155 results about "Dc fault" patented technology

The invention discloses an alternating-current and direct-current fault protection method of a hybrid commutation converter valve and related equipment thereof, and relates to the technical field of high-voltage direct-current power transmission. The method comprises the steps of obtaining an AC voltage of an AC side, a target trigger angle of a hybrid commutation converter valve and a DC current of a DC side, and determining an extinction angle margin risk factor and a volt-second area margin risk factor according to at least one of the above, the extinction angle margin risk factor being used for representing a commutation success margin, and the volt-second area margin risk factor being used for representing a target trigger angle of the hybrid commutation converter valve; the volt-second area margin risk factor is used for representing the commutation driving capability; determining a commutation failure risk index based on the extinction angle margin risk factor, the volt-second area margin risk factor and the prediction confidence factor; and when the commutation failure risk index is abnormal, controlling and triggering the hybrid commutation converter valve to enter a corresponding commutation enhancement mode or an active turn-off mode based on the commutation failure risk index. According to the embodiment of the invention, active intervention can be carried out before the commutation failure is caused by the AC / DC fault, so that the commutation failure can be fully resisted.

The invention relates to a direct current fault ride-through method, a direct current fault ride-through device, direct current fault ride-through equipment and a medium. The method comprises the following steps: switching a control mode of network-forming type energy storage into an alternating-current voltage control mode or a direct-current control strategy, carrying out coordinated control on devices in a multi-terminal direct-current collecting and sending-out system, clearing fault current, and clearing the fault current by utilizing an active step-down control strategy or the direct-current control strategy at the same time. According to the method, measures such as additional direct current circuit breakers are not needed, control is flexible and easy to achieve, the multi-terminal direct current collecting and sending-out system after fault clearing is controlled to be recovered by judging the operation state of the multi-terminal direct current collecting and sending-out system, and safe and stable operation of the multi-terminal direct current collecting and sending-out system is facilitated.

The present invention discloses a method for self-clearing DC faults in a new energy island power grid transmission system. The sending end adopts a constant AC voltage and frequency control strategy, and there is only one receiving end that adopts a constant DC voltage control strategy, while the remaining receiving ends adopt a constant active power control strategy. At the same time, each pole of the flexible DC converter station at the sending end real-time detects the DC current flowing out of this pole, and each pole of the flexible DC converter station at the receiving end real-time detects the DC current flowing into this pole. After detecting the occurrence of a DC fault, the DC fault is automatically cleared according to their respective control strategies, and the energy balance of the sending end island is achieved in cooperation with the AC energy consumption at the sending end. It solves the technical problems of coordinated control between flexible DC and new energy, power surplus, and self-clearing of DC faults on the DC side, and improves the power regulation ability and system stability of the new energy island power grid transmission system.

The invention discloses a flexible direct-current power transmission system and a fault ride-through method and system thereof. The flexible direct-current power transmission system comprises a main control module, and a new energy sending-out system, an alternating-current energy consumption device, a sending-end converter, a direct-current circuit breaker, a receiving-end converter and a receiving-end alternating-current power grid which are connected in sequence, the direct current circuit breaker is deployed on a direct current power transmission line between the sending end converter and the receiving end converter, and the receiving end converter is a modular multi-level converter formed by cascading a plurality of half-bridge sub-modules with damping branches; the main control module is in communication connection with the half-bridge sub-modules, the direct-current circuit breaker and the alternating-current energy consumption device and used for controlling the damping branches of the half-bridge sub-modules in the running state, the direct-current circuit breaker and the alternating-current energy consumption device to act when a direct-current fault occurs so as to restrain direct current and adjust direct-current voltage to be within a set voltage range. Therefore, no-locking fault ride-through is completed. According to the invention, high-reliability and low-cost DC fault ride-through can be realized.

The invention provides a direct-current boost collection converter of an offshore wind power full-direct-current sending-out system, and the converter can quickly suppress residual direct-current fault current, so that quick direct-current fault isolation is realized by utilizing a direct-current switch. And the fault clearing time is obviously shortened from about 500ms to below 14ms, so that rapid system recovery is realized. The working principle of the topology under the conditions of normal operation and direct-current fault is elaborated, and enhanced power equalization control is provided, so that direct-current voltage and current equalization among sub-modules of the topology is realized. In addition, after interleaving control is adopted, the number of direct-current reactors of the topology is remarkably reduced. A simulation result verifies the effectiveness of the hybrid DC / DC converter and the control scheme thereof in the aspects of blocking fault residual current and promoting direct current fault ride-through by using the DCS.

