A hybrid MMC receiving end fault under DC voltage adaptive regulation method

Abstract

The application discloses a kind of mixed MMC receiving end under fault DC voltage self-adaptive regulation method, belong to direct current grid field, the scheme collects receiving end converter station AC side three-phase voltage, extracts positive sequence amplitude to represent fault severity.Based on the allowable energy storage of MMC submodule capacitor, the preset fault duration and the receiving end AC output capability, the adaptive relationship between the DC voltage reference value and the positive sequence amplitude is established.During fault, the receiving end reduces DC voltage according to this relationship, reduces the input power of DC side, and the excess energy is temporarily stored in the submodule capacitor;When the submodule energy reaches the threshold, active energy control is put into operation, and after communication is established, the sending end converter station and the energy consumption device cooperate to balance power.After the fault is cleared, the DC voltage is ramped up, and the energy consumption device is grouped out, and the temporarily stored energy is gradually released.The application can inhibit submodule overvoltage and DC overvoltage, recover part of energy during fault, and reduce DC voltage fluctuation during recovery process.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission, and more specifically to a method for adaptive DC voltage regulation under hybrid MMC receiving-end faults. Background Technology

[0002] Modular multilevel converters are characterized by high modularity, low output harmonics, and high control freedom, and have been widely used in long-distance, large-capacity flexible DC transmission systems for new energy sources. In a two-end system where the sending-end converter station establishes the AC voltage and frequency on the new energy side and the receiving-end converter station transmits power to the AC grid, the receiving-end converter station typically undertakes the DC voltage control function.

[0003] When a short-circuit fault occurs on the AC side of the receiving-end converter station, the AC voltage drops, and the active power transmission capacity of the receiving end rapidly decreases due to the severity of the fault, current limiting, and sequence component control constraints. Because of delays in fault detection, inter-station communication, and control switching, the sending end may maintain the pre-fault power injection in the early stages of the fault, causing the DC-side input power to exceed the AC-side output power of the receiving end. This surplus energy enters the MMC submodule capacitors, leading to an increase in submodule voltage and inter-station DC voltage, which, in severe cases, may trigger overvoltage protection or converter station blocking.

[0004] Existing fault ride-through measures mainly include configuring large-capacity energy-consuming devices, reducing the power of new energy sources at the sending end, setting up additional energy storage units, or reducing DC voltage by a fixed ratio. Large-capacity energy-consuming devices have problems such as large equipment capacity, large footprint, and high heat dissipation requirements; reducing the power at the sending end is affected by communication delays and is difficult to cover the initial stage of a fault; additional energy storage units increase the costs of insulation, thermal management, and life management; fixed-ratio voltage reduction does not simultaneously consider the severity of the fault and the energy storage margin of the converter valve itself, which may result in insufficient or excessive voltage reduction.

[0005] Therefore, this invention proposes a receiving-end fault ride-through method that uses rapidly acquired fault characteristic quantities as a basis to continuously determine DC voltage reference values ​​and fully utilizes the short-term energy storage capacity of MMC submodule capacitors. Summary of the Invention

[0006] The purpose of this invention is to provide a method for adaptive DC voltage regulation under hybrid MMC receiving-end faults, so as to solve the problems of submodule overvoltage and DC overvoltage caused by the power imbalance between the DC and AC sides during receiving-end AC faults, and reduce the capacity requirements of energy-consuming devices and voltage fluctuations during fault recovery.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for adaptive DC voltage adjustment under hybrid MMC receiving-end faults.

