Direct-current fault ride-through method, device and equipment for flexible direct-current power transmission system

Abstract

The invention relates to a direct-current fault ride-through method, device and equipment of a flexible direct-current power transmission system. The method comprises the steps that the output power and fault signals of the system and the energy consumption resistance of a series centralized direct-current energy consumption device are acquired; voltage data is calculated according to the energy consumption resistance and the output power; when a fault signal is transmitted to an onshore converter station, the onshore converter station is controlled to operate in a constant direct-current voltage control mode, and the voltage of the positive electrode and the negative electrode of an overhead line port of the series centralized direct-current energy consumption device is controlled to be zero; when the fault signal is transmitted to the offshore converter station, a VF control mode is adopted to control the operation of the offshore converter station and control the voltage of the positive and negative electrodes of the submarine cable port of the series centralized direct-current energy consumption device as voltage data; when the fault signal is transmitted to the series centralized energy consumption device, all switching tubes in the series centralized energy consumption device are controlled to be in a turn-off state, and energy consumption elements of the switching tubes are controlled to be in an energy consumption working state; overhead line fault clearing and surplus power balance in the system are realized, and the reliability of the system is improved.

Description

Technical Field

[0001] The present application relates to the field of direct current fault ride-through technology, and in particular to a direct current fault ride-through method, device and equipment for a flexible direct current transmission system. Background Art

[0002] Offshore wind energy has the advantages of abundant reserves and higher energy efficiency. It is not restricted by land resources and population distribution. Offshore wind power has become the focus of current and future wind power development. As offshore wind power develops towards large capacity and deep sea, in order to further compress sea and land transmission lines and reduce transmission costs, the solution of offshore wind power directly transmitted to the load center via submarine cable-overhead line hybrid DC lines will become the preferred solution for the future ultra-large-scale offshore wind power direct transmission to the load center scenario.

[0003] Although overhead lines can significantly reduce transmission costs, the failure rate is high, requiring the flexible DC transmission system to have DC fault handling capabilities. Existing fault handling methods mainly include DC circuit breaker solutions and full-half-bridge hybrid MMC solutions, but DC circuit breaker equipment is expensive and reliability cannot be guaranteed.

[0004] In addition, during DC faults, the wind turbine power of offshore wind farms is difficult to respond in time, and surplus power will accumulate on the DC line, causing the DC voltage to rise rapidly. If no measures are taken, overvoltage protection will be triggered, causing the flexible DC transmission system to shut down, and even endangering the safety of power equipment in the system. Existing methods for handling surplus power include AC centralized energy consumption devices and parallel DC energy consumption devices, but AC centralized energy consumption devices will increase the investment cost and construction difficulty of offshore platforms, and are generally not used in offshore wind power transmission scenarios. The existing parallel DC energy consumption device needs to maintain a stable DC voltage, which conflicts with the logic of controlling the DC voltage to zero when the full half-bridge hybrid MMC DC fault is cleared, and must be used in conjunction with a DC circuit breaker. Therefore, the existing method for handling surplus power is difficult to directly apply to flexible DC transmission systems with hybrid DC lines composed of submarine cables and overhead lines. Summary of the invention

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

[0006] In order to achieve the above objectives, this application provides the following technical solutions:

[0007] On the one hand, a DC fault ride-through method of a flexible DC transmission system is provided, which is applied to the flexible DC transmission system, wherein the flexible DC transmission system includes 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, each of the hybrid DC lines is connected in series with a series centralized DC energy consumption device, and the DC fault ride-through method of the flexible DC transmission system includes the following steps:

[0008] 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;

[0009] 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;

[0010] 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;

[0011] When the fault signal is transmitted to the series centralized energy consumption device, all switch tubes in the series centralized energy consumption device are controlled to be in an off state and the energy consumption elements thereof are in an energy consumption working state.

[0012] Preferably, 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, and the DC fault ride-through method includes:

[0013] Get the reference voltage;

[0014] 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;

[0015] 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.

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

[0017] Preferably, 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:

[0018] 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;

[0019] 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.

[0020] Preferably, the DC fault ride-through method of the flexible DC power transmission system comprises: using a voltage calculation formula to calculate according to the energy dissipation resistor and the output power to obtain voltage data; 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.

[0021] On the other hand, a DC fault ride-through device of a flexible DC power transmission system is provided, which is applied to the flexible DC power transmission system, wherein the flexible DC power transmission system includes 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, each of the hybrid DC lines is connected in series with a series centralized DC energy consumption device, 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;

[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 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;

[0023] 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;

[0024] 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;

[0025] The third fault processing control module is used to control all switch tubes in the series centralized 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 energy consumption device.

