AC fault ride-through control method for modularized multi-level DC energy consumption device

Abstract

The invention provides an alternating-current fault ride-through control method for modularized multi-level direct-current energy consumption devices, and the method comprises the steps: enabling the modularized multi-level direct-current energy consumption devices to form a dual symmetric control mechanism, enabling the two multi-level direct-current energy consumption devices to be symmetrically arranged, and enabling the two multi-level direct-current energy consumption devices to be respectively connected to a positive wire and a negative wire; the energy consumption resistor Rd is centrally arranged outdoors, and two ends are respectively connected with the n sub-modules; the direct-current energy consumption device comprises an energy consumption resistor and a plurality of sub-modules with built-in switching tubes, and according to the method, the provided sub-modules have the alternating-current fault ride-through function by controlling the on-off states of the switching tubes in the sub-modules; the stability and reliability of the power supply system can be improved, and the complexity of the system can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore wind power high voltage direct current transmission, and in particular to an alternating current fault ride-through control method for a modular multi-level direct current energy consumption device. Background Art

[0002] Driven by my country's "dual carbon goals", new energy sources such as wind power and photovoltaics will play a key role in future energy consumption and low-carbon transformation. my country's offshore wind resources are abundant and stable. In recent years, offshore wind power has developed rapidly, and flexible direct current (Voltage-Source-Converter-Based-High-Voltage-Direct-Current, VSC-HVDC) technology has also developed rapidly. The offshore wind power grid-connected system based on VSC-HVDC has been widely used due to its flexible control mode, no phase change failure problem and strong fault ride-through (FRT) capability.

[0003] However, because offshore wind power uses a large number of power electronic devices through the flexible direct current transmission system, there are problems such as insufficient withstand voltage / current capacity and fast dynamic response speed. When an AC fault occurs in the onshore receiving power grid, causing a sudden rise or drop in voltage, the system will experience rapid overvoltage or overcurrent, and traditional power system protection technology can no longer meet the requirements of rapid response. When an AC fault occurs at the receiving end, the transmission power of the receiving end converter station will decrease. If the power of the sending-end wind farm is not reduced in time, the surplus power generated will charge the DC side capacitors, causing overvoltage in the DC system, and in severe cases, it may cause the system to exit operation.

[0004] In summary, the existing fault ride-through methods have the following main problems when dealing with power grid AC faults:

[0005] Unstable DC bus voltage: During AC faults, the DC bus voltage is prone to overvoltage and takes a long time to recover.

[0006] High pressure on power electronic devices: Traditional methods cause discontinuous current in the bridge arm, resulting in large di / dt, which causes large voltage and current stress on power electronic devices.

[0007] Low system reliability: Long-term overvoltage may cause the system to stop operating, affecting the reliability and stability of the system.

[0008] In order to solve the above problems, the present invention proposes an AC fault ride-through control method for a modular multi-level DC energy consumption device, aiming to improve the stability and reliability of the system and reduce the complexity of the system. Summary of the invention

[0009] The present invention provides an AC fault ride-through control method for a modular multi-level DC energy consumption device, which can improve the stability and reliability of a power supply system and reduce the complexity of the system.

[0010] The present invention adopts the following technical solutions.

[0011] A method for controlling AC fault ride-through of a modular multi-level DC energy consuming device, wherein a dual symmetrical control mechanism is formed by using a modular multi-level DC energy consuming device, so that two multi-level DC energy consuming devices are symmetrically arranged and connected to a positive line and a negative line respectively; an energy consuming resistor R d Centralized outdoor layout, with n submodules connected at both ends;

[0012] The DC energy dissipation device includes an energy dissipation resistor and a plurality of submodules with built-in switch tubes. The method controls the on-off state of the switch tubes in the submodule so that the proposed submodule has an AC fault ride-through function.

[0013] The switch tubes in the submodules are insulated gate bipolar transistors, and each submodule includes two insulated gate bipolar transistors, four diodes, one capacitor and three resistors. The specific circuit structure is as follows: the submodule includes an insulated gate bipolar transistor T1, an insulated gate bipolar transistor T2, a diode D1, a diode D2, a diode D3, a diode D4, a capacitor C, a resistor R1, a resistor R2 and a resistor R3; wherein: the source of the insulated gate bipolar transistor T1 is connected to the anode of the diode D3, and the drain is connected to the cathode of the diode D3; the source of the insulated gate bipolar transistor T2 is connected to the anode of the diode D4, and the drain is connected to the cathode of the diode D4. connected; diode D1 is connected in parallel with resistor R1; capacitor C is connected in parallel with resistor R2; diode D2 is connected in parallel with resistor R3; the drain of insulated gate bipolar transistor T1 and the cathode of diode D3 are connected with the anode of diode D1 and resistor R1, the cathode of diode D1 and the other end of resistor R1 are connected with capacitor C, resistor R2, the drain of insulated gate bipolar transistor T2 and the cathode of diode D4; the source of insulated gate bipolar transistor T2 and the anode of diode D4 are connected with resistor R3 and the cathode of diode D2; the source of insulated gate bipolar transistor T1 and the anode of diode D3 are connected with capacitor C, resistor R2, resistor R3 and the anode of diode D2.

[0014] The control method includes a switching-in mode and a switching-out mode of a multi-level DC energy consumption device;

[0015] The specific input mode is: when the main switch T1 is disconnected, the submodule is input, and the voltage at the submodule end is equal to the voltage across the DC capacitor C of the submodule;

[0016] The specific cutting-off mode is: when the main switch T1 is closed, the submodule is cut out, and the voltage at the submodule terminal is 0.

