A method for AC fault ride-through control of a modular multilevel DC power dissipation device

Abstract

This invention proposes an AC fault ride-through control method for a modular multilevel DC power dissipation device. In this method, a dual symmetrical control mechanism is formed using modular multilevel DC power dissipation devices, with two devices symmetrically arranged and connected to the positive and negative lines respectively; the power dissipation resistor... R d The device is centrally located outdoors, with n sub-modules connected to each end. The DC power dissipation device includes a power dissipation resistor and several sub-modules with built-in switching transistors. The method controls the on / off state of these switching transistors in the sub-modules, enabling the proposed sub-modules to have AC fault ride-through capability. This invention can improve the stability and reliability of the power supply system and reduce the complexity of the system.

Description

Technical Field

[0001] This invention relates to the field of offshore wind power high-voltage direct current transmission technology, and in particular to an AC fault ride-through control method for a modular multilevel DC energy dissipation device. Background Technology

[0002] Driven by my country's "dual carbon goals," new energy sources such as wind power and photovoltaics will play a crucial role in future energy consumption and low-carbon transformation. my country boasts abundant and stable offshore wind resources, and offshore wind power has developed rapidly in recent years, along with flexible direct current transmission (Voltage-Source-Converter-Based High-Voltage-Direct-Current, VSC-HVDC) technology. Offshore wind power grid-connected systems based on VSC-HVDC have been widely adopted due to their flexible control methods, absence of commutation failure issues, and strong fault-ride-through (FRT) capabilities.

[0003] However, offshore wind power utilizes numerous power electronic devices in its flexible DC transmission systems, resulting in insufficient voltage / current withstand capabilities and rapid dynamic response. When an AC fault occurs in the onshore receiving-end grid, causing a sudden voltage spike or drop, the system experiences rapid overvoltage or overcurrent, rendering traditional power system protection technologies inadequate for rapid response. During an AC fault at the receiving end, the transmission power of the receiving-end converter station decreases. If the power output of the sending-end wind farm fails to decrease in time, the resulting surplus power will charge the DC-side capacitors, leading to DC system overvoltage, which in severe cases may cause the system to shut down.

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

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

[0006] High stress on power electronic devices: Traditional methods result in discontinuous bridge arm current, generating a large di / dt, which causes significant voltage and current stress on power electronic devices.

[0007] Low system reliability: Prolonged overvoltage may cause the system to shut down, affecting the system's reliability and stability.

[0008] To address the aforementioned problems, this invention proposes an AC fault ride-through control method for a modular multilevel DC power dissipation device. The aim is to improve system stability and reliability while reducing system complexity. Summary of the Invention

[0009] This invention proposes an AC fault ride-through control method for a modular multilevel DC power consumption device, which can improve the stability and reliability of the power supply system and reduce the complexity of the system.

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

[0011] A method for AC fault ride-through control of a modular multilevel DC power dissipation device, wherein the method uses a modular multilevel DC power dissipation device to form a dual symmetrical control mechanism, so that two multilevel DC power dissipation devices are symmetrically arranged and respectively connected to the positive and negative lines; the power dissipation resistor R d The layout is centrally located outdoors, with n sub-modules connected to each end;

[0012] The DC power dissipation device includes a power dissipation resistor and a sub-module with several built-in switching transistors. The method enables the proposed sub-module to have AC fault ride-through capability by controlling the on / off state of these switching transistors in the sub-module.

[0013] The switching transistors in the submodules are insulated-gate bipolar transistors (IGBTs). Each submodule includes two IGBTs, four diodes, one capacitor, and three resistors. The specific circuit structure is as follows: each submodule contains IGBT T1, IGBT T2, diodes D1, D2, D3, and D4, capacitor C, and resistors R1, R2, and R3. Specifically, the source of IGBT T1 is connected to the anode of diode D3, and its drain is connected to the cathode of diode D3. The source of IGBT T2 is connected to the anode of diode D4, and its drain is connected to the cathode of diode D4. Connect the following: 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, the cathode of diode D3, the anode of diode D1, and resistor R1 are connected; the cathode of diode D1 and the other end of resistor R1 are connected to 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, the anode of diode D4, and resistor R3 are connected to the cathode of diode D2; the source of insulated-gate bipolar transistor T1, the anode of diode D3, and capacitor C, resistor R2, resistor R3, and the anode of diode D2 are connected.

[0014] The control method includes the activation and deactivation methods of the multi-level DC power consumption device;

[0015] The specific activation method is as follows: when the main switch T1 is open, the sub-module is activated, and the voltage at the sub-module terminals is equal to the voltage across the DC capacitor C of the sub-module.

[0016] The specific disconnection method is as follows: when the main switch T1 is closed, the sub-module is disconnected and the voltage at the sub-module terminal is 0.

