PhD Thesis Defense: Bahlakoana Mabetha

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"Hybrid DC-DC Converters for Soft Charging Capacitive Loads: Modeling, analysis and design"

Abstract

Recent trends in haptics, micro-robotics and ultrasound technology have shown an increasing use of piezoelectric and other electrostatic actuators. These actuators are suited for miniaturized applications due to their favorable scalability at small size, low power consumption, and faster response. Their electrical impedance at lower frequency (their typical operating range) is capacitive, therefore, they can be modeled as capacitive loads. The driving circuits for capacitive actuators need to deliver and recover (bidirectional) dominantly reactive power, unlike typical power electronics converters for resistive loads which deliver (unidirectional) real power to the load. Therefore, the circuits, operation, and optimization required to drive these capacitive loads differ from traditional DC-DC or DC-AC converter circuits that deliver real power.

Several DC-DC converter architectures have been explored to deliver reactive power to capacitive loads. Past works have been limited by efficiency, power density or voltage regulation. This thesis explores the use of hybrid DC-DC converters to drive capacitive loads where high voltage, high power (energy) density, and high efficiency are important. A hybrid converter merges a magnetic converter and a switched capacitor (SC) converter, using both capacitors and inductors as energy storage and energy processing elements. Hybrid converters leverage the benefits of magnetic converters to soft charge the load and regulate the output voltage, and the SC converter benefits of efficient voltage conversion and use of high energy density capacitors. The hybrid topology explored in this thesis merges the magnetic buck-boost converter and the multilevel series parallel SC converter.

In this work, modeling, operation, optimization, and implementation of the hybrid soft charging converter are presented, highlighting its benefits as a pathway towards high energy density converters for capacitive loads. The integrated circuit implementation of the hybrid converter designed in 180 nm SOI process is presented.

Thesis Committee

• Prof. Jason T. Stauth (Chair)
• Prof. Charles R. Sullivan
• Prof. William J. Scheideler
• Prof. Kaushik Jayaram (CU Boulder)

Contact

For more information, contact Thayer Registrar at thayer.registrar@dartmouth.edu.