Motional-Current-Sensing Method and Simplified Closed-Loop Control Strategy for Piezoelectric-Resonator-based DC-DC Converters

TL;DR

This paper introduces a novel motional current sensing method for piezoelectric resonator-based DC-DC converters, enabling improved control and stability with simplified hardware and software.

Contribution

It proposes a ring-dot shaped piezoelectric transformer-based sensing technique and an event-driven control strategy that enhances stability and reduces resource requirements.

Findings

Achieved zero-voltage switching (ZVS) for all transitions within a switching cycle.

Demonstrated robustness of the sensing method against non-ideal factors.

Enabled self-startup and improved stability in PR-based converters.

Abstract

Piezoelectric resonators (PRs) have been seen as a competitive alternative to magnetic components. In PR-based converters, the motional current (in the LC series branch of the equivalent circuit) is vital for control proposes but cannot be measured directly. The difficulties to detect the zero-crossing points or to measure the amplitude of the motional current has been one of the most dominating obstacles that complicates the control strategies and limits the frequency range of the PR-based converters. This work discusses a ring-dot shaped piezoelectric transformer (PT) based motional current sensing method that provides current information with low-delay, low-loss and intrinsic isolation. It is physically proven that the proposed method is robust with various non-ideal factors of the piezoceramic and circuit implementation. Based on this, an event-driven control strategy is introduced, consisting of only a finite state machine, a PI loop, a low-speed ADC and several comparators. Experiments on a step-down PR-based converter verify that the proposed approach realize ZVS for all transitions within a switching cycle with reduced hardware and software resources, enhances stability and is capable of self-startup.