WO1993011604A1 - Turbine eolienne a vitesse variable avec fluctuation reduite de la puissance et mode de fonctionnement a var statique - Google Patents

Turbine eolienne a vitesse variable avec fluctuation reduite de la puissance et mode de fonctionnement a var statique Download PDF

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Publication number
WO1993011604A1
WO1993011604A1 PCT/US1992/010225 US9210225W WO9311604A1 WO 1993011604 A1 WO1993011604 A1 WO 1993011604A1 US 9210225 W US9210225 W US 9210225W WO 9311604 A1 WO9311604 A1 WO 9311604A1
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WO
WIPO (PCT)
Prior art keywords
power
wind turbine
inverter
waveform
generator
Prior art date
Application number
PCT/US1992/010225
Other languages
English (en)
Inventor
William L. Erdman
Original Assignee
U.S. Windpower, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US07/799,416 external-priority patent/US5225712A/en
Application filed by U.S. Windpower, Inc. filed Critical U.S. Windpower, Inc.
Publication of WO1993011604A1 publication Critical patent/WO1993011604A1/fr

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D7/00—Controlling wind motors 
    • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
    • F03D7/0272—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor by measures acting on the electrical generator
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D7/00—Controlling wind motors 
    • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
    • F03D7/0276—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor controlling rotor speed, e.g. variable speed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D7/00—Controlling wind motors 
    • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
    • F03D7/04—Automatic control; Regulation
    • F03D7/042—Automatic control; Regulation by means of an electrical or electronic controller
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D9/00—Adaptations of wind motors for special use; Combinations of wind motors with apparatus driven thereby; Wind motors specially adapted for installation in particular locations
    • F03D9/20—Wind motors characterised by the driven apparatus
    • F03D9/25—Wind motors characterised by the driven apparatus the apparatus being an electrical generator
    • F03D9/255—Wind motors characterised by the driven apparatus the apparatus being an electrical generator connected to electrical distribution networks; Arrangements therefor
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
    • H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H02M7/53875—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
    • H02M7/53876—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output based on synthesising a desired voltage vector via the selection of appropriate fundamental voltage vectors, and corresponding dwelling times
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
    • H02P21/06—Rotor flux based control involving the use of rotor position or rotor speed sensors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/04—Control effected upon non-electric prime mover and dependent upon electric output value of the generator
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/42—Arrangements for controlling electric generators for the purpose of obtaining a desired output to obtain desired frequency without varying speed of the generator
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2220/00—Application
    • F05B2220/70—Application in combination with
    • F05B2220/706—Application in combination with an electrical generator
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2220/00—Application
    • F05B2220/70—Application in combination with
    • F05B2220/706—Application in combination with an electrical generator
    • F05B2220/7064—Application in combination with an electrical generator of the alternating current (A.C.) type
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2270/00—Control
    • F05B2270/10—Purpose of the control system
    • F05B2270/1016—Purpose of the control system in variable speed operation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2270/00—Control
    • F05B2270/10—Purpose of the control system
    • F05B2270/103—Purpose of the control system to affect the output of the engine
    • F05B2270/1032—Torque
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2270/00—Control
    • F05B2270/10—Purpose of the control system
    • F05B2270/104—Purpose of the control system to match engine to driven device
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2270/00—Control
    • F05B2270/10—Purpose of the control system
    • F05B2270/20—Purpose of the control system to optimise the performance of a machine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2270/00—Control
    • F05B2270/30—Control parameters, e.g. input parameters
    • F05B2270/327—Rotor or generator speeds
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P2101/00—Special adaptation of control arrangements for generators
    • H02P2101/15—Special adaptation of control arrangements for generators for wind-driven turbines
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/72—Wind turbines with rotation axis in wind direction
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/20—Active power filtering [APF]

Definitions

  • This invention relates generally to wind turbines that operate at variable speed under varying wind speeds, and relates more particularly to a power converter for converting varying wind energy into substantially smooth AC electrical power having a controlled reactive power.
  • Wind turbines provide a primary source of energy that can be converted into electricity and supplied to utility power grids. Conversion of wind energy to electrical energy is accomplished in a wind turbine by driving an electrical generator, which is commonly an AC induction generator. If the electrical power generated by a wind turbine is to be supplied to a utility power grid, then it must have a constant frequency. Conventionally, constant frequency operation is accomplished by driving the generator at a constant rotational speed which requires that the wind turbine rotate at a constant speed unless a variable speed transmission is used.
  • turbine rotor speed is controlled as a function of pitch angle and wind speed.
  • Variable speed wind turbines have been proposed for increasing the energy conversion efficiencies of constant speed wind turbines.
  • improved energy recovery can be achieved over a range of wind speeds.
  • mechanical stresses caused by wind gusts can be reduced by limiting the torque acting on the wind turbine by the generator and allowing the wind turbine to speed up in response to wind gusts.
  • variable speed wind turbines are variable speed wind turbines.
  • the electrical generation system is more complicated than that of a constant speed wind turbine. Since a generator is usually coupled to a variable speed rotor through a fixed-ratio gear transmission, the electrical power produced by the generator will have a variable frequency. This variable frequency AC must be converted to a constant frequency AC before it can be used by the utility power grid. The conversion can be accomplished either directly by a frequency converter or through an
  • VARs Volt-Ampere Reactive units
  • constant speed wind turbines provide output power with a lagging current.
  • constant speed wind turbine plants have employed large capacitor banks to pull the current in phase with the voltage.
  • the capacitor banks have all the disadvantages outlined above, including lack of ability to select the number of VARs necessary to precisely compensate for the VARs provided by the wind turbines.
  • capacitor banks produce unpredictable switching transients when switching the capacitor banks on- or off- line.
  • the present invention provides a wind turbine power converter that smooths the output power from a variable speed wind turbine, to reduce or eliminate substantial power fluctuations on the output line. Also, the present invention provides a wind turbine power converter that outputs a constant number of VARs independent of the real power; i.e., it can output a constant number of VARs whether or not the wind turbine is operating to produce real power. When the wind turbine is not operating, the power converter operates to produce VARs in what is termed a "static VAR" mode.
  • the preferred embodiment of the present invention comprises a wind turbine connected to a power converter.
  • the power converter has a DC voltage link that is connected to an electrical energy storage device.
  • the DC voltage link may be connected to any of a number of conventional electrical energy storage devices: a conventional battery such as a lead-acid battery, an electrochemical device such as a fuel cell,
  • photovoltaics or solar cells may be used to provide electrical energy during deficits in energy production, for example.
  • the use of energy storage in the wind turbine has at least two advantages.
  • One advantage is a reduced output power fluctuation to the grid, so that power fluctuations are reduced or even eliminated completely.
  • a second advantage is availability of energy to operate the wind turbine in the absence of utility power, for example during controlled shutdown.
  • the power converter can be operated as a VAR compensator that provides a selectable number of VARs to the utility.
  • the number of VARs can be selected independently of the amount of watts (real power) flowing through the power converter.
  • the ratio between the real power and the reactive power can be controlled; i.e., the power factor angle can be controlled.
  • the instantaneous current flowing through the active switches at the line side inverter can be controlled to supply output electricity with a desired relationship between voltage and current.
  • the inverter control unit a first inverter control unit that can control only the power factor angle, and a second inverter control unit that can control either the number of VARs or the power factor angle. Both inverter control units use a voltage waveform as a reference waveform for further operations. Specifically, the reference waveform is obtained with
  • the first inverter controller unit obtains a reference waveform, rotates the reference waveform by a selected power factor angle to yield a template waveform, and multiplies the template waveform by a multiplication factor Iref to form a current control waveform that defines desired output currents.
