Affiliations: [a] Department of Engineering Science and Ocean
Engineering, National Taiwan University, Taipei, Taiwan | [b] SATIE, ENS Cachan, Cachan, France | [c] Mi\'{e}zo Inc., Taiwan | [d] Universit\'{e} de Cergy-Pontoise, Neuville/Oise,
France | [e] IUFM, Universit\'{e} Paris Est Cr\'{e}teil, St Denis,
France | [f] Institute of Applied Mechanics, National Taiwan
University, Taipei, Taiwan
Correspondence:
[*]
Corresponding author: D. Vasic, SATIE, ENS Cachan, 94235 Cachan,
France. E-mail: dejan.vasic@satie.ens-cachan.fr
Abstract: In this paper, we propose a new design of a piezoelectric
transformer (PT) for low-profile DC/DC converter applications, which increases
the output power by using heat transfer equipment. We examined several
parameters, which allow us to produce a piezoelectric transformer with optimal
efficiency. Instead of looking at the typically optimal loading condition of
the PT, we consider the influence of the temperature rise on losses. When the
vibration velocity is too large, the piezoelectric transformer generates heat
unstably until it cracks. By maintaining the vibration mode and limiting the
heat produced by the PT, this design can enhance the power capacities of the PT
and thus increase the output power of the DC/DC converter. A finite element
analysis (FEA) approach with COMSOL Multiphysics was made to predict PT's
working temperature. A theoretical-phenomenological model was also developed to
explain the relationship between the equivalent losses resistances and the
input voltage at different temperatures. It will be shown that the vibration
velocity as well as the heat generation increases the losses. A large vibration
velocity and generated heat may cause the temperature feedback loop to enter
into an unstable state. We began by modeling a piezoelectric transformer in a
DC/DC converter configuration in order to determine the design constraints and
variables such as the maximum mechanical current, the temperature distribution,
the PT geometrical configuration and the energy balance. In our design, the PT
power capacity increases 3 times (i.e. from 4.54 W to 13.29 W) at specific
temperature and the effects of the different cooling methods of the system were
verified. The study comprises of a theoretical part and experimental
proof-of-concept demonstration of the proposed design method.
Keywords: Piezoelectric transformer, power capacity, power density
