Objective: The use of multiple-stage cycloconverters is suitable for variable-frequency
speed control of high-voltage, large-capacity motors, for which it is sometimes necessary to establish
separate controls for variable-frequency operation and the start-up phase. This approach effectively
limits the starting current of the large-capacity motor by switching the phase relationship of
the triple circuit’s output voltages to control the overall output voltage.
Methods: We analyze a triple circuit using voltage vector analysis and simulation analysis with
Results: We find that our tr
iple soft-start control strategy can be applied to large-capacity motors, as
this strategy results in a pure sine wave output voltage and current, and maintains balance in the
three-phase voltage during startup.