  • the current control waveform for each phase is applied to a current regulator which regulates the drive circuit that controls the currents for each phase of the inverter.
  • the current control waveform controls the active switches to produce output currents that correspond to the desired output currents.
  • the multiplication factor, Iref can be calculated in various ways. Described herein are two methods of
  • the first method is implemented in a
  • the P/I multiplier selector is particularly appropriate to maintain a constant voltage on the DC voltage link when the amount of energy storage is small.
  • the P/I multiplier selector applies a voltage error (the measured voltage on the DC voltage link less the desired voltage for the DC voltage link) to a
  • the multiplier selector may be unnecessary if a large energy source, such as a fuel cell, is used as an energy storage device. Such a fuel cell inherently regulates the voltage on the DC voltage link. In that instance, the multiplier I ref may be selected directly by an operator, or by a control system to output a desired real power amount. If the energy storage device includes a battery, or another substantial energy storage device that stores energy as well as sources energy, the second multiplier selector, a charge/discharge multiplier selector that produces a selected charge/discharge ratio in the energy storage device, is more appropriate. For the charge/discharge multiplier selector, a current sensor positioned between the active rectifier and the energy storage device measures the generator-side current supplied from the generator-side to the energy storage device.
  • This sensed current is multiplied by the voltage across the DC voltage link.
  • the voltage-current product is then multiplied by a factor inversely proportional to the product of the power factor and the RMS voltage on the utility grid.
  • This result is then added to a battery charge term which indicates the extent to which the battery needs to be charged or discharged.
  • the form of the battery charge term is highly dependent upon a particular battery or energy storage device.
  • the sum of the product and the battery charged term is applied to a low pass filter, with a low cut-off frequency of, for example 10 Hz or less.
  • the output of the low pass filter is applied as the
  • the type of multiplier selector that is appropriate for a particular application is dependent upon the energy storage device.
  • the type of multiplier selector is not dependent upon the inverter control unit and thus either of the multiplier selectors may be used with the first inverter control unit described above as well as the second control unit to be described below.
  • the second inverter control unit also uses the reference waveform to create, for each phase, two waveforms: a real waveform and an imaginary waveform.
  • the real waveform includes the reference waveform
  • the imaginary waveform includes the reference waveform rotated by 90°.
  • VAR multiplier M 1 that is selected with a VAR control signal to supply the desired number of VARs.
  • the real waveform is multiplied by a real multiplier M 2 .
  • the real multiplier M 2 is selected as described above to select the multiplier I ref .
  • the second inverter control unit can also provide an approximately constant power factor angle.
  • an additional constant defined as K
  • I ref the output of the multiplier selector
  • this product is then applied as the VAR multiplier M 1 in lieu of the previously described multiplier M 1 .
  • the value for K is supplied by an operator, thus allowing the operator to control the power factor angle.
  • the multiplied imaginary waveform and the multiplied real waveform are then added to provide a current control waveform for each phase.
  • the current control waveform is applied to a current regulator in a drive circuit that drives the switches of the inverter circuit to provide the instantaneous currents spedfied by the current control waveform.
  • reactive power can be specified and controlled by directly controlling the currents through each of the phase lines.
  • multiphase generator a power converter with active switches that control stator electrical quantities in each phase of the generator, and a generator controller operating under field orientation control and responsive to a torque reference signal for defining a desired quadrature axis current and for
  • Described herein is a method for controlling torque reacted by a multiphase generator of a wind turbine, where a power converter with active switches controls electrical quantities in the stator of the generator to establish a rotating flux field in the stator and rotor of the generator.
  • the method includes the steps of defining a torque reference signal indicative of a desired generator torque, converting the torque reference signal into a desired quadrature axis current representing torque in rotating field coordinates normal to the rotor flux field, and controlling the active switches of the power converter to produce stator electrical quantities that correspond to the desired quadrature axis current.
  • the field oriented control defines the desired
  • the desired generator operation in terms of a rotating frame of reference to decouple stator flux-producing currents from stator torque- producing currents.
  • the desired generator operation is defined by a desired direct axis (flux-producing) current in rotating field coordinates ahgned with the direction of the rotor flux field and a desired quadrature axis (torque- producing) current in field coordinates oriented normal to the rotor flux field.
  • Generator torque is controlled by controlling the quadrature axis current.
  • the angle of the field coordinate system with respect to a stationary frame of reference defines a desired rotor flux angle, which is periodically determined and used to convert the desired direct and quadrature axis currents from the field coordinates into stator coordinates.
  • a pulse width modulation circuit controls the active switches to produce stator electrical quantities.
  • the power converter is preferably a rectifier/inverter with a DC voltage link connected to an electrical energy storage device.
  • the rectifier has active switches in a bridge configuration that control the currents and voltages at the generator side of the power converter, while the inverter has active switches in a bridge configuration that control the instantaneous currents at the line side of the power converter.
  • the stator electrical quantities that are regulated are either currents or voltages.
  • desired currents defined by the field oriented control are converted to desired stator currents, and the active switches of the power converter are controlled to produce corresponding stator currents.
  • desired field oriented currents are converted into desired field oriented voltages by compensating for cross-coupling between the direct and quadrature axes, the desired field oriented voltages are converted into desired stator voltages, and the active switches are controlled to produce corresponding stator voltages.
  • the generator controller regulates the generator torque by controlling the stator currents at a low speed of rotation of the generator and by controlling the stator voltages at a higher speed of rotation of the generator.
  • the orientation of the rotor flux field with respect to the rotor is controlled by switching the active rectifier to regulate currents in the stator, while during the higher speed operation of the generator, the orientation of the rotor flux field is controlled by switching the active rectifier to regulate voltages in the stator.
  • Switching between current control and voltage control is preferably controlled by a rotor speed signal that indicates rotor speed.
  • This current controller includes an algorithm that determines optimum PWM
  • This algorithm reduces total harmonic distortion over competing algorithms operating at comparable sampling frequencies, whlle reducing switching losses by reducing the number of switching events.
  • One feature of the preferred embodiment is the use of field orientation control of the rectifier to control generator torque.
  • Field orientation decouples the torque-producing currents or voltages of the generator stator from the flux- producing currents or voltages and thus permits responsive control of generator torque.
  • Another feature is a hybrid control strategy for the rectifier in controlling either the stator currents or stator voltages.
  • Current control is used where the stator currents can be assumed to be supplied by current sources, which is a valid assumption at low rotor speeds due to a large margin between the DC bus voltage of the rectifier and the counter emf of the generator.
  • Voltage control is used at higher rotor speeds where current control would otherwise require increasing the DC bus voltage proportional to speed to maintain responsive control and constant volts/hertz operation.
  • Voltage control has an increased power capability over current control at higher speeds whlle mamtaining constant volts/hertz
  • the inverter controller of the present invention offers some of the same advantages as the generator controller in terms of efficient and low-distortion power conversion through the use of the current control algorithm that minimizes a distortion index.
  • the inverter controller provides reactive power control by adjusting the output current between fully leading and fully lagging the output voltage, thereby supplying or absorbing selectable amounts of reactive power.
  • the inverter controller can supply a selectable number of VARs either while operating or in a static VAR mode.
  • Fig. 1 is a block diagram of a wind turbine in accordance with the present invention.
