Hybrid line offshore wind power flexible direct system control method and device, terminal and medium

Abstract

The application discloses a kind of hybrid line offshore wind power flexible system control method, device, terminal and medium, the scheme provided in the application is applied to the hybrid line offshore wind power flexible system containing series type DC energy consumption device, the control method includes: when detecting the fault of hybrid line offshore wind power flexible system, control main loop switch module is disconnected, so that the DC current of hybrid line offshore wind power flexible system is transferred to the energy consumption loop where energy consumption valve module is located, to make the voltage value of each energy consumption valve unit be lifted;When the voltage value of each energy consumption valve unit reaches the preset voltage threshold, according to the sending power of offshore converter station and the preset control target voltage, combined with the preset system surplus power constraint condition, the on-off of switch element in energy consumption valve unit is controlled, the switching number of energy consumption resistance of each energy consumption valve unit is controlled, so as to control the total energy consumed by energy consumption loop, realize system surplus power balance.

Description

Technical Field

[0001] This application relates to the field of offshore wind power technology, and in particular to a control method, device, terminal and medium for a hybrid line offshore wind power flexible DC system. Background Technology

[0002] Offshore wind power, with its high utilization rate and abundant resource reserves, is rapidly becoming one of the key areas for current and future new energy development. As the scale of offshore wind power continues to expand and transmission distances increase, intensive and centralized unified development and utilization will be the main approach to utilizing offshore wind power in the future. Currently, offshore wind power is generally transmitted to onshore converter stations via submarine DC cables, and then converted from DC to AC by converters and integrated into the coastal power grid. However, with the rapid growth of offshore wind power development, this near-shore grid connection method is no longer suitable for future ultra-large-scale offshore wind power development scenarios. To further compress transmission corridors, reduce transmission costs, and avoid increasing short-circuit currents in near-shore power grids, direct transmission of offshore wind power to load centers via a hybrid submarine cable-overhead line DC transmission line will become one of the main methods for future ultra-large-scale offshore wind power development.

[0003] In existing offshore wind power flexible DC transmission projects, only DC submarine cables are generally used for power transmission, and parallel DC energy dissipation devices are used to achieve fault voltage regulation. The specific principle is: after a fault occurs in the receiving end of the power grid, the DC voltage rises, the parallel DC energy dissipation device starts, consumes the surplus power and maintains the DC voltage. However, this device is not suitable for offshore wind power flexible DC systems that combine submarine cables and overhead lines, which leads to the technical problem of low reliability in existing offshore wind power flexible DC systems that combine submarine cables and overhead lines. Summary of the Invention

[0004] This application provides a control method, device, terminal, and medium for a hybrid offshore wind power flexible DC system, which addresses the technical problem of low reliability in existing offshore wind power flexible DC systems that combine submarine cables and overhead lines.

[0005] To address the aforementioned technical problems, the first aspect of this application provides a control method for a hybrid-line offshore wind power flexible DC system, applied to a hybrid-line offshore wind power flexible DC system including a series-connected DC energy dissipation device. The method is characterized in that the series-connected DC energy dissipation device comprises: a submarine cable port, an overhead line port, a main circuit switch module, and an energy dissipation valve module; the main circuit switch module and the energy dissipation valve module are disposed between the submarine cable port and the overhead line port, and the main circuit switch module and the energy dissipation valve module are connected in parallel; the energy dissipation valve module contains multiple energy dissipation valve units connected in series, each energy dissipation valve unit including an energy dissipation resistor and a switching element for controlling the switching on or off of the energy dissipation resistor; the control method includes:

[0006] When a fault is detected in the hybrid offshore wind power flexible DC system, the main circuit switch module is controlled to disconnect, so that the DC current of the hybrid offshore wind power flexible DC system is transferred to the energy consumption circuit where the energy consumption valve module is located, so as to increase the voltage value of each energy consumption valve unit.

