A transverse traveling wave piezoelectric transformer

Piezoelectric transformers can be a promising candidate in isolated power converters to replace magnetic ones as they present high quality factor, high voltage gain and low electromagnetic compatibility issues. Herein a new topology of traveling wave piezoelectric transformer (TWPT) is proposed. Unlike conventional piezoelectric transformers, the proposed transformer uses progressive waves to carry out the electromechanical conversion. The main asset of the structure is the obtaining of a polyphase system of voltage at the output. Thus, associated with an appropriate converter circuit topology, it enables any kind of AC-DC or AC-AC power conversion. The proposed piezoelectric transformer consists in a multi-electrode ring architecture and uses transverse wave, i.e. the deformation is orthogonal to the propagation direction, to perform the electro-mechanical coupling. Furthermore an analytical modelling is exposed to describe the electro-mechanical behaviour of the transformer. The technique allows to obtain an admittance matrix that completely characterizes the coupling between all the electrodes and that can be used to simulate the transformer in electronic circuit software. With this model it is possible to predict numerically the voltages, currents, displacements and stresses in the piezoelectric transformer over time as a function of the geometrical and physical parameters of the materials in early design stage and it allows a co-design between the piezoelectric transformer and its power electronics circuitry. Finally, a prototype of the TWPT with four phase output voltage is presented to experimentally validate this new concept.