[0026] Preferably, the DC fault ride-through device of the flexible DC power transmission system 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 centralized DC energy consumption device located at the end of the overhead line with the reference voltage to obtain a first voltage; and process the first voltage using a PI controller to obtain a first inter-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 inter-pole control module, which is used to compare the positive and negative pole voltages of the ports of the series 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.

[0028] Preferably, the data acquisition module is further used to obtain voltage data by 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.

[0029] In another aspect, a terminal device is provided, comprising a processor and a memory;

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

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

[0032] The DC fault riding method, device and equipment of the flexible DC power transmission system, the DC fault riding method of the flexible DC power transmission system, including obtaining 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 obtaining the energy consumption resistance of the series centralized DC energy consumption device; according to the energy consumption resistance and the output power calculation, the voltage data is obtained; when the fault signal is transmitted to the onshore converter station, the fixed DC voltage control mode is adopted to control the operation of the onshore converter station, and the positive and negative voltages of the ports of the series 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 centralized DC energy consumption device at the end of the submarine cable are controlled to be voltage data. When the fault signal is transmitted to the series centralized energy consumption device, all the switch tubes in the series centralized energy consumption device are controlled to be in the off state and the energy consumption elements thereof are in the energy consumption working state.

[0033] It can be seen from the above technical scheme that the present application has the following advantages: the DC fault riding method of the flexible DC transmission system can realize overhead line fault clearing and surplus power balance in the flexible DC transmission system by obtaining the fault type and adopting different control methods to control the operation of the offshore converter station, the onshore converter station and the series centralized DC energy consumption device and the setting of parameters, thereby improving the reliability of the flexible DC transmission system and solving the technical problem that the existing surplus power processing method is difficult to directly apply to the flexible DC transmission system in which the submarine cable and the overhead line constitute a hybrid DC line.

[0034] The DC fault ride-through device of the flexible DC power transmission system cooperates with each other through the data acquisition module, the first fault processing control module, the second fault processing control module and the third fault processing control module to achieve overhead line fault clearance and surplus power balance in the flexible DC power transmission system, thereby improving the reliability of the flexible DC power transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0036] Figure 1 A flowchart of the steps of the DC fault ride-through method of the flexible DC transmission system described in an embodiment of the present application;

[0037] Figure 2 A framework flow chart of a DC fault ride-through method for a flexible DC power transmission system according to an embodiment of the present application;

[0038] Figure 3 A schematic diagram of the topological structure of the flexible direct current transmission system described in an embodiment of the present application;

[0039] Figure 4 A schematic diagram of the topological structure of energy-consuming components in the DC fault ride-through method of the flexible DC power transmission system described in an embodiment of the present application;

[0040] Figure 5 An equivalent circuit diagram of the flexible direct current transmission system in the direct current fault ride-through method of the flexible direct current transmission system described in the embodiment of the present application;

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

[0042] Figure 7 This is a block diagram of the inter-pole voltage control of an offshore converter station during a fault in a DC fault ride-through method of a flexible DC power transmission system described in an embodiment of the present application;

[0043] Figure 8 A schematic diagram of a framework of a DC fault ride-through device for a flexible DC power transmission system according to an embodiment of the present application;

[0044] Fig. 9 A schematic diagram of a terminal device described in an embodiment of the present application. DETAILED DESCRIPTION

[0045] In order to make the purpose, features, and advantages of the invention of this application more obvious and easy to understand, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the embodiments described below are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0046] In the description of the embodiments of the present application, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0047] In the embodiments of the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. 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 the specific circumstances.

[0048] Patent terms:

[0049] VF control mode refers to 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 transmission system, which can clear the fault and maintain the surplus power balance of the system when a DC fault occurs in the flexible DC transmission system, thereby avoiding shutdown of the flexible DC transmission system, and solving the technical problem that the existing surplus power processing method is difficult to directly apply to the flexible DC transmission system in which a hybrid DC line is composed of a submarine cable and an overhead line.

[0051] Embodiment 1:

[0052] Figure 1 This is a flowchart of the steps of the DC fault ride-through method of the flexible DC transmission system described in an embodiment of the present application. Figure 2 This is a framework flow chart of a DC fault ride-through method for a flexible DC transmission system according to an embodiment of the present application. Figure 3 This is a schematic diagram of the topological structure of the flexible direct current transmission system described in an embodiment of the present application.

