Patent Description:
Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modem wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor including one or more rotor blades. The rotor blades capture kinetic energy from wind using known airfoil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.

During operation of a wind turbine, various components of the wind turbine are subjected to various loads due to the aerodynamic wind loads acting on the blade. In particular, the rotor blades experience significant loading, and frequent changes in loading, during operation due to interaction with the wind. Changes in wind speed and direction, for example, may modify the loads experienced by the rotor blades. To reduce rotor blade loading, various control systems have been developed to allow the rotor blades to shed a portion of the loads experienced thereby. Such control systems include, for example, pitching the rotor blades and/or modifying generator torque during operation. In a variable rotor speed operational mode of the wind turbine, the control system can be designed to regulate the rotor speed so as to follow a defined Tip Speed Ratio (TSR) set point (through generator torque regulation), and maintain the pitch angle at a defined pitch set point. Further, TSR regulation can be based on measured TSR or estimated TSR.

Thus, modern wind turbines, like the ones described in <CIT> and <CIT>, operate according to one or more set points designed to achieve maximum power while also maintaining loads within safe limits. In particular, many wind turbine control schemes implement one or more operational constraints in order to achieve a trade-off between loads and power performance. For example, one such operational constraint is a thrust constraint that involves reducing loads when an estimated thrust value exceeds a pre-defined thrust limit.

The power coefficient (generally referred to as Cp) of a wind turbine is the measure of wind turbine aerodynamic efficiency and is the ratio of actual mechanical power produced by the wind turbine divided by the total power available in the wind flowing through the rotor at a specific wind speed. In certain instances, the power coefficient can be predicted from aerodynamic performance maps, which are dimensional or non-dimensional tables or graphs that describe rotor loading and performance (e.g. power, thrust, torque, bending moment, or similar) under given conditions (e.g. density, wind speed, rotor speed, pitch angles, or similar). As such, the aerodynamic performance map(s) may include: power coefficients, thrust coefficients, torque coefficients, and/or partial derivatives with respect to pitch angle, rotor speed, or tip speed ratio (TSR). Alternatively, the aerodynamic performance maps can be dimensional power, thrust, and/or torque values instead of coefficients.

For example, the aerodynamic performance maps may include a look-up table of the power coefficient as a function of pitch angle and TSR of the wind turbine. In other words, for normal wind turbine operation, the operational constraints are converted to aerodynamic coefficient values such that the optimal operating set point (e.g. the power coefficient) that satisfies all of the constraints and also maximizes power can be chosen from the aerodynamic performance map. The turbine controller can use the resulting optimal TSR and pitch set points obtained from the map to control the wind turbine. Generally, the TSR set point is a fixed value to which turbine is regulated during variable rotor speed operation of the wind turbine. When the operational constraint(s) are implemented by the turbine controller, the power coefficient decreases since a fixed TSR set point cannot be optimal across a range of operational constraints.

Accordingly, the present disclosure is directed to systems and methods for varying the TSR set point during such operational constraints so as optimize power, reduce loads, and/or lower acoustic noise emission from the wind turbine.

In one aspect, the present disclosure is directed to a method according to claim <NUM> for optimizing power production of a wind turbine. The method includes determining at least one operational constraint for the wind turbine. The method also includes operating the wind turbine with at least one operational constraint being activated. Further, the method includes varying a tip speed ratio for the wind turbine while the at least one operational constraint is activated so as to maximize a power coefficient of the wind turbine.

In one embodiment, the operational constraint(s) may include a thrust constraint, a rotor/generator speed constraint, a torque constraint, a noise constraint, and/ or an external set point, for example, from a farm wake management control scheme. In another embodiment, the operational constraint(s) may impose an operational limit on the wind turbine. For example, the operational limit may include a predetermined maximum thrust, a predetermined maximum speed, a predetermined maximum torque, a predetermined maximum noise limit, and/or a tip speed ratio set point received from an external source.