[0017] The control method is used in an offshore wind power high voltage direct current transmission system, which is connected to a main power grid to form a power supply system;

[0018] The multi-level DC energy consumption device has the following operating modes under normal working conditions;

[0019] Zero energy consumption mode: When the offshore wind power HVDC transmission system operates without fault, the power absorbed by the energy consumption device is zero, the insulated gate bipolar transistors T1 and T2 in all submodules are turned off, and the DC side voltage is supported by the capacitor voltage in the submodule. The capacitor voltage of a single submodule is:

[0020]

[0021] Full energy consumption mode: When the AC voltage on the grid side of the main grid drops to zero and the receiving-end converter station completely loses its power delivery capability, the multi-level DC energy consumption device absorbs all the transmission power;

[0022] At this time, the insulated gate bipolar transistors T1 in all sub-modules are turned on, and the transmission power is absorbed by the energy-consuming resistor, whose resistance satisfies:

[0023]

[0024] Among them, R d is the resistance value of the concentrated resistor; P N System rated transmission power;

[0025] Dynamic power adjustment mode: When the main grid encounters an abnormal low voltage situation, the multi-level DC energy consumption device needs to absorb energy in the range of zero to rated power.

[0026] The strategy adopted is to indirectly adjust the voltage level across the energy-consuming resistor by adjusting the sum of the output voltages of the submodules. In some submodules, the insulated gate bipolar transistor T1 is turned on, and the submodule output voltage is 0; in other submodules, the insulated gate bipolar transistor T1 is turned off, and T2 is turned on, and the submodule output voltage is the capacitor voltage U c At this time, the power absorbed by the energy dissipation resistor is as follows:

[0027]

[0028] Among them, P Rd The power absorbed by the energy consuming device; U o It is the sum of the submodule output voltages.

[0029] When the AC side voltage drops and fails, the control method only uses the multi-level DC energy dissipation device to dissipate the surplus energy in the power supply system, so as to improve the reliability of the system and reduce the complexity of the power supply system.

[0030] In the control method, the modular multi-level DC energy consumption device forms a DC energy consumption topology structure with flexible DC load characteristics with continuously adjustable resistance value, so as to reduce the impact on the DC system of the power supply system during its operation;

[0031] The multi-level DC energy dissipation device uses the switch tubes in the submodules to form the main switch and the auxiliary switch respectively, and the main switch and the auxiliary switch cooperate to participate in power modulation, so that the integrated resistance power inside the submodule is maintained at a low level, reducing the loss of the switching device.

[0032] When all submodule main switches T1 are disconnected, the voltage U dc Evenly distributed on each submodule, the rated operating voltage U n =U dc / N means:

[0033]

[0034] Wherein, N is the total number of submodules connected in series; when the main switches T1 of all submodules are closed, the DC line voltage is directly applied to both ends of the energy dissipation resistor, and the power absorbed by the energy dissipation resistor is equal to the system transmission power.

[0035] When the DC energy consumption device enters the energy consumption working mode, the voltage of each submodule capacitor C will be monitored in real time; when the submodule is put into operation, the submodule capacitor is charged and the voltage increases; the submodule capacitor voltage is at U L to U H The voltage of the capacitor fluctuates within a certain range, which is equivalent to maintaining a constant value. The specific control strategy is as follows:

[0036] When U C >U L When , switch T2 is closed and the voltage of capacitor C drops;

[0037] When U L ≤U C ≤U H When , switch T2 continues to remain closed, and the voltage of C continues to drop;

[0038] When U C <U H When , switch T2 is disconnected, the voltage of capacitor C increases, and the next cycle begins.

[0039] The method includes a submodule dynamic patrol switching method for flexibly controlling the DC bus voltage during a fault, specifically including:

[0040] Real-time power monitoring method: Under fault conditions, the total power output of the DC energy consumption device, including power dissipation and active output, is matched with the current power demand by adjusting the number of working submodules in the DC energy consumption device. When the fault is cleared, the voltage gradually recovers and corresponds to different powers, which can be quantified as kP rated , where P rated is the rated power of the DC energy consumption device, k is a dynamically changing coefficient, 0≤k≤1;

[0041] Calculate the number of submodules required for working state: according to the current power demand kP rated Calculate the number of submodules that need to be in working state; at this time, it is necessary to meet

[0042] N in =N B +ΔN in (5)

[0043] Where N in is the total number of submodules rotated in one cycle, N B is the number of submodules that rotate in a fixed manner per cycle, ΔN in The power change caused by the adjacent cycles is the number of additional submodules rotated, that is, the power corresponding to the voltage in the process of slowly recovering;

[0044] Dynamically adjust the operating state within the submodule working state. Specifically, when a submodule is put into operation, since the submodule capacitor discharges through the energy-consuming resistor R, a large loss will be generated in the energy-consuming resistor R. In order to ensure that the loss is evenly distributed among the voltage-stabilizing resistors R of each submodule, the submodules to be put into operation must be switched according to a predetermined rule so that the average time for each submodule to be put into operation is the same.

[0045] The method also includes a temperature control method, specifically:

[0046] By calculating the temperature rise ΔT of each energy dissipation resistor, ensure that it is within the safe range; the formula is:

[0047]

[0048] Among them, P dis is the average power dissipation of each energy dissipation resistor, C th is the heat capacity of the energy dissipation resistor, ΔT max is the maximum allowable temperature rise rate of the resistor, R th is the thermal resistance value, and t is the time.

