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Multivariable robust blade pitch control design to reject periodic loads on wind turbines

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Abstract

The demand on sustainable operations of large-scale wind turbines necessitates the concurrent advancement of power regulation and load mitigation through blade pitch control. Traditional collective pitch control (CPC) mechanisms can only deal with symmetric disturbances. The advent of individual pitch control (IPC) provides new opportunities to mitigate asymmetric or periodic loads on blades. Nevertheless, difficulties in control synthesis remain. In order for IPC to be truly effective, the complicated dynamic coupling between turbine components has to be accounted for. Moreover, wind turbine dynamics is highly nonlinear, and significant modeling uncertainties exist. In this research, a multivariable robust IPC framework is developed, aiming at rejecting periodic loads. The inter-blade coupling is explicitly modeled to provide response characteristics in the frequency domain. Subsequently, the structured singular values (μ)-synthesis strategy is adopted, as it shows distinct capability of dealing with periodic loads. In particular, weighting functions can be tailored to suppress response peaks at periodic frequencies with guaranteed robustness. Systematic case investigations indicate that, with the proposed IPC strategy, one can achieve significant periodic load mitigation as well as fatigue alleviation in speed-varying wind fields.
Multivariable Robust Blade Pitch Control Design to Reject Periodic Loads on Wind Turbines
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Abstract
      2      .  3  2      
32
*&, 32  
    *4&,    3                 2
5             4      4&    2      
   23 2    2     3
2                  6  3    2
34224&37
0.26
    8  28     *9,.
      3 2   3 2  
8432
 7   8 3  2   
34&3
.3
Keywords: :2  2 0   2  9.

1. Introduction
;3223
 8 2 22
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 *&,  3    2  0   3  
   3  <-.+>        
    2     A  6  ;  B4%C          3
.68*A.CB ,
223<$> %2327
2323
3<)!>%32
*%,23</))>
43323;20
   2  2 3       <)#>   
.324*4&,
3        2            7       
<)#>2
BDE  3     4 <)=>      
;    3    .  .     3      
3=P*,6 4
<)->4&233.223
3  33 6
32223236222
3 <->  %    3  3   2    3  
36
;  2  2   2
A3243
3 323  3  4&
2
2   : 2  
3%
8;
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 2 
322 8
73232<#@>
 37
3 :2
 3 3    C = 2   
22.32:2
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32323:.
2 *I,   8
233:;
  *
,.  2 2
7          3       4        3

.78%
2 22 23
2
;332I
 #2237 =
          -  
; /
2. Wind Turbine Modeling
2.1 General equations of motion
%3273 6
/$=J I;K3 <#+>32;32'
;632632G3;63
237.%;32
22326
  3 22 3 
8227
%  3  
  3         
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4 3   A % 2 *A% , 
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; 282 3LA *
,6;
3.8 <=#> 2023
3  3    3 LA    LA      
3LA.LA%30
322
2322
       A    2     2  ;  2.  3      
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      3 2 <@ #@>  4  2   3 
3 <#@==>3 
4;32
 3        ;    A%  
63
d d
d d
 
 
x Ax Bu B u
y Cx Du D u
*/,
3x2yu
d
u
2
2 )  
2 #  
2 =  
 
2 )  
2 #  
2 =  
 
2 )  2 
2 # 
 
 
 
 
 
 
 
 
 
 
 
x
y 2 
2 =  2 
 
 
 
 
 
 
*",
2 )  
2 #  
2 =  
; 2. 3 
; 3 
 3 
d
 
 
 
 
 
 
 
 
 
 
u
u
*@,
4 3 2    23.   8     
  3  2         6 
 4 2.          8 
6   G 3    2.     3   
8<#$>4333
22
;2.3
2.2 Multi-blade coordinate (MBC) transformation
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B43 L
33
3348*/,2A% 322
6 <=->4
23233
                3      3     .2    *I,
                       .  
*363,
3  3    I          .
 2 <=/>  C   3   I  3 2   
  23  ;  2      ;          2
2<=">;326
I<=->
2626
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   
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   
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 
 
