118 results about "Fault current limiting" patented technology

Solid-state circuit breakers (SSB) have a fault current limiting function that limit the fault current in power applications. It allows sustained overcurrent for a certain period while preventing the fast fault current increase in dc systems. For the conventional method of using switches alone to limit the current, the high loss results in a short withstand time and low current limiting capability of the SSCBs. Disclosed are various embodiments for a control strategy to use one or more energy absorption components to handle the major part of the energy during a current limiting stage to increase the current limiting capability for series-connected SSCB switching cells.

The invention discloses a converter collaborative current limiting method based on adaptive virtual impedance and a power loop, and the method comprises the steps: firstly building an equivalent impedance model of a converter and a power grid, analyzing the steady-state and transient characteristics of fault current, and extracting key parameters for current limiting design; when it is detected that the voltage drop of the grid-connected point exceeds a threshold value, a self-adaptive virtual impedance link is automatically put into use, and virtual resistance and reactance values are dynamically calculated according to the variation amplitude of voltage or current, so that the virtual resistance and reactance values are proportionally adjusted along with the fault degree; and when the system voltage returns to normal, the virtual impedance automatically quits, and the control continuity is ensured. Then, the active and reactive power reference values are dynamically corrected according to the voltage drop depth, a power reference signal matched with the voltage amplitude is generated, it is guaranteed that power output does not exceed the limit, and the voltage supporting capacity is improved. Finally, real-time current-limiting control of the converter and stable operation of the system are realized on the premise of not switching the control mode through the synergistic effect of the virtual impedance ring and the power ring. The method has the advantages of being high in response speed, excellent in current limiting effect, good in control continuity and the like, and is suitable for fault current limiting and voltage support control of the grid-forming converter.

The invention discloses a network construction type energy storage control method and system suitable for black start, and the method comprises the steps: obtaining a three-phase current actual value of a converter side to judge whether an overcurrent fault occurs or not, and switching off a pulse modulation signal of a switching device in a converter when the overcurrent fault is judged to occur; when it is judged that the overcurrent fault does not occur, a three-phase voltage instruction value, output by the power control loop, of the converter is obtained; obtaining a three-phase current actual value of the converter side, enabling the three-phase current actual value to sequentially pass through the virtual resistor and the high-pass filter to obtain a three-phase voltage compensation value, and obtaining a three-phase capacitance current actual value, corresponding to the three-phase voltage compensation value, in the high-pass filter; the difference value between the three-phase voltage instruction value and the three-phase voltage compensation value is used as a compensated three-phase voltage instruction value; and determining a pulse modulation signal of a switching device in the converter according to a difference value between the actual value of the three-phase capacitance current passing through the damping coefficient and the compensated three-phase voltage instruction value. Wave sealing control is applied, fault current limiting is achieved, and the stability of a power grid is improved.

The invention discloses a bidirectional hybrid output direct-current transformer and a fault current limiting design method thereof, and the medium-voltage side and the high-voltage side of the bidirectional hybrid output direct-current transformer are respectively composed of three thyristor valve groups and three sub-module bridge arms, and are connected through a medium-frequency transformer. The thyristor valve group is formed by reversely connecting two groups of series thyristors in parallel, and the medium-voltage side sub-module bridge arm and the high-voltage side sub-module bridge arm are respectively composed of NM half-bridge sub-modules and NH half-bridge sub-modules. According to the invention, the sub-module bridge arms with strong control capability are combined with the thyristors and the diode valve groups which are low in cost, low in loss and high in power density, bidirectional power transmission and reliable turn-off of the thyristors can be realized through coordination and cooperation of the middle-voltage side bridge arms and the high-voltage side bridge arms, smooth direct current is ensured, and a filter does not need to be installed. When a short-circuit fault occurs in the outgoing submarine cable, a fault current active suppression strategy is provided, and the scheme can effectively reduce the peak value of the fault current and eliminate the current-limiting inductance.