[0007] When the voltage value of each energy-consuming valve unit reaches the preset voltage threshold, the switching element in the energy-consuming valve unit is controlled to consume the system surplus power of the hybrid line offshore wind power flexible DC system, based on the output power of the offshore converter station and the preset control target voltage, combined with the preset system surplus power constraint conditions.

[0008] Preferably, the expression for the system surplus power constraint is as follows:

[0009]

[0010] In the formula, P w Let n be the output power of the offshore converter station. ch U represents the number of energy-consuming valve units with the energy-consuming resistor in the active state. C To control the target voltage, R ch This is the resistance value of the energy-consuming resistor.

[0011] Preferably, increasing the voltage value of each energy-consuming valve unit includes:

[0012] The first switch in the energy dissipation valve unit is turned off, so that the DC current flows to the energy storage capacitor in the energy dissipation valve unit. The first switch is a bypass switch for the energy storage capacitor and is used to control the connection or bypass of the energy storage capacitor.

[0013] Preferably, when the voltage value of each energy-consuming valve unit reaches a preset voltage threshold, the method further includes:

[0014] Monitor the capacitor voltage value of each energy-consuming valve unit, and control the on / off state of the first switch tube based on the comparison result of the capacitor voltage value and the upper and lower voltage thresholds.

[0015] Preferably, controlling the on / off state of the first switch transistor based on the comparison result between the capacitor voltage value and the upper and lower voltage thresholds specifically includes:

[0016] When the capacitor voltage value is not less than the lower voltage threshold and not greater than the upper voltage threshold, the current on / off state of the first switch is maintained.

[0017] When the capacitor voltage value is less than the lower voltage threshold, the first switch is disconnected;

[0018] When the capacitor voltage value is greater than the lower voltage threshold, the first switch is closed.

[0019] Preferably, the method for determining the upper and lower voltage thresholds specifically includes:

[0020] Based on the average capacitor voltage value of each energy-consuming valve unit, the upper and lower voltage thresholds are determined according to the sum and difference between the average capacitor voltage value and the preset equalization threshold.

[0021] Meanwhile, a second aspect of this application provides a control device for a hybrid-line offshore wind power flexible DC system, applied to a hybrid-line offshore wind power flexible DC system including a series-connected DC energy dissipation device. The series-connected DC energy dissipation device includes: a submarine cable port, an overhead line port, a main circuit switch module, and an energy dissipation valve module. The main circuit switch module and the energy dissipation valve module are disposed between the submarine cable port and the overhead line port, and are connected in parallel. The energy dissipation valve module contains multiple energy dissipation valve units connected in series, each energy dissipation valve unit including an energy dissipation resistor and a switching element for controlling the switching on or off of the energy dissipation resistor. The control device includes:

[0022] The current transfer unit is used to control the main circuit switch module to disconnect when a fault is detected in the hybrid offshore wind power flexible DC system, so that the DC current of the hybrid offshore wind power flexible DC system is transferred to the energy consumption circuit where the energy consumption valve module is located, so as to increase the voltage value of each energy consumption valve unit.

[0023] An active energy dissipation unit is used to control the switching elements in the energy dissipation valve unit to consume the system surplus power of the hybrid offshore wind power flexible DC system when the voltage value of each energy dissipation valve unit reaches a preset voltage threshold, based on the output power of the offshore converter station and the preset control target voltage, combined with the preset system surplus power constraint conditions.

[0024] Preferably, the expression for the system surplus power constraint is as follows:

[0025]

[0026] In the formula, P w Let n be the output power of the offshore converter station. ch U represents the number of energy-consuming valve units with the energy-consuming resistor in the active state. C To control the target voltage, R ch This is the resistance value of the energy-consuming resistor.

[0027] A third aspect of this application also provides a control terminal for a hybrid offshore wind power flexible DC system, comprising: a memory and a processor;

[0028] The memory is used to store program code, which corresponds to a hybrid line offshore wind power flexible DC system control method as described in the first aspect of this application;

[0029] The processor is used to read and execute the program code.

