798 results about "Low voltage ride through" patented technology

A wind powered turbine with low voltage ride-through capability. An inverter is connected to the output of a turbine generator. The generator output is conditioned by the inverter resulting in an output voltage and current at a frequency and phase angle appropriate for transmission to a three-phase utility grid. A frequency and phase angle sensor is connected to the utility grid operative during a fault on the grid. A control system is connected to the sensor and to the inverter. The control system output is a current command signal enabling the inverter to put out a current waveform, which is of the same phase and frequency as detected by the sensor. The control system synthesizes current waveform templates for all three-phases based on a sensed voltage on one phase and transmits currents to all three-phases of the electrical system based on the synthesized current waveforms.

A wind turbine system is provided with a wind turbine rotor, a pitch control mechanism, and an emergency power supply mechanism. The wind turbine rotor includes a blade having a variable pitch angle. The pitch control mechanism drives the blade to control the pitch angle. The emergency power supply mechanism generates electric power from rotation of the wind turbine rotor and feeds the electric power to the pitch control mechanism, in response to occurrence of an accidental drop of a system voltage of a power grid.

A wind turbine system is provided with a wind turbine rotor, a pitch control mechanism, and an emergency power supply mechanism. The wind turbine rotor includes a blade having a variable pitch angle. The pitch control mechanism drives the blade to control the pitch angle. The emergency power supply mechanism generates electric power from rotation of the wind turbine rotor and feeds the electric power to the pitch control mechanism, in response to occurrence of an accidental drop of a system voltage of a power grid.

A variable speed wind turbine having a doubly fed induction generator (DFIG) includes an exciter machine mechanically coupled to the DFIG and a power converter placed between a rotor of the DFIG and the exciter machine which guarantees a stable voltage to the power converter. Thus, the power converter is not directly connected to the grid allowing the continuous operation of the system during a low voltage event in the grid.

A wind powered turbine with low voltage ride-through capability. An inverter is connected to the output of a turbine generator. The generator output is conditioned by the inverter resulting in an output voltage and current at a frequency and phase angle appropriate for transmission to a three-phase utility grid. A frequency and phase angle sensor is connected to the utility grid operative during a fault on the grid. A control system is connected to the sensor and to the inverter. The control system output is a current command signal enabling the inverter to put out a current waveform, which is of the same phase and frequency as detected by the sensor. The control system synthesizes current waveform templates for all three-phases based on a sensed voltage on one phase and transmits currents to all three-phases of the electrical system based on the synthesized current waveforms.

A variable speed wind turbine having a doubly fed induction generator (DFIG) includes an exciter machine mechanically coupled to the DFIG and a power converter placed between a rotor of the DFIG and the exciter machine which guarantees a stable voltage to the power converter. Thus, the power converter is not directly connected to the grid allowing the continuous operation of the system during a low voltage event in the grid.

An LVRT control method for a grid-connected converter of distributed energy resources comprises steps of: obtain a positive sequence electrical component and a negative sequence electrical component during an LVRT period; outputting a compensation signal according to a power threshold withstood by a grid-connected converter to undertake reactive power compensation; and constraining the output power lower than the power threshold. The present invention uses the positive and negative sequence electrical components to undertake reactive power compensation, whereby to improve balance and stability of voltage during the LVRT period, avoid reverse torque and mechanical resonance, and prolong the service life of the power generator. Moreover, the present invention constrains the sum of the compensation currents below the power threshold to prevent the circuit of the power generator from being overloaded and damaged, whereby is prolonged the service life of the power system.

The invention discloses a low-voltage ride through control strategy for a grid-connected photovoltaic power generation system capable of providing the reactive support. The strategy comprises the steps of control over a preceding-stage DC / DC converter and control over a backward-stage grid side inverter. When grid faults occur, the backward-stage grid side inverter is controlled to provide needed reactive power for a power grid according to the voltage drop depth of the power grid; the feed-forward compensation dosage reflecting photovoltaic array output power and direct-current voltage fluctuation is added into a direct-current side voltage control ring of the inverter, and therefore over-voltage of the direct-current side of the inverter is reduced in the fault occurring process; a controller of the preceding-stage DC / DC converter controls a photovoltaic array to output active power according to the voltage drop depth and the rated capacity of the inverter, so that unbalanced energy in a photovoltaic system when the faults occur is reduced, and the purpose of reducing over-current and over-voltage in the photovoltaic system is achieved. According to the strategy, no hardware device is additionally arranged, the response speed is high, realizing is simple, the low-voltage ride through capacity of the photovoltaic system can be effectively improved, the reactive power can be provided for the power grid, and the voltage recovery of the power grid is supported.

