34results about How to "Suppress fault current" patented technology

The invention relates to a virtual synchronous generator fault current suppression method based on adaptive virtual impedance. When a power grid fails, the voltage of a power grid drops, a VSG can generate large fault current, particularly at the moment when a fault occurs and is removed, the VSG can generate large impact current; when the output current of the VSG exceeds the maximum value of thecurrent capable of being borne by an inverter, irreversible damage to the VSG system can be caused, and meanwhile, the stability of the power grid is further reduced. The VSG does not have a fault ride-through capability, so that the VSG can only have the fault ride-through capability through a reasonable control scheme. According to the method of the invention, VSG fault current is suppressed bythe self-adapting of virtual impedance and the modification of a VSG reference voltage during the fault, so that the VSG has the fault ride-through capability on the premise of not changing a controlstructure. The method has high control precision. With the method adopted, fault current and impact current can be effectively suppressed; and the control structure is not changed.

The invention provides an improved structure of a sub-module of a multilevel converter. The structure comprises a first switch module and a second switch interconnected in series, and a negative electrode is connected with a positive electrode of the second switch module. A positive electrode of a first capacitance is connected with a positive electrode of the first switch module, and a negative electrode of the first capacitance is connected with the negative electrode of the second switch module. The negative electrode of the second switch module is connected with the negative electrode of the second switch module, and the third switch module consists of a current-limiting device and a switch device connected in parallel. The switch device consists of an insulated gate bipolar transistor and a diode connected in anti-parallel, and the current-limiting device consists of a capacitance and a diode. The sub-module topological structure is mainly applied to high voltage high-capacity modular multilevel converters, when the side of direct current breaks down, the shut-off of the fault current of direct current is effectively achieved, and breakdown is effectively separated; meanwhile, action of an alternating current breaker is avoided. The sub-module topological structure of the modular multilevel converter is simple in structure and has quick recovery capability from faults.

The invention provides a sub-module topology structure and method for a flexible DC power transmission converter valve. The sub-module topology structure comprises a full-bridge structure sub-module (1) and a half-bridge structure sub-module (2) which are mutually connected, wherein an AC end A2 of the full-bridge structure sub-module (1) is connected with a DC end positive electrode D21 of the half-bridge structure sub-module (2), and a DC end negative electrode D12 of the full-bridge structure sub-module (1) is connected with a DC end negative electrode D22 of the half-bridge structure sub-module (2) through a diode D7. Through an additional diode, the full-bridge and half-bridge hybrid topology is reconstructed into a new topology capable of inhibiting a fault current, in the fault current inhibition process, voltage balance can be automatically kept in two capacitors of the sub-module, and problems of voltage imbalance and the overhigh withstanding voltage can be avoided.

The invention relates to a large-scale wind power integration flexible direct-current power transmission fault current cooperative inhibition method, and belongs to the technical field of flexible direct-current power transmission. When it is detected that the direct-current voltage is lower than a threshold value Udcth and the direct-current change rate is larger than a threshold value epsilon, the converter station is immediately switched to active current limiting control, that is, the total input number of all phases of sub-modules is reduced to kN (k is smaller than or equal to 1) in thenearest level approximation modulation process, and the k value is determined according to the wind power plant grid-connected bus voltage requirement. A dissipation resistor configuration method integrated with a current limiting function is designed, dissipation resistors are distributed and configured on upper and lower bridge arms of each phase, and meanwhile, the capacity of solving the problem of power surplus and reducing the current stress of a converter valve is achieved. Finally, a coordination and cooperation method of the two and the direct-current circuit breaker is designed, fault current is restrained cooperatively while safe operation of the wind power plant is guaranteed, and therefore the requirements for the on-off speed, capacity and manufacturing cost of the direct-current circuit breaker are reduced. The method has the advantages of being scientific, reasonable, high in applicability and good in effect.

The invention discloses a doubly-fed wind generator rotor linkage constant-frequency model prediction control method. According to the method, a three-voltage-vector selection method is selected based on the determination of the rotor linkage variation, a voltage vector selection mode requires that two effective vectors and a zero vector adjacent to the sector where a rotor voltage vector is are selected during each switching period, the rotor linkage follows a given value and optimizes the given value in real time to make the given value synchronous with the actual value of the stator linkage, and in order to weaken the fault impact of the stator linkage to the rotor linkage, the acting time of the selected effective vectors and the zero vector is determined based on a value function minimizing principle, and the switching state signals are obtained through the adoption of modulation technology. The method controls the converter by taking the rotor linkage error as the minimum during the switching period, and realizes the rapid tracking control of the rotor linkage. The switching frequency is constant, higher sampling frequency is not needed, control precision is high, and the rotor current can be effectively controlled within the allowed maximum current.

