Closed Loop Control for a Piezoelectric-Resonator-Based DC-DC Power Converter

Abstract

Miniaturization of power electronics reduces their cost and increases their scope of potential applications. Power electronics traditionally rely on magnetics for energy storage, but magnetics are fundamentally less efficient and power dense when scaled to small sizes. Piezoelectric resonators (PRs), which store energy in mechanical inertia and compliance, are promising alternatives to magnetic energy storage for miniaturized power electronics because of their high quality factors and favorable scaling properties. Dc-dc converters relying on only a PR for energy storage have been demonstrated to achieve high efficiency through specific behaviors including PR soft charging, ZVS of all active switches, and all-positive instantaneous power transfer. However, closed-loop control of PR-based dc-dc converters is necessary for them to be practically viable. Implementation of this closed loop control is challenging because achieving all desired high-efficiency behaviors requires simultaneous control of duty cycle, dead time, and frequency.

This thesis presents a closed-loop control scheme for PR-based dc-dc power converters that are implemented with six-stage switching sequences and two-half-bridge topologies. The voltage regulation range of a PR-based converter can be derived from its operating modes, referred to as switching sequences. The regulation range is then used to conceptualize each half-bridge in the converter topology as regulating or nonregulating. Control methods for the regulating and nonregulating half-bridges capable of achieving all desired high-efficiency behaviors are proposed.

This thesis also presents several methods for modeling the operation of PR-based dc-dc converters, both in periodic steady state (PSS) and in dynamic operation. PSS solutions are obtained using conservation equations associated with the switching sequence, including strategies for both ideal solutions and solutions considering the mechanical loss of the PR. Several methods for modeling converter dynamics are proposed, including a linearizable state space model.

Finally, this thesis designs and implements an example PR-based dc-dc converter and a microcontroller-based closed-loop controller. The converter is operated at 30 V to 10 V with a 0.5 W output power. The controller was verified to meet all of the desired high efficiency behaviors, and its transient response characteristics are evaluated.