The invention discloses a distribution line inter-phase permanent fault identification method and system based on SOP detection, and relates to the technical field of active injection protection. Based on an active detection idea, when an inter-phase short-circuit fault occurs in a distribution line containing SOP, a fault current limiting control measure is firstly started; limiting the output current of the fault side converter to be zero so as to enable the fault to extinguish arc; secondly, injecting pilot frequency positive sequence detection signals to obtain response characteristics by adopting a constant current injection strategy; solving the permanent fault equivalent model, and carrying out permanent fault identification by utilizing voltage structure similarity based on a model identification idea; and finally, fault isolation and power supply recovery are carried out based on a fault property identification result. Additional injection equipment is not needed, the fault property can be effectively judged, the fault section can be quickly determined under the permanent fault, and the power supply reliability of a power distribution system can be improved.

The invention discloses a time sequence fault current-limiting control method and system compatible with a grid-connected guide rule for a network construction type doubly-fed wind turbine generator, and the method comprises the following steps: freezing external power control when a low-voltage ride-through event of a power grid is detected at the initial stage of a fault, and suppressing transient overcurrent through dynamically adjusting the resistance component of virtual impedance; in the fault stable stage, an electromotive force compensation increment is calculated on the basis of grid-connected guide rule requirements at the moment 4 tau after the fault occurs; in the fault clearing stage, after it is detected that the fault is cleared, electromotive force compensation is stopped; gradually recovering the virtual impedance to a rated value through the dynamic coefficient A; in the fault recovery stage, active control and reactive control are recovered in sequence, power output is recovered to the level before the fault within one second, and meanwhile the virtual impedance amplitude is gradually recovered to the rated value along with the voltage phase difference; the voltage phase jump amplitude and the voltage drop amplitude determined by the method have high robustness.

The invention provides a network construction current limiting method, network construction type converter equipment and a new energy system, and relates to the technical field of new energy. The method comprises the following steps: in response to a condition that a power grid signal meets a preset condition, determining that network-forming converter equipment enters a current-limiting mode, and determining virtual impedance of a first stage of the current-limiting mode; determining that the network construction type converter equipment is in a first stage, and controlling the network construction type converter equipment by using the virtual impedance; and determining that the network construction type converter equipment is in a second stage of the current limiting mode, adjusting the virtual impedance according to the power grid signal, and controlling the network construction type converter equipment by using the adjusted virtual impedance. According to the embodiment of the invention, the current limiting mode of the network-forming converter equipment is divided into the first stage and the second stage, and the virtual impedance of the first stage is adjusted in the second stage, so that fault current limitation and power grid voltage support can be considered at the same time.

The invention discloses an adaptive virtual impedance-based fault current limiting method for a network-forming converter, and belongs to the technical field of converter control. Comprising the following steps: collecting grid-side voltage, converter-side voltage and converter output current; carrying out current amplitude calculation on the grid-side voltage quantity to obtain a current effective value of the port of the converter; judging whether the current effective value of the current transformer port exceeds a current threshold value of the current transformer; and if yes, self-adaptive virtual impedance is introduced to carry out converter fault current limitation. The resistance part of the virtual impedance is used for suppressing surge current at the beginning of a fault; and the reactance part is used for suppressing the effective value of the fault transient current within the current limiting range. In the fault process, the current virtual impedance value is adaptively changed according to the effective value of the current overcurrent, and the virtual impedance can be automatically quitted after the fault end stage. The method is suitable for fault current suppression of the network-forming converter in various control modes, and has good feasibility and practical value.

The invention discloses a multi-terminal flexible direct current transmission line protection method based on injection signals, and relates to the technical field of power distribution network line protection. After the bipolar short-circuit fault is detected, the modularized multi-level converter is controlled to enter an active current limiting mode, and the fault current is limited to be 1.1 times of rated current, so that the impact on equipment is reduced; a main control station injects current sinusoidal signals with different angular frequencies twice, current and voltage signals of a port of the main control station are extracted, the impedance amplitude difference under the two angular frequencies is obtained, and the fault section protection method based on the impedance amplitude difference is established. Through a cut-and-trial method, the number of current-limiting reactors through which fault current flows is calculated, a criterion for matching and detecting a fault line section is established, and the fault section is isolated by a protection action. According to the method, synchronous communication is not needed, fault line protection can be realized under high resistance and noise, and the protection reliability and the recovery efficiency of the complex topology multi-terminal flexible direct current power grid are remarkably improved.

