Direct-current fault ride-through method, direct-current fault ride-through device, equipment and medium

Abstract

The invention relates to a direct current fault ride-through method, a direct current fault ride-through device, direct current fault ride-through equipment and a medium. The method comprises the following steps: switching a control mode of network-forming type energy storage into an alternating-current voltage control mode or a direct-current control strategy, carrying out coordinated control on devices in a multi-terminal direct-current collecting and sending-out system, clearing fault current, and clearing the fault current by utilizing an active step-down control strategy or the direct-current control strategy at the same time. According to the method, measures such as additional direct current circuit breakers are not needed, control is flexible and easy to achieve, the multi-terminal direct current collecting and sending-out system after fault clearing is controlled to be recovered by judging the operation state of the multi-terminal direct current collecting and sending-out system, and safe and stable operation of the multi-terminal direct current collecting and sending-out system is facilitated.

Description

Technical Field

[0001] This invention relates to the field of DC collection and transmission technology, specifically to a DC fault ride-through method, DC fault ride-through device, equipment, and medium. Background Technology

[0002] Currently, vigorously developing new energy sources will become one of the important directions for the future development of the power grid. Some regions have a potential for new energy development resources of nearly 2 billion kilowatts, with an average annual growth rate of over 50% in some areas, showing huge development prospects. At the same time, the installed capacity of densely populated new energy areas in these regions far exceeds the load, the grid structure in these areas is weak and far from load centers, and the demand for external power transmission is urgent.

[0003] Current large-scale renewable energy aggregation and transmission solutions for isolated areas generally employ AC transmission or flexible DC transmission for grid connection. Traditional high-voltage AC transmission uses AC aggregators and progressively stepped voltage boosters for transmission. This technology is mature and suitable for renewable energy consumption scenarios with short transmission distances and small transmission capacities. However, with the large-scale integration of renewable energy, the transmission distance of this solution is limited by the synchronous and stable operation limits of the AC system, potentially leading to reduced system strength and stability. Furthermore, it requires the expansion of transmission and transformation facilities, occupying corridor resources around cities, thus making it difficult to support the demand for long-distance, large-scale renewable energy grid connection. Flexible DC transmission, on the other hand, involves renewable energy aggregating via AC and transmitting via flexible DC rectification, independent of the AC grid and capable of islanded operation. This solution boasts high technological maturity, flexible control, and the ability to construct grids, providing frequency and voltage support to the grid. However, this solution requires the construction of converter stations based on fully controlled devices, resulting in higher investment costs.

[0004] To address the shortcomings of existing solutions, some literature proposes rectifying the AC power generated by new energy sources using diode rectifiers (DRs) before sending it out. However, since DRs use uncontrollable power electronic components, they cannot establish the AC voltage for the offshore AC system. Therefore, grid-connected wind turbines or other auxiliary grid-connected equipment are needed to provide voltage and frequency support for the AC system. Furthermore, when the DC transmission lines in the system are overhead lines, the probability of temporary faults is relatively high, and the DC fault current is large and develops rapidly. In severe cases, this can lead to system shutdown, power outages, and affect the stability and reliability of the power system.

[0005] To address DC faults in DC transmission systems, existing technologies involve configuring DC circuit breakers at the receiving end to work in conjunction with AC circuit breakers at the sending end to enable DC short-circuit fault ride-through and clearing of DC short-circuit faults. However, using DC circuit breakers configured at the receiving end for DC fault ride-through increases the system's cost. Summary of the Invention

[0006] To address the problem that existing technologies use DC circuit breakers configured at the receiving end to facilitate fault ride-through in a system, thereby increasing system costs, this invention proposes a DC fault ride-through method, a DC fault ride-through device, equipment, and medium.

[0007] A first aspect of the present invention provides a DC fault ride-through method applicable to a multi-terminal DC collection and transmission system for new energy sources based on diode rectification, the method comprising: When a pole-to-ground fault occurs in the DC transmission line of a multi-terminal DC collection and transmission system, the control mode of the grid-type energy storage in the multi-terminal DC collection and transmission system is switched to the fault control mode according to the preset fault control strategy. The devices in the multi-terminal DC collection and transmission system are coordinated and controlled to clear the DC fault in the multi-terminal DC collection and transmission system. 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. Based on the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared, it is determined whether the fault in the multi-terminal DC collection and transmission system has disappeared. If the fault in the multi-terminal DC collection and transmission system disappears, the grid-type energy storage is used to restore control of the multi-terminal DC collection and transmission system.

[0008] Optionally, the step of switching the control mode of the grid-type energy storage in the multi-terminal DC collection and transmission system to a fault control mode according to a preset fault control strategy, and coordinating the control of the devices in the multi-terminal DC collection and transmission system to achieve DC fault clearing of the multi-terminal DC collection and transmission system includes: According to the active voltage reduction control strategy, the control mode of the grid-type energy storage is switched to the AC voltage control mode. Using the AC voltage control mode, the reference AC voltage value is reduced to actively reduce the AC voltage at the system's sending end and prevent fault current from feeding into the fault point. When the grid connection point voltage of the new energy power station is less than the first preset voltage threshold, the control mode of the new energy power station is switched to low-voltage fault ride-through mode. Based on the AC voltage control mode and the low-voltage fault ride-through mode, the new energy power station and the grid-type energy storage are coordinated and controlled to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

[0009] Optionally, the coordinated control of the new energy power station and the grid-type energy storage based on the AC voltage control mode and the low-voltage fault ride-through mode to achieve DC fault clearing of the multi-terminal DC collection and transmission system includes: In the AC voltage control mode, a preset AC voltage that is less than the voltage threshold is used as the first reference AC voltage. In the low-voltage fault ride-through mode, the adjustment current is calculated based on the reference AC current and the actual grid connection point voltage of the new energy power station, and the adjustment active power is calculated based on the actual grid connection point voltage and reference grid connection point voltage of the new energy power station and the reference active power of the new energy power station. Based on the first reference AC voltage, the active power and reactive power of the grid-type energy storage, the drive signal of the bridge valve in the grid-type energy storage is generated by utilizing the outer loop control and inner loop voltage and current control of the grid-type energy storage. Based on the adjusted current, the adjusted active power, the active power and reactive power of the new energy power station, the driving signal of the bridge valve in the new energy power station is generated by using the inner loop current control of the new energy power station. Based on the drive signals of the bridge valve in the grid-type energy storage and the bridge valve in the new energy power station, the new energy power station and the grid-type energy storage are coordinated and controlled to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

[0010] Optionally, the step of switching the control mode of the grid-type energy storage in the multi-terminal DC collection and transmission system to a fault control mode according to a preset fault control strategy, and coordinating the control of the devices in the multi-terminal DC collection and transmission system to achieve DC fault clearing of the multi-terminal DC collection and transmission system includes: According to the DC current control strategy, the control mode of the converter station where the fault pole is located in the grid-type energy storage and the receiving-end controllable phase-switching converter station is switched to DC current control mode respectively, and the current reference values ​​are equal. When the grid connection point voltage of the new energy power station is less than the first preset voltage threshold, the control mode of the new energy power station is switched to low-voltage fault ride-through mode. Based on the DC current control mode and the low-voltage fault ride-through mode, the new energy power station, the grid-type energy storage and the receiving-end controllable phase-commutation converter station are coordinated and controlled to realize the DC fault clearing of the multi-terminal DC collection and transmission system.

[0011] Optionally, the coordinated control of the new energy power station, the grid-type energy storage, and the receiving-end controllable commutator station based on the DC current control mode and the low-voltage fault ride-through mode to achieve DC fault clearing of the multi-terminal DC collection and transmission system includes: In the DC current control mode, based on the DC pole current and reference current of the fault electrode in the diode rectifier station, a second reference AC voltage and the minimum firing angle of the converter station where the fault electrode is located in the receiving-end controllable commutation converter station are generated respectively. In the low-voltage fault ride-through mode, the adjustment current is calculated based on the reference AC current and the actual grid connection point voltage of the new energy power station, and the adjustment active power is calculated based on the actual grid connection point voltage and reference grid connection point voltage of the new energy power station and the reference active power of the new energy power station. Based on the second reference AC voltage, the actual active power and actual reactive power of the grid-type energy storage, the drive signal of the bridge valve in the grid-type energy storage is generated by utilizing the outer loop control and inner loop voltage and current control of the grid-type energy storage. Based on the minimum firing angle and the DC voltage in the multi-terminal DC collection and output system, a drive signal is generated for the bridge valve where the faulty electrode is located in the diode rectifier station. Based on the adjusted current, the adjusted active power, the active power and reactive power of the new energy power station, the driving signal of the bridge valve in the new energy power station is generated by using the inner loop current control of the new energy power station. Based on the driving signals of the bridge valves in the grid-type energy storage, the driving signals of the bridge valves where the faulty poles are located in the diode rectifier station, and the driving signals of the bridge valves in the new energy power station, the new energy power station, the grid-type 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.

[0012] Optionally, determining whether the fault in the multi-terminal DC collection and transmission system has disappeared based on the DC voltage in the multi-terminal DC collection and transmission system after fault clearance includes: After the fault in the multi-terminal DC collection and transmission system is cleared, the control mode of the grid-type energy storage is switched to the power outer loop control mode. In the power outer loop control mode, based on the actual active power and reference active power output by the diode rectifier station, a standby reference AC voltage is generated using proportional-integral control. Based on the standby reference AC voltage, the reference angular frequency, and the active and reactive power of the grid-type energy storage, power droop control is used to achieve proportional distribution of internal power in the energy storage of multiple units, generating target phase and direct-axis voltage. Based on the target phase, the direct-axis voltage, and the preset quadrature-axis voltage, the bridge valve in the grid-type energy storage is controlled using the inner loop control of the grid-type energy storage. If, within a first preset time period, the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared continues to be greater than or equal to a second preset voltage threshold, it is determined that the fault in the multi-terminal DC collection and transmission system has disappeared.

