70results about How to "Fault Ride Through" patented technology

The invention discloses a grid fault ride-through control method for a flexible direct-current transmission system. Grid fault non-communication ride-through of the system is achieved by switching converter station control modes, direct-current side voltage is detected in real time to judge whether a grid breaks down or not, control module switching is carried out, grid fault ride-through is achieved, and a controller supporting grid fault non-communication ride-through of the flexible direct-current transmission system is formed. By optimizing an original controller with the control method, direct-current voltage is effectively controlled in a grid fault of a constant direct-current voltage side converter station when no communication exists between converter stations under the condition that no hardware circuit is additionally arranged, the converter stations still keep operating during the grid fault, and meanwhile the system can be restored to an operating state before the fault as soon as possible after the fault is removed; grid fault non-communication ride-through of the flexible direct-current transmission system is achieved on the whole, the alternating-current fault ride-through capability of flexible direct-current transmission is improved, and a good operating environment is provided for the safety and stability of the system.

A fault-tolerant control method for an MMC (modular multilevel converter) system without redundant submodules is a method for fault ride-through control in the situation that redundant submodules of an MMC system are used up, but the system does not allow shutdown for overhauling. According to the method, firstly, the positions of fault submodules are detected, the fault submodules are removed through a bypass switch, and other normal submodules are not processed; modulating waves of fault phases are subjected to amplitude limiting according to the number of the fault submodules, a zero-sequence voltage value is calculated, and capacitor voltage of remaining normal submodules of the fault-phase bridge arms is sequenced again; finally, zero-sequence voltage is injected to modulating waves of other normal phases, recombination of the modulating waves is realized, and balance of voltage of output lines is guaranteed. According to the fault-tolerant control method, migration of neutral points of a system is avoided, the equipment reliability is enhanced, the operation efficiency is improved, and ceaseless and stable running of the system is maintained. The invention applies to the field of electrotechnics.

The invention discloses a wind power flexible direct current delivery system with a distributed direct current energy consumption device; the wind power flexible direct current delivery system comprises a plurality of offshore wind power plants which are arranged in parallel, wherein electric energy sent out by the offshore wind power plants is fed into an alternating-current power grid through atransmitting end converter station and a receiving end converter station; the distributed direct current energy consumption device is integrated inside the transmitting-end converter station or the receiving-end converter station; when the wind power flexible direct current delivery system suffers from a receiving-end alternating-current fault, the voltage of the direct-current side system rises,a certain number of energy consumption resistors are input for consuming the surplus power, and the short-time stability of the system is maintained; and after the fault is recovered, the corresponding energy consumption resistors are removed, and the fault ride through of the system is completed. According to the system, the energy consumption components are averagely distributed into a large quantum module, so that accurate matching of surplus power can be realized, the fluctuation of the electric quantity in the switching process of the energy consumption device is greatly reduced, fault outage of the system is avoided, and fault ride-through is realized.

The invention provides a doubly-fed wind generator low voltage ride through method. The method specifically comprises the steps that the limit amplitude value output is conducted on the negative sequence component of rotor voltage according to the maximum controllable rotor voltage of a converter; after the limit amplitude value output is conducted, a grid-side converter operates on the basis of the maximum limit amplitude value of the given current, partial differential voltage energy between the negative sequence component of the rotor voltage and the negative sequence control voltage part of a machine-side converter is input into a power grid through the grid-side converter as far as possible; in addition, the partial differential voltage energy is released through a chopper device; after the power grid voltage is recovered, a converter of a doubly-fed draught fan is switched to the normal power control, and normal stable operation of the power grid is facilitated. According to the doubly-fed wind generator low voltage ride through method, the safety of the doubly-fed wind power converter can be effectively ensured when deep asymmetric short circuit faults occur, continuous operation of a doubly-fed wind generator can be ensured in the breakdown period, low voltage ride through is successfully achieved, and active power and reactive power are poured into the power grid in the falling process.

