Theoretical Assessment of a Variable-Frequency Envelope Cycloconverter

The operating principles and characteristics of a proposed variable-frequency envelope cycloconverter, constructed with relatively few thyristors, for three-phase variable-speed induction motor drive, are described. As the output frequency is varied, the output voltage wave-forms created by triggering the thyristors are found to vary for both the amplitude of the harmonic components and their phase displacements. Distortion factors, unbalance factors of the three-phase output voltages, and the nominal conversion efficiency of the system are given.