[0013] Optionally, the step of using the grid-type energy storage to perform recovery control on the multi-terminal DC collection and transmission system includes: The power outer loop control mode of the grid-type energy storage is used to regulate the power of the multi-terminal DC collection and transmission system; 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 the first preset voltage threshold and the duration is greater than or equal to the 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 the 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 are controlled by the inner loop current control of the new energy power station to restore normal power transmission, thereby realizing the recovery control of the multi-terminal DC collection and transmission system.

[0014] Optionally, determining whether the fault in the multi-terminal DC collection and transmission system has disappeared based on the DC voltage in the multi-terminal DC collection and transmission system after fault clearance includes: After the fault in the multi-terminal DC collection and transmission system is cleared, the control mode of the converter station where the faulty pole is located in the receiving-end controllable phase-switching converter station is switched to the current margin control mode. Under the current margin control, based on the actual pole current and margin current in the receiving-end controllable phase-commutation converter station and the DC voltage in the multi-terminal DC collection and output system after fault clearance, the current firing angle of the receiving-end controllable phase-commutation converter station is generated using maximum firing angle control and proportional-integral control. Based on the current trigger angle of the receiving-end controllable phase-commutation converter station, the bridge valve in the receiving-end controllable phase-commutation converter station is controlled. If, within a first preset time period, the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared continues to be greater than or equal to a second preset voltage threshold, it is determined that the fault in the multi-terminal DC collection and transmission system has disappeared.

[0015] Optionally, the step of using the grid-type energy storage to perform recovery control on the multi-terminal DC collection and transmission system includes: Switch the control mode of the grid-type energy storage to the power outer loop control mode; In the power outer loop control mode, based on the actual active power and reference active power output by the diode rectifier station, a standby reference AC voltage is generated using proportional-integral control. Based on the standby reference AC voltage, the reference angular frequency, and the active and reactive power of the grid-type energy storage, power droop control is used to achieve proportional distribution of internal power in the energy storage of multiple units, generating target phase and direct-axis voltage. Based on the target phase, the direct-axis voltage, and the preset quadrature-axis voltage, the bridge valve in the grid-type energy storage is controlled using the inner loop control of the grid-type energy storage. 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 the first preset voltage threshold and the duration is greater than or equal to the 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 the 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 are controlled by the inner loop current control of the new energy power station to restore normal power transmission, thereby realizing the recovery control of the multi-terminal DC collection and transmission system.

[0016] A second aspect of the present invention provides a DC fault ride-through device applicable to a multi-terminal DC collection and transmission system for new energy sources based on diode rectification. The device includes: a DC fault clearing unit, configured to, when a pole-to-ground fault occurs in the DC transmission line of the multi-terminal DC collection and transmission system, switch the control mode of the grid-type energy storage in the multi-terminal DC collection and transmission system to a fault control mode according to a preset fault control strategy, and coordinate the control of the devices in the multi-terminal DC collection and transmission system to achieve DC fault clearing of the multi-terminal DC collection and transmission system; 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; a fault disappearance determination unit, configured to, based on the DC voltage in the multi-terminal DC collection and transmission system after fault clearing, determine whether the fault in the multi-terminal DC collection and transmission system has disappeared; and a transmission system recovery unit, configured to, if the fault in the multi-terminal DC collection and transmission system has disappeared, utilize the grid-type energy storage to perform recovery control on the multi-terminal DC collection and transmission system.

[0017] Optionally, the DC fault clearing unit includes: a first control mode switching module, used to switch the control mode of the grid-type energy storage to an AC voltage control mode according to an active voltage reduction control strategy, thereby reducing the reference AC voltage value and actively reducing the AC voltage at the system's sending end to prevent fault current from feeding into the fault point; a second control mode switching module, used to switch the control mode of the new energy power station to a low-voltage fault ride-through mode when the grid connection point voltage of the new energy power station is less than a first preset voltage threshold; and a first DC fault clearing module, used to coordinate the control of the new energy power station and the grid-type energy storage based on the AC voltage control mode and the low-voltage fault ride-through mode to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

[0018] Optionally, the first DC fault clearing module is specifically used for: in the AC voltage control mode, using a preset AC voltage less than a voltage threshold as a first reference AC voltage; in the low-voltage fault ride-through mode, calculating an adjustment current based on a reference AC current and the actual grid connection point voltage of the new energy power station, and calculating an adjustment active power based on the actual grid connection point voltage and reference grid connection point voltage of the new energy power station, and the reference active power of the new energy power station; generating a drive signal for the bridge valve in the grid-type energy storage system using the inner loop control of the grid-type energy storage system based on the first reference AC voltage, the active power and reactive power of the grid-type energy storage system; generating a drive signal for the bridge valve in the new energy power station using the inner loop current control of the new energy power station based on the adjustment current, the adjustment active power, the active power and reactive power of the new energy power station; and coordinating the control of the new energy power station and the grid-type energy storage system based on the drive signal of the bridge valve in the grid-type energy storage system and the drive signal of the bridge valve in the new energy power station to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

[0019] Optionally, the DC fault clearing unit includes: a third control mode switching module, used to switch the control mode of the converter station where the fault pole is located in the grid-type energy storage and the receiving-end controllable phase-commutation converter station to DC current control mode according to the DC current control strategy, and the current reference values ​​are equal; a fourth control mode switching module, used to switch the control mode of the new energy power station to low-voltage fault ride-through mode when the grid connection point voltage of the new energy power station is less than a first preset voltage threshold; and a second DC fault clearing module, used to coordinate the control of the new energy power station, the grid-type energy storage and the receiving-end controllable phase-commutation converter station based on the DC current control mode and the low-voltage fault ride-through mode, so as to realize the DC fault clearing of the multi-terminal DC collection and transmission system.

[0020] Optionally, the second DC fault clearing module is specifically used for: in the DC current control mode, generating a second reference AC voltage and the minimum firing angle of the converter station where the faulty pole is located in the receiving-end controllable commutation converter station based on the DC pole current and reference current of the faulty pole in the diode rectifier station; in the low-voltage fault ride-through mode, calculating the adjustment current based on the reference AC current and the actual grid connection point voltage of the new energy power station, and calculating the adjustment active power based on the actual grid connection point voltage and reference grid connection point voltage of the new energy power station and the reference active power of the new energy power station; and utilizing the outer loop control and inner loop voltage and current of the grid-type energy storage based on the second reference AC voltage, the actual active power and actual reactive power of the grid-type energy storage. The system controls and generates drive signals for the bridge valves in the grid-type energy storage system; based on the minimum firing angle and the DC voltage in the multi-terminal DC collection and transmission system, it generates drive signals for the bridge valves in the diode rectifier station where the faulty electrode is located; based on the adjustment current, the adjustment active power, the active power and reactive power of the new energy power station, it uses the inner loop current control of the new energy power station to generate drive signals for the bridge valves in the new energy power station; based on the drive signals for the bridge valves in the grid-type energy storage system, the drive signals for the bridge valves in the diode rectifier station where the faulty electrode is located, and the drive signals for the bridge valves in the new energy power station, it coordinates and controls the new energy power station, the grid-type energy storage system, and the receiving-end controllable commutation converter station to achieve DC fault clearing in the multi-terminal DC collection and transmission system.

[0021] Optionally, the fault disappearance determination unit is specifically used for: after the fault in the multi-terminal DC collection and transmission system is cleared, switching the control mode of the grid-type energy storage to the 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; controlling the bridge valve in the grid-type energy storage using the outer loop control and inner loop voltage-current control of the grid-type energy storage based on the target phase, the direct-axis voltage, and the preset quadrature-axis voltage; and determining that the fault in the multi-terminal DC collection and transmission system has disappeared if the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared is continuously greater than or equal to a second preset voltage threshold within a first preset time period.

[0022] Optionally, the power transmission system recovery unit is specifically used for: using the power outer loop control mode of the grid-type energy storage to perform power regulation on the multi-terminal DC collection and transmission system; 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 is 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, and using the inner loop current control of the new energy power station, the new energy power station is controlled to restore normal power transmission, thereby realizing the recovery control of the multi-terminal DC collection and transmission system.

[0023] Optionally, the fault disappearance determination unit is specifically used for: after the fault in the multi-terminal DC collection and transmission system is cleared, switching the control mode of the converter station where the faulty pole is located in the receiving-end controllable commutation converter station to the current margin control mode; under the current margin control, based on the actual pole current and margin current in 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, generating the current firing angle of the receiving-end controllable commutation converter station using maximum firing angle control and proportional-integral control; controlling the bridge valve in the receiving-end controllable commutation converter station based on the current firing angle of the receiving-end controllable commutation converter station; and determining that the fault in the multi-terminal DC collection and transmission system has disappeared if the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared is continuously greater than or equal to a second preset voltage threshold within a first preset time period.

[0024] Optionally, the output system recovery unit is specifically configured to: switch the control mode of the grid-type energy storage to a power outer loop control mode; in the power outer loop control mode, based on the actual active power and 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, the reference angular frequency, and the active and reactive power of the grid-type energy storage, generate a target phase and direct-axis voltage using power droop control; based on the target phase, the direct-axis voltage, and the preset quadrature-axis voltage, use the outer loop control and inner loop voltage-current control of the grid-type energy storage to control the voltage and current of the grid-type energy storage. The bridge valve is used for 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 the first preset voltage threshold and the duration is greater than or equal to the 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 the 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, the inner loop current control of the new energy power station is used to 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.

