88results about How to "Limit short circuit current" patented technology

The present invention provides a multi-microgrid flexible interconnection system and a control method thereof. The system includes a plurality of microgrids and multi-port flexible interconnectors, wherein the multi-port flexible interconnectors are arranged between the feeder lines of the plurality of microgrids; and the multi-port flexible interconnectors are connected into the tail ends of the adjacent feeder lines of the plurality of microgrids, so that the flexible interconnection of the plurality of microgrids is realized. According to the multi-microgrid flexible interconnection system and the control method thereof of the invention, the multi-port flexible interconnectors, replacing traditional contact switches, are connected into the tail ends of the adjacent feeder lines between the different microgrids, so that the flexible interconnection of the plurality of microgrids is realized; due to the controllability of power electronic devices, power flow interaction among the plurality of microgrids can be realized. With the multi-microgrid flexible interconnection system and the control method thereof of the invention, multi-microgrid loop network operation can be realized with no short-circuit current increased; the local absorbing capacity of new energy resources can be improved; load balance between the feeder lines can be improved; mutual backup and mutual power supply of the adjacent microgrids can be realized; line loss can be decreased; the reliability of power supply can be improved; and voltage quality at the tail ends of the feeder lines can be maintained.

The invention discloses a single-phase ground fault positioning method for a ground protective device of a low-current system, which does not affect the protective performance of the ground protective device and can quickly find out a ground fault point. The method comprises the following steps that: a microcomputer intelligent controller judges whether a system is grounded or has a grounded phase difference or not according to the changes of a system line, a phase voltage and a zero sequence voltage; and when a single-phase ground fault happens, the microcomputer intelligent controller sends a switching command to a grounded phase breaker. The method is characterized in that: after being switched on, the grounded phase breaker is connected with a grounding network through a low-impedance current limiting reactor with a secondary coil; at the time, a grounding current of the system flows through a primary coil of the low-impedance current limiting reactor, and after the current is detected, the microcomputer intelligent controller gets into work with a high frequency signal generator connected with the secondary coil of the low-impedance current limiting reactor to inject a high frequency current into the system; and a handheld high frequency signal receiver moves along a fault line for searching the fault point, and the corresponding point where the received signal gradually becomes weak when the handheld high frequency signal receiver departs from some point is the ground fault point.

The invention discloses an insulated gate bipolar transistor (IGBT) gate driving push-pull circuit. The IGBT gate driving push-pull circuit is powered by a positive-negative power supply of a driving chip secondary side, and output positive-negative level. A pre-push-pull circuit, a level converting circuit and a post-push-pull circuit share the positive-negative power supply of the driving chip secondary side. The output of the driving chip is connected with the input of the pre-push-pull circuit; the output of the pre-push-pull circuit is connected with the level converting circuit; the output of the level converting circuit is connected with the post-push-pull circuit; and the output of the post-push-pull circuit is connected with a gate driving resistor of the IGBT. The pre-push-pull circuit is combined with the level converting circuit to provide a driving signal of interlocking and a hardware dead zone for MOS (metal oxide semiconductors) of the post-push-pull circuit, so that direct communications of the interior of the MOS push-pull structure is avoided; and GS voltage of the MOS is limited in a range of + / - 20V, so that reliable operation of the MOS is guaranteed. Adopting the MOS, the post-push-pull circuit can cooperate with effective IGBT gate clamps to limit IGBT short-circuit currents, and improve operation reliability of the IGBT.