The invention relates to the technical field of high-voltage direct-current transmission, and particularly provides an LCC-full-bridge MMC series light HVDC converter station control method, which comprises the following steps: a rectification side of a power grid commutation converter adjusts direct-current power through an outer ring and an inner ring adopts linear trigger angle control to generate a trigger pulse; transformer tap adjustment is supplemented; on the basis of the established stable direct current system, an inversion side selects a minimum trigger angle as a control signal by coordinating three control rings of a turn-off angle, direct current voltage and direct current to form a control system; the full-bridge modularized multi-level converter is switched to a power grid following and network construction control mode according to power grid conditions; and when a direct current fault is detected, setting the trigger angle of the commutation converter of the power grid to be 90 degrees and switching the full-bridge modular multi-level converter to an STATCOM mode, thereby realizing direct current fault ride-through without locking the converter. According to the invention, direct-current fault rapid ride-through of the non-locking converter is realized.

The invention relates to the technical field of direct-current transformer high-voltage side fault identification and ride-through, and discloses a direct-current transformer high-voltage side fault identification and ride-through method and system, and the method comprises the steps: obtaining a first parameter of a high-voltage side of a target direct-current boosting transformer; acquiring a first fault feature according to the first parameter; the first fault feature is used for identifying a direct-current boosting transformer high-voltage side fault type; and presetting a fault ride-through strategy, and if the first fault feature of any fault type is obtained, starting the fault ride-through strategy. According to the invention, reliable identification and fault ride-through of the DC fault of the collection system can be realized by using the local measurement information of the DC transformer, the method is not influenced by photovoltaic output, the accuracy and efficiency of fault identification are improved, a new idea and method are provided for fault diagnosis of the DC boosting transformer, and the fault diagnosis efficiency of the DC boosting transformer is improved through a control and protection cooperation mode. The accuracy and efficiency of fault recognition are improved, and a new thought and method are provided for fault diagnosis of the direct-current boosting transformer.

The invention relates to the technical field of power system fault simulation, and discloses a DC fault simulation method for a medium-voltage DC system, and the method comprises the steps: constructing an equivalent circuit containing line distribution parameters, and representing the transmission characteristics of resistance, inductance and capacitance per unit length, a linear mathematical model of arc voltage and arc length is established based on arc discharge experiment data, a dynamic resistance curve is generated in combination with an arc length time increase function, an initial value and a change rate of dynamic resistance are extracted as characteristic parameters, and a mapping relation table of the characteristic parameters with metallic short circuit and mild / severe arc faults is established. And according to a target fault type, matching a dynamic resistance parameter, injecting the dynamic resistance parameter into an equivalent circuit, solving a differential equation containing a time-varying resistor, and outputting a high-fidelity DC fault current signal. The method solves the problem that static resistance simulation cannot reproduce arc dynamic characteristics, and significantly improves the accuracy of fault simulation.

The invention provides a medium-voltage direct-hanging multi-level energy storage grid-connected direct-current fault isolation method and device. The method comprises the following steps of: establishing corresponding protection partitions on a phase arm, a bus section and a battery cluster, configuring a polarity controllable blocking sub-module capable of being inserted with reverse voltage on the phase arm, and respectively configuring direct-current circuit breakers on the bus section and the battery cluster; generating a criterion set based on the measured value, and performing consistency voting on the criterion set to obtain a direct current fault determination result and a partition positioning result; when a fault is determined, issuing modulation and zero setting, and calculating a reverse equivalent voltage according to the change rate of the phase arm current and the target current to trigger the insertion of a polarity controllable blocking sub-module; selectively driving a corresponding direct current circuit breaker to be switched on and off according to a partition positioning result, or splitting a fault phase arm; and after selective switching-off is completed, outputting an isolation state to a grid-connected control unit of the energy storage grid-connected system. According to the invention, millisecond-level robust fault discrimination, partition selective isolation, cooperation of current limiting and on-off can be realized, and the removal range is narrowed.