*+,
 
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  
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  
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T
   
   
 
 
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   
 
   
 
   
 
 
   
 
   
 
   
 
*$,
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%    * 3 ,  A%   ; .
 .2 ;   .        2
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2 2 2 2 2 2 2
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2.6%32B4
326332
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2.3 Open-loop transfer functions
% ##I B4 6
;332 72
564
33233 ;
2 G3 3
2 ; :
)+H)-H)"H#!H
##HA)A#
    .  8    23              3

-100
0
100 tilt
0
180
360
-100
0
100
10 010 2
-720
0
720
yaw
10 010 2
Uncertain model
Nominal model
Bode Diagram
Frequency (Hz)
A)833
23*)+H3,3
*)-H)"H#!H##H3,
A )3 833
:32
               8        ;  
2)+H 3A% :3)-H)"
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H#! H##H 382A% 
3332B4
*)+H,3323
8 22.
3
-50
0
50
100
ud avg
-720
0
720
1440
-100
0
100
10 0
-720
0
720
ud tilt
10 0
ud yaw
10 0
Uncertain model
Nominal model
Bode Diagram
Frequency (Hz)
A#823
23*)+H3,
3*)-H)"H#!H##H3,
A#382*;
2, 3  : 2 2 ; 
23*

d
u
3
d
u
,@!I+!I;3*

d
u
,
       #! I  =! I 3     
 2 2    2 2  
37
3. Robust Individual Control Formulation
6  3 2       
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    nP 8 *3 P    8     
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 % 3 2     20   2 6 
 3  3 3      <-> 3 3  2 
0  
 2 02; :
 3   27 5CB .2 3 2    
L3    23 3   
38
3.1 Baseline controllers
4       3
22.
*E &4,<#$>E &43;2
    2  2    :     3  3
2283023
      2    &4.2   
3..2 <)=>
: 72
3%3&4
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   ! 
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)P    4 3  3  8   # P =P  -P 8
3    3.8   4  3        3
2   6  I   3    4 
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2
3.2 Proposed control structure for individual pitch control
% ;67   
3243
      3             2  ;    
         A = 3 3   
273
       L                    3
            2  2; 
     4       2   
     3    6   I    
     3  27  
I3

G3
H

H

3..32323
34223
  3      0    8        8      
A226
;
H
2
r
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M
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A=27
3.3 Structured singular value (µ)-synthesis
4      3        ;        *9,.  
22;3A=

μ
.3222
  2           3
7   3       M. 
8
3A-:
2222G
3              2           2    
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332.<=@>
&2*C&,3A63
2w2238=P*
6,3206 S
      8     4            3  6
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W
    
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W W I
3
p
W
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l
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   .
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 =P *!"G;,80#P-PR8
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  
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  G 8 2 -P   
223
3 3 
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23 2   
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       2   
23:
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W W I
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u
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3
32323223 
82
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A/383
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3
2  2         6
  2         <=@>     
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         2      
..2
3320 3
3   2   ; 
  3  2         A "  4  2
238.33
 .        =P 8    3  
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A@.8333
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!)@+-C C&
  3     A @   2     3
        3      4                     
   L    2                8  
.383
      3  8   :    = P 8      .    
2                 .  .      2

4. Results and Performance Comparison
                      
362H 7
 5CBA%  <=#>   
27322 <#$>2
322 <-!>3)!.
I323323
26
  2 . *E &4, <#$> &4.2
 <)=>2243
2&4.22
E &4 
E &43</>
4.1 Nominal performance around the operating point
:      6               :    
323)+H3)-J2
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*,*2,
*,*,
A+.E &4&4.2
2*,:*)+H23,N*2,E
N*,&N*,I)3
A+*,323A+*2,S+*,3.
2)2)3:
2)  22# 2= 
AA +*2,322&4.2
2        62              
  D  C      
&4.22!!+#=
!!@-=    !!@/-                    3
 2    2   
        % 3  A +*,    2  
   8      3   5  
38 C 
        &4.2            2    
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8*B,3
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4.2 Robust performance
62333
 :3.
2)2)3)-H23
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 !!/$+!!/-"!!/-@   )+H 23
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C &4.2
          2        3    A  $*,  
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4.3 Load mitigation and fatigue alleviation
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    &  2 3  4
2& 2+@"$J+@+$J
2
4  3   2       &    =P 8
2 =P 8  223   =-

