A DC fault ride-through method, device and equipment for a flexible DC transmission system

Abstract

The present application relates to a DC fault ride-through method, device and equipment for a flexible DC transmission system. The method includes obtaining the output power of the system, a fault signal and the energy-consuming resistance of a series centralized DC energy-consuming device; calculating voltage data based on the energy-consuming resistance and the output power; when the fault signal is transmitted to the onshore converter station, controlling the onshore converter station to operate in a constant DC voltage control mode and controlling the positive and negative voltages of the overhead line ports of the series centralized DC energy-consuming device to be zero; when the fault signal is transmitted to the offshore converter station, controlling the offshore converter station to operate in a VF control mode and controlling the positive and negative voltages of the submarine cable ports of the series centralized DC energy-consuming device to be the voltage data; when the fault signal is transmitted to the series centralized energy-consuming device, controlling all the switching tubes in the series centralized energy-consuming device to be in the off state and its energy-consuming elements to be in the energy-consuming working state; realizing the clearing of overhead line faults and the balance of surplus power in the system, and improving the reliability of the system.

Description

Technical Field

[0001] The present application relates to the technical field of DC fault ride-through, and particularly to a DC fault ride-through method, device and equipment for a flexible DC power transmission system. Background Art

[0002] Offshore wind energy has the advantages of rich reserves and higher energy efficiency, and is not restricted by land resources and population distribution. Offshore wind power has become the focus of current and future wind power development. With the development of offshore wind power towards large capacity and deep sea areas, in order to further compress the land-sea transmission lines and reduce the transmission cost, the scheme of directly sending offshore wind power to the load center through a hybrid DC line of submarine cable - overhead line will become the preferred scheme for the scenario of directly sending ultra-large-scale offshore wind power to the load center in the future.

[0003] Although the overhead line can significantly reduce the transmission cost, its failure rate is relatively high, and the flexible DC power transmission system is required to have the ability to handle DC faults. The existing fault handling methods mainly include the DC circuit breaker scheme and the full half-bridge hybrid MMC scheme, but the equipment cost of the DC circuit breaker is relatively high and its reliability cannot be guaranteed.

[0004] In addition, during a DC fault, it is difficult for the fan power of an offshore wind farm to respond in a timely manner, and the surplus power will accumulate on the DC line, resulting in a rapid increase in the DC voltage. If no measures are taken, it will trigger overvoltage protection, causing the flexible DC power transmission system to shut down, and even endangering the safety of power equipment in the system. The existing methods for handling surplus power include AC centralized energy-consuming devices and parallel DC energy-consuming devices. However, the AC centralized energy-consuming device will increase the investment cost and construction difficulty of the offshore platform, and is generally not used in the scenario of transmitting offshore wind power. The existing parallel DC energy-consuming device conflicts with the logic that a stable DC voltage needs to be maintained and the DC voltage needs to be controlled to zero when the full half-bridge hybrid MMC clears a DC fault, and it must be used in cooperation with a DC circuit breaker. Therefore, the existing methods for handling surplus power are difficult to be directly applied to the flexible DC power transmission system composed of a submarine cable and an overhead line. Summary of the Invention

[0005] The present application provides a DC fault ride-through method, device and equipment for a flexible DC power transmission system, which are used to solve the technical problem that the existing methods for handling surplus power are difficult to be directly applied to the flexible DC power transmission system composed of a submarine cable and an overhead line.

[0006] To achieve the above object, the present application provides the following technical solutions:

[0007] On the one hand, a DC fault ride-through method for a flexible DC transmission system is provided, which is applied to a flexible DC transmission system. The flexible DC transmission system includes an offshore converter station, an onshore converter station, and multiple hybrid DC lines composed of submarine cables and overhead lines connected between the offshore converter station and the onshore converter station. A series centralized DC energy-consuming device is connected in series on each of the hybrid DC lines. The DC fault ride-through method for the flexible DC transmission system includes the following steps:

[0008] Obtain the output power of the wind farm in the flexible DC transmission system and the fault signal after a DC fault occurs on the overhead line, and also obtain the energy-consuming resistance of the series centralized DC energy-consuming device; calculate based on the energy-consuming resistance and the output power to obtain voltage data;

[0009] When the fault signal is transmitted to the onshore converter station, control the onshore converter station to operate in a constant DC voltage control mode, and control the positive and negative terminal voltages of the port of the series centralized DC energy-consuming device at the overhead line end to be zero;

[0010] When the fault signal is transmitted to the offshore converter station, control the offshore converter station to operate in a VF control mode, and control the positive and negative terminal voltages of the port of the series centralized DC energy-consuming device at the submarine cable end to be the voltage data;

[0011] When the fault signal is transmitted to the series centralized DC energy-consuming device, control all the switching tubes in the series centralized energy-consuming device to be in the off state and its energy-consuming element to be in the energy-consuming working state.

[0012] Preferably, to control the positive and negative terminal voltages of the port of the series centralized DC energy-consuming device at the overhead line end to be zero, the DC fault ride-through method includes:

[0013] Obtain a reference voltage;

[0014] Compare and process the positive and negative terminal voltages of the port of the series centralized DC energy-consuming device at the overhead line end with the reference voltage to obtain a first voltage;

[0015] Process the first voltage by using a PI controller to obtain a first pole-to-pole voltage control reference value for controlling the operation of the onshore converter station.

