DE102010054632A1 - Method and device for controlling a drive train of a wind turbine - Google Patents

Abstract

A method for controlling a drive train of a wind power plant, which comprises a rotor (101) with at least one rotor blade, a shaft (205) connected to the rotor and a generator (209) connected to the shaft directly or via a gear (208) a step of determining a manipulated variable influencing the rotational speed of the rotor (101) based on the blade bending moments of the at least one rotor blade.

Description

The present invention relates to a method and apparatus for controlling a driveline of a wind turbine.

Wind turbines drive a generator via a shaft connected to a rotor. A drive train of the wind energy plant consists of a rotor main shaft and - if available - a transmission. A rotational speed of the rotor can be controlled via a generator torque of the generator and a collective pitch of the rotor blades of the rotor.

It is the object of the present invention to provide an improved method and apparatus for controlling a driveline of a wind turbine.

This object is achieved by a method and a device for controlling a drive train of a wind turbine according to the main claims.

The present invention is based on the finding that from a driving moment, which acts from the rotor blades on the drive train of the wind turbine, both conclusions about the torsional load of the drive train and on the rotational acceleration of the rotor can be drawn. The driving torque can in turn be determined from measured values that are usually detected anyway in a wind turbine.

The inventive approach can be used, for example, in a wind turbine with horizontal axis and three rotor blades, in which by a synchronous adjustment of the blade angle, the speed above the rated wind speed can be controlled so that the change in the pitch aerodynamic lift and thus the drive torque in such The system is kept in the range of the rated speed. In this case, the generator torque of the generator of the wind turbine is either kept constant or adjusted so that the system delivers a constant electrical power.

Most of the current wind turbines use a gearbox to translate the low speed of the rotor into a higher speed on the generator side. Due to the fluctuating moment due to changing wind conditions on the side of the rotor, the transmission is exposed to constantly changing loads.

In the collective pitch adjustment arise due to asymmetric aerodynamic loads pitching and yawing moments on the nacelle. The asymmetric loads arise z. As by wind shear in the vertical direction (boundary layers), yaw angle errors, gusts and turbulence, impoundment of the flow at the tower, etc. A known approach to reduce these asymmetric aerodynamic loads is to adjust the pitch of the leaves individually (English: Individual Pitch Control, IPC). Typically, sensors are mounted in or on the rotor blades to measure the blade root bending moments. From this, then, with the help of the known pitch angle of the rotor blade, determines the impact bending moment. It is the moment that acts out of the rotor plane. This then serves as a control variable for the individual blade adjustment.

The inventive approach allows for improved adjustment or regulation of the generator torque of the generator of the wind turbine driven directly by the shaft or via a transmission, so that fluctuating torsional load on the shaft and the entire drive train are reduced. As a result, fatigue loads acting on the shaft are reduced. If the drive train has a transmission, damage to the transmission due to frequent load changes can be prevented.

In addition, an improved adjustment or control of the collective angle of attack is made possible so that a speed deviation of the rotor is reduced from a rated speed. In contrast to the sole measurement of the rotational speed of the rotor, the inventive approach allows a faster intervention in the speed control of the rotor by a direct measurement of the accelerating drive torque.

The present invention provides a method for controlling a drive train of a wind turbine, comprising a rotor with at least one rotor blade, a shaft connected to the rotor and a with the shaft directly or via a gear-connected generator, the method comprising the following step:
Determining a manipulating variable influencing the rotational speed of the rotor based on the sheet bending moments of the at least one rotor blade.