[0049] The control method optimizes and improves the energy release efficiency of the system by evenly distributing the input and output time of the energy-consuming resistors through a dynamic round-robin switching strategy. The dynamic round-robin switching strategy is characterized in that the working cycle of the multi-level DC energy consumption is set to T. Within a working cycle T, all sub-modules are switched on and off once on average, that is, the main switch T1 is switched on and off once on average within each working cycle T;

[0050] When dynamically adjusting the operating state within the submodule working state, the following submodule switching logic is used:

[0051] 1) Working cycle setting: In order to ensure stable operation and efficient energy consumption of the device, the working cycle of the DC chopper of the power supply system is set to T; in one working cycle T, all submodules are switched on and off once on average, that is, the main switch T1 is switched on and off once on average in each working cycle. This design helps to reduce switching losses and improve the overall efficiency of the system;

[0052] 2) Ratio of input and output time: In each working cycle, the input time ratio of the energy-consuming resistor is set to 70%, and the output time ratio is set to 30% to ensure sufficient energy consumption capacity during the fault period and avoid the problem of resistor overheating caused by long-term continuous operation;

[0053] 3) The number of modules in the system is set to 20 energy-consuming resistors, each module is independently controlled, and uniform energy consumption is achieved through a cyclic switching strategy. The specific switching logic is as follows: at the beginning of each working cycle, the energy-consuming resistors in each module are switched on in sequence according to the preset order. When the switching time reaches 70% of the working cycle, the energy-consuming resistors in each module are switched off in sequence until the next working cycle begins;

[0054] The control method further includes an external circuit deployment scheme, which includes: at least one processor; a memory in communication with the at least one processor; an external circuit interface module for connecting with an external circuit system and supporting multiple standard interface protocols to ensure compatibility; a fault detection and switching module, which can automatically detect various faults in the external circuit and automatically switch to a backup circuit configuration or manually trigger the switch according to a preset rule to ensure stable operation of the system;

[0055] The memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the control method of the DC energy consumption device;

[0056] Specifically, the external circuit interface module supports the following functions:

[0057] Achieve seamless connection with different types of external power supplies, loads and monitoring systems; support hot-swap operation, allowing external components to be replaced or added without power outage; provide data exchange capabilities to ensure that the internal control system can obtain status information of external circuits in real time;

[0058] The working mechanism of the fault detection and switching module is as follows:

[0059] In automatic mode, when a change in the DC bus voltage state is detected, the protection program is immediately started, the DC energy consumption device is put into operation, and the pre-configured backup circuit path is activated, and an alarm message is sent to the user; when the automatic mode cannot normally put the DC energy consumption device into operation, it is switched to manual mode;

[0060] In manual mode, the system also has fault detection capabilities, but during execution, the operator is required to manually select whether to put the DC energy-consuming device into operation based on the prompt information, which is suitable for occasions that require manual confirmation.

[0061] The present invention proposes an AC fault ride-through control method for a modular multi-level DC energy consumption device, aiming to improve the stability and reliability of the system and reduce the complexity of the system.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] The AC fault ride-through control method of a modular multi-level DC energy dissipation device proposed in the present invention can realize the dissipation of surplus energy in the system when the AC side voltage drops without adding other equipment to the system, thereby improving the system reliability and reducing the complexity of the system.

[0064] The proposed DC energy dissipation topology has flexible DC load characteristics with continuously adjustable resistance, and has little impact on the DC system during operation.

[0065] The main and auxiliary switches participate in power modulation at the same time, the integrated resistor power inside the sub-module is low, the switching device loss is small, and the safety margin is large.

[0066] It has good electromagnetic compatibility (EMI) characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0068] Attached Figure 1 It is a schematic diagram of the three-phase voltage waveform during the grid voltage drop and slope recovery process;

[0069] Attached Figure 2 It is a schematic diagram of the input DC bus voltage waveform during a grid voltage fault;

[0070] Attached Figure 3 It is a schematic diagram of the DC energy consumption topology;

[0071] Attached Figure 4 It is a schematic diagram of two switching modes of DC energy consumption topology;

[0072] Attached Figure 5 is a schematic diagram of the current flow path of the three operating states of the submodule (part a is a schematic diagram of the current flow path of the proposed modular multi-level DC energy consumption device when the output voltage is Uc in the zero energy consumption mode; part b is a schematic diagram of the current flow path of the proposed modular multi-level DC energy consumption device when the output voltage is 0 in the full energy consumption mode; part c is a schematic diagram of the current flow path of the proposed modular multi-level DC energy consumption device in the dynamic power adjustment mode);

[0073] Attached Figure 6 It is a schematic diagram of the operation control box of the DC energy consumption device;

[0074] Attached Figure 7 It is a schematic diagram of the dual symmetrical arrangement of the DC energy consumption topology;

[0075] Attached Figure 8 is a schematic diagram of a submodule voltage control method;

[0076] Attached Fig. 9 It is a schematic diagram of the submodule voltage discharge circuit;

[0077] Attached Fig.10 It is a schematic diagram of the submodule cyclic switching control flow;

[0078] Attached Fig.11 It is a schematic diagram of the external circuit layout of the DC energy consumption device. DETAILED DESCRIPTION

[0079] As shown in the figure, a method for controlling AC fault ride-through of a modular multi-level DC energy consuming device is provided. In the method, a dual symmetrical control mechanism is formed by using a modular multi-level DC energy consuming device, so that two multi-level DC energy consuming devices are symmetrically arranged and connected to a positive line and a negative line respectively; an energy consuming resistor R d Centralized outdoor layout, with n submodules connected at both ends;

[0080] The DC energy dissipation device includes an energy dissipation resistor and a plurality of submodules with built-in switch tubes. The method controls the on-off state of the switch tubes in the submodule so that the proposed submodule has an AC fault ride-through function.

