Blade Pitch System for a Wind Turbine Generator and Method of Operating the Same

A wind turbine blade pitch control system includes a blade pitch drive mechanism coupled to a wind turbine blade and an electric power source coupled to the blade pitch drive mechanism. The system also includes switch devices coupled to portions of the electric power source, and the switch devices are coupled to the blade pitch drive mechanism. The system further includes a controller coupled to the blade pitch drive mechanism and the switch devices. The controller is configured to store a plurality of operational measurements of the blade pitch drive mechanism and the switch devices. The controller is programmed to change an angular rate of change of a pitch angle of the wind turbine blade by opening and closing the switch devices in a predetermined sequence.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “blade” is intended to be representative of any device that provides reactive force when in motion relative to a surrounding fluid. As used herein, the term “wind turbine” is intended to be representative of any device that generates rotational energy from wind energy, and more specifically, converts kinetic energy of wind into mechanical energy. As used herein, the term “wind turbine generator” is intended to be representative of any wind turbine that includes an electric power generation device that generates electrical power from rotational energy generated from wind energy, and more specifically, converts mechanical energy converted from kinetic energy of wind to electrical power.

Technical effects of the methods, apparatus, and systems described herein include at least one of: (a) modulating direct current (DC) power to a plurality of blade pitch drive motors to control the rate of change of blade pitch on each blade to decelerate a wind turbine rotor in a predetermined manner; and (b) modulating the DC power transmitted to the blade pitch drive motors by operating a plurality of switches to place portions of a battery array into service and removing portions of the battery array from service.

The methods, apparatus, and systems described herein facilitate operation of wind turbine generators by actively controlling blade pitch during unplanned shutdowns of the wind turbine generators. Such methods, apparatus, and systems include implementation of a blade pitch control system that modulates the rate of change of the pitch angles of each of a plurality of wind turbine blades as a function of time. Specifically, modulating the rate of change of the pitch angles for each blade facilitates decelerating the wind turbine rotor in a predetermined manner. Further, specifically, decelerating the wind turbine rotor in a predetermined manner facilitates reducing a potential for accelerated component wear.

FIG. 1is a schematic view of an exemplary wind turbine generator100. In the exemplary embodiment, wind turbine generator100is a horizontal axis wind turbine. Alternatively, wind turbine100may be a vertical axis wind turbine. Wind turbine100has a tower102extending from a supporting surface104, a nacelle106coupled to tower102, and a rotor108coupled to nacelle106. Rotor108has a rotatable hub110and a plurality of rotor blades112coupled to hub110. In the exemplary embodiment, rotor108has three rotor blades112. Alternatively, rotor108has any number of rotor blades112that enables wind turbine generator100to function as described herein. In the exemplary embodiment, tower102is fabricated from tubular steel and has a cavity (not shown inFIG. 1) extending between supporting surface104and nacelle106. Alternatively, tower102is any tower that enables wind turbine generator100to function as described herein including, but not limited to, a lattice tower. The height of tower102is any value that enables wind turbine generator100to function as described herein.

Blades112are positioned about rotor hub110to facilitate rotating rotor108, thereby transferring kinetic energy from wind124into usable mechanical energy, and subsequently, electrical energy. Rotor108and nacelle106are rotated about tower102on a yaw axis116to control the perspective of blades112with respect to the direction of wind124. Blades112are mated to hub110by coupling a blade root portion120to hub110at a plurality of load transfer regions122. Load transfer regions122have a hub load transfer region and a blade load transfer region (both not shown inFIG. 1). Loads induced in blades112are transferred to hub110by load transfer regions122. Each of blades112also includes a blade tip portion125.

In the exemplary embodiment, blades112have a length between 50 meters (m) (164 feet (ft)) and 100 m (328 ft), however these parameters form no limitations to the instant disclosure. Alternatively, blades112may have any length that enables wind turbine generator to function as described herein. As wind124strikes each of blades112, blade lift forces (not shown) are induced on each of blades112and rotation of rotor108about rotation axis114is induced as blade tip portions125are accelerated. A pitch angle (not shown) of blades112, i.e., an angle that determines each of blades' 112 perspective with respect to the direction of wind124, may be changed by a pitch adjustment mechanism (not shown inFIG. 1). Specifically, increasing a pitch angle of blade112decreases a percentage of area126exposed to wind124and, conversely, decreasing a pitch angle of blade112increases a percentage of area126exposed to wind124.