The embodiment of the invention provides a method and a system for adjusting the capacitance value of a half-bridge sub-module. The method comprises the following steps: acquiring an initial capacitance value of a capacitor meeting steady-state operation voltage fluctuation constraint and dynamic response time constraint; obtaining a resistance value range of a resistor in the damping branch under the multi-condition constraint; wherein the multi-condition constraint comprises a current limiting condition constraint of the flexible direct-current power transmission system based on the initial capacitance value when a direct-current fault occurs, and a transient stability condition constraint of the flexible direct-current power transmission system when an alternating-current fault occurs; based on the resistance value range, obtaining an introduced transient voltage fluctuation range of the capacitor through simulation; obtaining a selectable capacitance value range in which the capacitance meets the transient operation condition constraint corresponding to the introduced transient voltage fluctuation range; and replacing the initial capacitance value with the capacitance value in the optional capacitance value range to obtain a target capacitance value of the capacitor. According to the invention, the engineering cost of the flexible DC power transmission system can be reduced on the basis of realizing AC / DC fault non-locking fault ride-through.

The invention discloses a fault power loss cooperative calculation method and system for a DC power transmission system of a parallel converter topology, and electronic equipment. The method comprises the following steps: establishing communication between a stability control device and DC control and protection equipment of the DC power transmission system; the stability control device judges that the fault-caused locking of the current converter comprises fault-caused locking of the current converter on the side, fault-caused locking of the current converter on the opposite side and locking faults of double sets of crashed fault-pole current converters on the basis of a signal sent by the direct-current control and protection system; according to the direct current pole control mode, whether the sound current converter has the power conversion capability or not when the intra-pole single current converter breaks down is judged, and the direct current fault power loss amount is calculated based on the maximum transmittable power of the remaining sound current converter after the fault. According to the method, the problem of inaccurate fault power loss calculation under complex working conditions of opposite-side single converter locking, bipolar control crash and the like is solved, the effect of accurately calculating the fault power loss amount is achieved, and the method is of great significance to fault analysis, reliability evaluation and safe and stable control of the parallel converter topology direct-current power transmission system.

The application discloses a DC line single-end fault ranging method and system with self-calibration capability, and belongs to the technical field of DC line fault positioning. The technical problem to be solved is that the anti-interference capability of a DC fault ranging technology is weak, parameter drift cannot be calibrated, double-end synchronization is required, and engineering implementation is complex. Technical scheme points are as follows: an excitation signal is injected into a fault line through an H-bridge circuit unit, an H-bridge output voltage and a line port voltage after an external calibration inductor are synchronously collected, and a line fault loop current zero-crossing moment is detected; at the zero-crossing moment, two groups of voltage equations are used to solve an external calibration inductor calculation value in real time, the inductor calculation value is compared with a nominal value to obtain an inductor correction coefficient, online self-calibration of the line inductor is realized; and based on the calibrated line inductor, fault discrimination and distance calculation are completed in combination with a relationship between a port voltage and a current slope.

The application discloses a method for controlling hybrid MMC sub-modules to clear DC short-circuit fault current. The method detects the real-time size of AC voltage, calculates the bridge arm voltage according to the principle of limiting AC current change and not affecting the speed of DC fault current clearing, and determines the number of improved sub-modules (sub-modules capable of providing counter electromotive force, such as full-bridge sub-modules) in each bridge arm according to the bridge arm voltage. Compared with the conventional method of directly locking all sub-modules to clear DC fault current, the application reduces the bridge arm current during the DC fault current clearing process, alleviates the overvoltage of the improved sub-modules, limits the influence on the speed of DC fault clearing, and improves the safety of the hybrid modular multilevel converter during the process of clearing DC fault current.

The present application relates to the technical field of power system stability control, and is a steady-state voltage control method and system for reducing transient voltage instability risk of a new energy collection station, the method comprising: establishing a new energy collection station bus transient voltage model of a new energy sending end power grid after a DC bipolar blocking fault; setting a new energy collection station transient voltage instability limit of the new energy sending end power grid after the DC bipolar blocking fault; and setting a steady-state voltage control threshold for reducing the transient voltage instability risk of the new energy collection station bus based on the new energy collection station bus transient voltage model. The present application can achieve the purpose of reducing transient voltage instability risk by controlling the steady-state operating voltage of a high-proportion new energy sending end power grid without increasing dynamic reactive power compensation equipment. The present application is used to solve the problem of transient voltage instability caused by new energy off-grid of a new energy collection station of a DC sending end power grid after a DC fault due to excessively high transient voltage caused by excessively high steady-state operating voltage of the power grid.

