A series centralized DC energy consumption device, control method thereof, and terminal equipment

Abstract

The present application relates to a series centralized DC energy consumption device, a control method thereof, and a terminal device. The device includes an energy consumption component, a current limiting element, and an energy consumption element. When a fault occurs in a flexible DC transmission system, the voltage across the energy consumption element can be increased by the current limiting element, and passive energy consumption is achieved before the fault signal is transmitted to the device, so that the series centralized DC energy consumption device responds faster and can consume surplus power after a fault occurs in the flexible DC transmission system; at the same time, the DC fault current can be limited by the energy consuming element and the current limiting element, and the DC fault current amplitude is lower. After the fault signal is transmitted to the device, the operation of the series centralized DC energy consumption device is controlled by obtaining the operating status of the flexible DC transmission system, so that the flexible DC transmission system can consume surplus power through the series centralized DC energy consumption device after a fault occurs, thereby improving the operating reliability of the flexible DC transmission system.

Description

Technical Field

[0001] The present application relates to the field of direct current (DC) energy consumption technology, and in particular to a series-connected centralized DC energy consumption device, a control method thereof, and a terminal device. Background Art

[0002] 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 directly transmitting offshore wind power to load centers via submarine cable-overhead line hybrid DC lines will become the preferred solution for future ultra-large-scale offshore wind power direct transmission to load centers.

[0003] Existing offshore wind power transmission projects only use submarine cables and do not need to consider DC fault ride-through. Therefore, parallel DC energy dissipation devices are generally used, such as Figure 7 As shown. Although overhead lines can significantly reduce transmission costs, their high failure rate requires flexible DC transmission systems 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. Existing parallel DC energy dissipation devices require the flexible DC transmission system to have a stable DC voltage when dissipating energy. This conflicts with the logic of full-half-bridge hybrid MMCs, which require the overhead line DC voltage to drop to zero or negative voltage when clearing DC faults. Therefore, parallel DC energy dissipation devices are difficult to apply to flexible DC transmission systems with submarine cable-overhead line hybrid DC lines. Summary of the Invention

[0004] The present application provides a series centralized DC energy dissipation device, a control method thereof, and a terminal device, which are used to solve the technical problem that the fault clearing solution of the existing parallel DC energy dissipation device is difficult to apply to the flexible DC transmission system of the submarine cable-overhead line hybrid DC line.

[0005] In order to achieve the above objectives, this application provides the following technical solutions:

[0006] On the one hand, a series centralized DC energy dissipation device 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 connected between the offshore converter station and the onshore converter station. A series centralized DC energy dissipation device is connected in series to each hybrid DC line. The series centralized DC energy dissipation device includes an energy dissipation component, a current limiting element, and an energy dissipation element. One end of the energy dissipation component is respectively connected to the first end of the energy dissipation element and the hybrid DC line located at the offshore converter station end, the other end of the energy dissipation component is respectively connected to the first end of the current limiting element, and the second end of the current limiting element is respectively connected to the second end of the energy dissipation element and the hybrid DC line located at the onshore converter station end.

[0007] Preferably, the energy consumption component includes a plurality of energy consumption valves connected in series, and each of the energy consumption valves includes an RCD snubber circuit and a switch tube, an anti-parallel diode and a bypass switch connected in parallel with the RCD snubber circuit.

[0008] Preferably, the RCD snubber circuit comprises a capacitor, a dynamic voltage balancing element and a semiconductor device, wherein the dynamic voltage balancing element is connected in parallel with the semiconductor device and then in series with the capacitor.

[0009] Preferably, the dynamic voltage balancing element is a resistor; and / or the semiconductor device is a diode; and / or the switching tube is an integrated gate-commutated thyristor.

[0010] Preferably, the current limiting element is an inductor; and / or the energy dissipation element is a resistor.