[0017] The control method is used in offshore wind power high-voltage direct current transmission systems, which are connected to the main power grid to form a power supply system.

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

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

[0020]

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

[0022] At this time, all insulated-gate bipolar transistors T1 in all submodules are turned on, and the transmitted power is absorbed by the power-consuming resistors, whose resistance values ​​satisfy:

[0023]

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

[0025] Dynamic power adjustment mode: When the main grid encounters a low voltage anomaly, the multi-level DC power dissipation device needs to absorb energy within the range of zero to rated power.

[0026] The strategy employed is to indirectly adjust the voltage level across the power-consuming resistor by adjusting the sum of the output voltages of the submodules. In one part of the submodules, the insulated-gate bipolar transistor T1 is turned on, and the submodule output voltage is 0; in another part of the 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 The power absorbed by the energy-consuming resistor at this time is as follows:

[0027]

[0028] Among them, P Rd Absorbs power for energy-consuming devices; U o This represents the sum of the output voltages of the submodules.

[0029] In the event of an AC-side voltage dip fault, the control method uses only multi-level DC power dissipation devices to dissipate excess energy in the power supply system, thereby improving system reliability and reducing the complexity of the power supply system.

[0030] In the control method, the modular multilevel DC power consumption device forms a DC power consumption topology with continuously adjustable resistance and flexible DC load characteristics, so as to reduce the impact of its operation on the DC system of the power supply system.

[0031] The multilevel DC power dissipation device uses the switching transistors in the submodule to form the main switch and auxiliary switch respectively, and the main switch and auxiliary switch work together to participate in power modulation so that the integrated resistor power inside the submodule is kept at a low level, thereby reducing the loss of the switching devices.

[0032] When the main switch T1 of all submodules is open, the voltage U of the DC pole line dc The voltage is evenly distributed across each submodule, and the rated operating voltage U of each submodule is... n =U dc / N is:

[0033]

[0034] Where N is the total number of submodules connected in series; when the main switch T1 of all submodules is closed, the DC pole line voltage is directly applied across the energy-consuming resistor, and the power absorbed by the energy-consuming resistor is equal to the power transmitted by the system.

[0035] When the DC power-consuming device enters power-consuming operation mode, the voltage of each submodule capacitor C will be monitored in real time; when the submodule is activated, the submodule capacitor charges, and the voltage rises; the submodule capacitor voltage is within U... L to U H Fluctuations within a certain range are equivalent to maintaining a constant capacitor voltage. The specific control strategy is as follows:

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

[0037] When U L ≤U C ≤U H At this time, switch T2 remains closed, and the voltage across C continues to decrease;

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

[0039] The method includes a submodule dynamic round-robin switching method for flexible control of the DC bus voltage during faults, specifically including:

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

[0041] Calculate the required number of operating state submodules: based on the current power requirement kP rated Calculate the number of submodules that need to be in a working state; at this point, the following conditions must be met.

[0042] N in =N B +ΔN in (5)

[0043] Where N in N represents the total number of submodules that rotate within a cycle. B ΔN is the number of submodules that are rotated in a fixed cycle. in Caused by power changes within adjacent cycles, it represents the number of additional sub-modules that rotate, i.e., the power corresponding to the gradual recovery of voltage.

[0044] The operating status of the submodule is dynamically adjusted. Specifically, when a submodule is put into operation, the capacitor of the submodule discharges through the energy-consuming resistor R, which will generate a large loss in the energy-consuming resistor R. In order to ensure that the loss is evenly distributed among the voltage regulator resistors R of each submodule, the submodules put into operation must be switched according to a predetermined rule so that the average duration of each submodule being 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-consuming resistor, we ensure it remains within a safe range; the formula is:

[0047]

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

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

[0050] When dynamically adjusting the running state of a submodule, the following submodule switching logic is used:

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

[0052] 2) Input and output time ratio: 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 faults and avoid overheating of the resistor due to long-term continuous operation.

[0053] 3) The system has 20 energy-consuming resistors, each controlled independently, and uses a cyclic switching strategy to achieve uniform energy consumption. The specific switching logic is as follows: At the beginning of each working cycle, the energy-consuming resistors in each module are put into operation in a preset order. When the operation time reaches 70% of the working cycle, the energy-consuming resistors in each module are switched out in turn 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 communicatively connected to the at least one processor; an external circuit interface module for connecting to an external circuit system, supporting multiple standard interface protocols to ensure compatibility; and 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 preset rules to ensure the stable operation of the system.

[0055] The memory stores instructions that can be executed by the at least one processor, which are executed by the at least one processor to enable the at least one processor to execute a control method for a DC power consumption device.