[0016] Preferably, the DC fault ride-through method for the flexible DC transmission system includes: if the flexible DC transmission system is in a steady-state operation working condition, control the energy-consuming element of the series centralized DC energy-consuming device to be in a bypass state, and control the operation of the offshore converter station by using the VF control mode and control the operation of the onshore converter station by using a constant DC voltage control mode.

[0017] Preferably, the port positive and negative voltages of the series centralized DC energy dissipation device located at this end of the submarine cable are controlled to be the voltage data, and this DC fault ride-through method includes:

[0018] Compare and process the port positive and negative voltages of the series centralized DC energy dissipation device located at this end of the submarine cable with the voltage data to obtain a second voltage;

[0019] Use a PI controller to process the second voltage to obtain a second pole-to-pole voltage control reference value for controlling the operation of the offshore converter station.

[0020] Preferably, this DC fault ride-through method of the flexible DC power transmission system includes: calculating voltage data according to the energy dissipation resistance and the output power using a voltage calculation formula; the voltage calculation formula is: , where U control is the voltage data, P0 is the output power, and R ch is the energy dissipation resistance.

[0021] On the other hand, a DC fault ride-through device for a flexible DC power transmission system is provided, which is applied to a flexible DC power transmission system. The flexible DC power transmission system includes an offshore converter station, an onshore converter station, and multiple hybrid DC lines composed of submarine cables and overhead lines connected between the offshore converter station and the onshore converter station. A series centralized DC energy dissipation device is connected in series on each of the hybrid DC lines. The DC fault ride-through device of the flexible DC power transmission system includes a data acquisition module, a first fault processing and control module, a second fault processing and control module, and a third fault processing and control module;

[0022] The data acquisition module is used to acquire the output power of the wind farm in the flexible DC power transmission system and the fault signal after a DC fault occurs on the overhead line, and also acquire the energy dissipation resistance of the series centralized DC energy dissipation device; calculate voltage data according to the energy dissipation resistance and the output power;

[0023] The first fault processing and control module is used to transmit the fault signal to the onshore converter station, control the operation of the onshore converter station in a constant DC voltage control mode, and control the port positive and negative voltages of the series centralized DC energy dissipation device located at this end of the overhead line to be zero;

[0024] The second fault processing and control module is used to transmit the fault signal to the offshore converter station, control the operation of the offshore converter station in a VF control mode, and control the port positive and negative voltages of the series centralized DC energy dissipation device located at this end of the submarine cable to be the voltage data;

[0025] The third fault handling control module is configured to control all the switching tubes in the series centralized DC energy dissipation device to be in an off state and its energy dissipation elements to be in an energy dissipation working state according to the fault signal transmitted to the series centralized DC energy dissipation device.

[0026] Preferably, the DC fault ride-through device of the flexible DC power transmission system includes an onshore pole-to-pole control module, which is configured to obtain a reference voltage; compare and process the positive and negative terminal voltages of the port of the series centralized DC energy dissipation device at the overhead line end with the reference voltage to obtain a first voltage; and process the first voltage by using a PI controller to obtain a first pole-to-pole voltage control reference value for controlling the operation of the onshore converter station.

[0027] Preferably, the DC fault ride-through device of the flexible DC power transmission system includes an offshore pole-to-pole control module, which is configured to compare and process the positive and negative terminal voltages of the port of the series centralized DC energy dissipation device at the submarine cable end with the voltage data to obtain a second voltage; and process the second voltage by using a PI controller to obtain a second pole-to-pole voltage control reference value for controlling the operation of the offshore converter station.

[0028] Preferably, the data acquisition module is further configured to calculate voltage data according to the energy dissipation resistor and the output power by using a voltage calculation formula; the voltage calculation formula is: , where U control is the voltage data, P0 is the output power, and R ch is the energy dissipation resistor.

[0029] On the other hand, a terminal device is provided, which includes a processor and a memory;

[0030] The memory is configured to store program codes and transmit the program codes to the processor;

[0031] The processor is configured to execute the DC fault ride-through method of the flexible DC power transmission system according to the instructions in the program codes.

[0032] The DC fault ride-through method, device and equipment for a flexible DC power transmission system. The DC fault ride-through method for the flexible DC power transmission system includes obtaining the output power of a wind farm in the flexible DC power transmission system and a fault signal after a DC fault occurs in an overhead line, and also obtaining the energy-consuming resistance of a series centralized DC energy-consuming device; calculating based on the energy-consuming resistance and the output power to obtain voltage data; when the fault signal is transmitted to an onshore converter station, controlling the onshore converter station to operate in a constant DC voltage control mode and controlling the positive and negative voltages of the ports of the series centralized DC energy-consuming device located at this end of the overhead line to be zero; when the fault signal is transmitted to an offshore converter station, controlling the offshore converter station to operate in a VF control mode and controlling the positive and negative voltages of the ports of the series centralized DC energy-consuming device located at this end of the submarine cable to be the voltage data. When the fault signal is transmitted to the series centralized DC energy-consuming device, controlling all switching tubes in the series centralized DC energy-consuming device to be in the off state and its energy-consuming elements to be in the energy-consuming working state.

