Variable tip speed ratio tracking control for wind turbines

The present invention relates to a method of controlling the aerodynamic load of a wind turbine blade by controlling the tip speed ratio (TSR) and/or blade pitch setting of the wind turbine blade so as to optimize power production. A wind turbine blade undergoes an aero-elastic response including deflection and twist that is a function of the blade loading. The blade loading is dependent on the wind speed, TSR, and pitch setting. The aero-elastic response requires a different TSR and/or pitch to be selected throughout the power curve in order to maintain the optimum power production and to improve energy capture.

FIELD OF THE INVENTION

The present invention is directed generally to wind turbines, and more particularly to a method for increasing energy capture and controlling the tip speed ratio and/or blade pitch of a wind turbine blade.

BACKGROUND OF THE INVENTION

Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.

Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted to a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in length). In addition, the wind turbines are typically mounted on towers that are at least 60 meters in height. Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators that may be rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid.

Wind turbine blades have continually increased in size in order to increase energy capture. However, as blades have increased in size, it has become increasingly more difficult to control optimum energy capture. As wind turbine blades grow larger, they undergo an increased aero-elastic response including deflection and twist when loaded that can negatively impact the energy capture. Additionally, turbine blades may be designed to have an aero-elastic response, with the twist of the blade dependent on the loading upon the blade. The blade loading is dependent on the wind speed, tip speed ratio (TSR) and/or pitch setting of the blade. TSR is the ratio of the rotational velocity of the blade tip to wind speed. It is important to optimize the operation of the wind turbine, including blade energy capture, to reduce the cost of the energy produced.

Therefore, what is needed is a method for operating a wind turbine that optimizes energy capture by controlling the TSR and blade pitch angle for the current operating condition.

SUMMARY OF THE INVENTION

A first embodiment of the present invention includes a method for controlling a wind turbine having twist bend coupled rotor blades on a rotor mechanically coupled to a generator. The method includes determining a speed of a rotor blade tip of the wind turbine and adjusting a torque of a generator to change the speed of the rotor blade tip to thereby increase an energy capture power coefficient of the wind turbine.

Another aspect of the present invention includes a method for controlling a wind turbine having twist bend coupled rotor blades on a rotor mechanically coupled to a generator, the method including determining wind speed and adjusting blade pitch to thereby increase an energy capture power coefficient of the wind turbine.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, an exemplary wind turbine100according to the present invention is disclosed. The wind turbine100includes a nacelle102mounted atop a tall tower104, only a portion of which is shown inFIG. 1. Wind turbine100also comprises a wind turbine rotor106that includes one or more rotor blades108attached to a rotating hub110. Although wind turbine100illustrated inFIG. 1includes three rotor blades108, there are no specific limits on the number of rotor blades108required by the present invention. The height of tower104is selected based upon factors and conditions known in the art.

In some configurations and referring toFIG. 2, various components are housed in nacelle102atop tower104. One or more microcontrollers (not shown) are housed within control panel112. The microcontrollers include hardware and software configured to provide a control system providing overall system monitoring and control, including pitch and speed regulation, high-speed shaft and yaw brake application, yaw and pump motor application and fault monitoring. In alternative embodiments of the disclosure, the control system may be a distributed control architecture not solely provided for by the control panel112as would be appreciated by one of ordinary skill in the art. The control system provides control signals to a variable blade pitch drive114to control the pitch of blades108(FIG. 1) that drive hub110as a result of wind. In some configurations, the pitches of blades108are individually controlled by blade pitch drive114.

The drive train of the wind turbine includes a main rotor shaft116(also referred to as a “low speed shaft”) connected to hub110and supported by a main bearing130and, at an opposite end of shaft116, to a gear box118. Gear box118, in some configurations, utilizes a dual path geometry to drive an enclosed high speed shaft. The high speed shaft (not shown inFIG. 2) is used to drive generator120, which is mounted on main frame132. In some configurations, rotor torque is transmitted via coupling122. Generator120may be of any suitable type, for example, a wound rotor induction generator.

Yaw drive124and yaw deck126provide a yaw orientation system for wind turbine100. Anemometry provides information for the yaw orientation system, including measured instantaneous wind direction and wind speed at the wind turbine. Anemometry may be provided by a wind vane128. In some configurations, the yaw system is mounted on a flange provided atop tower104.

