Patent Description:
Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation generates a torque that is normally transmitted through a rotor shaft to a generator, either directly or through a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

The wind turbine hub may be rotatably coupled to a front of the nacelle. The wind turbine hub may be connected to a rotor shaft, and the rotor shaft may then be rotatably mounted in the nacelle using one or more rotor shaft bearings arranged in a frame inside the nacelle. The nacelle is a housing arranged on top of a wind turbine tower that contains and protects e.g. the gearbox (if present) and the generator and, depending on the wind turbine, further components such as a power converter, and auxiliary systems.

In variable speed wind turbines, a wind turbine controller can change control settings of the wind turbine to adapt to varying wind conditions. In particular, pitch angles of the blades and generator torque may be varied to adapt to the wind conditions. At wind speeds below the nominal or "rated" wind speed, the control objective is generally to maximize electrical power output of the wind turbine i.e. pitch and generator torque are varied such that maximum electrical power output can be delivered to the grid. Above the nominal wind speed (and depending on the circumstances around the nominal wind speed), the control objective may be particularly to keep loads under control i.e. pitch and generator torque are varied to reduce the loads on the wind turbine to acceptable levels, while the power output is maintained at the highest possible level (given the constraint on the loads).

Wind turbines may be used in widely different settings: onshore, offshore, in warm climates and cold climates. If the ambient temperature rises, temperature of wind turbine components may also rise. If the ambient temperature is very high or remains high for a prolonged period of time, temperatures of wind turbine components may become too high and the operation of the wind turbine may need to be adapted to keep the temperatures of wind turbine components at acceptable levels.

Two different methods are known for dealing with such a situation. In one known solution, for different ambient temperatures, different maximum power setpoints (i.e. power limits) are defined. Such maximum power setpoints as a function of ambient temperatures may be fixed in contract between wind turbine manufacturers and operators.

In operation, the ambient temperature may be monitored and depending on the ambient temperature, the predefined maximum power setpoint is used. In particular this may mean that, above nominal wind speed, rated power is not delivered to the grid anymore, but rather a reduced amount of power is delivered. The operation of the wind turbine may be normal for lower wind speeds: even if a maximum power setpoint is determined based on ambient temperature, the prevailing wind conditions may be such that this maximum power cannot be reached even in optimum operation. One disadvantage of this approach is that the maximum power setpoint are generally set quite conservatively and this affects electrical power output.

In another known solution, temperatures of wind turbine components are measured during operation, and corresponding threshold values for wind turbine components are predefined. When the temperatures of the wind turbine components stays below the corresponding threshold, then the maximum power setpoint is not affected i.e. nominal rated power can be delivered to the grid if wind conditions are favorable. When one of the temperatures of the wind turbine components reaches a corresponding threshold, the power output is (generally) drastically reduced to cool the wind turbine components. One disadvantage of this approach is that power output, if reduced, generally needs to be reduced rapidly in order to guarantee safe operation of the components. Power output variations can thus be significant.

Documents mentioned during the patenting procedure are: <CIT> and <CIT>.

In an aspect of the present disclosure, a method for determining a maximum power setpoint for a wind turbine is provided. The method comprises determining a temperature of a first wind turbine component, and determining a first component temperature error by determining a difference between the temperature of the first wind turbine component and a corresponding threshold temperature for the first wind turbine component. The method further comprises determining a present power output of the wind turbine and determining the maximum power setpoint at least partially based on the first component temperature error, and on the present power output of the wind turbine.

With a method according to this aspect, a maximum power setpoint is determined that is based on an actual temperature of a wind turbine components, rather than an ambient temperature. At the same time, setpoint reduction can be smoothened by reacting before an actual temperature limit for a component is reached. By monitoring a temperature error (i.e. a difference between a temperature objective or temperature limit and an actual temperature), the control will react before such a limit has been reached. The present power output may act like a predictor of future temperature development.

In a further aspect, a control system of a wind turbine is provided, which is configured to determine a first temperature of a wind turbine component, and to determine a present power output of the wind turbine. The control system is further configured to determine a component temperature error by determining a difference between the first temperature of the wind turbine component and a threshold temperature for the first wind turbine component and determine the maximum power setpoint at least partially based on the first component temperature error and the present power output. The control system is further configured to control the wind turbine based on the maximum power setpoint.

