Nonlinear Losses and Material Limits of Piezoelectric Resonators for DC-DC Converters

Increasing power converter density by shrinking magnetic components faces an uphill battle against the physics of inductors at small volumes and high frequencies. As a solution, storing energy in mechanical vibrations via the piezoelectric effect enables power converter topologies free of magnetic components. Due to their intrinsic material properties, piezoelectric devices used for power conversion can be efficient and power dense even at small volumes and high frequencies. Despite these promising characteristics, previous analyses of piezoelectric materials for power conversion and modeling of piezoelectric-based power converters rely on small signal measurements, yet prototype converters have shown efficiency diverging from the small signal models at high power. Moreover, the theorized material limits of piezoelectrics have little experimental backing. This paper investigates nonlinearities arising from temperature, voltage bias, and power handling in piezoelectric resonators which account for divergent behavior from small signal modeling. An apparatus for testing the nonlinearities and material limits of piezoelectric materials is developed and measures the large-signal performance to failure of two common materials for piezoelectric power conversion, PZT and lithium niobate (LN).