converter station in a controllable commutation converter station at a receiving end to a DC current control mode according to a DC current control strategy, and the current reference values are equal; a fourth control mode switching module configured to switch the control mode of the new energy station to a low-voltage fault ride-through mode when a grid connection point voltage of the new energy station is smaller than a first preset voltage threshold; and a second DC fault clearing module configured to perform coordinated control on the new energy station, the grid-forming energy storage and the controllable commutation converter station at the receiving end based on the DC current control mode and the low-voltage fault ride-through mode, so as to realize DC fault clearing of the multi-terminal DC collection and transmission system.

[0226] Optionally, the second DC fault clearing module is specifically configured to: in the DC current control mode, based on the DC pole line current of the fault pole in the diode rectifier station and a reference current, generate a second reference AC voltage and a minimum trigger angle of the commutation station where the fault pole in the receiving end controllable commutation converter station is located, respectively; in the low-voltage fault ride-through mode, based on a reference AC current and an actual grid point voltage of the new energy station, calculate an adjustment current, and based on the actual grid point voltage of the new energy station and a reference grid point voltage, a reference active power of the new energy station, calculate an adjustment active power; based on the second reference AC voltage, an actual active power and an actual reactive power of the grid-forming energy storage, using inner loop control of the grid-forming energy storage, generate a driving signal of a bridge valve in the grid-forming energy storage; based on the minimum trigger angle and a DC voltage in the multi-terminal DC collection and transmission system, generate a driving signal of the bridge valve where the fault pole in the diode rectifier station is located; based on the adjustment current, the adjustment active power, an active power and a reactive power of the new energy station, using inner loop current control of the new energy station, generate a driving signal of a bridge valve in the new energy station; based on the driving signal of the bridge valve in the grid-forming energy storage, the driving signal of the bridge valve where the fault pole in the diode rectifier station is located, and the driving signal of the bridge valve in the new energy station, coordinate control of the new energy station, the grid-forming energy storage and the receiving end controllable commutation converter station, to realize DC fault clearing of the multi-terminal DC collection and transmission system.

[0227] Optionally, the fault disappearance determination unit is specifically configured to: after the fault clearing of the multi-terminal DC collection and transmission system, switch the control mode of the grid-forming energy storage to a power outer loop control mode; in the power outer loop control mode, based on an actual active power and a reference active power output by the diode rectifier station, generate a standby reference AC voltage using proportional integral control; based on the standby reference AC voltage, a reference angular frequency, and an active power and a reactive power of the grid-forming energy storage, generate a target phase and a direct-axis voltage using power droop control; based on the target phase, the direct-axis voltage and a preset quadrature-axis voltage, control the bridge valve in the grid-forming energy storage using inner loop control of the grid-forming energy storage; and within a first preset time period, if the DC voltage in the multi-terminal DC collection and transmission system after fault clearing is continuously greater than or equal to a second preset voltage threshold, determine that the multi-terminal DC collection and transmission system is fault-free.

[0228] Optionally, the sending system recovery unit is specifically configured to: utilize a power outer loop control mode of the network-constructed energy storage to perform power adjustment on the multi-terminal DC collection sending system; when the new energy station is in a low-voltage fault ride-through mode, if a current grid connection point voltage of the new energy station is greater than or equal to a first preset voltage threshold and a duration is greater than or equal to a second preset time period, the control mode of the new energy station is exited from the low-voltage fault ride-through mode; when an AC voltage at a sending end is greater than or equal to a third preset voltage threshold, based on a DC voltage in the multi-terminal DC collection sending system after fault clearing, active power and reactive power of the new energy station, the new energy station is controlled to restore normal power transmission by utilizing inner loop current control of the new energy station, so as to realize recovery control of the multi-terminal DC collection sending system.

[0229] Optionally, the fault disappearance determination unit is specifically configured to: after the multi-terminal DC collection sending system is cleared of fault, a control mode of a commutation station in a fault pole in the receiving terminal controllable commutation converter station is switched to a current margin control mode; under the current margin control, based on an actual pole line current and a margin current in the receiving terminal controllable commutation converter station and a DC voltage in the multi-terminal DC collection sending system after fault clearing, a current trigger angle of the receiving terminal controllable commutation converter station is generated by utilizing maximum trigger angle control and proportional integral control; based on the current trigger angle of the receiving terminal controllable commutation converter station, a bridge valve in the receiving terminal controllable commutation converter station is controlled; and within a first preset time period, if the DC voltage in the multi-terminal DC collection sending system after fault clearing is continuously greater than or equal to a second preset voltage threshold, it is determined that the multi-terminal DC collection sending system is cleared of fault.

