Adaptive Control and Formal Stability Analysis of Single-Phase Flying Capacitor Multicell DC-AC Inverters

Abstract

Multicell converters and inverters using flying capacitors are usually used for high voltage power conversion applications. This study is carried out in a general context concerning an N-cell flying capacitors converter described by an (N + 1)th order average mathematical model. A nonlinear adaptive backstepping controller suitable for regulating the voltages across the N-flying capacitors is proposed with the aim to reach equitably distributed stresses on the converter switches. The controller also aims at generating a sinusoidal voltage with a desired amplitude and frequency at the output of the converter as well as to estimate, in real time, the load resistance. Special attention is devoted to the stability analysis of the whole closed-loop system with load estimation by using Lasalle’s invariance principle and Lyapunov method. The system performance is tested by means of numerical simulations showing that the proposed controller meets its objectives in terms of tracking, regulation, robustness and adaptation and demonstrating that it outperforms the classical backstepping controller.