[0025] A third aspect of the present invention provides a computer device comprising: 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 described in the first aspect of the present invention is implemented.

[0026] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements a DC fault ride-through method as described in the first aspect of the present invention.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a DC fault ride-through method, a DC fault ride-through device, equipment, and medium. When a pole-to-ground fault occurs in a DC transmission line, the DC fault ride-through method switches the control mode of the grid-type energy storage to an AC voltage control mode or a DC current control strategy through an active step-down control strategy or a DC current control strategy. This coordinates the control of devices in the multi-terminal DC collection and transmission system, thereby clearing the fault current. At the same time, clearing the fault current using the active step-down control strategy or the DC current control strategy does not require additional measures such as DC circuit breakers. The control is flexible and easy to implement. Furthermore, by determining the operating status of the multi-terminal DC collection and transmission system, the system can be restored after the fault is cleared, which is beneficial to the safe and stable operation of the multi-terminal DC collection and transmission system. Attached Figure Description

[0028] Figure 1 A flowchart of a DC fault ride-through method provided by the present invention; Figure 2 A schematic diagram of the topology of a diode-rectified new energy multi-terminal DC collection and transmission system provided by the present invention; Figure 3 This is a schematic diagram of a diode rectifier station topology provided by the present invention; Figure 4 This is a schematic diagram of a CLCC inverter station topology provided by the present invention; Figure 5 This is a schematic diagram of a single-valve electrical topology for a CLCC inverter station provided by the present invention; Figure 6 A schematic diagram of a low-voltage fault ride-through mode provided by the present invention; Figure 7 A schematic diagram of a grid-type energy storage control switching provided by the present invention; Figure 8 A fault current distribution diagram of a multi-terminal DC collection and transmission system provided by the present invention; Figure 9 A schematic diagram of a grid-type energy storage control switching provided by the present invention; Figure 10 A schematic diagram of a controllable phase-switching converter station at the receiving end provided by the present invention; Figure 11 A schematic diagram of a steady-state control strategy for a multi-terminal DC collection and output system provided by the present invention; Figure 12 A schematic diagram of a simulation verification waveform for an "active buck control" provided by the present invention; Figure 13 A schematic diagram of a simulation verification waveform for "direct current control" provided by the present invention; Figure 14 A flowchart of an "active buck control" DC fault ride-through control strategy provided by the present invention; Figure 15 A flowchart of a "direct current control" DC fault ride-through control strategy provided by the present invention; Figure 16 A schematic diagram of a DC fault ride-through device provided by the present invention; Figure 17 A block diagram of a computer device provided by the present invention. Detailed Implementation

[0029] Example 1: Figure 1The flowchart of a DC fault ride-through method provided by this invention is applicable to a multi-terminal DC collection and transmission system for new energy sources based on diode rectification, such as... Figure 1 As shown, the method may include the following steps 101 to 103: In step 101, when a pole-to-ground fault occurs in the DC transmission line of the multi-terminal DC collection and transmission system, the control mode of the grid-type energy storage in the multi-terminal DC collection and transmission system is switched to the fault control mode according to the preset fault control strategy, and the devices in the multi-terminal DC collection and transmission system are coordinated and controlled to realize the DC fault clearance of the multi-terminal DC collection and transmission system.

[0030] 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.

[0031] In step 102, based on the DC voltage in the multi-terminal DC collection and output system after the fault is cleared, it is determined whether the fault in the multi-terminal DC collection and output system has disappeared.

[0032] In step 103, if the fault of the multi-terminal DC collection and transmission system disappears, the grid-type energy storage is used to restore the control of the multi-terminal DC collection and transmission system.

[0033] It should be noted that this invention proposes two DC fault ride-through control methods applicable to diode-rectified new energy multi-terminal DC collection and transmission systems. One is "active buck" control (i.e., active buck control strategy), which mainly relies on the coordinated cooperation between new energy power plants and grid-based energy storage to achieve fault ride-through; the other is "DC current control" (i.e., DC current control strategy), which mainly relies on the coordinated cooperation between new energy power plants, grid-based energy storage, and receiving-end controlled line commutated converters (CLCC) to achieve fault ride-through.

[0034] This invention addresses the rapid clearing of fault current and system recovery control strategies under temporary DC transmission line faults in a new energy island multi-terminal DC collection and transmission system based on grid-type energy storage and diode rectification.

[0035] This invention addresses the issue of temporary faults on the DC outgoing lines of isolated renewable energy DC collection and transmission systems. It proposes a DC fault ride-through control method for multi-terminal renewable energy DC collection and transmission systems based on diode rectification. Considering the differences in the uncontrolled characteristics of diode converter stations and the controllable shutdown characteristics of receiving-end converter stations, the invention studies coordinated control among renewable energy power plants with power control capabilities, grid-connected energy storage systems with power compensation and voltage support capabilities, and receiving-end converter stations with DC voltage control capabilities. This method solves the problems of electrical surges exceeding equipment limits and protection triggering leading to system shutdowns during temporary fault ride-through. Currently, there is a lack of relevant literature and engineering application cases for reference. Therefore, this invention provides a unipolar-to-ground fault ride-through control method for the system's DC transmission lines, achieving fault current clearance, post-fault system recovery, and safe and stable operation of equipment and the system. It is applicable to isolated or weak-grid renewable energy collection and grid connection scenarios and long-distance transmission, with wide application scenarios and significant advantages.

[0036] In some embodiments of the present invention, such as Figure 2 As shown, a new energy multi-terminal DC collection and transmission system based on diode rectification can include: an AC bus, a new energy power plant, a grid-type energy storage, a diode rectifier station (DR), a DC transmission line, and a receiving station. The grid-type energy storage and the new energy power plant are connected to the AC bus, the AC side of the diode rectifier station is connected to the AC bus, the DC side of the diode rectifier station is connected to the DC side of the receiving station through the DC transmission line, and the AC side of the receiving station is connected to the AC power grid.

[0037] Among these, the new energy power station can be a wind power station, a photovoltaic power station, a geothermal power station, or a hybrid power station (e.g., a hybrid power station consisting of wind power and photovoltaic power), etc. The receiving end station can be an inverter station based on a controllable commutation converter station (CLCC), and the DC transmission line can be an overhead DC line. In some scenarios, the new energy multi-terminal DC collection and transmission system also includes a filter device.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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 R d3 With capacitor C d3 Series connection, resistor R d3 With diode D d3 The parallel RCD circuit consists of an auxiliary fully controllable valve V13 connected in parallel with a surge arrester arr13, and a thyristor valve V11 connected in parallel with a saturated reactor L. SR A reactor L is connected in series between the auxiliary fully controllable IGBT valve V13 and the thyristor valve V14. FSR , Fully controlled IGBT valve with reverse parallel diode.

[0043] The AC filtering device uses BP11 / 13th resonant filters, HP24 / 36th and HP3rd resonant filters, while the DC filtering device uses HP12 / 24th resonant filters.

[0044] The CLCC's controllable commutation mode includes two states: natural commutation operation and forced commutation operation. During natural commutation operation, valves V11 and V12 are open, and current flows through the main branch. When the commutation current is less than a certain set value, valve V12 closes, and auxiliary branch valves V13 and V14 open, allowing current to flow through the main and auxiliary branches. At this time, valve V11 enters a blocking recovery period due to reverse voltage. Natural commutation is completed when the auxiliary branch current decays to zero under the influence of external AC voltage. When an AC system fault occurs in the receiving-end power grid, valve V13 closes, enabling the commutator valve to actively shut off current, and the CLCC enters forced commutation operation. The conduction sequence of each valve is consistent with normal operation. The difference is that after valve V13 closes, due to the AC system fault, the current cannot drop to zero. At this time, the current is transferred to surge arrester arr13, relying on the surge arrester's operating voltage to enhance the commutation voltage and complete the forced commutation process.

[0045] To address DC faults in DC transmission systems, a strategy (CN114825431A) was proposed for wind farms to transmit power to the grid via diode rectification and for the control and protection system. This strategy utilizes the fault current-limiting control capability of the wind turbine generators in conjunction with AC / DC circuit breakers at the receiving end and AC circuit breakers at the sending end to achieve DC short-circuit fault ride-through, clearing the DC short-circuit fault and rapidly restoring wind farm power after the fault is resolved. However, the system still requires DC circuit breakers at the receiving end, resulting in higher costs, and the complete disconnection of the sending and receiving systems during the fault makes it impossible to maintain the transmission of some active power.

[0046] The two DC ride-through strategies proposed in this invention, applicable to new energy DC collection and transmission systems, can eliminate fault currents without the need for additional DC circuit breakers or other measures, offering flexible and easy-to-implement control. Specifically, the "DC current control" process allows non-faulty DC lines to continue transmitting 50% of active power, significantly reducing the impact on active power generated by the AC systems at both ends, thus facilitating system recovery after temporary faults. From an equipment perspective, this reduces the number of switching operations, thereby decreasing equipment wear and maintenance costs. From a system perspective, rapid suppression of fault currents and system recovery avoids the time delays and energy losses associated with system restarts and power restoration after a power outage, effectively reducing system disturbances caused by faults. Furthermore, it helps improve the tolerance of new energy DC transmission systems to temporary DC line faults, ensuring reliable transmission and consumption of new energy power.

[0047] The above Figure 1 One possible implementation of step 101 shown may include the following steps 1011 to 1013: In step 1011, according to the active voltage reduction control strategy, the control mode of the grid-type energy storage is switched to the AC voltage control mode. Using the AC voltage control mode, the reference AC voltage value is reduced to actively reduce the AC voltage at the system's sending end and prevent fault current from feeding into the fault point.