[0081] The switch tubes in the submodules are insulated gate bipolar transistors, and each submodule includes two insulated gate bipolar transistors, four diodes, one capacitor and three resistors. The specific circuit structure is as follows: the submodule includes an insulated gate bipolar transistor T1, an insulated gate bipolar transistor T2, a diode D1, a diode D2, a diode D3, a diode D4, a capacitor C, a resistor R1, a resistor R2 and a resistor R3; wherein: the source of the insulated gate bipolar transistor T1 is connected to the anode of the diode D3, and the drain is connected to the cathode of the diode D3; the source of the insulated gate bipolar transistor T2 is connected to the anode of the diode D4, and the drain is connected to the cathode of the diode D4. connected; diode D1 is connected in parallel with resistor R1; capacitor C is connected in parallel with resistor R2; diode D2 is connected in parallel with resistor R3; the drain of insulated gate bipolar transistor T1 and the cathode of diode D3 are connected with the anode of diode D1 and resistor R1, the cathode of diode D1 and the other end of resistor R1 are connected with capacitor C, resistor R2, the drain of insulated gate bipolar transistor T2 and the cathode of diode D4; the source of insulated gate bipolar transistor T2 and the anode of diode D4 are connected with resistor R3 and the cathode of diode D2; the source of insulated gate bipolar transistor T1 and the anode of diode D3 are connected with capacitor C, resistor R2, resistor R3 and the anode of diode D2.

[0082] The control method includes a switching-in mode and a switching-out mode of a multi-level DC energy consumption device;

[0083] The specific input mode is: when the main switch T1 is disconnected, the submodule is input, and the voltage at the submodule end is equal to the voltage across the DC capacitor C of the submodule;

[0084] The specific cutting-off mode is: when the main switch T1 is closed, the submodule is cut out, and the voltage at the submodule terminal is 0.

[0085] The control method is used in an offshore wind power high voltage direct current transmission system, which is connected to a main power grid to form a power supply system;

[0086] The multi-level DC energy consumption device has the following operating modes under normal working conditions;

[0087] Zero energy consumption mode: When the offshore wind power HVDC transmission system operates without fault, the power absorbed by the energy consumption device is zero, the insulated gate bipolar transistors T1 and T2 in all submodules are turned off, and the DC side voltage is supported by the capacitor voltage in the submodule. The capacitor voltage of a single submodule is:

[0088]

[0089] Full energy consumption mode: When the AC voltage on the grid side of the main grid drops to zero and the receiving-end converter station completely loses its power delivery capability, the multi-level DC energy consumption device absorbs all the transmission power;

[0090] At this time, the insulated gate bipolar transistors T1 in all sub-modules are turned on, and the transmission power is absorbed by the energy-consuming resistor, whose resistance satisfies:

[0091]

[0092] Among them, R d is the resistance value of the concentrated resistor; P N System rated transmission power;

[0093] Dynamic power adjustment mode: When the main grid encounters an abnormal low voltage situation, the multi-level DC energy consumption device needs to absorb energy in the range of zero to rated power.

[0094] The strategy adopted is to indirectly adjust the voltage level across the energy-consuming resistor by adjusting the sum of the output voltages of the submodules. In some submodules, the insulated gate bipolar transistor T1 is turned on, and the submodule output voltage is 0; in other submodules, the insulated gate bipolar transistor T1 is turned off, and T2 is turned on, and the submodule output voltage is the capacitor voltage U c At this time, the power absorbed by the energy dissipation resistor is as follows:

[0095]

[0096] Among them, P Rd The power absorbed by the energy consuming device; U o It is the sum of the submodule output voltages.

[0097] When the AC side voltage drops and fails, the control method only uses the multi-level DC energy dissipation device to dissipate the surplus energy in the power supply system, so as to improve the reliability of the system and reduce the complexity of the power supply system.

[0098] In the control method, the modular multi-level DC energy consumption device forms a DC energy consumption topology structure with flexible DC load characteristics with continuously adjustable resistance value, so as to reduce the impact on the DC system of the power supply system during its operation;

[0099] The multi-level DC energy dissipation device uses the switch tubes in the submodules to form the main switch and the auxiliary switch respectively, and the main switch and the auxiliary switch cooperate to participate in power modulation, so that the integrated resistance power inside the submodule is maintained at a low level, reducing the loss of the switching device.

[0100] When all submodule main switches T1 are disconnected, the voltage U dc Evenly distributed on each submodule, the rated operating voltage U n =U dc / N means:

[0101]

[0102] Wherein, N is the total number of submodules connected in series; when the main switches T1 of all submodules are closed, the DC line voltage is directly applied to both ends of the energy dissipation resistor, and the power absorbed by the energy dissipation resistor is equal to the system transmission power.

[0103] When the DC energy consumption device enters the energy consumption working mode, the voltage of each submodule capacitor C will be monitored in real time; when the submodule is put into operation, the submodule capacitor is charged and the voltage increases; the submodule capacitor voltage is at U L toU H The voltage of the capacitor fluctuates within a certain range, which is equivalent to maintaining a constant value. The specific control strategy is as follows:

[0104] When U C >U L When , switch T2 is closed and the voltage of capacitor C drops;

[0105] When U L ≤U C ≤U H When , switch T2 continues to remain closed, and the voltage of C continues to drop;

[0106] When U C <U H When , switch T2 is disconnected, the voltage of capacitor C increases, and the next cycle begins.

[0107] The method includes a submodule dynamic patrol switching method for flexibly controlling the DC bus voltage during a fault, specifically including:

[0108] Real-time power monitoring method: Under fault conditions, the total power output of the DC energy consumption device, including power dissipation and active output, is matched with the current power demand by adjusting the number of working submodules in the DC energy consumption device. When the fault is cleared, the voltage gradually recovers and corresponds to different powers, which can be quantified as kP rated , where P rated is the rated power of the DC energy consumption device, k is a dynamically changing coefficient, 0≤k≤1;

[0109] Calculate the number of submodules required for working state: according to the current power demand kP rated Calculate the number of submodules that need to be in working state; at this time, it is necessary to meet

[0110] N in =N B +ΔN in (5)

[0111] Where N in is the total number of submodules rotated in one cycle, N B is the number of submodules that rotate in a fixed manner per cycle, ΔN inThe power change caused by the adjacent cycles is the number of additional submodules rotated, that is, the power corresponding to the voltage in the process of slowly recovering;

[0112] Dynamically adjust the operating state within the submodule working state. Specifically, when a submodule is put into operation, since the submodule capacitor discharges through the energy-consuming resistor R, a large loss will be generated in the energy-consuming resistor R. In order to ensure that the loss is evenly distributed among the voltage-stabilizing resistors R of each submodule, the submodules to be put into operation must be switched according to a predetermined rule so that the average time for each submodule to be put into operation is the same.