The invention provides a resistance-inductance hybrid fault current limiter and a control method thereof. The hybrid current limiter comprises an on-state low loss branch, a current transfer branch and a current limiting branch, adopts semi-controlled devices and is simple in logic, economic and reliable. According to the current limiter, a current limiting reactor and a current limiting resistorare inputted by utilizing the coordination of thyristors and a commutation capacitor, the steady-state loss is low, a bidirectional current limiting ability is possessed, and short-circuit current ofa DC power grid can be effective suppressed; meanwhile, the locking time of sub-module IGBTs is greatly delayed, and enough time is obtained for the operation of the remaining protective devices; andthe dissipated energy of a lightning arrester can be reduced, so that the hybrid current limiter has the advantages of economy and reliability. The control method provided by the invention of the resistance-inductance hybrid fault current limiter provided realizes control for the resistance-inductance hybrid fault current limiter when a DC line where the current limiter is located operates normally or before a fault of the DC line where the current limiter is located is detected and after the fault of the DC line where the resistance-inductance hybrid fault current limiter is located is detected.

The invention discloses a cold-insulating DC high-temperature superconducting current limiting cable, which comprises a cooling channel, a wire stranding frame, a semiconductor conductor layer I, a superconducting layer, a semiconductor conductor layer II, an insulating layer, a shielding layer and a protective layer. The cooling channel is arranged in the wire stranding frame. The wire strandingframe is wrapped with the semiconductor conductor layer I. The superconducting layer is wound outside the semiconductor conductor layer I. The superconducting layer is wrapped with the semiconductor conductor layer II. The semiconductor conductor layer II is wrapped with the insulating layer. The shielding layer is wound outside the insulating layer. The shielding layer is wrapped with the protective layer. A cooling medium is circulated in the cooling channel. The wire stranding frame is connected in parallel with the superconducting layer. The cable of the invention has double functions of transmission and current limitation. The cable does not need to be connected to a superconducting current limiter, and the device cost and the operation and maintenance costs are reduced. The wire stranding frame is made of a high-resistivity metal material, which can better inhibit the fault current when the cable fails. The structure of the wire stranding frame can improve the mechanical strengthand flexibility of the cable.

The invention discloses a method for suppressing a DC bipolar short-circuit fault current of a modular multi-level converter system. The method obtains a voltage value Usup to suppress a fault current according to calculation of margin based on modulation degrees and makes judgment of the fault current: (1) controlling the DC voltage as -Usup when the fault current is greater than the upper limit of current I1im; (2) controlling the DC voltage as Usup when the fault current is smaller than the lower limit of current -I1im; (3) controlling the DC voltage as zero when the fault current ranges between the upper limit and the lower limit wherein a system functions as two reactive power compensators connected in parallel and is capable of providing reactive support for a power grid. The method is capable of suppressing the fault current within a given range. The calculation of the method is simple and easy.

The invention relates to an ultrahigh voltage modular multilevel flexible DC transmission neutral point earthing method, which belongs to the field of ultrahigh voltage flexible DC transmission. The method comprises the following steps: a balancing winding is added to a transformer with Yny wiring; the capacity of the balancing winding and the voltage grade are calculated; and neutral point earthing resistance parameters are designed. A connecting transformer adopts a Ynyrd neutral point high-resistance earthing mode, and in the method, through adding a third wiring in delta connection as the balancing winding, the defect of large third harmonic loss when a power system of an early stage uses the Yny wiring transformer can be solved. The method has the advantages that the occupied area is small, an earthing transformer can be saved, the economic performance is higher, and the making difficulty is reduced.

The invention discloses a novel modular multilevel converter submodule topology circuit and a control method thereof. The invention relates to the field of power system DC power transmission and distribution protection control, in particular to an MMC sub-module topology circuit with DC side fault ride-through capability and a control method thereof. The invention provides the novel modular multilevel converter sub-module topology circuit is high in modular degree, higher in reliability, higher in forward and reverse fault current suppression capacity and more balanced and the control method thereof. The circuit comprises a wire inlet port X and a wire outlet port Y, wherein at least two half-bridge sub-modules are connected in series between the wire inlet port X and the wire outlet portY, each half-bridge sub-module is provided with an input port, a first output port and a second output port, and the power switch device can be an IGBT or an MOSFET. The circuit has very strong faultcurrent suppression capability.

