Wind energy I. Lesson 9. Control strategies

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Wind energy I. Lesson 9. Control strategies

  1. 1. Wind Energy I Control strategiesMichael Hölling, WS 2010/2011 slide 1
  2. 2. Wind Energy I Class content 5 Wind turbines in general 6/7 Wind - blades 2 Wind measurements interaction 8 Power losses at the rotor blade 9 Control strategies 3 Wind field characterization 4 Wind power 10 Generator 11 Electrics / gridMichael Hölling, WS 2010/2011 slide 2
  3. 3. Wind Energy I Control objectives and strategies Development of a wind turbine control system can be divided into four major steps: define clearly control objectives selection of suitable control strategies which determines the operation point of the wind turbine for each wind speed decide how the control strategy will be realized --> selection of the control schemes, the controlled variables, the reference signals, the switching procedure between different controllers, etc. design of the input-output map, meaning the characteristics of the controller according to the specificationsMichael Hölling, WS 2010/2011 slide 3
  4. 4. Wind Energy I Control objectives Control objectives for wind turbines Energy capture: Maximization of energy capture taking into account safe operation restrictions such as rated power, rated speed and cut-out wind speed, etc. Mechanical loads: Preventing WECS from excessive dynamic mechanical loads. This general goal includes reduction of transient loads, reduction of high frequency loads and resonance avoidance. Power quality: Conditioning the generated power to comply with interconnection standards.Michael Hölling, WS 2010/2011 slide 4
  5. 5. Wind Energy I Operation point Where / what is the steady-state of operation ? the steady-state of operation is reached when the aerodynamic torque developed by the rotor equals the reaction torque of the generator net torque applied to the system is zero At the steady-state operation point the aerodynamical power equals the converted power (minus losses at the generator): Pae = Pgen Tae · ω = Tgen · ω ω · (Tae − Tgen ) = 0 ⇒ Tae − Tgen = 0Michael Hölling, WS 2010/2011 slide 5
  6. 6. Wind Energy I Torque and power coefficient How does the aerodynamic torque change with u1 ?Aerodynamic torque Tae: Tae = Fae · R · cT 1 Tae = · ρ · π · R2 · u2 · R · cT 2 1The power converted by the WEC is given by: PW EC = Tae · ω = Pair · cp 1 ⇒ cT = cp · λMichael Hölling, WS 2010/2011 slide 6
  7. 7. Wind Energy I Aerodynamic torque The torque coefficient can be determined from the power coefficient. Until now we determined the maximum power coefficient by taking into consideration: Betz limit with the expansion by Schmitz losses at the rotor blades (drag losses and tip losses) 0.6 cpSchmitz cpSchmitz, z=3,"(#)=60 0.4 These curve represents the cpr(!) maximum power coefficient 0.2 for each tip speed ratio BUT λ0 design is only possible for one 0.0 0 5 10 15 20 tip speed ratio λ0! !Michael Hölling, WS 2010/2011 slide 7
  8. 8. Wind Energy I Aerodynamic torque Without control system the WEC is designed and optimized for one u1 and one ω. 0.6 cpr(!) 0.4 0.2 λ0 0.0 0 5 10 15 20 ! u2= 2/3.u1 u2= 2/3.u*1 the angle of urot urot attack changes β ures by changing u1 β* u*res and cl(α) to cl(α*) to u*1 and with and cd(α) to cd(α*) α it λ το λ* as well α*Michael Hölling, WS 2010/2011 slide 8