[0030] The fourth aspect of this application also provides a computer-readable storage medium storing program code corresponding to the hybrid-line offshore wind power flexible DC system control method as described in the first aspect of this application. When the program code is executed by a processor, the hybrid-line offshore wind power flexible DC system control method as described in the first aspect of this application can be implemented.

[0031] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0032] The solution provided in this application is applied to a hybrid offshore wind power flexible DC system that includes a series-connected DC energy dissipation device. The series-connected DC energy dissipation device includes: a submarine cable port, an overhead line port, a main circuit switch module, and an energy dissipation valve module. The control method includes: when a fault is detected in the hybrid offshore wind power flexible DC system, the voltage at the overhead line port of the series-connected distributed DC energy dissipation device is controlled to zero according to the constant DC voltage control commonly used in onshore converter stations. Considering the voltage drop of the overhead line, the DC voltage at the onshore converter station port is negative at this time. At this time, the main circuit switch module is disconnected, so that the DC current of the hybrid offshore wind power flexible DC system is transferred to the energy dissipation circuit where the energy dissipation valve module is located, so as to raise the voltage value of each energy dissipation valve unit. When the voltage value of each energy dissipation valve unit reaches the preset voltage threshold, according to the output power of the offshore converter station and the preset control target voltage, combined with the preset system surplus power constraint, the switching elements in the energy dissipation valve unit are controlled to control the switching quantity of the energy dissipation resistors in each energy dissipation valve unit, thereby controlling the total energy consumed by the energy dissipation circuit and realizing the system surplus power balance. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This application provides a schematic diagram of the architecture of an offshore wind power flexible DC system that includes a hybrid submarine cable-overhead line.

[0035] Figure 2A schematic diagram of the circuit structure of the energy dissipation valve unit in the series DC energy dissipation device provided in this application.

[0036] Figure 3 This is a flowchart illustrating an embodiment of a hybrid-line offshore wind power flexible DC system control method provided in this application.

[0037] Figure 4 A flowchart illustrating the overall logic of the control method for a hybrid-line offshore wind power flexible DC system provided in this application.

[0038] Figure 5 A flowchart illustrating the active voltage equalization strategy logic in the control method for a hybrid offshore wind power flexible DC system provided in this application.

[0039] Figure 6 This is a schematic diagram of the structure of an embodiment of a hybrid-line offshore wind power flexible DC system control device provided in this application.

[0040] Figure 7 This is a schematic diagram of the structure of a hybrid line offshore wind power flexible DC system control terminal embodiment provided in this application. Detailed Implementation

[0041] To address the problems of existing technologies, research has revealed that current offshore wind power flexible DC transmission projects generally only use DC submarine cables, eliminating the need to consider DC fault ride-through issues. However, overhead lines have a high failure rate, and DC faults cannot be ignored. After an overhead line fault occurs, the system needs to not only clear the DC fault but also consume surplus power to prevent excessive DC voltage from triggering system protection and causing shutdowns, or even endangering equipment safety. Therefore, energy dissipation devices need to be added to the system. However, offshore wind power flexible DC transmission systems using a hybrid submarine cable-overhead line DC line system need to consider DC fault ride-through issues, but based on a full-half-bridge hybrid... When clearing DC faults, the MMC (Multi-Mechanical Control Unit) needs to reduce the DC voltage to zero or negative, which conflicts with the need to maintain a stable DC voltage when the parallel DC power dissipation device is working. Therefore, the parallel DC power dissipation device is incompatible with the hybrid submarine cable-overhead line flexible DC system and cannot effectively dissipate the surplus power of the hybrid submarine cable-overhead line system. This results in the current technical status of low reliability of the existing hybrid submarine cable-overhead line offshore wind power flexible DC system. Therefore, finding a surplus power dissipation scheme that is compatible with the hybrid submarine cable-overhead line system has become one of the key research objectives for those skilled in the art.

[0042] This application provides a control method, device, terminal, and medium for a hybrid offshore wind power flexible DC system, which addresses the technical problem of low reliability in existing offshore wind power flexible DC systems that combine submarine cables and overhead lines.