The present invention discloses a short-circuit protection circuit with a current limiting function. The short-circuit protection circuit comprises an overcurrent detection circuit, an N-channel enhancement MOS tube circuit, a delay control circuit and a short-circuit protection circuit. The overcurrent detection circuit is configured to detect the size of a current when power supply is performedfrom a large current direct current bus to a small current load; the N-channel enhancement MOS tube circuit can replace a fuse to have effects on restricting a short-circuit current and cutting off the short-circuit current; the delay control circuit is configured to allow a circuit to determine whether a direct current input current exceeds a current limiting value or not after the direct currentinput current is detected by the overcurrent circuit and send turning-off signals to the short-circuit protection circuit after duration exceeds limiting time; and the short-circuit protection circuit is electrically connected with the delay control circuit to receive signals sent by the delay control circuit, and if the delay control circuit sends the turning-off signals, the short-circuit protection circuit sends the turning-off signals to the N-channel enhancement MOS tube circuit to cut off a bus current and enters a dead lock state.

The invention provides a flexible interconnection system between transformer station low voltage buses and a control method thereof; the system comprises a plurality of transformers and a multi-port flexible interconnection device; the transformers are arranged in the system transformer station; the adjacent transformer outlet buses are connected with the multi-port flexible interconnection device so as to realize multi-bus flexible interconnection. The system aims at the plurality of adjacent buses on the transformer outlet side in the same transformer station, and uses the multi-port flexible interconnection device to replace a buscouple switch, thus realizing the multi-bus flexible interconnection; the power electronic equipment controllability is employed to realize multi-bus trend interactions. The system and method can realize multi-bus parallel operations without increasing short circuit currents, thus improving the new energy local absorptive ability, improving the inter-bus load balancing level, improving the transformer load rate, reducing the transformer basic capacity, improving the power supply reliability, and improving the electric energy quality through proper control.

The invention discloses a novel multifunctional power electronic current-limiting system and a control method thereof. A PWM voltage stabilizing module is connected to a 10-kilovolt power grid in parallel through a shunt transformer Tb, a three-single-phase DVR module shares the direct current side of the PWM voltage stabilizing module to achieve energy supplying, a thyristor branch is placed between each contravariant unit output point of the three-single-phase DVR module and an output filter reactor and is connected with two output points of each contravariant unit of the DVR module, the output point of the DVR module is connected between the power grid and a load through a series transformers in series, and a small capacitor C filter branch is connected with a secondary side of the series transformer in parallel. According to the novel multifunctional power electronic current-limiting system, voltage fluctuation can be offset, the reliability and the stability of power supplying of a power grid system are improved, load voltage is stabilized, devices on the user side can operate normally, a short-circuit current is limited, the safety of a power grid system and the safety of a power supplying unit are improved, the short-circuit current is limited, the safety of a user device is protected, the time that the power grid bears a large short-circuit current in the process from short-circuit trouble occurrence to relay protective actions is shortened, and the safety of the power grid is improved.

The invention discloses a fault current limiting method for short circuit fault early detection. The method includes the steps of firstly, conducting A / D sampling on a current signal at a fixed sampling frequency, and conducting algorithm filtering on the sampling signal noise of the current signal; secondly, conducting algorithm processing on the filtered signal, extracting the current signal characteristic quantity and the voltage change ratio, and conducting short circuit fault early detection; thirdly, through short circuit fault early detection, judging whether the current signal characteristic quantity and the voltage change ratio which are obtained at present exceed a threshold value of a short current fault or not, if yes, judging that the short circuit fault occurs to a circuit, instantly triggering the FCL and continuing to conduct the next time of detection, and if not, restarting the detection. According to the method, firstly, A / D sampling is conducted on the circuit current, and noise interference is filtered out through the software algorithm; secondly, early detection and recognition of the fault are conducted through a signal singularity characteristic extraction algorithm, a trigger signal is sent out to control triggering of the FCL after recognition is conducted, and therefore early limitation of the short circuit current is achieved.

