Innovative Controller Design for a 5MW Wind Turbine Blade

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1 ; Vol. 11, No. 4; 218 ISSN E-ISSN Publihed by Canadian Center of Science and Education Innovative Controller Deign for a 5MW Wind Turbine Blade Ranjeet Agarwala 1 & Robert A. Chin 1 1 Department of Technology Sytem, College of Engineering and Technology, Eat Carolina Univerity, Greenville, NC, USA Correpondence: Ranjeet Agarwala, Department of Technology Sytem, College of Engineering and Technology, Eat Carolina Univerity, Greenville, NC, USA Tel: agarwalar@ecu.edu Received: March 3, 218 Accepted: May 31, 218 Online Publihed: July 29, 218 doi:1.5539/jd.v11n4p78 URL: Abtract The development and evaluation of a nonlinear pitch controller for wind turbine blade and the deign and modeling of an aociated actuator and controller wa examined. The pitch actuator and controller were modeled and analyzed uing Pneumatically Actuated Mucle (PAM) for actively pitching the wind turbine blade. PAM are very light and have a high pecific work and a good contraction ratio. Proportional Integral and Derivative (PID) controller were enviaged for the wind turbine pitching ytem at the blade tip due to it routine uage in the wind turbine indutry. Deployment of controller enable effective pitch angle tracking for power abatement at variou configuration. The controller wa ubjected to four pitch angle trajectory ignal. PID controller were tuned to achieve atifactory performance when ubjected to the tet ignal. Low pitch angle error reulted in atifactory blade pitch angle tracking. Deployment of thee controller enhance wind turbine performance and reliability. The data ugget that the pitch ytem and actuator that wa modeled uing PAM and PID controller i effective providing robut pitch angle trajectory tracking. The reult ugget that the propoed deign can be uccefully integrated into the family of wind turbine blade pitch angle controller technologie. Keyword: renewable energy, wind energy, wind turbine, wind turbine control 1. Introduction 1.1 Problem Introduction Wind turbine are primarily controlled by varying the pitch angle of the blade at their root where the blade are attached to the hub of the rotor. Minute deviation in pitch angle due to wind variation can lead to ignificant fluctuation in turbine blade load affecting rated turbine power output, tability, and turbine life. Actuation of pitch angle are inhibited by high blade inertia leading to lower control repone time at high or fluctuating peed. Power required for full length pitching for large blade are high thereby undermining power generation. Mechanim for full length pitching are large, complex, and expenive requiring higher manufacturing and maintenance cot. 1.2 Wind Turbine Blade Theory For a ection of blade ee Figure 1, the lift force and moment (Singh & Yim, 23; Fung, 22; Hoogedoorn, Jacob, & Beyene, 21) are given in Equation (1) and (2). The lift force of any blade ection reult in a preure difference between the upper and lower urface of the airfoil when the air flow pat it. The preure difference i caued due to the geometry and the camber of the airfoil which caue changing velocitie at the top and bottom urface of the airfoil. The preure difference when multiplied by the area of a ection of the blade length produce the lift force of dl. 78