[0033] As can be seen from the above technical solutions, the present application has the following advantages: The DC fault ride-through method for the flexible DC power transmission system can achieve the clearing of overhead line faults and the balance of surplus power in the flexible DC power transmission system by obtaining the fault type and using different control methods to control the operation of the offshore converter station, onshore converter station and series centralized DC energy-consuming device and the setting of parameters, improving the reliability of the flexible DC power transmission system and solving the technical problem that the existing surplus power processing method is difficult to be directly applied to the flexible DC power transmission system with a hybrid DC line composed of a submarine cable and an overhead line.

[0034] The DC fault ride-through device for the flexible DC power transmission system realizes the clearing of overhead line faults and the balance of surplus power in the flexible DC power transmission system through the mutual cooperation of a data acquisition module, a first fault processing control module, a second fault processing control module and a third fault processing control module, improving the reliability of the flexible DC power transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is a flowchart of the steps of the DC fault ride-through method for the flexible DC power transmission system described in the embodiments of the present application;

[0037] Figure 2 It is a framework flowchart of the DC fault ride-through method for the flexible DC power transmission system described in the embodiments of the present application;

[0038] Figure 3 Schematic diagram of the topological structure of the flexible DC power transmission system described in the embodiments of the present application;

[0039] Figure 4 Schematic diagram of the topological structure of the energy-consuming component in the DC fault ride-through method of the flexible DC power transmission system described in the embodiments of the present application;

[0040] Figure 5 Equivalent circuit diagram of the flexible DC power transmission system in the DC fault ride-through method of the flexible DC power transmission system described in the embodiments of the present application;

[0041] Figure 6 Polar voltage control block diagram of the onshore converter station during a fault in the DC fault ride-through method of the flexible DC power transmission system described in the embodiments of the present application;

[0042] Figure 7 Polar voltage control block diagram of the offshore converter station during a fault in the DC fault ride-through method of the flexible DC power transmission system described in the embodiments of the present application;

[0043] Figure 8 Frame schematic diagram of the DC fault ride-through device of the flexible DC power transmission system described in the embodiments of the present application;

[0044] Figure 9 Schematic diagram of the terminal device described in the embodiments of the present application. Detailed implementation manners

[0045] In order to make the object, features, and advantages of the present application more obvious and understandable, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the embodiments described below are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0046] In the description of the embodiments of the present application, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present application, "a plurality of" means two or more unless otherwise specifically defined.

[0047] In the embodiments of the present application, unless otherwise clearly specified and limited, terms such as "installation", "connection", "linkage", "fixation", etc. shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral one; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0048] Patent terms:

[0049] The VF control mode refers to the constant voltage and constant frequency control mode.

[0050] The embodiments of the present application provide a DC fault ride-through method, device and equipment for a flexible DC power transmission system, which can clear faults and maintain the surplus power balance of the system when a DC fault occurs in the flexible DC power transmission system, avoid the shutdown of the flexible DC power transmission system, and solve the technical problem that the existing surplus power processing method is difficult to be directly applied to the flexible DC power transmission system with a hybrid DC line composed of submarine cables and overhead lines.

[0051] Embodiment 1:

[0052] Figure 1 It is a step flowchart of the DC fault ride-through method for the flexible DC power transmission system described in the embodiments of the present application. Figure 2 It is a framework flowchart of the DC fault ride-through method for the flexible DC power transmission system described in the embodiments of the present application. Figure 3 It is a schematic diagram of the topological structure of the flexible DC power transmission system described in the embodiments of the present application.

[0053] As Figure 3 shown, the embodiments of the present application provide a DC fault ride-through method for a flexible DC power transmission system, which is applied to the flexible DC power transmission system. The flexible DC power transmission system includes an offshore converter station 10, an onshore converter station 20, and multiple hybrid DC lines 30 composed of submarine cables and overhead lines connected between the offshore converter station 10 and the onshore converter station 20. A series centralized DC energy dissipation device 40 is connected in series on each hybrid DC line 30.

[0054] It should be noted that as Figure 3As shown, the input end of the offshore converter station 10 is connected to the offshore wind farm, and the output end of the onshore converter station 20 is connected to the load center. In this embodiment, the output end of the offshore converter station 10 is connected to the positive submarine cable and the negative submarine cable, and the input end of the onshore converter station 20 is connected to the positive overhead line and the negative overhead line. A series centralized DC energy dissipation device 40 is connected in series between the positive submarine cable and the positive overhead line, and a series centralized DC energy dissipation device 40 is connected in series between the negative submarine cable and the negative overhead line. Among them, the positive submarine cable and the positive overhead line form a hybrid DC line 30, and the negative submarine cable and the negative overhead line form another hybrid DC line 30. Among them, the series centralized DC energy dissipation device is installed on each hybrid DC line 30, and the ports of the offshore converter station 10 are respectively connected to the DC submarine cables, and the ports of the onshore converter station 20 are respectively connected to the DC overhead lines.

[0055] In the embodiment of the present application, the series centralized DC energy dissipation device 40 includes an energy dissipation component 41, a current limiting element 42 and an energy dissipation element 43. One end of the energy dissipation component 41 is respectively connected to the second end of the energy dissipation element 43 and the hybrid DC line 30 at the offshore converter station 10 end, and the other end of the energy dissipation component 41 is respectively connected to the first end of the current limiting element 42. The second end of the current limiting element 42 is respectively connected to the second end of the energy dissipation element 43 and the hybrid DC line 30 at the onshore converter station 20 end.