In further embodiments, when the at least one operational constraint is activated, the method may include determining an acoustic noise emission of the wind turbine, and if a limiting value is reached, decreasing the tip speed ratio, sometimes along with an increase in blade pitch angles.

In several embodiments, the step of varying the tip speed ratio for the wind turbine while the at least one operational constraint is activated may include reducing the tip speed ratio when the predetermined maximum thrust is reached. In addition, the method may include increasing a pitch angle of at least one rotor blade of the wind turbine in addition to reducing the tip speed ratio.

In another embodiment, the method may include monitoring one or more turbine operating conditions or wind conditions of the wind turbine when the at least one operational constraint is activated, determining an estimated thrust value of the wind turbine based on the one or more turbine operating conditions or wind conditions, and varying the tip speed ratio for the wind turbine if the estimated thrust value is greater than or equal to the predetermined maximum thrust.

In additional embodiments, when the operational constraint(s) is activated, the method may further include monitoring a torque of the wind turbine. More specifically, during monitoring, if a rated torque value is reached, the method may include increasing the tip speed ratio. In addition, the method may include increasing a pitch angle of at least one rotor blade of the wind turbine in addition to increasing the tip speed ratio.

In particular embodiments, the method may also include operating the wind turbine with a plurality of operational constraints being activated. For example, in one embodiment, when the wake management control scheme and the thrust constraint are both activated, the method may include selecting the tip speed ratio based on a minimum tip speed ratio value between the wake management control scheme and the thrust constraint.

In certain embodiments, the method may further include restoring the tip speed ratio when the at least one operational constraint is deactivated.

In another aspect, the present disclosure is directed to a system according to claim <NUM> for optimizing power production of a wind turbine. The system includes a turbine controller having one or more processors configured to perform one or more operations, including but not limited to, determining at least one operational constraint for the wind turbine, operating the wind turbine with at least one operational constraint being activated, and varying a tip speed ratio for the wind turbine while the at least one operational constraint is activated so as to maximize a power coefficient of the wind turbine.

In yet another aspect, the present disclosure is directed to a wind turbine. The wind turbine includes a tower, a nacelle mounted on the tower, a rotor coupled to the nacelle, and a turbine controller. The rotor includes a rotatable hub having a plurality of rotor blades mounted thereto. The turbine controller includes at least one processor configured to perform one or more operations, including but not limited to, determining at least one operational constraint for the wind turbine, operating the wind turbine with at least one operational constraint being activated, and varying a tip speed ratio for the wind turbine while the at least one operational constraint is activated so as to maximize a power coefficient of the wind turbine.

Referring now to the drawings, <FIG> illustrates a perspective view of one embodiment of a wind turbine <NUM> according to the present disclosure. As shown, the wind turbine <NUM> includes a tower <NUM> extending from a support surface <NUM>, a nacelle <NUM> mounted on the tower <NUM>, and a rotor <NUM> coupled to the nacelle <NUM>. The rotor <NUM> includes a rotatable hub <NUM> and at least one rotor blade <NUM> coupled to and extending outwardly from the hub <NUM>. For example, in the illustrated embodiment, the rotor <NUM> includes three rotor blades <NUM>. However, in an alternative embodiment, the rotor <NUM> may include more or less than three rotor blades <NUM>. Each rotor blade <NUM> may be spaced about the hub <NUM> to facilitate rotating the rotor <NUM> to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub <NUM> may be rotatably coupled to an electric generator <NUM> (<FIG>) positioned within the nacelle <NUM> to permit electrical energy to be produced.