[0048] In step 1012, when the grid connection point voltage of the new energy power station is less than the first preset voltage threshold, the control mode of the new energy power station is switched to low-voltage fault ride-through mode.

[0049] In step 1013, based on the AC voltage control mode and the low-voltage fault ride-through mode, the new energy power station and the grid-type energy storage are coordinated and controlled to realize the DC fault clearing of the multi-terminal DC collection and transmission system.

[0050] It should be noted that this active voltage reduction control strategy uses grid-connected energy storage to "actively" reduce the AC voltage at the renewable energy grid connection point, thereby clearing the fault current. Subsequently, the voltage control capabilities of the grid-connected energy storage and inverter stations, along with coordinated control of the renewable energy units, are utilized to achieve system recovery. During the fault current clearing phase, the renewable energy plant and grid-connected energy storage work together, with the grid-connected energy storage "actively" reducing voltage and the renewable energy power rapidly dissipating to quickly clear the fault current. During the fault disappearance determination phase, the grid-connected energy storage switches to normal control mode and transmits a small current to the receiving end station. The failure is determined by whether the DC voltage can be successfully established. During the system recovery phase, the AC voltage establishment capability of the grid-connected energy storage, along with coordinated control of the renewable energy units, is used to restore system power.

[0051] In the fault current clearing stage, the control includes: a new energy side control switching stage and a grid-connected energy storage control switching stage. The new energy side control switching stage is used to ensure the safe operation of the unit under low AC voltage conditions; the grid-connected energy storage control switching stage directly controls the voltage at the new energy AC grid connection point to decrease, so that the DC voltage output by the DR station is lower than the voltage at the fault point port, suppressing current feeding into the fault point, thereby clearing the fault current.

[0052] Possible implementations of step 1013 above may include the following steps S1 to S5: In step S1, under the AC voltage control mode, a preset AC voltage that is less than the voltage threshold is used as the first reference AC voltage.

[0053] In step S2, under the low-voltage fault ride-through mode, the adjustment current is calculated based on the reference AC current and the actual grid connection point voltage of the new energy power station, and the adjustment active power is calculated based on the actual grid connection point voltage and reference grid connection point voltage of the new energy power station and the reference active power of the new energy power station.

[0054] In step S3, based on the first reference AC voltage, the active power and reactive power of the grid-type energy storage, the drive signal of the bridge valve in the grid-type energy storage is generated using the inner loop control of the grid-type energy storage.

[0055] In step S4, based on the adjusted current, the adjusted active power, the active power and reactive power of the new energy power station, the driving signal of the bridge valve in the new energy power station is generated by using the inner loop current control of the new energy power station.

[0056] In step S5, based on the drive signals of the bridge valve in the grid-type energy storage and the bridge valve in the new energy power station, coordinated control is performed on the new energy power station and the grid-type energy storage to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

[0057] The driving signal can be a PWM (Pulse Width Modulation) signal.

[0058] It should be noted that the fault causes the DC fault pole's voltage to ground to be near zero, thus the AC grid connection voltage of the wind farm will also drop. When it falls below the threshold, the wind turbine enters the low-voltage fault ride-through control mode and uses a current limiting circuit to restrict AC overcurrent. This process is the control switching stage for new energy sources. The dynamic reactive power support of the converter in the new energy power station is implemented as follows:

[0059] in, i dref Inverter in new energy power plants d Shaft current reference value, i qref Inverter in new energy power plants q Shaft current reference value, k p This is the proportionality coefficient. V s This refers to the actual grid connection point voltage (or AC voltage per unit value) of the new energy power station. I N This is the reference value for alternating current (i.e., the reference alternating current). I lim This is the AC current limiting value (or per-unit value). i dmax for d Upper limit of shaft current, i dmin for d Lower limit of shaft current, Δ i q To adjust the current, iq for q Axis current.

[0060] The generator-side converter appropriately reduces load based on AC voltage dips, and surplus power is absorbed by energy-consuming devices in the renewable energy power station. The active power reference value is switched to... P ref_frt The implementation method is as follows:

[0061] in, V sref This is a reference value for the AC voltage of new energy power plants. V s This refers to the actual grid connection voltage of the renewable energy power plant. k This is the power regulation proportional coefficient. P ref This is a reference value for active power under rated operating conditions. P ref_frt To adjust the active power.

[0062] When the AC voltage at the grid connection point of the grid-connected system drops, the grid-connected energy storage will control the generation of additional reactive power. By providing rapid reactive power response, it will support the AC voltage at the grid connection point and ensure the reactive power balance of the AC side of the system under transient conditions.

[0063] For example, such as Figure 6 As shown, when the grid connection point voltage of the new energy power station is less than the first preset voltage threshold, an enable signal FRT_flag1 is generated. The control system of the new energy power station receives the enable signal FRT_flag1 and switches the control mode of the new energy power station to the low-voltage fault ride-through mode.

[0064] When the grid-side converter receives the enable signal FRT_flag1, it controls the current based on the reference AC current. I N Actual grid connection point voltage V s and proportionality coefficient k p The adjustment current Δ is calculated. i q As shown below:

[0065] The actual reactive power of the grid-side converter Q m and reference reactive power Q ref The difference is calculated to obtain the reactive power difference. Then, PI (Proportional-Integral) control is used to process this reactive power difference to obtain... qShaft current, for adjusting current and q shaft current i q Add them together to get a reference. q shaft current i qref For DC voltage U dc and reference DC voltage U dcref The difference is calculated to obtain the voltage difference value, based on the AC current limiting value. I lim and reference q shaft current i qref The upper and lower limits of the generated d-axis current are calculated. Based on the voltage difference and the upper and lower limits of the d-axis current, a reference d-axis current is generated using PI control. i dref 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 (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.

[0066] 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 qrefBased 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.

[0067] 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.

[0068] For example, such as Figure 7 As shown, when a pole-to-ground fault occurs on the DC transmission line in a multi-terminal DC collection and transmission system, the system control and protection device can generate a protection signal. Using delay control, the protection signal is processed to generate a DC fault ride-through signal FRT_flag2. This signal switches the control mode of the grid-type energy storage from the power outer loop control mode to the AC voltage control mode. In the AC voltage control mode, a preset AC voltage is used. 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 reference active power P druref The difference is used to obtain the first reference AC voltage. V acref .

[0069] The above Figure 1 Another possible implementation of step 101 shown may include the following steps 1014 to 1016: In step 1014, according to the DC current control strategy, the control mode of the converter station where the fault pole is located in the grid-type energy storage and the receiving-end controllable commutation converter station is switched to DC current control mode respectively, and the current reference values ​​are equal.

[0070] In step 1015, when the grid connection point voltage of the new energy power station is less than the first preset voltage threshold, the control mode of the new energy power station is switched to low-voltage fault ride-through mode.

[0071] In step 1016, based on the DC current control mode and the low-voltage fault ride-through mode, the new energy power station, the grid-type energy storage and the receiving-end controllable phase-commutation converter station are coordinated and controlled to realize the DC fault clearing of the multi-terminal DC collection and transmission system.

[0072] It should be noted that this strategy utilizes the DC current regulation capabilities of the converter stations at both ends of the fault point to clear the fault current. Subsequently, it leverages the voltage control capabilities of the grid-connected energy storage and inverter stations, supplemented by coordinated control on the renewable energy side, to achieve system recovery. During the fault current clearing phase, the DC current regulation capabilities of the grid-connected energy storage and the receiving-end converter station at both ends of the fault point are used to control the DC current on both sides of the fault point to be consistent, thus clearing the fault current and ensuring that some active power is stably transmitted through the non-faulty pole. During the fault disappearance determination phase, the receiving-end station control strategy is switched, the minimum firing angle limit is adjusted, and the fault disappearance is determined by whether the DC voltage can be successfully established. During the system recovery phase, the voltage control capabilities of the inverter station and grid-connected energy storage, supplemented by coordinated control on the renewable energy side, are used to achieve system recovery. This includes: renewable energy side control switching, grid-connected energy storage control switching, and receiving-end converter station control switching.

[0073] In the fault current clearing phase, the control includes: a new energy side control switching stage, a grid-connected energy storage control switching stage, and an inverter station control switching stage. The new energy side control switching stage ensures safe operation of the unit under low AC voltage conditions; the grid-connected energy storage control switching stage controls the DC current of the diode rectifier station; and the inverter station control switching stage controls the DC current of the receiving-end station pole line where the fault occurs. By ensuring the current on both sides of the fault point is consistent, the fault current is cleared.

[0074] Possible implementations of step 1016 above may include the following steps S6 to S11: In step S6, under the DC current control mode, based on the DC pole current and reference current of the faulty pole in the diode rectifier station, a second reference AC voltage and the minimum firing angle of the converter station where the faulty pole is located in the receiving-end controllable commutation converter station are generated respectively.

[0075] In step S7, under the low-voltage fault ride-through mode, the adjustment current is calculated based on the reference AC current and the actual grid connection point voltage of the new energy power station, and the adjustment active power is calculated based on the actual grid connection point voltage and reference grid connection point voltage of the new energy power station and the reference active power of the new energy power station.

[0076] In step S8, based on the second reference AC voltage, the actual active power and the actual reactive power of the grid-type energy storage, the drive signal of the bridge valve in the grid-type energy storage is generated using the inner loop control of the grid-type energy storage.

[0077] In step S9, a drive signal for the bridge valve where the faulty electrode is located in the diode rectifier station is generated based on the minimum firing angle and the DC voltage in the multi-terminal DC collection and output system.

[0078] In step S10, based on the adjusted current, the adjusted active power, the active power and reactive power of the new energy power station, the drive signal of the bridge valve in the new energy power station is generated by using the inner loop current control of the new energy power station.

