WO2019238188A1

WO2019238188A1 - Adaptive dynamic control system for a hydraulic pitch system

Info

Publication number: WO2019238188A1
Application number: PCT/DK2019/050180
Authority: WO
Inventors: Christian Jeppesen
Original assignee: Vestas Wind Systems A/S
Priority date: 2018-06-11
Filing date: 2019-06-07
Publication date: 2019-12-19

Abstract

Embodiments herein describe a hydraulic pitch system where a velocity (e.g., the velocity of a hydraulic cylinder or the piston rod in the cylinder) is used to dynamically determine a flow gain for the hydraulic cylinder. The flow gain is then used by a pitch controller to generate a setting that controls a hydraulic cylinder which sets a desired pitch angle of a wind turbine blade. In one embodiment, dynamically determining the flow gain takes into account changes in pressure in the chambers of the hydraulic cylinder. That is, unlike other control systems that assume the pressure in the cylinder remains constant, the control system described herein can account for changes in pressure which affect the flow gain.

Description

ADAPTIVE DYNAMIC CONTROL SYSTEM FOR A HYDRAULIC PITCH SYSTEM

BACKGROUND

Field of the Invention

Embodiments presented in this disclosure generally relate to determining a dynamic flow gain associated with a hydraulic cylinder when controlling a hydraulic pitch system that sets a pitch angle of a wind turbine blade.

Description of the Related Art

Many wind turbines use a hydraulic pitch system to control the pitch angles of the rotor blades in order to optimize wind energy production and to ensure that the rotor blades are not subjected to extreme loads during strong winds. Each blade has a pitching arrangement that includes a pitch bearing between a rotor hub and the blade, and a pitching mechanism in the form of a hydraulic actuator that provides force for pitching the blade and maintaining it in a given position. This hydraulic actuator is typically powered by a hydraulic pump.

SUMMARY

One embodiment of the present disclosure is a method of controlling a pitch of a blade in a wind turbine. The method includes providing a reference setting for a hydraulic pitch system which controls the pitch of the blade using a hydraulic cylinder, comparing the reference setting to an actual setting of the wind turbine provided by a feedback loop to output a pitch error signal, determining a reference velocity or a reference acceleration associated with the hydraulic cylinder based on the reference setting, estimating a dynamic flow gain associated with the hydraulic cylinder based on the reference velocity or reference acceleration of the hydraulic cylinder and the pitch error signal, generating, using a pitch controller, a first setting for the hydraulic pitch system based on the pitch error signal and the flow gain, and controlling the hydraulic cylinder based on the first setting. Another embodiment described herein is a control system for controlling a pitch of a blade in a wind turbine. The control system includes a hydraulic cylinder configured to control the pitch of the blade, a first summation module configured to compare a reference setting to an actual setting of the wind turbine provided by a feedback loop to output a pitch error signal, a velocity calculator configured to determine a reference velocity of the hydraulic cylinder based on the reference setting, an active gain control configured to estimate a dynamic flow gain associated with the hydraulic cylinder based on the reference velocity of the hydraulic cylinder and the pitch error signal, a pitch controller configured to generate a first setting for controlling the hydraulic cylinder based on the pitch error signal and the flow gain, and hydraulic controls configured to control the hydraulic cylinder based on the first setting.

Another embodiment described herein is a computer-readable storage medium storing instructions, which, when executed on a processor, perform an operation for controlling a pitch of a blade in a wind turbine, the operation includes providing a reference setting for a hydraulic pitch system which controls the pitch of the blade using a hydraulic cylinder, comparing the reference setting to an actual setting of the wind turbine provided by a feedback loop to output a pitch error signal, determining a reference velocity or reference acceleration associated with the hydraulic cylinder based on the reference setting, estimating a dynamic flow gain associated with the hydraulic cylinder based on the reference velocity or reference acceleration of the hydraulic cylinder and the pitch error signal, generating, using a pitch controller, a first setting for the hydraulic pitch system based on the pitch error signal and the flow gain, and controlling the hydraulic cylinder based on the first setting.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

Figure 1 illustrates a diagrammatic view of a wind turbine, according to an embodiment described in this present disclosure.