For example, a blade pitch angle of approximately 0 degrees (sometimes referred to as a “power position”) exposes a significant percentage of a blade surface area126to wind124, thereby resulting in inducement of a first value of lift forces on blade112. Similarly, a blade pitch angle of approximately 90 degrees (sometimes referred to as a “feathered position”) exposes a significantly lower percentage of blade surface area126to wind124, thereby resulting in inducement of a second value of lift forces on blade112. The first value of lift forces induced on blades112is greater than the second value of lift forces induced on blades112such that values of lift forces are directly proportional to blade surface area126exposed to wind124. Therefore, values of lift forces induced on blades112are indirectly proportional to values of blade pitch angle.

Also, for example, as blade lift forces increase, a linear speed of blade tip portion125increases. Conversely, as blade lift forces decrease, linear speed of blade tip portion125decreases. Therefore, values of linear speed of blade tip portion125are directly proportional to values of lift forces induced on blades112and it follows that linear speed of blade tip portion125is indirectly proportional to blade pitch angle.

Moreover, as speed of blade tip portion125increases, an amplitude (not shown) of acoustic emissions (not shown inFIG. 1) from blade112increases. Conversely, as speed of blade tip portion125decreases, an amplitude of acoustic emissions from blades112decreases. Therefore, the amplitude of acoustic emissions from blades112is directly proportional to a linear speed of blade tip portions125and, it follows that the amplitude of acoustic emissions from blades112is indirectly proportional to the blade pitch angle.

The pitch angles of blades112are adjusted about a pitch axis118for each of blades112. In the exemplary embodiment, the pitch angles of blades112are controlled individually. Alternatively, the pitch of blades112may be controlled as a group. In the exemplary embodiment, the pitch of blades112is modulated in order to induce a braking action to expediently reduce the speed of blades112, and thereby reduce the rotational velocity of rotor108. Preferably, wind turbine100may be controlled to reduce the rotational velocity of rotor108by a local controller (not shown), or remotely by a remote controller (not shown).

FIG. 2is a cross-sectional schematic view of nacelle106of exemplary wind turbine100. Various components of wind turbine100are housed in nacelle106atop tower102of wind turbine100. Nacelle106includes one pitch drive mechanism130that is coupled to one blade112(shown inFIG. 1), wherein mechanism130modulates the pitch of associated blade112along pitch axis118. Only one of three pitch drive mechanisms130is shown inFIG. 2. In the exemplary embodiment, each pitch drive mechanism130includes at least one pitch drive motor131, wherein pitch drive motor131is any electric motor driven by electrical power that enables mechanism130to function as described herein. Alternatively, pitch drive mechanisms130include any suitable structure, configuration, arrangement, and/or components such as, but not limited to, hydraulic cylinders, springs, and servomechanisms. Moreover, pitch drive mechanisms130may be driven by any suitable means such as, but not limited to, hydraulic fluid, and/or mechanical power, such as, but not limited to, induced spring forces and/or electromagnetic forces.

Nacelle106also includes a rotor108that is rotatably coupled to an electric generator132positioned within nacelle106by rotor shaft134(sometimes referred to as low speed shaft134), a gearbox136, a high speed shaft138, and a coupling140. Rotation of shaft134rotatably drives gearbox136that subsequently rotatably drives shaft138. Shaft138rotatably drives generator132by coupling140, wherein shaft138rotation facilitates production of electrical power by generator132. Gearbox136and generator132are supported by supports142and144, respectively. In the exemplary embodiment, gearbox136utilizes a dual path geometry to drive high speed shaft138. Alternatively, main rotor shaft134is coupled directly to generator132by coupling140.

Nacelle106further includes a yaw adjustment mechanism146that may be used to rotate nacelle106and rotor108on axis116(shown inFIG. 1) to control the perspective of blades112with respect to the direction of the wind. Nacelle106also includes at least one meteorological mast148, wherein mast148includes a wind vane and anemometer (neither shown inFIG. 2). Mast148provides information to a turbine control system (not shown) that may include wind direction and/or wind speed. A portion of the turbine control system resides within a control panel150. Nacelle106further includes forward and aft support bearings152and154, respectively, wherein bearings152and154facilitate radial support and alignment of shaft134.

Wind turbine generator100includes a pitch control system200, wherein at least a portion of pitch control system200is positioned in nacelle106, or less preferably, outside nacelle106. Specifically, at least a portion of pitch control system200described herein includes at least one processor202and a memory device203coupled to processor202, and at least one input/output (I/O) conduit204, wherein conduit204includes at least one I/O channel (not shown). More specifically, processor202is positioned within control panel150. Pitch control system200substantially provides a technical effect of wind turbine noise reduction as described herein.