[0008] S1: Collect the three-phase voltage on the AC side of the receiving-end converter station, process the collected three-phase voltage, and extract the positive-sequence AC voltage amplitude; S2: Based on the submodule capacitor's allowed energy storage, the preset fault duration, and the AC output power at the receiving end, establish an adaptive relationship between the DC voltage reference value and the positive sequence AC voltage amplitude. S3: During an AC fault at the receiving end, reduce the DC voltage at the receiving end according to the adaptive relationship described in S2, and utilize the surplus energy generated by the submodule capacitor to temporarily store the system. S4: Real-time monitoring of submodule energy storage status. When the submodule energy reaches the threshold, active energy control is activated. After inter-station communication is established, the sending-end converter station and energy-consuming device work together to participate in system power balance control. S5: After the fault is cleared, ramp recovery control is performed on the DC voltage to gradually release the surplus energy temporarily stored in the submodule capacitor and complete the fault ride-through recovery.

[0009] Preferably, the extraction of the positive-sequence AC voltage amplitude in S1 specifically includes: transforming the three-phase voltage of the receiving-end AC side to... α , β A two-phase stationary coordinate system is used, and the positive-sequence voltage and negative-sequence voltage are separated by a quarter-power frequency cycle delay method. The amplitude of the positive-sequence AC voltage is determined by the positive sequence... α Axis voltage and positive sequence β The square root of the sum of the squares of the axis voltages is obtained, and the specific expression is as follows:

[0010] In the formula, Indicates the positive sequence AC voltage amplitude; and Representing the positive sequence voltage components respectively α and β Axial components.

[0011] 3. The method for adaptive DC voltage adjustment under hybrid MMC receiving-end fault according to claim 1, characterized in that: the basis for establishing the adaptive mapping relationship between the DC voltage reference value and the positive sequence AC voltage amplitude in S2 is as follows: after the receiving-end AC fault occurs, the AC output power of the receiving-end MMC immediately decreases. Under the condition of suppressing negative sequence current and only outputting positive sequence balance current, the average AC output power of the receiving-end MMC is constrained by the positive sequence voltage amplitude and the converter current limit. The magnitude of the positive sequence voltage amplitude can directly reflect the AC power output capability of the receiving-end converter station during the fault. Therefore, the DC voltage is directly adjusted during the fault, thereby quickly reducing the surplus power of the receiving-end converter station.

[0012] Preferably, the preset fault duration in S2 uses 100ms as the receiving-end AC fault ride-through evaluation time window. This time scale covers the main transient energy accumulation stages during fault detection, control switching, and protection clearing. Combined with the allowable voltage operating range of the submodule capacitor, the maximum allowable energy storage for the fault is calculated. The DC voltage reference values ​​corresponding to different positive-sequence voltage drop depths are obtained through energy balance solutions. The expression relating the DC voltage to the positive-sequence voltage amplitude is as follows:

[0013] In the formula, U DC This represents the magnitude of the DC voltage relative to the positive sequence voltage.

[0014] Preferably, after the active energy control is activated, when the total capacitor energy of the submodule... W MMC When the threshold is reached, subsequent energy input is limited by correcting the DC current command or DC voltage command to maintain the total capacitor energy of the submodule within the allowable range. After the fault is cleared, the active energy control gradually exits and releases the surplus energy temporarily stored during the fault. The specific expression for limiting subsequent energy input by correcting the DC current command or DC voltage command is as follows:

[0015] In the formula, Indicates the DC voltage command value; k p and k i These represent the control parameters of the power outer loop PI controller; W MMC This indicates the amount of energy stored in the converter station.

[0016] Preferably, after detecting an AC fault, the receiving end updates the DC voltage reference value based on the positive sequence voltage amplitude and sends fault and derating information to the sending end. After receiving the signal, the sending end converter station switches to constant DC current control, and its outer loop introduces stator module voltage control and power control on the basis of the original grid control. With the cooperation of the sending end converter station, the control of DC side power can be guaranteed, and the surplus power of the sending end converter station can also prevent the sub-module voltage from being charged by the sub-module voltage, which would cause the sub-module voltage to exceed the limit.

[0017] A computer-readable storage medium having a computer program stored thereon, the computer program being executed by a processor as a hybrid MMC receiver-side fault ride-through method based on fault severity adaptive DC voltage regulation.