Figure 2 illustrates a diagrammatic view of the components internal to the nacelle and tower of a wind turbine, according to an embodiment described in this present disclosure.

Figure 3 illustrates a diagram of a hydraulic pitch system, according to an embodiment described in this present disclosure.

Figure 4 is a flowchart for generating a dynamic flow gain for controlling a hydraulic pitch system, according to an embodiment described in this present disclosure. Figure 5 illustrates a control system for controlling a hydraulic pitch system using a dynamic flow gain, according to an embodiment described in this present disclosure.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments herein describe a hydraulic pitch system that uses a reference velocity (e.g., the velocity associated with a hydraulic cylinder or the piston rod in the cylinder) to dynamically determine a flow gain for the hydraulic cylinder (other type of hydraulic actuator). The dynamic flow gain is then used by a pitch controller to generate a setting for the hydraulic cylinder which sets a desired pitch angle of a wind turbine blade. In one embodiment, dynamically determining the flow gain takes into account changes in pressure in the chambers of the hydraulic cylinder. That is, unlike other control systems that assume the pressure in the cylinder remains constant, the control system described herein can account for changes in pressure which affect the dynamic flow gain.

The reference velocity of the hydraulic cylinder can be derived from the reference position of the hydraulic cylinder. The control system uses the reference velocity and a pitch error signal to determine the dynamic flow gain. In one embodiment, the pitch error signal represents the difference between a desired pitch angle or desired cylinder position from the current pitch angle or current cylinder position. A pitch controller uses the dynamic flow gain and the pitch error signal to generate a control setting for the hydraulic pitch system (e.g., a spool setting in a valve which controls the flow of hydraulic fluid into the hydraulic cylinder). The current pitch angle or cylinder position can be fed back using a feedback loop in the control system. In this manner, a dynamic flow gain (rather than a predefined or constant flow gain) can be used to control a hydraulic pitch system. Moreover, the control system can dynamically determine the flow gain without using pressure sensors to measure the actual pressure in the hydraulic cylinder.

EXAMPLE EMBODIMENTS Figure 1 illustrates a diagrammatic view of a horizontal-axis wind turbine generator 100. The wind turbine generator 100 typically comprises a tower 102 and a wind turbine nacelle 104 located at the top of the tower 102. A wind turbine rotor 106 may be connected with the nacelle 104 through a low speed shaft extending out of the nacelle 104. The wind turbine rotor 106 comprises three rotor blades 108 mounted on a common hub 110 which rotate in a rotor plane, but may comprise any suitable number of blades, such as one, two, four, five, or more blades. The blades 108 (or airfoil) typically each have an aerodynamic shape with a leading edge 112 for facing into the wind, a trailing edge 1 14 at the opposite end of a chord for the blades 108, a tip 1 16, and a root 1 18 for attaching to the hub 1 10 in any suitable manner.

For some embodiments, the blades 108 may be connected to the hub 110 using pitch bearings 120 such that each blade 108 may be rotated around its longitudinal axis to adjust the blade’s pitch. The pitch angle of a blade 108 relative to the rotor plane may be controlled by linear actuators, hydraulic actuators, or stepper motors, for example, connected between the hub 110 and the blades 108.

Figure 2 illustrates a diagrammatic view of typical components internal to the nacelle 104 and tower 102 of a wind turbine generator 100. When the wind 200 pushes on the blades 108, the rotor 106 spins and rotates a low-speed shaft 202. Gears in a gearbox 204 mechanically convert the low rotational speed of the low-speed shaft 202 into a relatively high rotational speed of a high-speed shaft 208 suitable for generating electricity using a generator 206.