[0230] Optionally, the output system recovery unit is specifically used for: switching the control mode of the grid-type energy storage to a power outer loop control mode; in the power outer loop control mode, generating a standby reference AC voltage based on the actual active power and reference active power output by the diode rectifier station using proportional-integral control; generating a target phase and direct-axis voltage based on the standby reference AC voltage, the reference angular frequency, and the active and reactive power of the grid-type energy storage using power droop control; and controlling the bridge valves in the grid-type energy storage using the inner loop control of the grid-type energy storage based on the target phase, the direct-axis voltage, and the preset quadrature-axis voltage. Control; when the new energy power station is in low-voltage fault ride-through mode, if the current grid connection point voltage of the new energy power station is greater than or equal to a first preset voltage threshold and the duration is greater than or equal to a second preset time period, the control mode of the new energy power station will be exited from the low-voltage fault ride-through mode; when the AC voltage at the sending end is greater than or equal to a third preset voltage threshold, based on the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared, the active power and reactive power of the new energy power station, using the inner loop current control of the new energy power station, control the new energy power station to restore normal power transmission, thereby realizing the recovery control of the multi-terminal DC collection and transmission system.

[0231] Example 3:

[0232] Based on the same inventive concept, the present invention also provides a computer device, such as... Figure 17 As shown, the computer device includes a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, and is suitable for implementing one or more instructions. Specifically, it is suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of a DC fault ride-through method in the above embodiment.

[0233] Example 4:

[0234] Based on the same inventive concept, the present application also provides a storage medium, specifically a computer readable storage medium (Memory), which is a memory device in a computer device, used for storing programs and data. It can be understood that the computer readable storage medium here can include the built-in storage medium in the computer device, and of course can also include the extended storage medium supported by the computer device. The computer readable storage medium provides a storage space which stores the operating system of the terminal. Moreover, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer readable storage medium here can be a high-speed RAM memory, or a non-volatile memory such as at least one disk memory. One or more instructions stored in the computer readable storage medium can be loaded and executed by the processor to realize the steps of the direct current fault ride-through method in the above embodiment.

[0235] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage, etc.) containing computer-usable program code.

[0236] The present application is described with reference to flowcharts and / or block diagrams of the method, device (system), and computer program product according to the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to produce a machine, so that the instructions executed by the computer or other programmable data processing devices produce a device implemented in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 an apparatus that performs the functions specified in the flow(s) or block(s).

[0237] These computer program instructions can also be stored in a computer readable memory capable of directing the computer or other programmable data processing devices to work in a specific manner, so that the instructions stored in the computer readable memory produce a manufactured product including instruction apparatus, which realizes the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1the function specified in the one or more blocks.

[0238] These computer program instructions can also be loaded into computer or other programmable data processing devices, so that a series of operation steps are performed on the computer or other programmable data processing devices to generate computer-implemented processes, so that the instructions executed on the computer or other programmable data processing devices provide processes for implementing the flows Figure 1 one or more flows and / or blocks Figure 1 the function specified in the one or more blocks.

[0239] The above merely illustrates the embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of the claims of the present application.