[0018] Compared with the prior art, the present invention has the following beneficial effects: Firstly, unlike traditional fault ride-through schemes that rely on inter-station communication to exchange fault signals, this invention uses the positive-sequence AC voltage amplitude collected locally at the receiving end to directly characterize the severity of AC faults. It can quickly calculate and generate DC voltage reference values ​​without waiting for inter-station communication messages, thus solving the problem of control response lag caused by communication delays in the early stages of a fault.

[0019] Secondly, compared with the traditional fixed-proportion DC voltage reduction strategy, this invention first uses the positive-sequence voltage amplitude as the basis for judging the voltage reduction, and then uses the allowable energy storage margin of the MMC submodule capacitor as a constraint condition, thereby establishing an adaptive DC voltage relationship. The voltage reduction amplitude is dynamically adjusted according to the actual severity of the fault, effectively avoiding the problem of insufficient voltage reduction in the fixed voltage reduction mode causing overvoltage of the submodule, or excessive voltage reduction causing severe disturbances in the system operating conditions.

[0020] Thirdly, unlike traditional methods that rely solely on energy-consuming devices or direct power reduction at the sending end, this invention achieves multi-stage, time-sequential coordinated control: in the initial stage of a fault transient, the receiving end relies on local adaptive control and submodule capacitors to absorb surplus energy, avoiding power imbalance during the period before inter-station communication is established; after the communication link is established, the sending-end converter station and energy-consuming devices work together to achieve power balance. This fully utilizes the energy storage potential of the converter valve itself and does not rely on DC energy-consuming devices, thus reducing the system's engineering requirements for the equipment capacity, heat dissipation, and footprint of energy-consuming devices.

[0021] Fourth, unlike the traditional recovery strategy where the DC voltage jumps directly back to the rated value after the fault is cleared, this invention adopts a recovery mechanism of DC voltage ramp-up and energy-consuming devices exiting in groups. This is combined with the orderly release of surplus energy temporarily stored in sub-modules to avoid secondary impacts on DC voltage caused by concentrated energy release at the moment the fault is cleared, thereby improving the operational stability of the DC power grid during the fault recovery phase. Attached Figure Description

[0022] Figure 1 This is the topology of the photovoltaic base transmitted to the outside via a flexible DC grid in Embodiment 1 of the present invention; Figure 2 This is the DC voltage adaptive control curve in Embodiment 2 of the present invention.

[0023] Figure 3 This is a flowchart of the AC fault ride-through control at the receiving end in Embodiment 3 of the present invention. Figure 4 This is a simulation result diagram of the positive sequence voltage dropping to 40% in Embodiment 4 of the present invention.

[0024] Figure 5 This is a simulation result diagram of a permanent fault on the AC side in Embodiment 5 of the present invention; Figure 6 This is a schematic diagram of the process of a QR code image super-resolution reconstruction method based on a complete reference map according to the present invention. Detailed Implementation

[0025] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0026] To address the problems mentioned in the technical solutions, this application provides a method for super-resolution reconstruction of QR code images based on a complete reference map. The invention also provides the correspondence between DC voltage and AC positive-sequence voltage amplitude during a fault at the receiving-end converter station, including: (1) Collect the three-phase voltage on the AC side of the receiving-end converter station and convert the three-phase voltage to α , β In a two-phase stationary coordinate system, the positive-sequence voltage component is extracted using a quarter-cycle delay method based on the power frequency, and the positive-sequence AC voltage amplitude is calculated. The positive-sequence AC voltage amplitude is compared with a preset fault criterion; if it falls below a preset threshold, an AC fault is determined to have occurred at the receiving end, and the positive-sequence AC voltage amplitude is used as a measure of fault severity. The expression for the positive-sequence AC voltage amplitude is: (1) In the formula, Indicates the positive sequence AC voltage amplitude; and Representing the positive sequence voltage components respectively α and β Axial components.