A controller 210 may sense the rotational speed of one or both of the shafts 202, 208. If the controller decides that the shaft(s) are rotating too fast, the controller may signal a braking system 212 to slow the rotation of the shafts, which slows the rotation of the rotor 106 - i.e., reduces the revolutions per minute (RPM). The braking system 212 may prevent damage to the components of the wind turbine generator 100. The controller 210 may also receive inputs from an anemometer 214 (providing wind speed) and/or a wind vane 216 (providing wind direction). Based on information received, the controller 210 may send a control signal to one or more of the blades 108 in an effort to adjust the pitch 218 of the blades using, for example, a hydraulic pitch system. By adjusting the pitch 218 of the blades with respect to the wind direction, the rotational speed of the rotor (and therefore, the shafts 202, 208) may be increased or decreased. Based on the wind direction, for example, the controller 210 may send a control signal to an assembly comprising a yaw motor 220 and a yaw drive 222 to rotate the nacelle 104 with respect to the tower 102, such that the rotor 106 may be positioned to face more (or, in certain circumstances, less) upwind. Figure 3 illustrates a diagram of a hydraulic pitch system 300, according to an embodiment described in this present disclosure. The system 300 includes a hydraulic cylinder 305 through which a piston rod 330 extends (also referred to as simply a “piston 330”). The hydraulic cylinder 305 is divided into two chambers depending on the location of the piston 330: Chamber A 310 and Chamber B 315. That is, the left end of the piston rod 330 divides Chamber A 310 from Chamber B 315. Thus, as the piston 330 moves left to right or right to left, the piston 330 changes the size of the chambers. For example, moving the piston 330 to the right as shown by the arrow 170 increases the size of the Chamber A 310 but decreases the size of Chamber B 315. The hydraulic cylinder 305 includes a first end 325 and a second end 320 (disposed on a distal end of the piston 330). In one embodiment, the first end 325 (which is part of the piston 330) is coupled to a blade actuator which changes the pitch of a wind turbine blade relative to the rotor hub. The second end 320 of the cylinder 305 may be fixably attached to a portion of the hub such that the second end 320 does not move while the piston 330 travels in and out of the cylinder 305. Alternatively, the second end 320 may be coupled to a blade actuator while the first end 325 remains stationary.

The position of the cylinder 305 controls the pitch of the blade. That is, for each position of the cylinder 305 (or more specifically, the position of the piston 330 in the hydraulic cylinder 305) there is a corresponding pitch angle of the blade. Thus, by moving the cylinder 305, the wind turbine controller can set the pitch of the blade.

To move the piston 330, the system 300 includes a valve 335, a pump 350, and a tank 360. The pump 350 pressurizes a hydraulic fluid (e.g., hydraulic oil) in the system 300. In this example, the pump 350 pumps the fluid towards the valve 335 (e.g., a

proportional valve) which includes a spool 340 for directing the fluid either to Chamber A 310 or to Chamber B 315. In Figure 3, the spool 340 is set to direct the fluid received from the pump 350 to Chamber A 310 as shown by the arrows. That is, the spool 340 directs the fluid received at port 345B to port 345A. As a result, the hydraulic fluid pushes the piston 330 to the right as shown by the arrow 170. The hydraulic fluid exits from Chamber B 315, flows into the valve 335 at port 345C, exits the valve 335 at port 345D, and flows into the tank 360.

This process can be reversed to move the piston 330 in the opposite direction of the arrow 170. That is, the setting of the spool 340 can change such that fluid received from the pump 350 at port 345B exits at port 345C and enters Chamber B 315. This then moves the piston 330 to the left thereby increasing Chamber B 315 and reducing Chamber A 310. The fluid flowing out of Chamber A 310 enters the port 345A and exits the port 345D as it flows into the tank 360. In this manner, the valve 335, and more specifically, the position of the spool 340 in the valve 335, controls the flow of the hydraulic fluid into and out of the Chambers A and B which controls the position of the piston 330 and the pitch of the blade.