  • Fig. 2 is a schematic diagram of a power converter circuit and block diagram of associated control circuits of the present invention.
  • Fig.3 is a block diagram of the control system used to control generator torque.
  • Fig. 4 is a graphical diagram illustrating the angular relationships between a fixed stator coordinate system, a rotating rotor coordinate system, and a rotating field oriented coordinate system.
  • Fig. 5 is a block diagram of a generator control unit of the present invention.
  • Fig. 6 is a block diagram of a field orientation converter of the present invention.
  • Fig. 7 is a block diagram of a delta modulator current controller of the present invention.
  • Fig. 8 is a block diagram of a distortion index current controller of the present invention.
  • Fig. 9 is a block diagram of an alternative
  • Fig. 10 is a graphical representation, in ⁇ , ⁇
  • Fig. 11 is a block diagram of a voltage controller of the present invention.
  • Fig. 12 is a block diagram of a computer program used in the generator control unit of the present invention.
  • Fig. 13 is a block diagram of an inverter control unit of the present invention.
  • Fig. 14 is a block diagram of a current controller used in the inverter control unit of Fig. 13.
  • Fig. 15 is a block diagram of a computer program used in the inverter control unit of the present invention.
  • Fig. 16 is a schematic diagram of a preferred embodiment of the energy storage device that includes
  • Fig. 17 is a graphical illustration of average power output and energy storage for a wind turbine that has
  • Fig. 18 is a graphical illustration of average power output for a wind turbine having energy sources to supply power during periods of deficits in generated power.
  • Fig. 19 is a diagram of the proportional/integral multiplier selector that produces the multiplier I ref for use with either inverter control unit.
  • Fig.20 is a block diagram of a charge/discharge multiplier selector for use with an inverter control unit.
  • Fig. 21 is an exemplary graph of average generator power output and actual output energy to the grid, plotted as average power versus time.
  • Fig. 22 is a flowchart illustrating operation of the second inverter control unit.
  • Fig. 23 is a diagrammatic illustration of the second inverter control unit.
  • Fig. 24 is a block diagram of a delta modulator current controller for controlling inverter currents in accordance with the current control waveform.
  • Fig.25 is an illustration of a number of installed wind turbines whose output energy is collected in a power collection center and supplied to a utility grid that also receives energy from generators.
  • FIGs. 1 through 25 of the drawings disclose aspects of the present invention for purposes of illustration only.
  • One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention.
  • a wind turbine 10 includes a variable pitch turbine rotor 12 that is mechanically coupled through a gear box 14 to two 3-phase AC induction generators 16 and 18.
  • the gear box 14 includes a fixed-ratio, step-up transmission, so that the generator rotors rotate at a fixed multiple of the speed of the turbine rotor.
  • the generators 16 and 18 produce 3-phase AC electricity at a variable frequency that is proportional to the speed of the turbine rotor.
  • the electricity generated by each generator 16 and 18 is converted from variable frequency AC to fixed frequency AC by power converters that comprise active rectifiers 20 and 22, DC voltage links 24 and 26, energy storage devices 25 and 27, inverters 28 and 30, and filters 32 and 34.
  • the outputs of the filters 32 and 34 are combined at a transformer 36, the output of which is supplied to the utility grid.
  • the two generators both of which rotate at all times whenever the turbine rotor rotates, are preferred over one generator in this embodiment in order to build a high capacity wind turbine while using readily available generators.
  • the invention can, of course, be implemented in a wind turbine with only one generator or more than two generators.
  • Each of the generators 16 and 18 is controlled separately by generator controllers 38 and 40 which, as explained below, control the torque reacted by the generators by controlling the stator currents or voltages.
  • Shaft speed sensors 42 and 44 monitor the rotor speed of the two
  • a power controller 54 directs the inverter controllers 50 and 52, as explained below, to provide control of real power flow and to provide control of reactive power by shifting the output current with respect to the output voltage.
  • the torque command device 46 monitors wind turbine performance parameters and generates torque control signals to the generator controllers 38 and 40 and pitch angle control signals to a pitch control unit 48.
  • Stored within the torque command device 46 is a table of optimal values of torque, pitch angle, and rotor speed for various operating conditions. These values are given as a function of an estimated wind speed, which is determined by an aerodynamic model of the wind turbine having inputs of rotor speed from the speed sensors 42 and 44, measured pitch angle from the pitch control unit 48, and measured torque from the generator controllers 38 and 40.
  • a speed control signal is used to adjust the optimal values of pitch angle and torque found from the table.
  • the speed control signal is proportional to the difference between the optimal desired speed from the table and the measured speed from the speed sensors 42 and 44.
  • the torque command device 46 thus determines desired values of torque and pitch angle based on the sensed operating conditions and supplies torque and pitch angle control signals to the generator controllers 38, 40 and pitch control unit 48, respectively.
  • the power converter for each generator includes an active rectifier, a DC voltage link connected to an energy storage means, an inverter, filters, and associated controls. Both power converters are identical; only one will be explained. More particularly, as illustrated in Fig. 2, the active rectifier 20 includes three pairs of active switching devices 60 arranged in a bridge circuit between a+v rall 68 and a -v rail 70 of the DC voltage link 24 and each of three stator power taps 72-74 of the generator 16. Each pair of switching devices is coupled between the DC rails 68 and 70, and connected at an intermediate point to one of the stator power taps.
  • Commutation signals that cause the active switching devices to switch on and off originate in a generator control unit 76, which supplies the signals to the switching devices through a drive circuit 78.
  • the generator control unit 76 and drive circuit 78 are isolated from the rectifier 20 by optical isolators to mi-nimize interference.
  • the commutation signals are complementary for each pair of switching devices, causing one switching device of each pair to switch on and the other switching device of the pair to switch off, as appropriate to achieve the desired stator currents or voltages.
  • the switching devices 60 of the rectifier 20 control the stator currents and voltages in the three phase stator windings.
  • the switching devices 60 of the rectifier can be any of the number of different types of active switches, including insulated gate bipolar transistors (IGBT), bipolar junction transistors, field effect transistors, Darlington transistors, gate turn-off thyristors, or silicon controlled rectifiers.
  • the switching devices 60 of the rectifier are IGBTs.
  • the generator control unit 76 which is part of the generator controller 38, receives sensor inputs of the stator currents i s1 , i s2 , i s3 , arid rotor speed ⁇ r , receives a torque reference value T ref from the torque command device 46 (Fig.
  • the operation of the generator control unit 76 will be
  • the DC voltage link 24 includes the +v rail 68 and the -v rail 70.
  • the energy storage device 25 may include a battery 80 such as a lead-acid or nickel-cadmium type.
  • Fig. 16 illustrates one battery configuration.
  • the energy storage 25 may include a plurality of batteries 80 in a series configuration between the +v rail 68 and the -v rail 70.
  • a plurality of battery series may be situated in parallel between the +v rail 68 and the -v rail 70. This configuration of the energy storage device 25 is termed a "series-parallel" configuration.
  • the energy storage device 25 may include any other conventional energy storage device: another type of battery, a SMES superconducting magnet, or a capacitor bank.
  • energy storage devices including an electrochemical device such as a full cell, or a photovoltaic or solar cell may be used to provide electrical energy during deficits.
  • the amount of electrical storage required for a particular wind turbine is highly dependent upon the particular site, cost factors, and the abiilty of the electrical grid to make up for deficits without substantially affecting the frequency. If cost, size and maintenance of electrical energy storage devices were not factors, then a larger energy storage would be advantageous for most uses. However, in any project, cost, size, and maintenance are common concerns.