[0043] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] First, a detailed description of an embodiment of a hybrid-line offshore wind power flexible DC system used to implement the control method of this application is provided below:

[0045] Please see the figure and Figure 2 ,like Figure 1 As shown in this embodiment, the hybrid offshore wind power flexible DC system based on a series-connected DC energy dissipation device and a submarine cable-overhead line includes an offshore converter station, a submarine cable, a terminal conversion station, an overhead line, and an onshore converter station. The series-connected distributed DC energy dissipation device in the terminal conversion station consists of a main circuit and a parallel energy dissipation circuit. This device is connected in series in the positive and negative DC lines, with one end connected to the submarine cable and the other end connected to the overhead line. The main circuit includes a main circuit mechanical switch and a main circuit power electronic switch array. The main circuit power electronic switch array is composed of submodules (SMs) connected in series and parallel. Since the main circuit is used to transfer current during the switching process, it only needs to withstand a voltage drop higher than the on-state voltage drop of the power devices in the energy dissipation circuit. The number of switches connected in series is very small, so the losses generated by the main circuit power electronic switch array are negligible. The main circuit mechanical switch carries the DC current during normal operation. During a fault, the main circuit current is completely transferred to the energy dissipation circuit and then quickly switched off, bearing half of the DC bus voltage. The sub-modules in the main circuit power electronic switch array consist of power electronic switch arrays, forming a full-bridge module composed of power devices, anti-parallel diodes, and capacitors. When the power devices are in the on state, the capacitor voltage is zero; when the power devices are in the off state, the DC current charges the capacitor, and the capacitor voltage rises.

[0046] An energy-consuming valve module consists of multiple energy-consuming valve units connected in series. One feasible energy-consuming valve topology is as follows: Figure 2 As shown, each energy-consuming valve unit specifically includes: a first diode D1, a first switching transistor T1, and a dynamic voltage equalization resistor R. d Energy storage capacitor C, second diode D2, second switch T2, and energy dissipation resistor R ch ;

[0047] The cathode of the first diode D1 is connected to the first port of the energy dissipation valve unit, and the anode is connected to the second port of the energy dissipation valve unit.

[0048] The first switching transistor is connected in parallel with the first diode D1, and the anode of the first switching transistor D1 is connected to the first port of the energy dissipation valve unit, and the cathode is connected to the second port of the energy dissipation valve unit.

[0049] Dynamic voltage equalization resistor R d It is connected in parallel with the second diode D2, and the dynamic voltage equalization resistor R d One end of the diode is connected to the anode of the second diode D2 and the first port of the energy dissipation valve unit, and the dynamic voltage equalization resistor R is connected to the first port of the energy dissipation valve unit. d The other end is connected in series with the cathode of the second diode D2 and the energy storage capacitor C, and then connected to the second port of the energy dissipation valve unit to form an RCD buffer circuit;

[0050] Energy-consuming resistor R ch The second switch T2 is connected in series to form an energy-consuming resistor circuit, and the energy-consuming resistor circuit is connected in parallel with the RCD buffer circuit.

[0051] It should be noted that a single energy-consuming valve consists of a capacitor C and a dynamic voltage-equalizing resistor R. d Diode D2, power-consuming resistor R ch It consists of integrated gate commutated thyristors (IGCTs) T1 and T2, anti-parallel diode D1, and bypass switch K, R d D2 is connected in parallel with capacitor C and then in series with capacitor C to form an RCD buffer circuit. ch Together with T2, they form a power dissipation circuit. The RCD snubber circuit and the power dissipation circuit are then connected in parallel with T1, D1, and K. When T1 is on, the capacitor voltage is zero. When T1 is off, current flows through the RCD snubber circuit to charge the capacitor. The capacitor voltage can be controlled by controlling the on and off states of T1. When the capacitor voltage is maintained at the rated voltage, T2 is on to connect the power dissipation resistor, consuming the system's surplus power. When T2 is off, the power dissipation resistor is disconnected. The system's surplus power can be accurately consumed by controlling the on and off states of T2. The anti-parallel diode D1 is used to reverse the flow of DC current during the startup of the offshore converter station.