The invention relates to a fault ride-through control device and method for alternating / direct current mixed microgrid, and belongs to the field of operational control of the alternating / direct current mixed microgrid. A power release unit, a direct current voltage adjusting unit, a direct current power release unit and a central monitoring unit are added to an alternating / direct current mixed microgrid system to form an alternating current fault ride-through coordination control structure of the alternating / direct current mixed microgrid system. By means of the fault ride-through control device and method for the alternating / direct current mixed microgrid, a controllable release access of excess power in a failure process is achieved, tide mutation is prevented from impacting equipment in the grid, voltage fluctuation of a low-voltage direct current bus is stabilized, lockout of alternating / direction current power exchanging equipment is avoided, the alternating / direction current power exchanging equipment is made to transmit power in the failure process, the impact to a power frequency conversion unit from failure current is reduced, tide distribution in the grid is controlled in an optimal mode, the excess power is controlled to be released, overcurrent loss is reduced, normal work in the failure process is guaranteed, and alternating current fault ride-through is achieved when alternating / direct current microgrids are connected. The fault ride-through control device is compact in structure, achieves fault ride-through with the minimum loss method, and has popularization significance.

The invention discloses a fault ride-through control method for an offshore wind power direct-current collection and transmission system. The method comprises the following steps: configuring a centralized unloading circuit at a direct-current collection bus of an offshore wind power plant; obtaining a first direct current bus voltage of a wind turbine generator, a second bus voltage of a direct current collection system and a third direct current bus voltage of a flexible direct current power transmission system; subtracting the first direct-current bus voltage, the second direct-current busvoltage and the third direct-current bus voltage from the corresponding starting threshold values respectively, multiplying the obtained maximum output value by a proportionality coefficient through an amplitude limiting link, and generating a duty ratio through a pulse modulation link so as to control the centralized unloading circuit to consume energy; and when the first direct-current bus voltage, the second direct-current bus voltage and the third direct-current bus voltage are all recovered to be below the corresponding starting threshold values, making the centralized unloading circuit quit operation, and recovering the system to normal. According to the invention, fault ride-through of an onshore AC system can be realized, and fault ride-through of a DC power transmission system canalso be realized.

The invention relates to the technical field of wind power converter control, in particular to a control method and a device of high voltage ride through for a full power wind power converter based onhysteresis current control. The method specifically comprises the following steps of: measuring a three-phase voltage of a grid in real time, performing positive and negative sequence separation on grid voltage, and calculating a per-unit value of positive-sequence grid voltage; and comparing the per-unit value of positive-sequence voltage with a high voltage threshold value of the grid, causinga grid-connected reactive power of a full power converter to come from an group main control unit if lower than the high voltage threshold value, and updating record of a given value of active currentvalue at this time. According to the invention, the grid voltage in real time is monitored, and whether the grid voltage is higher than the high voltage threshold of the grid is determined. When thegrid voltage is higher than the high voltage threshold of the grid, a given value of reactive current is calculated according to the grid voltage. The rise of the grid voltage is suppressed by absorbing a certain amount of reactive power from the grid, which is beneficial for the full power converter to operate without need to off-grid when the grid voltage rises, and to achieve high voltage faultride through successfully.

The invention discloses a control method for improving system damping characteristics of a photovoltaic energy storage power generation system in a multi-power coordinated manner. When a power grid operates normally, the energy storage system can stabilize fluctuations of photovoltaic output power, a photovoltaic grid-connected inverter keeps voltage of a DC bus to be stable, and achieves grid-connected current control. When the power grid fails, the power of the system oscillates since the photovoltaic system has no damping effect on a power system, the drop and recovery of voltage of the power grid can cause drastic fluctuations in the voltage of the DC bus, thereby affecting stable operation of the power grid. The coordinated control method provided by the invention regards DC bus voltage variation as a judging condition, achieves the switching of control modes of the photovoltaic grid-connected inverter and a storage battery during the system oscillating process. The control method can suppress power oscillation of the system, brings convenience for the photovoltaic energy storage power generation system to achieve fault ride-through, and improves system operation stability.