The invention discloses a cooperative control method of high and low voltage ride-through for a doubly-fed wind turbine set. According to the method, according to monitored stator end voltage level of the doubly-fed wind turbine set, the operating state of the doubly-fed wind turbine set is divided into three operating modes, to be specific, a normal node, a low voltage ride-through mode and a high voltage ride-through mode; by modifying a rotor side converter control structure, attenuation of direct current and negative sequence component in stator flux linkage of the doubly-fed wind turbine set after a failure occurs is accelerated, and quick injection of reactive current is made possible; according to rotor three-phase current and direct-current bus voltage level monitored in real time, breakover trigger logic of a hardware protective module is optimized, and operational safety of a set transformer and an alternating-current bus capacitor is protected. Especially, the provided cooperative control of high and low voltage ride-through and a protective scheme are implemented completely on basis of existing low voltage ride-through hardware of the set, no additional hardware protective equipment is required, and a general voltage fault ride-through implementing scheme for handling abrupt changes in grid voltage amplitude is provided.

The invention relates to a movable low-voltage ride-through testing device for a wind generating set. The device is connected between a tested wind generating set and an electric network in series, uses an impedance voltage-dividing type and a vehicle container structure, and tests the low-voltage ride-through performance of the wind generating set through analog voltage sag fault; a main connecting wire of the device consists of a serial reactor group, a parallel reactor group and a circuit breaker; the serial reactor group and the parallel reactor group both consist of at least one adjustable reactor; the impedance voltage-dividing ratio can be changed by regulating the impedance value of each adjustable reactor and / or the connecting manner of each adjustable reactor so as to change the voltage sag depth of testing points; and once recovery or a step recovery of the voltage sag can be implemented according to the system requirements. The device can complete the low-voltage ride-through testing experiments for various wind generating sets having a maximum rated capacity of 6 MW, and meet the requirements to the low-voltage ride-through testing experiment in wind electric network integrations in states in Europe and America and Technical Rule for Connecting Wind Farm to Power Networks.

The invention discloses a coordination control method for double-fed asynchronous wind driven generator high voltage ride through, on the basis of a mathematical model of a double-fed asynchronous wind driven generator and gird side and rotor side converters of the double-fed asynchronous wind driven generator, allocation principles of active and reactive power of the grid side and rotor side converters of the double-fed wind driven generator are calculated, extremity expressions of active and reactive current are given, and a high voltage ride through implementation scheme capable of effectively providing dynamic reactive support for a power grid and eliminating direct current bus voltage, active power, reactive power and electromagnetic torque ripples is provided. The coordination control method in the invention can overcome defects of weak ride through capability and poor power grid stability of a wind driven generator in the prior art, thereby achieving the goal of optimal control of the generator when the power grid voltage is high; and the method can perfectly be implemented on the basis of original low voltage rid through hardware, thereby realizing joining with an existing low voltage ride through scheme of the unit, and forming a generalized voltage fault ride through control strategy capable of coping with a sudden change of amplitude of network voltage.

The invention relates to a low-voltage traversing control method for a double-fed wind power generation system, which belongs to the technical field of wind power generation. The method comprises the following steps: firstly, the stator flux and the rotor flux of a double-fed generator are calculated according to the stator current and the rotor current of the double-fed generator which are measured by a current sensor; secondly, the stator flux is multiplied by a corresponding proportionality factor to serve as the set value of the rotor flux of the double-fed generator, so as to control therotor flux; and thirdly, the rotor flux is controlled in the way that as feedforward compensation decoupling is performed, closed-loop control is conducted to the decoupled system, and a rotor-side converter is controlled after pulse-width modulation is conducted to the obtained voltage control quantity of a rotor-side converter, so as to achieve low-voltage traversing control during failures. The low-voltage traversing control method provided by the invention has fast response, and very good traversing effect when symmetrical and asymmetrical drop failures of the network voltage occur, meanwhile, and oscillation of output electromagnetic torque of the double-fed generator can be effectively inhibited. The control method is simple and suitable for engineering application.