[0027] (2) Based on the rated total capacitance energy storage of the submodule, the upper limit of the allowable voltage, the preset fault duration, the DC current and the AC output power of the receiving end, determine the allowable DC input power during the fault, and then establish an adaptive relationship between the DC voltage reference value and the positive sequence AC voltage amplitude.

[0028] The MMC bridge arm connects numerous submodules in series, whose capacitors can absorb or release energy for short periods within the allowable voltage range. This energy storage margin is provided by the converter valve body, which can absorb part of the power difference during fault transients. The total capacitive energy storage of the receiving-end converter valve during rated operation is: (2) In the formula, N represents the number of submodules in a single bridge arm. C SM For a single submodule capacitor, V SM This is the rated voltage of the submodule. The capacitor voltage is allowed to rise within a specified range, which can temporarily store some energy not delivered from the AC side, thereby reducing the DC voltage drop and the instantaneous power borne by the energy-consuming device. However, the available energy is limited by the device's withstand voltage and the duration of the fault.

[0029] The submodule voltage limit must meet the withstand voltage requirements of the IGBT, capacitor, and control board. Referring to existing projects, the submodule uses a 4.5kV / 3kA IGBT with a rated operating voltage of approximately 2.2kV, and the capacitor's rated voltage is 2.8kV (1.27pu). According to IEC61071-2017 and the control board's margin, the capacitor voltage can operate at 1.0–1.4pu for a limited time, and can operate normally for more than 30 minutes under 3kV conditions. This invention… V SM =2.105kV, take 1.4 V SM (2.974kV) is the upper limit, corresponding to W MAX It is 1.96 times the rated capacitor energy. Assuming the fault duration is ΔT, the AC power during the fault duration is... P AC DC side voltage set to V DC_fault Ignoring energy loss, the energy balance of the receiving-end converter station is as follows: (3) In the formula, V DC_fault Indicates the DC side voltage; P AC Indicates the AC power during the fault duration; V sm Indicates the submodule voltage; I DC This represents direct current.

[0030] This invention uses 100ms as the receiving-end AC fault ride-through assessment time window, which covers the main transient energy accumulation stages during fault detection, control switching, and protection clearing. In an 800kV DC transmission system, to determine the relationship between the DC voltage reference value and the fault severity, a three-phase short-circuit fault is selected, and energy constraint calculations are performed with the positive-sequence AC voltage dropping to 0% and 50%. Based on the allowable energy margin of the receiving-end converter valve submodule capacitor, the corresponding upper limit of DC voltage can be obtained from the energy balance relationship. According to existing engineering, the submodule voltage reference value is set to 2.105kV, and the DC current reference value is 5kA. Therefore, the DC voltage should be 137.82kV (0.172pu) when the voltage drops to 0%, and 617.82kV (0.772pu) when the voltage drops to 50%. Considering the fault detection delay, control response delay and engineering margin of the receiving-end converter station, the DC voltage is taken as 0.1pu and 0.6pu when the positive sequence AC voltage amplitude drops to 0% and 50%, respectively. Thus, a corresponding relationship between DC voltage and positive sequence voltage amplitude is obtained, as shown in formula (4).

[0031] (4) In the formula, U DC This represents the magnitude of the DC voltage relative to the positive sequence voltage.

[0032] (3) In the initial stage of a fault, the local control at the receiving end reduces the DC voltage according to the adaptive relationship, thereby reducing the DC input power at the receiving end and using the submodule capacitors to temporarily store the remaining surplus energy within the allowable voltage range. When the total energy of the submodule capacitors reaches a preset threshold, active energy control is activated to further adjust the DC voltage and control the converter station energy to remain constant.