Processor202and other processors (not shown) as described herein process information transmitted from a plurality of electrical and electronic devices that may include, but are not limited to, blade pitch position feedback devices206(described further below) and electric power generation feedback devices (not shown). Memory devices203and storage devices (not shown) store and transfer information and instructions to be executed by processor202. Memory devices203and the storage devices can also be used to store and provide temporary variables, static (i.e., non-changing) information and instructions, or other intermediate information to processor202during execution of instructions by processor202. Instructions that are executed include, but are not limited to, resident blade pitch system200control commands. The execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions.

In the exemplary embodiment, at least a portion of pitch control system200including, but not limited to, processor202and memory device203are positioned within control panel150. Moreover, processor202and memory device203are coupled to blade pitch drive motors131by at least one I/O conduit204. I/O conduit204includes any number of channels having any architecture including, but not limited to, Cat 5/6 cable, twisted pair wiring, and wireless communication features. Pitch control system200may include distributed and/or centralized control architectures, or any combination thereof.

Pitch control system200also includes a plurality of independent blade pitch position devices206coupled with processor202and memory device203by at least one I/O conduit204. In the exemplary embodiment, each pitch drive mechanism130is associated with a single blade pitch position feedback device206. Alternatively, any number of position feedback devices206are associated with each mechanism130. Therefore, in the exemplary embodiment, mechanism130and associated drive motor131, as well as device206, are included in system200as described herein. Each position feedback device206measures a pitch position of each blade112, or more specifically an angle of each blade112with respect to wind124(shown inFIG. 1) and/or with respect to rotor hub110. Position feedback device206is any suitable sensor having any suitable location within or remote to wind turbine100, such as, but not limited to, optical angle encoders, magnetic rotary encoders, and incremental encoders, or some combination thereof. Moreover, position feedback device206transmits pitch measurement signals (not shown) that are substantially representative of associated blade112pitch position to memory device203and then processor202for processing thereof.

FIG. 3is a schematic view of blade pitch control system200that may be used with wind turbine generator100(shown inFIG. 1). In the exemplary embodiment, blade pitch control system200includes a controller208that includes processor202and memory203coupled together. Controller208is coupled to blade pitch position device206and blade pitch drive motor131by at least one I/O conduit204.

Also, in the exemplary embodiment, blade pitch control system200includes an electric power source, i.e., a battery array210. Blade pitch control system200also includes a switch array212coupled to battery array210by a plurality of switch devices including first switch device K1, second switch device K2, third switch device K3, and nthswitch device Kn, wherein “n” is any numeral that enables operation of blade pitch control system200as described herein. Switch devices K1 through Kn define a plurality of battery portions, or units, including first battery unit B1, second battery unit B2, third battery unit B3, and nthbattery unit Bn, wherein “n” is described above. Battery array210is coupled to blade pitch drive motor131by a first direct current (DC) power conduit214and switch array212is coupled to blade pitch drive motor131by a second DC power conduit216. Controller208is coupled to an actuating mechanism (not shown) and a position feedback mechanism (not shown) in each switch device K1 through Kn within switch array212by at least one I/O conduit204.

In the exemplary embodiment, switch devices K1 through Kn are contactors. Alternatively, any type of switch device may be used that enables operation of blade pitch control system200as described herein, including, without limitation, insulated gate bipolar transistors (IGBT) and gate turn-off thyristors (GTOs). Some considerations for selecting the switch devices include, without limitation, cost and operational speed of each switch type. For example, without limitation, switching times for the switch devices may vary from less than one microsecond to multiple milliseconds. In addition, depending on the type of switch device selected, speed control algorithms should be programmed in processor202accordingly.

Also, in the exemplary embodiment, a closed-loop proportional-integral-derivative (PID) control scheme is used. Alternatively, rather than typical PID control schemes, a simplified closed-loop control scheme with preset operational contact closing and opening periods and without a rate of pitch feedback feature may be used for contact control. Also, alternatively, open loop control schemes without rate of pitch feedback may also be used, wherein battery units may be coupled to drive motors for various durations that may be fixed or adjustable by control system parameter settings. Although open loop control schemes generally have lower precision than closed loop control schemes, such open loop control schemes typically have a better performance than non-controlled battery pitching.

I/O conduits204transmit operational measurements of each switch device K1 through Kn to memory device203within controller208. In the exemplary embodiment, switch devices K1 through Kn are discrete, binary switches with a “closed” state and an “open” state. Blade pitch position device206transmits operational measurements of blade112(shown inFIG. 1) that extend between the power position and the feathered position defined by blade pitch angles of approximately 0 degrees and 90 degrees, respectively, to memory device203within controller208by I/O conduits204. Processor202is programmed with at least one differentiating algorithm to determine a rate of pitch. Moreover, blade pitch drive motor131transmits operational measurements that include, without limitation, motor current (not shown) as drawn through DC power conduits214and216, to memory device203.