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

[0057] It enables seamless integration with different types of external power supplies, loads, and monitoring systems; supports hot-swapping operations, allowing external components to be replaced or added without power interruption; and provides data exchange capabilities to ensure that the internal control system can obtain the 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 is detected, the protection program is immediately activated, the DC power consumption device is engaged, and the pre-configured backup circuit path is activated, while an alarm message is sent to the user; when the automatic mode cannot properly engage the DC power consumption device, it switches to manual mode.

[0060] In manual mode, the system also has fault detection capabilities, but the operator needs to manually select whether to activate the DC power consumption device based on the prompts, making it suitable for occasions requiring manual confirmation.

[0061] This invention proposes an AC fault ride-through control method for a modular multilevel DC power dissipation device. The aim is to improve system stability and reliability while reducing system complexity.

[0062] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0063] The AC fault ride-through control method for a modular multilevel DC energy dissipation device proposed in this invention can dissipate surplus energy in the system during AC side voltage drop faults without adding other equipment, thereby improving system reliability and reducing system complexity.

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

[0065] The main and auxiliary switches participate in power modulation simultaneously. The integrated resistors inside the submodule have low power, the switching devices have low losses, and the safety margin is large.

[0066] It has good electromagnetic compatibility (EMI) characteristics. Attached Figure Description

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

[0068] Appendix Figure 1 This is a schematic diagram of the three-phase voltage waveforms during the grid voltage dip and ramp recovery process;

[0069] Appendix Figure 2 This is a schematic diagram of the input DC bus voltage waveform during a power grid voltage fault.

[0070] Appendix Figure 3 This is a schematic diagram of a DC power consumption topology;

[0071] Appendix Figure 4 This is a schematic diagram of two switching methods for DC power consumption topologies;

[0072] Appendix Figure 5 This is a schematic diagram of the current flow path for the three operating states of the submodule (where part a is the current flow path of the proposed modular multilevel DC energy dissipation device when the output voltage is Uc in zero energy dissipation mode; part b is the current flow path of the proposed modular multilevel DC energy dissipation device when the output voltage is 0 in full energy dissipation mode; and part c is the current flow path of the proposed modular multilevel DC energy dissipation device in dynamic power adjustment mode).

[0073] Appendix Figure 6 This is a schematic diagram of the operation control block of a DC energy-consuming device;

[0074] Appendix Figure 7 This is a schematic diagram of a dual-symmetric arrangement of a DC power dissipation topology;

[0075] Appendix Figure 8 This is a schematic diagram of the submodule voltage control method;

[0076] Appendix Figure 9 This is a schematic diagram of the submodule voltage discharge circuit;

[0077] Appendix Figure 10 This is a schematic diagram of the submodule cyclic switching control flow;

[0078] Appendix Figure 11 This is a schematic diagram of the external circuit layout of a DC power consumption device. Detailed Implementation

[0079] As shown in the figure, an AC fault ride-through control method for a modular multilevel DC power dissipation device is described. In this method, a dual-symmetric control mechanism is formed using the modular multilevel DC power dissipation device, with two multilevel DC power dissipation devices symmetrically arranged and connected to the positive and negative lines respectively; the power dissipation resistor R... d The layout is centrally located outdoors, with n sub-modules connected to each end;

[0080] The DC power dissipation device includes a power dissipation resistor and a sub-module with several built-in switching transistors. The method enables the proposed sub-module to have AC fault ride-through capability by controlling the on / off state of these switching transistors in the sub-module.

[0081] The switching transistors in the submodules are insulated-gate bipolar transistors (IGBTs). Each submodule includes two IGBTs, four diodes, one capacitor, and three resistors. The specific circuit structure is as follows: each submodule contains IGBT T1, IGBT T2, diodes D1, D2, D3, and D4, capacitor C, and resistors R1, R2, and R3. Specifically, the source of IGBT T1 is connected to the anode of diode D3, and its drain is connected to the cathode of diode D3. The source of IGBT T2 is connected to the anode of diode D4, and its drain is connected to the cathode of diode D4. Connect the following: 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, the cathode of diode D3, the anode of diode D1, and resistor R1 are connected; the cathode of diode D1 and the other end of resistor R1 are connected to 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, the anode of diode D4, and resistor R3 are connected to the cathode of diode D2; the source of insulated-gate bipolar transistor T1, the anode of diode D3, and capacitor C, resistor R2, resistor R3, and the anode of diode D2 are connected.

[0082] The control method includes the activation and deactivation methods of the multi-level DC power consumption device;

[0083] The specific activation method is as follows: when the main switch T1 is open, the sub-module is activated, and the voltage at the sub-module terminals is equal to the voltage across the DC capacitor C of the sub-module.