[0052] Furthermore, the energy-consuming valve unit mentioned in this embodiment is not only Figure 2 The topology shown can be used as long as the power dissipation resistor R can be controlled. ch The energy-consuming circuit topologies with input and output functions can be used as alternative implementation methods.

[0053] More specifically, the energy-consuming valve unit also includes: an energy-consuming valve bypass switch K, which is used to control the entry or exit of the energy-consuming valve unit. If the energy-consuming valve fails, the bypass switch will close. Under normal operating conditions, the switch will open or activate when the energy-consuming valve voltage is too high, in order to protect the device from overvoltage damage.

[0054] It is understood that the series-connected DC power consumption device mentioned in this embodiment is equipped with a control device. The control device is specifically used to control each switching element in the series-connected DC power consumption device according to the control method of this application, thereby realizing the control method provided by this application. The specific description of the control method and the control device can be found in the following embodiment description.

[0055] Then comes a detailed description of the control method for a hybrid-line offshore wind power flexible DC system provided in this application, as follows:

[0056] Please see Figure 3 and Figure 4 This embodiment provides a control method for a hybrid-line offshore wind power flexible DC system, including:

[0057] Step 101: When a fault is detected in the hybrid offshore wind power flexible DC system, the main circuit switch module is disconnected, so that the DC current of the hybrid offshore wind power flexible DC system is transferred to the energy consumption circuit where the energy consumption valve module is located, so as to increase the voltage value of each energy consumption valve unit.

[0058] It should be noted that when the system is not faulty, the mechanical switch of the main circuit is closed, the power devices of the power electronic switch array are turned on, and the current of the system only flows through the main circuit to the onshore converter station. In the energy consumption circuit, the power devices T1 of each energy consumption valve are turned on, T2 is turned off, and the energy consumption resistor is in the bypass cut-out state.

[0059] When a system fault occurs, it first enters the current transfer control stage corresponding to step 101, which specifically includes: shutting down the power devices of the power electronic switch array in the main circuit and raising the capacitor voltage; opening the mechanical switch when the main circuit current crosses zero. After the mechanical switch is in the open position, the power devices T1 of each energy-consuming valve in the energy-consuming circuit are closed, and the capacitor voltage is raised.

[0060] Step 102: When the voltage value of each energy-consuming valve unit reaches the preset voltage threshold, based on the output power of the offshore converter station and the preset control target voltage, combined with the preset system surplus power constraint, the switching elements in the energy-consuming valve unit are controlled to consume the system surplus power of the hybrid offshore wind power flexible DC system.

[0061] It should be noted that after the voltage value of each energy dissipation valve unit reaches a certain level, it enters the active energy dissipation processing stage corresponding to step 102. In order to ensure the consistency of the capacitor voltage of each energy dissipation valve, when the capacitor voltage of each energy dissipation valve rises to the rated voltage, the power device T2 is controlled to be turned on or off in accordance with the system surplus power constraint conditions of the embodiment to accurately consume the system surplus power.

[0062] More specifically, the expression for the system surplus power constraint is as follows:

[0063]

[0064] In the formula, P w For the output power of the offshore converter station, n ch U represents the number of energy-consuming valve units with the energy-consuming resistor in the active state. C To control the target voltage, R ch This is the resistance value of the energy-consuming resistor.

[0065] When an overhead line fault occurs, the offshore converter station continues to use VF control to maintain stable AC voltage. The onshore converter station continues to use constant DC voltage control, with the control objective being to bring the voltage at the overhead line port of the series-connected distributed DC energy dissipation device to zero. Considering the voltage drop of the overhead line, the DC voltage at the onshore converter station port is negative at this time. With both the mechanical switch and the power electronic switch array of the main circuit of the series-connected distributed energy dissipation device closed, DC current flows through the energy dissipation circuit. The energy dissipation valve controls the voltage across it by controlling the conduction and disconnection of the T1 switch transistor. The control objective is the rated voltage U. C And satisfy Where N is the number of energy-consuming valves in a single series distributed energy-consuming device, U dc This is the rated voltage for the DC system.