Claims

1. A direct current fault ride through method, characterized by, The method is suitable for a new energy multi-terminal direct current (DC) collection and sending-out system based on diode rectification, and the method comprises the following steps: When a pole-to-ground fault occurs in a DC sending-out line in a multi-terminal DC collection and sending-out system, a control mode of grid-connected energy storage in the multi-terminal DC collection and sending-out system is switched to a fault control mode according to a preset fault control strategy, devices in the multi-terminal DC collection and sending-out system are coordinately controlled, and DC fault clearing of the multi-terminal DC collection and sending-out system is realized; The fault control mode comprises an AC voltage control mode or a DC current control mode, and the preset fault control strategy comprises an active voltage reduction control strategy or a DC current control strategy; Whether the fault of the multi-terminal DC collection and sending-out system disappears is determined based on a DC voltage in the multi-terminal DC collection and sending-out system after the fault is cleared; If the fault of the multi-terminal DC collection and sending-out system disappears, the multi-terminal DC collection and sending-out system is controlled to recover by using the grid-connected energy storage; The step of switching the control mode of the grid-connected energy storage to the fault control mode according to the preset fault control strategy and coordinately controlling the devices in the multi-terminal DC collection and sending-out system to realize the DC fault clearing of the multi-terminal DC collection and sending-out system comprises the following steps: According to the active voltage reduction control strategy, the control mode of the grid-connected energy storage is switched to the AC voltage control mode, the AC voltage control mode is used to reduce a reference AC voltage value, and the system sending-end AC voltage is actively reduced to avoid fault current from being fed into a fault point; When a grid-connected point voltage of a new energy station in the multi-terminal DC collection and sending-out system is less than a first preset voltage threshold, a control mode of the new energy station is switched to a low-voltage fault ride-through mode; The new energy station and the grid-connected energy storage are coordinately controlled based on the AC voltage control mode and the low-voltage fault ride-through mode, and the DC fault clearing of the multi-terminal DC collection and sending-out system is realized; The step of switching the control mode of the grid-connected energy storage to the fault control mode according to the preset fault control strategy and coordinately controlling the devices in the multi-terminal DC collection and sending-out system to realize the DC fault clearing of the multi-terminal DC collection and sending-out system comprises the following steps: According to a DC current control strategy, control modes of the grid-connected energy storage and a fault pole of a controllable commutation converter station in a receiving terminal of the multi-terminal DC collection and sending-out system are switched to a DC current control mode, and current reference values are equal; When a grid-connected point voltage of a new energy station in the multi-terminal DC collection and sending-out system is less than a first preset voltage threshold, a control mode of the new energy station is switched to a low-voltage fault ride-through mode; The new energy station, the grid-connected energy storage and the controllable commutation converter station in the receiving terminal are coordinately controlled based on the DC current control mode and the low-voltage fault ride-through mode, and the DC fault clearing of the multi-terminal DC collection and sending-out system is realized. The control mode based on the direct current and the low-voltage fault ride-through mode is used to coordinate control of the new energy station, the grid-forming energy storage, and the controllable commutation converter station at the receiving end, so as to realize direct-current fault clearing of the multi-terminal direct-current collection and transmission system, including: In the direct current control mode, a second reference alternating current voltage and a minimum trigger angle of a commutation station of a fault pole in the diode rectifier station are generated based on a direct current of the fault pole and a reference current in the diode rectifier station. In the low-voltage fault ride-through mode, an adjustment current is calculated based on a reference alternating current and an actual grid connection point voltage of the new energy station, and an adjustment active power is calculated based on the actual grid connection point voltage and a reference grid connection point voltage of the new energy station and a reference active power of the new energy station. Based on the second reference alternating current voltage, actual active power and actual reactive power of the grid-forming energy storage, a driving signal of a bridge valve in the grid-forming energy storage is generated by using outer loop control and inner loop voltage and current control of the grid-forming energy storage. Based on the minimum trigger angle and a direct current voltage in the multi-terminal direct-current collection and transmission system, a driving signal of a bridge valve of a fault pole in the diode rectifier station is generated. Based on the adjustment current, the adjustment active power, active power and reactive power of the new energy station, a driving signal of a bridge valve in the new energy station is generated by using inner loop current control of the new energy station. Based on the driving signal of the bridge valve in the grid-forming energy storage, the driving signal of the bridge valve of the fault pole in the diode rectifier station, and the driving signal of the bridge valve in the new energy station, the new energy station, the grid-forming energy storage, and the controllable commutation converter station at the receiving end are coordinated and controlled, so as to realize direct-current fault clearing of the multi-terminal direct-current collection and transmission system.

2. The method of claim 1, wherein, The control mode based on the direct current and the low-voltage fault ride-through mode is used to coordinate control of the new energy station and the grid-forming energy storage, so as to realize direct-current fault clearing of the multi-terminal direct-current collection and transmission system, including: In the alternating current voltage control mode, a preset alternating current voltage less than a voltage threshold is used as a first reference alternating current voltage. In the low-voltage fault ride-through mode, an adjustment current is calculated based on a reference alternating current and an actual grid connection point voltage of the new energy station, and an adjustment active power is calculated based on the actual grid connection point voltage and a reference grid connection point voltage of the new energy station and a reference active power of the new energy station. Based on the first reference alternating current voltage, active power and reactive power of the grid-forming energy storage, a driving signal of a bridge valve in the grid-forming energy storage is generated by using inner loop control of the grid-forming energy storage. Based on the adjustment current, the adjustment active power, active power and reactive power of the new energy station, a driving signal of a bridge valve in the new energy station is generated by using inner loop current control of the new energy station. Coordinating control of the new energy station and the grid-forming energy storage based on the drive signal of the bridge valve in the grid-forming energy storage and the drive signal of the bridge valve in the new energy station, to realize the DC fault clearing of the multi-terminal DC collection and transmission system.