[0053] like Figure 3 As shown, an embodiment of the present application provides a DC fault ride-through method for a flexible DC transmission system, which is applied to a flexible DC transmission system. The flexible DC transmission system includes an offshore converter station 10, an onshore converter station 20, and a plurality of hybrid DC lines 30 composed of submarine cables and overhead lines connected between the offshore converter station 10 and the onshore converter station 20, each hybrid DC line 30 being connected in series with a series centralized DC energy consumption device 40.

[0054] It should be noted that if 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 consumption device 40 is connected in series between the positive submarine cable and the positive overhead line, and a series centralized DC energy consumption 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 constitute a hybrid DC line 30, and the negative submarine cable and the negative overhead line constitute another hybrid DC line 30. Among them, the series centralized DC energy consumption device is installed in each hybrid DC line 30, the ports of the offshore converter station 10 are connected to the DC submarine cable, and the ports of the onshore converter station 20 are connected to the DC overhead line.

[0055] In an 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 located at the offshore converter station 10 end, the other end of the energy dissipation component 41 is respectively connected to the first end of the current limiting element 42, and 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 located 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 is connected in series with the current limiting element 42 and then connected in parallel with the energy dissipation element 43. Considering the flexible DC transmission system with rated power P N When a fault occurs during operation, the maximum voltage that the energy-consuming component 41 can withstand is the DC bus voltage U dc In addition, the energy dissipation element 43 needs to consume all the power, so the resistance of the energy dissipation element 43 is In addition, during the fault period of the flexible DC transmission system, the maximum voltage of the energy-consuming components 41 connected in series is half of the DC bus voltage, that is, .

[0057] In an 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 fault ride-through and surplus power balance problems of the flexible DC power transmission system are solved by the series centralized DC energy dissipation device.

[0058] It should be noted that in the process of solving the fault ride-through and surplus power balance problems of the flexible DC power transmission system through the series centralized DC energy dissipation device, the voltage at both ends of the energy dissipation element 43 can be raised by the current limiting element 42 before the energy dissipation component 41 is activated, and passive energy dissipation is performed. Therefore, the series centralized DC energy dissipation device responds faster and can consume surplus power after a fault occurs in the flexible DC power transmission system. The energy dissipation element 43 and the current limiting element 42 simultaneously limit the DC fault current, and the DC fault current amplitude is lower.

[0059] Figure 4 A schematic diagram of the topological structure of energy-consuming components in the DC fault ride-through method of the flexible DC power transmission system described in an embodiment of the present application.

[0060] like Figure 4 As shown, in one embodiment of the present application, the energy consumption component 41 includes a plurality of energy consumption valves connected in series, each of which includes an RCD buffer circuit and a switch tube T, an anti-parallel 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 balancing element R d and semiconductor device D2, dynamic voltage equalizing element R d It 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 balancing element R d It can be selected as a resistor; and / or, the semiconductor device D2 can be selected as a diode; and / or, the switch tube T can be selected as an integrated gate-commutated thyristor. In an embodiment of the present application, when the switch tube T is turned on, the DC current of the flexible DC transmission system flows through the switch tube T; when the switch 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 at both ends of the energy consumption valve increases. The anti-parallel diode D1 is used to flow reverse DC current when the offshore converter station 10 is started. The bypass switch K is activated when the energy consumption valve voltage is too high to protect the device from overvoltage damage. Among them, the RCD buffer circuit is used to prevent 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-consuming valves connected in series in the energy-consuming component 41 is N. ch , then the maximum voltage that the energy-consuming component 41 can withstand is , U ch is the rated voltage of a single energy-consuming valve.

[0063] Figure 5 It is an equivalent circuit diagram of the flexible direct current transmission system in the direct current fault ride-through method of the flexible direct current transmission system described in the embodiment of the present application.

