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, our 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/cm 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 softswitching resonant drive circuitry is discussed, and experimental results on a soft-switching inverter incorporating no magnetic components are reported.