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A general procedure for maintaining soft switching in inductor-less half-bridge piezoelectric transformer (PT) inverter was analyzed by applying the equivalent circuit of the PT device. Soft switching capability of the PT was delineated and detailed guidelines are given for the load and frequency boundaries, voltage transfer function and the output voltage that will keep the operation under ZVS conditions. The analysis takes into account the maximum power dissipation of the PT, which is used to bind the permissible power transfer through the device. The analytical results for the half-bridge inductor-less PT inverter where verified by simulation and experiments for a radial vibration mode PT.

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Abstract-The objective of this study was to develop recommendations for an optimal design of piezoelectric transformer (PT) ac/dc converters. The paper presents a comprehensive comparison of the two commonly used rectifier topologies in a PT based power converters: current doubler and voltage doubler rectifiers. The advantages and disadvantages of the two rectifiers were investigated and the range of their applications with respect to output current, voltage, power capability, load resistance etc.-was delineated. Generic parameters are proposed and used to derive normalized and closed form equations that can help choosing a PT for a given set of requirements. Simulation and experimental results were found to be in a good agreement with the derivation of the theoretical analysis.Index Terms-Current doubler, piezoelectric transformer (PT) ac/dc converters, voltage doubler rectifiers.

An approximate analysis of LCL converters operating above and below resonance is presented. The study based on replacing the rectifier and load by an equivalent parallel resistance, applies the fundamental harmonics method and the assumption that the current through the diodes of the output rectifier has a sinusoidal waveform. Equations obtained for the conduction angle of these diodes (less than π in Discontinuous and equal to π in Continuous Conduction Modes) are used for the developing the output to input voltage ratio as a function of three independent parameters. The theoretical results coincide with good agreement with the experiments.