Synchronous Control of Cascaded Three-Level Inverters

Novel method of synchronous pulsewidth modulation (PWM) has been disseminated for control of cascaded neutral-point-clamped inverters feeding open-end winding induction motor drive with single dc voltage source. Control algorithms provide in this case full elimination of the common-mode voltages both in each inverter and in the load. Phase voltages of the drive system are characterised by quarter-wave symmetry during the whole control range including the zone of overmodulation, and its spectra do not contain even harmonics and sub-harmonics (combined harmonics). Simulations give the behaviour of the proposed methods of synchronous PWM in these systems. Continuous, discontinuous and "direct-direct" schemes of synchronous PWM, applied for control of cascaded three-level converters, have been analysed and compared.