[0033] On the other hand, the present invention provides a coordinated control strategy for the sending-end converter station during a fault and a recovery strategy after the fault ends, including: Upon detecting an AC fault, the receiving end updates the DC voltage reference value based on the positive sequence voltage amplitude and sends fault and derating information to the sending end. Upon receiving the signal, the sending-end converter station switches to constant DC current control, introducing stator module voltage control and power control into its outer loop based on the original grid control. Through the cooperation of the sending-end converter station, control of the DC-side power is ensured, while preventing excess power from the sending-end converter station from charging the sub-module voltage and causing it to exceed limits. In the initial stage of a fault, the receiving-end DC voltage adaptive control and sub-module capacitors handle power surges. After communication is established, the sending-end control and energy-consuming devices participate in power balancing. When the fault is cleared, the DC voltage ramp recovers, energy-consuming branches are decommissioned, and the sending end maintains constant DC current and stator module voltage control; the receiving-end sub-module voltage reference value recovers synchronously, allowing temporarily stored energy to be released gradually.

[0034] The specific expression for limiting subsequent energy input by the corrected DC current command or DC voltage command is as follows: (5) In the formula, Indicates the DC voltage command value; k p and k i These represent the control parameters of the power outer loop PI controller; W MMC This indicates the amount of energy stored in the converter station.

[0035] Example 2 Embodiment 2 of the present invention provides a topology for a photovoltaic base to transmit power to the outside world via a flexible DC grid. The specific process is as follows: Figure 1As shown, the photovoltaic units at the sending end form an islanded system after AC aggregation and multi-stage voltage boosting. The AC voltage and frequency are established by the sending-end MMC, and power is transmitted to the receiving-end grid through an ultra-high voltage DC line. Both converters at both ends adopt a hybrid configuration of half-bridge and full-bridge submodules. In the figure, SVPWM (Space Vector Pulse Width Modulation) and NLM (Nearest Level Modulation) represent the space vector pulse width modulation of the photovoltaic inverter and the nearest level modulation strategy of the flexible DC converter, respectively; PLL represents a phase-locked loop. u PCC This refers to the voltage at the grid connection point. θ The phase angle is output by the phase-locked loop; f 0 represents the input frequency for the flexible DC network control.

[0036] Example 3 Embodiment 3 of the present invention provides a DC voltage adaptive control curve, the specific process of which is as follows: In the case of asymmetrical faults, the MMC's transformer wiring method isolates the zero-sequence current path, and the inverter station is equipped with negative-sequence current suppression, which can suppress the second harmonic fluctuation of power and increase the power output capability of the AC side during the fault. The current during the fault only contains positive-sequence and negative-sequence components. There are many common methods for separating positive and negative-sequence voltages. This invention uses the quarter-cycle delay method. After separating the positive-sequence voltage, the positive-sequence voltage amplitude of the system is calculated by equation (1). Figure 1 As shown. By detecting the amplitude of the positive sequence voltage on the AC side, the DC voltage is reduced according to the decrease ratio of the positive sequence voltage. At this time, the DC voltage is calculated according to equation (4).

[0037] Example 4 Embodiment 4 of the present invention provides a flowchart of the AC side fault ride-through control for the receiving-end converter station, the specific process of which is as follows: Upon detecting a fault at the receiving end, i.e., when the positive-sequence voltage amplitude falls below the control threshold, the power surge is initially handled by the receiving-end DC voltage adaptive control and submodule capacitors. After communication is established, the sending-end control and energy-consuming devices participate in power balancing. Fault flags, positive-sequence AC voltage amplitude, and power derating information are transmitted via inter-station communication. Upon receiving the information, the sending-end converter station switches to constant DC current control and adjusts the active power reference value according to the reduction ratio of the receiving-end positive-sequence voltage amplitude, ensuring that the power injected by the sending end matches the power that can be transmitted from the receiving end. Energy-consuming devices are grouped according to the amount of surplus power to absorb the power difference that has not yet been completely eliminated by active energy control and sending-end derating.