[0084] The specific disconnection method is as follows: when the main switch T1 is closed, the sub-module is disconnected and the voltage at the sub-module terminal is 0.

[0085] The control method is used in offshore wind power high-voltage direct current transmission systems, which are connected to the main power grid to form a power supply system.

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

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

[0088]

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

[0090] At this time, all insulated-gate bipolar transistors T1 in all submodules are turned on, and the transmitted power is absorbed by the power-consuming resistors, whose resistance values ​​satisfy:

[0091]

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

[0093] Dynamic power adjustment mode: When the main grid encounters a low voltage anomaly, the multi-level DC power dissipation device needs to absorb energy within the range of zero to rated power.

[0094] The strategy employed is to indirectly adjust the voltage level across the power-consuming resistor by adjusting the sum of the output voltages of the submodules. In one part of the submodules, the insulated-gate bipolar transistor T1 is turned on, and the submodule output voltage is 0; in another part of the 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 The power absorbed by the energy-consuming resistor at this time is as follows:

[0095]

[0096] Among them, P Rd Absorbs power for energy-consuming devices; U o This represents the sum of the output voltages of the submodules.

[0097] In the event of an AC-side voltage dip fault, the control method uses only multi-level DC power dissipation devices to dissipate excess energy in the power supply system, thereby improving system reliability and reducing the complexity of the power supply system.

[0098] In the control method, the modular multilevel DC power consumption device forms a DC power consumption topology with continuously adjustable resistance and flexible DC load characteristics, so as to reduce the impact of its operation on the DC system of the power supply system.

[0099] The multilevel DC power dissipation device uses the switching transistors in the submodule to form the main switch and auxiliary switch respectively, and the main switch and auxiliary switch work together to participate in power modulation so that the integrated resistor power inside the submodule is kept at a low level, thereby reducing the loss of the switching devices.

[0100] When the main switch T1 of all submodules is open, the voltage U of the DC pole line dc The voltage is evenly distributed across each submodule, and the rated operating voltage U of each submodule is... n =U dc / N is:

[0101]

[0102] Where N is the total number of submodules connected in series; when the main switch T1 of all submodules is closed, the DC pole line voltage is directly applied across the energy-consuming resistor, and the power absorbed by the energy-consuming resistor is equal to the power transmitted by the system.

[0103] When the DC power-consuming device enters power-consuming operation mode, the voltage of each submodule capacitor C will be monitored in real time; when the submodule is activated, the submodule capacitor charges, and the voltage rises; the submodule capacitor voltage is within U... L to U H Fluctuations within a certain range are equivalent to maintaining a constant capacitor voltage. The specific control strategy is as follows:

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

[0105] When U L ≤U C ≤U H At this time, switch T2 remains closed, and the voltage across C continues to decrease;

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

[0107] The method includes a submodule dynamic round-robin switching method for flexible control of the DC bus voltage during faults, specifically including:

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

[0109] Calculate the required number of operating state submodules: based on the current power requirement kP rated Calculate the number of submodules that need to be in a working state; at this point, the following conditions must be met.

[0110] N in =N B +ΔN in (5)

[0111] Where N in N represents the total number of submodules that rotate within a cycle. B ΔN is the number of submodules that are rotated in a fixed cycle. inCaused by power changes within adjacent cycles, it represents the number of additional sub-modules that rotate, i.e., the power corresponding to the gradual recovery of voltage.

[0112] The operating status of the submodule is dynamically adjusted. Specifically, when a submodule is put into operation, the capacitor of the submodule discharges through the energy-consuming resistor R, which will generate a large loss in the energy-consuming resistor R. In order to ensure that the loss is evenly distributed among the voltage regulator resistors R of each submodule, the submodules put into operation must be switched according to a predetermined rule so that the average duration of each submodule being 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-consuming resistor, we ensure it remains within a safe range; the formula is:

[0115]

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

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

[0118] When dynamically adjusting the running state of a submodule, the following submodule switching logic is used:

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

[0120] 2) Input and output time ratio: 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 faults and avoid overheating of the resistor due to long-term continuous operation.

[0121] 3) The system has 20 energy-consuming resistors, each controlled independently, and uses a cyclic switching strategy to achieve uniform energy consumption. The specific switching logic is as follows: At the beginning of each working cycle, the energy-consuming resistors in each module are put into operation in a preset order. When the operation time reaches 70% of the working cycle, the energy-consuming resistors in each module are switched out in turn 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 communicatively connected to the at least one processor; an external circuit interface module for connecting to an external circuit system, supporting multiple standard interface protocols to ensure compatibility; and 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 preset rules to ensure the stable operation of the system.

[0123] The memory stores instructions that can be executed by the at least one processor, which are executed by the at least one processor to enable the at least one processor to execute a control method for a DC power consumption device.