A 3 6  2    3 3     
)+H:.3)-H)"H)+H#!H
##H8*B,A))3
C= 3
2 3B 2 3 B3 2. 
B32.BA)) %
          2   I    &4            2
23B 
3 #!J    3     2  3  B  2
 2 2    3        2 /J  
32.B66223
      3 2 .  B   2 =J.)!J 2  
   L    2     ;
233

*,*2,
#-
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/@"
/@@
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/+!
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/+#
/+=
/+-
/+/
/+"
/+@
/++
/+$
/$!
/$)
/$#
/$=
/$-
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
*,*,
A))23B*,23B*2,
32.B*,32.B*,
&42 ' '&4
 'C2
5. Conclusion
          3  2      3        2
%  7     3        3
22C=
3%322
223  .2  *I, 
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Acknowledgment
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References
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... For an offshore floating WT, stable power output and load mitigation are typically required to increase service life and lower maintenance costs [4,5]. Generally, this objective can be achieved via pitch control mechanisms [6,7]. Current designs employ collective pitch control (CPC) and individual pitch control (IPC) techniques, in which the IPC has been deemed as a more effective way for mitigating the load without affecting the turbine's power output [8][9][10]. ...
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To stabilize the power out and reduce the dynamic loads in the over‐rated state, the pitch system is key for regulating pitch angle to the desired one obtained from the command layer. Here, actuator failure of the pitch system is considered and a neural adaptive fault‐tolerant control strategy with a rate function is proposed. More specifically, a non‐linear model of the pitch system considering time‐varying parameter uncertainties and unknown disturbances is established firstly. Then, the neural network is used to counteract the external disturbance and system uncertainty. The rate function with adjustable parameters is designed to transform the error, which makes the tracking error decrease at a fast rate and converge to a small zero domain, and realize the control goal of accurate and fast tracking the desired pitch angle of the pitch system. A co‐simulation is developed, and the merits of the proposed method are verified.
... This makes it possible to use simple linear single-input and single-output (SISO) control approaches for IPC, such as proportional-integral (PI) controllers (Bossanyi, 2005;. More recently, other advanced IPC approaches, such as fixedstructure H ∞ feedback-feedforward IPC (Ungurán et al., 2019) and multivariable robust IPC (Yuan et al., 2020), were developed to mitigate the blade loads on the wind turbine. On the other hand, the application of IPC to wake load control in a wind farm is receiving increasing attention (Knudsen et al., 2015). ...
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Individual pitch control (IPC) is a well-known approach to reduce blade loads on wind turbines. Although very effective, IPC usually requires high levels of actuator activities, which significantly increases the pitch actuator duty cycle (ADC). This will subsequently result in an increase of the wear on the bearings of the blades and a decrease of the wind turbine reliability. An alternative approach to this issue is to reduce the actuator activities by incorporating the output constraints in IPC. In this paper, a fully data-driven IPC approach, which is called constrained subspace predictive repetitive control (cSPRC), is introduced. The output constraints can be explicitly considered in the control problem formulation via a model predictive control (MPC) approach. The cSPRC approach will actively produce the IPC action for the necessary load reduction when the blade loads violate the output constraints. In this way, actuator activities can be significantly reduced. Two kinds of scenarios are simulated to illustrate the unique applications of the proposed method: wake–rotor overlap and turbulent sheared wind conditions. Simulation results show that the developed cSPRC is able to account for the output constraints into the control problem formulation. Since the IPC action from cSPRC is only triggered to prevent violating the output constraints, the actuator activities are significantly reduced. This will help to reduce the pitch ADC, thus leading to an economical viable load control strategy. In addition, this approach allows the wind farm operator to design conservative bounds to guarantee the safety of the wind turbine control system.
... New coating materials for the protection of turbine blades from rain and wind erosion are also being developed ( Elhadi Ibrahim et al., 2020;Singh et al., 2020;Hong et al., 2021;Elhenawy et al., 2021). The efforts are being made to design variable rotor-speed pitch control systems for the turbine to operate C o p y r i g h t T a y l o r & F r a n c i s L L C / F o r P e r s o n a l U s e O n l y at high wind speeds ( Colombo et al., 2020;Bundi et al., 2020;Sarkar et al., 2020;Yuan et al., 2020). Various reliable controller algorithms based on fuzzy logic are being introduced for utilization in pitch controller units ( Civelek, 2020;Chavero-Navarrete et al., 2020). ...