[0066] To balance the system's surplus power, a series distributed energy dissipation device is used to acquire the power P transmitted from the offshore converter station. w When the T2 switching transistor of the energy-consuming valve is turned on, the energy consumed by the energy-consuming valve is Therefore, by controlling the switching transistors of each energy-consuming valve T2, the total energy consumed by the energy-consuming circuit can be controlled, and the following conditions are met. , where n ch The number of energy-consuming valves with switch T2 in the active state, according to The constraint formula is used to determine the number of energy-consuming valves that need to be connected to the energy-consuming resistor, and the on / off state of the T2 switch in each energy-consuming valve unit is controlled according to the number.

[0067] In addition, while controlling the power device T2 to consume the system's surplus power, a preset active voltage equalization strategy can be used to control the conduction and cutoff of the power device T1 to maintain the capacitor voltage stability, thereby further improving the system's stability and reliability in the surplus power processing process.

[0068] It should be noted that when the mechanical switch is in the open position, the power devices T1 of each energy-consuming valve in the energy-consuming circuit are disconnected, and the capacitor voltage rises. When the capacitor voltage rises beyond a certain limit, in order to ensure the consistency of the capacitor voltage of each energy-consuming valve, an active voltage equalization strategy can be adopted to control the conduction and cutoff of the power devices T1 to maintain the stability of the capacitor voltage. The active voltage equalization strategy is as follows: Figure 5As shown, where U sm_avg This represents the average voltage value of each energy-consuming valve. This is the voltage equalization threshold, used to reduce the switching frequency of power device T1. If the voltage U of the i-th energy dissipation valve... smi Greater than This indicates that the voltage of the energy-consuming valve is too high, which will turn on the power device T1. At this time, the capacitor will flow through R. d T1 discharges; if the voltage U of the i-th energy-consuming valve... smi Less than If the voltage of the energy dissipation valve is too low, then the power device T1 is disconnected. At this time, the DC current will charge the capacitor through diode D2. If the voltage of the i-th energy dissipation valve is U... smi In If so, the current switch state remains unchanged.

[0069] The above is a detailed description of an embodiment of a hybrid-line offshore wind power flexible DC system control method provided in this application. The following is a detailed description of an embodiment of a hybrid-line offshore wind power flexible DC system control device provided in this application.

[0070] Please see Figure 6 This embodiment provides a control device for a hybrid-line offshore wind power flexible DC system, applied to a hybrid-line offshore wind power flexible DC system including a series-connected DC energy dissipation device. The control device includes:

[0071] The current transfer unit 201 is used to control the main circuit switch module to disconnect when a fault is detected in the hybrid line offshore wind power flexible DC system, so that the DC current of the hybrid line offshore wind power flexible DC system is transferred to the energy consumption circuit where the energy consumption valve module is located, so as to increase the voltage value of each energy consumption valve unit.

[0072] The active energy dissipation unit 202 is used to control the switching elements in the energy dissipation valve unit to consume the system surplus power of the hybrid line offshore wind power flexible DC system when the voltage value of each energy dissipation valve unit reaches the preset voltage threshold, based on the output power of the offshore converter station and the preset control target voltage, combined with the preset system surplus power constraint conditions.

[0073] More specifically, the expression for the system surplus power constraint is as follows:

[0074]

[0075] In the formula, P w For the output power of the offshore converter station, n ch U represents the number of energy-consuming valve units with the energy-consuming resistor in the active state. C To control the target voltage, R ch This is the resistance value of the energy-consuming resistor.

[0076] Furthermore, increasing the voltage value of each energy-consuming valve unit includes:

[0077] The first switch in the energy dissipation valve unit is turned off, so that the DC current flows to the energy storage capacitor in the energy dissipation valve unit. The first switch is a bypass switch for the energy storage capacitor, used to control the connection or bypass of the energy storage capacitor.