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

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

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

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

[0068] S2. When the fault signal is transmitted to the onshore converter station, the fixed DC voltage control mode is adopted to control the operation of the onshore converter station, and the positive and negative voltages of the ports of the series-connected centralized DC energy-consuming device at this end of the overhead line are controlled 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 consumption device 40 is controlled according to the fault type obtained in step S1. In this embodiment, when the DC overhead line between the series centralized DC energy consumption device 40 and the onshore converter station 20 fails, in order to clear the fault, the positive and negative voltages of the ports of the series centralized DC energy consumption device at the end of the overhead line need to be reduced to zero or 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 the 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 negative pressure, the maximum positive and negative voltages of the ports of the series centralized DC energy consumption device 10 at the end of the overhead line need to be controlled to zero, that is, the positive and negative voltages of the ports of the series centralized DC energy consumption device 40 at the end of the overhead line are controlled to zero by controlling the inter-pole voltage of the onshore converter station 20 during the fault period. 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 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 this end of the submarine cable are controlled as 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-connected centralized DC energy consumption 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 is still controlled in the VF control mode to provide a stable grid-connected voltage for the wind farm; the common mode component (DC bias) of the offshore converter station 10, that is, the inter-pole voltage, needs to be adjusted according to the output power P0 of the wind farm, the positive and negative voltages U of the ports of the series-connected centralized DC energy consumption device 40 at this end of the submarine cable. pch_ca , U nch_ca And the energy dissipation resistor R ch To control, that is, the pole-to-pole voltage control target of the offshore converter station 10 during the fault is to control the positive and negative pole voltages of the ports of the series-connected centralized DC energy consumption device 10 at the end of the submarine cable to voltage data. Among them, the VF control mode is a relatively mature technology in this field, and the content of the VF control mode is not elaborated in detail in this embodiment. The pole-to-pole voltage of the offshore converter station 10 is equal to the common mode component multiplied by the submodule capacitor voltage.

[0072] S4. When the fault signal is transmitted to the series-connected centralized energy-consuming device, all the switch tubes in the series-connected centralized energy-consuming device are controlled to be in the off state and the energy-consuming elements thereof are in the energy-consuming working state.

[0073] It should be noted that in step S4, the fault signal obtained in step S1 is transmitted to the series centralized energy consumption device, which can be understood as: when the series centralized DC energy consumption device 40 detects that a fault has occurred, the switch tube T of each energy consumption valve is turned off, and the fault DC current of the flexible DC power transmission system flows through the energy consumption element 43, and the voltage at both ends of the energy consumption element 43 increases, thereby limiting the increase of the fault DC current.

[0074] The present application provides a DC fault riding method for a flexible DC transmission system, including obtaining the output power of a wind farm in the flexible DC transmission system and a fault signal after a DC fault occurs in an overhead line, and also obtaining the energy consumption resistance of a series centralized DC energy consumption device; calculating according to the energy consumption resistance and the output power, obtaining voltage data; when the fault signal is transmitted to an onshore converter station, a fixed DC voltage control mode is adopted to control the operation of the onshore converter station, and the positive and negative voltages of the ports of the series centralized DC energy consumption device at the end of the overhead line are controlled to be zero; when the fault signal is transmitted to an offshore converter station, a 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 centralized DC energy consumption device at the end of the submarine cable are controlled to be voltage data. When the fault signal is transmitted to the series centralized energy consumption device, all switch tubes in the series centralized energy consumption device are controlled to be in an off state and their energy consumption elements are in an energy consumption working state. The DC fault ride-through method of the flexible DC transmission system can realize the clearance of overhead line faults and the balance of surplus power in the flexible DC transmission system by obtaining the fault type and using different control methods to control the operation of the offshore converter station, the onshore converter station and the series centralized DC energy consumption device and the setting of parameters, thereby improving the reliability of the flexible DC transmission system. The technical problem that the existing surplus power processing method is difficult to directly apply to the flexible DC transmission system with a hybrid DC line composed of submarine cables and overhead lines is solved.

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

[0076] like Figure 6 As shown, in one embodiment of the present application, 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, and the DC fault ride-through method includes:

[0077] Get the reference voltage;

[0078] 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;

[0079] The first voltage is processed by 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. The PI controller is a relatively mature technology in this field, and the content of the PI controller is no longer elaborated in this embodiment. In other embodiments, the reference voltage can be set as required. In this embodiment, in order to control the positive and negative pole voltages of the ports of the series-connected centralized DC energy consuming device located at this end of the overhead line to be zero, a PI controller can generally be used. The positive and negative pole voltages of the ports of the series-connected centralized DC energy consuming device 40 located 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 by the PI controller to obtain the first inter-pole voltage control reference value for the operation of the onshore converter station 20. .

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

[0082] like Figure 7 As shown, in one embodiment of the present application, 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 as voltage data, and the DC fault ride-through method includes:

[0083] Compare and process the positive and negative voltages of the ports of the series-connected centralized DC energy consumption device at the end of the submarine cable with the voltage data to obtain a second voltage;

[0084] The second voltage is processed by a PI controller to obtain a second inter-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 is not elaborated in this embodiment. In this embodiment, in order to realize the control of the positive and negative voltages of the ports of the series-connected centralized DC energy-consuming device at this end of the submarine cable as voltage data, a PI controller can generally be used, and the positive and negative voltages of the ports of the series-connected 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 by the PI controller to obtain the second inter-pole voltage control reference value of the operation of the offshore converter station 10. .

