Overtone Piezoelectric Transformers for Magnetic-less Power Conversion

Piezoelectric transformers (PTs) have emerged as promising alternative passive components for power conversion, offering high efficiency and high energy densities with galvanic isolation and/or inherent voltage transformation. However, the maximum efficiencies of PT-based converters have been limited to applications characterized by high load impedances, thereby confining their utility to a narrow subset of power electronics. In this work, we propose use of overtones (i.e., higher-order resonant modes) in isolated PTs to extend their high-efficiency performance to significantly lower load impedances. We first present a modeling and design framework for overtone PTs. Then, we experimentally validate PT designs based on 1<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup>, 2<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup>, and 3<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> overtones in a dc-dc converter prototype that demonstrates a peak efficiency of ≥ 96 % with a 2.4x, 5.7x, and 9.1x reduction in maximum-efficiency load impedance, respectively, compared to fundamental-mode PT-based converters.