The invention discloses an anti-saturation equivalent virtual impedance grid-forming type SVG fault current-limiting control method, which comprises the following steps of: inverting a direct current into an alternating current through an inverter, and filtering high-frequency harmonics through a filter to obtain a sine wave alternating current meeting a grid-connected requirement. A three-phase alternating current signal is collected in real time, coordinate transformation is carried out through a Park transformation module, and a modulation signal is obtained. The modulation signal is compared with a triangular carrier signal, a driving signal is generated, the on-off time of a power switching device of the inverter is controlled, the amplitude and phase of output voltage and current are adjusted, accurate control over the output power of the grid-connected inverter is achieved, and the power grid access requirement is met. According to the method, the limitation of traditional fixed parameters is broken through, and the robustness of the system to a complex fault scene is improved. In addition, manual intervention or a complex mode switching program is not needed, automatic smooth transition between different working conditions can be achieved, and powerful technical guarantee is provided for stable operation of a power grid.

The invention discloses a medium-voltage power electronic transformer, and relates to the technical field of power transformers, the transformer is based on a CHB topological structure and is composed of a plurality of input-series output-parallel power subunits, and each subunit comprises an AC / DC rectifier module and a dual-active full-bridge isolation conversion module and outputs low-voltage AC and DC ports at the same time. A fault current control circuit is arranged, so that a direct-current short-circuit fault can be quickly limited and broken, and line voltage can be adjusted; a modular design is adopted, and a central controller and a local controller are configured for cooperative control. The rated capacity of the transformer is 1MVA, the rated working condition efficiency exceeds 96%, and the fault current-limiting response time is less than 0.5 ms. Compared with a traditional transformer, renewable energy access conversion links can be reduced, flexible networking and interconnection and complementation of different types of energy sources are achieved, the energy utilization efficiency is effectively improved, the system control capacity is enhanced, and the transformer has wide application prospects in an alternating current and direct current hybrid system containing large-scale renewable energy sources.

The invention provides a zero-loss deep current limiting device and a current limiting device control method, and relates to the technical field of transformer fault current limiting, the device comprises a main switch branch, an energy absorption branch, an artificial zero-crossing branch and a current limiting reactor; the main switch branch comprises a vacuum type quick switch which is positioned between the bus and the main transformer high-voltage winding connecting end part; the artificial zero-crossing branch and the modulation inductor are connected in series and then are connected in parallel to the main switch branch; the artificial zero-crossing branch comprises a zero-crossing energy storage capacitor and a vacuum trigger switch, and the zero-crossing energy storage capacitor and the vacuum trigger switch are connected in series; the current limiting reactor is connected in parallel to the vacuum type quick switch; and a controller for controlling the vacuum trigger switch and the vacuum type quick switch to work is also arranged in the device. The energy absorption branch comprises a zinc oxide resistor which is connected in parallel with the artificial zero-crossing branch. The current limiting reactor is small in loss in the normal running state of the system and high in running reliability when the system breaks down.

The invention discloses an inverter transient stability method and system based on adaptive phase compensation, belongs to the technical field of grid-connected inverter control, and aims to solve the contradiction between fault current limiting and transient stability in the prior art. According to the invention, a phase compensation coefficient for self-adaptively adjusting according to the real-time power grid voltage and the change rate thereof is introduced into the synchronous loop of the virtual synchronous generator, and the coefficient can dynamically optimize the equivalent active power reference, the equivalent inertia and the damping of the system and cooperate with the voltage feedback of the reactive loop, so that the real-time performance of the system is improved. Therefore, the stability margin of the system is effectively expanded during the power grid fault period. On the premise of not sacrificing the fault current limiting capability, the transient stability and the fault ride-through capability of the inverter are remarkably enhanced, power and frequency oscillation is effectively inhibited, collaborative optimization of multiple performance indexes is realized, and the method has the advantages of simple structure and high robustness.