[0056] It should be noted that the current limiting element 42 can be selected as an inductor; and / or, the energy dissipation element 43 can be selected as a resistor. In this embodiment, the energy dissipation component 41 and the current limiting element 42 are connected in series and then connected in parallel with the energy dissipation element 43. Considering that a fault occurs when the flexible DC transmission system operates at the rated power P N When running, the maximum voltage borne by the energy dissipation component 41 is the DC bus voltage U dc . In addition, if the energy dissipation element 43 needs to consume all the power, the resistance value of the energy dissipation element 43 is . In addition, during the fault of the flexible DC transmission system, the maximum pressure borne by the series-connected energy dissipation components 41 is half of the DC bus voltage, that is .

[0057] In the embodiment of the present application, the series centralized DC energy dissipation device is connected in series on each hybrid DC line of the submarine cable - overhead line, and the series centralized DC energy dissipation device is used to solve the fault ride-through and surplus power balance problems of the flexible DC transmission system.

[0058] It should be noted that during the process of solving the fault ride-through and surplus power balance problems of the flexible DC transmission system by this series centralized DC energy dissipation device, the voltage across the energy dissipation element 43 can also be lifted by the current limiting element 42 before the energy dissipation component 41 operates, for passive energy dissipation. Therefore, the series centralized DC energy dissipation device has a faster response and can consume the surplus power immediately after a fault occurs in the flexible DC transmission system. The energy dissipation element 43 and the current limiting element 42 jointly limit the DC fault current, and the amplitude of the DC fault current is lower.

[0059] Figure 4 Schematic diagram of the topology structure of the energy dissipation component in the DC fault ride-through method of the flexible DC transmission system described in the embodiment of the present application.

[0060] As Figure 4 shown, in an embodiment of the present application, the energy dissipation component 41 includes several energy dissipation valves connected in series. Each energy dissipation valve includes an RCD buffer circuit and a switching tube T, an antiparallel diode D1, and a bypass switch K connected in parallel with the RCD buffer circuit. The RCD buffer circuit includes a capacitor C, a dynamic voltage equalizing element R d and a semiconductor device D2. The dynamic voltage equalizing element R d is connected in parallel with the semiconductor device D2 and then in series with the capacitor C.

[0061] It should be noted that the dynamic voltage equalizing element R d can be selected as a resistor; and / or, the semiconductor device D2 can be selected as a diode; and / or, the switching tube T can be selected as an integrated gate-commutated thyristor. In the embodiment of the present application, when the switching tube T is turned on, the DC current of the flexible DC transmission system flows through the switching tube T; when the switching tube T is turned off, the DC current of the flexible DC transmission system flows through the RCD buffer circuit and charges the capacitor C at the same time, and the port voltage across the energy dissipation valve increases. The antiparallel diode D1 is used to conduct the reverse DC current when the offshore converter station 10 starts. The bypass switch K operates when the voltage of the energy dissipation valve is too high to protect the device from overvoltage damage. Among them, the RCD buffer circuit is used to avoid excessive charging and discharging currents when the capacitor C is charged and discharged.

[0062] In the embodiment of the present application, the number of energy dissipation valves connected in series in the energy dissipation component 41 is N ch , then the maximum voltage borne by the energy dissipation component 41 is , U ch is the rated voltage of a single energy dissipation valve.

[0063] Figure 5 Equivalent circuit diagram of the flexible DC transmission system in the DC fault ride-through method of the flexible DC transmission system described in the embodiment of the present application.

[0064] As Figure 5 shown, in the embodiment of the present application, Up_off , U n_off and U pch_ca , U nch_ca are respectively the positive and negative bus voltages of the offshore converter station 10, and U pch_oh , U nch_oh are respectively the positive and negative port voltages of the series centralized DC energy-consuming device 40 located at this end of the submarine cable, and U p_on , U n_on are respectively the positive and negative port voltages of the series centralized DC energy-consuming device 40 located at this end of the overhead line, and U p_on , U n_on are respectively the positive and negative bus voltages of the onshore converter station 20. R ca represents the equivalent resistance of the submarine cable, and R oh represents the equivalent resistance of the overhead line.

[0065] As Figure 1 and Figure 2 shown, the DC fault ride-through method of this flexible DC power transmission system includes the following steps:

[0066] S1. Obtain the output power of the wind farm in the flexible DC power transmission system and the fault signal after a DC fault occurs in the overhead line, and also obtain the energy-consuming resistance of the series centralized DC energy-consuming device; calculate based on the energy-consuming resistance and the output power to obtain voltage data.

[0067] It should be noted that in step S1, data of the flexible DC power transmission system and the series centralized DC energy-consuming device are obtained. The data includes the output power of the wind farm in the flexible DC power transmission system, the fault signal after a DC fault occurs in the overhead line of the flexible DC power transmission system, and the energy-consuming resistance of the series centralized DC energy-consuming device.

[0068] S2. When the fault signal is transmitted to the onshore converter station, control the operation of the onshore converter station in the constant DC voltage control mode, and control the positive and negative port voltages of the series centralized DC energy-consuming device located at this end of the overhead line to be zero.

