Control Strategy for a Merged Switched-Capacitor Piezoelectric Resonator-Based DC-DC Converter Enabling Output Regulation at Fixed Frequency

Piezoelectric resonator-based dc-dc converters have recently been proposed and demonstrated to have high efficiency and high power density. Past research has explored operation modes and control strategies for such converters that are able to achieve output regulation with variable frequency control. However, piezoelectric resonators generally have spurious vibration modes across a range of frequencies which make such control approaches unattractive. This paper proposes a new control approach for a merged switched-capacitor piezoelectric-resonator based dc-dc converter that achieves output regulation at fixed frequency. In this converter, a switched capacitor and a piezoelectric resonator are combined to form a merged multi-level resonant converter structure. The converter is operated to alternate between two states that deliver charge to the resonator: one in which the capacitor is connected in series with the current path, and the other in which the capacitor is bypassed. The modulation between these two states controls the energy delivered to the resonator and can be used for output regulation. Such operation of the proposed topology enables the switched capacitor to be soft-charged by the current from the piezoelectric resonator and achieve zero-voltage-switching (ZVS) for all the transistors. The steady-state operation of the converter under the proposed control strategy is analyzed in detail. Finally, simulation and experimental results are presented to verify the advantages of the proposed control strategy.