  • the energy storage device can absorb or supply 200-300KW for short periods of time such as 10-15 minutes.
  • Fig. 17 is a graphical illustration of energy storage and withdrawal from the energy storage device 25. Power is plotted on the vertical axis vs. time on the horizontal axis. An interval of time during operation of the wind turbine is shown in Fig. 17. A line 81 shows the instantaneous output power from the generator fluctuating as a function of time. To obtain an appreciation of the time scale of Fig. 17, the time interval from time t 0 to time t 6 may be several minutes, for example. Such power fluctuations are typical in variable speed operation, in which the rotor speed (and thus the output power) varies with the wind over a time period. A line extending along the power level P 1 illustrates constant average output power for delivery to the grid.
  • the area between the lines 81 shows the amount of energy storage into, or withdrawal from, the energy storage device 25.
  • output power will remain approximately constant despite wind speed fluctuations on a short time scale.
  • the average output power may vary with the average wind speed.
  • Fig. 17 specifically from time t 0 to t 1 , an interval during which more energy is generated than supplied to the grid, energy is stored in the energy storage device 25.
  • the generator power output drops below the power to be supplied to the utility grid, and thus from time t 1 until time t 2 , some electrical energy is being withdrawn from the energy storage device 25.
  • the generator output has again exceeded the average output power, and therefore, this excess energy is stored in the energy storage device until time t 3 .
  • the cycle continues throughout operation of the variable speed wind turbine, alternately charging and discharging the electrical energy storage device 25.
  • Fig. 18 is a graphical illustration of power output for an alternative embodiment in which the energy storage device includes an energy source that provides output power during periods of deficits in generated power, but does not store substantial excess generated power during periods of excess generation.
  • the energy storage device may comprise a fuel cell which cannot be charged.
  • the generated power is illustrated by a line 83, and the target real power is defined by a line extending from P 2 .
  • excess power is generated at a level above P 2 , and this energy is suppHed to the grid.
  • the energy storage device 25 can supply substantial deficit energy during periods of deficits in generated power. And if energy storage device 25 can be charged, it should have sufficient capacity to store a substantial amount of the excess energy during intervals of excess generated power.
  • the amount of that energy storage is highly dependent upon a number of factors including cost, size and maintenance of the batteries, or other energy storage devices, the expected windspeed fluctuations, and the grid's ability to make up for power deficits and fluctuations.
  • the amount of energy storage in one embodiment is the amount necessary to supply 200 kilowatts for 5 minutes.
  • the amount of energy storage may have a value in the range of 200 Kw-min to 4000 Kw-min.
  • a capacitor may be used as an energy storage device without affecting the ability to control real and reactive power.
  • the capacitance of the capacitor may be about 15,000 microfarads, and the nominal voltage of the DC link may be about 750 volts.
  • the voltage links 24, 26 between the active rectifiers and the inverters may comprise any of a number of conventional bus configurations
  • the bus structure is as set forth in a commonly assigned, copending patent application having Serial No. 07/728,112, filed on July 10, 1991 and entitled “Low-Noise Power Bus", the disclosure of which is incorporated by reference herein.
  • rectifiers and the inverters preferably comprise the
  • the power bus provides performance advantages including reduced magnetic emissions that reduce interference with sensitive switching equipment located nearby.
  • the inverter 28 also includes three pairs of active switching devices 82 arranged in a bridge circuit between the +v rail 68 and -v rail 70 of the DC voltage link 24.
  • the intermediate points of the pairs of active switching devices 82 form three output taps 84-86 from which three phase electricity flows through the filters 32 and transformer 36 to the utility grid.
  • Commutation signals for the active switching devices 82 originate in an inverter control unit 88, which supplies the signals to the switching devices through a drive circuit 90.
  • the inverter control unit 88 and drive circuit 90 are isolated from the inverter 28 by optical isolators.
  • the switching devices 82 of the inverter 28 comprise single IGBTs.
  • the inverter control unit 88 which is part of the inverter controller 50, receives sensor inputs of the inverter currents i 01 , i 02 , i 03 , inverter voltages v 01 , v 02 , v 03 , and DC link voltage v dc .
  • the inverter currents are sensed at the output taps, while the inverter voltages are sensed at the output of the filters 32 and are isolated through potential transformers 92.
  • the inverter control unit 88 also receives, from the power controller 54, a power factor signal, a reactive power signal, and an operation mode signal, which define the desired power factor.
  • the inverter control unit 88 In response, as will be explained in further detail below, the inverter control unit 88 generates pulse width modulated commutation signals and supplies them to the inverter switches 82 through the drive circuit 90. In addition, the inverter control unit 88 also supplies a feedback signal Qfb, to the power controller 54 that indicates the reactive power being supplied by the inverter 50.
  • the control structure of the wind turbine is illustrated in Fig. 3 for one of the generators 16.
  • the generator control unit 76 includes a field orientation converter 94 that converts the torque reference T ref , and the rotor speed, cor, into field oriented control currents £ and £ and a rotor flux angle, These control variables, which are identified as reference variables by the * superscript, are used by a PWM controller 95 along with the sensed 3 phase stator currents, i s1 , i s2 , i s3 , to generate the PWM commutation signals, D 1 , D 2 , D 3 ,
  • the notation D n and for example, refers to the base
  • the PWM controller 95 controls stator electrical quantities, either the stator currents or the stator voltages, depending on the rotor speed.
  • a torque monitor 97 monitors the stator currents, generates a signal indicative of actual torque, T fb , and feeds it back to the torque command device 46. Controlling the generator currents and voltages in terms of field coordinates is a useful feature.
  • the electric torque of an AC induction machine can be expressed in terms of the stator and rotor currents, but such an expression is difficult to use in a torque control system since the rotor currents of a squirrel-cage induction generator cannot be directly measured.
  • the rotor flux of an induction machine can be represented by a radial vector ⁇ r vector with magnitude ⁇ r and angle ⁇ s .
  • the field orientation principle defines the stator current in terms of rotating d, q coordinate system, where a direct (d) axis is aligned with the instantaneous rotor flux vector ⁇ r at angle ⁇ s and a quadrature (q) axis is perpendicular to the rotor flux vector. This is illustrated in Fig.4.
  • the stator current i s can be broken into a component, i sd , that is parallel to the rotor flux ⁇ r vector and a component, i sq , that is perpendicular to the rotor flux vector.
  • the currents i sd and i sq at angle ⁇ s are the field coordinate representation of the stator current vector.
  • Fig. 4 also illustrates that cor is defined as the rotor angular speed and ⁇ s is defined as the angular speed of the rotor flux vector.
  • the machine slip speed, ⁇ s ⁇ which is the speed of the stator current vector with respect to the rotor, is the difference between ⁇ s and ⁇ r .
  • the d, q coordinate system isolates or decouples a current that creates the rotor flux field, i sd , on the direct axis, from a current that creates torque, i sq , on the quadrature axis. Defining the generator currents in field orientation
  • the stator currents in a balanced, 3-phase coordinate system as represented by the currents on the three stator power taps 72-74 (Fig. 2), can be designated by the variables i s1 , i s2 , and i s3.
  • the 2-phase stator currents, i s ⁇ and i s ⁇ can be converted into the field coordinate currents, i sd and i sq , as a function of the rotor flux angle, ⁇ s , by the following
  • the structure of the generator control unit 76 is shown in block diagram form in Fig. 5.