[0113] The method also includes a temperature control method, specifically:

[0114] By calculating the temperature rise ΔT of each energy dissipation resistor, ensure that it is within the safe range; the formula is:

[0115]

[0116] Among them, P dis is the average power dissipation of each energy dissipation resistor, C th is the heat capacity of the energy dissipation resistor, ΔT max is the maximum allowable temperature rise rate of the resistor, R th is the thermal resistance value, and t is the time.

[0117] The control method optimizes and improves the energy release efficiency of the system by evenly distributing the input and output time of the energy-consuming resistors through a dynamic round-robin switching strategy. The dynamic round-robin switching strategy is characterized in that the working cycle of the multi-level DC energy consumption is set to T. Within a working cycle T, all sub-modules are switched on and off once on average, that is, the main switch T1 is switched on and off once on average within each working cycle T;

[0118] When dynamically adjusting the operating state within the submodule working state, the following submodule switching logic is used:

[0119] 1) Working cycle setting: In order to ensure stable operation and efficient energy consumption of the device, the working cycle of the DC chopper of the power supply system is set to T; in one working cycle T, all submodules are switched on and off once on average, that is, the main switch T1 is switched on and off once on average in each working cycle. This design helps to reduce switching losses and improve the overall efficiency of the system;

[0120] 2) Ratio of input and output time: In each working cycle, the input time ratio of the energy-consuming resistor is set to 70%, and the output time ratio is set to 30% to ensure sufficient energy consumption capacity during the fault period and avoid the problem of resistor overheating caused by long-term continuous operation;

[0121] 3) The number of modules in the system is set to 20 energy-consuming resistors, each module is independently controlled, and uniform energy consumption is achieved through a cyclic switching strategy. The specific switching logic is as follows: at the beginning of each working cycle, the energy-consuming resistors in each module are switched on in sequence according to the preset order. When the switching time reaches 70% of the working cycle, the energy-consuming resistors in each module are switched off in sequence until the next working cycle begins;

[0122] The control method further includes an external circuit deployment scheme, which includes: at least one processor; a memory in communication with the at least one processor; an external circuit interface module for connecting with an external circuit system and supporting multiple standard interface protocols to ensure compatibility; a fault detection and switching module, which can automatically detect various faults in the external circuit and automatically switch to a backup circuit configuration or manually trigger the switch according to a preset rule to ensure stable operation of the system;

[0123] The memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the control method of the DC energy consumption device;

[0124] Specifically, the external circuit interface module supports the following functions:

[0125] Achieve seamless connection with different types of external power supplies, loads and monitoring systems; support hot-swap operation, allowing external components to be replaced or added without power outage; provide data exchange capabilities to ensure that the internal control system can obtain status information of external circuits in real time;

[0126] The working mechanism of the fault detection and switching module is as follows:

[0127] In automatic mode, when a change in the DC bus voltage state is detected, the protection program is immediately started, the DC energy consumption device is put into operation, and the pre-configured backup circuit path is activated, and an alarm message is sent to the user; when the automatic mode cannot normally put the DC energy consumption device into operation, it is switched to manual mode;

[0128] In manual mode, the system also has fault detection capabilities, but during execution, the operator is required to manually select whether to put the DC energy-consuming device into operation based on the prompt information, which is suitable for occasions that require manual confirmation.

[0129] Example:

[0130] In order to demonstrate the deficiencies of traditional technologies, this example first simulates a fault condition in which the power grid drops from 0.05s to 0.15s and then recovers on a ramp from 0.15s to 0.25s.

[0131] The three-phase voltage waveform of the power grid during the fault process is shown in the attached manual. Figure 1 During the fault process, the input DC bus voltage without fault ride-through strategy control is as shown in the attached manual. Figure 2 As shown in the figure, due to the grid voltage failure, the power transmitted by the offshore wind farm cannot be absorbed, and the transmitted power will be applied to the input bus of the converter. Figure 2 It can be seen that after the fault occurs, the DC bus voltage continues to rise. Even if the grid voltage returns to normal operation after 0.25s, it still takes a long time for the bus voltage to return to the rated voltage. Therefore, during the fault process, the DC bus voltage will be subjected to excessive voltage stress for a long time. A long fault time may lead to serious consequences such as excessive bus voltage and device damage.

[0132] This example proposes a modular multi-level DC energy dissipation device as shown in the attached manual Figure 3 As shown. The device includes several submodules and an energy dissipation resistor. Each submodule includes:

[0133] Insulated gate bipolar transistor T1, insulated gate bipolar transistor T2, diode D1, diode D2, diode D3, diode D4, capacitor C, resistor R1, resistor R2 and resistor R3; wherein:

[0134] The source of the insulated gate bipolar transistor T1 is connected to the anode of the diode D3, and the drain is connected to the cathode of the diode D3;

[0135] The source of the insulated gate bipolar transistor T2 is connected to the anode of the diode D4, and the drain is connected to the cathode of the diode D4;

[0136] The diode D1 is connected in parallel with the resistor R1;

[0137] Capacitor C is connected in parallel with resistor R2;

[0138] The diode D2 is connected in parallel with the resistor R3;

[0139] The drain of the insulated gate bipolar transistor T1 and the cathode of the diode D3 are connected to the anode of the diode D1 and the resistor R1, and the cathode of the diode D1 and the other end of the resistor R1 are connected to the capacitor C, the resistor R2, the drain of the insulated gate bipolar transistor T2, and the cathode of the diode D4;

[0140] The source of the insulated gate bipolar transistor T2 and the anode of the diode D4 are connected to the resistor R3 and the cathode of the diode D2;

[0141] The source of the insulated gate bipolar transistor T1 and the anode of the diode D3 are connected to the capacitor C, the resistor R2, the resistor R3, and the anode of the diode D2.