Referring now to <FIG>, a simplified, internal view of one embodiment of the nacelle <NUM> of the wind turbine <NUM> is illustrated. As shown, the generator <NUM> may be disposed within the nacelle <NUM>. In general, the generator <NUM> may be coupled to the rotor <NUM> of the wind turbine <NUM> for generating electrical power from the rotational energy generated by the rotor <NUM>. For example, the rotor <NUM> may include a main rotor shaft <NUM> coupled to the hub <NUM> for rotation therewith. The generator <NUM> may then be coupled to the rotor shaft <NUM> such that rotation of the rotor shaft <NUM> drives the generator <NUM>. For instance, in the illustrated embodiment, the generator <NUM> includes a generator shaft <NUM> rotatably coupled to the rotor shaft <NUM> through a gearbox <NUM>. However, in other embodiments, it should be appreciated that the generator shaft <NUM> may be rotatably coupled directly to the rotor shaft <NUM>. Alternatively, the generator <NUM> may be directly rotatably coupled to the rotor shaft <NUM> (often referred to as a "direct-drive wind turbine").

It should be appreciated that the rotor shaft <NUM> may generally be supported within the nacelle <NUM> by a support frame or bedplate <NUM> positioned atop the wind turbine tower <NUM>. For example, the rotor shaft <NUM> may be supported by the bedplate <NUM> via a pair of pillow blocks <NUM>, <NUM> mounted to the bedplate <NUM>.

Additionally, as shown, the wind turbine <NUM> may also include a turbine control system or a turbine controller <NUM> located within the nacelle <NUM>. For example, as shown in the illustrated embodiment, the turbine controller <NUM> is disposed within a control cabinet <NUM> mounted to a portion of the nacelle <NUM>. However, it should be appreciated that the turbine controller <NUM> may be disposed at any location on or in the wind turbine <NUM>, at any location on the support surface <NUM> or generally at any other location. Moreover, as described herein, the turbine controller <NUM> may also be communicatively coupled to various components of the wind turbine <NUM> for generally controlling the wind turbine and/or such components, as well as the various operating modes (e.g., start-up or shut-down sequences) of the wind turbine <NUM>. For example, the controller <NUM> may be configured to control the blade pitch or pitch angle of each of the rotor blades <NUM> (i.e., an angle that determines a perspective of the rotor blades <NUM> with respect to the direction <NUM> of the wind) to control the loading on the rotor blades <NUM> by adjusting an angular position of at least one rotor blade <NUM> relative to the wind. For instance, the turbine controller <NUM> may control the pitch angle of the rotor blades <NUM>, either individually or simultaneously, by transmitting suitable control signals/commands to various pitch drives or pitch adjustment mechanisms <NUM> (<FIG>) of the wind turbine <NUM>. Specifically, the rotor blades <NUM> may be rotatably mounted to the hub <NUM> by one or more pitch bearing(s) (not illustrated) such that the pitch angle may be adjusted by rotating the rotor blades <NUM> about their pitch axes <NUM> using the pitch adjustment mechanisms <NUM>. Further, as the direction <NUM> (<FIG>) of the wind changes, the turbine controller <NUM> may be configured to control a yaw direction of the nacelle <NUM> about a yaw axis <NUM> to position the rotor blades <NUM> with respect to the direction <NUM> of the wind, thereby controlling the loads acting on the wind turbine <NUM>. For example, the turbine controller <NUM> may be configured to transmit control signals/commands to a yaw drive mechanism <NUM> (<FIG>) of the wind turbine <NUM> such that the nacelle <NUM> may be rotated about the yaw axis <NUM>.

Still further, the turbine controller <NUM> may be configured to control the torque of the generator <NUM>. For example, the turbine controller <NUM> may be configured to transmit control signals/commands to the generator <NUM> in order to modulate the magnetic flux produced within the generator <NUM>, thus adjusting the torque demand or set point of the generator <NUM>. Such temporary de-rating of the generator <NUM> may reduce the rotational speed of the rotor blades <NUM>, thereby reducing the aerodynamic loads acting on the blades <NUM> and the reaction loads on various other wind turbine <NUM> components.