[0079] In step S11, based on the driving signals of the bridge valves in the grid-type energy storage, the driving signals of the bridge valves where the faulty poles are located in the diode rectifier station, and the driving signals of the bridge valves in the new energy power station, coordinated control is performed on the new energy power station, the grid-type energy storage, and the receiving-end controllable phase-commutation converter station to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

[0080] It should be noted that the fault causes the voltage at the grid connection point of the renewable energy power station to drop below the threshold, thereby triggering the renewable energy to enter the low-voltage fault ride-through control mode. A DC fault ride-through signal is generated through characteristic quantity identification. This triggers the grid-type energy storage control switching circuit, switching the auxiliary power outer loop control to DC current control, with the current reference value being the rated current. The current control implementation method for grid-type energy storage is as follows:

[0081] in, V acref This is the AC voltage reference value at the sending end (i.e., the second reference AC voltage). k p This is the proportionality coefficient. k i The integral coefficient is... i dcref This is the reference value for DC current (i.e., the reference current). i dc s is the measured value of DC pole current of DR station (i.e., DC pole current of faulty pole in diode rectifier station), and s is a complex variable.

[0082] On the other hand, it triggers the switching circuit of the fault pole converter at the CLCC station by adjusting the current margin value Δ. i Setting it to zero switches the CLCC from actual DC voltage control mode to DC current control mode, with the current reference value being the rated current. Simultaneously, the minimum firing angle limit is adjusted. α min The constant current control of the CLCC station is implemented as follows:

[0083] in, α min It is the minimum firing angle of the bridge valve where the faulty pole of the CLCC station is located (i.e., the minimum firing angle of the converter station where the faulty pole is located in the controlled phase-switching converter station at the receiving end). k p This is the proportionality coefficient. k i The integral coefficient is... i dcref This is the reference value for DC current (i.e., the reference current). i dc s is the measured value of the fault pole line current in the CLCC station (i.e., the DC pole line current of the fault pole in the diode rectifier station), and s is a complex variable.

[0084] At this point, the system forms two current loops, such as Figure 8 As shown, fault circuit 1 flows through the DC pole to the right of the fault point and the Y-bridge converter station of CLCC, while fault circuit 2 flows through the 12-pulsating diode rectifier station, the DC pole to the left of the fault point and the D-bridge converter station of CLCC. The two currents can cancel each other at the fault point, thus clearing the fault current. At the same time, in conjunction with the low-voltage fault ride-through control of new energy and the power dynamic compensation capability of grid-type energy storage, the active power of circuit 2 is stably transmitted and sent out through the non-faulty pole.

[0085] For example, when a pole-to-ground fault occurs on a DC transmission line in a multi-terminal DC collection and transmission system, the system control and protection device can generate a protection signal, such as... Figure 9 As shown and as Figure 10 As shown, delay control is used to process the protection signal and generate the DC fault ride-through signal FRT_flag2, as follows. Figure 9 As shown, the control mode of the grid-type energy storage is switched from the power outer loop control mode to the DC current control mode through the DC fault ride-through signal FRT_flag2. In the DC current control mode, the DC pole current of the faulty pole in the DR station is used. i dc and reference DC current i dcref By using PI control, a second reference AC voltage is obtained. V acrefIn the power outer loop control mode, the actual active power output by the DR station is calculated. P drum and reference active power P druref The difference is used to obtain the second reference AC voltage. V acref .

[0086] like Figure 10 As shown, the control mode of CLCC is switched to DC current control mode by the DC fault ride-through signal FRT_flag2, based on the DC pole current of the faulty pole in the DR station. i dc and reference DC current i dcref By using PI control, the minimum firing angle of the converter station where the faulty pole is located in the controllable commutation converter station at the receiving end is obtained. α min Based on the actual pole-to-ground voltage of the faulty pole at the LCCC station U dc and reference voltage U dcref By using PI control and maximum firing angle control, the maximum firing angle of the converter station where the faulty pole is located is generated. α max Based on the maximum trigger angle α max and minimum trigger angle α min The trigger angle of the converter station where the faulty pole is located is generated. α .

[0087] The above Figure 1 One possible implementation of step 102 shown may include the following steps 1021 to 1025: In step 1021, after the fault of the multi-terminal DC collection and transmission system is cleared, the control mode of the grid-type energy storage is switched to the power outer loop control mode.

[0088] In step 1022, under the power outer loop control mode, based on the actual active power and reference active power output by the diode rectifier station, a standby reference AC voltage is generated using proportional-integral control.

[0089] In step 1023, based on the standby reference AC voltage, the reference angular frequency, and the active and reactive power of the grid-type energy storage, the target phase and direct-axis voltage are generated using power droop control.

[0090] In step 1024, based on the target phase, the direct-axis voltage, and the preset quadrature-axis voltage, the bridge valve in the grid-type energy storage is controlled using the inner loop control of the grid-type energy storage.

[0091] In step 1025, if the DC voltage in the multi-terminal DC collection and output system after the fault is cleared continues to be greater than or equal to the second preset voltage threshold within the first preset time period, it is determined that the fault in the multi-terminal DC collection and output system has disappeared.

[0092] It should be noted that after the fault point is deionized, the grid-type energy storage will switch the control to the normal additional power outer loop control mode (i.e., power outer loop control mode), such as... Figure 7 As shown, by controlling the power command of the "active power-AC voltage" outer loop to a low power value, a small current is transmitted to the receiving station. If the CLCC station can successfully establish a DC voltage and maintain it for a period of time, the fault is determined to have disappeared, and a DC fault crossover exit signal is generated. Otherwise, the fault clearing stage continues. After two failed system restarts, if the fault is determined to be permanent, the system shuts down. Specifically, in the fault disappearance determination stage, the control includes: switching the grid-type energy storage control back to the "active power-AC voltage" outer loop control mode (i.e., power outer loop control mode), controlling the power command to a low power value, and transmitting a small current to the receiving station. If the CLCC station can successfully establish a DC voltage and maintain it for a period of time, the fault is determined to have disappeared, and a DC fault crossover exit signal is generated. Otherwise, the fault clearing stage continues. After two failed system restarts, if the fault is determined to be permanent, the system shuts down.

[0093] The above Figure 1 Another possible implementation of step 102 shown may include the following steps 1021 to 102: In step 1026, after the fault in the multi-terminal DC collection and transmission system is cleared, the control mode of the converter station where the faulty pole is located in the receiving-end controllable phase-switching converter station is switched to the current margin control mode.

[0094] In step 1027, under the current margin control, based on the actual pole current and margin current in the receiving-end controllable phase-commutation converter station and the DC voltage in the multi-terminal DC collection and output system after fault clearance, the current firing angle of the receiving-end controllable phase-commutation converter station is generated using maximum firing angle control and proportional-integral control.

[0095] In step 1028, the bridge valve in the controlled phase-commutation converter station is controlled based on the current trigger angle of the controlled phase-commutation converter station.

[0096] In step 1029, if the DC voltage in the multi-terminal DC collection and output system after the fault is cleared continues to be greater than or equal to the second preset voltage threshold within the first preset time period, it is determined that the fault in the multi-terminal DC collection and output system has disappeared.

[0097] It should be noted that after deionization at the fault point is completed, the current margin of the receiving-end control strategy is increased, and the minimum firing angle limit α is adjusted and increased. min ,like Figure 10 As shown, the current margin control of the CLCC station is implemented as follows:

[0098] Where, α p For the Y-bridge valve trigger angle of CLCC station, k p k is the proportionality coefficient. i The integral coefficient is... i dcref This is a reference value for DC current. i dc The measured value of the faulty pole line current at the CLCC station is Δ. i Here, s represents the current margin value of the CLCC station, and s is a complex variable. If the DC voltage can be continuously established and the fault current is cleared to near zero, the fault is determined to have disappeared, and a DC fault crossover exit signal is generated. Otherwise, the fault clearing phase continues. After two failed system restarts, if the fault is determined to be permanent, the system shuts down. In the fault disappearance determination phase, the control includes: after completing the deionization of the fault point, increasing the current margin of the receiving-end control strategy, and adjusting the minimum firing angle limit α. min This can increase the firing angle of the CLCC fault electrode. If the DC voltage can be continuously established and the fault current is cleared to near zero, the fault is determined to have disappeared, and a DC fault crossover exit signal is generated. Otherwise, it continues to enter the fault clearing stage. After two failed system restarts, if the fault is determined to be permanent, the system will shut down.

[0099] The above Figure 1 One possible implementation of step 103 shown may include the following steps 1031 to 1033: In step 1031, the power of the multi-terminal DC collection and transmission system is regulated using the power outer loop control mode of the grid-type energy storage.

[0100] In step 1032, 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 low-voltage fault ride-through mode.

[0101] In step 1033, when the AC voltage at the sending end is greater than or equal to the 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 are controlled by the inner loop current control of the new energy power station to restore normal power transmission, thereby realizing the recovery control of the multi-terminal DC collection and transmission system.

[0102] It should be noted that the voltage reference value of the grid-connected energy storage is gradually increased to restore the AC voltage at the sending-end grid connection point. When the AC grid connection point voltage of the wind power recovers to the threshold and remains there for a period of time, the low-voltage ride-through exit signal of the wind turbine is triggered, and the wind turbine exits the low-voltage ride-through control mode and enters normal power control. Figure 6 As shown, the renewable energy units then increase their active power output at a higher slope, while simultaneously adjusting the outer loop reference value of the grid-connected energy storage's additional power to restore active power transmission after a system fault. Specifically, during the system recovery phase, the control includes: after confirming the fault has disappeared, re-establishing the system's AC voltage through the aforementioned grid-connected energy storage control switching mechanism; when the wind power AC grid connection point voltage recovers to the threshold and remains there for a period of time, triggering the wind turbine's low-voltage ride-through exit signal, the wind turbine exits the low-voltage ride-through control mode and enters normal power control; subsequently, the wind turbines increase their active power output at a higher slope, thus restoring the renewable energy power regulation capability through the aforementioned renewable energy-side control switching mechanism.