The invention discloses a permanent-magnetic AC reactor current restrictor, which comprises a reactance bridge circuit and a permanent magnet, wherein the reactance bridge circuit mainly comprises an iron core, an upper iron yoke, a lower iron yoke and an AC winding; the iron core comprises a central pillar and a side pillar; the side pillar is sleeved with the AC winding; the AC winding is formed by serially connecting the same-named ends of AC coils in a reverse direction; the permanent magnet is arranged in the central pillar; the side pillar and the central pillar of the iron core, the upper iron yoke, the lower iron yoke and the middle-arranged permanent magnet form an AC magnetic field loop and a bias magnetic field loop. The current restrictor has the advantages of simple structure and reliable operation. When the current restrictor is applied to AC systems, the current restrictor can effectively reduce reactive power loss and voltage drop during normal operation, and can quickly respond to short circuit faults and effectively suppress short circuit current.

The invention relates to a series-parallel connection comprehensive compensation device for power distribution network low-voltage treatment. The series-parallel connection comprehensive compensation device comprises a series connection compensating module, a parallel connection compensating module, and a controller. The series connection compensating module is disposed in a main loop circuit and is connected with a rapid vacuum switch in the main loop circuit. The parallel connection compensating module is connected with the main loop circuit through a vacuum contactor. The controller is connected with the rapid vacuum switch and the vacuum contactor and is used for controlling the operation of the series connection compensating module and the parallel connection compensating module via the rapid vacuum switch and the vacuum contactor according to the voltage and the load at the tail end of a power distribution network system. Compared with a product in the prior art, the series-parallel connection comprehensive compensation device is simultaneously provided with the series connection compensating module and the parallel connection compensating module, comprehensively controls a series capacitor loop circuit and a parallel capacitor loop circuit according to a system requirement, may change circuit reactance and system reactive power flow, and may absorb harmonic waves so as to greatly enhance the voltage regulating capability and range of a device.

The invention provides a method for automatically resetting the grounding protection device of a small-current system, which has the function of automatically resetting. The method comprises the following steps: an intelligent controller of a microcomputer judges whether the small-current system is grounded and further judges the grounding phase if the system is grounded; when the system is subjected to a grounding fault, a switching-on instruction is given to a fault-phase circuit breaker, and the fault-phase circuit breaker is rapidly switched on; the fault phase is connected with a grounding grid via a low-impedance current-limiting reactor provided with a secondary coil; then, a system grounding current flowing through the primary coil of the low-impedance current-limiting reactor is detected by a zero-sequence current transformer, and a high-frequency voltage signal generator connected with the secondary coil of the low-impedance current-limiting reactor is put into operation, so a high-frequency voltage and a high-frequency current are injected into the fault phase of the system; the high-frequency impedance of the fault phase of the system can be calculated by the intelligent controller of the microcomputer, so as to obtain the grounding resistance of the faulted return circuit; and the grounding resistance thereof is further compared with that in the normal system to judge whether the grounding fault disappears, if so, an automatic resetting instruction is given, so as to switch off the fault-phase circuit breaker, thereby automatically resetting the device.

The current limiter comprises a transformer, a parallel-resonant circuit and voltage detection and trigger circuit. Primary side of the transformer is cascaded into busbar of power network. The parallel-resonant circuit includes capacitor C, inductance L and thyristor K; inductance L cascaded to thyristor K is connected to capacitor C in parallel; two ends of capacitor C are connected to secondary ends of transformer. The current limiter with the said structure makes peak of short circuit current in power network be clipped off, and plays good effect of restraining whole short circuit current so as the prevent electrical equipments from impulsion of large electrical current. Utilization of the current limiter will reduce breaking capacity of breaker accordingly, bringing economic benefit. Structure of the invention is simple. thyristor K is only needed to close, but not needed of turnning off. closing time is less than 200ms so as to raise service life and reliability of thyristor.

The invention discloses a voltage compensation and fault current limiting hybrid system and a control method thereof. The hybrid system control method comprises three parts of direct current voltage stabilization module control, voltage compensation module control and fault current limiting module control. The direct current voltage stabilization module control uses SVPWM control to provide an active power energy exchange channel for a direct current side. The voltage compensation module control uses wide area prediction change PI control, and carries out precise tracking compensation on voltage fluctuations of a power grid. According to the control method provided by the invention, real-time voltage compensation can be effectively realized; short-circuit current can be timely limited; and the reliability and the safety of power supply of the power grid are improved.