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

[0125] It enables seamless integration with different types of external power supplies, loads, and monitoring systems; supports hot-swapping operations, allowing external components to be replaced or added without power interruption; and provides data exchange capabilities to ensure that the internal control system can obtain the 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 is detected, the protection program is immediately activated, the DC power consumption device is engaged, and the pre-configured backup circuit path is activated, while an alarm message is sent to the user; when the automatic mode cannot properly engage the DC power consumption device, it switches to manual mode.

[0128] In manual mode, the system also has fault detection capabilities, but the operator needs to manually select whether to activate the DC power consumption device based on the prompts, making it suitable for occasions requiring manual confirmation.

[0129] Example:

[0130] To demonstrate the shortcomings of traditional technologies, this example first simulates a fault condition in which the power grid drops by 0.05s to 0.15s and then recovers from the slope between 0.15s and 0.25s.

[0131] The three-phase voltage waveforms of the power grid during the fault process are shown in the attached instruction manual. Figure 1 As shown. During a fault, the input DC bus voltage for the faultless ride-through strategy control is as specified in the attached manual. Figure 2 As shown, due to a voltage drop caused by a grid fault, the power transmitted from the offshore wind farm cannot be absorbed, and all the transmitted power will be applied to the input bus of the converter. (See attached manual.) Figure 2 As can be seen, after the fault occurs, the DC bus voltage rises continuously. Even if the grid voltage returns to normal operation after 0.25 seconds, the bus voltage still needs a long time to recover to its rated voltage. Therefore, during the fault process, the DC bus voltage will be subjected to excessive voltage stress for a long time. The prolonged fault time may lead to serious consequences such as excessively high bus voltage and damage to components.

[0132] This example presents a modular multilevel DC power dissipation device, as shown in the attached instruction manual. Figure 3 As shown. The device comprises several sub-modules and a power-consuming resistor. Each sub-module includes:

[0133] Insulated-gate bipolar transistor T1, insulated-gate bipolar transistor T2, diodes D1, D2, D3, and D4, capacitor C, resistors R1, R2, and R3; where:

[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] Diode D1 is connected in parallel with resistor R1;

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

[0138] Diode D2 is connected in parallel with resistor R3;

[0139] The drain of the insulated gate bipolar transistor T1, the cathode of diode D3, the anode of diode D1, and resistor R1 are connected. The cathode of diode D1 and the other end of resistor R1 are connected to capacitor C, resistor R2, the drain of insulated gate bipolar transistor T2, and the cathode of 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, 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 insertion and removal in this example

[0143] The AC fault ride-through control method for a modular multilevel DC power dissipation device includes two activation and deactivation methods, as shown in the appendix to the specification. Figure 4 As shown.

[0144] Input 1: When the main switch T1 is open, the sub-module is engaged, and the voltage across the sub-module is equal to the voltage across the DC capacitor C of the sub-module.

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

[0146] 3. Working Status

[0147] The operating status of the AC fault ride-through control method for the modular multilevel DC power dissipation device is as shown in the attached manual. Figure 5 As shown.

[0148] State 1 (Zero Power Consumption Mode): 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 As shown in (a).

[0149] State 2 (Full Power Consumption Mode): Insulated Gate Bipolar Transistor T1 in all submodules is turned on, and the output voltage of all submodules is 0; For example... Figure 5 As shown in (b).

[0150] State 3 (Dynamic Power Adjustment Mode): In some sub-modules, the insulated gate bipolar transistor T1 is turned on, and the sub-module output voltage is 0; in some sub-modules, the insulated gate bipolar transistor T1 is turned off, and T2 is turned on, and the sub-module output voltage is the capacitor voltage. Figure 5 As shown in (c). The block diagram for the operation and control of the DC energy-consuming device is as follows. Figure 6 As shown.

[0151] The dual symmetric control in this example

[0152] The AC fault ride-through control method for a modular multilevel DC power dissipation device includes a dual symmetrical control, as shown in the appendix to the specification. Figure 7 As shown. Two multi-level DC power dissipation devices are arranged symmetrically and connected to the positive and negative lines respectively; the power dissipation resistor R d The layout is centrally located outdoors, with n sub-modules connected to each end.

[0153] This example illustrates a symmetrical arrangement of multi-level DC power consumption.

[0154] When the main switch T1 of all submodules is open, the voltage U of the DC pole line dc The voltage is evenly distributed across each submodule; therefore, the rated operating voltage U of each submodule is... n for:

[0155]

[0156] Where N is the total number of submodules connected in series. When the main switch T1 of all submodules is closed, the DC pole voltage is directly applied across the energy-consuming resistor, and the power absorbed by the energy-consuming resistor is equal to the power transmitted by the system.