[0142] The method of input and removal in this case

[0143] The AC fault ride-through control method of a modular multi-level DC energy consumption device includes two switching-on and switching-off modes, as shown in the attached manual. Figure 4 shown.

[0144] Input 1: When the main switch T1 is disconnected, the submodule is turned on, and the voltage at the submodule terminal is equal to the voltage across the DC capacitor C of the submodule;

[0145] Cut-off 2: When the main switch T1 is closed, the submodule is cut out and the voltage at the submodule terminal is 0.

[0146] 3. Working status

[0147] The working state of the AC fault ride-through control method of a modular multi-level DC energy consumption device is as shown in the attached manual. Figure 5 shown.

[0148] State 1 (zero energy consumption mode): The insulated gate bipolar transistors T1 and T2 in all submodules are turned off, and the output voltage of all submodules is the DC side voltage U dc like Figure 5 (a) shown.

[0149] State 2 (full energy consumption mode): the insulated gate bipolar transistors T1 in all sub-modules are turned on, and the output voltage of all sub-modules is 0; Figure 5 (b) as shown.

[0150] State 3 (dynamic power adjustment mode): the insulated gate bipolar transistor T1 in some submodules is turned on, and the submodule output voltage is 0; the insulated gate bipolar transistor T1 in some submodules is turned off, T2 is turned on, and the submodule output voltage is the capacitor voltage. Figure 5 (c) is shown. The DC energy consumption device operation control block diagram is shown in Figure 6 shown.

[0151] Double symmetry control in this example

[0152] The AC fault ride-through control method of a modular multi-level DC energy consumption device includes a dual symmetric control, as shown in the attached manual. Figure 7 As shown. The two multi-level DC energy consumption devices are arranged symmetrically and connected to the positive and negative lines respectively; the energy consumption resistor R d Centralized outdoor layout, with n submodules connected at both ends.

[0153] The multi-level DC energy dissipation symmetrical arrangement in this example

[0154] When all submodule main switches T1 are disconnected, the voltage U dc Evenly distributed on each submodule, therefore, the rated operating voltage U n for:

[0155]

[0156] Where N is the total number of submodules connected in series. When the main switches T1 of all submodules are closed, the DC line voltage is directly applied to the two ends of the energy dissipation resistor, and the power absorbed by the energy dissipation resistor is equal to the system transmission power.

[0157] Submodule voltage control method in this example

[0158] When the energy consumption device enters the energy consumption working mode, the voltage of each submodule capacitor C will be monitored in real time. When the submodule is put into operation, the submodule capacitor is charged and the voltage increases. L to U H The voltage of the capacitor fluctuates within a certain range, which is equivalent to maintaining a constant value. The specific control strategy is as follows:

[0159] When U C >U L When , switch T2 is closed and the voltage of capacitor C drops;

[0160] When U L ≤U C ≤U H When , switch T2 continues to remain closed, and the voltage of C continues to drop;

[0161] When U C H When , switch T2 is disconnected, the voltage of capacitor C increases, and the next cycle begins.

[0162] Dynamic loop switching method in this example

[0163] When a submodule is put into operation, since the submodule capacitor discharges through the energy-consuming resistor R, a large loss will be generated in the energy-consuming resistor R. In order to ensure that the loss is evenly distributed between each submodule voltage-stabilizing resistor R, the submodules to be put into operation must be switched according to a certain rule so that the average time for each submodule to be put into operation is the same. For this purpose, the following submodule switching logic is designed. The submodule capacitor discharge circuit through the energy-consuming resistor R is shown in the attached manual. Figure 8 shown.

[0164] The AC fault ride-through control method of a modular multi-level DC energy consumption device includes a dynamic cyclic switching method. The working cycle of the multi-level DC energy consumption is set to T. In one working cycle T, all sub-modules are switched once on average, that is, the main switch T1 is switched once on average in each working cycle T.

[0165] Specifically: When the bus voltage U bus Higher than the preset threshold U high When , a switching mode is adopted in which 6 energy-consuming resistors are grouped together, and each resistor works at T on ​After switching, the working time of each energy dissipation resistor is T on =0.7T; when bus voltage U bus Below the preset threshold U low When the switching mode is adopted, 10 energy-consuming resistors are grouped together, and each resistor works T on After switching, the working time of each energy dissipation resistor is T on =0.7T. The calculation method of the energy dissipation resistance is shown in formula (8).

[0166]

[0167] Where N B is the number of submodules that rotate in a fixed manner per cycle, ΔN in is the number of additional submodules rotated, f is the switching frequency of the switch tube, T ctl The energy dissipation resistor switching diagram is attached to the manual. Fig. 9 The submodule cyclic switching control flow chart is shown in the attached manual. Fig.10 shown.

[0168] Temperature control in this example

[0169] The AC fault ride-through control method of a modular multi-level DC energy dissipation device includes a temperature control, which ensures that the temperature rise ΔT of each energy dissipation resistor is within a safe range by calculating the temperature rise ΔT of each energy dissipation resistor. The formula is:

[0170]

[0171] Among them, P dis is the average power dissipation of each energy dissipation resistor, C th is the heat capacity of the energy dissipation resistor, ΔT max is the maximum allowable temperature rise rate of the resistor, R th is the thermal resistance value.