Chapter
The energy demand is rapidly increasing globally, and extensive use of conventional energy resources is causing global warming, environmental pollution, health issues, etc. Fossil energy resources are declining rapidly, while wind energy is a cost-effective and promising energy source amongst renewable energy resources. The understanding and development of wind energy technologies is thus a necessity in the field of green energy production. This chapter provides exposure to the wind energy conversion systems along with the current status and future perspective of wind energy technologies. Furthermore, the socio-economic and environmental challenges of wind energy systems are also discussed in this chapter.
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In a wind turbine (WT), the maximum power can be achieved using a suitable and smooth signal, which should be applied to the pitch angle of the blades (PABLE). On the contrary, the uncertainties of the WT models cause the fatigue due to the mechanical stresses. To overcome these two problems, dynamic sliding mode control (D-SMC) is used because it is robust against uncertainties and can suppress the chattering by providing smooth signals. In D-SMC, an integrator is located before the actuator, as a low-pass filter, to suppress the high-frequency chattering. Then, the states number of the overall augmented system is one more than the states number of the actual system. To control such an augmented system, the added state variable needs to be estimated and hence, a novel sliding mode observer (SMO) is proposed. A trusty comparison is also presented using the conventional sliding mode control (C-SMC) with the proposed SMO. To implement D-SMC and C-SMC, a new state feedback is applied to the turbine at first. Therefore, a linear model with uncertainty is obtained, where its input is the PABLE. Lyapunov theory is used to proof the stability of the proposed SMO, D-SMC, and also the C-SMC. The presented comparison demonstrates the advantages of the D-SMC with respect to the C-SMC in removing the chattering and simplicity in concept and in implementation.
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This work proposes a robust tuning method for full-load pitch control by deriving new design formulae for collective Proportional Integral (PI) pitch controllers. The paper investigates the frequency domain characteristics of a full state linearized turbine model extracted from the aeroelastic simulation tool HawcStab2, and suggests a reduced order model that captures the low-frequency behaviour and may be used to derive PI tuning formulae that account for collective blade flap modes. The proposed controllers are then compared to traditional PI controllers based on a single degree of freedom (1-DOF) model of the drive-train using linearized NREL5MW and DTU10MW models. The 10 MW model is investigated in more detail through non-linear simulations in HAWC2 using wind step and turbulent wind conditions. The proposed design formulae show robust results, giving more consistent gain and phase margins than 1-DOF designs throughout the above rated wind speed region, and may be used to increase controller bandwidth while maintaining acceptable stability margins, achieving 49% and 63% reductions in standard deviation of the output power for the DTU10MW model in turbulent conditions. Statistical analysis for both controllers was also performed to investigate fatigue loading on the main shaft caused by the pitch actuation.
Article
The individual pitch controller can mitigate asymmetric loads in wind turbines. However, wind turbine dynamics have strong nonlinearity and high uncertainty. In addition to target value tracking, suppression of wind disturbance is also a performance requirement of the individual pitch controller, while the traditional PI controller cannot take into account the tracking and disturbance rejection performance simultaneously. Therefore, the two-degree-of-freedom (2DoF) robust individual pitch controller is proposed to reduce loads in the above-rated region. Besides, parameter tuning is complicated in the design of the robust individual pitch controller. So the reference model method is proposed to preset the closed-loop system response. Firstly, the state-space model is established to describe the dynamics of the wind turbine. The multi-blade coordinate transformation is applied to transform the model into the fixed coordinate system. Subsequently, the μ-synthesis problem is solved by the D-K iterative algorithm to get the controller parameter. Finally, the control method is verified in GH Bladed. It is shown that rotor loads are suppressed without affecting the output power. Tower loads are also mitigated. Moreover, the relationship between the pitch actuator action and the load reduction capability is discussed by designing different bandwidths of the proposed method.