The invention provides a method for controlling low-voltage ride-through of the grid-connected converter of a wind-driven generating set. On the basis of back-to-back voltage or current-typed grid-connected converter, a motor-side converter detects the middle direct current voltage; a voltage adjuster controls the middle direct current voltage to follow with the middle direct current voltage instruction value; a torque adjuster controls the practical torque to follow with the torque instruction value; an active power adjuster controls the grid-side converter and leads the grid-connected active power to follow with the active power instruction value. The transfer of the dump energy is realized by the coordinated control of the motor-side converter and the grid-side converter, elements such as additional resistance and the like are not required so as to consume the rest energy, thus ensuring that the wind-driven generating set does not run without the grids during the falling period of the network voltage at the access point. The method improves the efficiency of the unit, reduces the energy loss, simplifies the structure of the system, reduces the volume of the device, reinforces the compactness of the structure and reduces the cost of the device.

An integrated high and low voltage ride through test system, comprising a primary system and a secondary system; the secondary system controls the primary system to realize information interaction, and is connected to a power grid and a wind generation set via an inlet wire switch cabinet and an outlet wire switch cabinet of the primary system; the integrated high and low voltage ride through test system actually simulates voltage drop and rise characteristics in a power grid failure, ensures that when generating a low voltage and a high voltage, the change of a voltage phase angle and power quality are consistent with actual power grid failure characteristics, and enables coherent low voltage and high voltage ride through capacity testing on the wind generation set in a primary test process. The test system employs a structural design of a mobile vehicle-mounted container, with all component modules thereof being integrally installed in a standard container, free from the impact of weather and geographical environment, being able to conduct all-weather on-site testing in any wind farm, and having good environment adaptability.

The invention relates to an electromechanical transient modeling method and an electromechanical transient model of a wind turbine generator system, in particular to an electromechanical transient modeling method and an electromechanical transient model of a direct-drive-type wind turbine generator system. The modeling method includes the following steps: firstly, a generator-side model of the wind turbine generator system is constructed. Secondly, a direct current and unloading circuit model of the wind turbine generator system is constructed. Thirdly, a grid-side converter and control system model of the wind turbine generator system is constructed. And lastly, a low voltage ride through control model of the wind turbine generator system is constructed. Based on a practical physical device, by means of a reasonable presume, an electromagnetic transient model of the direct-drive-type wind turbine generator system is simplified, and meanwhile, the dynamic process of direct current voltage and low voltage ride through characteristics of the converter are taken into account. The simulation result shows that the simulation curve of the model is consistent with practically detected low voltage ride through curve of the direct-drive-type wind turbine generator system, and the result is accurate and reliable. The electromechanical transient modeling method and the electromechanical transient model of the direct-drive-type wind turbine generator system are used for analyzing influence on transient stability of a power system when a large-size direct-drive-type wind power plant is introduced.

The invention provides a low-voltage ride through (LVRT) control system of a photovoltaic inverter and a method thereof. The system comprises a solar cell panel, a photovoltaic inverter, a power grid and a controller, wherein the solar cell panel, the photovoltaic inverter and the power grid are sequentially connected; and the controller is respectively connected with the photovoltaic inverter and the power grid. The system and the method have the advantages that 1) when the power grid breaks down to cause power grid voltage balance sag, good dynamic response is provided, and grid-connected current can be steadily outputted by three phases of current sharing of the photovoltaic inverter; and 2) in unbalanced voltage sag, the positive and negative sequence voltage influence of the power grid can be eliminated by the control system, only the positive sequence current component is outputted, and the three-phase current sharing is ensured and has a lower harmonic component, so that the loss caused by the faults of the power grid is reduced, and the power supply reliability of the power grid is improved. The special situation of the unbalanced power grid is supported by the system, and the stable operation of the normal three-phase current sharing is guaranteed.