Figure 4 is a flowchart of a method 400 for generating a dynamic flow gain for controlling a hydraulic pitch system (such as the one illustrated in Figure 3), according to an embodiment described in this present disclosure. For clarity, Figure 4 is discussed in tandem with a blade pitch control system 500 illustrated in Figure 5. Generally, the control system 500 in Figure 5 can control a hydraulic pitch system using a dynamic flow gain, according to an embodiment described in this present disclosure.

At block 405 of method 400, the blade pitch control system 500 receives a reference pitch angle {0_ref) from an upstream control system (e.g., a wind turbine controller for controlling the overall wind turbine, or a wind plant controller which controls a plurality of wind turbines in a plant). Generally, the reference pitch angle indicates a desired pitch angle of the blades. The reference pitch angle may change due to changing wind conditions or changing demand for power in the grid.

At block 410, the control system 500 converts the reference pitch angle to a reference position setting of the hydraulic cylinder. Although a hydraulic cylinder is specifically described, the embodiments herein can be used with any type of hydraulic actuator that sets the pitch angle of a wind turbine blade. In Figure 5, a position converter 505 converts the reference pitch angle to a position setting of the hydraulic cylinder [x_{P re}f)· In one embodiment, each reference pitch angle corresponds to a particular reference position of the hydraulic cylinder. For example, to achieve a particular blade pitch (e.g., 3 degrees), there is a corresponding position setting of the hydraulic cylinder where moving the cylinder to that setting results in the desired blade pitch. The position converter 505 may store a mapping between the reference pitch angles and the position settings of the hydraulic cylinder.

At block 415, the control system 500 compares the position setting to an actual position setting of the hydraulic cylinder to output a pitch error signal. As shown in Figure 5, the control system 500 includes a summation module 525 which receives the position setting {x_pxef) from the position converter 505 and the actual setting (which can be measured or derived) of the position of the hydraulic cylinder (x_p) using a feedback loop 560. Put differently, the feedback loop 560 permits the current value of the position setting (x_p) of the hydraulic cylinder to be fed back and compared to the desired or reference value of the position setting [x_pxef)· The pitch error signal outputted by the summation module 525 represents the difference between the current value of the position setting and the desired value of the position setting.

At block 420, the control system 500 determines a reference velocity of the hydraulic cylinder using the reference position setting. This is performed in the control system 500 by a velocity calculator 515. In Figure 5, the velocity calculator 515 receives the reference position setting of the hydraulic cylinder {x_pxef) and generates a reference velocity of the hydraulic cylinder (or a reference velocity of the piston rod in the cylinder) {x_p.ref)· ^{ln one} embodiment, this velocity is calculated by comparing the current desired position setting to at least one previous desired position setting. For example, the velocity calculator 515 may store values of previous position settings derived from previous pitch reference signals. In one embodiment, the velocity calculator 515 performs a backward Euler approximation using the current position setting and a previous (or historical) position setting or settings to derive the velocity. Although a backward Euler approximation is specifically mentioned, the velocity calculator 515 can use any control algorithm or technique to derive the reference velocity using current and historical values of a control setting (e.g., a reference pitch angle or a position setting of the hydraulic cylinder).

Although block 420 is described as generating a reference velocity using the reference position setting, the control system 500 may also generate a reference acceleration of the hydraulic cylinder instead. Nonetheless, the explanation that follows is described using a reference velocity but could be adapted for use with a reference acceleration.