The application discloses a DC fault ride-through method of a sea-land integrated DC system of offshore wind power based on a fast communication link, and the method comprises the following steps: when a DC fault occurs, the voltage drop speed and the voltage drop amplitude of an onshore converter station are obtained; when the voltage drop speed is lower than a voltage drop speed threshold value and the voltage drop amplitude is lower than a voltage drop amplitude threshold value, a fan energy consumption input instruction is sent to an offshore converter station, so that the offshore converter station transmits the fan energy consumption input instruction to each communication forwarding device through a bidirectional ring network optical fiber channel, and then the fan energy consumption input instruction is transmitted to corresponding fan energy consumption devices by the communication forwarding devices, so that the fan energy consumption devices absorb the fault surplus power according to the fan energy consumption input instruction; wherein the time from the issuance of the fan energy consumption input instruction from the HVDC side to the start of the fan energy consumption device is not greater than the maximum allowable delay duration.

The invention discloses a DC fault current analysis and calculation method suitable for multi-type MMC converters, and the method comprises the steps: determining the topology type of an MMC converter related to a fault line, and collecting core parameters; constructing an RLC series unified equivalent circuit model of the MMC, and correcting the RLC series unified equivalent circuit model based on the topology type to obtain an equivalent circuit correction model; and determining a DC fault current based on the equivalent circuit correction model. According to the method, a technical architecture of'unified modeling + differential correction 'is constructed, multiple types of MMC converters are abstracted into an RLC basic equivalent model, local parameter correction is carried out only for fault characteristic differences of different topologies, and the tedious process of repeated modeling is effectively avoided; meanwhile, converter active current limiting strategies such as locking and negative input control are considered in the modeling process of fault current analytical calculation, the model architecture has good expansibility, various control strategies can be flexibly fused, and deep fusion of the electromagnetic transient process and the control process is achieved.

The application discloses a kind of hybrid line DC fault ride-through control method, device and system, belong to flexible HVDC transmission technology.The DC fault ride-through control method of the application, first, the actual DC current corresponding to DC line in flexible HVDC transmission system is monitored, and the actual DC current in abnormal target line is obtained;Then according to the actual DC current corresponding to target line, the DC reference voltage corresponding to target line is adjusted to fault ride-through voltage reference value, to control the DC current corresponding to target line to be set value of fault ride-through;Finally, in the case where the actual DC voltage corresponding to target line satisfies preset recovery condition, the DC reference voltage corresponding to target line is restored to preset reference voltage value.The DC fault ride-through method of the application is fast in response speed, can also reduce the influence on output power, reduce power loss, improve the stability and reliability of flexible HVDC transmission system operation.

The invention provides a low-conduction-loss direct-current circuit breaker with a fault type judgment function and a judgment method, and belongs to the field of circuit fault detection. In order to solve the problems that in an existing hybrid high-voltage direct-current circuit breaker, the conduction loss of a load commutation switch is high, and a circuit device does not have the fault type discrimination capability, the direct-current circuit breaker comprises a load branch, a multifunctional branch, a main breaking branch and an energy absorption branch. The discrimination method comprises the following steps: in a normal operation mode, a load branch is conducted; the capacitor pre-charging mode operates in parallel to charge the capacitor C; when the circuit is short-circuited, a thyristor turn-off mode is entered, and the T1 is turned off; and entering a load commutation mode, converting the fault current to a main breaking branch, introducing an energy absorption branch, and entering an energy absorption mode. And injecting a controlled RLC oscillation current, analyzing current waveform characteristics to judge a direct current fault type, and performing reclosing or maintenance of the circuit breaker according to the analyzed direct current fault type.

The invention provides a direct-current fault arc extinguishing system, which is applied to a direct-current power grid and comprises a magnetic core module with an air gap, a driving module and a control module, and the driving module is connected with the magnetic core module and the control module; the magnetic core module is used for reconstructing and generating reverse voltage based on fault current in the direct-current power grid; and the control module is used for acquiring fault current at a first sampling frequency, determining a current change rate based on the first sampling frequency and the fault current, determining a control strategy for the air gap when the current change rate is greater than or equal to a preset threshold value, controlling the driving module to adjust the air gap based on the control strategy, and changing the magnetic coupling strength of the magnetic core module. Therefore, the reverse voltage is controlled to reach a voltage arc extinguishing threshold value. The magnetic coupling strength of the magnetic core is changed by dynamically adjusting the air gap, accurate control over reverse voltage is achieved, stable arc extinguishing voltage output is maintained when fault current fluctuates, and the action reliability of an arc extinguishing system is improved.

