Microcontroller-Based, Multi-Mode 3-Level Pulse-Width Modulator

SummaryThe 3-levelvoltage inverter is an efficient solution for high power variable speed drives, as it combines high voltage capabilities(due to GTOs in series)and significant reduction of losses and/or switching frequency(due to the intermediate level leading to lower voltage harmonics). This paper shows how the subhar-monic and precalculated 3-level pulse-width modulation methods, used to control the inverter, can be implemented by a fully programmed modulator. The subharmonic modulation uses modulating and carrier waves to generate the commutations orders for the inverter. In addition to the classical bipolar 2-level and unipolar 3-level methods, our laboratory has developped a new “dipolar”3-level subharmonic modulation, which is described in the paper. The precalculated modulation, also present is based on optimized waveforms stored in EPROM, and reproduced in real time by the modulator. Concerning the implementation of these modulations, a new sampling method for the subharmonic modulation, and an ...