[0157] The submodule voltage control method in this example

[0158] When the energy-consuming device enters the energy-consuming operating mode, the voltage of each submodule capacitor C will be monitored in real time. When the submodule is activated, the submodule capacitor charges, and the voltage rises. The submodule capacitor voltage is within U... L to U H Fluctuations within a certain range are equivalent to maintaining a constant capacitor voltage. The specific control strategy is as follows:

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

[0160] When U L ≤U C ≤U H At this time, switch T2 remains closed, and the voltage across C continues to decrease;

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

[0162] The dynamic loop switching method in this example

[0163] When a submodule is activated, its capacitor discharges through the energy-consuming resistor R, resulting in significant losses within R. To ensure these losses are evenly distributed across the voltage regulator resistors R of each submodule, the activated submodules must be switched according to a specific pattern to maintain the same average activation time for each submodule. The following submodule switching logic was designed for this purpose. The discharge circuit of the submodule capacitor through the energy-consuming resistor R is shown in the attached manual. Figure 8 As shown.

[0164] The AC fault ride-through control method for a modular multilevel DC power consumption device includes a dynamic cyclic switching method. The working cycle of the multilevel DC power consumption device is set to T. Within one working cycle T, all sub-modules are switched on and off an average of once, meaning that the main switch T1 switches on and off an average of once within each working cycle T.

[0165] Specifically: when the bus voltage U bus Higher than the preset threshold U high At that time, a switching method is adopted in which 6 energy-consuming resistors are grouped together, and each resistor operates for T hours. on ​Switching after a certain time, the operating time of each energy-consuming resistor is T. on =0.7T; when the bus voltage U bus Below the preset threshold U low At that time, a switching method is adopted in which 10 energy-consuming resistors are grouped together, and each resistor operates for T hours. on Switching after a certain time, the operating time of each energy-consuming resistor is T. on =0.7T. The calculation method for the energy-consuming resistor is shown in equation (8).

[0166]

[0167] Where N B ΔN is the number of submodules that are rotated in a fixed cycle. in The number of additional submodules to rotate, f is the switching frequency of the switching transistor, and T is the number of submodules to rotate. ctl This is the valve control cycle. A schematic diagram of the power consumption resistor switching is attached to the instruction manual. Figure 9 As shown. The submodule cyclic switching control flowchart is attached to the instruction manual. Figure 10 As shown.

[0168] Temperature control in this example

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

[0170]

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

[0172] External circuit layout in this example

[0173] The AC fault ride-through control method for a modular multilevel DC power consumption device includes an external circuit deployment scheme. It achieves seamless integration with different types of external power supplies, loads, and monitoring systems; supports hot-swapping operations, allowing for the replacement or addition of external components without power interruption; and provides data exchange capabilities, ensuring that the internal control system can obtain real-time status information of the external circuit. 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 is detected, the system will immediately activate the protection program, put the DC power consumption device into operation, activate the pre-configured backup circuit path, and send an alarm message to the user. When the automatic mode cannot put the DC power consumption device into operation normally, it will switch to manual mode.

[0175] In manual mode, although the system also has fault detection capabilities, the operator needs to manually select whether to activate the DC power consumption device based on the prompts, which is suitable for occasions that require manual confirmation.

Claims

1. A method for AC fault ride through control of a modular multilevel DC energy consuming device, characterized in that: In the method, a double symmetric control mechanism is formed by the modular multi-level direct current energy consumption device, two multi-level direct current energy consumption devices are symmetrically arranged and respectively connected to a positive line and a negative line; an energy consumption resistor R d The n sub-modules are arranged in a centralized outdoor manner and respectively connected at two ends The direct current energy consumption device includes an energy consumption resistor and a plurality of sub-modules with built-in switching tubes, and the method controls the on-off state of the switching tubes in the sub-modules to enable the proposed sub-modules to have AC fault ride-through function. The control method includes a putting-in mode and a cutting-off mode of the multi-level direct current energy consumption device; The putting-in mode is specifically: when the main switch is opened, the sub-modules are put in, and the voltage at the end of the sub-modules is equal to the voltage between the two ends of the direct current capacitor C of the sub-modules; The cutting-off mode is specifically: when the main switch is closed, the sub-modules are cut off, and the voltage at the end of the sub-modules is 0; The control method is used in an offshore wind power high voltage direct current transmission system, and the offshore wind power high voltage direct current transmission system is connected with a main power grid to form a power supply system; The multi-level direct current energy consumption device has the following operation modes under normal working conditions; Zero energy consumption mode: when the offshore wind power high voltage direct current transmission system is fault-free, the energy consumption device absorbs zero power, all insulated gate bipolar transistors T1 and T2 in the sub-modules are turned off, and the direct current side voltage is supported by the capacitor voltage in the sub-modules; the capacitor voltage of a single sub-module is: (1)； Full energy consumption mode: when the grid side AC voltage of the main power grid drops to zero and the receiving end converter station completely loses the power transmission capability, the multi-level direct current energy consumption device absorbs all the transmission power; At this time, all the insulated gate bipolar transistors T1 in the sub-modules are turned on, the transmission power is absorbed by the energy consumption resistor, and the resistance value of the energy consumption resistor satisfies: (2) wherein R d is the concentrated resistance value; P N the system rated transmission power; Dynamic power adjustment mode: when the main grid side encounters a low voltage abnormality, the multi-level direct current energy consumption device needs to absorb energy in the range of zero to rated power, The strategy is to indirectly adjust the voltage level across the energy consumption resistor by adjusting the sum of the output voltages of the sub-modules; a part of the insulated gate bipolar transistors T1 in the sub-modules are turned on, and the output voltage of the sub-module is 0; another part of the insulated gate bipolar transistors T1 in the sub-modules are turned off, and the insulated gate bipolar transistors T2 are turned on, and the output voltage of the sub-module is the capacitor voltage U c ; at this time, the power absorbed by the energy consumption resistor is as follows: (3) Wherein, P Rd is the power absorbed by the energy consumption device; U o is the sum of the output voltages of the sub-modules, N is the total number of sub-modules in series, the voltage of the DC polar line is U dc .