The invention provides a quantitative evaluation method and system suitable for the voltage supporting capability of multiple types of reactive power equipment, and a storage medium. By setting alternating current and direct current faults, grid-connected point data of different reactive power devices are obtained; based on the dynamic characteristics of the reactive power equipment and factors affecting the power grid strength, a reactive power equipment voltage supporting capacity multi-index evaluation system considering the two aspects of the reactive power equipment and a power system is provided; constructing a cooperative game combination weight optimization model by adopting a deviation minimization principle, and calculating the weight of each index; proposing a construction method of a central point mixed sine whitening weight function, and carrying out gray fixed weight clustering evaluation on the voltage supporting capability of the multi-type reactive power equipment; and finally, verifying the accuracy and universality of the method provided by the invention based on PSASP simulation. According to the method, the influence of the dynamic characteristics of the reactive power equipment on the voltage supporting capacity is considered, and the index system is more comprehensive, the index weighting is more reasonable and the evaluation result is more credible based on the improved grey whitening weight function fixed weight clustering evaluation.

The present application relates to the field of high-voltage direct current transmission, and aims to provide a topology of bridge arm integrated current-limiting energy-consuming device, a converter valve and a coordinated control method. The topology is a modular MMC architecture of three-phase double bridge arms, which comprises a plurality of MMC sub-modules connected in series in the upper bridge arm, and a current-limiting energy-consuming device composed of a plurality of current-limiting energy-consuming sub-modules connected in series in the lower bridge arm; the current-limiting energy-consuming sub-module comprises a sub-module main power unit and a sub-condition energy-consuming unit, the latter at least contains two energy-consuming units adapted to different fault conditions, and each contains an energy-consuming resistor and an adaptive condition switching device. The present application integrates the functions of direct-current fault current limiting and alternating-current fault energy consumption in the same integrated device, realizes integrated protection of AC and DC faults, does not need to configure multiple sets of separate equipment, and solves the problem of functional redundancy of the traditional scheme. Redundant configuration can be reduced, hardware cost is reduced, system size is reduced, and operation and maintenance complexity is simplified; the risk of device overvoltage breakdown is avoided, and the service life of the equipment is improved.

The invention relates to the technical field of direct current fault detection, and discloses a direct current series arc fault detection method and device, a photovoltaic inverter and a medium. And processing the input voltage and the input current of the photovoltaic inverter to obtain a characteristic data training set under the condition that the arc generator simulates the photovoltaic inverter to generate a direct current series arc fault and the condition of normal operation, wherein each arc fault detection model is obtained by pre-training based on the corresponding characteristic data set. The method comprises the following steps: firstly, acquiring an input side voltage and an input side current of the photovoltaic inverter, and processing the input side voltage and the input side current respectively to obtain multiple groups of feature data including voltage feature parameters and current feature parameters; then, the multiple sets of feature data are input into a pre-trained corresponding arc fault detection model for processing, and multiple fault detection results are obtained. And finally, based on a plurality of fault detection results, a voting mechanism is adopted to determine whether the photovoltaic inverter has a DC series arc fault.

The application discloses a new energy sending end power grid DC fault transient overvoltage influence evaluation method and system and a readable storage medium, and belongs to the technical field of power grid fault detection. The method takes overvoltage amplitude, overvoltage duration, fault type and system impedance as influencing factors, determines the membership degrees of various factors at different influence levels according to the corresponding single-factor fuzzy evaluation membership degree matrix of the factor level query, and performs weighted summation on the membership degrees of various factors at different influence levels and the influence weights of various factors to calculate the final membership degrees of various influence levels, and takes the influence level corresponding to the maximum final membership degree as the evaluation level. Through effective processing of fuzzy information, the application can make accurate evaluation under complex power grid fault conditions, thereby reducing the potential risk of overvoltage to the system and equipment and improving the safety and reliability of the power system.

The application discloses a kind of flexible direct current transmission line fault transient electrical quantity determination methods, comprising: according to the circuit parameter of MMC converter station, construct MMC equivalent circuit when inter-pole short circuit;According to the transmission line parameter obtained, establish the equivalent model of two-port of direct current transmission line under complex frequency domain;According to the equivalent circuit of MMC when inter-pole short circuit and the equivalent model of two-port of direct current transmission line, obtain the expression of direct current fault transient under complex frequency domain;The expression of direct current fault transient under complex frequency domain is carried out Laplace transformation to obtain time domain response, the whole trend of transient process after fault can be given more accurately by the application.The calculation process is simple, avoids the complicated modeling simulation process in traditional simulation method.Meanwhile, it can well reflect the occurrence wave process when overhead line fails.The method can accurately express the overall development trend of the fault current flowing through the protection installation before the converter station is locked after the fault occurs, and has a positive significance for the fault current suppression and protection setting design of MMC-HVDC system.