In operation, processor202of controller208is programmed with sufficient algorithms and instructions to change a pitch angle of wind turbine blade112during grid voltage fluctuations that may include low voltage transients with voltage fluctuations that approach zero volts. Processor202commands each switch device K1 through Kn to open and close through a predetermined sequence to facilitate attaining predetermined pitch angle change rates as a function of time. Only one of switch devices K1 through Kn is closed at any one time, thereby coupling a predetermined number of battery units B1 through Bn to blade pitch drive motor131. Motor131is a DC motor that drives the associated blade112at a rate that is at least partially determined by the voltage applied to motor131. Therefore, opening and closing switch devices K1 through Kn changes the voltage induced on motor131from battery array210to predetermined discrete voltage values, thereby changing the predetermined discrete angular rate of change of the pitch of blade112. In general, as the value of n increases from 1, the number of battery units Bn increases, the voltage applied to motor131increases, and the angular rate of pitch change increases.

FIG. 4is a graphical view, i.e., graph300of an exemplary blade pitch angle control strategy for a single blade112(shown inFIG. 1) that may be used with blade pitch control system (200) shown inFIG. 3. Graph300includes an ordinate (y-axis)302that represents pitch rate in degrees per second (°/sec) in increments of 1°/sec ranging from 0°/sec to 8°/sec. Graph300also includes an abscissa (x-axis)304that represents time in seconds (sec) in increments of 1 sec from 0 secs to 13 secs. Graph300further includes a first section306extending from approximately 0 secs to approximately 0.33 secs along x-axis304. In the exemplary embodiment, n=6. Referring toFIG. 3withFIG. 4, switch device K6 closes and switch devices K1 through K5 are open, thereby applying the full voltage of battery array210of battery units 1 through 6 in series to blade pitch drive motor131. Blade112(shown inFIG. 1) is rotated about pitch axis118(shown inFIG. 1) at a rate of approximately 7.5°/sec, wherein 7.5°/sec is the predetermined high end parameter. Such rate is shown as a portion of an actual rate curve308and is compared to a desired rate curve310.

Graph300also includes a second section312extending from approximately 0.33 secs along x-axis304to approximately 1.1 sec. Switch device K6 opens and switch device K3 closes at approximately 0.33 secs to apply approximately half of the rated voltage of battery array210, including battery units 1 through 3 in series, to blade pitch drive motor131. Blade112is rotated about pitch axis118at a rate that decreases from approximately 7.5°/sec to approximately 7.0°/sec.

Graph300further includes a third section314extending from approximately 1.1 secs along x-axis304to approximately 1.4 sec. Switch device K3 opens and no switch device closes at approximately 1.1 secs to apply approximately zero volts to blade pitch drive motor131. Blade112is rotated about pitch axis118at a rate that decreases from approximately 7.0°/sec to approximately 1.0°/sec.

Graph300also includes a fourth section316extending from approximately 1.4 secs along x-axis304to approximately 2.7 sec. Switch device K3 closes at approximately 1.4 secs to apply half of the rated voltage of battery array210, including battery units 1 through 3 in series, to blade pitch drive motor131. Blade112is rotated about pitch axis118at a rate that increases from approximately 1.0°/sec to approximately 2.0°/sec.

Graph300also includes a fifth section318extending from approximately 2.7 secs along x-axis304to approximately 3.1 sec. Switch device K3 opens and switch device K6 closes at approximately 3.1 secs to apply the full voltage of battery array210of battery units 1 through 6 in series to blade pitch drive motor131. Blade112is rotated about pitch axis118at a rate that increases from approximately 2.0°/sec to approximately 7.8°/sec.

Graph300also includes a sixth section320extending from approximately 3.1 secs along x-axis304to approximately 12.0 sec. Switch devices K3, K4, and K5 open and close successively through the time period such that curve308modulates between approximately 7.8°/sec and approximately 7.3°/sec to simulate a steady rate of approximately 7.5°/sec as shown in desired rate curve310. The applied voltage from battery array210to blade pitch drive motor131varies accordingly.

Graph300further includes a seventh section322extending from approximately 12.0 secs along x-axis304to approximately 12.3 sec. All switch devices are open and no switch device closes to apply approximately zero volts to blade pitch drive motor131. Blade112is rotated about pitch axis118at a rate that decreases from approximately 7.8°/sec to approximately 0.0°/sec. In the exemplary embodiment, processor202of controller208is programmed to change an angular rate pitch angle of wind turbine blade112by opening and closing switch devices K1 through Kn in a predetermined sequence. It is estimated that by this point, i.e., after 12.0 secs, rotor108is decelerated sufficiently due to the braking action of blades118induced by blade pitch control system200to significantly reduce a probability of accelerated wear of components of wind turbine generator100due to unplanned grid voltage fluctuations that may include low voltage transients with voltage fluctuations that approach zero volts.

