Adaptive sigma-delta modulator applied to control a five level multilevel inverter

Multilevel inverters have recently acquired importance in the number of publications in scientific literature. The PWM modulation technique is the general technique to control it. But it can be complicated to implement, moreover if the reference changes. Sigma-delta modulation can be a more simple solution, but has a problem. Its output signal frequency spectrum is worse than the PWM frequency spectrum. This paper describes the development of an adaptive sigma-delta modulator that allows to control a floating capacitors five levels multilevel inverter from, at the moment, a single tone 50 Hz reference signal. The modulator sample frequency is 200 kHz and it improves greatly the frequency spectrum of a simple sigma-delta modulator. Instead the sigma-delta modulation can perfectly be used in resonant DC-link converters, in this paper the prototype developed works with hard switching.

I. Introduction

Important advances in DC-AC converter topologies have been recently developed, improving their operation to increase the switching frequency. In traditional switching techniques the inverter transistors switch with the whole voltage applied in the DC bus. This situation causes high swithching losses and dv/dt.