The invention provides a resistance sensing type capacitor commutation hybrid current limiter and a control method thereof. The hybrid current limiter includes an on-state low-loss branch, a current-transfer branch and a current-limiting branch. The hybrid current limiter adopts a half-controlled device, is simple in logic, and is economical and reliable. The current limiter has low steady-state loss and has bidirectional current limiting capability, which can effectively suppress the short-circuit current of a DC grid and reduce the dissipated energy of a lighting arrester. The current limiter greatly delays the blocking time of a sub-module IGBT, and obtains sufficient time for the remaining protection devices. The use of half-controlled power electronic device can save the parallel number of power electronic devices and save costs, and ensure that a current limiting resistor and corresponding heat sinks are fully utilized to improve the current limiting effect. The control method ofthe resistance sensing type capacitor commutation hybrid current limiter provided by the invention realizes the control of the resistance sensing type capacitor commutation hybrid current limiter ina condition when a DC line where the current limiter is located operates normally or in a condition before or after the DC line where the resistance sensing type capacitor commutation hybrid current limiter is located is disconnected.

The invention discloses an energy discharging device, a DC power transmission system and an energy discharging method, which are suitable for the field of power transmission of offshore wind power plant. The system comprises an offshore wind power plant, an offshore converter, a DC submarine cable, an energy discharging device, a land converter and an AC main network. Except power grid fault ride-through, DC overcurrent prevention, DC overvoltage prevention and rapid power control, the system also has other properties higher than those of a traditional energy discharging device, large du / dt and di / dt caused by working is eliminated, and energy is smoothly discharged; and meanwhile, a cascaded DC capacitor has a wave smoothing effect, the fluctuation of a DC-side voltage can be reduced under various running modes, and the recovery time after working of the energy discharging device is greatly accelerated.

The invention provides a MMC topology structure applied to flexible direct current power transmission. The structure comprises three phase units. Each phase unit comprises an upper bridge arm and a lower bridge arm. The upper bridge arm and the lower bridge arm of each phase unit comprise reactors which are connected in series and a plurality of submodules. Each submodule comprises a first half-bridge circuit, a second half-bridge circuit and a guiding transistor which are connected to each other. The first half-bridge circuit and the second half-bridge circuit comprise offset capacitors. The topology structure also comprises a control unit which is used for determining whether a system has a direct current fault, making the guiding transistor in each first submodule be turned off when the system is determined to have the direct current fault and making a fault current flow through the offset capacitor of the first half-bridge circuit of each first submodule and the offset capacitor of the second half-bridge circuit and then flow into a fault point so as to restrain the fault current. In the invention, when the direct current fault is generated, the fault current is effectively reduced and an electronic device can be prevented from being burnt.

The invention provides a capacitive commutation hybrid fault current limiter and a control method thereof. The capacitive commutation hybrid fault current limiter comprises an on-state low-loss branch, a current transfer branch and a current limiting branch. A semi-controlled device is simple in logic and economical and reliable. The hybrid fault current limiter is low in loss of the steady state,has a bidirectional current limiting capability and can effectively inhibit the short-circuit current of a DC grid; the locking time of a sub module IGBT is delayed to obtain enough time for motion of other protection devices; it is ensured that a current limiting resistor and a corresponding heat-dissipating device can be fully utilized to improve the current limiting effect. The control methodof the capacitive commutation hybrid fault current limiter comprises two conditions of the normal operation of the DC line where the current limiter is located or before detection of the generation offaults of the DC line where the current limiter is located or after detection of the generation of faults of the DC line where the capacitive commutation hybrid fault current limiter is located to achieve control for a resistance-inductive capacitor commutation hybrid current limiter.

According to the flexible DC power transmission system centralized energy consumption device topology provided by the invention, the second controllable semiconductor device T2 is additionally arranged on the switch sub-module, so a problem that the controllable semiconductor device in the semiconductor switch is simplified is effectively solved, and a problem that the semiconductor switch cannotbe used when a single controllable semiconductor switch refuses to operate is avoided; the second controllable semiconductor device T2 is added to effectively replace the rejected first controllable semiconductor device T1, sustainability of the semiconductor switch is improved, effective bypass of the switch sub-module is ensured, and after the controllable semiconductor device T1 breaks down, the MOV cannot be exploded. When the offshore wind power flexible direct-current power transmission system has an alternating-current fault on a land station, the energy release device can consume surplus energy, and the fault is prevented from being diffused to an offshore system; direct current is monitored, and surplus energy is discharged; DC overvoltage is reliably suppressed by presetting a target DC voltage; emergency power control becomes possible, and more control is provided for operation and maintenance personnel.