A rotation of the rotor can be transmitted via the shaft to the generator and used to generate electrical energy. The rotor may be rigidly connected to the shaft. The rotation of the rotor can be transmitted via the shaft directly or via an intermediate gear to the generator. The speed can be influenced by changing the aerodynamic properties of the rotor. For example, a position of the rotor or the rotor blades can be changed to the wind. In particular, a collective angle of attack of the rotor blades can be changed in order to influence the rotational speed. Additionally or alternatively, the rotational speed can be influenced by a change on the shaft. In this case, one of the rotation of the shaft and thus the rotor counteracting moment can be changed. In particular, a generator torque counteracting the rotation can be changed in order to influence the rotational speed. Thus, the manipulated variable may include a value for a corresponding change or represent a value that is itself changed to cause the change on the rotor or on the shaft. For example, the manipulated variable may include a value by which the collective angle of attack of the rotor blades or by which the generator torque is changed. Likewise, the manipulated variable may include a value to which the collective angle of attack or to which the generator torque is set. A blade bending moment can be understood as the bending moment that acts on the rotor shaft from the rotor blade at the transition region between a rotor blade and the rotor shaft in the rotor plane. The blade bending moments cause the rotor to rotate about the rotor axis. The sheet bending moments add up to a driving moment acting on the shaft. Each of the leaf bending moments can be determined from leaf root bending moments of the respective rotor blade. Accordingly, the manipulated variable can be determined based on the blade root bending moments of the at least one rotor blade. A blade root bending moment can be understood to mean that bending moment which acts on the rotor shaft from the rotor blade at the transition region between a rotor blade and the rotor shaft along an axis spanning the rotor plane. Each of the blade root bending moments may be measured by one or more appropriately located and suitable sensors. The manipulated variable can be determined from the bending moments using a corresponding determination rule. To determine the manipulated variable can also be used the current speed of the rotor or the shaft. Thus, the manipulated variable can be further determined based on the current speed. The speed can be measured.

According to one embodiment, the manipulated variable may represent a generator torque of the generator driven by the shaft directly or via a transmission. The influencing of the speed by the generator torque is particularly advantageous in operating points of the wind turbine, which are below the rated wind speed of the wind turbine. At these operating points, the angles of incidence of the rotor blades are kept as optimal as possible. The optimum value may be a value at which the wind energy acting on the rotor can best be used to drive the rotor. Accordingly, a change in the angle of attack for influencing the speed is not useful in these operating points.

The generator torque can be determined from a fixed value of the generator torque adapted to a current operating point of the wind turbine and from a variable value of the generator torque which is dependent on the blade bending moments. The operating point may depend on an actual wind speed of the wind acting on the rotor. The fixed value may correspond to an optimum generator torque for the current operating point. For example, by means of the fixed value of the generator torque, an optimal high-speed number of the wind turbine, i. H. an optimal ratio of wind speed and rotational speed of the rotor can be adjusted. When the operating point changes, for example as a result of a change in the wind strength, the fixed value of the generator torque can also be adjusted. The variable value of the generator torque may change due to a change in the sheet bending moments. For example, the variable value may be subtracted from the fixed value of the generator torque to determine the generator torque. The generator torque determined in this way can be set on the generator.

The variable value of the generator torque may be configured to counteract a change in a torsional moment acting on a drive train comprising the shaft. In this way, a rotation of the drive train can be kept constant or nearly constant. As a result, material fatigue or damage to elements of the drive train can be counteracted.

For example, the variable value of the generator torque in addition to the bending moments of a rotational inertia of a hub of the rotor, additionally or alternatively of a rotational inertia of the shaft, additionally or alternatively of one or more rotational inertia of individual or all rotating transmission parts, additionally or alternatively by a rotational inertia of the Generator and additionally or alternatively be dependent on a transmission ratio of the transmission. This allows the main parameters that influence the rotation of the drive train to be taken into account.

According to an embodiment in which the at least one rotor blade has an adjustable angle of attack, the manipulated variable may represent the angle of attack of the at least one rotor blade. This can be done additionally or alternatively to the representation of the generator torque by the manipulated variable. The manipulated variable can represent a value for a collective angle of attack of all rotor blades. The influencing of the speed by the angle of attack is particularly advantageous in operating points of the wind turbine, which are above the rated wind speed of the wind turbine. At these operating points, the pitch of the rotor blades are not set to an optimum value but to a value at which the wind energy acting on the rotor is only partially used to drive the rotor, so that an excessive load on the system is avoided. Accordingly, a change in the angle of attack for influencing the speed can be used in these operating points. Also, in these operating points, the generator torque already have a maximum value, so that the generator torque for further throttling the speed can no longer be used.

For example, the angle of attack can be determined based on the sheet bending moments and a current speed of the wind turbine. This is possible because the driving moment that results from the sum of the bending moments depends on the angles of attack. About such a determination of the angle of attack speed fluctuations can be very well prevented, since it can be reacted to a changing driving torque, even before this causes a speed change.

According to one embodiment, in a step of setting, the generator torque of the generator and additionally or alternatively the angle of attack of the at least one rotor blade can be adjusted based on the manipulated variable. In this way, the method can be advantageously used to perform a powertrain control of a wind turbine.

The present invention further provides an apparatus for controlling a power train of a wind turbine having a rotor with at least one rotor blade, a shaft connected to the rotor and a generator connected directly to the shaft or via a gearbox, with the following feature:
a device for determining a variable influencing the rotational speed of the rotor based on the sheet bending moments of the at least one rotor blade.