The invention discloses a current limiting method and system for a virtual synchronous generator after a power grid fault. The method comprises the following steps: monitoring a ratio of a power grid voltage to a rated voltage; comparing the ratio with a voltage drop degree threshold value; when the ratio is smaller than a voltage drop degree threshold value, a fault current limiting strategy is started; when a current-limiting strategy stopping condition is reached, judging whether the amplitude of the power grid current is smaller than or equal to a current-limiting threshold value or not; if the amplitude of the power grid current is smaller than or equal to the current limiting threshold value, ending, otherwise, carrying out the fault current limiting strategy again; when the ratio is greater than or equal to the voltage drop degree threshold value, the fault current limiting strategy does not need to be started; wherein the fault current limiting strategy comprises an active ring adjustment strategy based on angular frequency deviation feedback and a reactive adjustment strategy based on an adaptive adjustment reactive droop coefficient. According to the invention, the response capability and the operation stability of the converter during sudden power grid disturbance can be improved.

The invention discloses a network construction type converter fault current limiting method considering power angle stability, and belongs to the power electronic technology. According to the method, firstly, an active power adaptive adjustment coefficient is introduced into an active-frequency control loop, the power angle variation of the converter at the moment of a fault is suppressed, and the transient power angle stability of the converter is guaranteed; secondly, an output voltage reference value is adjusted through a reactive power-voltage control loop, the voltage difference between the converter and the power grid is reduced, and the current steady-state component in the fault period is restrained; and finally, a variable virtual reactance is introduced into a voltage outer ring, and a transient current impact component at the fault moment is suppressed. The current limiting method is provided for the grid-forming type converter when the grid-side voltage symmetrically drops, continuous increase of the output current in the converter fault period can be restrained, meanwhile, power angle instability is prevented, and the method has the advantages of being high in response speed, good in current limiting effect and high in power angle stability.

The invention provides a self-adaptive short-circuit fault current-limiting control method and system for a primary and secondary fusion circuit breaker, and relates to the technical field of circuit protection and manufacturing, and the method comprises the steps: collecting a current value, a voltage value and a state quantity of a circuit breaker, and forming a first operation parameter set; performing feature extraction based on the amplitude abrupt change, the phase offset and the harmonic component, generating a first feature vector, and matching the first feature vector with a preset short-circuit fault feature template to obtain a fault recognition result, a fault type and a position identifier; a dynamic current-limiting control curve is calculated according to the identifier and the current value, a current-limiting control parameter set is generated, and a current-limiting execution mechanism is controlled to obtain current-limiting response data; after the action is completed, a second operation parameter set is collected, current limiting effect analysis is executed to generate state feedback data, and a current limiting control parameter set is updated based on the feedback data; and factory calibration can be carried out on the power electronic current limiting module serving as a current limiting execution mechanism. According to the method, the adaptive capacity and accuracy of current limiting control are improved.

This invention relates to the field of power distribution network technology and discloses a direct-connected integrated energy storage-power flow conversion device and its control method. It employs a direct-connected multi-module series-parallel composite topology, organically integrating multiple functions—power flow conversion module, energy storage module, voltage support and current limiting module—into a single device. Based on a hierarchical coordinated control architecture designed for the three functional circuits, it achieves flexible and precise control of power flow between the two-terminal grids and efficient coordinated management of the energy storage units within the device. It also provides active voltage support and transient fault current limiting protection for the sending-end grid. This integrated design significantly reduces equipment redundancy, simplifies the overall system architecture, and, through the internal coordinated control of each functional module, significantly improves the device's operational reliability under complex conditions such as power flow reversal, load surges, and transient faults.

The invention discloses a multi-level modular converter fault current control method and related equipment, and the method comprises the steps: measuring the voltage and current of the output end of a multi-level modular converter, obtaining the amplitude information of the current of the output end, generating a current reference signal of the output end, and obtaining the amplitude phase information of the current and voltage of the output end, generating switching signals for controlling the conventional controller and the fault current controller switch based on the logic switch; establishing a multi-level modular converter mathematical model, and designing a fault current controller based on a logic switch for generating a signal representing the output voltage of the multi-level modular converter; and generating a pulse signal for controlling the switching device so as to realize fault current control. The control method is simple and clear in principle, the fault current controller does not relate to specific parameters of circuit elements of the converter, the design process is simple and easy to implement, and the fault current can be rapidly controlled and limited not to exceed a locking threshold value of the converter under the condition of a symmetric fault, and a reference value is accurately tracked.