[0103] The above Figure 1 Another possible implementation of step 103 shown may include the following steps 1034 to 1039: In step 1034, the control mode of the grid-type energy storage is switched to the power outer loop control mode.

[0104] In step 1035, under the power outer loop control mode, a standby reference AC voltage is generated based on the actual active power and reference active power output by the diode rectifier station using proportional-integral control.

[0105] In step 1036, based on the standby reference AC voltage, the reference angular frequency, and the active and reactive power of the grid-type energy storage, the target phase and direct-axis voltage are generated using power droop control.

[0106] In step 1037, based on the target phase, the direct-axis voltage, and the preset quadrature-axis voltage, the bridge valve in the grid-type energy storage is controlled using the inner loop control of the grid-type energy storage.

[0107] In step 1038, 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.

[0108] In step 1039, when the AC voltage at the sending end is greater than or equal to the 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 are controlled by the inner loop current control of the new energy power station to restore normal power transmission, thereby realizing the recovery control of the multi-terminal DC collection and transmission system.

[0109] It should be noted that when a grid-connected energy storage system receives a DC fault ride-through exit signal, it switches the DC current control to an additional power outer loop control, such as... Figure 9 As shown, the AC voltage at the grid connection point is restored to its rated value. When the AC grid connection point voltage recovers to the threshold and remains there for a period of time, the low-voltage ride-through exit signal of the wind turbine is triggered, and the wind turbine exits the low-voltage ride-through control mode and enters normal power control. Figure 6 As shown, the wind turbine slope-increased active power generation enables system recovery after a fault. Specifically, during the system recovery phase, control includes: a new energy source side control switching stage, a grid-based energy storage control switching stage, and an inverter station control switching stage. After confirming the fault has disappeared, the power regulation capability of the new energy source is restored through the new energy source side control protection switching stage, the system AC voltage is re-established through the grid-based energy storage control switching stage, and the stable control capability of the system DC voltage is restored through the inverter station control switching stage.

[0110] For example, in an embodiment of the present invention, the schematic diagram of a new energy multi-terminal DC collection and transmission system based on diode rectification is as follows: Figure 11 As shown, it includes: AC wind turbine control system, grid-type energy storage control system, and CLCC station control.

[0111] The AC wind turbine control system includes: a machine-side converter, a DC power dissipation device, and a grid-side converter. The machine-side converter adopts zero-voltage switching. d Power regulation is achieved through a dual-loop vector control mode. d The shaft current reference value is zero, which is achieved by eliminating... d Shaft reactive current to reduce losses q Shaft-controlled active power, generating inner-loop control reference values ​​through control. i dref , i qref ; Grid-side converter controls the DC side voltage of the wind turbine U dc and reactive power Q m The inner loop control reference value is generated through control. i dref , i qref ; The trigger signal for the DC power dissipation device of the wind turbine is the deviation between the DC voltage amplitude of the wind turbine converter and the threshold value. It consists of controllable devices and resistors. The surplus power is consumed by switching the resistor through hysteresis control, so as to avoid DC side overvoltage and rotor overcurrent on the machine side.

[0112] The grid-type energy storage adopts a dual-loop voltage and current control based on the droop characteristics of "active power-frequency, reactive power-AC voltage" to establish AC side voltage and frequency. An additional power outer loop generates voltage deviation to correct the rated voltage at the grid connection point, realizing the regulation of DR station output power under the condition of fluctuation in new energy output. The reactive power generated by the system is jointly borne by new energy and grid-type energy storage, and is adjusted in real time according to the capacity of both to achieve reactive power balance under the transient steady-state condition.

[0113] The implementation method of active power-frequency droop control (i.e., Pf droop control) is as follows:

[0114] in: θ For phase value, m p ω is the droop coefficient, and ω is the reference value for angular frequency. P ref This is a reference value for active power. P This refers to the active power measurement value of grid-type energy storage. t For time.

[0115] The implementation method of reactive power-AC voltage droop control (i.e., Qf droop control) is as follows:

[0116] in: v ref AC voltage d Axis reference components, m Q The droop coefficient is... Q ref This is a reference value for reactive power. Q This refers to the reactive power measurement value of grid-type energy storage.

[0117] The power outer loop control is implemented as follows:

[0118] in: V acref For reference AC voltage, k p This is the proportionality coefficient. k i The integral coefficient is... P druref This is the reference value for the active power output by the DR station. Pdrum s represents the measured active power output from the DR station, where s is a complex variable.

[0119] Inner loop control can be either inner loop voltage control or inner loop current control. The inner loop current control is implemented as follows:

[0120] in, v dref AC voltage d Axial components ，v qref AC voltage q Axial components, k p This is the proportionality coefficient. k i The integral coefficient is... i dref and i qref These are the inner loop currents. d Shaft reference value and inner loop current q Axis reference value, V acref For reference AC voltage, v ref AC voltage d Axis reference component, V d for d Shaft AC voltage ，V q for q The AC voltage is s, where s is a complex variable.

[0121] The inner loop current is generated by controlling the inner loop voltage through inner loop current control. d Shaft reference value and inner loop current q The control signal for the valve bridge in the grid-type energy storage is obtained by processing the shaft reference value.

[0122] Both the Y-bridge and D-bridge of the receiving-end CLCC converter station employ constant DC voltage control to stabilize the DC bus voltage. The current margin control of the CLCC station is implemented as follows:

[0123] in, α p and α n These are the trigger angles for the Y-bridge and D-bridge valves at the CLCC station. k p This is the proportionality coefficient. k i The integral coefficient is... i dcref Here is the reference value for DC current, and s is a complex variable.i dcp and i dcn These are the measured values ​​of the positive and negative currents, respectively. Δi This is the current margin value for the CLCC station, typically 0.1 pu. In steady state, i dc -i dcref +Δi Since the value is positive, the firing angle reaches its upper limit, which is the output value of the constant DC voltage control loop, determined by the following formula:

[0124] in, α pmax and α nmax These are the upper limits of the firing angles of the Y-bridge and D-bridge valves at the CLCC station, respectively. k p This is the proportionality coefficient. k i The integral coefficient is... U dcref This is the DC voltage reference value. U dcp and U dcn , respectively, are the absolute values ​​of the voltage measurements between the positive and negative poles and ground, and s is a complex variable.

[0125] In the embodiments of the present invention, the example analysis provided in this application is as follows: Figure 12 As shown in Figure 13, a system was established in PSCAD / EMTDC as follows. Figure 2 The simulation model shown is for a new energy multi-terminal DC collection and transmission system based on diode rectification. The rated voltage of the DC transmission line is ±200kV, the rated power is 600MW, and the inverter side adopts a 12-pulse CLCC structure with neutral grounding, that is, there are two 6-pulse converter valves. The rated DC voltage of a single valve group is 200kV, and the smoothing reactance is 150mH.

[0126] To address pole-to-ground faults on the DC transmission line of this system, two DC fault ride-through strategies are proposed. The specific flow of the first control strategy is as follows: Figure 14 As shown, taking a fault duration of 100ms as an example, the specific steps are as follows: Step T1: After a short-circuit fault occurs between pole and ground on 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 AC voltage at the grid connection point of the sending-end wind turbine to drop.

[0127] Step T2: Upon receiving the DC ride-through enable signal FRT_sig2, the grid-type energy storage switches the "active power - AC voltage" outer loop to voltage control. Simultaneously, the grid-type energy storage generates reactive power, such as... Figure 7 As shown, a voltage reference value of 1.1 pu is given. Figure 12 It can be seen that the system can clear the fault point current within 25ms; when the voltage at the wind turbine grid connection point is lower than the threshold of 0.8pu, the low voltage ride-through signal FRT_sig1 is triggered, and the wind turbine control switches to low voltage ride-through control, such as... Figure 5 As shown, the wind turbine consumes energy in conjunction with the rapid dissipation of surplus power.

[0128] Step T3: After waiting for the first deionization time of 150ms, perform the first restart. The grid-type energy storage restores the "active power - AC voltage" outer loop and provides a low power reference value of 0.1pu. If the DC voltage recovers to the rated value and remains there for a certain period of 50ms, it proves that the fault has been cleared, and proceed to step T5; otherwise, it proves that the fault has not been cleared, and proceed to step T4. In this embodiment, if the fault duration is 100ms, the restart is successful, and proceed to step T5; if the fault duration is 300ms, the restart is unsuccessful, and step T4 should be performed.

[0129] Step T4: After the first restart fails, wait for the second deionization time of 200ms before performing a second restart. The grid-type energy storage receives the DC fault crossover exit signal, restores the "active power - AC voltage" outer loop, and provides a low power reference value of 0.1 pu. If the DC voltage recovers to its rated value and remains there for a certain period of 50ms, it proves that the fault has been cleared, and proceed to step T5; otherwise, it proves that the fault is permanent, and the system should be gradually shut down.

[0130] Step T5: After the line restart is successful, the active power reference value of the grid-type energy storage increases to the rated value at a rate of 1 p.u. / 100 ms.

[0131] Step T6: When the voltage at the wind turbine's grid connection point exceeds the threshold of 0.9 pu and remains there for a certain period of 100 ms, the low voltage ride-through signal FRT_sig1 exits, the wind turbine exits the low voltage ride-through mode, and rises to the rated value at a rate of 1 p.u. / 100 ms. The system then enters normal operation, realizing system recovery after a fault.