The invention discloses a voltage source type wind turbine generator fault ride-through control method suitable for a weak power grid, and overcomes the problems of unstable fault ride-through and grid connection of a doubly-fed fan under the condition of the weak power grid in the prior art. The method comprises two parts of control strategy switching and control strategy parameter calculation when a power angle is unstable under the condition of the fault ride-through. According to the invention, the voltage angle and amplitude of a fan port are controlled by using active current-frequency droop and reactive current-voltage droop; the external characteristics of a wind power plant can be changed from a PQ node (based on traditional vector control) to a V theta node; reactive current meeting the power grid standard can be provided under an asymmetric fault, the asymmetry degree of the power grid is reduced, the voltage stability after the fault is removed is enhanced, a Park conversion angle can be switched into a phase-locked loop angle when power angle instability occurs in the transient process, and the system stability problem caused by the power angle instability is avoided.

The invention discloses a fault ride-through system and ride-through method of a vessel direct-current networking electric propulsion system, and solves the problems that the oil consumption is high and the use rate of fuel is low caused by the condition that when a vessel propulsion system is under a low-power running state, a diesel generating set and a spare diesel generating on the vessel still need to keep a joint working state. The fault ride-through system comprise a first diesel generating set (1), wherein the first diesel generating set (1) is connected with a public direct-current bus (5) through a first rectification frequency converter (2); a main propulsion motor inversion frequency converter (6) and a side propulsion motor inversion frequency converter (9) are separately connected to the public direct-current bus (5); a chopper (15) is connected to the public direct-current bus (5); and a super capacitor set (16) is connected to the input end of the chopper (15). According to the fault ride-through system disclosed by the invention, under an underload running condition of the vessel, fault ride-through of the diesel generating set can be realized by super capacitors.

The invention provides a fault ride-through method and system for a wind power delivery system of a flexible DC power grid. The method includes the following steps: when a flexible DC power grid malfunctions, a flexible DC converter station locks a fault level on the basis of a detected voltage fault type and sends an active control demand to a wind electric field, and the wind electric field enables active power of a wind turbine generator to be locked urgently on the basis of the control demand of the active power; when faults of the flexible DC power grid are removed, the flexible DC converter station restarts the fault level and controls tripping of the wind turbine generator on the basis of conveying capabilities of the flexible DC power grid after the faults occur, active power output of the wind turbine generator that stays in a grid-connected operating condition and stays in a power locked state is restored, and thus fault ride-through is completed. The fault level converter station is locked after the DC power grid malfunctions, and the wind turbine generator unlocks converters after the faults are removed, thereby ensuring that the flexible DC power grid will not run overload. Moreover, it can be judged that part of the wind turbine generator needs to be cut off, active power output of the grid-connected wind turbine generator is restored, and then fault ride-throughis completed.

The invention discloses a fault riding-through method applicable to a photovoltaic power generation system. The fault riding-through method comprises the following steps: acquiring a voltage deviationamount and a measured current value of a photovoltaic panel, and converting the voltage deviation amount into a current inner loop reference value; judging whether a voltage deviation amount of a direct current busbar is greater than a dead zone threshold value; if the voltage deviation amount of the direct current busbar is greater than the dead zone threshold value, outputting a deviation valuebetween the voltage deviation amount of the direct current busbar and the dead zone threshold value, and multiplying the deviation value by a proportional coefficient to obtain a current deviation amount; calculating a value obtained by subtracting the measured current value of the photovoltaic panel and the current deviation amount from the current inner loop reference value to obtain a currentreference value of the photovoltaic panel; converting the current reference value into a duty cycle signal so as to enable the photovoltaic power generation system to control the stability of the voltage of the direct current busbar according to the duty cycle signal. The invention further discloses a fault riding-through device and the photovoltaic power generation system. Under the premise of nocommunication, effective limitation of the injection power of the photovoltaic panel during an alternating current grid failure can be achieved, fluctuation of the voltage of the direct current busbar is reduced, and ultimately the fault ride-through of the photovoltaic power generation system is achieved.

The invention discloses a multi-voltage grade direct current grid system. The direct current grid system comprises at least one direct current transformer, at least two direct current buses and at least one outgoing line current limiter. One end of the direct current transformer is connected with a first direct current bus, and the other end of the direct current transformer is connected with a second direct current bus, so that the conversion of direct current voltage is realized. The outgoing line current limiter comprises a group of direct current switches and a first current limiting unit,wherein the first current limiting unit is composed of a first by-pass switch and a first current limiting resistance unit. The invention further comprises a control protection method of the multi-voltage grade direct current grid system, when a bus or an outgoing line of a direct current grid is in a short-circuit fault, a current limiting resistance unit comes into service rapidly, short-circuit current is reduced, and the voltage of the bus is maintained to be normal, so that the fault ride-through is realized, and the operational reliability of the direct current grid is greatly improved.