[0172] External circuit layout of this example

[0173] The AC fault ride-through control method of a modular multi-level DC energy consumption device includes an external circuit deployment scheme. It realizes seamless connection with different types of external power supplies, loads and monitoring systems; supports hot-swap operation, allowing external components to be replaced or added without power failure; provides data exchange capability to ensure that the internal control system can obtain the status information of the external circuit in real time. The working mechanism of the fault detection and switching module is as follows:

[0174] In automatic mode, when a change in the DC bus voltage state is detected, the system will immediately start the protection program, put the DC energy consumption device into operation, activate the pre-configured backup circuit path, and send an alarm message to the user; when the automatic mode cannot normally put the DC energy consumption device into operation, it will switch to manual mode.

[0175] In manual mode, although the system also has fault detection capabilities, the operator is required to manually choose whether to put the DC energy consumption device into operation based on the prompt information. This mode is suitable for situations where manual confirmation is required.

Claims

1. A method for controlling AC fault ride-through of a modular multi-level DC energy consumption device, characterized in that: In the method, a modular multi-level DC energy consumption device is used to form a dual symmetrical control mechanism, so that two multi-level DC energy consumption devices are symmetrically arranged and connected to the positive line and the negative line respectively; the energy consumption resistor R d Centralized outdoor layout, with n submodules connected at both ends; The DC energy dissipation device includes an energy dissipation resistor and a plurality of submodules with built-in switch tubes. The method controls the on-off state of the switch tubes in the submodule so that the proposed submodule has an AC fault ride-through function.

2. The AC fault ride-through control method of a modular multi-level DC energy consumption device according to claim 1, characterized in that: The switch tubes in the submodules are insulated gate bipolar transistors, and each submodule includes two insulated gate bipolar transistors, four diodes, one capacitor and three resistors. The specific circuit structure is as follows: the submodule includes an insulated gate bipolar transistor T1, an insulated gate bipolar transistor T2, a diode D1, a diode D2, a diode D3, a diode D4, a capacitor C, a resistor R1, a resistor R2 and a resistor R3; wherein: the source of the insulated gate bipolar transistor T1 is connected to the anode of the diode D3, and the drain is connected to the cathode of the diode D3; the source of the insulated gate bipolar transistor T2 is connected to the anode of the diode D4, and the drain is connected to the cathode of the diode D4. connected; diode D1 is connected in parallel with resistor R1; capacitor C is connected in parallel with resistor R2; diode D2 is connected in parallel with resistor R3; the drain of insulated gate bipolar transistor T1 and the cathode of diode D3 are connected with the anode of diode D1 and resistor R1, the cathode of diode D1 and the other end of resistor R1 are connected with capacitor C, resistor R2, the drain of insulated gate bipolar transistor T2 and the cathode of diode D4; the source of insulated gate bipolar transistor T2 and the anode of diode D4 are connected with resistor R3 and the cathode of diode D2; the source of insulated gate bipolar transistor T1 and the anode of diode D3 are connected with capacitor C, resistor R2, resistor R3 and the anode of diode D2.

3. The AC fault ride-through control method of a modular multi-level DC energy consumption device according to claim 2, characterized in that: The control method includes a switching-in mode and a switching-out mode of a multi-level DC energy consumption device; The specific input mode is: when the main switch T1 is disconnected, the submodule is input, and the voltage at the submodule end is equal to the voltage across the DC capacitor C of the submodule; The specific cutting-off mode is: when the main switch T1 is closed, the submodule is cut out, and the voltage at the submodule terminal is 0.

4. The AC fault ride-through control method of a modular multi-level DC energy consumption device according to claim 3, characterized in that: The control method is used in an offshore wind power high voltage direct current transmission system, which is connected to a main power grid to form a power supply system; The multi-level DC energy consumption device has the following operating modes under normal working conditions; Zero energy consumption mode: When the offshore wind power HVDC transmission system operates without fault, the power absorbed by the energy consumption device is zero, the insulated gate bipolar transistors T1 and T2 in all submodules are turned off, and the DC side voltage is supported by the capacitor voltage in the submodule. The capacitor voltage of a single submodule is: Full energy consumption mode: When the AC voltage on the grid side of the main grid drops to zero and the receiving-end converter station completely loses its power delivery capability, the multi-level DC energy consumption device absorbs all the transmission power; At this time, the insulated gate bipolar transistors T1 in all sub-modules are turned on, and the transmission power is absorbed by the energy-consuming resistor, whose resistance satisfies: Among them, R d is the resistance value of the concentrated resistor; P N System rated transmission power; Dynamic power adjustment mode: When the main grid encounters an abnormal low voltage situation, the multi-level DC energy consumption device needs to absorb energy in the range of zero to rated power. The strategy adopted is to indirectly adjust the voltage level across the energy-consuming resistor by adjusting the sum of the output voltages of the submodules. In some submodules, the insulated gate bipolar transistor T1 is turned on, and the submodule output voltage is 0; in other submodules, the insulated gate bipolar transistor T1 is turned off, and T2 is turned on, and the submodule output voltage is the capacitor voltage U c At this time, the power absorbed by the energy dissipation resistor is as follows: Among them, P Rd The power absorbed by the energy-consuming device; U o It is the sum of the submodule output voltages.

5. The AC fault ride-through control method of a modular multi-level DC energy consumption device according to claim 4, characterized in that: When the AC side voltage drops and fails, the control method only uses the multi-level DC energy dissipation device to dissipate the surplus energy in the power supply system, so as to improve the reliability of the system and reduce the complexity of the power supply system.

6. The AC fault ride-through control method of a modular multi-level DC energy consumption device according to claim 4, characterized in that: In the control method, the modular multi-level DC energy consumption device forms a DC energy consumption topology structure with flexible DC load characteristics with continuously adjustable resistance value, so as to reduce the impact on the DC system of the power supply system during its operation; The multi-level DC energy dissipation device uses the switch tubes in the submodules to form the main switch and the auxiliary switch respectively, and the main switch and the auxiliary switch cooperate to participate in power modulation, so that the integrated resistance power inside the submodule is maintained at a low level, reducing the loss of the switching device.