3. The method of claim 1, wherein, The method further includes: After the fault of the multi-terminal DC collection and transmission system is cleared, the control mode of the grid-forming energy storage is switched to a power outer loop control mode; In the power outer loop control mode, a standby reference AC voltage is generated by using proportional integral control based on the actual active power and the reference active power of the diode rectifier station; Based on the standby reference AC voltage, a reference angular frequency, and the active power and the reactive power of the grid-forming energy storage, power droop control is used to realize proportional distribution of internal power of the multi-unit energy storage, to generate a target phase and a direct-axis voltage; Based on the target phase, the direct-axis voltage, and a preset quadrature-axis voltage, the bridge valve in the grid-forming energy storage is controlled by using outer loop control and inner loop voltage and current control of the grid-forming energy storage; In a first preset time period, if the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared is greater than or equal to a second preset voltage threshold, it is determined that the fault of the multi-terminal DC collection and transmission system is cleared.

4. The method of claim 1, wherein, The method further includes: The power of the multi-terminal DC collection and transmission system is adjusted by using the power outer loop control mode of the grid-forming energy storage; When the new energy station is in a low-voltage fault ride-through mode, if the current grid-connected point voltage of the new energy station is greater than or equal to a first preset voltage threshold and the duration is greater than or equal to a second preset time period, the control mode of the new energy station is exited from the low-voltage fault ride-through mode; When the sending end AC voltage is greater than or equal to a third preset voltage threshold, the new energy station is controlled to restore normal power transmission by using inner loop current control of the new energy station based on the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared, the active power and the reactive power of the new energy station, to realize the recovery control of the multi-terminal DC collection and transmission system.

5. The method of claim 1, wherein, The method further includes: After the fault of the multi-terminal DC collection and transmission system is cleared, the control mode of the faulty converter station of the receiving end controllable commutation converter station is switched to a current margin control mode; In the current margin control mode, the current trigger angle of the receiving end controllable commutation converter station is generated by using maximum trigger angle control and proportional integral control based on the actual pole line current and the margin current of the receiving end controllable commutation converter station, and the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared; The bridge valve in the receiving end controllable commutation converter station is controlled based on the current trigger angle of the receiving end controllable commutation converter station. In a first preset time period, if the DC voltage in the multi-terminal DC collection and sending system after fault removal is greater than or equal to a second preset voltage threshold, it is determined that the fault of the multi-terminal DC collection and sending system disappears.

6. The method of claim 1, wherein, The recovery control of the multi-terminal DC collection and sending system by the grid-forming energy storage comprises: switching the control mode of the grid-forming energy storage to a power outer loop control mode; in the power outer loop control mode, generating a standby reference AC voltage by proportional integral control based on the actual active power and the reference active power output by the diode rectifier station; based on the standby reference AC voltage, the reference angular frequency, and the active power and the reactive power of the grid-forming energy storage, realizing proportional distribution of internal power of the multi-machine energy storage by power droop control to generate a target phase and a direct-axis voltage; based on the target phase, the direct-axis voltage, and a preset quadrature-axis voltage, controlling the bridge valve in the grid-forming energy storage by the inner loop control of the grid-forming energy storage; when the new energy station is in a low-voltage fault ride-through mode, if the current grid-connected point voltage of the new energy station is greater than or equal to a first preset voltage threshold and the duration is greater than or equal to a second preset time period, the control mode of the new energy station is exited from the low-voltage fault ride-through mode; when the sending-end AC voltage is greater than or equal to a third preset voltage threshold, based on the DC voltage in the multi-terminal DC collection and sending system after fault removal, the active power and the reactive power of the new energy station, the inner loop current control of the new energy station is used to control the new energy station to restore normal power transmission, and the recovery control of the multi-terminal DC collection and sending system is realized.