The invention discloses a distribution network fault current limiting method based on a hybrid distribution transformer. The method comprises the following steps: detecting load current in the hybrid distribution transformer; when no fault occurs, the secondary winding current of the series transformer is controlled, so that the primary side voltage of the series transformer is compensated to be 0, the equivalent impedance of the series transformer connected into a main loop is 0, and the series transformer has no influence on the normal operation of the system; after a fault occurs, the fault detection link is delayed, the phase and the amplitude of the current of the secondary side of the series transformer are controlled to remain unchanged by default during the delay period, and the fault current is limited to a certain extent; when it is detected that the load current is larger than a set threshold value, it is determined that a fault occurs, and the amplitude and phase of the secondary winding current of the series transformer are controlled through a converter in the hybrid distribution transformer, so that the primary side voltage of the series transformer is not zero, namely, current-limiting voltage is generated, and reverse voltage is provided for a main circuit to suppress fault current. According to the invention, fault ride-through of the hybrid distribution transformer under the ground fault can be realized.

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 provides an adjusting method and system for a network construction converter, electronic equipment and a storage medium, and the method comprises the steps: switching the network construction converter from a droop control mode to a fault current limiting mode under the condition of a network fault of the network construction converter; under the condition that the network construction converter network is in the fault current limiting mode, the control of a voltage loop of the network construction converter network fails, and the maximum current amplitude allowed to flow through by the network construction converter and the output value of the voltage loop are determined; and obtaining a current loop reference value according to the maximum current amplitude and the output value of the voltage loop. Rapid fault recovery of the network construction converter can be realized, the network construction converter is prevented from being locked in a current limiting mode after the fault is removed, and the transient stability of the network construction converter is improved.

The medium voltage direct-hung DC power supply belongs to the field of power electronics. The power supply includes two converters and an output filter capacitor C o The two converters are converter No. 1 and converter No. 2. Converter No. 1 and converter No. 2 use the same circuit topology and control method. Each converter consists of a medium voltage rectifier circuit, a medium voltage inverter circuit, a single-phase transformer, a low voltage rectifier circuit and an output filter capacitor C. o1 Composition. The power supply uses a diode valve group and a thyristor valve group to bear current and transmit power, and adjusts the output voltage and transmission power by controlling the voltage at both ends of the bridge arm in series with the submodule; the structure of two converter outputs in parallel significantly improves the transmission power of the power supply, and at the same time, the medium voltage side is directly connected to the power grid, with a simple structure and high ease of use. The present invention has the advantages of a small number of devices, high power density, low cost, a wide output voltage range, and fault current limiting capability, and is also suitable for data centers, electric vehicle charging stations, hydrogen production and other fields.

A Solid-State Circuit Breaker Device and Method Without Current Limiting Inductor. According to an exemplary embodiment of this disclosure, described is a high-density, high-efficiency megawatt (MW) medium-voltage (MV) solid-state circuit breaker (SSCB) for, example only, aviation hybrid electric propulsion applications. The SSCB is based on the mature silicon (Si) insulated gate bipolar transistor (IGBT) devices. With reduced IGBT gate voltage, the disclosed SSCB can limit the peak fault current without the fault current limiting inductor. Thus, the specific power density of the SSCB is substantially improved compared with the traditional design.

Systems and methods for transferring a load between power sources may include monitoring voltage waveforms of power sources, in response to a power quality event affecting a first power source, switching a first switch device off to disconnect the load from the first power source, calculating a phase angle difference between the power sources based on the monitored voltage waveforms, selecting one of a first and second algorithms for transferring the load to a second power source based on the phase angle, selectively switching a second switch device using the selected one of the first algorithm and the second algorithm to transfer the load to the second power source. A controller may select the one of the first algorithm and the second algorithm based on the phase angle and a metric of the load transfer associated with the algorithms.

