Observability and Observed-Based Control for a Class of Output Modular Systems With Application to Modular Multilevel Power Converters

Modularity, understood as the property that allows a complex system to be decomposed into well-defined compartments, is a distinctive element in modern engineering systems. Modularity increases scalability, facilitates mass production, and simplifies maintenance. Nonetheless, modular systems may exhibit complex dynamics, and the establishment of their structural properties can be challenging. In this brief, observability and observer-based control for a class of modular nonlinear systems are analyzed, with particular focus on the modular multilevel power converter. Analytical conditions to verify observability are given, a separation principle that enables observer-based control is formulated, and an experimental validation on a pilot-scale converter is conducted to corroborate the analytical findings.

I. Introduction

Numerous novel engineering systems are built by harmonically integrating well-defined compartments or modules, and are thereby called modular, or based on modularity. These modular systems may exhibit complex dynamics arising from the interaction of identical or heterogeneous modules and thus require sophisticated control schemes to operate them [1]. In this setting, the existence of formal guarantees for the attainment of properties such as observability and/or controllability is relevant for a sound control design.