In yet a further aspect, a method for determining a maximum power setpoint for a wind turbine is provided, which comprises A method for determining a maximum power setpoint for a wind turbine comprising measuring a first temperature of a first electrical component of the wind turbine, and comparing the first temperature with a first temperature threshold established for the first electrical component to determine a first temperature error value. The method further comprises determining a present power output of the wind turbine and controlling a first power setpoint of the wind turbine including a feedback control based on the first temperature error value, and a feedforward control based on the present power output of the wind turbine.

Throughout the present disclosure, nominal power or "rated power" is to be understood as the maximum power output according to standard operation of the wind turbine i.e. this nominal or rated power may be delivered to the grid at wind speeds at or above the nominal wind speed.

Throughout this disclosure, a maximum power setpoint is to be understood as the maximum power output of a wind turbine independent from prevailing wind conditions i.e. even if wind speeds are high enough such that more electrical power could be delivered to the grid, and particularly that the nominal rated power output could be delivered to the gird, the operation of the wind turbine is limited in such a manner to produce less electrical power than possible.

"Setpoint reduction" is to be understood as a wind turbine operation which is limited to produce and deliver to the grid less than the nominal or rated power. This operational limitation is not due to the prevailing wind conditions, but due to other circumstances. And within the present disclosure particularly, this operational limitation is due to temperatures or thermal limitations including predefined ambient and component temperatures and thermal limitations relating to either the ambient temperature or component temperatures.

Each example is provided by way of explanation of the invention, not as a limitation of the invention.

<FIG> illustrates a perspective view of one example of a wind turbine <NUM>. 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.

<FIG> illustrates a simplified, internal view of one example of the nacelle <NUM> of the wind turbine <NUM> of <FIG>. 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>.

It should be appreciated that the rotor shaft <NUM>, gearbox <NUM>, and generator <NUM> may generally be supported within the nacelle <NUM> by a support frame or bedplate <NUM> positioned atop the wind turbine tower <NUM>.

The nacelle <NUM> may be rotatably coupled to the tower <NUM> through a yaw system <NUM> in such a way that the nacelle <NUM> is able to rotate about a yaw axis YA, or there may be other ways to position the rotor in the desired angle to the wind. If there is a yaw system <NUM>, such system will usually comprise a yaw bearing having two bearing components configured to rotate with respect to the other. The tower <NUM> is coupled to one of the bearing components and the bedplate or support frame <NUM> of the nacelle <NUM> is coupled to the other bearing component. The yaw system <NUM> comprises an annular gear <NUM> and a plurality of yaw drives <NUM> with a motor <NUM>, a gearbox <NUM> and a pinion <NUM> for meshing with the annular gear <NUM> for rotating one of the bearing components with respect to the other.

As indicated above, blades <NUM> are coupled to the hub <NUM> by a pitch bearing <NUM> in between the blade <NUM> and the hub <NUM>. The pitch bearing <NUM> comprises an inner ring <NUM> and an outer ring <NUM>. A wind turbine blade may be attached either at the bearing inner ring or at the bearing outer ring, whereas the hub is connected at the other. A blade <NUM> may perform a relative rotational movement with respect to the hub <NUM> when a pitch system <NUM> is actuated. The inner bearing ring may therefore perform a rotational movement with respect to the outer bearing ring in <FIG>. The pitch system <NUM> of <FIG> comprises a pinion <NUM> that meshes with an annular gear <NUM> provided on the inner bearing ring to set the wind turbine blade into rotation around a pitch axis PA.

<FIG> schematically illustrates an example of a maximum power setpoint curve based on ambient temperatures. For a variety of ambient temperatures, maximum power outputs are defined. Such a contract may be included in a contract between a wind turbine manufacturer and a wind turbine operator or client.

At relatively low ambient temperatures, the maximum power output may be the nominal power of the wind turbine. At lower ambient temperatures, there is no risk that component temperatures can reach their operational limits and thus no power curtailment is necessary.

At higher ambient temperatures, component temperatures may reach their operational limits, particularly if the wind turbine has been operating at its maximum capacity for a while. In order to protect the wind turbine components and to ensure safe operation, the power output of the wind turbine may be limited and the maximum power setpoint may be reduced.