It should be appreciated that the turbine controller <NUM> may generally comprise a computer or any other suitable processing unit. Thus, in several embodiments, the turbine controller <NUM> may include one or more processor(s) and associated memory device(s) configured to perform a variety of computer-implemented functions, as shown in <FIG> and discussed herein. As used herein, the term "processor" refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Additionally, the memory device(s) <NUM> of the turbine controller <NUM> may generally comprise memory element(s) including, but are not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s) <NUM> may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) <NUM>, configure the controller <NUM> to perform various computer-implemented functions including, but not limited to, performing proportional integral derivative ("PID") control algorithms, including various calculations within one or more PID control loops, and various other suitable computer-implemented functions. In addition, the turbine controller <NUM> may also include various input/output channels for receiving inputs from sensors and/or other measurement devices and for sending control signals to various components of the wind turbine <NUM>.

It should additionally be understood that the controller <NUM> may be a singular controller or include various components, such as pitch controllers and/or yaw controllers, which communicate with a central controller for specifically controlling pitch and yaw as discussed. Additionally, the term "controller" may also encompass a combination of computers, processing units and/or related components in communication with one another.

The present disclosure is further directed to methods for optimizing power production of the wind turbine <NUM>, e.g. when one or more operational constraints are implemented by the turbine controller <NUM>. In particular, the controller <NUM> may be utilized to perform such methods. Thus, as shown in <FIG>, there is illustrated a block diagram of one embodiment of suitable components that may be included within the turbine controller <NUM> in accordance with aspects of the present subject matter. As shown, the controller <NUM> may include one or more processor(s) <NUM> and associated memory device(s) <NUM> configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and the like disclosed herein). Additionally, the controller <NUM> may also include a communications module <NUM> to facilitate communications between the controller <NUM> and the various components of the wind turbine <NUM>. For instance, the communications module <NUM> may serve as an interface to permit the turbine controller <NUM> to transmit control signals to each pitch adjustment mechanism <NUM> for controlling the pitch angle of the rotor blades <NUM>. Moreover, the communications module <NUM> may include a sensor interface <NUM> (e.g., one or more analog-to-digital converters) to permit input signals transmitted from, for example, various sensor, to be converted into signals that can be understood and processed by the processor(s) <NUM>.

Referring now to <FIG>, a flow diagram of one embodiment of a method <NUM> for optimizing power production of the wind turbine <NUM> when one or more operational constraints are implemented by the turbine controller <NUM> is illustrated. More specifically, as shown at <NUM>, the method <NUM> includes determining at least one operational constraint for the wind turbine <NUM>. As shown at <NUM>, the method <NUM> includes operating the wind turbine <NUM> with the operational constraint(s) being activated. In one embodiment, for example, the operational constraint(s) may include a thrust constraint, a speed constraint, a torque constraint, a noise constraint, and/or a wake management control scheme. Such constraints can be measured with physical sensors or estimated. For example, in certain embodiments, the constraints may be estimated using available turbine sensor measurements and/or dynamic models using prediction or estimation techniques. As such, measured or predicted/estimated signals may be compared to threshold values (defined as operational parameters) to determine if constraints are active. In addition, the method <NUM> may include defining the constraint using the aerodynamic performance maps in the TSR/ pitch angle space for prevailing measured or estimated wind conditions, which allows the method to define an optimal TSR and pitch set point to maximize the power coefficient while satisfying the constraint.

In further embodiments, the method <NUM> may include operating the wind turbine <NUM> with a plurality of operational constraints being activated. For example, in one embodiment, the wind turbine <NUM> may be operated with both the wake management control scheme and the thrust constraint activated. Thus, in certain embodiments, the operational constraint(s) may impose an operational limit on the wind turbine <NUM>. For example, methods according to the present disclosure may in some embodiments further include establishing a maximum thrust, a maximum generator speed, a maximum torque, and/or a predetermined maximum noise limit. In exemplary embodiments, the maximum torque is a maximum generator torque, although in alternative embodiments a maximum aerodynamic torque could be established and the maximum generator torque established through calculation therefrom. Such maximum values are generally pre-established values or ratings which it is generally desirably are not exceeded during operation of the wind turbine <NUM>.