The application discloses a kind of generator phase-advancing capability analysis method and system based on power grid transient stability constraint, comprising the following steps: according to power grid system stability and converter station bus voltage control condition obtains single machine maximum phase-advancing depth;According to single machine maximum phase-advancing depth, obtain the phase-advancing depth of power plant and the phase-advancing depth reserved by whole plant.This application mainly aims at the problem that the regulation range of other regulating means such as shunt reactor is limited when voltage is too high due to excessive reactive power, fully considers factors such as stator end heating and power angle static stability, determines single machine maximum phase-advancing depth, considers the most serious situation of overvoltage of DC converter station, determines the phase-advancing capability of power plant and the phase-advancing capability reserved by whole plant after DC fault tripping based on whether steady-state overvoltage exceeds voltage limit, fully develops the voltage regulating capability of generator, so as to more economically and efficiently ensure the stable operation of power grid voltage.

The invention provides a DC fault ride-through method and device of a current converter, a storage medium and a current conversion system, the current converter comprises three phases, each phase comprises two bridge arms, and the method comprises the following steps: a first obtaining step: obtaining a first current and a historical bridge arm state; a first determination step of determining that the first bridge arm operates in a first target state according to the magnitude of the first current and the number of locking states, the number of the locking states being the number of second bridge arms corresponding to the locking states in the historical bridge arm states; a first control step of controlling the first bridge arm to operate in a first target state; and a first repeating step: sequentially repeating the first obtaining step, the first determining step and the first control step for at least one time, and in the repeating process, updating the first bridge arm in the first obtaining step to be the next bridge arm of the first bridge arm until the control of all bridge arms is completed, the technical problem of how to avoid the overall locking of the converter in the DC fault ride-through process of the converter in the prior art is solved.

The application relates to a short-arc type hybrid DC fault circuit breaker and a control method thereof. The circuit breaker disclosed by the patent does not use IGBT, fully plays the advantages of low thyristor cost, small conduction voltage drop, current zero natural turn-off and the like, realizes short-time arc breaking between fast mechanical switch (FMS) contacts, low-cost removal of fault current and adaptive reclosing after breaking, the main flow branch of the circuit breaker is only composed of FMS, power devices are not needed to be connected in series, power loss during normal operation of the system is reduced, and the capacitor in the additional oscillation circuit is pre-charged by the system, an additional pre-charging power supply is not needed, and the economy of the system is improved. The application has good use value and economic benefits in flexible DC power transmission and distribution and the like.

The application discloses a hybrid MMC control method and system, which comprises the following steps: under the working conditions of voltage reduction / half voltage operation of a converter station, on-line switching of a single valve group and DC fault ride-through, a control pulse is formulated according to a converter voltage reference value formulated by capacitor voltage of a sub-module in an MMC converter valve, an arm current loop injection voltage value formulated by a time-varying value of an arm current loop and a DC voltage given value formulated by a DC current given value, and the hybrid MMC is controlled to be put into operation. According to the converter voltage reference value formulated by the capacitor voltage of the sub-module in the MMC converter valve, the hybrid MMC can ensure that the MMC arm current zero-crossing point is guaranteed, capacitor voltage balance is realized and system collapse caused by separation of capacitor voltage of a full-bridge sub-module and the capacitor voltage of the sub-module is avoided under special working conditions. The time-varying value formulated by the arm current loop of the MMC converter valve obtains an expected value of the arm current loop injection, and the arm current always has a zero-crossing point through an arm current loop injection link, so that the safe operation of the MMC arm is ensured.

According to the multi-mode programmable direct-current cable fault current simulation device and the control method thereof, the coil is wound on the magnetic core of the Hall current sensor of the direct-current cable, and the current source is controlled to inject the programmable current into the coil, so that non-intrusive fault current simulation is realized; the system can effectively reproduce steady-state fault current, transient sudden-increase fault current and a superposition process thereof, is convenient for testing, debugging and verification of a direct-current fault early warning system, and has the advantages of simple structure, flexible control, safety and reliability.