This work set out to investigate the adaptation, operating modes and integration of the reverse blocking GTO within multi-MW brushless dc machines with the specific intention to maximise torque density and power density of variable speed drives without taking undue risks. A major aspect of this work was to develop an understanding of the roles played by power electronics and machine topology in a novel commutation process that allowed the elapsed time of commutation events to be minimised whilst the timing of commutation events, relative to rotor position, was freely adjustable. This elapsed time had a direct bearing upon the highest order of current harmonics that could be exploited whilst the adjustable timing of commutation events allowed load angle to be optimised. In order to maximise power density it was necessary to fully integrate the static power electronic commutator within the machine. Standard reverse blocking GTO wafers were selected as the preferred switching device because they were expected to provide adequate performance at the low switching frequencies that would be used in such machines, and they presented a relatively low commercial risk. Stacks of unhoused pressure contact GTO devices and heatsinks were immersed in the same force-circulated liquid dielectric coolant that was used by the machine. As such, it was found possible to house the converter within the confines of a normal size motor terminal box and to allow the use of a common cooling system. The GTOs were operated in unity gain turn off mode and a remotely located gate drive was employed so as to permit unimpeded flow of the liquid dielectric coolant. As such it was necessary to understand the commutation implications of gate drive interconnections. The effects of rotor geometry and dampers upon commutation and harmonic exploitation were taken into account and were demonstrated using a small experimental machine. A series of tests on full scale components led to the manufacture of a multi-MW machine that was used to demonstrate the benefits of physical and functional integration under normal running and fault conditions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:754212 |
| Date | January 2015 |
| Creators | Crane, Allan |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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