FIG. 5is a flow chart of an exemplary method400of assembling blade pitch control system200(shown inFIG. 3). In the exemplary embodiment, at least one blade pitch drive mechanism130(shown inFIG. 3) is coupled402to wind turbine blade112(shown inFIG. 1). At least one electric power source, i.e., battery array210(shown inFIG. 3) is coupled404to blade pitch drive mechanism130. At least two switch devices K1 through Kn (shown inFIG. 3) are coupled406to at least one of a first portion B1 and a second portion Bn (both shown inFIG. 3) of battery array210. Switch devices K1 through Kn are coupled408to blade pitch drive mechanism130. Controller208(shown inFIG. 3) is coupled410to blade pitch drive mechanism130and switch devices K1 through Kn. Controller208is programmed412to open and close each of switch devices K1 through Kn in a predetermined sequence to drive each blade pitch drive mechanism130at predetermined angular rates to change a pitch angle of wind turbine blade112.

FIG. 6is a flow chart of an exemplary method500of operating blade pitch control system200(shown inFIG. 3). In the exemplary embodiment, one of a plurality of portions, i.e., portions B1 through Bn of battery array210(all shown inFIG. 3) is coupled502to blade pitch drive mechanism130(shown inFIG. 3) by closing one of switch devices K1 through Kn (shown inFIG. 3). Also, an angular rate of change of a pitch angle of wind turbine blade112(shown inFIG. 1) is controlled504by opening and closing switch devices B1 through Bn in a predetermined sequence to drive blade pitch drive mechanism130at predetermined angular rates.

The above-described methods, apparatus, and systems facilitate operation of wind turbine generators by actively controlling blade pitch during unplanned shutdowns of the wind turbine generators. Such methods, apparatus, and systems include implementation of a blade pitch control system that modulates the rate of change of the pitch angles of each of a plurality of wind turbine blades as a function of time. Specifically, modulating the rate of change of the pitch angles for each blade facilitates decelerating the wind turbine rotor in a predetermined manner. Further, specifically, decelerating the wind turbine rotor in a predetermined manner facilitates reducing a potential for accelerated component wear.

Exemplary embodiments of methods, apparatus, and systems for operating wind turbine generators are described above in detail. The methods, apparatus, and systems are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods may also be used in combination with other wind turbine generators, and are not limited to practice with only the wind turbine generator as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other wind turbine generator applications.

BLADE PITCH SYSTEM FOR A WIND TURBINEGENERATOR AND METHOD OF OPERATING THESAMEPARTS LIST100Wind Turbine Generator102Tower104Tower Supporting Surface106Nacelle108Rotor110Hub112Blades114Rotation Axis116Yaw Axis118Pitch Axis120Blade Root Portion122Load Transfer Regions124Wind125Blade Tip Portion126Blade Surface Area130Pitch Drive Mechanism131Pitch Drive Motor132Generator134Low Speed Shaft136Gearbox138High Speed Shaft140Coupling142Gearbox Supports144Generator Supports146Yaw Drive Mechanism148Meteorological Mast150Control Panel152Forward Support Bearing154Aft Support Bearing200Blade Pitch Control System202Processor203Memory204Input/Output (I/O) Conduit206Blade Pitch Position Feedback Devices208Controller210Battery Array212Switch ArrayK1First Switch DeviceK2Second Switch DeviceK3Third Switch DeviceKnnthSwitch DeviceB1First Battery UnitB2Second Battery UnitB3Third Battery UnitBnnthBattery Unit214First Direct Current (DC) Power Conduit216Second Direct Current (DC) Power Conduit300Graph302Y-axis304X-axis306First Section308Actual Rate Curve310Desired Rate Curve312Second Section314Third Section316Fourth Section318Fifth Section320Sixth Section322Seventh Section400Method of assembling402Coupling at least one blade pitch drive mechanism . . .404Coupling at least one electric power source to the blade . . .406Coupling at least two switch devices to at least one of a first . . .408Coupling the switch devices to the blade pitch drive mechanism, . . .410Coupling a controller to the blade pitch drive mechanism and . . .412Programming the controller to open and close each of the . . .500Method of operating502Coupling one of a plurality of portions of an electric power source . . .504Controlling an angular rate of change of a pitch angle of the . . .