Modeling and experimental analysis of a Coupling Inductor employed in a high performance AC power source

A large number of papers regarding Coupling Inductors (CIs) for interleaved parallel connected converter stages is available in literature. However, to the knowledge of the authors, a comprehensive summary of the basics and a description of the modeling and the experimental analysis, as well as the conditions which must be satisfied to avoid saturation of the CI´s core are still missing. This paper intends to close this gap partially based on research conducted on a multi-phase 3-level voltage source converter which is intended to be employed as a high performance AC power source. The main focus of the investigations is on CIs with high coupling factors k ≈ 1. Besides a detailed CI literature review, the focus is on the modeling of the component itself and on the analysis of the requirements for the targeted application. The separation of the coupling inductor currents and bridge-leg output voltages into longitudinal and transverse components is introduced to illustratively explain the CI´s behavior. A complete investigation to avoid saturation in all operating conditions is conducted. Finally, the derived theoretical analysis and their conclusions are successfully verified by extensive measurements on a phase leg of a 10 kW 3-level voltage source converter prototype.