Novel Multirate Modulator for High-Bandwidth Multicell Converters

The series and parallel multicell converters have been introduced because they provide benefits in terms of efficiency and power density. However, they also allow reducing the amount of energy stored in the filters, which potentially allows for faster dynamic responses. Interleaving the control patterns of different cells is another distinctive feature of these converters and is also the root of another potential improvement of the dynamic response: with one pulsewidth modulation (PWM) update at each subcycle of the switching period, the n-cell converter may change its average output voltage over each of these intervals, while standard converters can only control the voltage over half the switching period. In this article, a general multirate modulation strategy taking advantage of this property, while avoiding an overswitching, and compatible with any n-cell converter is proposed and validated by simulation and experimental results.

I. Introduction

In recent years, several topologies of converters have been reported in the literature to improve their performances, especially the efficiency and power density. Among them, there are multilevel converters with some of the following characteristic features [1], [2]. 1)

They include several commutation cells, which are the building blocks of the converters.

2)

The two-level chopped voltage and/or current waveforms of the different cells are added in the circuit to form voltage and/or current waveforms with more levels.

3)

The control pattern can be interleaved to optimize the output total waveform.

4)

The filters take advantage of these improved waveforms; storing less energy, they can be smaller than those of classical two-level converters.