The invention discloses a fault ride-through control method and system for load short circuit of a direct-current transformer, and belongs to the technical field of control of direct-current converters. The method comprises the following steps: when a fault does not occur, the DAB direct current converter is modulated under a rated working condition; when a fault occurs, after the time of a switching period of driving signals of internal switching tubes of a primary full bridge and a secondary full bridge is blocked, a modulation method of the DAB direct current converter is set to be extended phase shift modulation, and meanwhile, the driving signals of the internal switching tubes of the primary full bridge and the secondary full bridge are recovered to enter a current limiting state; at the moment, the output current of the circuit which breaks down is larger than the operating value of the circuit breaker, and the circuit breaker completes breaking. According to the control method provided by the invention, the transient overcurrent phenomenon of the fault is inhibited, and the fault branch can trigger the action of the circuit breaker of the short-circuit branch in the current limiting state through the matching of the current limiting value and the action value of the circuit breaker, so that the automatic fault breaking and circuit recovery without a current sensor are realized, and the fault ride-through of the direct-current transformer is realized.

The invention discloses an inverter integrating the function of energy consumption circuits. The converter comprises a single phase bridge arm formed by connecting at least two submodules in series, wherein each submodule comprises an energy consumption circuit, and the energy consuming circuit is composed of an energy consumption resistor, a first power device and an anti-parallel diode of the first power device. According to the inverter integrating the function of energy consumption circuits, no independent energy consumption circuit valve tower needs to be individually arranged and the inverter has advantages of a compact structure, small land occupation, low cost, strong fault ride-through capability, etc.

The invention discloses a ride-through control method applied to an enhanced Direct Current (DC) short-circuit fault of a Modular Multi-level Converter (MMC). The short-circuit fault is a single-polegrounded short-circuit fault occurred by only one pole in positive and negative poles, and the control method relates to the control of the pole where the fault is located and the control of the otherpole opposite to the pole where the fault is located. According to the method, not only is a control target of each of the positive and negative poles (the pole where the fault is located and the other pole) of a sending end and a receiving end when a Modular Multi-level Converter-High Voltage Direct Current (MMC-HVDC) system takes place a DC single-pole grounded short-circuit fault stated, but also a principle for configuring active and reactive powers is optimized; the capacity of the MMC-HVDC system can be fully used to provide active and reactive supports for a power grid, so that the MMC-HVDC can implement fault ride-through under the DC single-pole grounded short-circuit fault by fully using the own capacity; and thus, the fault ride-through capacity of the MMC-HVDC system under theDC single-pole grounded short circuit and the stable operation capacity of a connected alternating-current power grid thereof are improved.

The invention discloses a transient fault ride-through control method of a high-voltage frequency converter. The method comprises the following steps: an output current value of the frequency converter is sampled in real time; if the output current value is greater than a set protection value, the operating frequency and an output voltage of the frequency converter are set to the lowest value, so that the output voltage of the frequency converter is rapidly reduced, and a motor stator current is also rapidly reduced so to prevent the stator current from rising to a shutdown protection value and causing a halt, thereby realizing fault ride-through; then, through automatic flexible recovery, the output voltage and frequency of the motor rise, and the pressure of a hydraulic pump of a well-wall corer gets recovered; and a drill bit can continue drilling to realize the fault ride-through. The invention also provides the system of realizing the above method. According to the invention, when the current of a sticking stator surges, the current is reduced to be in a safety scope to avoid occurrence of protective shutdown, and flexible automatic recovery can be realized so that a continuous power can be provided for timely drill withdrawing and subsequent drilling when sticking of drilling of the well-wall corer occurs.