[0132] Simulated waveforms such as 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.

[0133] 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: 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.

[0134] 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.

[0135] Step T3: After waiting for the first deionization time of 150ms, perform the first restart. Add a current margin of 0.1pu to the CLCC control and adjust the minimum firing angle, i.e., adjust the lower limit of the current control output from 80° to 110°. During the restart process, the CLCC station Y-bridge firing angle is rapidly adjusted (rate 6000° / s) before reaching 110°, and slowly adjusted (rate 1200° / s) after reaching 110°. If the DC voltage returns to its rated value and remains there for a certain period of 50ms, and there is no current at the fault point in the line, it proves that the fault has been cleared, and proceed to step T5; otherwise, it proves that the fault has not been cleared, and proceed to step T2. In this embodiment, since the fault duration is 100ms, the restart is successful, and step T5 should be performed; if the fault duration is 300ms, the restart is unsuccessful, and step T4 should be performed.

[0136] Step T4: After the first restart fails, wait 200ms for the second deionization time before performing a second restart. Add a current margin of 0.1 pu to the CLCC control and adjust the minimum firing angle, i.e., adjust the lower limit of the current control output from 80° to 110°, attempting to adjust the firing angle using a variable rate method. If the DC voltage returns to its rated value and there is no current at the fault point in the line, the fault has been cleared, and proceed to step T5; otherwise, the fault is permanent, and the system should be gradually shut down.

[0137] Step T5: When the DC voltage reaches 1p.u., send a DC fault crossover exit enable signal to the grid-type energy storage, switch the constant DC current control to the "active power-AC voltage" outer loop, and give the active power command of 1p.u.

[0138] Step T6: When the voltage at the wind turbine's grid connection point exceeds the threshold of 0.9 pu and remains there for a certain period of 100 ms, the low voltage ride-through signal FRT_sig1 exits, the wind turbine exits the low voltage ride-through mode, and rises to the rated value at a rate of 1 p.u. / 100 ms. The system then enters normal operation, realizing system recovery after a fault.

[0139] Simulated waveforms such as Figure 13 As shown, after a fault occurs in the DC transmission line, considering the protection output and communication delay of about 3ms, the grid-type energy storage and CLCC station will receive the DC fault ride-through enable signal and switch to DC current control mode with the current reference value set to the rated value. The fault current can be cleared within 25ms. At this time, the system still maintains a 300MW active power transmission capacity. After the first deionization time of 150ms at the fault point ends, since the system still has power transmission, the CLCC can establish a DC voltage. Therefore, it is determined that the fault has disappeared. Finally, the system is restored to normal operation without impact through control.

[0140] Example 2: Figure 16 This is a schematic diagram of a DC fault ride-through device provided by the present invention, applicable to a multi-terminal DC collection and transmission system for new energy sources based on diode rectification, such as... Figure 16 As shown, the device includes: a DC fault clearing unit, used to switch the control mode of the grid-type energy storage in the multi-terminal DC collection and transmission system to a fault control mode according to a preset fault control strategy when a pole-to-ground fault occurs in the DC transmission line of the multi-terminal DC collection and transmission system, and to coordinate the control of the devices in the multi-terminal DC collection and transmission system to achieve DC fault clearing of the multi-terminal DC collection and transmission system; 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; a fault disappearance determination unit, used to determine whether the fault in the multi-terminal DC collection and transmission system has disappeared based on the DC voltage in the multi-terminal DC collection and transmission system after fault clearing; and a transmission system recovery unit, used to restore the multi-terminal DC collection and transmission system by utilizing the grid-type energy storage if the fault in the multi-terminal DC collection and transmission system has disappeared.

[0141] Optionally, the DC fault clearing unit includes: a first control mode switching module, used to switch the control mode of the grid-type energy storage to an AC voltage control mode according to an active voltage reduction control strategy, thereby reducing the reference AC voltage value and actively reducing the AC voltage at the system's sending end to prevent fault current from feeding into the fault point; a second control mode switching module, used to switch the control mode of the new energy power station to a low-voltage fault ride-through mode when the grid connection point voltage of the new energy power station is less than a first preset voltage threshold; and a first DC fault clearing module, used to coordinate the control of the new energy power station and the grid-type energy storage based on the AC voltage control mode and the low-voltage fault ride-through mode to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

[0142] Optionally, the first DC fault clearing module is specifically used for: in the AC voltage control mode, using a preset AC voltage less than a voltage threshold as a first reference AC voltage; in the low-voltage fault ride-through mode, calculating an adjustment current based on a reference AC current and the actual grid connection point voltage of the new energy power station, and calculating an adjustment active power based on the actual grid connection point voltage and reference grid connection point voltage of the new energy power station, and the reference active power of the new energy power station; generating a drive signal for the bridge valve in the grid-type energy storage system using the inner loop control of the grid-type energy storage system based on the first reference AC voltage, the active power and reactive power of the grid-type energy storage system; generating a drive signal for the bridge valve in the new energy power station using the inner loop current control of the new energy power station based on the adjustment current, the adjustment active power, the active power and reactive power of the new energy power station; and coordinating the control of the new energy power station and the grid-type energy storage system based on the drive signal of the bridge valve in the grid-type energy storage system and the drive signal of the bridge valve in the new energy power station to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

[0143] Optionally, the DC fault clearing unit includes: a third control mode switching module, used to switch the control mode of the converter station where the fault pole is located in the grid-type energy storage and the receiving-end controllable phase-commutation converter station to DC current control mode according to the DC current control strategy, and the current reference values ​​are equal; a fourth control mode switching module, used to switch the control mode of the new energy power station to low-voltage fault ride-through mode when the grid connection point voltage of the new energy power station is less than a first preset voltage threshold; and a second DC fault clearing module, used to coordinate the control of the new energy power station, the grid-type energy storage and the receiving-end controllable phase-commutation converter station based on the DC current control mode and the low-voltage fault ride-through mode, so as to realize the DC fault clearing of the multi-terminal DC collection and transmission system.

[0144] Optionally, the second DC fault clearing module is specifically used for: in the DC current control mode, generating a second reference AC voltage and the minimum firing angle of the converter station where the faulty pole is located in the receiving-end controllable commutation converter station based on the DC pole current and reference current of the faulty pole in the diode rectifier station; in the low-voltage fault ride-through mode, calculating the adjustment current based on the reference AC current and the actual grid connection point voltage of the new energy power station, and calculating the adjustment active power based on the actual grid connection point voltage and reference grid connection point voltage of the new energy power station and the reference active power of the new energy power station; and generating an adjustment current based on the second reference AC voltage, the actual active power and the actual reactive power of the grid-type energy storage using the inner loop control of the grid-type energy storage. The system generates drive signals for the bridge valves in the grid-type energy storage system; based on the minimum firing angle and the DC voltage in the multi-terminal DC collection and transmission system, it generates drive signals for the bridge valves in the diode rectifier station where the faulty electrode is located; based on the adjustment current, the adjustment active power, the active power and reactive power of the new energy power station, it uses the inner loop current control of the new energy power station to generate drive signals for the bridge valves in the new energy power station; based on the drive signals for the bridge valves in the grid-type energy storage system, the drive signals for the bridge valves in the diode rectifier station where the faulty electrode is located, and the drive signals for the bridge valves in the new energy power station, it coordinates the controllable phase-commutation converter station at the receiving end to achieve DC fault clearing in the multi-terminal DC collection and transmission system.

[0145] Optionally, the fault disappearance determination unit is specifically used for: after the fault in the multi-terminal DC collection and transmission system is cleared, switching the control mode of the grid-type energy storage to the 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; controlling the bridge valve 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; and determining that the fault in the multi-terminal DC collection and transmission system has disappeared within a first preset time period if the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared is continuously greater than or equal to a second preset voltage threshold.

[0146] Optionally, the power transmission system recovery unit is specifically used for: using the power outer loop control mode of the grid-type energy storage to perform power regulation on the multi-terminal DC collection and transmission system; 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 is 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, and using the inner loop current control of the new energy power station, the new energy power station is controlled to restore normal power transmission, thereby realizing the recovery control of the multi-terminal DC collection and transmission system.

[0147] Optionally, the fault disappearance determination unit is specifically used for: after the fault in the multi-terminal DC collection and transmission system is cleared, switching the control mode of the converter station where the faulty pole is located in the receiving-end controllable commutation converter station to the current margin control mode; under the current margin control, based on the actual pole current and margin current in 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, generating the current firing angle of the receiving-end controllable commutation converter station using maximum firing angle control and proportional-integral control; controlling the bridge valve in the receiving-end controllable commutation converter station based on the current firing angle of the receiving-end controllable commutation converter station; and determining that the fault in the multi-terminal DC collection and transmission system has disappeared if the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared is continuously greater than or equal to a second preset voltage threshold within a first preset time period.

[0148] 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.

[0149] Example 3: 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.

[0150] Example 4: Based on the same inventive concept, this invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and extended storage media supported by the computer device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of a DC fault ride-through method in the above embodiments.

[0151] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0152] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0153] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1The function specified in one or more boxes.

[0154] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0155] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention pending approval.

Claims

1. A DC fault ride-through method, characterized in that, The method, applicable to a diode-rectified multi-terminal DC collection and transmission system for new energy sources, includes: When a pole-to-ground fault occurs in the DC transmission line of a multi-terminal DC collection and transmission system, the control mode of the grid-type energy storage in the multi-terminal DC collection and transmission system is switched to the fault control mode according to the preset fault control strategy. The devices in the multi-terminal DC collection and transmission system are coordinated and controlled to clear the DC fault in the multi-terminal DC collection and transmission system. 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. Based on the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared, it is determined whether the fault in the multi-terminal DC collection and transmission system has disappeared. If the fault in the multi-terminal DC collection and transmission system disappears, the grid-type energy storage is used to restore control of the multi-terminal DC collection and transmission system.

