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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 26, NO. 11, NOVEMBER 2011

3395

A Method for Parameter Extraction of Piezoelectric Transformers
Svetlana Bronshtein, Alexander Abramovitz, Member, IEEE, Alexander Bronshtein, and Inna Katz
Abstract—A methodology for obtaining the parameter’s values of a linearized piezoelectric transformers model is proposed. The suggested technique treats thepiezoelectric transformer as an all electrical two port and relies on measurement of the electrical transfer function magnitude and phase of a loaded piezoelectric transformer. Only a single test setup is required to establish all six piezoelectric transformer’s parameter’s values. Neither manufacturer’s data nor acoustical measurements are required. The proposed approach employs the least-squaresmethod for tuning the model parameter’s values. This paper presents the theoretical foundation of the proposed method validated by experimental results. Excellent agreement is found in between the measured and the modeled transfer functions. Index Terms—Equivalent circuit, piezoelectric transformer (PT), parameters estimation, voltage conversion ratio.

Fig. 1.

Lumped equivalent circuit of aPT [2].

I. INTRODUCTION

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RADITIONALLY, power electronic converters rely on inductive energy transfer. Recent advances in magnetic technology, introduction of new materials, advent of planar magnetic cores and application of integrated magnetic design techniques, allow constructing relatively compact magnetic devices. Yet, inductors and transformers are still bulky and costly as comparedto other circuit components. Moreover, leakage inductance of high turn ratio transformers adversely affects the performance and is a menace in high voltage output converters. Moreover, transformer saturation is a limitation always to be considered. One possible alternative to the conventional magnetic transformer is the piezoelectric transformer (PT). Piezoelectric transducers are known for quitea while and are mainly used as sensors and actuators. However, owing to newly developed piezoelectric materials with improved piezoelectric characteristics, PTs are gaining a renewed attention for power electronics applications. PTs are low power devices that can be used in low power dc/dc converters, ac adapters, and electronic ballasts for fluorescent lamps. PTs are free from the aforementioneddrawbacks of inductive transformers [1]. PTs are compact, low weight, have good efficiency, and can help miniaturizing modern power supplies. Among the advantages of a PT are the absence of wind-

Manuscript received December 1, 2010; revised February 4, 2011; accepted March 8, 2011. Date of current version November 18, 2011. Recommended for publication by Associate Editor S. Williamson. S.Bronshtein, A. Abramovitz, I. Katz are with the Department of Electrical Engineering, Sami Shamoon College of Engineering, Beer-Sheva 84100, Israel (e-mail: Svetlanab@sce.ac.il; alabr@hotmail.com; innak@sce.ac.il). A. Bronshtein is with the ELTA, Beer-Sheva 77102 Israel (e-mail: alik.bronshtein@gmail.com). Digital Object Identifier 10.1109/TPEL.2011.2139225

ings, simple geometry and potentially lowcost. Moreover, PTs possess the benefits of inherently sinusoidal operation and emit no electromagnetic interference. Furthermore, PTs can withstand very high voltage and, thus, provide good isolation. These features are especially valuable in small size applications. However, PTs are complex devices. The piezoelectric material responses to the electric voltage applied to the primary port bydeveloping a mechanical stress. An acoustic wave is generated in within the bulk of the piezoelectric material that excites the secondary port and develops an electrical voltage across the secondary port electrodes. The structure of PT’s acoustical resonator can support a multitude of vibration modes and resonant frequencies. The modes depend on PT geometry and boundary conditions. The later are defined...