2 Vol. 11, No. 4; 218 Figure 1. Cro-ection of a wind turbine blade. 2D quai-teady aerodynamic equation of an airfoil and the t SePCaT are baed on parameter a depicted here The lift coefficient i a non-dimenional term baed on the geometry of the airfoil impacted by lift force. Similarly, the aerodynamic moment i calculated by multiplying the vertical force with the chord length.. The moment coefficient i a non-dimenional term that capture the geometry of the airfoil impactedd by aero-dynamic moment dl = ρu dcla dl+ ρu d PB CL dl CA dm = ρu dcm Adl + ρu dpb CM PB dl (2) CA PB 2 2 U i wind velocity in m/, d i the airfoil chord length for main blade in m, dll i the incremental length of o the blade for main blade in m, dl PB i the incremental airfoil chord length for SePCaT in m, ρ i the denity of air a in kg/m 3, CM A i the moment coefficient per angle of attack, CL A i the lift coefficient per angle of attack, CMPB CA i the moment coefficient per partial blade control angle, CLPB CA i the lift coefficient per partial blade control angle. The total combined lift and moment for the main blade and SePCaT i obtained by integrating the lift and moment value for the entire blade length expoed to wind. 1.3 Relevant Scholarhip Many reearcher have propoed alternate control trategie for wind turbine. Akram et al. (217) conducted ucce aerodynamic load control uing pitch actuation tudie on vertical wind turbine. Chen and Qin (217) ued trailing edge controller to control and actuate wind turbine blade and for load control. Gao and Gao ( 216) ued optimization and compenation control method to control non-linear wind turbine. A wind turbine continue to grow and achieve power rating up to 2 MW (Steel, 215) capacitie, independent or collective full-length pitch control become increaingly cumberome. Some wind turbine control deign include telecopic blade, trailing edge- flap, tranitional tab, plama actuation, flow detector, and active flap to name a few. Dayne and Weaver (212a) and Dayne and Weaver (212b) tudied a NACA blade ection compriing a 2 percent chord length trailing edge-flap controller and found that the lift coefficient changed by a value of 1. when the flap angle wa varied from -1 to t 1 degree. Veraille et al. (211) evaluated the efficacy of plama actuation to control lift force of a wind turbine bladee and oberved a lift reduction of 3 to 5 percent. Wilon and Robinett (211) invetigated trailing edge-flap for controlling and reducing aerodynamic load by 2-3 percent allowing energy optimization. Thee wind turbine tudie were baed on 2D analyi. 2D analyi doe not conider the geometrical twit of the blade, the effect of varying airfoil ectional geometrie, and the type of airfoil. Agarwala and Ro (213) focued on 3D aerodynamic analyi and control of a wind turbine blade via 3D control urface deign and deployment of trailing edge mid and end-flap. Although trailing edge-flap, tranitional tab, plama actuation, flow detector, and active flap offer excellent alternative, neverthele they add to rotor complexity, increae manufacturing, maintenance, and deployment cot. They alo create dicontinuitie in the 79 B PB PB (1)

3 Vol. 11, No. 4; 218 blade which lead to intallation and actuation complexitie. Imraan et al. (213) conceptualized telecopic wind turbine blade having chord ratio of.6 and tudied the influence of blade extenion on blade load. Mechanim propoed by them allowed linear actuation of the blade b length for load adaptation. Their method although novel preent complexitie and increaed manufacturing cot. Agarwala and Ro (214, 215) propoed focued on the deign, evaluation, and analyi of innovative rotor blade for large wind turbine throughh the formulation of a novel and imple eparated pitch control trategy at blade tip (SePCaT) for a large MW wind turbine. SePCaT5 indicate 5% of the total blade length while w SePCaT3 indicate 3% of the total blade length. Deployment of SePCaT facilitated new innovative deign whereby a larger portion of the blade wa aerodynamically available while maintaining tructural effectivene thu treamlining blade geometric and tructural characteritic. The entire blade along with the root wa aerodynamically more effective when compared to the traditional deign and contribute to the aerodynamic effectivene for power extraction. 1.4 Deign Overview Due to the inherent tructural nonlinearitie of wind turbine (Singh & Yim, 23), it wa paramount to deign an effective nonlinear controller for controlling the pitching mechanim of the wind turbine blade. Thi tudy focued on the deign of non-linear pitch control of wind turbine blade and the deign and modeling of a non-linear actuator and aociated controller. The pitch actuator and controller were modeled and analyzed uing u PAM for actively pitching the blade. The goal of the actuator deign wa to keep them a light a poible while w exhibiting trong actuator force. PID controller were enviioned for the wind turbine pitching ytem at a the blade tip. PID controller were then incorporated to control the pitch angle due to it routine uage in the wind turbine indutry. A PAM ( engb/pdf/en/dmsp-mas EN.PDF) wa enviioned to actuate the SePCaT (Wood, Kothera, & Wereley, 214; Wood, Kothera, Sirohi & Wereley, 211; Wood, Kothera, & Wereley, 211). The goal of the actuator deign wa to keep them a light a poible while w exhibiting trong actuator force. PAM are very light and have a high pecific work and a good contraction ratio. r PAM are compried of an inner elatomeric ring, outer braided leeve, and two end fitting ee Figure 2. Figure 2. PAM operation. PAM contract when the inner bladder expand when air preuree i applied. The braided leeve expand radially. / engb/pdf/en/dmsp-mas EN. PDF PAM or cluter of PAM were ued to pitch the SePCaT during high wind in a wind tunnel. A depicted in Figure 3 and 4, PAM combination 1 and 2, when actuated, allowed the SePCaT to be pitched to feather while w PAM 3 and 4, when actuated, allowed the SePCaT to be pitched to tall. Here, L i the lift force; W i the weight of SePCaT; xm i the ditance of the aerodynamic center from the SePCaT pitching axi; xg i the ditance of the center of gravity from the SePCaT pitching axi; kpam 1 and k PAM 2 are PAM contant; δ1 andδ 2 are PAM deflection; and are ditance of the PAM line of action to the SePCaT pitching axi. d PAM1 d d PAM 2 8