The invention relates to a low-voltage intelligent circuit breaker fault condition test and evaluation method and system based on a deep neural network. The method comprises the following steps: collecting real-time operation data of a low-voltage intelligent circuit breaker; performing normalization, denoising and feature extraction on the collected real-time operation data of the low-voltage intelligent circuit breaker in sequence; constructing an overcurrent control circuit for executing a fault current limiting (FCL) function; based on the extracted features, a complete protection closed loop from detection, current limiting, isolation to recovery is realized by using a constructed overcurrent control circuit for executing an FCL function; based on the fault record characteristics and the equipment operation state parameters, intelligent fault current detection is carried out by using a deep neural network method to obtain fault data so as to realize an FCL function; and designing heat capacity based on the system thermal resistance parameter and the fault current parameter, and obtaining a low-voltage intelligent circuit breaker fault condition test evaluation result based on thermal performance through thermal simulation and transient modeling. According to the invention, the performance and reliability of the system under the actual fault condition can be predicted and evaluated.

This application provides a VSG fault current limiting control strategy based on reactive power deviation integral feedback, including: constructing a reactive power deviation integral feedback control branch between the reactive power droop control output and the voltage command generation in the VSG reactive power loop; determining an integral feedback compensation value based on reactive power deviation control based on the reactive power deviation integral feedback control branch; and limiting the short-circuit current amplitude based on the integral feedback compensation value. The strategy proposed in this application, by introducing reactive power deviation integral feedback compensation control during fault periods, can equivalently adjust the reactive power droop coefficient and voltage command value, effectively reducing the fault current amplitude during fault periods and providing reactive power support for the system.

1. Name of the product in this design: Current-limiting reactor. 2. Purpose of this design: To limit excessively rapid fault current. 3. The key design feature of this product is its shape. 4. The image or photograph that best illustrates the design's key points: 3D view 1.

The invention provides a transformer short-circuit fault current limiting device and a capacitor maintenance management method in the device. The transformer short-circuit fault current limiting device comprises a main branch, a current limiting branch, a modulation inductor, an artificial zero-crossing branch and an energy consumption detection branch. The main branch is provided with a vacuum quick switch which is connected in series between the bus and the primary side port of the transformer; the current-limiting branch is provided with a current-limiting reactor which is connected in parallel with the vacuum quick switch. The artificial zero-crossing branch is connected in series with the modulation inductor and then is connected in parallel with the current-limiting branch, and the artificial zero-crossing branch comprises an energy-storage capacitor bank module and a vacuum trigger switch which are connected in series. In the application, when the fault current on the main branch is detected, the vacuum quick switch is firstly controlled to be switched off, and then the vacuum trigger switch is controlled to be switched on, so that the vacuum quick switch can be switched on and off conveniently; furthermore, the vacuum trigger switch is controlled to be turned off, the current limiting reactor is connected between the power distribution system bus and the transformer, short-circuit fault current limiting is achieved, and damage to the transformer when the load is short-circuited is reduced.

The embodiment of the invention relates to a fault current limiting method between solid state circuit breakers. The circuit breaker network includes a solid state circuit breaker (SSCB), one or more circuit breakers, and a current limiting control circuit of the SSCB. The current limiting control circuit is programmed to determine a first period of time for holding the SSCB in an on state, determine a second period of time for holding the SSCB in an off state, and cyclically switch the SSCB to the off state for the second period of time and then to the on state for the first period of time, the controller is configured to control the fault current within a predetermined inter-band range for the fault clearing duration, the predetermined inter-band range being lower than the first current threshold and higher than the second current threshold.

The invention discloses a magnetic saturation bridge arm coupling reactor and a flexible direct current transmission system, the magnetic saturation bridge arm coupling reactor comprises: two magnetic cores, six groups of coils, two permanent magnets and a direct current power supply; the first, third and fifth coils are wound on the first magnetic core, the second, fourth and sixth coils are wound on the second magnetic core, the first and second coils are connected end to end, the third and fourth coils are connected end to end, the first and third coils are connected at opposite ends, and the center tap is connected to the AC end of the converter valve, the taps of the fourth and second coils are respectively connected to the upper bridge arm and the lower bridge arm of the converter valve, the winding direction of the six groups of coils is the same, and all are right-hand spiral winding directions; two permanent magnets are respectively arranged on the first magnetic core and the second magnetic core; the fifth and sixth coils are connected end to end, and form a direct current excitation circuit with the direct current power supply; the two permanent magnets and the direct current excitation circuit form a hybrid excitation structure. The invention is applied to the converter valve of the flexible direct current transmission system, can realize power transmission, and can automatically realize circulating current and fault current limitation.