61results about How to "Improve fault ride-through capability" patented technology

The invention discloses a PR (proportional resonant) controller-based NMC-HVDC (modular multilevel converter-high voltage direct current) circulating current suppression method. PR controller-based circulating current suppression is adopted at the inverter end to suppress positive-sequence and negative-sequence circulating currents, and meanwhile, a zero-sequence circulating current controller is used to suppress DC voltage fluctuation and zero-sequence circulating current; PR controller circulating current suppression is adopted at the rectifier end; or PR controller circulating current suppression is used at the rectifier end to suppress positive-sequence and negative-sequence circulating current, meanwhile, the zero-sequence circulating current controller is used to suppress the DC voltage fluctuation and zero-sequence circulating current, and PR controller circulating current suppression is adopted at the inverter end; or both the rectifier end and the inverter end use PR controller circulating current suppression to suppress positive-sequence and negative-sequence components and both use the zero-sequence circulating current controller to suppress the DC voltage fluctuation and zero-sequence circulating current. In each AC side system failure, the positive-sequence, negative-sequence and zero-sequence components of the circulating current can all be completely suppressed; the DC voltage fluctuation can also be suppressed; fault ride-through ability of an AC system during a fault can be improved; the problems occurring in the use of the traditional PR control method in NMC-HVDC are solved.

The invention provides a modularization multi-level converter redundancy fault-tolerant control method. According to the method, an inverter controller is arranged on the alternating current side of a modularization multi-level converter; redundancy fault-tolerant model prediction control is carried out on the modularization multi-level converter, wherein the redundancy fault-tolerant model prediction control is composed of three control objects of alternating current tracking, sub-module capacitive voltage equalization and circulation suppression; each control object defines an objective function to calculate all possible switching state objective function values under the corresponding objective function; an alternating current tracking objective function and a sub-module capacitive voltage equalization objective function calculate numerical values under all switching states of MMC; a circulation suppression objective function calculates numerical values under all circulation suppression compensation levels; the minimum value of the objective functions is selected; the switching state corresponding to the minimum value of the objective functions is recorded; and the switching state is input into the MMC and is used as the switching state of the MMC of next moment. Circulation suppression and sub-module capacitive voltage equalization of the modularization multi-level converter in the case of redundancy fault-tolerance are realized.

The invention discloses an unsymmetrical fault ride-through method of a double-fed wind generating set. According to the method, a rotor-side convertor control circuit comprises a rotating speed outer ring and a rotor positive and negative sequence current control inner ring, and in order to eliminate the influence of direct-current decrement of a stator flux linkage, a corresponding compensation item is introduced at an outlet of a positive sequence current controller; in order to avoid the overcurrent or overvoltage of the rotor convertor, a novel current amplitude limiting link is designed, and an integral saturation link and an output amplitude limiting link are respectively introduced for the current controller; according to a network-side convertor, actual active power of a rotor is introduced in an outer ring direct-current voltage circuit to balance power on the two sides of a direct-current bus in real time; meanwhile, actual measurement negative sequence network voltage is an inner ring positive sequence current control circuit to eliminate the influence of negative sequence voltage. The defect that an existing control strategy cannot take the influences, on the network-side/rotor-side convertor, of occurrence of the generator terminal negative sequence voltage and the requirement for idle supporting of a power network in the failure period into account at the same time yet is overcome, and therefore the fault ride-through capacity of the double-fed wind generating set is improved.

The invention discloses a DFIG (doubly fed induction generator) control method based on resonant feedback in an unbalanced power network. By the aid of resonant feedback control technology, the DFIG control method in the unbalanced power network can be simplified, positive and negative sequence separation for the electromagnetic volume of a system and negative sequence current reference value calculation link for a rotor in any links are omitted, accordingly, the problems of time delay, phase angle and amplitude detection errors and the like caused by the positive and negative sequence separation process can be avoided, the requirements of different targets are met, and fine dynamic characteristics are realized. By the aid of the DFIG control method, reinforced operation and control of a DFIG system can be realized under the condition of the unbalanced power network, and fault ride-through capability of the DFIG system is improved. Moreover, the DFIG control method can be applied to various PWM (pulse width modulation) three-phase or single-phase inverter devices such as a solar power generation and biomass energy grid-connected inverter device and an alternating-current transmission inversion device, so that different control effects in the unbalanced power network are achieved.

The invention discloses a hybrid wind power plant group coordination control method under power grid asymmetrical faults, and relates to control of a grid-side converter and a machine-side converter of a permanent magnet direct drive wind power system; the hybrid wind power plant group comprises a permanent magnet direct drive wind power plant and an asynchronous wind power plant; in the premise of not increasing hardware equipment, the active power output of the permanent magnet direct drive wind power plant is limited while the current margin of the grid-side converter is fully utilized; on the basis of controlling the output of the grid-side converter to satisfy positive sequence reactive power of the power grid guiding rule, the residual current margin is utilized to output a negative sequence current to realize synergistic inhibition of the grid-connected point negative sequence voltage, reduce adverse influence of the operation behaviors of the permanent magnet direct drive wind power plant to the operation behaviors of the asynchronous wind power plant, and effectively improve the power-grid fault operation capability and the grid-connected electric energy quality of the asynchronous wind power plant.