  9. 9. Wind Energy I Aerodynamic torque 0.6 cp From Betz we know that there is one optimum ratio between u3 and u1. 0.4 The WEC meets this at the design forcp 0.2 λ0. λ0 0.0 0.0 0.5 1.0 u3/u1 The cp coming from Betz in cpSchmitz 0.6 combination with the cpSchmitz, changing angle of attack 0.4 z=3,"(#)=60 for different u1, we get a cp! (!,#) cpr(!) 0 power coefficient that 0.2 depends on λ and α - λ0 cp(λ,α) 0.0 0 5 10 15 20 ! Michael Hölling, WS 2010/2011 slide 9
  10. 10. Wind Energy I Aerodynamic torque Note: In reality λmax and λ0 must NOT necessarily coincide !! 1 With cT = cp · cp(λ) and cT(λ) can be plotted: ⇒ λ 0.6 0.15 cp(!) cT(!) 0.4 0.10 cT(!) cp(!) 0.2 0.05 0.0 0.00 0 4 8 12 !Michael Hölling, WS 2010/2011 slide 10
  11. 11. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ 0.6 cp(!) 0.4cp(!) cp(!) 0.2 0.0 0 4 8 12 ! ! Michael Hölling, WS 2010/2011 slide 11
  12. 12. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s torque [Nm]cp(!) ! ! Michael Hölling, WS 2010/2011 slide 12
  13. 13. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm]cp(!) ! ! Michael Hölling, WS 2010/2011 slide 13
  14. 14. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/scp(!) ! ! Michael Hölling, WS 2010/2011 slide 14
  15. 15. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/s u1 = 17m/scp(!) ! ! Michael Hölling, WS 2010/2011 slide 15
  16. 16. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/s u1 = 17m/scp(!) u1 = 14m/s ! ! Michael Hölling, WS 2010/2011 slide 16
  17. 17. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/s u1 = 17m/scp(!) u1 = 14m/s u1 = 12m/s ! ! Michael Hölling, WS 2010/2011 slide 17
  18. 18. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/s u1 = 17m/scp(!) u1 = 14m/s u1 = 12m/s u1 = 10m/s ! ! Michael Hölling, WS 2010/2011 slide 18
  19. 19. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/s u1 = 17m/scp(!) u1 = 14m/s u1 = 12m/s u1 = 10m/s u1 = 8m/s ! ! Michael Hölling, WS 2010/2011 slide 19
  20. 20. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/s u1 = 17m/scp(!) u1 = 14m/s u1 = 12m/s u1 = 10m/s u1 = 8m/s u1 = 6m/s ! ! Michael Hölling, WS 2010/2011 slide 20
  21. 21. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/s u1 = 17m/scp(!) u1 = 14m/s u1 = 12m/s u1 = 10m/s u1 = 8m/s u1 = 6m/s u1 = 4m/s ! ! Michael Hölling, WS 2010/2011 slide 21
  22. 22. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/s u1 = 17m/scp(!) u1 = 14m/s u1 = 12m/s u1 = 10m/s u1 = 8m/s u1 = 6m/s u1 = 4m/s ! ! Tcpmax Michael Hölling, WS 2010/2011 slide 22
  23. 23. Wind Energy I Aerodynamic torque How does the torque change with changing ω for different but fixed u1? 1 ω·R 1 Tae = · ρ · π · R2 · u3 · cp · 2 1 u1 ω λ u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/s u1 = 17m/scp(!) u1 = 14m/s u1 = 12m/s u1 = 10m/s u1 = 8m/s u1 = 6m/s u1 = 4m/s ! ! Tcpmax Trated power Michael Hölling, WS 2010/2011 slide 23
  24. 24. Wind Energy I Control strategies Points in this torque-rotational speed plane (Tae-ω plane) that intersect with the generator torque define the steady-state operating conditions of the WEC. Different WEC control strategies results in different power curves P(u1), power coefficients cp(u1) and dynamical behavior. Different strategies are: fixed-speed, fixed-pitch (FS-FP) variable-speed, fixed-pitch (VS-FP) fixed-speed, variable-pitch (FS-VP) variable speed, variable-pitch (VS-VP)Michael Hölling, WS 2010/2011 slide 24
  25. 25. Wind Energy I Control strategiesThe interesting region for the control system is marked in thered box. u1 = 25m/s u1 = 22m/s torque [Nm] u1 = 20m/s u1 = 17m/s u1 = 14m/s u1 = 12m/s u1 = 10m/s u1 = 8m/s u1 = 6m/s u1 = 4m/s ! Tcpmax Trated powerMichael Hölling, WS 2010/2011 slide 25
