Abstract:
The aim of present work has been to develop a 3-phase to single phase six pulse noncirculating current type cydoconverter controlled with a small sclae in-terface and a 8085 microprocessor based control program suitable for driving a small single phase induction motor for laboratory investigations.
The power circuit consists of two converters connected in antiparallel, each made up of six thyristors connected in bridge configuration
In the present work the firing instants for the various thyristors are deter-mined following cosine wave crossing principle by comparing a series of constant cosine waves with an adjustable frequency and adjustable voltage refrence sig-nal. As exact digital implementation is too slow and impractical for microprocessor therefore, a straight line approximation of the input cosine waves and the refrence wave have been used. The algorithm used gives a nearly sinusoidal output volt-age. A complete hardware and software design of the scheme is given and the test results are presented.
For implementing noncirculating current mode a current sensor is used which is in the form of two power diodes connected in antiparallel in the output line of the cycloconverter.
The developed cycloconverter has been tested for R - load, R-L load & Induction motor load. The oscilloscopic records of cycloconverter output voltage and current are obtained and presented for different frequency settings in the frequency range 2.5 to 16.67 Hz.