The invention discloses a method for controlling a photovoltaic grid-connected inverter. The method comprises: obtaining output voltage and output power of a photovoltaic cell at preset moment; according to variation trends of the output voltage and output power, performing iterative computation on an output current set value, until an output current reference value of a maximum power point tracking (MPPT) control module at a maximum power point of the photovoltaic cell is obtained; according to the output current reference value, calculating to obtain a current set value of a current inner loop, finally, based on a proportional resonance (PR) control strategy, realizing maximum power point tracking and photovoltaic inverter grid connected. Through the variation trends of the output voltage and output power of the photovoltaic cell, iterative computation is directly performed on the output current set value, and finally the current set value of the current inner loop is obtained. Compared with the prior art, voltage outer loop control is not needed, the method can track the maximum power point more rapidly and accurately, and simplifies a photovoltaic grid-connected inverter control system, and photovoltaic grid-connected fault through capability is improved, so as to ensure safe operation of a power grid.

The invention belongs to the technical field of hybrid micro-grids and power distribution networks, and specifically relates to a suppression method for series compensation transformer direct currentmagnetic bias between a micro-grid and a power distribution network. Thus, the problems of series compensation transformer direct current magnetic bias between an alternating current/direct current micro-grid and a power distribution network caused by the rapid output of series link voltage can be solved. The method includes collecting the voltage amplitude of the power distribution network in real time; judging whether voltage dropping occurs, and recording alpha and voltage dropping depth; and calculating the first half period amplitude of compensation voltage and outputting the compensationvoltage until the voltage dropping disappears. The suppression on the series compensation transformer direct current magnetic bias under fault situations of single-phase voltage dropping and three-phase voltage dropping of a power grid can be realized, so that the normal operation of series links can be guaranteed, the normal operation of loads carried by an alternating current bus and the safetyof power electronic devices can be effective guaranteed, the fault ride-through capabilities of alternating current/direct current HMG on the voltage dropping of the power distribution network can beenhanced, and the power supply quality of the alternating current bus can be improved as well.

The invention discloses a sub-module redundancy configuration method and system of a modular multilevel converter. The method comprises the following steps: determining the number of fault sub-modulesin the modular multilevel converter; calculating and acquiring a capacitance reference voltage of the sub-modules of the modular multilevel converter based on the number of the fault sub-modules; obtaining a target output voltage of an upper bridge arm and a target output voltage of a lower bridge arm of the modular multilevel converter; and determining the number of sub-modules input by the upper bridge arm by utilizing the capacitance reference voltage and the target output voltage of the upper bridge arm, and determining the number of sub-modules input by the lower bridge arm by utilizingthe capacitance reference voltage and the target output voltage of the lower bridge arm. In the invention, a maximum voltage output capability is reserved by increasing a capacitor voltage so that thesystem operates stably, and a fault ride-through capability is enhanced; and loss of a converter valve is reduced, redundant modules are fully utilized, a harmonic content of an output voltage is reduced, and operation performance of the modular multilevel converter is optimized.

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 relates to an offshore wind power system fault combined ride-through method based on a flexible direct current MMC converter. According to the method, a grid-side MMC is allowed to redistribute an active and reactive reference current through a reactive priority link when a fault happens to a power grid and the voltage drops, and reactive current support is provided for the voltage recovery of the power grid. The wind power plant increases the pitch angle of a fan and reduces the active output of the fan by adjusting the active power set value of the fan, that is, the absorptionof wind power during a fault period is reduced, the power imbalance phenomenon between a grid-side MMC and an offshore MMC is improved, excessive power in a direct current link is effectively prevented from being stored in a direct current capacitor, the MMC converter is prevented from being damaged due to overvoltage during a fault period, so that the fault ride-through capability of the offshoreflexible direct-current wind power system is effectively improved, and the safe and stable operation of the system is ensured.

An embodiment of the invention discloses fault ride-through control method for an inversion type new energy power supply. The method includes: adding a positive and negative sequence current limiter into a vector orientation based positive and negative sequence d-q current control loop of the inversion type new energy power supply; monitoring network voltage positive sequence component and direct-current bus voltage of the inversion type new energy power supply; using the network voltage positive sequence component to start or stop control signals of a direct-current unloading circuit of the inversion type new energy power supply, and balancing unbalanced power on a direct-current side of an inverter by the aid of a direct-current voltage PI (proportional integral) controller. The control method is used for overcoming defects of existing unbalanced control strategies to improve fault ride-through capability of the inversion type new energy power supply.