The apparatus may be configured to perform the steps of the method for controlling a driveline of a wind turbine. In the present case, a device can be understood as meaning an electrical device which processes sensor signals and outputs control signals in dependence thereon. The device may have an interface, which may be formed in hardware and / or software. The device can receive sensor values, determine the bending moments and the manipulated variable therefrom, and output the manipulated variable to an adjusting device or use it to directly set an element of the wind turbine.

A computer program product with program code which can be stored on a machine-readable carrier such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out the method according to one of the embodiments described above if the program is on a computer corresponding to a computer is also of advantage Device is running.

The invention will now be described by way of example with reference to the accompanying drawings. Show it:

1 a schematic representation of a rotor according to an embodiment of the invention;

2 a schematic representation of a wind turbine according to an embodiment of the invention;

3 a flowchart of a method according to an embodiment of the invention; and

4 a flowchart of another method according to an embodiment of the invention.

The same or similar elements may be provided in the following figures by the same or similar reference numerals. Furthermore, the figures of the drawings, the description and the claims contain numerous features in combination. It is clear to a person skilled in the art that these features are also considered individually or that they can be combined to form further combinations not explicitly described here.

1 shows a schematic representation of a rotor 101 a wind turbine according to an embodiment of the invention. The rotor 101 has three rotor blades whose angle of attack β ₁ , β ₂ , β ₃ can be adjusted. A setting of one of the angles of incidence β ₁ , β ₂ , β ₃ causes a rotation of the respective rotor blade about the longitudinal axis of the rotor blade.

2 shows a schematic representation of a wind turbine with a device 203 for controlling a drive train of the wind turbine. The wind turbine has a tower arranged on a nacelle with a rotor 101 on. The rotor 101 may be one or more or corresponding to 1 have three rotor blades. The rotor 101 is with a nearly horizontal wave 205 over a hub 207 connected. The hub 207 is the rotating part outside the nacelle to which the rotor blades are attached. The wave 205 can be rotatably mounted in a bearing and directly or via a transmission 208 a generator 209 drive. Is the transmission 208 present, so are two individual waves 205 intended. A slowly rotating shaft during operation 205 connects the rotor 101 with the gearbox 208 and a fast rotating shaft during operation 205 connects the transmission 208 with the generator 209 ,

Through one on the rotor 101 acting wind forces act on the rotor blades of the rotor 101 which in turn cause blade root bending moments on the blade roots of the rotor blades. By way of example, a coordinate system arranged on a rotor blade is shown, which is connected to the rotor 101 rotates. The z-axis points in the longitudinal direction of the sheet. Leaf root bending moments acting in the x direction cause a bending moment in the rotor plane M _{BL, i} for each rotor blade _i . The sum of the bending moments in the rotor plane M _{BL, i} correspond to a driving moment that leads to a rotation O of the rotor 101 and thus to a rotation of the shaft 205 leads. The rotation O and the bending moments in the rotor plane M _{BL, i} are rectified. The rotation of the hub acts on the generator torque M _{Gen of} the generator 209 opposite. Thus, the generator torque M _{Gen is} the rotation O of the rotor 101 and the pivotal bending moments M _{BL, i} directed against. The bending moments in the rotor plane M _{BL, i} at one end of the drive train 205 and the generator torque M _Gen at the opposite end of the powertrain 205 lead to a twist of the drive train 205 , A magnitude of the bending moments in the rotor plane M _{BL, i} can be changed by a pitch angle of the rotor blades to the wind while the wind remains the same. The angle of attack can be adjusted by arranged on the blade roots of the rotor blades actuators. The blade root bending moments acting on the blade roots can be detected by suitable measuring devices arranged on the blade roots, for example strain gauges.

The device 203 is configured to determine the rotational speed of the rotor from the values of the blade root bending moments acting on the blade roots from the values detected by the measuring devices 101 determine influencing manipulated variable. This can be done by the device 203 be formed to receive the relevant measured values via an interface of the measuring devices. The device 203 may further comprise an interface for outputting the manipulated variable. According to this embodiment, the manipulated variable on the one hand relate to the generator torque M _gene and on the other hand, the angle of attack of the rotor blades. Thus, the device is 203 designed to set the generator torque M _gene according to the manipulated variable. Furthermore, the device 203 designed to adjust the angle of attack of the rotor blades. In this case, the device 203 be configured to either affect only the generator torque M _gene , only the angle of attack or at the same time the generator torque M _gene and the angle of attack or set. In addition to the leaf root bending moments, the device 203 use further parameters to determine the manipulated variable. The device 203 can be combined with a known pitch control for adjusting the pitch of the rotor blades or include such a pitch control.

