Controllability Analysis and Verification for High-Order DC-DC Converters Using Switched Linear Systems Theory

Output voltages of renewable energy sources, such as photovoltaic units and fuel cells, are normally low, and multistage boost converters or single-stage high step-up converters are usually employed to increase the output voltage to be connected to the electric grid. Among all converter technologies, single-stage high-order dc-dc converters with multiple cells have gained significant popularity in recent years due to their high power density, low cost, and high efficiency. With an increased number of cells, the number of switching variables and dynamic components in multicell converters also increases, leading to control difficulties and consequently system malfunction. In order to understand and ensure the controllability of these converter systems, in this article, we establish high-order mathematical models for typical single-stage multicell high-order dc-dc converters and study their controllability using switched linear systems theories. The structure controllability, state controllability, and output controllability of the converters are analyzed in detail based on the proposed mathematical model. The theoretical analysis is substantiated by simulation and experimental verification on the improved four-cell switched-inductor dc-dc converter. The outcome of this article will provide a theoretical framework and useful references for parameter and control designs for high-order converters in practical applications.