The invention relates to a low leakage reactance power transformer with a current limiting reactor function; an iron core comprises a non-close iron core ring and a movable composite iron core block; the composite iron core block is formed by bonding the iron core block with a core in parallel, wherein the core is made of non-magnetic conductive material; a low voltage coil end is connected with a current detection unit; the current detection unit outputs a signal so as to control a push structure to move; the push structure uses a push rod to push the composite iron core block to move in a running track; the iron core block in the composite iron core block moves to the gap of the non-close iron core ring, and is combined with the non-close iron core ring, thus forming a complete closed iron core to carry out transformer works; the core of the composite iron core block moves to the gap of the non-close iron core ring, thus changing magnetic resistance, and changing external performance of the electric equipment; the low leakage reactance power transformer serves as the transformer under normal conditions, and serves as a short circuit reactor under fault conditions; the winding quantity in the low voltage side cannot be changed when the low leakage reactance power transformer serves as the reactor, and the short circuit level is very high, thus bearing vary large short circuit current.

The invention discloses a fault current limiter installation design method for alleviating voltage sag of a sensitive load. The method comprises the following steps of 1, selecting the sensitive load and determining a voltage sag threshold: selecting the sensitive load required to be subjected to voltage sag alleviation from a power grid of a to-be-installed fault current limiter, and determining the voltage sag threshold Uthre of the selected sensitive load; 2, obtaining a busbar voltage sag matrix of a sensitive load access point: obtaining the busbar voltage sag matrix of the sensitive load access point when the power grid has a three-phase short circuit fault; 3, obtaining a sensitive load voltage sag field matrix; 4, obtaining a sensitive load voltage sag field; 5, determining a fault current limiter installation branch; and 6, determining a fault current limiter reactance value of the fault current limiter installation branch. The method is simple in step, reasonable in design, convenient to implement and good in use effect; and the fault current limiter installation branch and the reactance value of the installed fault current limiter in the power grid can be simply, conveniently and quickly determined.

The invention discloses a multi-phase fault-tolerant permanent magnet synchronous motor disk rotor, belonging to the field of permanent magnet motors. The invention solves the problem that the short-circuit current suppression effect of the traditional surface-mount disk permanent magnet motor is bad. The multi-phase fault-tolerant permanent magnet synchronous motor disk rotor comprises a rotor core and p permanent magnets, wherein the rotor core comprises a rotor core yoke and p rotor core poles; the p rotor core poles are arranged on the disk surface of the annular rotor core yoke; the p rotor core poles are uniformly distributed along the peripheral direction; a permanent magnet slot is formed between every two adjacent rotor core poles; a permanent magnet is embedded into each permanent magnet slot; the central angle of the sector of the permanent magnet is smaller than or equal to the central angle of the sector of the permanent magnet slot; the surfaces of the p permanent magnets opposite to a stator have the same polarity, and axial magnetization is adopted; and p is the pole pair number of the rotor.

Being connected to bus line at exit of AC power system wire, the disclosed circuit of energy storage through n pieces of connection transformer [T1, T2...Tn] respectively is connected in series to paralleled n pieces of general load feeder. N pieces of transformer are connected to ends at AC side of n pieces of current limiting inductance [L1, L2...Ln] and n pieces of converter. Through same DC capacitance, ends at DC side of n pieces of converter are connected. DC capacitance is also connected to voltage inversion unit of chopper. Current inversion unit of chopper is connected to superconducting coil. In normal operation of system, the invention can adjust asymmetric voltages in n pieces of feed line, and can play functions: filtering, reactive and wattful compensation, and regulating system tidal current. When system is in fault. The invention can limit peak value and steady state value in short circuit, increase value of breakdown voltage of bus, and compensate depressed voltage etc.