[0011] In another aspect, a control method for a series-connected centralized DC energy consumption device is provided, which is applied to the above-mentioned series-connected centralized DC energy consumption device. The control method comprises the following steps:

[0012] Obtaining the DC bus voltage of the series-connected centralized DC energy consumption device, the operating status of the flexible DC power transmission system, and the fault DC current in its fault state;

[0013] If the operating state is a normal operating state, controlling the switch tubes of each energy consumption valve in the series centralized DC energy consumption device to be in a conducting working state and the energy consumption elements thereof to be in a bypass state;

[0014] If the operating state is a fault state in the passive energy consumption stage, controlling the switch tubes of each energy consumption valve in the series-connected centralized DC energy consumption device to be in a conducting working state, and using the current limiting element of the series-connected centralized DC energy consumption device to reduce the increase rate of the fault DC current while increasing the voltage across the energy consumption element;

[0015] If the operating state is a fault state in the active energy consumption stage, the switch tube of each energy consumption valve in the series centralized DC energy consumption device is controlled to be in a cut-off closed state and the energy consumption element is in a working state, the fault DC current charges the capacitor of each energy consumption valve and obtains the voltage data at both ends of each energy consumption valve after charging, and an active voltage equalization strategy is adopted to control the operation of the corresponding energy consumption valve according to each voltage data; and an adjustment strategy is adopted to adjust the port pole-to-pole voltage of the offshore converter station and the onshore converter station in the flexible DC transmission system.

[0016] Preferably, the active voltage balancing strategy includes:

[0017] Obtaining the average voltage value and the pressure equalization threshold of each of the energy-consuming valves;

[0018] If the voltage data is greater than the sum of the corresponding average voltage value and the voltage balancing threshold, the switch tube corresponding to the energy consumption valve is turned on, and the capacitor corresponding to the energy consumption valve is discharged through the dynamic voltage balancing element and the switch tube;

[0019] If the voltage data is less than the difference between the corresponding average voltage value and the voltage-sharing threshold, the switch corresponding to the energy consumption valve is closed, and the fault DC current charges the capacitor through the semiconductor device corresponding to the energy consumption valve.

[0020] Preferably, the adjustment strategy includes:

[0021] Obtaining the pre-fault transmission power and AC side fault loss power of the flexible DC transmission system and the fault type of the fault state;

[0022] If the fault type is a DC fault, the port inter-pole voltage of the onshore converter station is adjusted to 0, and the port inter-pole voltage of the offshore converter station is set according to the pre-fault transmission power;

[0023] If the fault type is an AC fault, the port inter-pole voltage of the offshore converter station is adjusted to the DC bus voltage, and the port inter-pole voltage of the onshore converter station is set according to the AC side fault power loss.

[0024] Preferably, the control method of the series centralized DC energy consumption device includes: if the operating state is a fault state of the passive energy consumption stage or the active energy consumption stage, controlling the maximum voltage across the energy consumption element to not exceed half of the DC bus voltage.

[0025] In another aspect, a terminal device is provided, comprising a processor and a memory;

[0026] The memory is used to store program code and transmit the program code to the processor;

[0027] The processor is configured to execute the aforementioned series-connected centralized DC energy consumption device according to instructions in the program code.

[0028] The series centralized DC energy dissipation device, its control method, and terminal equipment are 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 connected between the offshore converter station and the onshore converter station. Each hybrid DC line is connected in series with a series centralized DC energy dissipation device. The series centralized DC energy dissipation device includes an energy dissipation component, a current limiting element, and an energy dissipation element. One end of the energy dissipation component is respectively connected to the second end of the energy dissipation element and the hybrid DC line located at the offshore converter station end, the other end of the energy dissipation component is respectively connected to the first end of the current limiting element, and the second end of the current limiting element is respectively connected to the second end of the energy dissipation element and the hybrid DC line located at the onshore converter station end.

[0029] It can be seen from the above technical solution that the present application has the following advantages: when a fault occurs in the flexible direct current transmission system, the series centralized direct current energy dissipation device can increase the voltage across the energy dissipation element through the current limiting element, and perform passive energy dissipation. Passive energy dissipation is achieved before the fault signal is transmitted to the series centralized direct current energy dissipation device, so that the series centralized direct current energy dissipation device responds faster and can consume surplus power after a fault occurs in the flexible direct current transmission system; at the same time, the energy dissipation element and the current limiting element can also limit the direct current fault current, and the amplitude of the direct current fault current is lower, which solves the technical problem that the fault clearing solution of the existing parallel direct current energy dissipation device is difficult to apply to the flexible direct current transmission system of the submarine cable-overhead line hybrid direct current line.