The invention discloses a fault ride-through control method and system for a double-wind-wheel wind generating set, and belongs to the technical field of wind power generation. The method comprises the steps of judging whether a parallel power grid has a voltage fault or not by detecting the voltage of a grid-connected point of a three-port fan converter, and if the parallel power grid has the voltage fault, calculating the voltage value of a direct-current bus of the three-port fan converter and the rotating speed of a wind wheel with a relatively lower rotating speed in a current double-wind-wheel generator set; and according to the real-time rotating speed and the power value of the low-speed wind wheel, switching the working state of the machine-side converter corresponding to the low-rotating-speed wind wheel rapidly, so that the electric and power generation state of the motor is changed, and the low-rotating-speed wind wheel absorbs instantaneous electric energy from a direct-current bus or releases electric energy to a power grid system through a three-port fan converter. According to the technical scheme, the double wind wheels of the wind turbine generator are rapidly controlled to be mutually loaded, the problems of low efficiency, high cost, poor safety and the like caused by the fact that fan fault ride-through is achieved through the consumption electric energy consumption of the resistors in the prior art, are solved, and the method has good application prospect.

The invention discloses a step-down operation control method for a hybrid MMC flexible direct current power transmission system. The method includes the following steps: determining the step-down coefficient eta on an MMC direct current side and the stable voltage U on an MMC alternating current side according operation requirements; obtaining the alternating current system voltage Us and reactivepower Qv of the MMC alternating current side during step-down operation, obtaining the power factor of the MMC alternating current side, entering the next step if a condition shown in the descriptionis met, and otherwise, returning to the last step; judging the operation conditions of the MMC alternating current side, controlling MMC to absorb a certain reactive power if Us is greater than U, and adjusting the power factor to 1.45 eta; and controlling the MMC to emit a certain reactive power output if Us is less than or equal to U, and adjusting the power factor to 1.45 eta. The control method can be realized by depending on the self and original control capabilities of a control system, so that the problems of the unable voltage-sharing of the bridge arm sub-module of a hybrid MMC flexible direct current power transmission system during step-down operation can be solved, the capabilities of the hybrid MMC to realize step-down operation can be strengthened, and fault ride-through capabilities under the condition of direct current voltage reduction such as direct current line insulation faults can be enhanced.

The invention relates to a current blocking method and device for a direct-current power transmission system fault, a multi-terminal direct-current power transmission system and a storage medium, the method is applied to the multi-terminal direct-current power transmission system, and the system comprises a plurality of sending-end converter stations and a plurality of receiving-end converter stations. Under the condition that a fault occurs in a direct-current power transmission line, a fault current on the direct-current power transmission line is obtained, and a target voltage of a first sending end converter station which enables the fault current of the direct-current power transmission line to be zero is determined according to the fault current and a preset reference current; and after the first sending-end converter station is controlled to output the target voltage, a switch between the direct-current transmission line and the first sending-end converter station is controlled to be switched off, and under the condition, the current of the second sending-end converter station flows into the first sending-end converter station. According to the method, the fault current can be reduced to zero under the condition that the second sending end converter station does not need to quit operation, so that fault current blocking is realized; and then, the second sending end converter station continues to operate, and the fault ride-through capability of the direct-current power transmission system is improved.

The invention relates to current limiting equipment applicable to bidirectional flow direct current system distributed capacitance configuration. The current limiting equipment comprises an H bridge circuit composed of two diode bridge arms, two switch bridge arms and an intermediate branch circuit; the diode bridge arms and the intermediate branch circuit are respectively formed by connecting power diodes in series; the switch bridge arms are respectively formed by connecting switch elements in series, wherein the switch elements can be conducted unidirectionally and can be turned on and off,a collector, anode or drain electrode end of each switch bridge arm is called as a bridge arm positive pole, and a transmitter, cathode or source electrode end of each switch bridge arm is called asa bridge arm negative pole; the two diode bridge arms share the cathode; the negative pole of each switch bridge arm is connected with the anode of one of the diode bridge arms, and the switch bridgearms share the anode and are connected with an anode of a capacitor; and a cathode of the intermediate branch circuit is connected with a common point of the diode bridge arms, and an anode of the intermediate branch circuit is connected with a common point of the switch bridge arms. One of the common point of the diode bridge arms and the common point of the switch bridge arms is connected with adirect current bus, and the other one of the two common points is connected with a direct current circuit.

The invention relates to a valve control overvoltage-overcurrent cooperative protection method and system for a flexible direct current converter valve, and relates to the field of direct current transmission, and the method comprises the steps: obtaining a voltage-current operation capability curve of a sub-module in the flexible direct current converter valve during unlocking operation; obtaining the maximum voltage of each current unlocking operation based on the voltage-current operation capability curve, and calculating a voltage-current protection constant value curve of a sub-module in the flexible DC converter valve based on the maximum voltage of each current unlocking operation; and each sub-module controller performs overvoltage protection by using a dynamic overvoltage protection constant value according to the real-time operation current of the bridge arm and the voltage-current protection constant value curve of the sub-module. The constant value of overvoltage protection is dynamically adjusted according to the magnitude of the current in the operation process, the constant value of overvoltage protection is high when the current is small, the constant value of overvoltage protection is low when the current is large, the risk of overvoltage protection action locking of the converter valve under the alternating-current and direct-current fault of the system can be reduced, and the fault ride-through capacity is improved.