Thus, as shown at <NUM>, the method <NUM> further includes varying a tip speed ratio (TSR) for the wind turbine <NUM> while the operational constraint(s) is activated so as to maximize a power coefficient of the wind turbine <NUM>. For example, in several embodiments, the controller <NUM> may be configured to reduce the TSR when the predetermined maximum thrust is reached. In addition, the controller <NUM> may be configured to increase a pitch angle of at least one rotor blade <NUM> of the wind turbine <NUM> in addition to reducing the TSR. As used herein, the tip speed ratio or TSR generally refers to the ratio between the tangential speed of the tip of one of the rotor blades <NUM> and the actual wind speed. Thus, the TSR may generally be calculated by multiplying the current rotational speed of the wind turbine <NUM> (such as the rotor <NUM> thereof) (measured by suitable sensors in the wind turbine <NUM>) by the maximum radius of the rotor <NUM>, and dividing this result by the wind speed. As such, to reduce the TSR as described herein, the controller <NUM> may reduce the turbine speed (i.e. the rotor speed or the generator speed). Accordingly, in such embodiments, the present disclosure is configured to increase power output of the wind turbine <NUM> without increasing the noise generated by the turbine <NUM> (which is a function of turbine speed).

Referring now to <FIG>, various graphs (also generally referred to as aerodynamic performance maps) are provided to illustrate advantages of the present disclosure. More specifically, <FIG> illustrates one embodiment of an aerodynamic performance map according to normal or unconstrained wind turbine operation. <FIG> and <FIG> illustrate various aerodynamic performance maps according to constrained wind turbine operation. As shown particularly in <FIG>, the unconstrained optimal operating set point <NUM> corresponds to the optimal operational set point for the wind turbine <NUM> without any constraints in place. Further, as shown, the optimal operation set point <NUM> is chosen to maximize power performance of the wind turbine <NUM>.

Referring particularly to <FIG> and <FIG>, various constraints have been implemented by the turbine controller <NUM> to further illustrate advantages of the present disclosure. More specifically, <FIG> illustrates a thrust constraint implemented by the turbine controller <NUM>, as indicated by region <NUM>. Similarly, as shown in <FIG>, a torque constraint has been implemented by the turbine controller <NUM>, as indicated by region <NUM>. In other words, for both maps, the wind turbine <NUM> is limited to operation within regions <NUM> and <NUM>, respectively, and cannot operate with regions <NUM>, <NUM>. As such, the controller <NUM> must select new operating points within regions <NUM> and <NUM>. For example, operating points <NUM>, <NUM> represent conventional wind turbine control schemes that utilize a fixed TSR during times of operational constraint(s). More specifically, as shown in <FIG>, for thrust constraints, conventional control systems increase pitch and maintain the TSR at a fixed value to obtain a new power coefficient Cp. Similarly, as shown in <FIG>, for torque constraints, conventional control systems also increase pitch and maintain the TSR at a fixed value to obtain a new power coefficient Cp.

In contrast, as shown by operating points <NUM>, <NUM>, the control methodology of the present disclosure varies the TSR during times of operational constraint(s) so as to maximize the power coefficient of the wind turbine <NUM>. More specifically, as shown in <FIG>, for thrust constraints, the turbine controller <NUM> of the present disclosure may increase pitch and reduce the TSR to obtain a new power coefficient Cp as shown at <NUM> that is higher than the power coefficient Cp for conventional control schemes. In addition, as shown in <FIG>, for torque constraints, the turbine controller <NUM> of the present disclosure is configured to increase TSR to obtain a new power coefficient Cp as shown at <NUM> that is also higher than the power coefficient Cp for conventional control schemes.

