Abstract
A three-phase stepped-wave voltage source inverter is presented in which the pulse-width and amplitude are variable. The different step levels that can be synthesized from a dual bridge inverter system are derived and they are grouped appropriately to produce three-phase stepped waveforms. It is found that, using a dual bridge inverter and a set of transformers, four basic types of step waveforms can be generated, which have different fundamental voltage content. In order to have a stepless control of fundamental voltage, a control scheme is presented, wherein the switching pattern of the bridge inverter is varied so as to have low harmonic content. The stepped output waveform has only (12n ± 1)th harmonic content, where n = 1, 2, 3,… The control system has been experimentally verified and found to give good performance.
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