[0030] The control method of the series centralized DC energy dissipation device is to obtain the operating status of the flexible DC transmission system as a fault; before the fault signal is transmitted to the series centralized DC energy dissipation device, passive energy dissipation is achieved, so that the flexible DC transmission system can consume surplus power through the series centralized DC energy dissipation device after the fault occurs. At the same time, the use of energy dissipation elements and current limiting elements can also limit the fault DC current, making the fault DC current amplitude lower; after the fault signal is transmitted to the series centralized DC energy dissipation device, the operation of the series centralized DC energy dissipation device is controlled by obtaining the operating status of the flexible DC transmission system, so that the flexible DC transmission system can consume surplus power through the series centralized DC energy dissipation device after the fault occurs, thereby improving the operational reliability of the flexible DC transmission system; through the adjustment strategy, the inter-electrode voltage of each port in the offshore converter station and the onshore converter station is adjusted, and the surplus power of the flexible DC transmission system is consumed in conjunction with the energy dissipation elements, so that the power fluctuation of the flexible DC transmission system is small, solving the technical problem that the fault clearing solution of the existing parallel DC energy dissipation device is difficult to apply to the flexible DC transmission system of the submarine cable-overhead line hybrid DC line. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. 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 any creative labor.

[0032] Figure 1 This is a schematic diagram of the topological structure of the series-connected centralized DC energy consumption device according to an embodiment of the present application;

[0033] Figure 2 A schematic diagram of the topological structure of energy-consuming components in a series-connected centralized DC energy-consuming device according to an embodiment of the present application;

[0034] Figure 3 This is a flowchart of the steps of the control method of the series-connected centralized DC energy consumption device according to an embodiment of the present application;

[0035] Figure 4 This is a schematic diagram of the framework of the control method of the series-connected centralized DC energy consumption device according to an embodiment of the present application;

[0036] Figure 5 This is a flow chart of the active voltage balancing strategy in the control method of the series-connected centralized DC energy consumption device according to the embodiment of the present application;

[0037] Figure 6 A schematic diagram of a terminal device according to an embodiment of the present application;

[0038] Figure 7 A schematic diagram of the framework for connecting an existing parallel DC energy consumption device with a flexible DC transmission system. DETAILED DESCRIPTION

[0039] 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 the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0040] In the description of the embodiments of the present application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "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 "plurality" is two or more, unless otherwise clearly and specifically defined.

[0041] In the embodiments of the present application, unless otherwise expressly specified or limited, the terms "installed," "connected," "connected," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections, electrical connections; direct connections, or indirect connections through an intermediate medium; internal connections between two components, or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0042] The embodiments of the present application provide a series centralized DC energy consumption device, a control method thereof, and a terminal device. When a DC fault occurs in a flexible DC transmission system, the device can cooperate with a full half-bridge hybrid MMC to achieve fault clearing and surplus power balance, thereby avoiding overvoltage shutdown of the flexible DC transmission system and improving the operational reliability of the flexible DC transmission system. The device solves the technical problem that the fault clearing solution of the existing parallel DC energy consumption device is difficult to apply to the flexible DC transmission system of the submarine cable-overhead line hybrid DC line.

[0043] Example 1:

[0044] Figure 1 This is a schematic diagram of the topological structure of the series-connected centralized DC energy consumption device described in an embodiment of the present application.

[0045] like Figure 1 As shown, an embodiment of the present application provides a series centralized DC energy consumption device, 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 connected between the offshore converter station 10 and the onshore converter station 20. A series centralized DC energy consumption device 40 is connected in series to each hybrid DC line 30.

[0046] It should be noted that the input of the offshore converter station 10 is connected to the offshore wind farm, and the output of the onshore converter station 20 is connected to the load center. In this embodiment, the output of the offshore converter station 10 is connected to the positive and negative submarine cables, and the input of the onshore converter station 20 is connected to the positive and negative overhead lines. 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. The positive submarine cable and the positive overhead line form one hybrid DC line 30, and the negative submarine cable and the negative overhead line form another hybrid DC line 30.

