Empiric analysis of zero voltage switching in piezoelectric transformer based resonant converters

Abstract

Research and development within piezoelectric transformer (PT) based converters are rapidly increasing, as the technology is maturing and starts to prove its capabilities. High power density and high efficiencies are reported and recently several inductor-less converters have emerged, which demonstrates soft switching capabilities. The elimination of a bulky inductor, reduces size and price of the converter, but demands a soft switching optimised PT. Several attempts of expressing the soft switching capability have been made [5][12], with some shortcomings. The goal of this paper is to derive a simple expression of the maximal obtainable soft switching capability (ZVS factor), for a specific PT design, assuming a matched load. The expression has been derived through series of parametric sweep simulations of the inductor-less halfbridge topology, which revealed that a linearization of the maximal soft switching capability can be performed, in the area of interest. This expression is intended to form a basic tool for development of soft switching optimised PT's, which enables the utilisation of inductor-less topologies.

State-of-the-art piezoelectric transformer-based switch mode power supplies

“…The obtainable ZVS region of PTs is very small regarding load and frequency [13]. Moreover, maximum obtainable soft switching has been derived in a simple relation [14] in order to design PTs under the matched load condition. This expression relates ZVS to the input and output capacitors of PTs in addition to efficiency (1).…”

“…In [14], this topology has been applied and a simple expression of soft switching capability has been revealed by empirical deriving of the ZVS factor. However, the shortcoming is that this factor is valid only when the load is matched.…”

Forward Conduction Mode Controlled Piezoelectric Transformer-Based PFC LED Drive

“…The proposed PT LED drive utilizes an inductorless halfbridge topology [3], [14]- [16], [22], [26], which eliminates the bulky series inductor and only converts energy through the electromechanical PT resonance tank. Fig.…”

“…LED drive, which consist of an input filter, a full-bridge rectifier, an inductorless half-bridge drive, with FCM control, and the PT, followed by an output rectifier and the LED load. In order to achieve consistent and efficient operation, the inductorless half-bridge topology requires a zero voltage switching (ZVS) optimized PT [3], [14]- [16]. This application utilizes a 20-mm radial mode ZVS optimized PT [7], [17]- [19].…”

“…The operation frequency is one of the most critical parts, when utilizing PT-based converters, as the PT resonance frequency is very narrow [3], [5]- [7], [14]- [16], [20]- [22]. Some of the most common control methods are phase lock loop (PLL) [23]- [27] and resonance current control [28], but self-tuned control has also been proposed [29].…”