At block 425, the control system 500 generates a dynamic flow gain using the reference velocity and the pitch error signal. To do so, the reference velocity of the hydraulic cylinder and the pitch error signal are provided to an active gain control 520 which determines a dynamic flow gain corresponding to the hydraulic cylinder using the reference velocity and the error signal. Thus, unlike control systems that use a predefined or constant flow gain which may be set once and then used for the entire life of the turbine, the active gain control 520 dynamically determines the flow gain as the pressure in the hydraulic cylinder fluctuates as a result of loading on the wind turbine caused by, e.g., changes in wind speed. Put differently, rather than assuming the pressure in the hydraulic cylinder is constant, the active gain control 520 can adjust the flow gain in response to changing chamber pressure. Further, the active gain control 520 can dynamically calculate the flow gain without directly measuring the pressure in the chambers of the hydraulic cylinder.

The following equation illustrates the relationship between the reference velocity of the hydraulic cylinder position (x_s) of the hydraulic cylinder (or the position of the piston rod in the cylinder), the dynamic flow gain (K_g), and the flow (Q_A) across an orifice in a proportional value of a hydraulic pitch system.

Equation 1 illustrates the flow (Q_A) across the orifice when flowing into Chamber A of the hydraulic cylinder. As shown, the flow is determined by the dynamic flow gain ( K_g ), the pressure of the pump (P_s) supplying fluid to the hydraulic cylinder, the pressure of Chamber A ( P_A ) in the hydraulic cylinder, and the current position or setting of the spool (x_s) in the valve. The flow into Chamber B ( Q_B ) (i.e., when the piston rod has a negative velocity or a velocity in the opposite direction) can be expressed using a similar equation as Equation 1 except P_A is replaced with the pressure in Chamber B (P_s). Moreover, the value of the flow gain K_g may change as the reference velocity changes between negative and positive values. Equation 1 can be rearranged to express a relationship between velocity (x_p) and the flow gain as follows:

Equation 3 can be simplified by defining a gain term T_p that represents the simplified dynamics of the hydraulic pitch system.

A similar gain term can be identified when the reference velocity is negative (and hydraulic fluid flows into Chamber B).

The inverse dynamics of the gain term can be expressed as follows:

Equation 6 introduces an inverse gain term (G) which can be correlated to a particular spool position or setting using the current velocity of the hydraulic cylinder. However, there may also be some uncertainties associated with Equation 5 which are represented by v in the following equation. Put differently, the value g represents uncertainties that may occur when estimating the inverse gain term G. x_s = G x_p + v (6) Based on the system described in Equation 6, a control algorithm can be expressed as:

In Equation 7, e is the pitch error signal outputted by the summation module 525 and can be expressed as x_p - x_pref, while k_p is a proportional controller gain. Further, the (^L) above the inverse gain term G and the uncertainties value v indicate these terms are estimates. That is, because the control system cannot directly measure the pressures in Chambers A and B, these terms are estimated values. For example, the control system may have not have any pressure sensor capable of measuring the pressure in the hydraulic cylinder, or may have a sensor for measuring a pressure in only one chamber, but not both. In any case, Equation 7 represents a control algorithm for estimating the inverse gain term and the uncertainties that may be involved when doing so.

Using Equation 7, the terms f and v can be put into vector form.

The other terms in Equation 7 can also be expressed in vector form as follows:

Combining the vectors in Equations 8 and 9 yields: x_s = Ya (10) An adaption law for the estimate in Equation 8 can be expressed as:

(1 1 )

In Equation 1 1 , g_± and y₂ are positive controller scalar values. In one embodiment, these positive scalar values are constant for the life of the wind turbine. Because the pitch error signal (e) and the reference velocity

are provided as inputs and the scalar values (y_{1 ;} y₂ , and k_p) are known, the active gain control 520 can use Equation 1 1 to calculate the gain term f and the uncertainty term v in Equation 8. These estimated values of the gain term and the uncertainty term are then transmitted to the pitch controller 530. The velocity calculator 515 and the active gain control 520 use the reference position of the hydraulic cylinder to generate the gain term f and the uncertainty term v which are used to adjust (or adapt) the pitch controller 530 in parallel with the pitch error signal and the reference velocity x_{P re}f-

In one embodiment, Equation 1 1 can be modified to remove the k_pe term and the resulting relationship can be used to estimate the gain and uncertainty terms in

Equation 8.

