Abstract
Piezoelectric resonators have shown promise as efficient, power-dense energy storage element alternatives to continue the miniaturization of DC-DC converters. However, practical piezoelectric resonators diverge from their ideal behavior due to spurious modes that cause high loss regions throughout their operating frequency range. Typically, control of piezoelectric resonator DC-DC converters is constrained to unidirectional power flow each resonant cycle for maximum efficiency operation. However, output power depends on the frequency with such control, which means the converter cannot operate at loads corresponding to spurious mode frequencies. This paper presents a fixed-frequency control mode utilizing the high-quality factor of piezoelectric resonators to avoid spurious modes. The fixed-frequency control enables efficient operation spanning the converters full load range, demonstrated through a prototype DC-DC converter with a custom fabricated lithium niobate resonator. At a conversion ratio of 60 V to 30 V, spurious modes limit the converters operating range from 33 W to 51 W using unidirectional power-constrained control, yet the fixed-frequency control extends operation from 33 W to 2 W.
Highlights
The drive to increase DC-DC converter power density has led switch-mode converters to higher operating frequencies where the volume of energy storage elements can decrease
Many converter topologies require inductors as energy storage elements, and inductors experience shortcomings at both high frequencies and small volumes [1]. These deficiencies of inductors have prompted the exploration of power converters with new energy storage elements
To verify the fixed-frequency control, a prototype piezoelectric resonator DC-DC converter was tested with the lithium niobate resonator from [6]
Summary
The drive to increase DC-DC converter power density has led switch-mode converters to higher operating frequencies where the volume of energy storage elements can decrease. The series and parallel resonant frequencies of the BVD circuit define the inductive region of the resonator’s impedance and bound a converter’s ideal operating frequency range. Maximum-efficiency control of ideal piezoelectric resonator DC-DC converters, referred to here as standard control, requires unidirectional power flow each resonant cycle and soft charging of the resonator’s parallel input capacitance. These requirements of standard control create a fully constrained system where a converter’s switching frequency determines the output power for a given conversion ratio.
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