The invention discloses an improved positive-negative sequence component separation method. By adopting the method, bigger errors which are caused by a 'one-quarter cycle delay' method used in a one-quarter cycle after the happening and the ending of unsymmetrical faults are avoided, and the advantages of simplicity, high detection performance and the like of the 'one-quarter cycle delay' method are well used. The invention also discloses a method realizing low voltage ride through of a single-stage photovoltaic grid-connected inverter by using the improved positive-negative sequence component separation method. By adopting the methods, low voltage sag of an electric network can be quickly detected, the influence caused by unsymmetrical sag negative sequence components is inhibited, reactive power is provided, the voltage of a support grid connection point is recovered, and the requirement on the low voltage ride through of a high-power grid-connected inverter is met.

The invention discloses a photovoltaic grid-connected inverter low voltage ride through (LVRT) control method, and relates to the field of grid-connected photovoltaic power generation. The method is characterized by comprising a distribution procedure of active power and reactive power in the LVRT process, and procedures about elimination of current peak and protection to an inverter. The procedure of protection to the inverter includes that when a grid is in a grid voltage drop stage or in a grid voltage recovery stage, if an average current value of any phase of three-phase current outputted by the inverter is detected to exceed an average threshold value, a pulse-width modulation (PWM) control signal of the inverter is switched off, and the PWM control signal of the inverter can be recovered after duration of half PWM control signal cycle time; and if an instantaneous value of any phase of the three-phase current of an output end of the inverter is detected to exceed an instantaneous threshold value, the connection between the inverter and the grid can be switched off. The instantaneous threshold value is higher than the average threshold value and the like.

The invention provides a simulation verification method for low voltage ride through (LVRT) of a wind farm. The method comprises the following steps of: analyzing operating characteristics of a wind generation set according to a verified wind generation set electric simulation model; establishing a wind farm electric simulation model, and verifying whether the wind farm has LVRT or not; and establishing a regional power system simulation model comprising the wind farm electric simulation model, and verifying influence of wind farm grid connection on secure and stable operation of a power system. The invention provides a complete and effective method for verifying the LVRT of the wind farm; and the method has positive significance on judging whether the wind farm meets the grid connection requirement or not, avoiding large-scale wind power off-line accidents and ensuring secure and stable operation of a power grid, and lays a foundation for establishing and perfecting a wind power grid-connected authentication system in China.

The invention relates to a symmetrical drop-off low voltage ride through reactive power control method of a photovoltaic power generation system. A controller detects whether a grid connection point voltage drops off in real time, and if the voltage does not drop off to 90% of a nominal voltage, an active current reference value id* is taken from an outer voltage loop, and grid connection control when the voltage is normal is adopted; if the grid connection point voltage drops off below 90% of the nominal voltage, the outer voltage ring is disconnected, low-voltage ride through control is adopted, namely inner current loop control is adopted, definite reactive power is output to a power grid by the photovoltaic power generation system according to the drop-off amplitude, and recovery of the voltage of the power grid is facilitated; if it is detected that the voltage recovers, the active power of the photovoltaic power generation system recovers at 10% rated power / second, reactive power is gradually reduced to zero at the same time, and finally the grid connection control when the voltage is normal is adopted. According to the method, an outlet current of a photovoltaic grid-connected inverter is limited within an over-current protection action current, reactive power support is provided for the grid voltage to recover to the normal value, investment of reactive power equipment is saved, and resources are saved.

The invention provides a method and system for cooperatively controlling a low voltage ride through of a full-power fan converter. The method comprises the following steps of: judging dropping and resilient stability of a voltage of a power grid; when the voltage of the power grid is in a dropping transient state or a rising transient state, carrying out temporary forced locking on a driving signal of a power switching tube device of a network side converter; and when the voltage of the power grid is in a dropping stable state or is recovered to the normal stable state, relieving locking of the driving signal of the power switching tube device of the network side converter. Meanwhile, the method and the system are matched with work of a crowbar circuit so as to realize the low voltage ride through of the network side converter. In the invention, different states of the voltage of the power grid are judged by a positive sequence component and a negative sequence component of the voltage of the power grid so as to carry out different controls. Moreover, only the network side converter is controlled and a machine side converter can always normally operate, so that the mechanical stress of a wind machine and a driving chain, which is caused by electromagnetic torque pulsation of a generator, is reduced.