In one embodiment, when hydraulic pitch systems have a valve and a hydraulic cylinder that have unmatched cross sectional errors, two different gain terms may be tracked. That is, the active gain control may determine first adaptive terms when the reference velocity (or pitch rate) is negative and second adaptive terms when the reference velocity (or pitch rate) is positive.

At block 430, the control system 500 generates a setting for controlling the hydraulic cylinder using the dynamic flow gain and the pitch error signal. The active gain control 520 provides the gain term f (which is derived from the dynamic flow gain K_g) and the uncertainty term y to the pitch controller 530 which, along with the pitch error signal, outputs the first position setting. In this example, the pitch controller 530 outputs a valve spool position (x_{s pc}). That is, in this embodiment, the first position setting is a position setting for the spool in the valve that controls the flow of hydraulic fluid into the hydraulic cylinder. While Figure 5 illustrates controlling the position of the hydraulic cylinder using the position of the spool, the embodiments herein are not limited to such and can use any technique for controlling the position setting of a hydraulic cylinder.

Non-limiting advantages of using the active gain control 520 to generate the adaptive values include improved robustness when load conditions on the wind turbine change (e.g., as a result of changing wind conditions) and reducing the number of sensors in the wind turbine. Stated differently, the active gain control 520 can calculate (or estimate) the gain term and any uncertainty associated therewith without using pressure sensors that measure the pressure in the chambers in the hydraulic cylinder. That is, the control system 500 can react to changes in pressure in the hydraulic cylinder (as a result of changing load conditions) without measuring the pressures in the cylinder using a sensor.

At block 435, the control system controls the hydraulic cylinder using the setting (e.g., the valve spool position) generated by the pitch controller 530. Continuing with the control system 500, the valve spool position generated by the pitch controller 530 is provided to a spool reference generator 540 which calculates a valve spool position reference x_sxef. ^|n one embodiment, the spool reference generator 540 includes a dead band compensator which adjusts the valve spool position reference to compensate for a dead band where flow does not change (e.g., -10% to 10%).

The output of the spool reference generator 540 is provided to valve controls 545 that adjust the spool valve position according to x_s. This setting then affects hydraulic controls 550 and causes the cylinder to change its position x_p - e.g., the piston rod moves relative to the cylinder - thereby causing a corresponding movement in a blade actuator 555 which sets the pitch of the blade. In one embodiment, the moment on the blade M_made is the moment around the center axis of the blade. As shown, the moment M_blade can affect the hydraulic cylinder with a force which affects the pressure in both chambers.

As discussed above, the feedback loop 560 permits the current value of the position setting (x_p) of the hydraulic cylinder to be fed back and compared to the desired or reference value of the position setting {x_pxef)·

In the preceding, reference is made to embodiments presented in this disclosure. However, the scope of the present disclosure is not limited to specific described embodiments. Instead, any combination of the features and elements provided above, whether related to different embodiments or not, is contemplated to implement and practice contemplated embodiments. Furthermore, although embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the scope of the present disclosure. Thus, the aspects, features, embodiments and advantages described herein are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s).

As will be appreciated by one skilled in the art, the embodiments disclosed herein may be embodied as a system, method or computer program product. Accordingly, aspects may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a“circuit,”“module” or“system.” Furthermore, aspects may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.

The present invention may be a system, a method, and/or a computer program product. The computer program product may include a computer-readable storage medium (or media) (e.g., a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention. Aspects of the present disclosure are described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments presented in this disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality and operation of possible implementations of systems, methods and computer program products according to various embodiments. In this regard, each block in the flowchart or block diagrams may represent a module, segment or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. In view of the foregoing, the scope of the present disclosure is determined by the claims that follow.

