Design and implementation of piezoelectric technology based power devices

In this dissertation, piezoelectric materials were adopted in various power devices, and were further developed more specifically to power converters. The main purpose of this dissertation is to use piezoelectric transformer to replace the conventional electromagnetic transformer in power converters. A piezoelectric transformer based converter may reduce the electromagnetic interferences (EMI), the thickness ofthe converters and may increase the power density of the converter. Cold cathode fluorescent lamp (CCFL) based inverters, DC/DC converters and optimization of the piezoelectric layer fed rectifiers are the three main parts in this dissertation. Previous researches used the concept of the optimal loading condition as the major design parameter. However, practical power converters require regulating output current or voltage. Considering the power converters with current or voltage regulation, the concept of the optimal loading condition is no longer suitable to be the major design parameter. In this dissertation, the vibration velocity was adopted as the major design parameter, which makes the design procedure of piezoelectric transformers easier and clearer compared to the usual design rule. The proposed design procedure can predict the temperature rise as well as the losses of the piezoelectric transformers clearly. Both cold cathode fluorescent lamp based inverters and DC/DC converters can be designed to fit the requirements and the specifications well by the proposed design procedure. A 32 inches LCDTV inverter and a lOWatt step-down DC/DC converter were developed successfully, based on the design procedure detailed in this thesis. In addition, although the piezoelectric transformer itself does not radiate EMI , it still remains the conducted EMI problem. Due to the effect of parasitic capacitors and to the specific effect of the rectifier connected to the piezoelectric transformers, the EMI behaviour of the piezoelectric transformer based converter is quite different from typical converters. The model and analysis of the conducted EMI were studied and detailed in this dissertation. On the other hand, a piezoelectric layer fed rectifier is a non-linear device, which is not easy to analyze in general. The concept of work cycle analysis was proposed to simplify the analysis and the design procedure. Based on these work cycle analysis, a new concept of velocity controlled piezoelectric layer fed rectifier was proposed to optimize the energy flow out of the piezoelectric layer. This technique, also presented herein, was applied successfully to the structural damping.