The invention discloses an all-digital testbed for an electric pitch control system of a wind generating set, which comprises a motor butting fixed platform, wherein a plurality of fixing positions for fixing a pitch control motor of the wind generating set are arranged on the motor butting fixed platform, a load assistant motor is detachably arranged on each fixing position and coaxially opposite to the pitch control motor, and the rotating shafts of the load assistant motors and the pitch control motor are connected together through couplers. The all-digital testbed further comprises a servo driver which connects and controls all the load assistant motors, a controller which controls the servo driver, and a host computer which contains a human-machine interaction interface and is provided for operators to input control commands. The all-digital testbed can effectively test the response condition of the electric pitch control system when the paddle load varies (i.e. when the wind speed is disturbed), and meanwhile, feathering, low voltage riding through and other functions of the standby power supplies of the pitch control system can be tested. The construction of the testbed provides an effective way for ground test research of the electric pitch control system.

The invention relates to a dynamic voltage stabilizer for assisting a wind driven generator in realizing low voltage ride through (LVRT), and belongs to the technical field of power system flexible alternating current power transmission and distribution and power electronics. The dynamic voltage stabilizer consists of three same single phase alternating current and direct current (AC-DC-AC) conversion full bridge structures; a normal AC transformer is connected with a single phase H bridge structure uncontrolled rectifier to form each phase; a capacitor is connected with a single phase H bridge inverter; and an AC port of the inverter is directly connected with the capacitor and a power grid through a filter inductor. The dynamic voltage stabilizer has the functions of voltage compensation and active power absorption, can assist doubly-fed induction wind motor in realizing the LVRT function when voltage drops off, improves the power generation capacity of a wind power station when the power grid fails, has a simple structure, can obtain good voltage compensation effect and dynamic response characteristic, is suitable for industrial production, and improves the reliability of the wind power station.

The invention provides a low-voltage ride-through testing system of a wind generating set. The testing system comprises a voltage dropping system, an on-site measuring system, a remote monitoring system and an on-site controlling system, wherein the on-site measuring system is in bidirectional connection with the remote monitoring system; the remote monitoring system is in bidirectional connection with the on-site controlling system; the on-site controlling system is in bidirectional connection with the voltage dropping system; the voltage dropping system is in one-way connection with the on-site measuring system; and the on-site measuring system is in bidirectional connection with the on-site controlling system. The low-voltage ride-through testing system of the wind generating set, disclosed by the invention, is in accordance with criterion IEC61400-21, can realize voltage drop of different degrees and various types and can satisfy requirements of wind generating sets in all countries on low-voltage ride-through testing. The low-voltage ride-through testing system is a movable detecting system which is adaptable to performing the low-voltage ride-through characteristic testing on all wind generating sets which have been operated in the wind power field, and has high safety as well as high stability.

The invention discloses a low voltage ride through control method and device of a photovoltaic grid-connected inverter, and is designed to solve the problem of poor ride through stability caused by neglecting control of a current waveform and an amplitude when the low voltage ride through control is performed on the inverter in the prior art. The method includes the steps as follows: step S1, whether a voltage value of a power grid is smaller than the upper limit of a low voltage value is judged, if the voltage value of the power grid is smaller than the upper limit of the low voltage value, the step S2 is executed, and otherwise, the inverter is controlled to work normally; step S2, whether the voltage value of the power grid is not more than the lower limit of the lower value is judged, if the voltage value of the power grid is not more than the lower limit of the lower value, the inverter is controlled to stop working, and otherwise, an active power current value output by the inverter is controlled to be equal to a target active power current value and the output reactive power current value is equal to a reactive power current value; and a comparison difference value of a total current output by the inverter and a current output by a photovoltaic grid in a normal state is smaller than a preset value. The change of total currents before and after voltage sag is small by controlling an active power current and a reactive power current of the inverter, so that the functions of supporting and stabilizing the power grid are realized.