[0047] In an embodiment of the present application, the series centralized DC energy consumption device is installed on 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.

[0048] 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 first 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.

[0049] 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 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 R ch =U dc 2 / (2P N ), in addition, during the fault period of the flexible DC transmission system, the maximum pressure of the energy-consuming components 41 connected in series is half of the DC bus voltage, that is, U dc / 2.

[0050] 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 transmission system are solved by the series centralized DC energy dissipation device.

[0051] It should be noted that in solving the fault ride-through and surplus power balance issues of the flexible DC transmission system using this series centralized DC energy dissipation device, even before energy dissipation component 41 is activated, current-limiting element 42 can raise the voltage across energy dissipation element 43, thereby passively dissipating energy. Therefore, the series centralized DC energy dissipation device responds more quickly and can dissipate surplus power after a fault in the flexible DC transmission system occurs. Energy dissipation element 43 and current-limiting element 42 simultaneously limit the DC fault current, resulting in a lower DC fault current amplitude.

[0052] The present application provides a series centralized DC energy dissipation device, 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 connected between the offshore converter station and the onshore converter station. A series centralized DC energy dissipation device is connected in series to each hybrid DC line. The series centralized DC energy dissipation device includes an energy dissipation component, a current limiting element, and an energy dissipation element. One end of the energy dissipation component is respectively connected to the second end of the energy dissipation element and the hybrid DC line located at the offshore converter station end, the other end of the energy dissipation component is respectively connected to the first end of the current limiting element, and the second end of the current limiting element is respectively connected to the second end of the energy dissipation element and the hybrid DC line located at the onshore converter station end. When a fault occurs in the flexible direct current transmission system, the series centralized direct current energy dissipation device can increase the voltage across the energy dissipation element through the current limiting element, thereby performing passive energy dissipation. Passive energy dissipation is achieved before the fault signal is transmitted to the series centralized direct current energy dissipation device, making the series centralized direct current energy dissipation device respond more quickly and consume surplus power after a fault occurs in the flexible direct current transmission system. At the same time, the energy dissipation element and the current limiting element can also limit the direct current fault current, resulting in a lower amplitude of the direct current fault current, thereby solving the technical problem that the fault clearing solution of the existing parallel direct current energy dissipation device is difficult to apply to the flexible direct current transmission system of the submarine cable-overhead line hybrid direct current line.

[0053] Figure 2 This is a schematic diagram of the topological structure of the energy-consuming components in the series-connected centralized DC energy-consuming device described in an embodiment of the present application.

[0054] like Figure 2 As shown, in one embodiment of the present application, the energy consumption component 41 includes several energy consumption valves connected in series, each energy consumption valve includes an RCD snubber circuit and a switch tube T, an anti-parallel diode D1 and a bypass switch K connected in parallel with the RCD snubber circuit. The RCD snubber 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.

[0055] It should be noted that the dynamic voltage balancing element R dIt 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 snubber 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 pass 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 snubber circuit is used to avoid excessive charging and discharging currents when the capacitor C is charged and discharged.

[0056] 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 dc =N ch ×U ch , U ch is the rated voltage of a single energy-consuming valve.

[0057] Example 2

[0058] Figure 3 This is a flowchart of the steps of the control method of the series-connected centralized DC energy consumption device according to the embodiment of the present application. Figure 4 This is a schematic diagram of the framework of the control method of the series-connected centralized DC energy consumption device described in an embodiment of the present application.

[0059] like Figure 3 and Figure 4 As shown, an embodiment of the present application provides a control method for a series-connected centralized DC energy consumption device, which is applied to the above-mentioned series-connected centralized DC energy consumption device. The control method includes the following steps:

[0060] S1. Obtain the DC bus voltage of the series-connected centralized DC energy consumption device, the operating status of the flexible DC transmission system, and the fault DC current under its fault state.