The invention provides a fault ride-through control system for an alternating-current excitation power supply. When a point of common coupling (PCC) voltage drops slightly, a three-phase electronic switch K1 is switched on, K2 is switched off, a current inner loop in a double-loop control strategy adopts a method combining proportional integral resonant control and variable damper control, and a PCC voltage valid value outer loop output serves as a given value of current inner loop current. When the PCC voltage drops deeply, the three-phase electronic switch K1 is switched off, K2 is switchedon, direct-current voltage output loops of a machine-side converter (MC) and a grid-side converter (GC) adopt a proportional integral resonant control method, and a current inner loop adopts a proportional integral resonant control method. Through adoption of the control system, rotor overcurrent of a doubly fed induction generator (DFIG) caused by a PCC voltage dropping fault is restrained; ripple voltage on a direct-current side of the alternating-current excitation power supply caused by a PCC voltage asymmetrical dropping fault can be reduced; and the alternating-current size current resonant content is lowered.

The invention provides a method and a device for realizing new energy fault ride-through control under the coordination control of an energy storage device and a flexible DC converter station. For theflexible grid with the island access to new energy, when the DC power grid fails, the transmission power is limited, signals on an AC bus (voltage change, frequency change, etc.) are controlled by the predetermined DC converter station, the energy storage device is subjected to fast active power control to reduce the impact of island access to the new energy power station to ensure that the DC converter station is not overloaded, then, according to the given power transmission capacity of the DC power grid after the fault is restored, a power control system of a new energy power station and the energy storage device are started to perform power control to achieve a balance with the capacity of the converter station, and fault ride-through is achieved. The method is advantaged in that theimpact of island access to the new energy power station can be reduced through rapid active power adjustment, moreover, the control system of the converter station of the DC power grid is further veryflexible, and coordinated adjustment of the two can effectively reduce the effect of the fault.

The invention provides a virtual synchronous power generator-based fault ride-through control method and system. During a power grid fault, a DC / DC converter of a virtual synchronous machine is switched to a constant-voltage and feedforward control mode from a constant-voltage control mode, a first current instruction value is obtained by subtracting a voltage instruction value from a voltage feedback value and by PI regulation, a first voltage value is obtained by subtracting the first current instruction value from a current feedback value and by PI regulation, the DC / DC converter is controlled, a DC / AC converter of the virtual synchronous machine is switched to a current-constant control mode from a VSG control mode, a reactive current is obtained by reactive voltage regulation control,an active current is calculated according to the reactive current, and the DC / AC converter of the virtual synchronous machine is controlled according to the reactive current and the active current which are obtained by calculation. By mode conversion of a virtual synchronous power generation system and control strategy optimization, fault ride-through of a station-type virtual synchronous power generator is achieved, and the stability of a power system is ensured.

The invention provides a low-loss modular multilevel converter fault ride-through method. A converter comprises three phase units, each unit is divided into an upper bridge arm and a lower bridge arm,and each bridge arm comprises a plurality of sub-modules which are connected in series. Each sub-module consists of two half-bridge structures, four capacitors and two fly-wheel diodes, the first half-bridge comprises a first switch module and a second switch module, and the second half-bridge comprises a third switch module and a fourth switch module. The cathode of the first switch module is connected with the anode of the second switch module, the cathode of the second switch module is connected with the anode of the third switch module, and the cathode of the third switch module is connected with the anode of the fourth switch module. By utilizing the properties of the reverse-blocking insulated gate bipolar transistors, when a direct-current side inter-electrode short-circuit fault occurs, a two-way switch composed of the reverse-blocking insulated gate bipolar transistors is turned off, and a fault loop is blocked. According to the method, the fault blocking of direct-current side short circuit can be achieved by controlling the on-off of the switch modules, and meanwhile loss is not increased.

The invention provides a fault handling system of a doubly-fed wind generator set and a generator set structure. The fault handling system of the doubly-fed wind generator set controls sequential on-off of three-phase electronic switches K1, K2, K3 and K4 according to the condition that common connection points generate drop faults, and meanwhile according to a fault handling logic controller, a mild fault handling controller or an in-depth fault handling controller is selected to work. According to the fault handling system of the doubly-fed wind generator and the generator structure, a hardware circuit is arranged, and a software control strategy is improved so that the doubly-fed wind generator set can achieve different levels of voltage drop fault ride-through; the fault handing system of the doubly-fed wind generator set is additionally arranged to provide reactive power; dynamic overvoltage and overcurrent of a generator side converter control can be effectively inhibited; complex hardware devices are not needed to be added, the control method is easy, and the fault handling system is convenient for engineering practice; harmonic pollution of the 102 alternating current side of a back-to-back PWM converter is reduced, the start-stop number of a doubly-fed wind generator (DFIG) is reduced, and certain technical support is provided for mass application of the doubly-fed wind generator set.

