Synchronous Machines Adapted for Six Step Converters–Part II: Experimental Evidence

ABSTRACT

An investigation has been carried out to evaluate converter driven synchronous machines including a machine which is specially adapted for use with converters. The adapted machine has been designed so that the internally generated voltage is tailored to produce a desired current waveform when the machine is driven by a six step voltage source inverter. In this manner, the energy flows associated with commutation are supplied by electromechanical means. In the specific example presented, an armature current waveform is produced which is congrument with the applied armature voltage.

A short design study has been carried out which compares a conventional machine and an adapted machine of similar volume under converter driven operation. The rating of the adapted machine is slightly better than the conventional machine, although both are derated compared to the sinusoidal operation of the conventional machine.The adapted machine has a significantly improved power factor as well as smaller armature currents and reduced variations in shaft output power. Because of the reduced requirements for reactive power and armature current, it is expected that a simpler converter could be utilized. In addition to the design study, an experimental program has been carried out to demonstrate that the adapted machines will operate as predicted. An experimental machine in the 6 kw range was constructed and tested in a variety of conditions. The results of the experimental work agreed well with predicted behavior.