[0061] It should be noted that in step S1 , the parameters of the series centralized DC energy consuming device and the operating parameters of the flexible DC transmission system (operating state and fault DC current in its fault state) are obtained. In this embodiment, the content of the series centralized DC energy consuming device has been explained in the first embodiment.

[0062] S2. If the operating state is a normal operating state, control the switch tubes of each energy-consuming valve in the series-connected centralized DC energy-consuming device to be in an on-state and the energy-consuming elements thereof to be in a bypass state.

[0063] It should be noted that in step S2, the operating state of the flexible DC transmission system is first in a normal operating state according to step S1. It can be understood that when the flexible DC transmission system operates stably, the switch tubes of each energy-consuming valve are turned on and the energy-consuming elements are in a bypass state.

[0064] S3. If the operating state is a fault state in the passive energy consumption stage, control the switch tubes of each energy consumption valve in the series-connected centralized DC energy consumption device to be in the on-state, and use the current-limiting elements of the series-connected centralized DC energy consumption device to reduce the rate of increase of the fault DC current while increasing the voltage across the energy consumption element.

[0065] It should be noted that in step S3, the operating state obtained in step S1 is the passive energy dissipation stage. From the moment the VDC system fault occurs to the moment the energy dissipation valve begins to operate, the transient increase in fault DC current causes the voltage across current-limiting element 42 to rise, and the voltage across energy dissipation element 43 also increases. In this operating state, current-limiting element 42 limits the rate of increase of the fault DC current while simultaneously increasing the voltage across energy dissipation element 43, further reducing the magnitude of the fault DC current and consuming excess power. The passive energy dissipation stage can be understood as the operating stage after a fault occurs in the VDC system but before the fault signal is transmitted to the series centralized DC energy dissipation device.

[0066] S4. If the operating state is a fault state in the active energy consumption stage, the switch tubes of each energy consumption valve in the series centralized DC energy consumption device are controlled to be in the cut-off state and the energy consumption elements are in the working state. The fault DC current charges the capacitor of each energy consumption valve and obtains the voltage data at both ends of each energy consumption valve after charging. The active voltage equalization strategy is adopted according to the voltage data to control the operation of the corresponding energy consumption valve; and the adjustment strategy is adopted to adjust the port pole-to-pole voltage of the offshore converter station and the onshore converter station in the flexible DC transmission system.

[0067] It should be noted that in step S4, based on the fault state of the active energy consumption phase obtained in step S1, the switch tubes T of each energy-consuming valve in the series-connected centralized DC energy-consuming device are controlled to close, forcing the fault DC current to flow through the RCD buffer circuit and charge capacitor C, increasing the voltage across each energy-consuming valve. As the port voltage of each series-connected energy-consuming valve increases, the voltage across energy-consuming element 43 also increases. Energy-consuming element 43 consumes energy to dissipate the surplus power of the flexible DC transmission system after the fault occurs. The active energy consumption phase can be understood as the operating phase after a fault occurs in the flexible DC transmission system, but before the fault signal is transmitted to the series-connected centralized DC energy-consuming device.

[0068] The present application provides a control method for a series centralized DC energy consumption device, comprising obtaining a DC bus voltage of the series centralized DC energy consumption device, an operating state of a flexible DC transmission system, and a fault DC current under a fault state thereof; if the operating state is a normal operating state, controlling the switch tubes of each energy consumption valve in the series centralized DC energy consumption device to be in a conducting working state and the energy consumption element thereof to be in a bypass state; if the operating state is a fault state in a passive energy consumption stage, controlling the switch tubes of each energy consumption valve in the series centralized DC energy consumption device to be in a conducting working state, and adopting the series centralized DC energy consumption. The current limiting element of the energy-consuming device reduces the rate of increase of the fault DC current and increases the voltage across the energy-consuming element. If the operating state is the fault state of the active energy consumption stage, the switch tube of each energy-consuming valve in the series centralized DC energy-consuming device is controlled to be in the cut-off state and the energy-consuming element is in the working state. The fault DC current charges the capacitor of each energy-consuming valve and obtains the voltage data across each energy-consuming valve after charging. The active voltage balancing strategy is adopted to control the operation of the corresponding energy-consuming valve according to the voltage data. The adjustment strategy is also adopted to adjust the port pole-to-pole voltage of the offshore converter station and the onshore converter station in the flexible DC transmission system. The control method of the series centralized DC energy dissipation device controls the operation of the series centralized DC energy dissipation device by obtaining the operating status of the flexible DC transmission system, so that the flexible DC transmission system can consume surplus power through the series centralized DC energy dissipation device after a fault occurs. Energy dissipation elements and current limiting elements are used to simultaneously limit the fault DC current, so that the amplitude of the fault DC current is lower, thereby improving the operating reliability of the flexible DC transmission system. The adjustment strategy is used to adjust the inter-electrode voltage of each port in the offshore converter station and the onshore converter station, and the energy dissipation elements are used to consume the surplus power of the flexible DC transmission system, so that the power fluctuation of the flexible DC transmission system is small, which solves the technical problem that the fault clearing solution of the existing parallel DC energy dissipation device is difficult to apply to the flexible DC transmission system of the submarine cable-overhead line hybrid DC line.