The circuit of energy storage includes connection transformer, converter, chopper, DC capacitance, coil of high-temperature superconductor, diode rectification bridge, and controller based on DSP chip. Primary side of transformer is connected to side of sensitive load feeder in series, and secondary side is connected to AC side of converter. Current inversion unit of chopper is connected to DC side of coil and the diode bridge. AC side of the bridge is connected in series to feed line side of general loads. Chopper is composed of current inversion unit, voltage inversion unit, and transformer. Being connected to bus line at exit of AC power system, chopper is connected in series to feed lines from paralleled sensitive load and general load. In normal time, the circuit can adjust asymmetric voltages; carry out filtering, reactive and wattful compensation, and regulating system tidal current. In fault of system, the circuit can limit peak value and steady state value.

The invention relates to a magnetron type fault current limiter which utilizes the adjustable reactance characteristic of a magnetron reactor, enables the magnetron reactor to follow the change of system current and appropriately adjusts the reactance. When a system has a short-circuit fault, high impedance can appear instantaneously, so that the growth of short-circuit current is limited, and the short-circuit current is limited at a degree which is acceptable by a power grid. The magnetron type fault current limiter comprises a three-phase magnetron reactor, a hollow reactor, a direct current excitation unit and an automatic control unit; the input end and the output end of the three-phase magnetron reactor are connected in series with the power grid; a lead-out terminal of the three-phase magnetron reactor is connected in series with the hollow reactor; the hollow reactor is connected in series with the direct current excitation unit; and the direct current excitation unit is connected in parallel with the automatic control unit. The magnetron type fault current limiter has the advantages of large capacity, simple structure, high reliability, low cost and the like, can meet the technical requirement on the current limiting of the system, is easy to realize high voltage and large capacity, and is expected to be widely applied in the power supply system.

The invention discloses a motor controller active discharge system and a control method. The system comprises a film capacitor arranged on a bus, an IGBT circuit, a motor, an IGBT temperature samplingcircuit and a driving circuit which are connected with the IGBT circuit, a bus voltage sampling circuit connected with the film capacitor, and a motor temperature sampling circuit, a motor rotating speed sampling circuit and a driving circuit which are connected with the motor, wherein the driving circuit is with a power supply circuit. When the system finds that a motor winding or an IGBT modulegoes wrong, the system can select discharge paths respectively, the risk of active discharge IGBT failure is reduced, and a discharge speed problem is solved.

The invention provides a flexible direct current transmission system. The system comprises a transformer, a current converter and a coupling reactor, wherein the coupling reactor comprises an upper bridge arm coupling reactor and a lower bridge arm coupling reactor; the upper bridge arm coupling reactor and the lower bridge arm coupling reactor are connected through a connection of a same-polarityterminal and a different-polarity terminal; a connection point between the same-polarity terminal and the different-polarity terminal is a grid connection point; one end of the transformer is connected with an alternating-current power grid, and the other end is connected with the grid connection point; the current converter comprises three phase units; the phase units include an upper bridge armand a lower bridge arm; and the coupling reactor is connected between the upper bridge arm and the lower bridge arm.

The invention discloses an electric network positive and negative reactive power compensation device which is applied to compensate the voltage and the reactive power of an electric network. The electric network positive and negative reactive power compensation device comprises a pressure regulator (2), one or a plurality of capacitors (9) and one or a plurality of reactors (6), wherein the line inlet end of the pressure regulator (2) is connected with a bus (7) by a circuit breaker (1); the capacitor (9) and the reactor (6) are connected with the line outlet end of the pressure regulator by one or a plurality of switches; after being connected with the reactor and the switch (4) connected in front of the reactor in parallel, the capacitor and the switch (3) connected in front of the capacitor are connected to the line outlet end of the pressure regulator (2); and the reactor is connected to the inside of a branch circuit of the capacitor in series. The invention provides a still reactive power compensation device which can supply capacitive compensation and inductive compensation, regulates the reactive power output of the capacitor and the reactor by regulating the output voltage of the pressure regulator, does not switch the capacitor at rated voltage, prevents serious overvoltage and inrush current and can realize finite order fine regulation in a total range from rated capacitive compensation capacity to rated inductive compensation capacity.

