Reluctance machines with flux assistance
thesisposted on 15.12.2014, 10:37 by Ewan Roderick Tearlach Goodier
This thesis presents three reluctance machines with flux assistance. These machines provide alternative novel geometries that provide high efficiencies with a reduction in the ampere turns in the armature windings for torque production, lowering armature winding switching losses and reducing the power electronic rating. The Dual Stack Variable Reluctance Machine is a switched reluctance variant of the homopolar inductor alternator topology. The Single Stack Variable Reluctance Machine is a simplification of the Dual Stack machine. Both machines use a toroidal field winding to provide additional flux. The methods of connecting armature coils on each stator pole to utilise the armature flux and the choice of power electronic circuitry are important. Testing shows that such machines favour unipolar excitation with single coil per pole for the armature windings. Use of the field winding in series with the armature windings improves torque production. The Dual Stack Variable Reluctance Machine can have the mechanical angular displacement between the two stator stacks varied to provide an improved back emf waveshape for smoother torque production. The Single Stack Variable Reluctance Machine has parasitic and axial air gaps that pose interesting design issues (e.g. end thrust). Magnets can be placed in steel sections where flux is unidirectional. An ideal candidate for magnet insertion is the Flux Switching Motor. A Permanent Magnet Flux Switching Motor has been built that replaces the field windings with ferrite magnets. The Permanent Magnet Flux Switching Motor achieves efficiencies of over 80%. It adds no additional cost to the fan application as cost savings in lower temperature rated thermoplastics offsets the cost of magnets. A prototyping circuit incorporating a novel micro-processor program to alter the commutation timings as the machine operates has been designed to allow fast optimisation of each machine for minimum input power..