The invention discloses an MMC sub-module topological structure with DC fault blocking capability equivalent to that of a full-bridge sub-module. The MMC sub-module topological structure comprises a first output end, a second output end, a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, a seventh diode, an eighth diode, a first voltage stabilizing capacitor and a second voltage stabilizing capacitor, wherein the first voltage stabilizing capacitor, the first transistor, the second transistor, the first diode and the second diode form a first half-bridge sub-module; and the second voltage stabilizing capacitor, the third transistor, the fourth transistor, the third diode and the fourth diode form a second half-bridge sub-module. The structure has the DC fault blocking capacity equal to that of the full-bridge sub-module, caneffectively block fault current when a direct current fault occurs, and is low in cost.

The invention provides a fault processing method and device and a power grid commutation high-voltage direct-current power transmission system. The method comprises the steps: in response to a fault signal of a direct-current power transmission system, acquiring the current of a power transmission line; obtaining the voltage of the power transmission line after the deionization duration when the current drops to the current threshold value; comparing the magnitude relationship between the voltage and the voltage threshold; determining a fault state of the direct-current power transmission system according to a magnitude relation between the voltage and a voltage threshold value; and controlling the DC transmission system according to the fault state. Therefore, the fault state can be identified after the deionization stage is finished; and the locking sequence is executed and the fault line is isolated only after the instantaneous fault disappears and under the permanent fault, so thatthe fault self-adaptive restart of the direct-current power transmission system is realized, the secondary impact on the power transmission system caused by restart of the permanent fault is effectively avoided, the equipment safety is ensured, the safety of the direct-current power transmission system is improved, and the service life is prolonged.

The invention provides a self-bypass type fault current limiter and a control method thereof. The self-bypass type fault current limiter comprises a current passing branch, a current transfer branch and a current limiting branch. A full-control type device is adopted, the logic is simple, and the controllability is high; the current transfer branch of the current limiter comprises a brand-new single-clamp sub-module with a single-quadrant operation capability of two-way bypass and one-way clamp. An action process of the current limiter does not depend on a protection effect of a lightning arrester, so that the service life of the current limiter is effectively prolonged. According to the control method of the self-bypass type fault current limiter, the self-bypass type fault current limiter is controlled during normal operation of a direct current line where the current limiter is located or before and after detection of a fault of the direct current line where the current limiter is located.

The invention discloses a strong magnetic coupling and magnetic saturation switch-type fault current limiter and a control method thereof, and belongs to the technical field of electrician. The strong magnetic coupling and magnetic saturation switch-type fault current limiter is divided into a single-phase structure and a three phase structure, and comprises a plurality of hollow-square-shaped iron cores, a direct current coil and alternating current coils, wherein the adjacent edges of the hollow-square-shaped iron cores are combined together to form a combined middle column; the alternating current coils are respectively wound on the adjacent edges of the hollow-square-shaped iron cores; the inphase alternating current coils are connected to a power grid in serial after being connected through dotted terminals; the direct current coil is wound at the outside of the alternating current coils, and can be connected with an adjustable field power supply; an air gap is formed on each hollow-square-shaped iron core; and the adjustable field power supply can be controlled during the control process, so that the fault current limiter can respectively show low impedance and high impedance under a non-fault running status and a fault running status of an electrical power system. The strong magnetic coupling and magnetic saturation switch-type fault current limiter is simple and compact in structure, and is easy to realize, and is high in reliability.

The invention provides a mixed current limiter based on a clamping submodule and a control method thereof. The mixed current limiter comprises a through-flow branch and a current limiting branch, adopts a full-control device, and is simple in logic and high in controllability; and the current limiter clamping submodule topology has a plurality of alternative topologies. The motion process of the current limiter does not depend on the protection effect of a lightning arrester so that the service life of the current limiter is effectively prolonged. The control method of the mixed current limiter based on the clamping submodule controls the mixed current limiter based on the clamping submodule through two conditions of normal operation of the direct-current line where the current limiter islocated or prior to detection of the faults of the direct-current line where the current limiter is located and after detection of the faults of the direct-current line where the current limiter is located based on the clamping submodule.