4 Vol. 11, No. 4; 218 Figure 3. SePCaT actuation enabled (PAM). The etup depict the ide view of SePCaT Figure 4. Concept of SePCaT actuation enabled by PAM The equation for SePCaT derived from Lagrange equation are given a follow (Wood, Kothera, & Wereley, 214; Wood, Kothera, Sirohi & Wereley, 211; Wood, Kothera, & Wereley, 211) d L L = Q i dt q & i qi (3) Here the Lagrangian L i given a a difference of SePCaT kinetic T and potential energie V The force Q acting of the SePCaT i given a follow i L = T V (4) Q i = Q + Q + Q damping aero control (5) 81

5 jd.ccenet.org Vol. 11, No. 4; 218 The Lagrange kinteic energy of the SePCaT i given a 1 2 T = I & θ 2 The Lagrange potential energy of the SePCaT i given a The damping force i given a follow 1 1 V = kθθ + k 2 4 θ 2 4 θ, NL Q = ( c & θ + c ign( & θ)) damping θ θ, NL (6) (7) (8) Therefore the equation of motion of SePCaT i given a I θ& + k θ + k θ + ( c & θ + c ign( & θ)) = Q + Q 3 θ θ, NL θ θ, NL aero control (9) I i the moment of inertia of SePCaT, c θ and c θ,nl are linear and non-linear damping term,and, k θ and k θ,nl are linear and non-linear pring tifne term. Q i the change in aerodynamic moment and aero Q i the control controller moment applied. PAM actuator force i expreed in term of the overall PAM actuator force F, Deflection δ, and PAM contant k PAM F = kpamδ. Both PAM are treated having ame geometrical and dynamical propertie. Q and aero Q control are related a follow. Here d i the ditance of the PAM line of action to the SePCaT PAM (1) pitching axi and Δ δ i the change in PAM diplacement. 2k PAM Δδ d PAM Q aero = Q control Thererfore Equation (1-11) become I θ& + k θ + k θ + ( c & θ + c ign( & θ)) = 2k Δδd 3 θ θ, NL θ θ, NL PAM PAM (11) (12) Finally, expreing Equation (12) a function of θ, and contoller inputu and parameter b, θ& = f ( θ) + bu 3 c & c, NLign( ) k θθ & θ θ kθθ θ, NLθ f ( θ) = θ& = I I I I (13) 2kPAM Δδ dpam 2kPAM dpam bu =, b =, u =Δ δ = δu I I 2. Method 2.1 Wind Turbine Blade Model The entire blade along with SePCaT wa digitized uing the 5MW National Renewable Energy Laboratory (NREL) (Jonkman, 29) turbine pecification in three-dimenion (3D) and analyzed uing 3D computational fluid dynamic (CFD) routine. 82