Article
Individual pitch control technology can reduce asymmetric loads of wind turbines. The assumption of three completely symmetrical blades is the design premise of traditional individual pitch controller. However, production, assembly, and operation will inevitably lead to aerodynamic imbalanced characteristics for blades. Therefore, the failure mechanism of the traditional individual pitch controller is analyzed based on the frequency-domain decomposition method and verified by the simulation analysis. Based on the failure mechanism, the uncertainty modeling method is proposed to handle aerodynamic imbalanced loads. Then the robust individual pitch control is designed based on the product perturbation model. The D–K iterative algorithm is used to solve the H∞-optimization for the controller. The proposed robust individual pitch controller can effectively suppress imbalanced loads through simulation verification.
Chapter
A typical wind turbine is a complex piece of equipment that integrates thousands of devices and components to generate energy from the wind. From the late 1990s to the present, average turbine generation capacity has expanded considerably to supply the global demand for clean energy, with offshore-commissioned turbines expected to reach around 15 MW of nominal power by the year 2025. However, there is still a growing need for wind farms with less visual impact, greater energy efficiency, and increasingly affordable operation and maintenance costs. This chapter provides an overview of the recent advances and technology trends of wind energy in the field of production, operation, maintenance, and recycling of wind turbines. The development of high-tech machines—with taller towers, longer and lighter blades, performance-optimized control systems, and more reliable electrical transmission grids—is discussed. The importance of ensuring the integrity of large-scale turbines during their lifetime in adverse environmental conditions and the consumption of more sustainable materials are considered. Efforts for continuous improvement focused on quality and productivity of rotor blade manufacturing processes are ongoing and the consolidation of hybrid farms and wind energy storage systems has a key role in energy transition.
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This present paper considers a novel strategy for energy management and intelligent power control of a stand-alone electric generation system (EGS). The considered system consists of a wind energy conversion system, which contains a wind turbine with permanent magnet synchronous generator associated with a battery storage system and a direct current (DC) load. According to different climatic changes, load variations, and battery state of charge, the considered EGS is studied as a switched and uncertain nonlinear system. The main control objectives are, first, to regulate the wind power generation to satisfy the required power and second, to maintain the battery state of charge within a certain limits to extend its life cycle. Thus, a strategy of energy management is proposed based on different modes of system operation. Furthermore, a neural network-based integral sliding mode controller (NN-ISMC) is developed, as a robust and intelligent control method, to satisfy the reference power of each operation areas and to improve the robustness and the stability of such stand-alone system under high perturbations and external disturbances. The analytical stability of the proposed approach is demonstrated and assured using Lyapunov function method. In addition, the simulation results, realized using Matlab software, show that the suggested NN-ISMC control strategy ensures faster transient response and smaller steady-state error performances, compared to the other presented methods.
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A simple superposition method of two separate pitch control loops is adopted in the traditional tower load control and output power control, ignoring the coupling of rotor rotation and tower movement under aerodynamic force. Besides, tower load control performance is dependent on the accuracy of the tower motion sensor, resulting in a decrease in system reliability. Therefore, a pitch controller without sensor is proposed to achieve the coordinated control of tower load and output power. First, a low-order wind turbine state–space model is derived which is suitable for the design of pitch controller and compared with the linearized model from GH Bladed to verify the rationality of the deduced model. Then, based on the theory of multi-input and multi-output (MIMO) control, a linear quadratic Gaussian (LQG) pitch controller is designed integrated with disturbance accommodation controller (DAC). The Loop transfer recovery (LTR) method is used to restore dynamic characteristics of closed-loop to improve the performance of the pitch controller. The feasibility of the LTR method is proved by detailed theoretical analysis. Finally, compared with traditional controllers, it is verified that the proposed LTR pitch controller can further reduce tower load while stabilizing output power in different wind conditions.