However, there is no direct or linear relationship between ambient temperature and component temperatures. Particularly, component temperature may lag behind ambient temperature. Moreover, component temperature does not only depend on the ambient temperature, but also on a thermal history and inertia of the component, which in turn depend on the electrical power production in the recent operation of the wind turbine.

The present disclosure relates inter alia to a method for determining a maximum power setpoint for a wind turbine comprising determining a temperature of one or more wind turbine components. The method further comprises determining one or more component temperature errors by determining a difference between the temperatures of the wind turbine components and a corresponding threshold temperature for the components, and determining the maximum power setpoint at least partially based at least on the component temperature errors.

In particular, the one or more wind turbine components may include one or more electrical wind turbine components, or components or parts of electrical wind turbine components. Electrical components of the wind turbine may be more prone to overheating than other components, and their temperature depends at least partially on the electrical power output of the turbine. Their temperature can be controlled at least partially by controlling the wind turbine power output, and particularly by ensuring that the maximum power output it not (too) high.

<FIG> and <FIG> schematically illustrate an example of method of determining a maximum power setpoint. <FIG> schematically illustrates how a temperature error may be determined for a transformer, in particular a main transformer. A temperature of the transformer may be measured and compared to a temperature objective. The temperature objective may be a temperature threshold. The threshold may correspond to an operational limit of the component, and in this case, the transformer. In other examples, the temperature threshold may be set lower than the operational limit, e.g. a predetermined amount or predetermined percentage lower than an operational limit of the component.

By comparing, at <NUM>, the actual temperature with the objective, a temperature error value is obtained. The error value may be used in a feedback control at block <NUM>. If the error value is smaller, than the temperature of the component is closer to the threshold. The output of the feedback control may be a maximum power setpoint for the transformer. In <FIG>, the output of the feedback control <NUM>, may be a power setpoint increment, i.e. an amount of a decrease or increase of power setpoint.

At <NUM>, increase or decrease of power setpoint is added to the nominal or rated power of the wind turbine. The outcome in the example of <FIG> is a power setpoint for the transformer, i.e. a maximum power setpoint determined based on the transformer temperature. It should be noted that the maximum power setpoint based on transformer temperature may be higher than the actual rated power of the wind turbine. This does not mean that the wind turbine will be operated at such a higher power setpoint, as will be explained herein.

Such methods may be carried out substantially continuously, e.g. every minute, or every <NUM> - <NUM> minutes, temperatures may be determined, and maximum power setpoints may be recalculated. The method may be carried out a constant frequency, or the frequency may be varied. the frequency of determining, measuring and/or calculating may increase as a temperature closer to a limit temperature is reached.

In some examples, determining the maximum power setpoint comprises a PID control based on the component temperature error. A proportional-integral-derivative controller (PID controller) is a control loop mechanism employing feedback. A PID controller continuously calculates an error value ("temperature error value" in this example) as the difference between a desired setpoint (temperature threshold) and a measured process variable (component temperature) and applies a correction based on proportional, integral, and derivative terms (denoted P, I, and D respectively).

PID control should not be understood herein that necessarily all three terms (proportional, integral and derivative) are used. In examples of the present disclosure, one or two of the terms may have a gains factor of zero, i.e. the PID control may be e.g. a PI control, or a PD control.

Alternatively, the feedback control herein embodied as a PID control may be embodied as any of Model Predictive Control (MPC), H-infinity methods, Linear-Quadratic (LQ) regulator. Further suitable algorithms for feedback control may also be used.

An output of the PID (or other feedback) control may be a power setpoint based on component temperature.

In examples, the maximum power setpoint may be determined as a rated power for the wind turbine if the power setpoint based on component temperature is higher than the rated power. The maximum power setpoint based on temperature of one or more of the components of the wind turbine may be implemented only if the calculated maximum power setpoint is lower than the nominal power, and not if the calculated maximum power setpoint is equal to or higher than the nominal power. Otherwise, the nominal power may be taken as the maximum power setpoint. In this case, wind turbine operation may be normal.