The invention discloses a low voltage ride-through control method of a doubly fed induction aero-generator, which is used when a power network has short circuit faults. The control method is characterized in that a rotor exciting voltage positive-sequence control current and a rotor exciting voltage negative-sequence control signal are respectively formed through limiting a rotor slip frequency current and a rotor (2-s) rated frequency current when the power network has faults, and a generator is utilized for realizing the attenuation of stator flux transient DC components and reducing the rotor side influences of the stator flux transient components, positive-sequence components and negative-sequence components. The control method has the advantages that no hardware protecting device is required to be added; under the condition that the power network has symmetrical and asymmetrical faults, the overcurrent occurrence of the rotor can be effectively restrained, and the safe operations of the generator and a rotor exciting converter are protected; in the process that the power network has the faults, the transient generator impact to the power network and a mechanical system can be effectively reduced; the normal operation of the generator can be fast recovered after the faults are removed, and the timely support to the power network can be realized.

The invention discloses a grid-connected photovoltaic power generation system and a control method of the grid-connected photovoltaic power generation system. The system comprises a plurality of photovoltaic cell arrays, a plurality of maximum power point tracking devices correspondingly connected with the photovoltaic cell arrays one to one, a converging unit and a grid-connected inverter. The grid-connected inverter comprises a chopper assembly unit and an inversion unit which are sequentially and electrically connected. The chopper assembly unit comprises a first switching tube and an energy consumption resistor which are connected between direct-current buses of the grid-connected inverter in series, and further comprises an inverter control unit. The grid-connected photovoltaic power generation system and the control method have the advantages that when the voltages of the direct-current buses rise due to the fact that faults such as low voltage ride through and high voltage ride through happen to a power grid, the first switching tube in the chopper assembly unit is controlled to be powered on, releasing is conducted through the energy consumption resistor, and therefore the voltages of the direct-current buses are reduced and made to rapidly return to normal, and reliable running of the whole grid-connected photovoltaic power generation system is ensured.

The invention relates to a low voltage ride through control circuit of doubly-fed variable-speed constant-frequency wind power generator unit, which comprises a power grid, a doubly-fed power generator and a doubly-fed frequency converter and which is mainly technically characterized in that: first three-phase alternating current switches are connected in series between stators of the power grid and the doubly-fed power generator, second three-phase alternating current switches are connected in series between a rotor of the doubly-fed power generator and a rotor-side inverter of the doubly-fed frequency converter, and third three-phase alternating current switches are connected in series between the rotor-side inverter of the doubly-fed frequency converter and a grid side inverter of the doubly-fed frequency converter. The low voltage ride through control circuit has the characteristics of reasonable design, great simplicity and stable and reliable performance, guarantees the implementation of low voltage ride through function of doubly-fed power generator unit and safe and stable power grid, reduces the cost thereof, and can be widely applied to the field of wind power generation.

The invention discloses a comprehensive series compensation voltage ride-through device of a wind turbine generator. The comprehensive series compensation voltage ride-through device of the wind turbine generator is mounted on a three-phase circuit between a wind driven generator and a control device of the wind driven generator and a PCC (point of common coupling) of a power grid, and comprises a three-phase standard transducer, a series coupling transformer, a two-way charge-discharge circuit, a DC bus capacitor and a by-pass switch. With the adoption of a dynamic voltage restorer, a chopper circuit and a super capacitor with high-capacity energy storage in the power electronic technology, low voltage ride through, high voltage ride through and harmonic compensation are realized under the condition that generator terminal voltage drops off during power grid fault, generator terminal voltage rises due to excessive reactive power of the power grid and the harmonic content of the power grid is overlarge, the wind turbine generator is prevented from being separated from the grid, and harmful effects of harmonic are prevented; and moreover, a conventional wind turbine generator is not required to be transformed, and the device can be taken as an independent control module and added at the stator output port of the wind turbine generator and is convenient to mount.

The invention discloses a photovoltaic grid-connected inverter low-voltage ride through method based on reactive current injection. The method is based on a low-voltage ride through strategy supported by reactive current voltage, is aimed at an photovoltaic grid-connected inverter, switches voltage and current double-loop control of an inverter circuit into current single-loop control, switches an maximum power point tracking (MPPT) of a boost circuit into voltage stability control, and finally achieves low-voltage ride through of the photovoltaic grid-connected inverter. The method is simple and practical. When a power grid breaks down and the voltage of the power grid is reduced, the photovoltaic grid-connected inverter can be made to achieve low-voltage ride through by switching the control strategy of the photovoltaic grid-connected inverter, and the voltage of the power grid is supported to recover.