2. The method of AC fault ride through control of a modular multilevel DC energy consuming device according to claim 1, characterized in that In the AC side voltage drop fault, the control method only uses the multi-level direct current energy consumption device to dissipate the excess energy in the power supply system, so as to improve the reliability of the system and reduce the complexity of the power supply system; The switching tubes in the sub-modules are insulated gate bipolar transistors, and each sub-module includes two insulated gate bipolar transistors, four diodes, one capacitor and three resistors, and the specific circuit structure is that the sub-module includes 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: the source electrode of the insulated gate bipolar transistor T1 is connected with the anode of the diode D3, and the drain electrode is connected with the cathode of the diode D3; the source electrode of the insulated gate bipolar transistor T2 is connected with the anode of the diode D4, and the drain electrode is connected with the cathode of the diode D4; the diode D1 is connected with the resistor R1 in parallel; the capacitor C is connected with the resistor R2 in parallel; the diode D2 is connected with the resistor R3 in parallel; the drain electrode of the insulated gate bipolar transistor T1, the cathode of the diode D3 and the anode of the diode D1 and the resistor R1 are connected, the cathode of the diode D1 and the other end of the resistor R1 are connected with the capacitor C, the resistor R2, the drain electrode of the insulated gate bipolar transistor T2 and the cathode of the diode D4; the source electrode of the insulated gate bipolar transistor T2, the anode of the diode D4 and the resistor R3 and the cathode of the diode D2 are connected; the source electrode of the insulated gate bipolar transistor T1, the anode of the diode D3 and the capacitor C, the resistor R2, the resistor R3 and the anode of the diode D2 are connected.

3. The method of AC fault ride through control of a modular multilevel DC energy consuming device according to claim 1, characterized in that: The control method is characterized in that the modular multi-level direct-current energy consumption device forms a direct-current energy consumption topology structure with flexible direct-current load characteristics with continuously adjustable resistance, so as to reduce the influence on the direct-current system of the power supply system during operation. The multi-level direct-current energy consumption device forms a main switch and an auxiliary switch by each switch tube in the sub-module, and the main switch and the auxiliary switch cooperatively participate in power modulation, so that the integrated resistance power in the sub-module is maintained at a low level, and the loss of the switch device is reduced.

4. The method of AC fault ride through control of a modular multilevel DC energy consuming device according to claim 1, characterized in that: When the insulated gate bipolar transistors T1 of all sub-module main switches are turned off, the voltage U of the direct current pole line dc The rated working voltage of each sub-module is evenly distributed on each sub-module is: (4) When all the insulated gate bipolar transistors T1 of the main switches of the sub-modules are closed, the direct-current pole line voltage is directly applied across the energy consumption resistors, and the power absorbed by the energy consumption resistors is equal to the system transmission power.

5. The method of AC fault ride through control of a modular multilevel DC energy consuming device according to claim 4, characterized in that When the DC energy consumption device enters the energy consumption mode, the voltage of each sub-module capacitor C will be monitored in real time; when the sub-module is put into operation, the sub-module capacitor is charged and the voltage rises; the voltage of the sub-module capacitor fluctuates in the range of U L to U H , which is equivalent to maintaining a constant value of the capacitor voltage; the specific control strategy is as follows: When U C > U L , the insulated gate bipolar transistor T2 of the switch is closed and the voltage of the capacitor C drops. When U L ≤ U C ≤ U H , the insulated gate bipolar transistor T2 of the switch continues to remain closed, and the voltage of C continues to drop; When U C When U H The insulated gate bipolar transistor T2 of the switch is turned off, the capacitor C voltage rises and the next cycle begins.