The invention provides a current source-mixed voltage source series type current converter topology with flexible voltage output capability. The mixed series type current converter topology consist ofa current source type current conversion unit and a voltage source type current conversion unit connected in series; the current source type current conversion unit has an LCC structure and the likewhich are formed based on a diode or thyristor; and each phase of bridge arm of the voltage source type current conversion unit comprises sub module units (such as a half-bridge sub module, an IGBT assembly and the like) without negative level output capability, and sub module units (such as a full-bridge sub module) with negative level output capability in a serial connection manner. When the mixed series type current converter topology is applied to the direct current power transmission system, the direct current system is controlled to block a direct current faulty current, and quick powerflow conversion (no need of an extra mechanical switch) can be realized; and therefore, the mixed series type current converter topology not only is suitable for high-voltage direct current power transmission systems at two ends, but also can be applied to a direct current power grid.

The invention provides a new energy island overvoltage control method and a converter station pole control system. The method comprises the following steps: firstly judging whether the fault of an alternating current circuit in a new energy system is a three-phase short-circuit fault by the converter station pole control system; then when the fault of the alternating current circuit is the three-phase short-circuit fault, issuing a dropout voltage reference value to an outer ring power controller in the converter station pole control system by the converter station pole control system, so thatthe outer ring power controller and an inner ring current controller in the converter station pole control system are used for performing outer ring power control and inner ring current control respectively until the voltage and power of a point of common coupling are greater than a first voltage threshold value and a first power threshold value, and issuing a recovery voltage reference value tothe outer ring power controller by the converter station pole control system. The method is simple in process and easy to realize, the voltage output by a converter station port after the three-phaseshort-circuit fault is solved can be rapidly controlled below 1.0 pu, the voltage output by the converter station port after the system is stabilized is recovered to be 1.0 pu, and finally fault rid-through of a new energy unit is realized.

The invention relates to a dynamic voltage restorer-based double-fed asynchronous wind generator unit control method. The method comprises the following steps: (1) building a dynamic voltage compensator-based double-fed asynchronous wind generator unit control system; (2) when a sudden change of a voltage is caused by a fault, obtaining a suddenly changed voltage vector for negative and negative sequence separation by a dynamic voltage restorer DVR; (3) calculating to-be-compensated voltage amount changing along with the time, and simultaneously giving a control signal; (4) outputting the voltage amount by the dynamic voltage restorer DVR, compensating a stator terminal voltage of a variable-speed and constant-frequency double-fed induction generator DFIG to stabilize the stator terminal voltage; (5) obtaining a suddenly changed new grid voltage vector when the sudden change is caused again during a fault period; (6) calculating the to-be-compensated voltage amount changing along with the time according to the suddenly changed voltage vector; and (7) outputting the voltage compensation amount by the dynamic voltage restorer DVR, and compensating the stator terminal voltage of the variable-speed and constant-frequency double-fed induction generator DFIG to stabilize the stator terminal voltage. The dynamic voltage restorer-based double-fed asynchronous wind generator unit control method can achieve stable fault ride-through.

The invention provides a fault crossing control method and a system of a doubly-fed wind turbine generator system, comprising the following steps of: collecting the terminal voltage of the doubly-fedwind turbine generator system; According to the terminal voltage and the preset threshold, the doubly-fed wind turbine generator system enters the preset fault crossing control mode or the normal control mode. The fault ride-through control mode includes determining the rotor control voltage of the doubly fed wind turbine generator system according to the phase jump value of the terminal voltage.The fault crossing control mode provided by the method and the system takes the dynamic influence of the voltage phase into consideration, does not affect the stable operation state of the system, effectively improves the accuracy of the unit control when the terminal voltage phase jumps, and ensures the fault crossing of the doubly-fed wind turbine unit.