  • the generator control unit is preferably implemented in a digital signal processor ("DSP"), a Texas Instruments model TMS320C25. Computer code for implementing the invention in a DSP is disclosed in the microfiche appendix.
  • the generator control unit 76 includes the field orientation converter 94, the torque monitor 97, and the PWM controller 95.
  • the PWM controller 95 includes a current controller 96, a voltage controller 98, and a selector circuit 100.
  • the field orientation converter 94 generates control parameters based on the rotor speed and torque reference signals
  • the current controller 96 or the voltage controller 98 generates PWM commutation signals for the active switching devices 60
  • the selector circuit 100 chooses which of the PWM
  • the torque monitor 97 senses the actual stator currents, i s1 , i s2 , i s3 , converts them to field coordinate values using equations (1) and (2), and calculates a torque signal, Tfb, using equation (8) (see below) for feedback to the torque command device 46.
  • the torque monitor 97 thus infers generator torque from the measured currents.
  • the computations performed within the DSP of the generator control unit 76 are digital, which requires A/D conversion of the external signals.
  • the field orientation converter 94 converts the torque control and rotor flux signals into field coordinates. Using a desired direct axis current, the field orientation converter 94 computes the desired magnitude of the rotor flux, £ The desired flux-producing direct axis current, , is a function of the particular generator used, and
  • the notation * designates a desired value generated by the control system as opposed to an actual value.
  • the desired rotor flux, ⁇ £ is defined by the following equation:
  • ⁇ r time derivative of desired rotor flux
  • R r rotor resistance
  • the torque reference can be converted into quadrature axis current.
  • T generator torque
  • i sq quadrature axis current.
  • Tref is the torque reference signal supplied to the generator control unit by the torque command device 46.
  • the computed values for desired field oriented currents, and rotor flux, £ rotor flux speed, and rotor flux angle, ⁇ £ are avallable to the current and voltage controllers 96 and 98 (Fig. 5) for determination of the PWM commutation signals. Transformation of the desired stator currents from field coordinates into stationary 2-phase ⁇ , ⁇ coordinates or balanced 3-phase coordinates, if required by the PWM controller, can be accomplished either in the field orientation converter or in the PWM controller. Here, it is assumed that the transformations occur outside of the field orientation converter 94.
  • either the current controller 96 of the voltage controller 98 determines switch states for the active switching devices (Fig. 5).
  • the current controller 96 generates PWM commutation signals by choosing a switch state that causes stator currents to approximate the desired currents defined by the field
  • the voltage controller 98 generates PWM commutation signals by converting the desired field oriented currents into desired field oriented voltages,
  • stator coordinates transforming them into stator coordinates, and then selecting the appropriate switch state to obtain the desired stator voltages.
  • a delta modulator current controller One simple method of current control is illustrated in Fig. 7, a delta modulator current controller.
  • modulator current controller converts the desired field oriented currents into stationary 2-phase stator coordinates, and then to 3-phase stator currents,
  • the desired stator currents are then transformed into 3-phase coordinates using equation (4).
  • the delta modulator current controller After converting the desired stator currents from field coordinates into 3-phase coordinates, the delta modulator current controller then periodically compares each desired stator current with the corresponding actual stator current i s1 , i s2 , i s3 , using compare and hold devices 102. If the desired stator current for a phase is greater than the actual stator current, then the upper switching device is switched on and the lower switching device switched off, otherwise, the upper device is switched on and the lower device is switched off.
  • the compare and hold devices 102 set the PWM commutation signals, D 1 , D 2 , D 3 , to accomplish the desired switching. The switch state so selected remains in effect until the next sample period occurs, at which time the comparisons are performed with updated actual and desired values.
  • Figs. 8-10 Another method of current control, one that minimizes a distortion index, is illustrated in Figs. 8-10.
  • This method generates PWM signals by periodically minimizing a distortion index related directly to total harmonic distortion (THD).
  • THD total harmonic distortion
  • this method is preferable due to lower THD at comparable frequencies, while requiring fewer switching events and, consequently, less power loss due to switching.
  • the distortion index that is minimized may be defined as the sum of the squares of the current errors:
  • J 1 - i s1 ) 2 + ⁇ 2 - i s2 ) 2 + ⁇ - i s3 ) 2 (15)
  • i si, i s2, i s3 are the desired 3-phase stator currents
  • i s1 , i s2 , i s3 are the actual 3-phase stator currents.
  • the distortion index can be defined as the sum of the absolute values of the current errors.
  • the projected stator currents i s1 (k+1), i s2 (k+1), and i s3 (k+1) are found by modeling the generator and rectifier according to the following equation derived from a simplified model:
  • V voltage vector resulting from a
  • the projected stator currents can thus be found for each switch state by evaluating equation (18) using the voltage vector that would result from that switch state.
  • the distortion index, J can be computed by equations (15) or (16) for each possible switch state.
  • the switch state that yields the minimum value of J is output to the selector 100.
  • converter 94 (Fig.5), are converted into desired ⁇ , ⁇ stator currents at time (k), ⁇ (k) and ⁇ (k), using equation (3).
  • the generator emf, in ⁇ , ⁇ coordinates, is estimated by:
  • These voltage vectors shown in Fig. 10, have a magnitude of either zero or the DC link voltage, vdc, and are aligned with the s 1 , s 2 , and s 3 axes.
  • the voltage vectors are defined according to the following table:
  • the ⁇ , ⁇ coordinate space can be divided into seven regions: an inner circle 104 of radius v dc /2, plus six 60° sectors 106-111 of outer radius v dc surrounding the inner circle, each sector having a switch state centered at the outer radius thereof.
  • Determining the closest voltage vector is a matter of finding in to which region the desired voltage vector falls. To do so, the magnitude of the desired voltage vector is first compared to v dc /2 to determine whether the desired voltage vector falls within the inner circle 104. If the magnitude of the desired voltage vector is less than one-half of v dc , then state 0 or state 7 is the desired switch state. Choosing between state 0 and state 7 is accomplished by selecting the state that requires the fewest number of switches to change state from the previous switch setting.
  • operation with the current controller 96 generating the PWM commutation signals occurs at relatively low speeds, where the DC voltage link offers substantial ceiling voltage.
  • the current controller 96 keeps the stator currents in close agreement with the desired stator current values. This operation effectively results in current sources for the stator windings, which allows the current controller to ignore the stator voltages.
  • the voltage controller 98 takes the stator voltages into
  • the selector 100 senses the rotor speed, cor, and selects the voltage controller 98 instead of the current controller 96 when the rotor speed exceeds a predetermined value.
  • This value can be determined empirically by observing the distortion of the current waveform during operation of the current controller at various speeds.
  • the switching point is about 1780 rpm.
  • some hysteresis is bullt into the switching point of the selector 100 so that small oscillations of rotor speed about the switching point do not cause repeated switching between current control and voltage control.
  • the DC link voltage and the generator emf can be monitored to determine at which point to switch between current control and voltage control.
  • the voltage controller 98 periodically generates a set of PWM commutation signals for switching on and off the active switches of the rectifier.
  • the voltage controller monitors the desired and actual torque and flux, as defined by the field oriented currents, d and
  • stator voltages in field coordinates, are defined by the following equations:
  • ⁇ total or global leakage factor
  • R s stator resistance
  • the operation of the voltage controller 98 is shown in Fig. 11.
