H02M 5/2937

Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only {with automatic control of output voltage, current or power using whole cycle control, i.e. switching an integer number of whole or half cycles of the AC input voltage}