[0038] After the fault is cleared, the positive sequence voltage amplitude returns to the steady state value. At this time, the DC voltage reference value is not immediately restored to the rated value by a step, but gradually increases according to the preset slope. At the same time, the energy-consuming devices are disconnected in groups, the DC current and power reference values ​​of the sending end are smoothly restored, and the voltage reference value of the receiving terminal module is restored synchronously, so that the energy temporarily stored during the fault is gradually released, thereby avoiding secondary overvoltage during the DC voltage recovery stage.

[0039] Example 5 Embodiment 5 of this invention provides the transient response process of the receiving-end converter station when the positive sequence voltage amplitude drops to 40% under an AC side fault. The simulation was conducted in a single-pole, 800kV hybrid MMC DC transmission system. The fault was set to occur at 2.6 seconds, and the specific waveforms are as follows: Figure 4 (a) is the positive sequence voltage waveform on the AC side. During the fault, the positive sequence voltage drops to 40%. Figure 4 (b) shows the DC voltage waveform of the MMC at the sending and receiving ends. From equation (4), we can obtain that the DC voltage should be 400kV at this time. Figure 4 (b) It can be seen that the DC voltage at the receiving end remained at around 411.8kV during the fault period. During the fault recovery period, the highest DC voltage at the sending end was 809.5kV (1.02pu) and the highest DC voltage at the receiving end was 892.5kV (1.06pu). Figure 4 (c) shows the voltage waveform of the submodule of the receiving-end converter station during the fault. During the fault, the submodule of the receiving-end converter station absorbs the transient surplus power. The submodule voltage reaches 2.92kV (1.39pu) after the fault ends. After the fault ends, the submodule voltage releases energy and returns to the steady-state value. Figure 4 (d) shows the current value of the receiving-end converter station arm during the fault. It can be seen that no overcurrent phenomenon occurred in the receiving-end converter station arm during the fault.

[0040] Example 6 Embodiment 6 of this invention provides a transient response process in which the receiving-end converter station actively adjusts the DC voltage based on the converter station's energy under a permanent AC side fault. The fault is set to occur at 2.6 seconds, and the specific waveform is as follows: Figure 5 (a) is the positive sequence voltage waveform on the AC side. During the fault, the positive sequence voltage drops to 20%. Figure 5 (b) shows the DC voltage waveform of the MMC at the sending and receiving ends. From equation (4), we can obtain that the DC voltage should be 240kV at this time. Figure 5 (b) It can be seen that the DC voltage at the receiving end remained at around 260.6kV during the fault period. After the converter station energy reached the threshold, the DC voltage further decreased to 3.1kV. Figure 5(c) shows the voltage waveform of the submodule of the receiving-end converter station during the fault. During the fault, the submodule of the receiving-end converter station absorbs the transient surplus power. The submodule voltage reaches 2.93kV (1.39pu) after the fault ends, and then the submodule voltage remains stable. Figure 5 (d) represents the energy level of the receiving-end converter station during the fault. It can be seen that during the fault, the energy of the converter station rose to 1.96 pu and then remained unchanged.

[0041] In summary, after an AC fault occurs at the receiving-end converter station, the system responds quickly by reducing the DC voltage. During the fault ride-through, the system's energy storage margin is considered to recover energy, and no overcurrent occurs in the converter station arm. Meanwhile, the DC voltage remains within the safe threshold during the recovery period.

Claims

1. A method for adaptive DC voltage regulation under hybrid MMC receiving-end faults, characterized in that: S1: Collect the three-phase voltage on the AC side of the receiving-end converter station, process the collected three-phase voltage, and extract the positive-sequence AC voltage amplitude; S2: Based on the submodule capacitor's allowed energy storage, the preset fault duration, and the AC output power at the receiving end, establish an adaptive relationship between the DC voltage reference value and the positive sequence AC voltage amplitude. S3: During an AC fault at the receiving end, reduce the DC voltage at the receiving end according to the adaptive relationship described in S2, and utilize the surplus energy generated by the submodule capacitor to temporarily store the system. S4: Real-time monitoring of submodule energy storage status. When the submodule energy reaches the threshold, active energy control is activated. After inter-station communication is established, the sending-end converter station and energy-consuming device work together to participate in system power balance control. S5: After the fault is cleared, ramp recovery control is performed on the DC voltage to gradually release the surplus energy temporarily stored in the submodule capacitor and complete the fault ride-through recovery.

