PWM method to eliminate power sources in a nonredundant 27-level inverter for machine drive applications. http://dx.doi.org/10.1109/TIE.2008.927233

Abstract

A non-redundant, three-stage, 27-level inverter using “H” converters, is analysed for medium and high power machine drive applications. The main advantage of this converter is the optimisation of levels with a minimum number of semiconductors. However, the system needs six bi-directional and isolated power supplies, and three more unidirectional if the machine is not using regenerative braking. In this paper these nine power supplies are reduced to only four, all of them unidirectional, using three strategies: 1) the utilization of independent and isolated windings for each phase of the motor, 2) the utilization of independent input transformers, and 3), the most important of them, the application of special PWM strategies on the 27-level converter, to keep positive average power at the medium power bridges, and zero average power at the low power bridges. The generation of this PWM and control of this multi-converter was implemented using DSP controllers, which give flexibility to the system.