Fundamental limits on energy transfer and circuit considerations for piezoelectric transformers

This work investigates fundamental limits on electromechanical energy conversion capacity of piezoelectric transformers by considering a work cycle analysis. Fundamental limitations in a lossless piezoelectric transformer are imposed by maximum electric field strength, maximum surface charge density, maximum stress and maximum strain. For the lossless case, the authors´ analysis indicates that the mechanical stress limit is the effective constraint in typical PZT materials. For a specific PZT-5H sample considered, a mechanical stress-limited work cycle indicates that this material can handle 330 W/cm³ at 100 kHz. A second direction this work has taken has been an investigation into a soft-switching drive and control circuit, that does not require any magnetic components. The theory of operation of soft-switching resonant drive circuitry is discussed, and experimental results on a soft-switching inverter incorporating no magnetic components are reported