[0078] Furthermore, when the voltage value of each energy-consuming valve unit reaches a preset voltage threshold, the following steps are also included:

[0079] Monitor the capacitor voltage value of each energy-consuming valve unit, and control the on / off state of the first switching transistor based on the comparison result of the capacitor voltage value with the upper and lower voltage thresholds.

[0080] Furthermore, based on the comparison results between the capacitor voltage value and the upper and lower voltage thresholds, controlling the on / off state of the first switch specifically includes:

[0081] When the capacitor voltage is not less than the lower voltage threshold and not greater than the upper voltage threshold, maintain the current on / off state of the first switch.

[0082] When the capacitor voltage is lower than the lower voltage threshold, the first switch is disconnected;

[0083] When the capacitor voltage is greater than the lower voltage threshold, the first switch is closed.

[0084] Furthermore, the methods for determining the upper and lower voltage thresholds specifically include:

[0085] Based on the average capacitor voltage value of each energy-consuming valve unit, the upper and lower voltage thresholds are determined according to the sum and difference between the average capacitor voltage value and the preset equalization threshold.

[0086] like Figure 7 As shown, this application also provides a hybrid line offshore wind power flexible DC system control terminal, including: a memory and a processor;

[0087] The memory is used to store program code, which corresponds to a hybrid line offshore wind power flexible DC system control method mentioned in the above embodiments;

[0088] The processor is used to read and execute program code.

[0089] This application also provides a computer-readable storage medium storing program code corresponding to a hybrid-line offshore wind power flexible DC system control method mentioned in the above embodiments. When the program code is executed by a processor, the hybrid-line offshore wind power flexible DC system control method mentioned in the above embodiments can be implemented.

[0090] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the terminals, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0091] In the several embodiments provided in this application, it should be understood that the disclosed terminals, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between devices or units, and may be electrical, mechanical, or other forms.

[0092] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0093] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0094] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0095] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0096] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0097] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A control method for a hybrid-line offshore wind power flexible DC system, applied to a hybrid-line offshore wind power flexible DC system including a series-connected DC energy dissipation device, characterized in that, The series-connected DC energy dissipation device includes: a submarine cable port, an overhead line port, a main circuit switch module, and an energy dissipation valve module. The main circuit switch module and the energy dissipation valve module are disposed between the submarine cable port and the overhead line port. The main circuit switch module and the energy dissipation valve module are connected in parallel. The main circuit switch module includes: a mechanical switch and a power electronic switch component. Multiple energy dissipation valve units are connected in series in the energy dissipation valve module. Each energy dissipation valve unit includes a first switching transistor, an energy storage capacitor, an energy dissipation resistor, and a second switching transistor. The first switching transistor is connected in parallel with the energy storage capacitor to control the connection or bypass of the energy storage capacitor. The energy dissipation resistor and the second switching transistor are connected in series and then in parallel with the energy storage capacitor. The control method includes: When a fault is detected in the hybrid offshore wind power flexible DC system, the power electronic switch power component is controlled to shut down and the mechanical switch is opened when the main circuit current crosses zero, so that the DC current of the hybrid offshore wind power flexible DC system is transferred to the energy consumption circuit where the energy consumption valve module is located, and the first switch tube in the energy consumption valve unit is controlled to open, so that the DC current flows to the energy storage capacitor in the energy consumption valve unit. When the voltage value of each energy-consuming valve unit reaches the preset voltage threshold, the second switch tube in the energy-consuming valve unit is controlled to consume the system surplus power of the hybrid line offshore wind power flexible DC system, based on the output power of the offshore converter station and the preset control target voltage, combined with the preset system surplus power constraint conditions.

2. The control method for a hybrid offshore wind power flexible DC system according to claim 1, characterized in that, The specific expression for the system surplus power constraint is as follows: P w = n ch * U C 2 / R ch In the formula, P w This refers to the output power of the offshore converter station. n ch This represents the number of energy-consuming valve units where the energy-consuming resistor is in the active state. U C To control the target voltage, R ch This is the resistance value of the energy-consuming resistor.