2. The method for adaptive DC voltage adjustment under hybrid MMC receiving-end faults according to claim 1, characterized in that: The extraction of the positive-sequence AC voltage amplitude described in S1 specifically includes: transforming the three-phase voltage of the receiving-end AC side to... α , β A two-phase stationary coordinate system is used, and the positive-sequence voltage and negative-sequence voltage are separated by a quarter-power frequency cycle delay method. The amplitude of the positive-sequence AC voltage is determined by the positive sequence... α Axis voltage and positive sequence β The square root of the sum of the squares of the axis voltages is obtained, and the specific expression is as follows: In the formula, Indicates the positive sequence AC voltage amplitude; and Representing the positive sequence voltage components respectively α and β Axial components.

3. The method for adaptive DC voltage adjustment under hybrid MMC receiving-end faults according to claim 1, characterized in that: The basis for establishing the adaptive mapping relationship between the DC voltage reference value and the positive sequence AC voltage amplitude in S2 is as follows: After an AC fault occurs at the receiving end, the AC output power of the receiving end MMC immediately decreases. Under the condition of suppressing negative sequence current and only outputting positive sequence balance current, the average AC output power of the receiving end MMC is constrained by the positive sequence voltage amplitude and the converter current limit. The magnitude of the positive sequence voltage amplitude can directly reflect the AC power output capability of the receiving end converter station during the fault. Therefore, the DC voltage is directly adjusted during the fault to quickly reduce the surplus power of the receiving end converter station.

4. The method for adaptive DC voltage adjustment under hybrid MMC receiving-end faults according to claim 1, characterized in that: The preset fault duration mentioned in S2 uses 100ms as the receiving-end AC fault ride-through evaluation time window. This time scale covers the main transient energy accumulation stages during fault detection, control switching, and protection clearing. Combined with the allowable voltage operating range of the submodule capacitor, the maximum allowable energy storage for the fault is calculated. The DC voltage reference value corresponding to different positive sequence voltage drop depths is obtained through energy balance solution. The corresponding expression of DC voltage with respect to the positive sequence voltage amplitude is as follows: In the formula, U DC This represents the magnitude of the DC voltage relative to the positive sequence voltage.

5. The method for adaptive DC voltage adjustment under hybrid MMC receiving-end faults according to claim 1, characterized in that: After the active energy control is activated, when the total capacitor energy of the submodule... W MMC When the threshold is reached, subsequent energy input is limited by correcting the DC current command or DC voltage command to maintain the total capacitor energy of the submodule within the allowable range. After the fault is cleared, the active energy control gradually exits and releases the surplus energy temporarily stored during the fault. The specific expression for limiting subsequent energy input by correcting the DC current command or DC voltage command is as follows: In the formula, Indicates the DC voltage command value; k p and k i These represent the control parameters of the power outer loop PI controller; W MMC This indicates the amount of energy stored in the converter station.

6. The method for adaptive DC voltage adjustment under hybrid MMC receiving-end fault according to claim 1, characterized in that: After detecting an AC fault, the receiving end updates the DC voltage reference value based on the positive sequence voltage amplitude and sends fault and derating information to the sending end. After receiving the signal, the sending end converter station switches to constant DC current control, and its outer loop introduces stator module voltage control and power control on the basis of the original grid control. With the cooperation of the sending end converter station, the control of DC side power can be guaranteed, and the surplus power of the sending end converter station can also prevent the sub-module voltage from being charged by the sub-module voltage, which would cause the sub-module voltage to exceed the limit.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the hybrid MMC receiver-side fault ride-through method based on fault severity adaptive DC voltage regulation as described in any one of claims 1-6.

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