  26. 26. Wind Energy I Fixed-speed, fixed-pitch Fixed rotational-speed ω0 is realized by coupling an asynchronous generator directly to the grid. 0.6 B u1 = 17m/s cp(!) u1max u1 = 8m/s C torque [Nm] 0.4 C u1 = 4m/scp(!) Trated power D Tcpmax 0.2 D B 0.0 12 A Aω 0 4 ! 8 u1min ! 0 Michael Hölling, WS 2010/2011 slide 26
  27. 27. Wind Energy I Fixed-speed, fixed-pitch For the characterization of the WEC power curve P(u1) and cp(u1) are of interest. For FS-FP the P(u1) curve looks in principle like: C u1 = 17m/s D u1max u1 = 8m/s torque [Nm]P(u1)/Prated C u1 = 4m/s Trated power D Tcpmax B ideal power curve B power curve A5 Aω 0 10 15 20 25 30 u1min ! 0 u1 [m/s] Michael Hölling, WS 2010/2011 slide 27
  28. 28. Wind Energy I Fixed-speed, fixed-pitch For the characterization of the WEC power curve P(u1) and cp(u1) are of interest. For FS-FP the cp(u1) curve looks in principle like: B u1 = 17m/s u1max u1 = 8m/s torque [Nm] C u1 = 4m/scp(u1) C Trated power D Tcpmax ideal cp real cp D B A Aω 0 5 10 15 20 25 30 u1min ! 0 u1 [m/s] Michael Hölling, WS 2010/2011 slide 28
  29. 29. Wind Energy I Fixed-speed, fixed-pitch Power regulation by passive stallMichael Hölling, WS 2010/2011 slide 29
  30. 30. Wind Energy I Variable-speed, fixed-pitch For a variable-speed, fixed.pitch machine the rotational speed ωrot can be adapted to meet the optimum tip speed ratio λ0. λ0 · u1 ωrot = R The rotational speed ωrot changes linearly with the ambient wind speed u1. This is applied in the region below rated wind speed.Michael Hölling, WS 2010/2011 slide 30
  31. 31. Wind Energy I Variable-speed, fixed-pitch Variable rotational-speed ωrot is realized by adding AC/DC-DC/ AC converter before feeding into the grid. 0.6 A-E cp(!) 0.4 Dcp(!) 0.2 G 0.0 0 4 8 12 ! Michael Hölling, WS 2010/2011 slide 31
  32. 32. Wind Energy I Variable-speed, fixed-pitch For the characterization of the WEC power curve P(u1) and cp(u1) are of interest. For VS-FP the P(u1) curve looks in principle like:Michael Hölling, WS 2010/2011 slide 32
  33. 33. Wind Energy I Variable-speed, fixed-pitch For the characterization of the WEC power curve P(u1) and cp(u1) are of interest. For VS-FP the cp(u1) curve looks in principle like:Michael Hölling, WS 2010/2011 slide 33
  34. 34. Wind Energy I Fixed-speed, variable-pitch There are two different ways to adjust the pitch to keep the power above rated wind speed constant:pitch to feather pitch to stallMichael Hölling, WS 2010/2011 slide 34
  35. 35. Wind Energy I Fixed-speed, variable-pitch By adjusting the angle of attack the cp(λ) curves are different for each pitch angle: tip speed ratioMichael Hölling, WS 2010/2011 slide 35
  36. 36. Wind Energy I Fixed-speed, variable-pitch These modified cp(λ) curves result in modified torque above rated wind speed to meet the rated power:Michael Hölling, WS 2010/2011 slide 36
  37. 37. Wind Energy I Fixed-speed, variable-pitch For the characterization of the WEC power curve P(u1) and cp(u1) are of interest. For FS-VP the P(u1) curve looks in principle like:Michael Hölling, WS 2010/2011 slide 37
  38. 38. Wind Energy I Fixed-speed, variable-pitch For the characterization of the WEC power curve P(u1) and cp(u1) are of interest. For FS-VP the cp(u1) curve looks in principle like:Michael Hölling, WS 2010/2011 slide 38
  39. 39. Wind Energy I Variable-speed, variable-pitchMichael Hölling, WS 2010/2011 slide 39

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