[0069] It should be noted that in step S2, the operation of the offshore converter station 10, the onshore converter station 20, and the series centralized DC energy dissipation device 40 is controlled according to the fault type obtained in step S1. In this embodiment, when a fault occurs in the DC overhead line between the series centralized DC energy dissipation device 40 and the onshore converter station 20, in order to clear the fault, it is necessary to reduce the positive and negative terminal voltages of the port of the series centralized DC energy dissipation device at this end of the overhead line to zero or a negative voltage. Therefore, when the fault signal is transmitted to the onshore converter station 20 (it can be understood that the onshore converter station 20 detects the occurrence of a fault), considering the voltage drop of the hybrid DC line, in order to ensure that the inter-pole voltage of the entire overhead line is equal to zero or a negative voltage, the maximum positive and negative terminal voltages of the port of the series centralized DC energy dissipation device 40 at this end of the overhead line need to be controlled to zero, that is, by controlling the inter-pole voltage of the onshore converter station 20 during the fault, the positive and negative terminal voltages of the port of the series centralized DC energy dissipation device 40 at this end of the overhead line are controlled to zero. Among them, the constant DC voltage control mode is a relatively mature technology in this field, and the content of the constant DC voltage control mode will not be elaborated in detail in this embodiment.

[0070] S3. When the fault signal is transmitted to the offshore converter station, the VF control mode is used to control the operation of the offshore converter station, and the positive and negative terminal voltages of the port of the series centralized DC energy dissipation device at this end of the submarine cable are controlled to the voltage data.

[0071] It should be noted that in step S3, the fault signal obtained in step S1 is transmitted to the offshore converter station to control the operation of the offshore converter station and the parameters of the series centralized DC energy dissipation device. In this embodiment, after the fault signal is transmitted to the offshore converter station 10, the differential mode component (dq-axis component) of the offshore converter station 10 still adopts the VF control mode to control and provide a stable grid-connected voltage for the wind farm; the common mode component (DC offset) of the offshore converter station 10, that is, the inter-pole voltage, needs to be controlled according to the output power P0 of the wind farm, the positive and negative terminal voltages U pch_ca 、U nch_ca of the port of the series centralized DC energy dissipation device 40 at this end of the submarine cable, and the energy dissipation resistor R ch That is, the control target of the inter-pole voltage of the offshore converter station 10 during the fault is to control the positive and negative terminal voltages of the port of the series centralized DC energy dissipation device 40 at this end of the submarine cable to the voltage data. Among them, the VF control mode is a relatively mature technology in this field, and the content of the VF control mode will not be elaborated in detail in this embodiment. The inter-pole voltage of the offshore converter station 10 is equal to the common mode component multiplied by the sub-module capacitor voltage.

[0072] S4. When the fault signal is transmitted to the series centralized DC energy dissipation device, control all the switching tubes in the series centralized DC energy dissipation device to be in the off state and its energy dissipation element to be in the energy dissipation working state.

[0073] It should be noted that in step S4, the fault signal obtained in step S1 is transmitted to the series centralized DC energy dissipation device. It can be understood that when the series centralized DC energy dissipation device 40 detects a fault, the switching tubes T of each energy dissipation valve are turned off, and the fault DC current of the flexible DC transmission system flows through the energy dissipation element 43, and the voltage across the two ends of the energy dissipation element 43 increases, restricting the increase of the fault DC current.

[0074] A DC fault ride-through method for a flexible DC transmission system provided by this application includes obtaining the output power of a wind farm in the flexible DC transmission system and the fault signal after a DC fault occurs on the overhead line, and also obtaining the energy dissipation resistance of the series centralized DC energy dissipation device; calculating based on the energy dissipation resistance and the output power to obtain voltage data; when the fault signal is transmitted to the onshore converter station, controlling the onshore converter station to operate in a constant DC voltage control mode, and controlling the positive and negative terminal voltages of the port of the series centralized DC energy dissipation device located at this end of the overhead line to be zero; when the fault signal is transmitted to the offshore converter station, controlling the offshore converter station to operate in a VF control mode, and controlling the positive and negative terminal voltages of the port of the series centralized DC energy dissipation device located at this end of the submarine cable to be the voltage data. When the fault signal is transmitted to the series centralized DC energy dissipation device, controlling all the switching tubes in the series centralized DC energy dissipation device to be in the off state and its energy dissipation element to be in the energy dissipation working state. This DC fault ride-through method for the flexible DC transmission system can achieve the clearing of the overhead line fault and the balance of the surplus power in the flexible DC transmission system by obtaining the fault type and using different control methods to control the operation and parameter settings of the offshore converter station, the onshore converter station, and the series centralized DC energy dissipation device, improving the reliability of this flexible DC transmission system. It solves the technical problem that the existing surplus power processing method is difficult to be directly applied to the flexible DC transmission system with a hybrid DC line composed of a submarine cable and an overhead line.

[0075] Figure 6 It is the inter-pole voltage control block diagram of the onshore converter station during the fault in the DC fault ride-through method for the flexible DC transmission system described in the embodiment of this application.

[0076] As Figure 6 shown, in an embodiment of this application, controlling the positive and negative terminal voltages of the port of the series centralized DC energy dissipation device located at this end of the overhead line to be zero, this DC fault ride-through method includes:

[0077] Obtaining a reference voltage;

[0078] Comparing and processing the positive and negative terminal voltages of the port of the series centralized DC energy dissipation device located at this end of the overhead line with the reference voltage to obtain a first voltage;

[0079] Processing the first voltage by using a PI controller to obtain a first inter-pole voltage control reference value for controlling the operation of the onshore converter station.