The temperature measurement and determination of a corresponding maximum power setpoint was shown to be applied to a transformer in <FIG>. Similar measurements and determinations may be made for other wind turbine components, specifically electrical wind turbine components, and more specifically the generator of the wind turbine and the power converter, as illustrated in <FIG>. For each of these components, corresponding maximum power setpoint based on their individual temperatures may be determined. In accordance with what is illustrated in <FIG>, the most limiting power setpoint may be used for the control of the wind turbine, specifically if these are lower than the rated power of the wind turbine.

According to the example of <FIG>, the methods for determining a maximum power setpoint further comprises determining a present power output of the wind turbine, and determining the maximum power setpoint based on the component temperature error and on the present power output. Power output of the wind turbine determines heat production in the different electrical components and may thus form input to help estimate future temperature of the electrical components.

In some examples, as illustrated in <FIG>, a first offset power setpoint is determined based on the component temperature error (at feedback controller <NUM>) and a second offset power setpoint is determined based on the present power output (at feedforward controller <NUM>).

In the example of <FIG>, the maximum power setpoint is determined at <NUM>, as a sum of a rated power of the wind turbine Pn, the first offset power setpoint and the second offset power setpoint. At block <NUM>, the maximum power setpoint is fed to wind turbine controller <NUM> if the sum is less than the rated power of the wind turbine. If the sum is more than the rated power, then the rated power is delivered to the wind turbine controller <NUM>.

At block <NUM>, the wind turbine generator (WTG) is controlled based on the maximum power setpoint and the actual wind conditions. The result is the present power output of the wind turbine, which may be delivered to feedforward controller <NUM>.

Depending on the prevailing wind conditions, operation of the wind turbine may be standard. However, in particular at higher winds, the operation of the wind turbine may be adapted to reduce the power to the maximum power setpoint.

In the example of <FIG>, a wind turbine transformer, and in particular the main wind turbine transformer, is shown as an example of an electrical component whose temperature condition can lead to a setpoint reduction and limit the wind turbine operation. In further examples, the method may be applied to other wind turbine components, particularly electrical components, and more particularly, a generator and/or a power converter.

A further example of a method for determining a maximum power setpoint is schematically illustrated in <FIG>. The example of <FIG> largely corresponds to the example of <FIG>, in that both a feedforward control and a feedback control are incorporated. However, on the feedback side of the control, a number of elements have been added. It should be clear that these same or similar elements might be added in examples having only a feedback control as well.

As for the examples of <FIG>, the temperature of the transformer may be measured or otherwise determined. The temperature of the transformer is used, at <NUM> to determine a transformer temperature error as before. This may form the basic input for a PID control as in the examples of <FIG>.

A temperature measurement may be supplemented with information on the transformer's cooling system as well as on the transformer's operation as determined by the present power output of the wind turbine. A thermodynamic model may be used to complement actual temperature measurements. Input for the thermodynamic model includes information on the activity and characteristics of the cooling system and information on the present power output. The resulting transformer temperature may form input for determining the activity of the transformer cooling system, as illustrated in <FIG>. In this example again, a wind turbine transformer was chosen as an example, but it will be clear that this teaching may be applied to or expanded to other electrical components, and their corresponding cooling systems as well.

In a further aspect, a control system for a wind turbine is provided which is configured to carry out any of the methods for determining a maximum power setpoint as herein disclosed. A control system of a wind turbine may be configured to determine a first temperature of a first wind turbine component, determine a first component temperature error by determining a difference between the first temperature of the wind turbine component and a threshold temperature for the first component. The control system may further be configured to determine a present power output and determine the maximum power setpoint at least partially based on the first component temperature error and the present power output. The control system may further be configured to control the wind turbine based on the maximum power setpoint.

The wind turbine component may be an electrical generator (rotor or stator or both), a power converter or an electrical transformer.

In examples, the wind turbine control system may include one or more sensors to determine the temperature(s) of the wind turbine component(s). In other examples, the wind turbine control system may receive temperature information through a wired or wireless connection.

In yet a further aspect, the present disclosure relates to a wind turbine comprising the wind turbine control system according to any of the examples disclosed herein.

In the examples illustrated so far, the focus has been on a single (electrical) wind turbine component. However, the method may be carried out for several different components simultaneously. Different components may prescribe different maximum power setpoints or setpoint reductions.