In some configurations and referring toFIG. 3, an exemplary control system300for wind turbine100includes a bus302or other communications device to communicate information. Processor(s)304are coupled to bus302to process information, including information from sensors configured to measure displacements or moments. Control system300further includes random access memory (RAM)306and/or other storage device(s)308. RAM306and storage device(s)308are coupled to bus302to store and transfer information and instructions to be executed by processor(s)304. RAM306(and also storage device(s)308, if required) can also be used to store temporary variables or other intermediate information during execution of instructions by processor(s)304. Control system300can also include read only memory (ROM) and or other static storage device310, which is coupled to bus302to store and provide static (i.e., non-changing) information and instructions to processor(s)304. Input/output device(s)312can include any device known in the art to provide input data to control system300and to provide yaw control and pitch control outputs. Instructions are provided to memory from a storage device, such as magnetic disk, a read-only memory (ROM) integrated circuit, CD-ROM, DVD, via a remote connection that is either wired or wireless providing access to one or more electronically-accessible media, etc. In some embodiments, hard-wired circuitry can be used in place of or in combination with software instructions. Thus, execution of sequences of instructions is not limited to any specific combination of hardware circuitry and software instructions. Sensor interface314is an interface that allows control system300to communicate with one or more sensors. Sensor interface314can be or can comprise, for example, one or more analog-to-digital converters that convert analog signals into digital signals that can be used by processor(s)304.

A method and system for controlling a wind turbine having twist bend coupled rotor blades on a rotor mechanically coupled to a generator includes determining a speed of a rotor blade tip of the wind turbine, measuring a current twist distribution and current blade loading, and adjusting a torque of a generator to change the speed of the rotor blade tip to thereby increase and energy capture power coefficient of the wind turbine is disclosed in U.S. Pat. No. 7,118,338 B2, which is hereby incorporated by reference in the entirety.

In some configurations of the present invention, an aero-elastic blade is provided that changes its aerodynamic twist as it is loaded. For example and referring toFIG. 1andFIG. 4, a rotor blade108is provided having a passive aero-elastic response and one or more shear webs (for example, two shear webs404and406). An optimum pitch setting for maximum energy capture varies in wind turbines100having blades108with an aero-elastic response. However, to avoid loss of energy capture, the tip speed ratio and blade pitch angle are tracked and varied for maximum or at least favorable power coefficient by adjusting rotor106speed (i.e., rotation rate) and blade pitch angle through actuators114. In some configurations, this adjustment is made by using optical sensors (not shown) or any other suitable sensors to measure rotational speed as rotor106rotates.

In some configurations, hub rotational speed is known from an encoder on a high speed shaft connected to the aft end of the generator, and blade length, which is known, is used to determine tip speed. This tip speed data is received by control system300, which utilizes a table or equation that relates generator120torque to an optimum or at least favorable tip speed ratio (TSR), which is the ratio of rotational speed of the blade tip to wind velocity, for the current twist distribution occurring at the current blade loading. The equation or table can be empirically determined or calculated using known physical laws. Control system300controls generator120torque in accordance to the equation or table to produce a rotor106speed that provides the optimum or at least a favorable power coefficient. This technique can be used to augment a below-rated pitch schedule or used alone to restore energy capture to levels closer to the entitlement associated with an uncoupled blade.

In order to maintain the optimum power production and improve energy capture, a different TSR and/or pitch setting is required throughout the variable speed region of the power curve below rated wind speed as shown inFIG. 5. As can be seen inFIG. 5, tracking a variable TSR and pitch setting below rated wind allows the turbine to operate at a point that minimizes the impact of the deflection and twist that the blade undergoes during operation.

For standard turbine operation, with blades that undergo minimum aero-elastic deformation, only one TSR may be tracked at a selected pitch setting to maintain a maximum power coefficient. The rotational speed of the wind turbine rotor is measured and the torque of the generator is adjusted to maintain efficient energy capture of the wind turbine. The rotational speed of the wind turbine may be measured at the blade, hub, or shaft as would be appreciated by one of ordinary skill in the art.

For a turbine equipped with blades that undergo an aero-elastic response, the pitch setting and TSR for maximum energy capture varies with wind speed and resulting blade loading. To maintain optimum energy capture, the pitch angle of the blades and the torque of the generator are varied for the current turbine operating condition to provide the optimum or at least favorable energy capture. The control system controls the generator torque and pitch setting in accordance to an equation or table relating generator torque and blade pitch to rotational speed, which results in turbine operation at the optimum or at least favorable power coefficient. This technique can be used to define the below-rated pitch and torque schedule. The method could similarly be accomplished through measurements of wind speed, blade loading, and/or power, for example by measuring the wind speed and setting the desired blade pitch and generator torque.