[0086] like Figure 1 As shown, in one 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 elements of the series-connected centralized DC energy-consuming device to be in a bypass state, using a VF control mode to control the operation of the offshore converter station and using a fixed DC voltage control mode to control the operation of the onshore converter station.

[0087] It should be noted that, when the flexible DC power transmission system is in steady-state operation, 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 fixed 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 power transmission system. The energy consumption element 43 in the series centralized energy consumption device 40 is controlled to be in a bypass state, and the fault DC current of the flexible DC power transmission system flows through each cascade energy consumption valve.

[0088] In one embodiment of the present application, the DC fault ride-through method of the flexible DC power transmission system includes: using a voltage calculation formula to calculate according to the energy consumption resistance and the output power to obtain voltage data; 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.

[0089] Embodiment 2:

[0090] Figure 8 A schematic diagram of the framework of a DC fault ride-through device of a flexible DC power transmission system described in an embodiment of the present application.

[0091] like Figure 8 As shown, an embodiment of the present application provides a DC fault ride-through device of a flexible DC transmission system, which is applied to a flexible DC transmission system. The flexible DC transmission system includes 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. A series centralized DC energy consumption 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 control module 200, a second fault processing control module 300, and a third fault processing control module 400;

[0092] The data acquisition module 100 is used to obtain 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 obtain the energy dissipation resistance of the series-connected centralized DC energy dissipation device; and obtain the voltage data according to the energy dissipation resistance and the output power;

[0093] The first fault processing control module 200 is used to control the operation of the onshore converter station by adopting a fixed DC voltage control mode according to the fault signal transmitted to the onshore converter station, and to control the positive and negative voltages of the ports of the series-connected centralized DC energy consumption device at the end of the overhead line to be zero;

[0094] The second fault processing control module 300 is used to control the operation of the offshore converter station by adopting a VF control mode according to the fault signal transmitted to the offshore converter station, and to 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 voltage data;

[0095] The third fault processing control module 400 is used to control all switch tubes in the series-connected centralized energy consuming device to be in the off state and the energy consuming elements thereof to be in the energy consuming working state according to the fault signal transmitted to the series-connected centralized energy consuming device.

[0096] It should be noted that the content of the module in the DC fault ride-through device of the flexible DC transmission system corresponds to the step content of the DC fault ride-through method of the flexible DC transmission system. The step content of the DC fault ride-through method of the flexible DC transmission system has been described in the first embodiment, and the content of the module in the DC fault ride-through device of the flexible DC transmission system is not repeated in this embodiment. The DC fault ride-through device of the flexible DC transmission system realizes the clearance of overhead line faults and the balance of surplus power in the flexible DC transmission system through the cooperation of the data acquisition module, the first fault processing control module, the second fault processing control module and the third fault processing control module, thereby improving the reliability of the flexible DC transmission system.

[0097] In one embodiment of the present application, the DC fault ride-through device of the flexible DC transmission system 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 located at this end of the overhead line with the reference voltage to obtain a first voltage; and process the first voltage using a PI controller to obtain a first inter-pole voltage control reference value for controlling the operation of the onshore converter station.

[0098] In one embodiment of the present application, the DC fault ride-through device of the flexible DC transmission system includes an offshore inter-pole control module, which is used to compare and process 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.

[0099] In one embodiment of the present application, the data acquisition module is further used to obtain voltage data by using a voltage calculation formula according to the energy consumption resistance 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.

[0100] Embodiment three:

[0101] Fig. 9A schematic diagram of a terminal device described in an embodiment of the present application.

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

[0103] A memory, used for storing program codes and transmitting the program codes to a processor;

[0104] The processor is used 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-mentioned embodiment of the DC fault ride-through method of a flexible DC power transmission system according to the instructions in the program code. Alternatively, the processor implements the functions of each module / unit in the above-mentioned system / device embodiments when executing the computer program.

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

[0107] The terminal device may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The terminal device may include, but is not limited to, a processor and a memory. Those skilled in the art will appreciate that this does not constitute a limitation on the terminal device, and may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the terminal device may also include input and output devices, network access devices, buses, etc.

[0108] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (dSIC), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

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

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

[0111] In the 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 only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as 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 mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

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

[0113] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0114] If 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 the present application is essentially 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. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., various media that can store program codes.

[0115] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present 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 energy consumption device, all switch tubes in the series centralized 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 consumption resistance of the series centralized DC energy consumption device; and calculate and obtain voltage data according to the energy consumption 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 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 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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