Inductance characterization of high-leakage transformers

In this paper the inductances of high-leakage transformers are investigated by analysis, measurement, and finite-element simulation. Series-coupling tests, featuring differential coupling (series opposing) and cumulative coupling (series aiding), are conducted in addition to the standard open-circuit and short-circuit tests. This paper initially reviews and discusses the various test approach featuring the open-circuit, short-circuit and series-coupling tests. Two very different types of high-leakage transformers are then characterized based on these tests. The short-circuit and series-coupling tests performed comparably for investigating the spatial variations of the primary and secondary leakage inductances of the high-power, high-leakage transformer first investigated. For the second low-power, high-leakage, high-resistance planar transformer the differential-coupling test proves to be a more useful, accurate, and insightful test than the short-circuit test.

I. Introduction

High-leakage transformers play an important role in power conversion in areas ranging from resonant conversion for dcdc applications to the separable-transformer based systems used in transcutaneous, marine, mining, and automotive power transfer [1], [2]. Outside these technical areas, transformer leakage can critically impact the operation of standard converters [3]–[5]. Thus, we are interested in quantifying the magnitude of the leakage parameters associated with the transformer primary and secondary windings. Characterization of these discrete leakages can be especially important for optimising the functionality, efficiency, and modelling of power converters using loosely-coupled transformers.