The invention relates to a novel impedance-variable energy-saving transformer. The novel impedance-variable energy-saving transformer comprises a transformer oil tank (6), wherein the transformer oil tank (6) is internally provided with a transformer iron core and a transformer winding (5). The novel impedance-variable energy-saving transformer is characterized in that the transformer oil tank (6) is internally provided with a shielding plate (3) so that the inner part of the transformer oil tank (6) is separated into a transformer chamber and a current-limiting reactor chamber; the transformer chamber is internally provided with the transformer iron core and the transformer winding (5); the current-limiting reactor chamber is internally provided with a current-limiting reactor (1) and a rapid switch (2); the rapid switch (2) is connected with the current-limiting reactor (1) in parallel; after the rapid switch (2) is connected with the current-limiting reactor (1) in parallel, the rapid switch (2) is connected with a high-voltage winding in the transformer winding (5) in series. With the adoption of the novel impedance-variable energy-saving transformer, the automatic adjustment of impedance can be realized; meanwhile, the loss is reduced and the economic benefits are improved.

The invention relates to a 35 kV combined transformer used for photovoltaic power generation. The 35 kV combined transformer comprises a transformer body. A high-voltage operating chamber and a low-voltage chamber used for containing a first low-voltage cable and a second low-voltage cable are arranged below the transformer body respectively. A high-voltage cable chamber used for containing a high-voltage cable is arranged beside the transformer body. An axial double-split winding transformer is arranged in the transformer body, the axial double-split winding transformer comprises two low-voltage windings and a high-voltage winding connected to a fuse, and the two low-voltage windings are connected with one end of a breaker and one end of the other breaker respectively, and the other ends of the two breakers are connected with the first low-voltage cable and the second low-voltage cable. The first low-voltage cable and the second low-voltage cable are connected to loads through a first dry-type transformer and a second dry-type transformer. The fuse is further connected to the high-voltage cable through a load switch. The 35 kV combined transformer combines an axial double-split structure, and investment of electrical equipment such as transformers and building projects is saved.

The invention relates to a low excitation impedance transformer single-phase grounding protection device and a protection method. Through bypass grounding current shunting, grounding arcs are eliminated, the grounding protection effect is improved, grounding and line selection can be realized, and line selection and fault positioning are accurate. The device comprises three single-phase breakers, a low excitation impedance transformer, a signal generator, a zero sequence current transformer and a control detection device, wherein wire incoming sides of the three single-phase breakers are respectively connected with a corresponding bus through an isolation switch or a separation breaker, wire outgoing sides are connected with an original edge winding of the low excitation impedance transformer, the low excitation impedance transformer is a single-phase three winding dry core transformer having the original edge winding, a secondary edge main winding and a secondary edge secondary winding, one end of the original edge winding is connected with a ground network or a ground row through the zero sequence current transformer, the secondary edge main winding is connected with the signal generator, the secondary edge secondary winding is connected with the control detection device, the secondary edge main winding is for signal injection, and the secondary edge secondary winding is for signal measurement.

