Design and Analysis of Piezoelectric Transformer Converters

Piezoelectric ceramics are characterized as smart materials and have been widely used in the area of actuators and sensors. The principle operation of a piezoelectric transformer (PT) is a combined function of actuators and sensors so that energy can be transformed from electrical form to electrical form via mechanical vibration.

Since PTs behave as band-pass filters, it is particularly important to control their gains as transformers and to operate them efficiently as power-transferring components. In order to incorporate a PT into amplifier design and to match it to the linear or nonlinear loads, suitable electrical equivalent circuits are required for the frequency range of interest. The study of the accuracy of PT models is carried out and verified from several points of view, including input impedance, voltage gain, and efficiency.

From the characteristics of the PTs, it follows that the efficiency of the PTs is a strong function of load and frequency. Because of the big intrinsic capacitors, adding inductive loads to the PTs is essential to obtain a satisfactory efficiency for the PTs and amplifiers. Power-flow method is studied and modified to obtain the maximum efficiency of the converter. The algorithm for designing a PT converter or inverter is to calculate the optimal load termination, YOPT, of the PT first so that the efficiency (power gain) of the PT is maximized. And then the efficiency of the dc/ac inverter is optimized according to the input impedance, ZIN, of the PT with an optimal load termination.

Because the PTs are low-power devices, the general requirements for the applications of the PTs include low-power, low cost, and high efficiency. It is important to reduce the number of inductive components and switches in amplifier or dc/ac inverter designs for PT applications. High-voltage piezoelectric transformers have been adopted by power electronic engineers and researchers worldwide. A complete inverter with HVPT for CCFL or neon lamps was built, and the experimental results are presented. However, design issues such as packaging, thermal effects, amplifier circuits, control methods, and matching between amplifiers and loads need to be explored further.