According to one embodiment, the device 203 or any other suitable device used to allow improved driveline control of the wind turbine by means of sensors, as it is also used for the individual pitch control.

For this purpose, the bending moments M _{BL, i} , ie the bending moments of the rotor blades in the xy rotor plane are determined from the blade root bending moments measured for the individual pitch control, and from this, in turn, by summation that from the rotor 101 calculated torque acting on the drivetrain. From the knowledge of this torque, the generator torque M _gene can be chosen appropriately, so that the torsional load of the drive train is reduced.

The drive train of a wind turbine needs the torque from the rotor 101 on the generator 209 transfer. As a first approximation, the drive train can be modeled as a two-mass oscillator. The differential equation of the drive train is then

Here e describes the displacement of the drive train, ie the twist due to the load by the transmitted torque. The deflection is negative when the generator 209 from the rotor 101 is driven. J _Hub is the rotational inertia of the hub 207 , J _gene the rotational inertia of the generator 209 , converted to the slowly rotating shaft 205 , J _Gen ie = i ² · _GB * J _Gen wherein J * _gene the actual inertia of the generator 209 is on the fast wave. The slow wave is the shaft driven by the rotor 205 in front of the gearbox 208 , The fast wave is the fast-spinning wave 205 after the transmission 208 , C _Dr and D _Dr are the stiffness and damping of the drive train and i _GB describes the gear ratio. M _gene is the moment acting on the generator. M _{BL, i} is that of the leaves on the hub 207 acting bending moment in the rotor plane. This moment M _{BL, i} can be calculated from the measured blade root bending moments, since it is only rotated by the pitch angle β of the rotor blade. So it applies M _{BL, i} = M _{x, i} cosβ _i + M _{y, i} sinβ _i where M _{x, i} and M _{y, i are} the bending moments measured on the rotor blade by means of corresponding sensors.

wobei unter normalen Betriebsbedingungen e < 0 ist, d. h. der Rotor treibt den Generator an. Basierend auf den gegebenen Gleichungen bestehen nun mehrere Varianten einer verbesserten Regelung.The speed Ω. of the rotor obeys the differential equation

under normal operating conditions e <0, ie the rotor drives the generator. Based on the given equations, there are now several variants of improved control.

According to an embodiment of the present invention, a reduction of driveline vibrations occurs.

From equation (1) it can be seen that the excitation of vibrations of the drive train can be prevented by selecting the generator torque as follows

For constant M _fix is achieved by the fact that the right side of the differential equation is constant. Since the differential equation for the drive train is stable, a constant e is obtained. As a result, the rotation of the drive train is kept constant, whereby no more fatigue loads are introduced. In particular, the torque fluctuations that are introduced due to the tower jam in the drive train (3p excitation frequency in systems with three rotor blades) can cause no damage to the transmission by this method more.

Here, M _{fix is} adapted to the current operating point of the wind turbine. In region 2, below the rated speed of the wind turbine, M _{fix is} constantly being adjusted. A wind turbine can usually be operated at the optimum operating point, if M _{fix is set} in quadratic dependence on the system speed. M _fix is thus constantly changed in this operating area. However, this can be done in a form that causes the least possible load on the drive train by the speed is filtered, so changes of M _fix take place slowly. In region 3, above the rated wind speed, M _{fix is} kept constant.

3 shows a flowchart of a corresponding method for controlling a drive train of a wind turbine, according to an embodiment of the invention. In a first step 311 the relevant leaf root bending moments are measured. From the leaf root bending moments are in one step 313 determines the blade bending moments that act as driving torques for the rotor. Depending on the sheet bending moments is in one step 315 determined according to a determination rule, a value for the generator torque. In one step 317 will be the one in the step 315 used certain value for the generator torque as a manipulated variable for setting the generator.

According to a further embodiment of the invention, an improved speed control takes place.

If equation (2) is considered, a better speed control above the nominal wind speed for the wind turbine can be implemented by measuring the bending moments in the rotor plane M _{BL, i} .

The driving moment M of a wind turbine, ie the sum of the bending moments in the rotor plane M _{BL, i of} the rotor blades, depends on the current speed coefficient λ and the pitch angle β of the rotor blades.

