UBC Theses and Dissertations
Novel concepts for power electronics control : introducing the dynamic physical limits, the average natural trajectories, and the centric-based controller Galiano Zurbriggen, Ignacio
Controllers are an essential component in power conversion systems that have a significant impact on characteristic features such as performance, efficiency, size, and cost, among many others. During the last four decades, countless efforts have been made to find better controllers for power electronics systems in order to improve the converters steady state and dynamic behaviour, increase power densities and reduce losses in the system. Small-signal based linear controllers have been the preferred alternative during decades. This technique features fixed switching frequency and low computation/sensing requirements, while the dynamic response can be improved to only a limited extent and the global stability cannot be ensured. On the other hand, excellent dynamic performances and global stability are achieved by boundary controllers, in which the switching frequency is variable and faster sensors are required. The first part of this work presents a practical tool which allows to objectively quantize improvements made by the controllers to the performance of power converters. The theoretical optimal dynamic behaviour of buck converters is determined, analyzed, and characterized using closed-form mathematical expressions, setting a strong benchmark point for the performance evaluation. Taking the physical limits of dynamic performance into account, and merging the advantages of linear and boundary techniques, a novel control scheme is developed for buck converters. The proposed controller is based on a large-signal model introduced here: the Average Natural Trajectories (ANTs). Enhanced dynamic performance and global stability are achieved while low sensing and computational requirements are maintained, which makes the technique very appealing for use in high-volume production applications. Due to the outstanding results in the basic buck converter, and in order to illustrate the application of the ideas introduced in this work for different topologies, the ANTs and the centric-based controller are developed for boost converters. The obtained results confirm the enhanced dynamic response and fixed frequency operation as natural advantages of the proposed control scheme. The theoretical findings are supported by detailed mathematical procedures and validated by experimental results, which highlight the practical usefulness of the concepts introduced in this work.
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