The invention discloses a method for improving a grid-connected operation capability of a doubly-fed wind turbine generator under a power grid fault. The method comprises the following steps of when agenerator terminal voltage Usm is less than or equal to 0.9 p.u. and a rotor current Irm is greater than or equal to 2.0 p.u. due to a power grid fault, inputting Crowbar and locking a rotor side converter; when the rotor current Irm is detected to be less than or equal to 1.9 p.u., quitting the Crowbar, and setting a rotor side converter control instruction value to be Psc and Qsc; calculating the generator terminal voltage and minimum grid-connected duration time td, min after control is implemented; when t is less than td and Usm is greater than 0.9 p.u. within min, setting the instructionvalue to be Psn and Qsn; otherwise, maintaining the Psc and Qsc, detecting whether a parameter is out of limit; if so, when the t is greater than td, quitting the doubly-fed wind turbine generator after the min; and if not, when the Usm is greater than 0.9 p.u., setting the instruction value to be Psn and Qsn. By using the method, a flexible power control capability and a safety margin of the doubly-fed wind turbine generator can be fully used, a continuous grid-connected operation capability of the doubly-fed wind turbine generator under the power grid fault is improved, and effective technical measures can be provided for operation control of a high-proportion wind power system.

The invention discloses a microgrid single-end rapid fault positioning method and a related device. Whether a fault occurs or not is judged according to an output voltage or a three-phase grid entering current of a microgrid inverter; when the microgrid breaks down, the droop control mode of the inverter is switched into a current control mode, and fault ride-through is achieved; a fault loop differential equation of a protected line with the fault is construced; then harmonic waves of different times are superposed on a microgrid modulating wave and a plurality of high-frequency harmonic waves of different frequencies are injected into the microgrid so that the microgrid filters the harmonic voltage of the protected line with the fault through the high-frequency harmonic waves to obtain a high-frequency signal; and finally, fault distance calculation is carried out by adopting high-frequency signals in a power grid. According to the invention, rapid, accurate and reliable discrimination and positioning of the microgrid system fault can be completed without communication so that the technical problems of low positioning accuracy, long time and unreliability of the existing microgrid fault positioning technology are solved.

The present invention discloses a flexible access substation. The flexible access substation includes N sets of frequency conversion access systems, where N is an integer greater than or equal to 1, each set of frequency conversion access system includes a first AC-DC-AC converter, a first output circuit breaker, and a first power distribution system. The first power distribution system includes an AC incoming line, an AC bus, and at least one outgoing line. An output side of the first AC-DC-AC converter is connected to one end of the AC incoming line of the first power distribution system byusing the first output breaker. The present invention further discloses a control method of the flexible access substation, a set of converters can be simultaneously connected to a plurality of berths, and a docking vessel can access a shore power in a plug-and-play manner, so that investment costs of the shore power equipment are reduced, convenience of accessing the shore power is improved. In an interconnection mode, mutual support between AC buses can be implemented with high reliability.

The invention discloses a hybrid cascade type direct-current fault ride-through system based on a fault current limiter and a control method. The hybrid cascade type direct-current fault ride-through system is characterized in that: the fault current limiter is arranged between a hybrid cascade type direct current receiving end high-end LCC direct current outlet and a corresponding hybrid cascade type direct current receiving end low-end MMC direct current inlet; after an LCC has a commutation failure fault, a fault current limiter control system detects that MMC direct current reaches fault current limiter starting criterion current, a current limiting resistor is put in, the direct current fault current is suppressed, and an MMC valve group is prevented from being locked; and when a low-end MMC at the receiving end has a single-pole grounding fault, the fault current limiter blocks a discharge loop from the normal MMC and the fault MMC to a fault point by means of the topology of the fault current limiter, and the MMC valve group is protected. Through simple control, ride-through of a high-end LCC commutation failure fault of the receiving end is achieved, the recovery process is good, ride-through of the low-end MMC single-pole grounding fault of the receiving end can be achieved without any control receiving end, the fault current limiter does not adopt a full-control device, and meanwhile the development problem of a large-capacity direct-current circuit breaker is avoided.