  • the actual 3-phase stator currents, i s1 , i s2 , i s3 are converted into field oriented coordinates by equations (1) and (2).
  • the desired voltage on the quadrature axis, is
  • PI controller 114 the resultant through a proportional-integral (PI) controller 114 to generate which is a measure of a quadrature axis
  • the PI controller supplies a
  • the desired voltage on the direct axis is generated by first subtracting the rotor flux divided by the mutual inductance, /L o , from desired direct axis current,
  • the resultant is then input to another PI controller 116,
  • PI controller 116 is simflar to the PI controller 114 for the quadrature component. The value of is then compensated by adding a decoupling terms on the right side of equation (28), which results in as follows: l Once the desired field coordinate voltages, and have been generated, they are transformed into 3-phase
  • triangular carrier wave has a frequency of about 8 kHz, while the comparisons between the reference voltages and the carrier wave are performed continuously or at a rate much higher than 8kHz.
  • Fig. 12 illustrates how a computer program is structured for execution in the digital signal processor of the generator control unit.
  • the program consists primarily of a main loop and an interrupt service routine.
  • the main loop initializes the necessary variables, and then loops until it is interrupted, which occurs periodically, at about 8 kHz in the preferred embodiment.
  • the interrupt service routine performs the calculations necessary for generating the PWM
  • the interrupt service routine first reads the stator currents, and then executes the code of either the current controller or the voltage controller to generate and output the appropriate switch states. The interrupt routine then reads a value for the torque reference, T ref , and updates the
  • the routine then reads the speed sensor and computes a new value for the rotor speed ⁇ r .
  • the routine updates the value for desired rotor flux and the desired instantaneous rotor flux angle
  • the interrupt routine then returns to the main loop, which waits until the next periodic interrupt, at which time the updated values will be used to compute the switch states. All constants used in the calculations are computed in advance, and the expressions are arranged to avoid division which executes relatively slowly in a DSP.
  • the steps performed in the computer program can be executed in different order than is shown in Fig. 12, but it is important to calculate and output the switch states as soon as possible after reading the actual stator currents.
  • the inverter control unit 88 is preferably implemented with a digital signal processor, a Texas Instruments model TMS320C25. Computer code for implementing the inverter control function in a DSP is disclosed in the microfiche appendix.
  • the inverter control unit 88 controls the inverter switch matrix to supply power to the utility grid with low THD.
  • the inverter 28 can be controlled by the control unit 88 to supply or absorb reactive power as needed by adjusting the current flowing through each of the active switching devices 82.
  • Low harmonic distortion can be achieved in the same way as in the current controller of the generator control unit, by periodically minimizing a distortion index.
  • the inverter control unit 88 can also control the voltage of the DC voltage link 24, to maintain it at a desired value.
  • Different embodiments of the inverter control unit 88 are disclosed herein. For illustrative purposes, two embodiments are designated inverter control units 88a and 88b.
  • the inverter control unit 88a disclosed in Fig. 13 is suitable for supplying an selectable power factor output, and the inverter control unit 88b is better suited for operation in a static VAR mode than the inverter control unit 88a.
  • a multiplier controller can be implemented either for charging and
  • the inverter control unit 88a senses the output voltage as a sinusoidal reference waveform v 01 , v 02 , v 03 for each phase.
  • the reference waveforms are rotated by a certain phase angle ⁇ , as illustrated in a box 200, to generate a rotated reference waveform, or a "template" waveform for each phase.
  • the template waveforms are multiplied by a factor, Iref, to
  • the rotational transformation of the reference waveform can be accomplished in either 3-phase or 2-phase coordinates.
  • the reference waveform can be transformed into 2-phase coordinates using equation (1) and rotated
  • the current regulator 204 of the inverter control unit 88 can be implemented in the several ways described above for the current controller 96 of the generator control unit, including the delta modulator.
  • the current regulator 204 generates switch states that minimize the distortion index, J, in a manner similar to that described above with respect to Figs. 9 and 10. Referring to Fig. 14, this embodiment of the inverter current controller generates desired output voltages, and V , according to the
  • L o is the output impedance
  • i o ⁇ and i o ⁇ are the measured output currents in ⁇ . ⁇ coordinates
  • v o ⁇ and v o ⁇ are the measured output voltages in ⁇ , ⁇ coordinates
  • Figs. 19 and 20 disclose alternative embodiments of the multiplier selector 203 that calculates the multiplication factor, I ref .
  • a proportional/integral (P/I) multiplier selector 203a is disclosed that maintains a constant voltage on the DC voltage link 24.
  • the P/I multiplier selector 203a is particularly suitable when the energy storage device 25 has relatively small storage capacity, such as the storage of a capacitor rather than that of a battery.
  • the measured DC link voltage, v dc is subtracted from a desired value of the DC link voltage, to generate
  • I ref k p - v dc ) + k i ⁇ ( - v dc ) dt (39)
  • k p and k i are coefficients selected to provide adequate stability.
  • the constants k p and k i can be determined using conventional control techniques, such as the root-locus method, the frequency domain (Bode plot) method, or by empirically testing the device. The values are highly dependent upon the particular embodiment. In discrete time, equation (39) can be evaluated as follows:
  • I ref(k) I ref (k-1) + (k p + At k i ) (( - V dc(k) ) - k p ((v
  • the energy storage device 25 has a larger storage capacity than a capacitor and can act as a voltage source, voltage regulation is not required. In other words, the voltage regulating function is automatically performed by the voltage source, and in that instance the P/I multiplier selector 203a is unnecessary.
  • the multiplier selector 203 may comprise another arrangement, such as a multiplier I ref selected directly by an operator to output a desired real power amount. For example, the operator could monitor the real power, and adjust the multiplier selector 203 until Iref
  • the multiplier selector 203 could include a circuit that automatically selects I ref to provide an amount of real power flow based on an operator's input of the desired real power flow and feedback indicative of the amount of real power.
  • This simple arrangement for selection of a multiplier Iref is suitable for an energy source such as a fuel cell that maintains a constant voltage.
  • the following multiplier selector 203b to be described with reference to Fig. 20, is more appropriate.
  • Fig.20 shows a charge/discharge multiplier selector 203b suitable for battery control, i.e., battery charging and discharging.
  • the battery charge e.g. 80%
  • a current sensor 210 is positioned between the active rectifier 20 and the energy storage device 25 to measure the generator-side current supplied from the generator side to the energy storage device 25.
  • the sensed current i dc is supplied as an input to the charge/discharge multiplier selector 203b.
  • Another input into the charge/discharge multiplier selector 203b is the voltage v dc across the DC voltage link 24.
  • the DC link voltage, vdo is multiplied by the sensed current idc, as illustrated in a box 212 within the charge/discharge multiplier selector 203b.
  • This product from the box 212 is then applied to a gain box 214 which multiplies the product by a factor of the following:
  • v ac is the rms voltage at the utility grid, measured at its connection with the line side inverter 28.
  • the output of the box 214, a generated power term is applied to an adder 215 which adds it to a battery charge term.
  • the added term, the battery charge term is dependent upon the particular battery and indicates the extent to which the battery needs to be charged or discharged. For example, in a lead-acid battery the amount of charge or discharge can be inferred from a difference between the voltage sensed and the desired voltage, and thus the battery charge term for a lead-acid battery is a function of the difference between the sensed and the desired voltages, i.e., the voltage error.
  • the sum of the above two terms, added in the adder 215, is applied to a low pass filter 216.