3. The control method for a hybrid offshore wind power flexible DC system according to claim 1, characterized in that, When the voltage value of each energy-consuming valve unit reaches a preset voltage threshold, the method further includes: Monitor the capacitor voltage value of each energy-consuming valve unit, and control the on / off state of the first switching transistor based on the comparison result of the capacitor voltage value with the upper and lower voltage thresholds.

4. The control method for a hybrid offshore wind power flexible DC system according to claim 3, characterized in that, Controlling the on / off state of the first switch transistor based on the comparison result between the capacitor voltage value and the upper and lower voltage thresholds specifically includes: When the capacitor voltage value is not less than the lower voltage threshold and not greater than the upper voltage threshold, the current on / off state of the first switch is maintained. When the capacitor voltage value is less than the lower voltage threshold, the first switch is disconnected; When the capacitor voltage value is greater than the upper voltage threshold, the first switch is closed.

5. The control method for a hybrid offshore wind power flexible DC system according to claim 3, characterized in that, The method for determining the upper and lower voltage thresholds specifically includes: Based on the average capacitor voltage value of each energy-consuming valve unit, the upper and lower voltage thresholds are determined according to the sum and difference between the average capacitor voltage value and the preset equalization threshold.

6. A control device for a hybrid-line offshore wind power flexible DC system, applied to a hybrid-line offshore wind power flexible DC system including a series-connected DC energy dissipation device, characterized in that, The series-connected DC energy dissipation device includes: a submarine cable port, an overhead line port, a main circuit switch module, and an energy dissipation valve module. The main circuit switch module and the energy dissipation valve module are disposed between the submarine cable port and the overhead line port. The main circuit switch module and the energy dissipation valve module are connected in parallel. The main circuit switch module includes: a mechanical switch and a power electronic switch component. Multiple energy dissipation valve units are connected in series in the energy dissipation valve module. Each energy dissipation valve unit includes a first switching transistor, an energy storage capacitor, an energy dissipation resistor, and a second switching transistor. The first switching transistor is connected in parallel with the energy storage capacitor to control the connection or bypass of the energy storage capacitor. The energy dissipation resistor and the second switching transistor are connected in series and then in parallel with the energy storage capacitor. The control device includes: The current transfer unit is used to control the power electronic switch power component to shut down when a fault is detected in the hybrid line offshore wind power flexible DC system, and to open the mechanical switch when the main circuit current crosses zero, so that the DC current of the hybrid line offshore wind power flexible DC system is transferred to the energy consumption circuit where the energy consumption valve module is located, and to control the first switch tube in the energy consumption valve unit to open, so that the DC current flows to the energy storage capacitor in the energy consumption valve unit; The active energy dissipation unit is used to control the on / off state of the second switch tube in the energy dissipation valve unit when the voltage value of each energy dissipation valve unit reaches the preset voltage threshold, based on the output power of the offshore converter station and the preset control target voltage, combined with the preset system surplus power constraint conditions, so as to consume the system surplus power of the hybrid line offshore wind power flexible DC system.

7. A hybrid-line offshore wind power flexible DC system control device according to claim 6, characterized in that, The specific expression for the system surplus power constraint is as follows: P w = n ch * U C 2 / R ch In the formula, P w This refers to the output power of the offshore converter station. n ch This represents the number of energy-consuming valve units where the energy-consuming resistor is in the active state. U C To control the target voltage, R ch This is the resistance value of the energy-consuming resistor.

8. A control terminal for a hybrid offshore wind power flexible DC system, characterized in that, include: Memory and processor; The memory is used to store program code, which corresponds to the hybrid line offshore wind power flexible DC system control method as described in any one of claims 1 to 5; The processor is used to read and execute the program code.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores program code corresponding to the hybrid-line offshore wind power flexible DC system control method as described in any one of claims 1 to 5. When the program code is executed by a processor, the hybrid-line offshore wind power flexible DC system control method as described in any one of claims 1 to 5 can be implemented.

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