7. A DC fault ride-through device, characterized by The device is suitable for a diode-rectified new energy multi-terminal DC collection and sending system, and the device comprises: a DC fault removal unit configured to, when a pole-to-ground fault occurs in a DC sending line in a multi-terminal DC collection and sending system, switch the control mode of a grid-forming energy storage in the multi-terminal DC collection and sending system to a fault control mode according to a preset fault control strategy, coordinate control devices in the multi-terminal DC collection and sending system, and realize DC fault removal of the multi-terminal DC collection and sending system; the fault control mode comprises an AC voltage control mode or a DC current control strategy, and the preset fault control strategy comprises an active voltage reduction control strategy or a DC current control strategy; a fault disappearance determination unit configured to determine whether the fault of the multi-terminal DC collection and sending system disappears based on the DC voltage in the multi-terminal DC collection and sending system after fault removal; a sending system recovery unit configured to, if the fault of the multi-terminal DC collection and sending system disappears, use the grid-forming energy storage to perform recovery control on the multi-terminal DC collection and sending system; the DC fault removal unit comprises: a first control mode switching module configured to switch the control mode of the grid-forming energy storage to an AC voltage control mode according to an active voltage reduction control strategy, reduce the reference AC voltage value by using the AC voltage control mode, and realize active reduction of the sending-end AC voltage to avoid fault current feeding into a fault point. The second control mode switching module is configured to switch the control mode of the new energy station to a low-voltage fault ride-through mode when the grid-connected point voltage of the new energy station is less than a first preset voltage threshold. The first DC fault clearing module is configured to perform coordinated control on the new energy station and the grid-connected energy storage based on the AC voltage control mode and the low-voltage fault ride-through mode, so as to realize DC fault clearing of the multi-terminal DC collection and transmission system. The DC fault clearing unit comprises: The third control mode switching module is configured to switch the control modes of the grid-connected energy storage and the faulty converter station of the receiving end controllable commutation converter station to a DC current control mode according to a DC current control strategy, and the current reference values are equal. The fourth control mode switching module is configured to switch the control mode of the new energy station to a low-voltage fault ride-through mode when the grid-connected point voltage of the new energy station is less than a first preset voltage threshold. The second DC fault clearing module is configured to perform coordinated control on the new energy station, the grid-connected energy storage and the receiving end controllable commutation converter station based on the DC current control mode and the low-voltage fault ride-through mode, so as to realize DC fault clearing of the multi-terminal DC collection and transmission system. The second DC fault clearing module is specifically configured to: In the DC current control mode, a second reference AC voltage and a minimum trigger angle of the faulty converter station of the receiving end controllable commutation converter station are respectively generated based on the DC pole line current and the reference current of the faulty pole of the diode rectifier station. In the low-voltage fault ride-through mode, an adjustment current is calculated based on the reference AC current and the actual grid-connected point voltage of the new energy station, and an adjustment active power is calculated based on the actual grid-connected point voltage and the reference grid-connected point voltage of the new energy station, and the reference active power of the new energy station. Based on the second reference AC voltage, the actual active power and the actual reactive power of the grid-connected energy storage, the drive signals of the bridge valves of the grid-connected energy storage are generated by using the outer loop control and the inner loop voltage and current control of the grid-connected energy storage; and based on the minimum trigger angle and the DC voltage in the multi-terminal DC collection and transmission system, the drive signals of the bridge valves of the faulty pole of the diode rectifier station are generated. Based on the adjustment current, the adjustment active power, the active power and the reactive power of the new energy station, the drive signals of the bridge valves of the new energy station are generated by using the inner loop current control of the new energy station. The new energy station, the grid-connected energy storage and the receiving end controllable commutation converter station are coordinated and controlled based on the drive signals of the bridge valves of the grid-connected energy storage, the drive signals of the bridge valves of the faulty pole of the diode rectifier station and the drive signals of the bridge valves of the new energy station, so as to realize DC fault clearing of the multi-terminal DC collection and transmission system.

8. A computer device, comprising: Comprise: One or more processors: The processor is configured to store one or more programs; When the one or more programs are executed by the one or more processors, a DC fault ride-through method as claimed in any one of claims 1 to 6 is realized.

9. A computer-readable storage medium, characterized in that, A computer program product comprising a computer program which, when executed, implements a direct current fault ride through method according to any one of claims 1 to 6.

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