  • the output of the low pass filter 216 is applied directly to the multiplier 202 as Iref-
  • the low pass filter 216 has a cut-off frequency of tens of Hertz or less, possibly less than 1Hz.
  • the low pass filter 216 outputs the multiplier value, I ref , that is applied to the multiplier 202.
  • charge/discharge multiplier selector 203b is the generator-side current i dc .
  • Other inputs, such as vdc and the battery charge term, will fluctuate at a much lower rate.
  • the effect of a low pass filter 216 on the varying generator-side current i dc is to smooth out typical fluctuations that occur with wind variations in normal operations.
  • Fig. 21 is a graphical illustration that compares the generator-side power illustrated by a curve 218 with the average line-side output power illustrated by a curve 220, in an embodiment implementing the battery charge multipHer selector 203b shown in Fig.20.
  • the generator-side power curve 218 fluctuates much more rapidly than the average line-side output power curve 220 which is smoothed by the effect of the low pass filter and multipHer selector 203b.
  • the real power is proportional to voltage * current, and therefore the current sensor 210 provides the value i dc that is proportional to the generator-side power.
  • the low-pass filter 216 uses the generator-side current i dc to provide a multipHer value I ref that, when appHed by the multipHer 202, substantially smooths the output power. Battery charging occurs when the generator-side power is greater than the line-side power, and conversely, discharging occurs when the generator-side power is less than the line-side power.
  • a computer program directs the operation of the digital signal processor of the inverter control unit 88a or 88b (to be described with reference to Figs.22-24) to perform the calculations described above.
  • the computer program is structured like that of the generator control unit in that a main loop executes until periodically interrupted, and then an interrupt service routine updates the sensed inputs, PWM switch state, and calculated variables.
  • the interrupt service routine running on the inverter control unit DSP first reads the output currents, output voltages and DC link voltage. Then it calculates the optimal switch state, which it outputs to the inverter switches.
  • interrupt routine performs calculations necessary for the next calculation of switch state by rotating the voltage reference to define the template waveform, computing the multiplication factor Iref, and multiplying the template waveform by I ref to compute the desired currents for the next interrupt. Then control passes to the main loop, where it waits until
  • interruptions occur at a rate of about 8 kHz.
  • the power controller 54 can control the magnitude of reactive power to supply VARs (volt- ampere-reactive) to the utllity either when operating, or in a static VAR mode while not operating. If the power factor angle ⁇ is controlled, the power controller 54 outputs to the inverter control unit 88 a constant value for ⁇ . In an alternate embodiment to be described with reference to Figs. 22-24, the power controller 54 can control either the power factor angle ⁇ or directly control real power and reactive power levels. The type of power factor control can be specified by the operation mode signal that is input into the power controller.
  • the reactive power can also be controlled to some extent by monitoring the reactive power feedback signal Qfb, comparing it to a desired reactive power level defined by the reactive power input signal, and adjusting the power factor angle ⁇ , to obtain the desired reactive power.
  • the power factor angle ⁇ gets increasingly closer to 90°, control becomes difficult. At angles very close to 90°, control is lost.
  • Figs.22, 23, and 24 illustrate the structure and method and operation of an inverter control unit 88b.
  • the inputs to the inverter control unit 88b are provided, as illustrated in Fig.2, through the power controller 54.
  • the inputs to the inverter control unit 88 include the voltage sensed across the voltage link 24, vdc, a reactive power signal, a power factor, which may be termed K (if appropriate) and an optional operation mode to select any of a number of operational modes. Particularly the
  • the operational mode for the inverter control unit 88b may be able to select between a mode in which a number of VARs can be selected independently of the real power, and an alternate mode in which the power factor angle is selected.
  • the inputs to the inverter control unit 88b include the 3-phase reference signals signified by v 01 , which produces the phase A reference waveform, v 02 which provides a phase B reference waveform, and v 03 which provides a phase C reference waveform.
  • the voltage, used as a reference for each of the phase is provided by transformation to a low voltage level by voltage transformers 92 (Fig. 2).
  • a control waveform for each phase is generated by the inverter control unit 88b in accordance with the algorithm to be described with reference to Figs. 22, 23, and 24 below.
  • the output of the inverter control unit 88a outputs control waveforms for three phases: a phase A control waveform, a phase B control waveform, and a phase C control waveform.
  • phase control waveforms controls a specific switch pair coupled to a particular output.
  • the phase A control waveform may control the switch pairs 82 on the output line 84
  • the phase B control waveform may control the switch pairs 82 on the output line 85
  • the phase C control waveform may control the switch 82 on the output line 86.
  • Fig. 22 is a flowchart illustrating operation of the inverter control unit 88b.
  • control waveform is produced digitally at a rate between 8 kHz and 16 kHz, which means that the sample period for the control waveform is between 125 or 62.5 microseconds, depending upon the selected frequency.
  • the reference waveform is split two ways. In one, the reference waveform is applied to form an imaginary waveform as illustrated in a box 302. As will be described in more detail , the imaginary waveform may be obtained by rotating the
  • the imaginary waveform is then applied, as illustrated in a box 304, to a multiplier M 1 which is calculated as will be described below with reference to Fig. 23.
  • the multiplied imaginary waveform is then added in a box 306 to the multiplied real waveform described below.
  • the reference waveform is applied to form the real waveform as in a box 308.
  • the real waveform may be substantially similar to the reference waveform.
  • the real waveform is applied to a box 310, in which it is multiplied by a real multiplier M 2 .
  • the multiplied real waveform is then added to the multiplied imaginary waveform to obtain a control waveform.
  • Applying the control waveform, as illustrated in a box 312, the inverter 28 is controlled with the control waveform in order to provide a current in accordance with the control waveform.
  • Fig. 23 is a more detailed illustration of the inverter control unit 88b. Beginning from the left in Fig. 25, the 3-phase reference waveform is applied to a 3- to 2-phase converter 220.
  • the 3- to 2-phase converter 220 converts the three phases of the reference waveform to two phases in accordance with the following matrix equation: A 2 1 cos(2 ⁇ /3) cos(4 ⁇ /3 A
  • a 2 , B 2 are the 2-phase reference quantities and A, B, and C are the 3-phase reference quantities.
  • the outputs of the 3- to 2-phase converter 320 i.e. the two 2-phase reference waveforms, are provided to two separate processing lines, one of which produces and processes an imaginary waveform and one of which produces and processes a real waveform.
  • the 2-phase reference waveforms are provided to two separate processing lines, one of which produces and processes an imaginary waveform and one of which produces and processes a real waveform.
  • each phase is multiplied by e j90° .
  • the 2-phase reference waveform is applied to a box 324 in which each phase is multiplied by e j0° (or 1).
  • multiplication by 1 may be unnecessary, and the reference waveform may be used directly to form the real waveform at the output of the box 328 without the need for 3- to 2-phase conversion and 2- to 3-phase conversion.
  • Each phase of the 3-phase imaginary waveform is then multiplied by a VAR multiplier M 1 selected as illustrated in a box 329.
  • the VAR multiplier M 1 has the same value for each phase.
  • the VAR multiplier M 1 is selected to be either the VAR control signal or the product KI ref to be described below.
  • the VAR control signal can be manually selected by an operator who is observing the number of VARs output and who adjusts the multiplier M 1 accordingly, to produce the desired number of VARs.
  • the VAR control signal can also be selected automatically by a hierarchical control loop such as a voltage regulator that can be operator
  • the VAR multiplier M 1 may be selected to provide a constant power factor angle.