Claims

CLAIMS:

1. A method of controlling a pitch of a blade in a wind turbine, comprising:

providing a reference setting for a hydraulic pitch system which controls the pitch of the blade using a hydraulic actuator;

comparing the reference setting to an actual setting of the wind turbine provided by a feedback loop to output a pitch error signal;

determining at least one of a reference velocity and a reference acceleration associated with the hydraulic actuator based on the reference setting;

estimating a dynamic flow gain associated with the hydraulic actuator based on at least one of the reference velocity and reference acceleration and the pitch error signal;

generating, using a pitch controller, a first setting for the hydraulic pitch system based on the pitch error signal and the flow gain; and

controlling the hydraulic actuator based on the first setting.

2. The method of claim 1 , wherein the dynamic flow gain represents a flow through an orifice in a valve controlling flow of hydraulic fluid to the hydraulic actuator.

3. The method of any of the preceding claims, wherein determining the dynamic flow gain comprises:

determining the dynamic flow gain using a plurality of positive constant scalar values associated with a control system of the wind turbine.

4. The method of any of the preceding claims, further comprising:

generating an uncertainty value associated with estimating the dynamic flow gain,

wherein generating, using the pitch controller, the first setting for the hydraulic pitch system is also based on the uncertainty value.

5. The method of any of the preceding claims, further comprising:

receiving a reference pitch; and

deriving the reference setting for the hydraulic actuator using the reference pitch using a predefined geometric relation.

6. The method of any of the preceding claims, further comprising:

determining the reference velocity of the hydraulic actuator based on comparing the reference setting to at least one historical value of the reference setting.

7. The method of any of the preceding claims, wherein the actual setting of the wind turbine is based on at least one of a current pitch angle of the blade and a current position setting of the hydraulic actuator which is provided by the feedback loop.

8. A control system for controlling a pitch of a blade in a wind turbine, the control system comprising:

a hydraulic actuator configured to control the pitch of the blade;

a first summation module configured to compare a reference setting to an actual setting of the wind turbine provided by a feedback loop to output a pitch error signal; a velocity calculator configured to determine a reference velocity of the hydraulic actuator based on the reference setting;

an active gain control configured to estimate a dynamic flow gain associated with the hydraulic actuator based on the reference velocity and the pitch error signal;

a pitch controller configured to generate a first setting for controlling the hydraulic actuator based on the pitch error signal and the flow gain; and

hydraulic controls configured to control the hydraulic actuator based on the first setting.

9. The control system of claim 8, wherein the dynamic flow gain represents a flow through an orifice in a valve controlling flow of hydraulic fluid to the hydraulic actuator.

10. The control system of claims 8 or 9, wherein determining the dynamic flow gain comprises:

1 1. The control system of any of claims 8-10, wherein the active gain control is configured to generate an uncertainty value associated with estimating the dynamic flow gain, and wherein the pitch controller is configured to generate the first setting based on the uncertainty value.

12. The control system of any of claims 8-11 , further comprising:

a position converter configured to:

receive a reference pitch angle, and

derive the reference setting for the hydraulic actuator using the reference pitch using a predefined geometric relation, wherein the reference setting comprises a reference position of the hydraulic actuator.

13. The control system of any of claims 8-12, wherein the velocity calculator is configured to determine the reference velocity of the hydraulic actuator based on comparing the reference setting to at least one historical value of the reference setting.

14. The control system of any of claims 8-13, wherein the actual setting of the wind turbine is based on at least one of a current pitch angle of the blade and a current position setting of the hydraulic actuator which is provided by the feedback loop.

15. A computer-readable storage medium storing instructions, which, when executed on a processor, perform an operation for controlling a pitch of a blade in a wind turbine, the operation comprising:

providing a reference setting for a hydraulic pitch system which controls the pitch of the blade using a hydraulic actuator; comparing the reference setting to an actual setting of the wind turbine provided by a feedback loop to output a pitch error signal;

controlling the hydraulic actuator based on the first setting.