A New Non-Isolated Low-Power Inductorless Piezoelectric DC–DC Converter

Abstract

A new non-isolated low-power inductorless piezoelectric resonant converter is presented. The piezoelectric material is used as an energy storage element like an inductance in a classical Buck-Boost power electronic converter. As opposed to most existing piezoelectric converters, the proposed topology enables to dynamically adjust the output power and ratio keeping a high efficiency for a large range of output powers and for a large range of conversion ratios taking advantage of piezoelectric high quality factor and achieving zero voltage switching. A theoretical analysis of the step-up converter using an energetic approach is introduced and enables a fast and reliable pre-design of the piezoelectric component. This analysis is in perfect agreement with the simulation model performed on Matlab/Simulink. For a given piezoelectric resonator both analytical and simulation models provide very high efficiencies for different output powers. The converter is tested experimentally with a 10 V input voltage using the piezoelectric radial resonance mode. An efficiency higher than 98% for a 160 mW power conversion was achieved, decreasing slowly to 78% at 1.4 W. For a large range of voltage gains, the efficiency remains higher than 90% up to an output power of 750 mW. The experimental results are in perfect agreement with the theoretical analysis until 500 mW.

Effects of Disc-Shaped Piezoelectric Size Reduction on Resonant Inductorless DC-DC Converter

“…The model presented in [4] is built considering the equivalent circuit of the piezoelectric resonator at resonance that can be seen in Figure 1. R represents the mechanical damping (and its associated losses) but thermal effects and semiconductor losses are neglected.…”

“…Table 1 highlights the fact that reducing the diameter and thickness have very positive effects until getting close to the material limits. The more restrictive limit is current (measured maximum current amplitude of 650 mA in [4] for D = 25mm and th = 0.75mm) whereas the maximal electric field is around 1600V/mm for C213 Fuji ceramic® resonators. In conclusion, although thickness and radius diminutions both lead to positive effects, it is more advantageous to reduce the thickness compared to the radius considering the limits when operating at low voltage.…”

“…For low-power range (until some dozen of Watts) piezoelectric elements have inherent advantages compared to magnetic such as a very high quality factor leading to very high efficiency, a planar shape, a high-power density, low EMI radiations [2] and should be suitable for integration in silicon . The converter described in Figure1 and first presented in [3], [4], has the particularity of using the piezoelectric material as an energy storage element, contrary to most common converters with piezoelectric transformers. It has the advantage of being inductorless, working in zero voltage switching (ZVS) mode (no switching losses) and keeping high efficiency for a very wide range of output ratios and output powers, always driving the system at resonance.…”

“…In a steady state, there is, at each cycle, an energy balance (the taken energy equals the released one), a charge balance and ZVS operations. For a given piezoelectric resonator, very promising efficiencies have been reported [4] but only one piezoelectric resonator was tested. The impact of the material thickness and diameter is only partially mentioned but not fully developed.…”

“…However, understanding their role is essential to properly design the piezoelectric transducer. This work is based on the analytical model presented in [4] for a step-up converter but the resonator thickness and diameter are added in the model. Five different piezoelectric transducers are tested in experimentation work.…”