Variable AC supply control circuit for e.g. asynchronous motor - has two thyristor controlled output groups each with three stages in parallel for positive and negative half-cycles

摘要

The circuit has a pair of controlled switching or amplifier stages, or a pair of cascade circuits each with at least two stages in series. These are connected to two groups of controlled switching or amplifier stages, with three positive or negative stages in each group, and connected in parallel to three output terminals (R, S, T) providing a variable 3-phase current. The voltage supplied to the 'positive' and 'negative' stages is varied dependent on the frequency of the output AC. Two thyristors may be used, with a specific firing point within the second quadrant of the network voltage for the positive voltage end a specific firing point within the fourth quadrant for the negative voltage corresponding to each frequency.