[0069] It should be noted that the control method of the series centralized DC energy consumption device obtains the operating status of the flexible DC transmission system as a fault; before the fault signal is transmitted to the series centralized DC energy consumption device, passive energy consumption is achieved, so that the flexible DC transmission system can consume surplus power through the series centralized DC energy consumption device after the fault occurs. At the same time, the use of energy consumption elements and current limiting elements can also limit the fault DC current, making the fault DC current amplitude lower; after the fault signal is transmitted to the series centralized DC energy consumption device, the operation of the series centralized DC energy consumption device is controlled by obtaining the operating status of the flexible DC transmission system, so that the flexible DC transmission system can consume surplus power through the series centralized DC energy consumption device after the fault occurs, thereby improving the operating reliability of the flexible DC transmission system; the inter-pole voltage of each port in the offshore converter station and the onshore converter station is adjusted through the adjustment strategy, and the surplus power of the flexible DC transmission system is consumed in conjunction with the energy consumption elements, so that the power fluctuation of the flexible DC transmission system is small.

[0070] Figure 5 This is a flow chart of the active voltage balancing strategy in the control method of the series-connected centralized DC energy consumption device described in the embodiment of the present application.

[0071] like Figure 5 As shown, in one embodiment of the present application, the active voltage balancing strategy includes:

[0072] Obtain the average voltage value and pressure equalization threshold of each energy consumption valve;

[0073] If the voltage data is greater than the sum of the corresponding average voltage value and the voltage balancing threshold, the switch tube of the corresponding energy consumption valve is turned on, and the capacitor of the corresponding energy consumption valve is discharged through the dynamic voltage balancing element and the switch tube;

[0074] If the voltage data is less than the difference between the corresponding average voltage value and the voltage balancing threshold, the switch of the corresponding energy consumption valve is closed, and the fault DC current charges the capacitor through the semiconductor device of the corresponding energy consumption valve.

[0075] It should be noted that when the voltage of each energy-consuming valve increases, in order to avoid overvoltage of the corresponding energy-consuming valve, it is necessary to ensure the voltage consistency at both ends of each energy-consuming valve, and an active pressure-balancing strategy can be adopted to control each energy-consuming valve. Figure 5 As shown, U sm_avg is the average voltage value of the energy consumption valve, is the voltage balancing threshold of the energy consumption valve, which is used to reduce the switching frequency of the switch tube T. If the voltage data U smi Greater than U sm_avg + , indicating that the voltage of the energy consumption valve is too high, it is necessary to turn on the switch tube T. At this time, the capacitor C will pass through the dynamic voltage equalizing element R dAnd the switch tube T discharges; if the voltage data U of the i-th energy consumption valve smi Less than U sm_avg - , indicating that the voltage of the energy consumption valve is too low, the switch tube T is turned off, and the fault DC current will charge the capacitor C through the semiconductor device D2; .