Usually, the system speed Ω is above the rated wind speed. measured and deviations from the target speed by changing the pitch angle β of the rotor blades, the driving torque influenced so that the speed deviations become smaller again. If the driving moment, ie the sum of the bending moments in the rotor plane M _{BL, i of} the rotor blades, can now be measured directly, this allows faster intervention of the speed control. The control can intervene immediately if the measured driving torque deviates from the desired setpoint torque. As a result, speed deviations of the system can be prevented. Prior art system controllers could only react after the acceleration resulting from the moment has been integrated into a speed deviation.

The advantage of the method described is that the disturbance in the control loop is measured directly. Owing to the faster reaction of the regulation, for example, overspeeds in the case of extreme gusts of wind can be better prevented.

To implement the method according to the invention, recourse may be had to known sensor systems for measuring blade root bending moments, as used, for example, for individual pitch control. The measured quantities can be used to control the generator torque and pitch angles, thereby achieving lower torque fluctuations in the driveline and also reducing rotor speed deviations.

Such a regulation can also be used as an addition to existing plant regulations. By the regulation described here, a significant reduction of the loads of the transmission of wind turbines can be achieved.

4 shows a flowchart of a corresponding method for controlling a drive train of a wind turbine, according to an embodiment of the invention. In a first step 311 The relevant leaf root bending moments are measured. From the leaf root bending moments are in one step 313 determines the blade bending moments that act as driving torques for the rotor. Depending on the sheet bending moments is in one step 415 determined according to a determination rule, a value for a collective pitch angle of the rotor blades. In one step 417 will be the one in the step 415 used certain value for the collective pitch angle as a manipulated variable for adjusting the angle of attack of the individual rotor blades.

The exemplary embodiments shown are chosen only by way of example and can be combined with one another. In particular, the inventive approach can also be used in wind turbines having a different type of rotor and a different drive train, for example with a vertically arranged shaft.

LIST OF REFERENCE NUMBERS

101

rotor

203

contraption

205

wave

207

hub

208

transmission

209

generator

311

step

313

step

315

step

317

step

415

step

417

step

Claims (10)

Method for controlling a drive train of a wind turbine, comprising a rotor ( 101 ) with at least one rotor blade, a shaft connected to the rotor ( 205 ) and one with the shaft directly or via a transmission ( 208 ) connected generator ( 209 ), the method comprising the steps of: determining ( 315 ) of the rotational speed of the rotor influencing manipulated variable based on the sheet bending moments of the at least one rotor blade. Method according to Claim 1, in which the manipulated variable has a generator torque from that of the shaft ( 205 ) directly or via a gearbox ( 208 ) driven generator ( 209 ). Method according to Claim 2, in which the generator torque is determined from a fixed value of the generator torque adapted to a current operating point of the wind turbine and from a variable value of the generator torque which is dependent on the blade bending moments. Method according to Claim 3, in which the variable value of the generator torque is designed to allow a change in one of the shafts ( 205 ) To counteract comprehensive powertrain torsional torque acting. Method according to one of claims 3 or 4, in which the variable value of the generator torque is further determined by a rotational inertia of a hub ( 207 ) of the rotor and / or rotational inertia of the shaft ( 205 ) and / or one or more rotational inertias of individual or all rotating gear parts and / or rotational inertia of the generator ( 209 ) and / or a transmission ratio of the transmission ( 208 ) is dependent. Method according to one of the preceding claims, wherein the at least one rotor blade adjustable pitch (β ₁ , β ₂ , β ₃ ) and in which the manipulated variable represents the angle of attack of the at least one rotor blade. The method of claim 6, wherein the angle of attack is determined based on the sheet bending moments and a current speed of the wind turbine. Method according to one of the preceding claims, comprising a step of adjusting the generator torque of the generator ( 209 ) and / or the angle of attack (β ₁ , β ₂ , β ₃ ) of the at least one rotor blade based on the manipulated variable. Contraption ( 203 ) for controlling a drive train of a wind turbine, which has a rotor ( 101 ) with at least one rotor blade, a shaft connected to the rotor ( 205 ) and one with the shaft directly or via a transmission ( 208 ) connected generator ( 209 ), having the following feature: a device for determining a variable influencing the rotational speed of the rotor based on the sheet bending moments of the at least two rotor blades. Computer program product with program code for carrying out the method according to one of claims 1 to 8, when the program is executed on a device.

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