Synchronous balanced control of cascaded two-level inverters with separated DC sources

The paper presents results of dissemination of novel method of synchronized pulsewidth modulation (PWM) for wide-range control of dual inverter-fed motor drives with power balancing capability between dc-links. This drive topology includes two insulated dc sources (with equal or different voltages), feeding two standard three-phase inverters, connected with an open-end winding induction motor. Algorithms of synchronized PWM provide both continuous synchronization of the phase voltage of the induction motor and required sharing of the output power between two dc sources. Special attention has been given to analysis of operation of the drive system with synchronized PWM in the zone of overmodulation. Simulations give the behavior of dual inverter-fed systems with continuous and discontinuous versions of synchronized pulsewidth modulation in both undermodulation and overmodulation control ranges. The spectra of the motor phase voltages do not contain even harmonics and sub-harmonics during the whole control range for any ratio between the switching and fundamental frequencies, which is especially important for the medium/high power systems.