[0080] It should be noted that the reference voltage can be selected as 0. The PI controller is a proportional-integral controller, which is a relatively mature technology in this field, and the content of the PI controller will not be elaborated in this embodiment. In other embodiments, the reference voltage can be set according to requirements. In this embodiment, in order to control the positive and negative terminal voltages of the series centralized DC energy-consuming device at this end of the overhead line to be zero, a PI controller is generally adopted. The positive and negative terminal voltages of the series centralized DC energy-consuming device 40 at this end of the overhead line are compared with the reference voltage, and the difference result of the comparison is used as the first voltage. The first voltage is output through the PI controller to obtain the first pole-to-pole voltage control reference value for the operation of the onshore converter station 20 .

[0081] Figure 7 It is the pole-to-pole voltage control block diagram of the offshore converter station during the fault in the DC fault ride-through method of the flexible DC transmission system described in the embodiment of the present application.

[0082] As Figure 7 shown, in an embodiment of the present application, controlling the positive and negative terminal voltages of the series centralized DC energy-consuming device at this end of the submarine cable to be voltage data, the DC fault ride-through method includes:

[0083] Comparing and processing the positive and negative terminal voltages of the series centralized DC energy-consuming device at this end of the submarine cable with the voltage data to obtain a second voltage;

[0084] Using a PI controller to process the second voltage to obtain a second pole-to-pole voltage control reference value for controlling the operation of the offshore converter station.

[0085] It should be noted that the PI controller is a proportional-integral controller, which is a relatively mature technology in this field, and the content of the PI controller will not be elaborated in this embodiment. In this embodiment, in order to control the positive and negative terminal voltages of the series centralized DC energy-consuming device at this end of the submarine cable to be voltage data, a PI controller is generally adopted. The positive and negative terminal voltages of the series centralized DC energy-consuming device 40 at this end of the submarine cable are compared with the voltage data, and the difference result of the comparison is used as the second voltage. The second voltage is output through the PI controller to obtain the second pole-to-pole voltage control reference value for the operation of the offshore converter station 10 .

[0086] As Figure 1 shown, in an embodiment of the present application, the DC fault ride-through method of the flexible DC transmission system includes: if the flexible DC transmission system is in a steady-state operating state, controlling the energy-consuming element of the series centralized DC energy-consuming device to be in a bypass state, and using the VF control mode to control the operation of the offshore converter station and using the constant DC voltage control mode to control the operation of the onshore converter station.

[0087] It should be noted that during the steady-state operation of the flexible DC transmission system, the VF control mode is adopted to control the offshore converter station 10 to provide a stable grid-connected voltage for the wind farm, and the constant DC voltage control mode is adopted to control the operation of the onshore converter station 20 to provide a stable DC voltage for the flexible DC transmission system. The energy-consuming element 43 in the series centralized DC energy-consuming device 40 is controlled to be in a bypass state, and the fault DC current of the flexible DC transmission system flows through each cascaded energy-consuming valve.

[0088] In an embodiment of the present application, the DC fault ride-through method of the flexible DC transmission system includes: calculating voltage data according to the energy-consuming resistance and the output power by using a voltage calculation formula; the voltage calculation formula is: , where U control is the voltage data, P0 is the output power, and R ch is the energy-consuming resistance.

[0089] Embodiment 2:

[0090] Figure 8 It is a frame schematic diagram of the DC fault ride-through device of the flexible DC transmission system described in the embodiment of the present application.

[0091] As Figure 8 shown, the embodiment of the present application provides a DC fault ride-through device for a flexible DC transmission system, which is applied to the flexible DC transmission system. The flexible DC transmission system includes an offshore converter station, an onshore converter station, and multiple hybrid DC lines composed of submarine cables and overhead lines connected between the offshore converter station and the onshore converter station. A series centralized DC energy-consuming device is connected in series on each hybrid DC line. The DC fault ride-through device of the flexible DC transmission system includes a data acquisition module 100, a first fault processing and control module 200, a second fault processing and control module 300, and a third fault processing and control module 400;

[0092] The data acquisition module 100 is configured to acquire the output power of the wind farm in the flexible DC transmission system and the fault signal after a DC fault occurs on the overhead line, and also acquire the energy-consuming resistance of the series centralized DC energy-consuming device; calculate voltage data according to the energy-consuming resistance and the output power;

[0093] The first fault processing and control module 200 is configured to transmit the fault signal to the onshore converter station, control the operation of the onshore converter station by using a constant DC voltage control mode, and control the positive and negative voltages of the ports of the series centralized DC energy-consuming device at the overhead line end to be zero;

[0094] The second fault handling control module 300 is used to transmit the fault signal to the offshore converter station, control the operation of the offshore converter station in the VF control mode, and control the positive and negative pole voltages of the ports of the series centralized DC energy dissipation device at the submarine cable end to voltage data.

[0095] The third fault handling control module 400 is used to transmit the fault signal to the series centralized DC energy dissipation device, and control all the switching tubes in the series centralized DC energy dissipation device to be in the off state and its energy dissipation components to be in the energy dissipation working state.