The invention discloses a current limiting method of a transformer current limiting device based on manual zero-crossing current limiting. When a short circuit fault occurs, a controller immediately sends a switching-off instruction to a rapid vacuum circuit breaker after judging the short-circuit fault; when the rapid vacuum circuit breaker is switched off and the distance between contacts reaches a rated opening distance, the controller switches on a controllable discharge gap Spark2; a capacitor C2 and an inductor L2 are connected in series for resonance so as to generate reverse high-frequency current equivalent to the instantaneous amplitude of the short-circuit current and superpose the reverse high-frequency current on a rapid vacuum circuit breaker loop; the quick vacuum circuit breaker completes short-circuit current switching-on and switching-off; then, the short-circuit current is transferred to a ZnO branch of a zinc oxide arrester and the capacitor C2 is charged; when thevoltage of the capacitor C2 tends to be stable and reaches the residual voltage of the zinc oxide arrester ZnO, the zinc oxide arrester ZnO is switched on, the controllable discharge gap Spark2 is switched off, then the zinc oxide arrester ZnO continuously absorbs short-circuit current energy, and the zinc oxide arrester ZnO is switched off when the current crosses zero.

The invention relates to a mixed solid state DC current-limiting type circuit breaker comprising a rectifying synchronous generator or a DC bus (1), a high-speed repulsion force mechanical switch (2),a composite electronic power switch (3), an on-state switch (4), a first buffer circuit (5), a second buffer circuit (6), a high resistance current-limiting circuit (7), a reverse voltage charging circuit (8), a freewheeling circuit (9), a smoothing reactor (10) and a direct current load (11). The high resistance current-limiting circuit provided by the invention is continuously on after the composite electronic power switch is switched off, so that the direct current power system of the ship is more stable; the freewheeling circuit is arranged on the load side, so that after the direct current circuit is broken, a release loop is provided for energy stored in the direct current circuit and the load, and the raising speed of the short circuit current is limited; the current-limiting rangeof the short circuit current can be self-designed according to the requirement of the direct current system of the ship, the breaking speed is fast, the raising speed of the short circuit current ofthe direct current circuit and the range of the short circuit current are limited, and the short circuit current of the direct current circuit is effectively broken.

The present invention provides a multi-microgrid flexible interconnection system and a control method thereof. The system includes a plurality of microgrids and multi-port flexible interconnectors, wherein the multi-port flexible interconnectors are arranged between the feeder lines of the plurality of microgrids; and the multi-port flexible interconnectors are connected into the tail ends of the adjacent feeder lines of the plurality of microgrids, so that the flexible interconnection of the plurality of microgrids is realized. According to the multi-microgrid flexible interconnection system and the control method thereof of the invention, the multi-port flexible interconnectors, replacing traditional contact switches, are connected into the tail ends of the adjacent feeder lines between the different microgrids, so that the flexible interconnection of the plurality of microgrids is realized; due to the controllability of power electronic devices, power flow interaction among the plurality of microgrids can be realized. With the multi-microgrid flexible interconnection system and the control method thereof of the invention, multi-microgrid loop network operation can be realized with no short-circuit current increased; the local absorbing capacity of new energy resources can be improved; load balance between the feeder lines can be improved; mutual backup and mutual power supply of the adjacent microgrids can be realized; line loss can be decreased; the reliability of power supply can be improved; and voltage quality at the tail ends of the feeder lines can be maintained.

The invention relates to an isolated alternating current fault current limiting circuit comprising a transformer and a conducting loop. The transformer has a primary side winding that is arranged in series between a power supply input system and a load output system; And a secondary side winding and the primary side winding share an iron core and are electrically isolated windings. Being connected with the secondary side winding, the conducting loop is formed by a switch and a power-off element in a series connection mode. When a power source system is short-circuited, the power-off element of the conducting loop induces large short-circuit currents of the primary side winding and thus is fused and conduction is cut off; therefore, the transformer is converted into an open circuit state to provide high impedance exciting reactance and the equivalent internal impedance in the power supply input system is increased; and thus an objective of limitation of the fault current is achieved. As a result, a circuit interrupting device of the power source system enables the short circuit fault to be isolated successfully, so that it can be avoided that the influence area of the short-circuit accident is enlarged and there is a power failure for a long time.