State control of MMC-fed ship propulsion induction machine

Multilevel converters are indispensable for ship propulsion motors. The Modular Multilevel Converter allows a nearly unlimited cascading of voltage levels at the same complexity in construction. This allows to minimise unacceptable motor terminal overvoltages and motor insulation stress. A current-oriented control is mandatory for this drive control, because the Modular Multilevel Converter is not of the voltage-impressing converter type. For that reason, a novel state-control approach for induction machines is used to control this drive. The magnetising currents and the stator currents of the machine are the control signals. An overlaid control is used to balance the converter sub-module voltages. The basic ideas of the multivariable control of the introduced drive and the excellent control behaviour of a 17-level Modular Multilevel Converter feeding a 3.9-MW 4.16-kV induction machine are presented.