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

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 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 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 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 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 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 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 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.