6. The method of AC fault ride through control of a modular multilevel DC energy consuming device according to claim 5, characterized in that The method includes a dynamic round-robin switching method of the sub-modules, which is used for flexible control of the direct-current bus voltage during a fault, and specifically includes: The monitoring real-time power method: under the fault condition, by adjusting the number of working sub-modules in the DC energy consuming device, the total power output of the DC energy consuming device including power dissipation and active output is matched with the current power demand; when the fault is cleared, the voltage corresponds to different power in the slow recovery process, which can be quantified as kP rated , wherein P rated is the rated power of the DC energy consuming device, k is a dynamically changing coefficient, 0≤k≤1; Calculate the number of sub-modules needed in working state: according to the current power demand kP rated Calculate the number of sub-modules needed in working state; at this time, the following needs to be met (5) wherein is the total number of sub-modules in a cycle, is the number of sub-modules in each cycle, is the number of additional sub-modules in a cycle due to the change in power from the previous cycle, The dynamic adjustment of the operating state of the sub-modules includes: when the sub-modules are put into operation, the capacitor of the sub-module discharges through the energy consumption resistor R, which will generate a large loss in the energy consumption resistor R. In order to ensure that the loss is evenly distributed among the energy consumption resistors R of each sub-module, the sub-modules must be switched according to a predetermined rule, so that the average time of each sub-module is the same. The method also includes a temperature control method, which is characterized by: The temperature rise ΔT of each energy consumption resistor is calculated to ensure that it is within a safe range. The formula is: (6) where P dis is the average dissipated power of each energy-consuming resistor, C th is the heat capacity of the energy-consuming resistor, ΔT max is the maximum allowed temperature rise rate of the resistor, R th is the thermal resistance value, is the time.

7. The method of AC fault ride through control of a modular multilevel DC energy consuming device according to claim 6, 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 consumption resistors through the dynamic round-robin switching strategy. In the dynamic round-robin switching strategy, the working period of the multi-level direct-current energy consumption device is set as T, and all the sub-modules are switched on and off once on average in each working period T, that is, the insulated gate bipolar transistor T1 of the main switch is switched on and off once on average in each working period T. When the operating state of the sub-modules is dynamically adjusted, the following sub-module switching logic is adopted: 1) Working period setting: In order to ensure stable operation and efficient energy consumption of the device, the working period of the direct-current chopper of the power supply system is set as T. In each working period T, all the sub-modules are switched on and off once on average, that is, the insulated gate bipolar transistor T1 of the main switch is switched on and off once on average in each working period. This design helps to reduce the switching loss and improve the overall efficiency of the system. 2) Input and output time ratio: In each working period, the input time ratio of the energy consumption resistor is set to 70%, and the output time ratio is set to 30%, so as to ensure sufficient energy consumption capacity during a fault 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 consumption resistors, and each module is independently controlled to achieve uniform energy consumption through a cyclic switching strategy. The specific switching logic is as follows: at the beginning of each working period, the energy consumption resistors in each module are sequentially put into operation according to a predetermined order, and when the input time reaches 70% of the working period, the energy consumption resistors in each module are sequentially cut off, and the process is repeated until the next working period begins. The control method also comprises an external circuit deployment scheme, which comprises: at least one processor; a memory connected in communication with the at least one processor; an external circuit interface module for connecting with external circuit systems, supporting multiple standard interface protocols to ensure compatibility; and a fault detection and switching module capable of automatically detecting various faults in the external circuit and automatically switching to a backup circuit configuration or manually triggering switching according to preset rules 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 to enable the at least one processor to perform the control method of the direct current energy consumption device. Specifically, the external circuit interface module supports the following functions: Seamless connection with different types of external power sources, loads and monitoring systems; support for hot plug operation, allowing replacement or addition of external components without power loss; and data exchange capability to ensure that the internal control system can obtain real-time state information of the external circuit; The working mechanism of the fault detection and switching module is as follows: In the automatic mode, when a change in the DC bus voltage state is detected, the protection program is immediately started, the direct current energy consumption device is put into operation, and the pre-configured backup circuit path is activated, and the user is sent an alarm message; when the automatic mode cannot normally put the direct current energy consumption device into operation, the manual mode is switched; In the manual mode, the system also has fault detection capability, but the execution needs the operator to manually select whether to put the direct current energy consumption device into operation according to the prompt information, so as to be suitable for occasions requiring manual confirmation.

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