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This article provides a survey of recently emerged methods for wind turbine control. Multivariate control approaches to the optimization of power capture and the reduction of loads in components under time-varying turbulent wind fields have been under extensive investigation in recent years. We divide the related research activities into three categories: modeling and dynamics of wind turbines, active control of wind turbines, and passive control of wind turbines. Regarding turbine dynamics, we discuss the physical fundamentals and present the aeroelastic analysis tools. Regarding active control, we review pitch control, torque control, and yaw control strategies encompassing mathematical formulations as well as their applications toward different objectives. Our survey mostly focuses on blade pitch control, which is considered one of the key elements in facilitating load reduction while maintaining power capture performance. Regarding passive control, we review techniques such as tuned mass dampers, smart rotors, and microtabs. Possible future directions are suggested.
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We transform the National Renewable Energy Laboratory (NREL) 5-MW geared equipped monopile wind turbine model into a hydrostatic wind turbine (HWT) by replacing its drivetrain with a hydrostatic transmission (HST) drivetrain. Then, we design an H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> loop-shaping torque controller (to regulate the motor displacement) and a linear parameter varying (LPV) blade pitch controller for the HWT. To enhance the performances of the pitch control system during the transition region around the rated wind speed, we add an antiwindup (AW) compensator to the LPV controller, which would otherwise have had undesirable system responses due to pitch saturation. The LPV AW pitch controller uses the steady rotor effective wind speed as the scheduling parameter, which is estimated by the light detection and ranging preview. The simulations based on the transformed NREL 5-MW HWT model show that our torque controller achieves a very good tracking behavior, while our pitch controller (no matter with or without AW) gets much improved overall performances over a gain-scheduled PI pitch controller.
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The increasing size of modern wind turbines also increases the structural loads caused by effects such as turbulence or asymmetries in the inflowing wind field. Consequently, the use of advanced control algorithms for active load reduction has become a relevant part of current wind turbine control systems. In this paper, an individual blade pitch control law is designed using multivariable linear parameter-varying control techniques. It reduces the structural loads both on the rotating and non-rotating parts of the turbine. Classical individual blade pitch control strategies rely on single-control loops with low bandwidth. The proposed approach makes it possible to use a higher bandwidth since it accounts for coupling at higher frequencies. A controller is designed for the utility-scale 2.5 MW Liberty research turbine operated by the University of Minnesota. Stability and performance are verified using the high-fidelity nonlinear simulation and baseline controllers that were directly obtained from the manufacturer. Copyright
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Disturbance observer based (DOB) control has been implemented in motion control to reject unknown or time-varying disturbances. In this research, an internal model-based disturbance observer (DOB) design combined with a PID type feedback controller is formulated for wind turbine speed and power regulation. The DOB controller facilitates model-based estimation and cancellation of disturbance using an inner feedback control loop. The disturbance observer combined with a compensator is further designed to deal with the model mismatch. The proposed method is applied to National Renewable Energy laboratory (NREL) offshore 5-MW wind turbine. Our case studies show that the DOB controller can achieve improved speed and power regulation compared to the baseline PID controller, and exhibit excellent robustness under different turbulent wind fields. Copyright © 2016 by ASME Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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Time-varying unknown wind disturbances influence significantly the dynamics of wind turbines. In this research, we formulate a disturbance observer (DOB) structure