Distributed control of hybrid motor drives

The hybrid inverter motor drive with two cascaded multilevel inverters is an attractive option for naval ship propulsion systems due to a number of unique features. There is a natural split between a higher-voltage lower-frequency "bulk" inverter and a lower-voltage higher-frequency "conditioning" inverter in the cascaded system which matches the availability of semiconductor devices. Furthermore, the bulk inverter may be a commercial-off-the-shelf (COTS) motor drive meaning that only the conditioning inverter needs be custom made. However, a drive involving a COTS bulk inverter would require a distributed conditioning inverter control which works completely independent of the bulk inverter control. In this paper, a distributed control method is developed for the hybrid inverter drive with cascaded bulk and conditioning inverters. Moreover, a solution to the practical problem of instant synchronization between the two inverters is presented. Laboratory measurements on a 3.7-kW induction motor drive validate the proposed control