The invention provides a micro-network coordination control system and method based on a wireless network. The system of the invention comprises a coordination controller, a first wireless communication module, a second wireless communication module, a third wireless communication module, a fourth wireless communication module, a fifth wireless communication module circuit breaker, a transformer,a superconducting fault current limiter, a common coupling point, a superconducting magnetic energy storage device and a photovoltaic distributed power source. The method of the invention collects three-phase voltages of a common coupling point through a coordination controller through a wireless communication mode, and subjects the three-phase voltages of the common coupling point to Clark transformation. The coordination controller judges the state of the microgrid by the three-phase voltage of the common coupling point and the voltage of the common coupling point after Clark transformation.The coordination controller coordinates and controls the micro-grid by wireless communication according to the state of the micro-grid. Compared with the prior art, the invention can improve the transient performance of the microgrid under the short-circuit fault.

The invention discloses a converter, a DC-side grounded three-stage flexible DC system and a control method. The DC electrodes of the converter include a positive pole, a negative pole and a third pole, wherein each DC electrode includes a smoothing reactor and has a A modular level shifter capable of bidirectional operation of DC voltage and DC current. The modular level shifter includes an AC side and a DC side. The AC side is used to connect to the three-phase power supply of the converter transformer. The DC side includes the first terminal and the second terminal. Two terminals, the first terminal is connected to the DC line as a DC electrode after passing through the smoothing reactor, and the second terminal is grounded. The flexible DC system with the converter has a normal bipolar operation mode, a single-stage operation mode, two unipolar parallel operation modes and a capacity-increasing operation mode. Through the control of the fault pole voltage and the flexible switching of the operation mode, the rapid transfer of fault transient energy on the DC side can be realized, the DC fault current can be effectively suppressed, and the stability and continuity of power transmission during the fault period can be ensured.

The invention discloses a twisted wire core spiral linear inductor which includes a twisted wire core and an inner sleeve. The twisted wire core is wound in a spiral groove of the inner sleeve. The twisted wire core is formed by spirally twisting a plurality of metal wires and a plurality of aluminum wires. The inner sleeve is in a hollow cylinder shape, the outer wall of the inner sleeve is provided with the spiral groove, the bottom of the spiral groove is provided with a semicircular groove, the radius of the semicircular groove is the same as that of the twisted wire core, and each metal wire is a stainless steel wire or a manganese copper wire. The twisted wire core is formed by spirally twisting the plurality of metal wires and the plurality of aluminum wires. When a capacitor is subjected to internal breakdown, a large current passes through the inductor, the aluminum wires with a low melting point and low yield strength are melted, and stainless steel and the manganese copper wire are high in tensile strength and are still kept intact. The inductor impedance is significantly increased, which is equivalent to absorbing energy of the remaining capacitors to prevent the faultycapacitor from bursting.

The present invention proposes an improved structure of a modular multilevel converter sub-module, including a first switch module and a second switch module connected in series, the negative pole of the first switch module is connected to the positive pole of the second switch module; the first capacitor The positive pole of the first capacitor is connected to the positive pole of the first switching module, the negative pole of the first capacitor is connected to the negative pole of the second switching module; the negative pole of the third switching module is connected to the negative pole of the second switching module, and the third switching module is composed of a current limiting device and a switching device Composed in parallel, the switching device is composed of insulated gate bipolar transistors and diodes connected in antiparallel, and the current limiting device is composed of capacitors and diodes connected in series. The invention is mainly applied to high-voltage and large-capacity modular multilevel converters. When the DC side fails, it can effectively block the DC fault current, better realize fault isolation, and does not need AC circuit breaker action at the same time. . The invention has a simple structure and has fast fault recovery capability after the fault is cleared.

The invention discloses a capacitance type mixing DC breaker for DC power grid and a control method thereof. The breaker topology comprises one mechanical switch, two IGBTs and anti-parallel diodes thereof, two current-limiting inductance and N sub-modules, wherein a first sub-module comprises three capacitance, six thyristors and four diodes; the left (N-1) sub-modules are of the same; each module comprises one capacitance, one thyristor and one diode. The mechanical switch and two IGBTs and the anti-parallel diodes form a current-carrying branch circuit, which is a normal work channel. N sub-modules form a fault current transferring branch circuit, which provides a fault current transferring channel during short circuit. Under normal condition, the system delivers power through the current-carrying branch, and pre-charging is conducted on each sub-module through the control switch. Once faults occur, the breaker can transfer the fault current through the transferring branch circuit,and thereby the zero-voltage turning-off of the mechanical switch can be realized, and at the same time the pre-charging voltage of the capacitance can effectively limit the short circuit current.

