Contrarotating wind turbines and generators

Thesis

Contrarotating wind turbines are wind energy harvesting machines with two sets of blades mounted on concentric shafts that rotate in opposite directions. The mechanical energy of the shafts can be converted to elec- trical energy through a contrarotating generator, where one shaft spins the magnets of the generator, and the other shaft spins the output coils of the generator in the opposite direction. This thesis discusses various aspects of contrarotating wind turbines and contrarotating generators.

Chapter 2 presents a theoretical introduction to magnetism and the mod- elling of the components of a generator. Chapter 3 extends this existing theory by developing a special purpose numerical integration technique for calculating integrals of harmonic functions over polyhedral regions, which arise in the modelling of electromagnets and in the calculation of the magnetic flux through a coil.

Chapter 4 presents some contrarotating generators that have been de- signed and constructed.

Chapter 5 calculates theoretical power coefficients of contrarotating wind turbines and shows that these are greater than the power coefficients of a conventional, single rotor wind turbine.

Newton’s third law implies that the torque exerted by a contrarotating generator against the motion of both sets of blades is equal and opposite. Chapter 6 presents a control strategy for varying this equal torque to maximise the power extracted from the wind.

Authors: Henderson, WJ

• DOI: 10.5287/ora-z52kr1699
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English