A discontinuous carrier-based multilevel modulation for multilevel converters

Multilevel modulators based on carrier shifting reach their minimum harmonic content only through asymmetrical sampling and proper phase shifting. Since their implementation is critical for microcontrollers and DSP's peripherals, field programmable gate array (FPGA) becomes attractive because it allows the design and realization of "ad hoc" digital modulators with the desired number of timers. On the other hand discontinuous modulation, poorly investigated in single-phase systems, may lead to results similar to those of asymmetrical carrier-shifted modulation, but with less implementation burden. When modulation index is near unity (typical in active rectifier applications), the discontinuous modulation can outperform other choices. In this paper a new single-phase multilevel modulation technique is proposed, analyzed and compared with other multilevel modulation techniques. The implementation of the considered multilevel modulations using standard microcontrollers is discussed and the use of FPGA is proposed and analyzed.