Page 13 - Wind Energy Handbook

CONTENTS xiii

8 The Controller 471
8.1 Functions of the Wind-turbine Controller 472
8.1.1 Supervisory control 472
8.1.2 Closed-loop control 472
8.1.3 The safety system 473
8.2 Closed-loop Control: Issues and Objectives 475
8.2.1 Pitch control 475
8.2.2 Stall control 476
8.2.3 Generator torque control 476
8.2.4 Yaw control 477
8.2.5 Influence of the controller on loads 478
8.2.6 Defining controller objectives 478
8.2.7 PI and PID controllers 479
8.3 Closed-loop Control: General Techniques 480
8.3.1 Control of fixed-speed, pitch-regulated turbines 480
8.3.2 Control of variable-speed pitch-regulated turbines 481
8.3.3 Pitch control for variable-speed turbines 484
8.3.4 Switching between torque and pitch control 484
8.3.5 Control of tower vibration 486
8.3.6 Control of drive train torsional vibration 488
8.3.7 Variable-speed stall regulation 489
8.3.8 Control of variable-slip turbines 490
8.3.9 Individual pitch control 492
8.4 Closed-loop Control: Analytical Design Methods 493
8.4.1 Classical design methods 493
8.4.2 Gain scheduling for pitch controllers 498
8.4.3 Adding more terms to the controller 498
8.4.4 Other extensions to classical controllers 500
8.4.5 Optimal feedback methods 500
8.4.6 Other methods 504
8.5 Pitch Actuators 505
8.6 Control System Implementation 506
8.6.1 Discretization 507
8.6.2 Integrator desaturation 508
References 509

9 Wind-turbine Installations and Wind Farms 511
9.1 Project Development 511
9.1.1 Initial site selection 512
9.1.2 Project feasibility assessment 514
9.1.3 The measure–correlate–predict technique 514
9.1.4 Micrositing 515
9.1.5 Site investigations 517
9.1.6 Public consultation 517
9.1.7 Preparation and submission of the planning application 517
9.2 Visual and Landscape Assessment 519
9.2.1 Landscape character assessment 520