that is added to a proportional-integral-derivative (PID) feedback controller, aiming at asymptotically rejecting disturbances to wind turbines at above-rated wind speeds. Specifically, our objective is to maintain a constant output power and achieve better generator speed regulation when a wind turbine is operated under time-varying and turbulent wind conditions. The fundamental idea of DOB control is to conduct internal model-based observation and cancelation of disturbances directly using an inner feedback control loop. While the outer-loop PID controller provides the basic capability of suppressing disturbance effects with guaranteed stability, the inner-loop disturbance observer is designed to yield further disturbance rejection in the low frequency region. The DOB controller can be built as an on-off loop, that is, independent of the original control loop, which makes it easy to be implemented and validated in existing wind turbines. The proposed algorithm is applied to both linearized and nonlinear National Renewable Energy Laboratory (NREL) offshore 5-MW baseline wind turbine models. In order to deal with the mismatch between the linearized model and the nonlinear turbine, an extra compensator is proposed to enhance the robustness of augmented controller. The application of the augmented DOB pitch controller demonstrates enhanced power and speed regulations in the above-rated region for both linearized and nonlinear plant models.
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In this research, a new adaptive control strategy is formulated for the pitch control of wind turbine that may suffer from reduced life owing to extreme loads and fatigue when operated under high wind speed and internal structural uncertainties. Specifically, we aim at making a trade-off between the maximum energy captured and the load induced. The adaptive controller is designed to both regulate generator speed and mitigate component loads under turbulent wind field when blade stiffness uncertainties exist. The proposed algorithm is tested on the NREL offshore 5-MW benchmark wind turbine. The control performance is compared with those of the gain scheduled proportional integral (GSPI) control and the disturbance accommodating control (DAC) that are used as baselines. The results show that with the proposed adaptive control the blade root flapwise load can be reduced at a slight expense of optimal power output. Moreover, the blade load mitigation performance under uncertain blade stiffness reduction is improved over the baseline controllers. The control approach developed in this research is general, and can be extended to mitigating loads on other components.
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Vibration suppression is of fundamental importance to the performance of industrial robot manipulators. Cost constraints, however, limit the design options of servo and sensing systems. The resulting low drive-train stiffness and lack of direct load-side measurement make it difficult to reduce the vibration of the robot’s end-effector and hinder the application of robot manipulators to many demanding industrial applications. This paper proposes a few ideas of iterative learning control (ILC) for vibration suppression of industrial robot manipulators. Compared to the state-of-the-art techniques such as the dual-stage ILC method and the two-part Gaussian process regression (GPR) method, the proposed method adopts a two degrees-of-freedom (2DOF) structure and gives a very lean formulation as well as improved effects. Moreover, in regards to the system variations brought by the nonlinear dynamics of robot manipulators, two robust formulations are developed and analyzed. The proposed methods are explained using simulation studies and validated using an actual industrial robot manipulator.
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This paper studies the active rotor load controller design for a large wind turbine via individual pitch control (IPC). A multivariable IPC is designed to reject the periodic load disturbances, in an optimal manner, by penalizing the control effort according to the pitch actuator constraints. Frequency response analysis of the well-known multi-blade coordinate (MBC) transformation describes how the rotational speed variations influence the flexible modes of the blades. Therefore, a multivariable plant is constructed in the frequency-domain, compatible with applying the disturbance rejection control approaches. Then, a mixed sensitivity H∞ optimization problem is formulated based on the obtained MIMO model. The performance of the synthesized controller is analyzed and compared with the PI-based IPC. Finally, the dynamic load mitigation of the developed controller is studied through the fatigue load analysis with a high-fidelity aeroelastic simulator. Results show a significant amount of load alleviation in return for an even lower level of the pitch activity, with respect to the PI-based IPC.