Current Mode Control for High Frequency Piezoelectric Resonator-Based DC-DC Converters

Theoretically, increasing dc-dc converter switching frequency enables smaller passive components and high system power density, as required by many applications. However, inductors and transformers intrinsically scale poorly to high frequency and small volumes, creating a bottleneck to realizing high frequency, high power density dc-dc converters. Designing dc-dc converters without inductors, and instead using piezoelectric resonators for passive energy storage, bypasses this bottleneck. While prototype piezoelectric resonator based dc-dc converters have demonstrated high power density and efficiency at MHz switching frequencies, these converters rely on open-loop control. Practical applications necessitate closed-loop control for these converters, but the present methods for closed-loop control do not scale to MHz frequencies. This article presents a closed-loop control method for piezoelectric resonator based dc-dc converters using current mode control, feedforward compensation, and real-time calculated switch timings. The method scales to MHz switching frequency and is demonstrated with a 750 kHz, 100 W, 99.3% efficient prototype converter using paralleled, radial mode lithium niobate resonators.