More specifically, in certain embodiments, when the operational constraint(s) is activated, the controller <NUM> may also monitor a torque of the wind turbine <NUM>. As such, during monitoring, if a rated torque value is reached, the controller <NUM> is configured to increase the TSR to a maximum value. In addition, as shown in <FIG>, the controller <NUM> may increase a pitch angle of one or more of the rotor blades <NUM> of the wind turbine <NUM> in addition to increasing the TSR.

As mentioned, multiple constraints may be implements by the turbine controller <NUM> at the same time. In such instances, the controller <NUM> may vary the TSR as a function of both of the constraints. For example, in one embodiment, when the wake management control scheme and the thrust constraint are both activated, the controller <NUM> may modify the TSR based on a minimum TSR value between the wake management control scheme and the thrust constraint.

In addition, in certain embodiments, the turbine controller <NUM> may monitor one or more turbine operating conditions and/or wind conditions of the wind turbine <NUM>, e.g. when the operational constraint(s) is activated. For example, the turbine operating conditions and/or wind conditions may be measured, such as through use of various suitable sensors. More specifically, suitable wind sensors <NUM> (<FIG>) may include, for example, Light Detection and Ranging ("LIDAR") devices, Sonic Detection and Ranging ("SODAR") devices, anemometers, wind vanes, barometers, and radar devices (such as Doppler radar devices). In further embodiments, the turbine operating conditions may include tower sensors <NUM>, generator sensors <NUM>, main shaft sensors <NUM>, and/or blade sensors <NUM>. Still further, any suitable measurement devices may be utilized to directly or indirectly measure the turbine operating conditions and/or wind conditions of the wind turbine <NUM>. As such, in certain embodiments, the controller <NUM> is further configured to determine an estimated thrust value of the wind turbine <NUM> based on the turbine operating condition(s) and/or the wind conditions. Thus, the controller <NUM> may vary the TSR for the wind turbine <NUM> if the estimated thrust value is greater than or equal to the predetermined maximum thrust. Such a control scheme may further be provided for any of the constraints described herein.

In additional embodiments, the turbine controller <NUM> may also be configured to restore (e.g. increase) the TSR when the operational constraint(s) (e.g. the thrust constraint) is deactivated so as to resume normal operation and maximize the power coefficient.

Referring now to <FIG>, one embodiment of a plot of tip speed ratio versus wind speed according to the present disclosure is illustrated. More specifically, as shown, the plot illustrates thrust <NUM>, pitch angle <NUM>, generator speed <NUM>, generator torque <NUM> as a function of varying TSR <NUM> and wind speed. Further, as shown at <NUM>, the plot illustrates an increase in torque <NUM> due to a lower TSR. Moreover, the plot illustrates a reduced TSR in the thrust control region <NUM>. In addition, in the thrust control region <NUM>, the plot illustrates a decrease <NUM> in pitch compared to the baseline pitch112 as well as a decrease <NUM> in generator speed.

Claim 1:
A method (<NUM>) for optimizing power production of a wind turbine (<NUM>), the method (<NUM>) comprising:
determining an operational constraint for the wind turbine (<NUM>), the operational constraint being one of: a thrust constraint for a rotor of the wind turbine (<NUM>), the thrust constraint imposing a predetermined maximum thrust, and a torque constraint for a generator of the wind turbine (<NUM>), the torque constraint imposing a predetermined maximum torque;
providing an aerodynamic performance map, the aerodynamic performance map corresponding to the determined operational constraint and being a table or a graph that describes, in a tip speed ratio - pitch angle space and for given wind condition, a power coefficient of the wind turbine (<NUM>) and rotor thrust or generator torque;
operating the wind turbine (<NUM>) with the operational constraint being activated such that operation of the wind turbine is constrained to a limited region (<NUM>, <NUM>) of the aerodynamic performance map; and,
varying a tip speed ratio for the wind turbine (<NUM>) while the operational constraint is activated so as to maximize the power coefficient of the wind turbine (<NUM>) within the limited region of the aerodynamic performance map.