2. The method according to claim 1, characterized in that, The step of switching the control mode of the grid-type energy storage in the multi-terminal DC collection and transmission system to the fault control mode according to the preset fault control strategy, and coordinating the control of the devices in the multi-terminal DC collection and transmission system to achieve DC fault clearing of the multi-terminal DC collection and transmission system includes: According to the active voltage reduction control strategy, the control mode of the grid-type energy storage is switched to the AC voltage control mode. Using the AC voltage control mode, the reference AC voltage value is reduced to actively reduce the AC voltage at the system's sending end and prevent fault current from feeding into the fault point. When the grid connection point voltage of the new energy power station is less than the first preset voltage threshold, the control mode of the new energy power station is switched to low-voltage fault ride-through mode. Based on the AC voltage control mode and the low-voltage fault ride-through mode, the new energy power station and the grid-type energy storage are coordinated and controlled to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

3. The method according to claim 2, characterized in that, The coordinated control of the new energy power station and the grid-type energy storage based on the AC voltage control mode and the low-voltage fault ride-through mode, to achieve DC fault clearing of the multi-terminal DC collection and transmission system, includes: In the AC voltage control mode, a preset AC voltage that is less than the voltage threshold is used as the first reference AC voltage. In the low-voltage fault ride-through mode, the adjustment current is calculated based on the reference AC current and the actual grid connection point voltage of the new energy power station, and the adjustment active power is calculated based on the actual grid connection point voltage and reference grid connection point voltage of the new energy power station and the reference active power of the new energy power station. Based on the first reference AC voltage, the active power and reactive power of the grid-type energy storage, the drive signal of the bridge valve in the grid-type energy storage is generated by utilizing the inner loop control of the grid-type energy storage. Based on the adjusted current, the adjusted active power, the active power and reactive power of the new energy power station, the driving signal of the bridge valve in the new energy power station is generated by using the inner loop current control of the new energy power station. Based on the drive signals of the bridge valve in the grid-type energy storage and the bridge valve in the new energy power station, the new energy power station and the grid-type energy storage are coordinated and controlled to achieve DC fault clearing of the multi-terminal DC collection and transmission system.

4. The method according to claim 1, characterized in that, The step of switching the control mode of the grid-type energy storage in the multi-terminal DC collection and transmission system to the fault control mode according to the preset fault control strategy, and coordinating the control of the devices in the multi-terminal DC collection and transmission system to achieve DC fault clearing of the multi-terminal DC collection and transmission system includes: According to the DC current control strategy, the control mode of the converter station where the fault pole is located in the grid-type energy storage and the receiving-end controllable phase-switching converter station is switched to DC current control mode respectively, and the current reference values ​​are equal. When the grid connection point voltage of the new energy power station is less than the first preset voltage threshold, the control mode of the new energy power station is switched to low-voltage fault ride-through mode. Based on the DC current control mode and the low-voltage fault ride-through mode, the new energy power station, the grid-type energy storage and the receiving-end controllable phase-commutation converter station are coordinated and controlled to realize the DC fault clearing of the multi-terminal DC collection and transmission system.

5. The method according to claim 4, characterized in that, The coordinated control of the new energy power station, the grid-type energy storage, and the receiving-end controllable phase-commutation converter station based on the DC current control mode and the low-voltage fault ride-through mode, to achieve DC fault clearing of the multi-terminal DC collection and transmission system, includes: In the DC current control mode, based on the DC pole current and reference current of the faulty pole in the diode rectifier station, a second reference AC voltage and the minimum firing angle of the converter station where the faulty pole is located in the receiving-end controllable commutation converter station are generated respectively. In the low-voltage fault ride-through mode, the adjustment current is calculated based on the reference AC current and the actual grid connection point voltage of the new energy power station, and the adjustment active power is calculated based on the actual grid connection point voltage and reference grid connection point voltage of the new energy power station and the reference active power of the new energy power station. Based on the second reference AC voltage, the actual active power and actual reactive power of the grid-type energy storage, the drive signal of the bridge valve in the grid-type energy storage is generated by utilizing the outer loop control and inner loop voltage and current control of the grid-type energy storage. Based on the minimum firing angle and the DC voltage in the multi-terminal DC collection and output system, a drive signal is generated for the bridge valve where the faulty electrode is located in the diode rectifier station. Based on the adjusted current, the adjusted active power, the active power and reactive power of the new energy power station, the driving signal of the bridge valve in the new energy power station is generated by using the inner loop current control of the new energy power station. Based on the driving signals of the bridge valves in the grid-type energy storage, the driving signals of the bridge valves where the faulty poles are located in the diode rectifier station, and the driving signals of the bridge valves in the new energy power station, the new energy power station, the grid-type 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.

6. The method according to claim 2, characterized in that, The determination of whether the fault in the multi-terminal DC collection and transmission system has disappeared based on the DC voltage in the multi-terminal DC collection and transmission system after fault clearance includes: After the fault in the multi-terminal DC collection and transmission system is cleared, the control mode of the grid-type energy storage is switched to the power outer loop control mode. In the power outer loop control mode, based on the actual active power and reference active power output by the diode rectifier station, a standby reference AC voltage is generated using proportional-integral control. Based on the standby reference AC voltage, the reference angular frequency, and the active and reactive power of the grid-type energy storage, power droop control is used to achieve proportional power distribution within the multi-unit energy storage, generating the target phase and direct-axis voltage. Based on the target phase, the direct-axis voltage, and the preset quadrature-axis voltage, the bridge valve in the grid-type energy storage is controlled using the outer loop control and inner loop voltage and current control. If, within a first preset time period, the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared continues to be greater than or equal to a second preset voltage threshold, it is determined that the fault in the multi-terminal DC collection and transmission system has disappeared.

7. The method according to claim 2, characterized in that, The method of using the grid-type energy storage to perform recovery control on the multi-terminal DC collection and transmission system includes: The power outer loop control mode of the grid-type energy storage is used to regulate the power of the multi-terminal DC collection and transmission system; 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 the first preset voltage threshold and the duration is greater than or equal to the 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 the 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 are controlled by the inner loop current control of the new energy power station to restore normal power transmission, thereby realizing the recovery control of the multi-terminal DC collection and transmission system.

8. The method according to claim 4, characterized in that, The determination of whether the fault in the multi-terminal DC collection and transmission system has disappeared based on the DC voltage in the multi-terminal DC collection and transmission system after fault clearance includes: After the fault in the multi-terminal DC collection and transmission system is cleared, the control mode of the converter station where the faulty pole is located in the receiving-end controllable phase-switching converter station is switched to the current margin control mode. Under the current margin control, based on the actual pole current and margin current in the receiving-end controllable phase-commutation converter station and the DC voltage in the multi-terminal DC collection and output system after fault clearance, the current firing angle of the receiving-end controllable phase-commutation converter station is generated using maximum firing angle control and proportional-integral control. Based on the current trigger angle of the receiving-end controllable phase-commutation converter station, the bridge valve in the receiving-end controllable phase-commutation converter station is controlled. If, within a first preset time period, the DC voltage in the multi-terminal DC collection and transmission system after the fault is cleared continues to be greater than or equal to a second preset voltage threshold, it is determined that the fault in the multi-terminal DC collection and transmission system has disappeared.

9. The method according to claim 4, characterized in that, The method of using the grid-type energy storage to perform recovery control on the multi-terminal DC collection and transmission system includes: Switch the control mode of the grid-type energy storage to the power outer loop control mode; In the power outer loop control mode, based on the actual active power and reference active power output by the diode rectifier station, a standby reference AC voltage is generated using proportional-integral control. Based on the standby reference AC voltage, the reference angular frequency, and the active and reactive power of the grid-type energy storage, power droop control is used to achieve proportional power distribution within the multi-unit energy storage, generating the target phase and direct-axis voltage. Based on the target phase, the direct-axis voltage, and the preset quadrature-axis voltage, the bridge valve in the grid-type energy storage is controlled using the inner loop control of the grid-type energy storage. 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 the first preset voltage threshold and the duration is greater than or equal to the 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 the 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 are controlled by the inner loop current control of the new energy power station to restore normal power transmission, thereby realizing the recovery control of the multi-terminal DC collection and transmission system.

10. A DC fault ride-through device, characterized in that, The device is applicable to a diode-rectified multi-terminal DC collection and transmission system for new energy sources, and includes: A DC fault clearing unit is used to switch the control mode of the grid-type energy storage in the multi-terminal DC collection and transmission system to a fault control mode when a pole-to-ground fault occurs in the DC transmission line of the multi-terminal DC collection and transmission system, according to a preset fault control strategy. This allows for coordinated control of the devices in the multi-terminal DC collection and transmission system, thereby clearing the DC fault. 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. The fault disappearance determination unit is used to determine whether the fault in the multi-terminal DC collection and transmission system has disappeared based on the DC voltage in the multi-terminal DC collection and transmission system after the fault has been cleared. The system recovery unit is used to restore the multi-terminal DC collection and transmission system by utilizing the grid-type energy storage if the fault of the multi-terminal DC collection and transmission system disappears.

11. A computer device, characterized in that, include: One or more processors: The processor is used 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 described in any one of claims 1 to 9 is implemented.

12. A computer-readable storage medium, characterized in that, It contains a computer program, which, when executed, implements a DC fault ride-through method as described in any one of claims 1 to 9.

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