[0076] In one embodiment of the present application, the adjustment strategy includes:

[0077] Obtain the pre-fault transmission power of the flexible HVDC system, the AC side fault loss power, and the fault type of the fault state;

[0078] If the fault type is a DC fault, the port pole voltage of the onshore converter station is adjusted to 0, and the port pole voltage of the offshore converter station is set according to the transmission power before the fault;

[0079] If the fault type is an AC fault, the port pole voltage of the offshore converter station is adjusted to the DC bus voltage, and the port pole voltage of the onshore converter station is set according to the AC side fault loss power.

[0080] It should be noted that when a DC fault occurs, the port inter-pole voltage at the onshore converter station is adjusted to zero, while the port inter-pole voltage at the offshore converter station is set based on the pre-fault transmission power. This setting can be customized based on user needs. When an AC fault occurs, the port inter-pole voltage at the offshore converter station is equal to the DC bus voltage, while the port inter-pole voltage at the onshore converter station is set based on the AC side fault power loss. This setting can be customized based on user needs.

[0081] In one embodiment of the present application, the control method of the series centralized DC energy consumption device includes: if the operating state is a fault state of the passive energy consumption stage or the active energy consumption stage, controlling the maximum voltage across the energy consumption element to not exceed half of the DC bus voltage.

[0082] It should be noted that the control method of the series centralized DC energy dissipation device can adjust the inter-pole voltage of each port in the offshore converter station and the onshore converter station according to the fault type. The maximum voltage across the energy dissipation element does not exceed half of the DC bus voltage, and cooperates with the energy dissipation element to consume the surplus power of the flexible DC transmission system.

[0083] Example 3:

[0084] Figure 6 This is a schematic diagram of the terminal device described in an embodiment of the present application.

[0085] like Figure 6 As shown, an embodiment of the present application provides a terminal device, including a processor and a memory;

[0086] A memory, configured to store program codes and transmit the program codes to a processor;

[0087] The processor is configured to execute the control method of the series-connected centralized DC energy consumption device according to the instructions in the program code.

[0088] It should be noted that the processor is configured to execute the steps of the aforementioned embodiment of a control method for a series-connected centralized DC energy consuming device according to the instructions in the program code. Alternatively, the processor implements the functions of the modules / units in the aforementioned system / device embodiments when executing the computer program.

[0089] For example, a computer program may be divided into one or more modules / units, one or more of which 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 performing specific functions, and the instruction segments are used to describe the execution process of the computer program in a terminal device.

[0090] Terminal devices can be computing devices such as desktop computers, laptops, PDAs, and cloud servers. Terminal devices may include, but are not limited to, processors and memory. Those skilled in the art will appreciate that this does not constitute a limitation on terminal devices and may include more or fewer components than shown, or a combination of certain components, or different components. For example, terminal devices may also include input / output devices, network access devices, buses, and the like.

[0091] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (dSICs), 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.

[0092] Memory can be an internal storage unit of a terminal device, such as a hard drive or memory. It can also be an external storage device, such as a plug-in hard drive, a Smart Memory Card (SMC), a Secure Digital (SD) card, or a flash memory card. Furthermore, memory can include both internal and external storage units. Memory is used to store computer programs and other programs and data required by the terminal device. Memory can also be used to temporarily store data that has been output or is about to be output.

[0093] Those skilled in the art will 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.

[0094] In the several embodiments provided in this 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 schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, 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.