A method for reducing the failure rate of a wind indicator through a wind sensor comprises the steps of: A, setting the constant temperature of a heater of the wind sensor to be 40-60 DEG C, and installing the wind sensor with the constant temperature set on a wind measuring support; B, coating conductive paste at a connection interface of the wind sensor and the wind measuring support; C, when a cable of the wind sensor enters a cabin cabinet, enabling a protective layer of the cable to need to be stripped out to expose a shielding layer, and then installing the cable on a shielding clip for 360-degree grounding processing; and D, respectively arranging the shielding layers of the connecting lines between the temperature measurement junction box and the cabin cabinet of the generator temperature measurement loop at the temperature measurement junction box and the cabin cabinet, exposing the protective layers of the cables needing to be stripped out of the shielding layers, and then mounting the cables on shielding clips for 360-degree grounding treatment, so that the double ends of the shielding layers of the connecting lines are grounded. By means of the method, the wind indicator fault current can be effectively restrained, the wind indicator fault rate is reduced, and normal operation of a draught fan is guaranteed.

The invention provides a fault isolation system and method. The system comprises a primary system and a secondary system, and the secondary system is coupled with the primary system. The input end of the primary system is connected with the new energy system through a positive direct-current bus and a negative direct-current bus, and the output end of the primary system is connected with the public direct-current power grid; and the primary system comprises a current sensor, a switch module and an alternating current circuit breaker which are sequentially connected in series on the positive pole direct current bus and the negative pole direct current bus. According to the invention, the alternating-current circuit breaker and the switch module are connected in series, so that physical switching-on and switching-off of the new energy system and the public direct-current power grid are realized, that is, isolation of the new energy system and the public direct-current power grid is realized, and low-cost fault isolation is realized on the premise of ensuring the opening speed of the alternating-current circuit breaker.

The invention relates to an ultrahigh voltage modular multilevel flexible DC transmission neutral point grounding method, which belongs to the field of ultrahigh voltage flexible DC transmission. Themethod comprises the steps that: a balancing winding is additionally arranged on a transformer with Yny wiring; a capacity and a voltage class of the balancing winding are calculated; and neutral point grounding resistance parameters are designed. A connecting transformer adopts a Ynyrd neutral point high-resistance grounding mode, and in the method, the defect of large third harmonic loss when apower system at an early stage uses the Yny wiring transformer can be solved through additionally arranging a third wiring in delta connection as the balancing winding. The ultrahigh voltage modular multilevel flexible DC transmission neutral point grounding method has the advantages that the occupied area is small, a grounding transformer can be saved, the economic performance is higher, and themanufacturing difficulty is reduced.

The invention proposes a wireless network-based micro-grid coordination control system and method. The system of the present invention includes a coordination controller, a first wireless communication module, a second wireless communication module, a third wireless communication module, a fourth wireless communication module, a fifth wireless communication module circuit breaker, a transformer, a superconducting fault current limiter, a public Coupling points, superconducting magnetic energy storage devices, and photovoltaic distributed power sources. The method of the present invention collects the three-phase voltage of the public coupling point through wireless communication through the coordination controller, and performs Clarke transformation on the three-phase voltage of the public coupling point; The state of the microgrid; the coordination controller coordinates and controls the microgrid through wireless communication according to the state of the microgrid. Compared with the prior art, the invention can improve the transient performance of the microgrid under the short-circuit fault.

The invention discloses a grounding device for an offshore wind power flexible direct current delivery system and a control method thereof. The grounding device comprises a reactance group, an isolation switch group and a grounding resistor. The reactance group is formed by star connection of three-phase iron core large reactance and forms an artificial neutral point. The isolation switch group isformed by three-phase rapid BPS star connection and forms a manual grounding point. The reactor group and the isolation switch group form double-star connection, and the two artificial neutral pointsare connected through the isolation on-off SN. The grounding resistor is composed of two groups of resistors. The resistor R1 and the resistor R2 are respectively connected with the neutral points ofthe reactor and the isolating switch, and the lightning arrester is connected in parallel with the grounding resistor R2. The device freely switches the grounding resistance value according to the requirements of steady-state operation, modulation mode, starting process, transient process, fault state and the like of the system so as to meet different operation conditions and modulation modes. And the adopted star-shaped isolating switch device is used for protecting the reactor group in a transient severe fault, so that the safety of the device is ensured.