Synchronous control of multilevel cascaded converters with separate DC-link sources

Novel method of direct synchronised pulsewidth modulation is applied for control of a dual inverter-fed open-end winding induction motor drive with separate DC-link sources with different voltages. New strategy and algorithms of synchronised pulsewidth modulation (PWM) provide quarter-wave symmetry of multilevel actual phase voltage of the system during the whole control range including the zone of over modulation. Spectra of the actual phase voltage do not contain even harmonics and sub-harmonics, which is especially important for the drive systems with increased power rating. Simulations gave the behavior of dual inverter-fed drives with synchronised modulation for the drive topologies with both equal and different DC-link voltages