6 Vol. 11, No. 4; 218 Figure 5(a). Full blade-3d view Figure 5 (b). CFD imulation Figure 5(c). SePCaT Figure 5(d). SePCaT pictorial view Figure 5. SePCaT wind turbine configuration The blade wa firt modeled a a tandalone computer-aided deign (CAD) model a hown in Figure 5(a) uing u Daault Sytème SolidWork. Airfoil hape from variou location of the wind turbine blade were baed on geometrical propertie and co-ordinate of the model 5MW NREL wind turbine blade. Airfoil curve at variou cro-ection were generated uing Carteian coordinate ytem. Airfoil at each ection were caledd and rotated by their chord length and value of angular twit. Variou cro-ection were connected uing inbuilt CAD modeling interpolation routine. Three-dimenional control urface are deployed a eparated ection of partial blade length at the blade tip a depicted in Figure 5(a) through 5(d). 2.2 Model Input The deired trajectory for SePCaT pitch angle in repone to power abatement (hed exceivee power to maintain 5MW) in region 3 ha been dicued in Agarwala and Ro (214). SePCaT configuration, which varied from 5 to 3% of the blade length in 5% increment (SePCaT5, SePCaT1, SePCaT15, SePCaT2, SePCaT25, and SePCaT3), were evaluated by comparing them to aerodynamic repone of the traditional blade. A the wind peed increaed by a factor of 1.1U (1%), the rotorr power increaed to around 6.75 MW warranting a reduction to a factor of approximately.74. Thi wa achieved by feathering SePCaT3 by 14, SePCaT25 by 16, SePCaT2 by 26, and SePCaT15 by 3 degree repectively. If wind peed increaed by a factor of 1.2U (2%), the rotor power increaed to around 8.33MW warranting a reduction to a factor of approximately.6. Thi wa achieved by feathering SePCaT3 by 18, SePCaT25 by 26 and SePCaT2 by 3 degree repectively. A the wind peed increaed by a factor of 1.3U (3%), the rotor power increaed to around MW warranting a reductionn to a factor of approximately.43. Thi wa achieved by feathering SePCaT3 by 26 degree. If wind peed increaed by a factor of 1.4U (4%), the rotor power increaed to around 14.3MW warranting a reduction to a factor of.35 approximately. Thi wa achieved by feathering SePCaT3 by 32 degree. The etting in Table 1 were ued to build the deiredd SePCaT pitch angle trajectory for power hedding. Table 1. SePCaT pitch angle trajectory etup value for deired pitch ignal Wind Speed Power Rated SePCaT3 SePCaT25 SePCaT2 Factor Produced Power Angle ( ) Angle ( ) Angle ( ) MW 5 MW MW 5MW MW 5MW MW 5MW SePCaT15 Angle ( ) Reult Analyi focued on numerical invetigation of the ytem and controller repone to deired pitch angle a trajectorie baed on Table 1. MATLAB and Simulink were ued to tudy the repone of the pitch dynamic a 83

7 Vol. 11, No. 4; 218 laid out in deign overview in ection1.3. Initially the value weree et to P=1, I= =1, D=1 for the unit tep input and the repone i oberved a depicted in Figure 6. Figure 6 indicate the controller reponee when the value of are et to P=1, I=1, D=1. The deired ignal wa plotted with a blue line and the repone, with a red line. Examination of pitch error aroundd the deired ettling time a hown in Figure 7 indicate an error of.5 degree. Subequently, the value were et to P=1, I=6, D=1 a depicted in Figure 8. The reult of a pitch error of.25 degree i hown in Figure SePCaT Angle [degree] SePCaT Angle Actual SePCaT Angle deired Time [] Figure 6. SePCaT repone when PID i deployed. Thi reponee i for tet ignal Figure 7. Pitch error when PID i deployed. Thi repone i for tet ignal Due to the unatifactory performance, optimum m value of P, I, and D were ought to tune the ytem atifactorily. The repone i optimized by tuning the parameter until the ettling time i around 1 econd. The value are tuned to P=1..5, I=18, D=.15 for the tep input and the repone i oberved a depicted in Figure 1. A hown in Figure 11, the pitch error wa atifactory at around. 15 degree. 84