[0096] It should be noted that the content of the modules in the DC fault ride-through device of this flexible DC transmission system corresponds to the step content of the DC fault ride-through method of this flexible DC transmission system. The step content of the DC fault ride-through method of this flexible DC transmission system has been described in Embodiment 1, and the content of the modules in the DC fault ride-through device of this flexible DC transmission system will not be repeated here. The DC fault ride-through device of this flexible DC transmission system cooperates with each other through the data acquisition module, the first fault handling control module, the second fault handling control module and the third fault handling control module to achieve the clearing of overhead line faults and the balance of surplus power in the flexible DC transmission system, improving the reliability of this flexible DC transmission system.

[0097] In an embodiment of the present application, the DC fault ride-through device of this flexible DC transmission system includes an onshore pole-to-pole control module. The onshore pole-to-pole control module is used to obtain a reference voltage; compare and process the positive and negative pole voltages of the ports of the series centralized DC energy dissipation device at the overhead line end with the reference voltage to obtain a first voltage; use a PI controller to process the first voltage to obtain a first pole-to-pole voltage control reference value for controlling the operation of the onshore converter station.

[0098] In an embodiment of the present application, the DC fault ride-through device of this flexible DC transmission system includes an offshore pole-to-pole control module. The offshore pole-to-pole control module is used to compare and process the positive and negative pole voltages of the ports of the series centralized DC energy dissipation device at the submarine cable end with the voltage data to obtain a second voltage; use a PI controller to process the second voltage to obtain a second pole-to-pole voltage control reference value for controlling the operation of the offshore converter station.

[0099] In an embodiment of the present application, the data acquisition module is further used to calculate according to the energy dissipation resistance and the output power using a voltage calculation formula to obtain voltage data; the voltage calculation formula is: , where U control is the voltage data, P0 is the output power, and R ch is the energy dissipation resistance.

[0100] Embodiment 3:

[0101] Figure 9 Schematic diagram of the terminal device according to an embodiment of the present application.

[0102] As Figure 9 shown, an embodiment of the present application provides a terminal device, including a processor and a memory;

[0103] The memory is used to store program code and transmit the program code to the processor;

[0104] The processor is configured to execute the DC fault ride-through method of the flexible DC transmission system according to the instructions in the program code.

[0105] It should be noted that the processor is used to execute the steps in the above-described embodiment of a DC fault ride-through method of a flexible DC transmission system according to the instructions in the program code. Alternatively, when the processor executes the computer program, it realizes the functions of each module / unit in the above-described system / device embodiments.

[0106] Exemplarily, the computer program can be divided into one or more modules / units. One or more modules / units are stored in the memory and executed by the processor to complete the present application. One or more modules / units can be a series of computer program instruction segments capable of performing specific functions, and these instruction segments are used to describe the execution process of the computer program in the terminal device.

[0107] The terminal device can be a computing device such as a desktop computer, a notebook, a palm computer, and a cloud server. The terminal device may include, but is not limited to, a processor and a memory. Those skilled in the art can understand that this does not limit the terminal device, and it may include more or fewer components than shown in the figure, or combine certain components, or different components. For example, the terminal device may also include input / output devices, network access devices, a bus, etc.

[0108] The so-called processor may be a central processing unit (CPU), or may also be 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. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0109] The memory can be an internal storage unit of the terminal device, such as the hard disk or memory of the terminal device. The memory can also be an external storage device of the terminal device, such as a plug-in hard disk equipped on the terminal device, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. Further, the memory can also include both the internal storage unit of the terminal device and the external storage device. The memory is used to store computer programs and other programs and data required by the terminal device. The memory can also be used to temporarily store the data that has been output or will be output.

[0110] Those skilled in the art can clearly understand that for the convenience and conciseness of description, the specific working processes of the systems, devices, and units described above can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0111] In several embodiments provided in the present application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division, and there can be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the couplings, direct couplings, or communication connections shown or discussed with each other can be through some interfaces. The indirect couplings or communication connections of the devices or units can be in electrical, mechanical, or other forms.

[0112] The units described as separate components may or may not be physically separated. The components shown as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0113] In addition, the functional units in the various embodiments of the present application can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above integrated units can be implemented in the form of hardware or in the form of software functional units.

[0114] When the integrated unit is implemented in the form of 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 this application, in essence, or the part that contributes to the prior art, or all or part of this 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 for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of this application. The foregoing storage medium includes: various media that can store program codes such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs.

[0115] As described above, the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit them; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of various embodiments of this application.

Claims

1. A DC fault ride-through method for a flexible DC power transmission system, applied to a flexible DC power transmission system, wherein the flexible DC power transmission system comprises an offshore converter station, an onshore converter station, and a plurality of hybrid DC lines consisting of submarine cables and overhead lines connected between the offshore converter station and the onshore converter station, characterized in that: A series centralized DC energy dissipation device is connected in series on each of the hybrid DC lines. The DC fault ride-through method of the flexible DC power transmission system comprises the following steps: The output power of the wind farm in the flexible DC power transmission system and the fault signal after the DC fault occurs in the overhead line are obtained, and the energy dissipation resistance of the series centralized DC energy dissipation device is obtained; and voltage data is obtained by calculation based on the energy dissipation resistance and the output power; When the fault signal is transmitted to the onshore converter station, the onshore converter station is controlled to operate in a constant DC voltage control mode, and the positive and negative voltages of the ports of the series-connected centralized DC energy consumption device at the end of the overhead line are controlled to be zero; When the fault signal is transmitted to the offshore converter station, the VF control mode is adopted to control the operation of the offshore converter station, and the positive and negative voltages of the ports of the series-connected centralized DC energy consumption device at the end of the submarine cable are controlled to be the voltage data; When the fault signal is transmitted to the series centralized DC energy consumption device, all switch tubes in the series centralized DC energy consumption device are controlled to be in an off state and the energy consumption elements thereof are in an energy consumption working state.

