Cost-effective Design & Operation of Variable Speed Wind Turbines: Closing the Gap between Control Engineering & the Wind Engineering Community by David-Pieter Molenaar

By Paul Gipe

“Free, and Still too Expensive” opens Molenaar’s doctoral thesis on designing variable speed wind turbines.

Molenaar’s work is not for the faint of heart. Much of it is well beyond my skill level. But there is an interesting chapter on the design of the innovative Lagerwey 50/750 direct-drive, variable speed turbines and its large ring generator. The ring generator is 5.5 meters in diameter, or about 10 percent of the 50 meter rotor. Even on such a large diameter generator, the air gap is limited to 5 mm.

He also provides a useful discourse on the main computer design codes available for wind turbine engineers.

No doubt attorneys on both sides of the variable-speed patent dispute will carefully peruse Molenaar’s book for ammunition to use in the ongoing legal jousting on both sides of the Atlantic.

Cost-effective Design & Operation of Variable Speed Wind Turbines: Closing the Gap between Control Engineering & the Wind Engineering Community by David-Pieter Molenaar, Delft University Press, ISBN: 90-407-2383-4, 347 pages, 6.5 x 9.5 inches, paper, $74.00, 2003. Delft University Press, P.O. Box 98, NL-2600 MG, Delft, The Netherlands, Phone: +31 15 27 85 678, Fax: +31 15 85 706,


Table of Contents

1 Introduction
1 1.1 Motivation and background
1 1.1.1 History: from windmill to wind turbine
1.1.2 The future of wind power
1.1.3 Cost-effective wind turbine design and operation
1.2 Problem formulation
1.3 Outline
1.4 Typographical conventions
Part I: Modeling of flexible wind turbines
2 State-of-the-art of wind turbine design codes
2.1 Introduction
2.2 Overview wind turbine design codes
2.3 Main features overview
2.3.1 Rotor aerodynamics
2.3.2 Structural dynamics
2.3.3 Generator description
2.3.4 Wind field description
2.3.5 Wave field description
2.3.6 Control design
2.3.7 Summary main features in tabular form
2.4 Conclusions
3 Dynamic wind turbine model development
3.1 Introduction: general wind turbine model
3.2 Wind module
3.3 Aerodynamic module
3.3.1 Introduction
3.3.2 Rankine-Froude actuator-disk model
3.3.3 Blade element momentum model
3.3.4 Calculation of the blade element forces
3.4 Mechanicalmodule
3.4.1 Introduction
3.4.2 Superelement approach
3.4.3 Generation of the equations of motion of MBS
3.4.4 Automated structural modeling procedure
3.4.5 Soil dynamics
3.4.6 Example: three bladed wind turbine
3.5 Electrical module
3.5.1 Introduction
3.5.2 Synchronous generator: physical description
3.5.3 Synchronous generator: mathematical description
3.5.4 Dynamic generator model
3.6 Summary 103
Part II: Model validation issues
4 Module verification and validation
4.1 Introduction
4.1.1 Verification versus validation
4.1.2 Model verification and validation approach
4.2 Mechanical module verification and validation
4.2.1 Case 1: Euler-Bernoulli beam (verification)
4.2.2 Case 2: APX-45 rotor blade (validation)
4.2.3 Case 3: APX-70 rotor blade (validation)
4.2.4 Case 4: RB-51 rotor blade (validation)
4.2.5 Case 5: RB- 70 rotor blade (validation)
4.2.6 Discussion
4.2.7 Case 6: Lagerwey LW-50j750 wind turbine
4.3 Electrical module verification and validation
4.3.1 Literaturereview
4.3.2 Synchronous generator parameter identification 4
.3.3 MSR test applied to the LW-50j750 generator
4.4 Conclusions
5 Model parameter updating using time-domain data
5.1 Introduction
5.2 Identifiability of model parameters
5.2.1 Persistence of excitation
5.2.2 Model parametrization
5.3 Off-line parameter optimization procedure
5.3.1 Unconstrained optimization
5.3.2 Constrained optimization
5.3.3 Selectingamethod
5.4 Verification using simulated data
5.4.1 Beam1sd
5.4.2 SDLW1
5.5 Discussion
Part III: Model based control design
6 Frequency converter controller design
6.1 Introduction
6.2 Frequency converter controller objectives
6.3 Frequency converter controller configuration
6.3.1 Rectifiercontroller
6.3.2 Invertercontroller
6.4 Rectifier frequency converter controller design
6.4.1 Open-loop analysis
6.4.2 Set-point computation and controller design
6.4.3 Closed-loop analysis
6.5 Conclusions 194
7 Economic control design
7.1 Introduction
7.2 Closed-loop wind turbine control
7.2.1 History of windmill and wind turbine control
7.2.2 State-of-the-art variable speed wind turbine control
7.3 The cost of generating electricity using wind
7.3.1 Performance increase
7.3.2 Cost reduction
7.4 Closed-loop control design methodology: design guidelines
Part IV: Conclusions and recommendations
8 Conclusions
9 Recommendations for future research
Part V: Appendices
A Main features Lagerwey LW-50j750 wind turbine
A.l The Lagerwey LW-50j750 wind turbine
A.2 Rotor
A.3 Support structure 224 A.4 Generator
B Flow states of a wind turbine rotor
C Comparison of the finite element, lumped-mass and superelement method
C.l Exact eigen frequencies
C.2 Finite Element approximation
C.3 Lumped-mass approximation
C.4 Superelement approximation
C.5 Comparison
D Proofs of Section 3.5
D.l Direct-axis
D.2 Quadrature-axis
E Main wind turbine modes of operation
F Modal analysis measurement equipment
F.l Cable
F.2 Data acquisition system
F.3 Forcetransducer
F.4 Accelerometers
F .4.1 Accelerometer mounting
F .4.2 Accelerometer positions
G Frequency response functions
G.l Single degree of freedom
G.2 Two degrees of freedom
H Modified step-response test measurement equipment
H.l Generator
H.2 Transfoshunt
H.3 Low power DC voltage source
H.4 Thyristor
H.5.Data-acquisition system
H.5.1 Input-output boards
H.5.2 Digital Signal Processor (DSP) board
H.5.3 Personal computer
I DAWIDUM: a new wind turbine design code
1.1 Introduction
1.2 Modeling
1.2.1 Wind module library
1.2.2 Aerodynamic module library
1.2.3 Mechanical module library
1.2.4 Electrical module library
Glossary of symbols