8 jd.ccenet.org Vol. 11, No. 4; SePCaT Angle [degree] SePCaT Angle Actual SePCaT Angle deired Time [] Figure 8. SePCaT repone when PID i deployed. Thi reponee i for tet ignal Figure 9. Pitch error when PID i deployed. Thi repone i for tet ignal SePCaT Angle [degree] SePCaT Angle Actual SePCaT Angle deired Time [] Figure 1. SePCaT repone when PID i deployed. Thi repone i for tet ignal 85

9 Vol. 11, No. 4; 218 Figure 11. Pitch error when PID i deployed. Thi repone i for tet ignal The remaining ignal were imulated and atifactory tracking wa achieved a hown in Figure 12, 13, and SePCaT Angle [degree] SePCaT Angle Actual SePCaT Angle deired Time [] Figure 12. SePCaT repone when PID i deployed. Thi repone i for ignal Pitch error-degree time Figure 13. SePCaT pitch error when PID i deployed. Thi repone i for ignal 1 86

10 jd.ccenet.org Vol. 11, No. 4; SePCaT Angle [degree] SePCaT Angle Actual SePCaT Angle deired Time [] Figure 14. SePCaT repone when PID i deployed. Thi repone i for ignal 2 Figure 12 indicate atifactory controller tracking repone to ignal 2, and Figure 13 indicate the reulting error. The repone indicate atifactory tracking. However, harp change experienced during large tep change generated large error during the tart of the wind turbine ignal change at 2 and 3 econd. Figure 14 indicate atifactory controller tracking repone to ignal Concluion Thi tudy focued on the development of an effective nonlinear pitch controller for wind turbine blade. The data ugget that the pitch ytem and actuator that wa modeled uing PAM and PID controller i effective in providing robut pitch angle trajectory tracking. The reult ugget that the propoed deign can be uccefully integrated into the family of wind turbine blade pitch angle controller technologie. The deign and analyi of the pitch angle actuator and controller ytem provide effective tracking at variou pitch angle trajectory etting. The model repone and reult ugget that the pitch controller deign i robut and reliable. Initially the PID controller were tuned to achieve atifactory performance when ubjected to the tet ignal. Pitch error range from.5 degree to.14 degree for given tet ignal and PID value were elected for atifactory tracking. For the remaining ignal, tuned PID value were deployed and exhibited robut trajectory tracking. The controller and actuator deign include PAM for actively pitching the blade thereby keeping the ytem light and exhibiting trong actuator force. Reference Agarwala, R. (214). Separated Pitch Control at Tip (SePCaT): A Novel Blade Deign and Aociated Control Strategie for Large MW Wind Turbine (Doctoral diertation, North Carolina State Univerity, Raleigh, North Carolina, USA). Retrieved from Agarwala, R., & Ro, P. I. (213). 3D analyi of lift and moment adaptation via control urface deployment on a 5 MW wind turbine blade. Wind Engineering, 37(5), Agarwala, R., & Ro, P. I. (215). Separated Pitch Control at Tip: Innovative Blade Deign Exploration for Large MW Wind Turbine Blade. Journal of Wind Energy, 215. Hindawi. Akram, B., Branger, H., Paillard, B., Roy, S., Chritopher, L., & Bourra, D. (217, September). Study of the aerodynamic propertie of a wind VAWT turbine blade and evaluation of the effect of the pitch control. In 13th EAWE on Wind Energy. Chen, H., & Qin, N. (217). Trailing-edge flow control for wind turbine performance and load control. Renewable Energy, 15, Dayne, S., & Weaver, P. M. (212a). A morphing trailing edge device for a wind turbine. Journal of Intelligent Material Sytem and Structure, 23(6), Dayne, S., & Weaver, P. M. (212b). Deign and teting of a deformable wind turbine blade control urface. 87

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