7. The AC fault ride-through control method of a modular multi-level DC energy consumption device according to claim 4, characterized in that: When all submodule main switches T1 are disconnected, the voltage U dc Evenly distributed on each submodule, the rated operating voltage U n =U dc / N means: Wherein, N is the total number of submodules connected in series; when the main switches T1 of all submodules are closed, the DC line voltage is directly applied to both ends of the energy dissipation resistor, and the power absorbed by the energy dissipation resistor is equal to the system transmission power.

8. The AC fault ride-through control method of a modular multi-level energy consumption device according to claim 7, characterized in that: When the DC energy consumption device enters the energy consumption working mode, the voltage of each submodule capacitor C will be monitored in real time; when the submodule is put into operation, the submodule capacitor is charged and the voltage increases; the submodule capacitor voltage is at U L to U H The specific control strategy is as follows: C >U L When , switch T2 is closed and the voltage of capacitor C drops; When U L ≤U C ≤U H When , switch T2 continues to remain closed, and the voltage of C continues to drop; When U C <U H When , switch T2 is disconnected, the voltage of capacitor C increases, and the next cycle begins.

9. The AC fault ride-through control method of a modular multi-level energy consumption device according to claim 8, characterized in that: The method includes a submodule dynamic patrol switching method for flexibly controlling the DC bus voltage during a fault, specifically including: Real-time power monitoring method: Under fault conditions, the total power output of the DC energy consumption device, including power dissipation and active output, is matched with the current power demand by adjusting the number of working submodules in the DC energy consumption device. When the fault is cleared, the voltage gradually recovers and corresponds to different powers, which can be quantified as kP rated , where P rated is the rated power of the DC energy consumption device, k is a dynamically changing coefficient, 0≤k≤1; Calculate the number of submodules required for working state: according to the current power demand kP rated Calculate the number of submodules that need to be in working state; at this time, it is necessary to meet N in =N B +ΔN in (5) Where N in is the total number of submodules rotated in one cycle, N B is the number of submodules that rotate in each cycle, ΔN in The power change caused by the adjacent cycles is the number of additional submodules rotated, that is, the power corresponding to the voltage in the process of slowly recovering; Dynamically adjust the operating state within the submodule working state. Specifically, when a submodule is put into operation, since the submodule capacitor discharges through the energy-consuming resistor R, a large loss will be generated in the energy-consuming resistor R. In order to ensure that the loss is evenly distributed among the voltage-stabilizing resistors R of each submodule, the submodules to be put into operation must be switched according to a predetermined rule so that the average time for each submodule to be put into operation is the same. The method also includes a temperature control method, specifically: By calculating the temperature rise ΔT of each energy dissipation resistor, ensure that it is within the safe range; the formula is: Among them, P dis is the average power dissipation of each energy dissipation resistor, C th is the heat capacity of the energy dissipation resistor, ΔT max is the maximum allowable temperature rise rate of the resistor, R th is the thermal resistance value, and t is the time.

10. The AC fault ride-through control method of a modular multi-level energy consumption device according to claim 9, characterized in that: The control method optimizes and improves the energy release efficiency of the system by evenly distributing the input and output time of the energy-consuming resistors through a dynamic round-robin switching strategy. The dynamic round-robin switching strategy is characterized in that the working cycle of the multi-level DC energy consumption is set to T. Within a working cycle T, all sub-modules are switched on and off once on average, that is, the main switch T1 is switched on and off once on average within each working cycle T; When dynamically adjusting the operating state within the submodule working state, the following submodule switching logic is used: 1) Working cycle setting: In order to ensure stable operation and efficient energy consumption of the device, the working cycle of the DC chopper of the power supply system is set to T; in one working cycle T, all submodules are switched on and off once on average, that is, the main switch T1 is switched on and off once on average in each working cycle. This design helps to reduce switching losses and improve the overall efficiency of the system; 2) Ratio of input and output time: In each working cycle, the input time ratio of the energy-consuming resistor is set to 70%, and the output time ratio is set to 30% to ensure sufficient energy consumption capacity during the fault period and avoid the problem of resistor overheating caused by long-term continuous operation; 3) The number of modules in the system is set to 20 energy-consuming resistors, each module is independently controlled, and uniform energy consumption is achieved through a cyclic switching strategy. The specific switching logic is as follows: at the beginning of each working cycle, the energy-consuming resistors in each module are switched on in sequence according to the preset order. When the switching time reaches 70% of the working cycle, the energy-consuming resistors in each module are switched off in sequence until the next working cycle begins; The control method further includes an external circuit deployment scheme, which includes: at least one processor; a memory in communication with the at least one processor; an external circuit interface module for connecting with an external circuit system and supporting multiple standard interface protocols to ensure compatibility; a fault detection and switching module, which can automatically detect various faults in the external circuit and automatically switch to a backup circuit configuration or manually trigger the switch according to a preset rule to ensure stable operation of the system; The memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the control method of the DC energy consumption device; Specifically, the external circuit interface module supports the following functions: Achieve seamless connection with different types of external power supplies, loads and monitoring systems; support hot-swap operation, allowing external components to be replaced or added without power outage; provide data exchange capabilities to ensure that the internal control system can obtain status information of external circuits in real time; The working mechanism of the fault detection and switching module is as follows: In automatic mode, when a change in the DC bus voltage state is detected, the protection program is immediately started, the DC energy consumption device is put into operation, and the pre-configured backup circuit path is activated, and an alarm message is sent to the user; when the automatic mode cannot normally put the DC energy consumption device into operation, it is switched to manual mode; In manual mode, the system also has fault detection capabilities, but during execution, the operator is required to manually select whether to put the DC energy-consuming device into operation based on the prompt information, which is suitable for occasions that require manual confirmation.

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