2. The DC fault ride-through method of the flexible DC transmission system according to claim 1, characterized in that: The positive and negative voltages of the ports of the series-connected centralized DC energy consuming device at the end of the overhead line are controlled to be zero. The DC fault ride-through method includes: Get the reference voltage; Compare the positive and negative voltages of the ports of the series-connected centralized DC energy consuming device at the end of the overhead line with the reference voltage to obtain a first voltage; The first voltage is processed by using a PI controller to obtain a first inter-pole voltage control reference value for controlling the operation of the onshore converter station.

3. The DC fault ride-through method of the flexible DC transmission system according to claim 1, characterized in that: include: If the flexible direct current transmission system is in a steady-state operating state, the energy-consuming elements of the series centralized direct current energy-consuming device are controlled to be in a bypass state, the VF control mode is adopted to control the operation of the offshore converter station, and the fixed direct current voltage control mode is adopted to control the operation of the onshore converter station.

4. The DC fault ride-through method of the flexible DC transmission system according to claim 1, characterized in that: The positive and negative voltages of the ports of the series-connected centralized DC energy consumption device at the end of the submarine cable are controlled to be the voltage data, and the DC fault ride-through method includes: Compare the positive and negative voltages of the ports of the series-connected centralized DC energy consuming device at the end of the submarine cable with the voltage data to obtain a second voltage; The second voltage is processed by using a PI controller to obtain a second inter-pole voltage control reference value for controlling the operation of the offshore converter station.

5. The DC fault ride-through method of the flexible DC transmission system according to claim 1, characterized in that: include: The voltage data is obtained by calculating the voltage according to the energy consumption resistance and the output power using a voltage calculation formula; The voltage calculation formula is: , where U control is the voltage data, P0 is the output power, R ch It is an energy dissipation resistor.

6. A DC fault ride-through device of a flexible DC power transmission system, applied to a flexible DC power transmission system, wherein the flexible DC power transmission system comprises an offshore converter station, an onshore converter station, and a plurality of hybrid DC lines consisting of submarine cables and overhead lines connected between the offshore converter station and the onshore converter station, characterized in that: A series centralized DC energy consumption device is connected in series on each of the hybrid DC lines, and the DC fault ride-through device of the flexible DC power transmission system includes a data acquisition module, a first fault processing control module, a second fault processing control module and a third fault processing control module; The data acquisition module is used to acquire the output power of the wind farm in the flexible DC power transmission system and the fault signal after the DC fault occurs in the overhead line, and also acquire the energy dissipation resistance of the series centralized DC energy dissipation device; and obtain the voltage data according to the energy dissipation resistance and the output power; The first fault processing control module is used to control the operation of the onshore converter station in a constant DC voltage control mode according to the fault signal transmitted to the onshore converter station, and control the positive and negative voltages of the ports of the series-connected centralized DC energy consumption device at this end of the overhead line to be zero; The second fault processing control module is used to control the operation of the offshore converter station in a VF control mode according to the fault signal transmitted to the offshore converter station, and control the positive and negative voltages of the ports of the series-connected centralized DC energy consumption device at this end of the submarine cable to be the voltage data; The third fault processing control module is used to control all switch tubes in the series centralized DC energy consumption device to be in an off state and its energy consumption elements to be in an energy consumption working state according to the fault signal transmitted to the series centralized DC energy consumption device.

7. The DC fault ride-through device of the flexible DC power transmission system according to claim 6, characterized in that: It includes an onshore inter-pole control module, which is used to obtain a reference voltage; compare the positive and negative pole voltages of the ports of the series-connected centralized DC energy consuming device at this end of the overhead line with the reference voltage to obtain a first voltage; and use a PI controller to process the first voltage to obtain a first inter-pole voltage control reference value for controlling the operation of the onshore converter station.

8. The DC fault ride-through device of the flexible DC power transmission system according to claim 6, characterized in that: It includes an offshore inter-pole control module, which is used to compare the positive and negative pole voltages of the ports of the series-connected centralized DC energy consumption device located at this end of the submarine cable with the voltage data to obtain a second voltage; and use a PI controller to process the second voltage to obtain a second inter-pole voltage control reference value for controlling the operation of the offshore converter station.

9. The DC fault ride-through device of the flexible DC power transmission system according to claim 6, characterized in that: The data acquisition module is also used to calculate the voltage data using a voltage calculation formula according to the energy consumption resistor and the output power; the voltage calculation formula is: , where U control is the voltage data, P0 is the output power, R ch It is an energy dissipation resistor.

10. A terminal device, characterized in that: including a processor and a memory; The memory is used to store program codes and transmit the program codes to the processor; The processor is used to execute the DC fault ride-through method of the flexible DC transmission system according to any one of claims 1 to 5 according to the instructions in the program code.

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