As illustrated in <FIG>, taking into account the different maximum power setpoints as prescribed by different components such as the main wind turbine transformer, the wind turbine generator and the power converters (or specific parts of these components), a wind turbine setpoint reduction may be determined as the most limiting maximum power setpoint. An actual power setpoint reduction only occurs if one or more of the maximum power setpoint for different components is lower than the nominal power of the wind turbine.

As illustrated in <FIG>, the resulting setpoint reduction may be fed to the wind turbine controller, which controls the operational settings of e.g. pitch system, generator torque. Other operational settings include e.g. the yaw angle. The actual operational settings do not only depend on the setpoint reduction but also on the prevailing wind conditions. In examples, a method may further comprise pitching the blades and/or reducing rotor speed in order to operate according to the setpoint reduction. By pitching the blades and reducing rotor speed, the power output may be reduced.

In accordance herewith, in yet a further aspect, a method for determining a maximum power setpoint for a wind turbine is provided. A method for determining a maximum power setpoint for a wind turbine comprising measuring a first temperature of a first electrical component of the wind turbine, and comparing the first temperature with a first temperature threshold established for the first electrical component to determine a first temperature error value. The method further comprises determining a present power output of the wind turbine and controlling a first power setpoint of the wind turbine including a feedback control based on the first temperature error value, and a feedforward control based on the present power output of the wind turbine.

As in <FIG>, the first electrical component may be a generator part.

In some examples, the method may further comprise measuring a second temperature of a second electrical component of the wind turbine, comparing the second temperature with a second temperature threshold established for the second electrical component to determine a second temperature error value and controlling a second power setpoint of the wind turbine including a feedback control based on the second temperature error value, and a feedforward control based on the present power output of the wind turbine. A second electrical component may be e.g. a converter (part).

In some examples, the methods may further comprise determining the maximum power setpoint for the wind turbine to be the lower of a rated power of the wind turbine, the first power setpoint, and the second power setpoint.

In some examples, the methods may further comprise operating the wind turbine according to the maximum power setpoint, wherein the operating the wind turbine comprises pitching one or more blades of the wind turbine and/or reducing a rotor speed to operate according to the maximum power setpoint.

In some examples, the method may further comprise measuring a third temperature of a third electrical component of the wind turbine (e.g. the transformer). The method may further comprise comparing the third temperature with a third temperature threshold established for the third electrical component to determine a third temperature error value and determining a third power setpoint based on the third temperature error value. In this case, the method may further comprise determining the maximum power setpoint to be the lower of the rated power of the wind turbine, the first power setpoint, the second power setpoint and the third power setpoint.

As illustrated before, the method may further comprise determining a present power output of the wind turbine, and determining the first and second power setpoints based the first and second temperature error values respectively and on the present power output of the wind turbine.

Both the feedforward control and the feedback control of the examples of <FIG> and <NUM> may rely on PID algorithms. As mentioned before with respect to the example of <FIG>, suitable alternative control algorithms include e.g. H-infinity, LQ, and MPC. The gains values for the PID (or other algorithms) for the feedforward control and the feedback control for individual components may be different.

Those of skill in the art would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both.

The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with one or more general-purpose processors, a digital signal processor (DSP), cloud computing architecture, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) , programmable logic controller (PLC) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein.

The present disclosure also related to computing systems adapted to carry out any of the methods disclosed herein.

The present disclosure also relates to a computer program or computer program product comprising instructions (code), which when executed, performs any of the methods disclosed herein.

The computer program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the processes. The carrier may be any entity or device capable of carrying the computer program.

If implemented in software/firmware, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD/DVD or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. For example, if the software/firmware is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers.

Claim 1:
A method for determining a maximum power setpoint for a wind turbine (<NUM>) comprising:
determining a temperature of a first wind turbine component;
determining (<NUM>) a first component temperature error by determining a difference between the temperature of the first wind turbine component and a corresponding threshold temperature for the first wind turbine component;
determining a present power output of the wind turbine; and
determining (<NUM>) the maximum power setpoint at least partially based on the first component temperature error, and on the present power output of the wind turbine, wherein
determining the maximum power setpoint comprises a feedback control (<NUM>) based on the first component temperature error and comprises a feedforward control (<NUM>) based on present power output.