  • the reactive power output may be monitored.
  • compensators are in operation, for example at a site having numerous wind turbines whose electrical power is collected at central collection centers, measurement is readily performed at the collection centers. Such a site is discussed below with reference to Fig. 25.
  • the VARs can be measured by sensors positioned elsewhere on the line
  • the 3-phase real waveform output from the 2- to 3-phase converter 328 is multiplied by a real multiplier M 2 .
  • the multiplier M 2 is preferably the same multiplier for each of the 3-phase lines.
  • the multiplier M 2 is calculated in a manner consistent with calculation of Iref, described with above reference to Figs. 19 and 20.
  • a value K is selected to specify a predetermined power factor angle. Then, the value K is multiplied by Iref, as illustrated in a box 340. This product is applied to the VAR multiplier box 329 which then selects this product to be the VAR multiplier M 1 .
  • the imaginary multipHer M 1 is proportional to the real multipHer M 2 .
  • the results of the multiplication of the real waveforms and the imaginary waveforms are added to obtain the control waveforms for each phase.
  • the multiplied real waveform for phase A is added to the multipli ed imaginary waveform for phase A in order to obtain the control waveform for phase A.
  • the multipHed real waveform is added to the multipHed imaginary waveform to yield a control waveform.
  • the control waveforms for each phase are then appHed to a current regulator 350 shown in Fig. 24, which controls the inverter 28 through the drive circuit 90 (Fig. 2).
  • the static VAR compensator described above with reference to Figs.22, 23, and 24 can provide a fixed number of VAR s to compensate for reactive loads. For example, if the power company were experiencing a lagging current, then the static VAR compensator in each wind turbine could be adjusted to provide the VARs for a leading current. The effect of combining the leading current with the lagging current is to cause the current and voltage to be in phase.
  • a delta modulator current regulator 350 which applies the 3-phase line currents specified by the
  • the delta modulator current regulator 350 periodically compares each desired line current with the corresponding actual line current i A , i B , i C , sensed by sensors 352 positioned to sense the line currents from each of the switch pair 82 (Fig. 2). The current comparison is
  • compare device 360 for each of the lines.
  • the comparisons are performed at a rate between 8 and 16 kHz, which is equivalent to a sample period between 125 or 62.5 microseconds. For each sample period, if the desired line current for a phase is greater than the actual line current, then the upper switching device is switched on and the lower switching device switched off, otherwise, the upper device is switched off and the lower device is switched on.
  • the compare devices 360 select PWM (Pulse Width
  • the drive circuits 90 preferably include conventional transistors and additional circuitry necessary to drive the gates of the respective IGBT switches in response to the on or off signal specified by the PWM commutation signals. For each sample period, a switch state is specified by the PWM commutation signals. The switch state so selected remains in effect until the next sample period, at which time the
  • Fig. 25 illustrates a collection of wind turbines 10 that provide power to a central power collection center 400.
  • Fig. 5 is illustrative of a
  • Generators 401 provide another source of electrical energy for the grid, and may include coal-fired generating plants, oil generators, or nuclear reactors, for example.
  • a reactive power signal such as Q fb indicative of the amount of reactive power in VARs or as a power factor angle.
  • Q fb indicative of the amount of reactive power in VARs or as a power factor angle.
  • a real power signal indicative of the number of watts supplied to the utility grid.
  • the real power signal and the reactive power signal are useful in providing feedback to the power controller 54 that supplies the inputs to the inverter control unit 88 (Fig.2).
  • one or. more of the wind turbines 10 may be producing differing amounts of power, for example one wind turbine may be producing twice as much power at any instant of time as another wind turbine. The differences are due to a variety of factors, such as location and windspeed variations due to the location.
  • the DC voltage link 24 is connected to a substantial energy storage device 25
  • the power fluctuations are smooth and a
  • the wind turbine 10a is connected to a DC energy storage 402
  • the wind turbine 10b is also connected to the DC energy storage 402.
  • the centralized common DC energy storage 402 may be
  • the common DC energy storage 402 would function like the energy storage device 25, and supply a source of constant voltage, or (if the common DC energy device 402 is capable of energy storage) the device can function to collect and store the generated power until it can be delivered to the power collection center 400 through the inverter of each of the wind turbines 10a, 10b.
  • the invention provides a novel and advantageous variable speed wind turbine.
  • the foregoing discussion discloses and describes merely exemplary methods and embodiments of the present invention.
  • the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.
  • some aspects of the current controller can be performed in various ways equivalent to those disclosed herein, including using hysteresis control or forced osculation with triangular intersection.
  • the generator need not be a three-phase squirrel-cage induction generator, but may be any multiphase generator, including a wound field or permanent magnet synchronous generators or a switched reluctance generator.
  • the generator control could be performed open-loop, instead of the closed loop control disclosed herein.
  • the power converter could have a DC current link, or could be a cyclo-converter instead of a DC voltage link.
  • the torque monitor could directly measure torque with a transducer, instead of inferring torque from the measured stator currents. Accordingly, the disclosure of the present invention is intended to be illustrative, but not Hmiting, of the scope of the invention, which is set forth in the following claims.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
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  • Sustainable Energy (AREA)
  • Chemical & Material Sciences (AREA)
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  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
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Abstract

L'invention concerne un convertisseur de puissance d'une turbine éolienne qui égalise la puissance de sortie d'une turbine éolienne (10) à vitesse variable afin de réduire les fluctuations de puissance sur la ligne de sortie. Le convertisseur de puissance consiste en un convertisseur (20) du type courant alternatif/courant continu côté générateur connecté à un générateur (16) de vitesse variable qui convertit l'énergie éolienne en énergie électrique, un onduleur (28) du type courant continu/courant alternatif côté ligne connecté à un réseau de distribution, et une liaison (24) de tension à courant continu connectée à un dispositif (25) de stockage d'énergie électrique tel qu'une batterie ou une cellule à combustible, ou une cellule photovoltaïque ou solaire. Un contrôleur (50) de l'onduleur et un régulateur (54) de puissance régulent le courant passant par les commutateurs actifs (82) au niveau de l'onduleur côté ligne pour fournir une combinaison sélectionnée de puissances réelle et réactive au réseau de distribution. Une forme d'onde de tension est utilisée comme référence pour former une forme d'onde de régulation du courant dans une unité (88) de commande de l'onduleur pour chaque phase de sortie. La forme d'onde de régulation du courant est appliquée à un régulateur de courant puis au circuit de commande (90) qui régule les courants pour chaque phase de l'onduleur côté ligne.
PCT/US1992/010225 1991-11-27 1992-11-25 Turbine eolienne a vitesse variable avec fluctuation reduite de la puissance et mode de fonctionnement a var statique WO1993011604A1 (fr)

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US07/799,416 US5225712A (en) 1991-02-01 1991-11-27 Variable speed wind turbine with reduced power fluctuation and a static VAR mode of operation
US799,416 1991-11-27

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WO2002086315A1 (fr) * 2001-04-24 2002-10-31 Aloys Wobben Procede d'exploitation d'une installation d'energie eolienne
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US6809431B1 (en) 1998-09-26 2004-10-26 Dewind Ag Control logic for a wind energy system
DE19844258A1 (de) * 1998-09-26 2000-03-30 Dewind Technik Gmbh Windenergieanlage
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US6566764B2 (en) 2000-05-23 2003-05-20 Vestas Wind Systems A/S, R&D Variable speed wind turbine having a matrix converter
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