[0095] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0096] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0097] 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, 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 and includes a number of instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program code, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0098] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 control method for a series-connected centralized DC energy dissipation device, applied to a series-connected centralized DC energy dissipation device, wherein the series-connected centralized DC energy dissipation device is disposed on a flexible DC power transmission system, the flexible DC power transmission system comprising an offshore converter station, an onshore converter station, and a plurality of hybrid DC lines connected between the offshore converter station and the onshore converter station, wherein each hybrid DC line is connected in series with a series-connected centralized DC energy dissipation device, the series-connected centralized DC energy dissipation device comprising an energy dissipation component, a current limiting element, and an energy dissipation element, wherein one end of the energy dissipation component is respectively connected to a first end of the energy dissipation element and the hybrid DC line at the offshore converter station end, the other end of the energy dissipation component is respectively connected to a first end of the current limiting element, and the second end of the current limiting element is respectively connected to a second end of the energy dissipation element and the hybrid DC line at the onshore converter station end, characterized in that: The control method comprises the following steps: Obtaining the DC bus voltage of the series-connected centralized DC energy consumption device, the operating status of the flexible DC power transmission system, and the fault DC current in its fault state; If the operating state is a normal operating state, controlling the switch tubes of each energy consumption valve in the series centralized DC energy consumption device to be in a conducting working state and the energy consumption elements thereof to be in a bypass state; If the operating state is a fault state in the passive energy consumption stage, controlling the switch tubes of each energy consumption valve in the series-connected centralized DC energy consumption device to be in a conducting working state, and using the current limiting element of the series-connected centralized DC energy consumption device to reduce the increase rate of the fault DC current while increasing the voltage across the energy consumption element; If the operating state is a fault state in the active energy consumption stage, the switch tube of each energy consumption valve in the series centralized DC energy consumption device is controlled to be in a cut-off closed state and the energy consumption element is in a working state, the fault DC current charges the capacitor of each energy consumption valve and obtains the voltage data at both ends of each energy consumption valve after charging, and an active voltage equalization strategy is adopted to control the operation of the corresponding energy consumption valve according to each voltage data; and an adjustment strategy is adopted to adjust the port pole-to-pole voltage of the offshore converter station and the onshore converter station in the flexible DC transmission system.

2. The control method of the series centralized DC energy consumption device according to claim 1, characterized in that: The active voltage balancing strategy includes: Obtaining the average voltage value and the pressure equalization threshold of each of the energy-consuming valves; If the voltage data is greater than the sum of the corresponding average voltage value and the voltage balancing threshold, the switch tube corresponding to the energy consumption valve is turned on, and the capacitor corresponding to the energy consumption valve is discharged through the dynamic voltage balancing element and the switch tube; If the voltage data is less than the difference between the corresponding average voltage value and the voltage-sharing threshold, the switch corresponding to the energy consumption valve is closed, and the fault DC current charges the capacitor through the semiconductor device corresponding to the energy consumption valve.

3. The control method of the series centralized DC energy consumption device according to claim 1, characterized in that: The adjustment strategies include: Obtaining the pre-fault transmission power and AC side fault loss power of the flexible DC transmission system and the fault type of the fault state; If the fault type is a DC fault, the port inter-pole voltage of the onshore converter station is adjusted to 0, and the port inter-pole voltage of the offshore converter station is set according to the pre-fault transmission power; If the fault type is an AC fault, the port inter-pole voltage of the offshore converter station is adjusted to the DC bus voltage, and the port inter-pole voltage of the onshore converter station is set according to the AC side fault power loss.

4. The control method of the series centralized DC energy consumption device according to claim 1, characterized in that: include: If the operating state is a fault state of the passive energy consumption stage or the active energy consumption stage, the maximum voltage across the energy consumption element is controlled not to exceed half of the DC bus voltage.

5. The control method of the series centralized DC energy consumption device according to claim 1, characterized in that: The energy consumption component includes a plurality of energy consumption valves connected in series, and each of the energy consumption valves includes an RCD snubber circuit and a switch tube, an anti-parallel diode and a bypass switch connected in parallel with the RCD snubber circuit.

6. The control method of the series centralized DC energy consumption device according to claim 5, characterized in that: The RCD snubber circuit includes a capacitor, a dynamic voltage balancing element, and a semiconductor device. The dynamic voltage balancing element is connected in parallel with the semiconductor device and then in series with the capacitor.

7. The control method of the series centralized DC energy consumption device according to claim 6, characterized in that: The dynamic voltage balancing element is a resistor; and / or the semiconductor device is a diode; and / or the switch tube is an integrated gate-commutated thyristor.

8. The control method of a series-connected centralized DC energy consumption device according to any one of claims 1 to 7, characterized in that: The current limiting element is an inductor; and / or the energy dissipation element is a resistor.

9. A terminal device, characterized in that: including a processor and a memory; The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the control method for the series-connected centralized DC energy consumption device according to any one of claims 1 to 8 according to the instructions in the program code.

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