Dartmouth Events

Pseudo-Resonant Switched-Capacitor Drive Circuits for Electrostatic Loads

Thesis Committee

Prof. Jason T. Stauth (Chair)

Prof. Charles R. Sullivan

Prof. John X.J. Zhang

Abstract:

In recent years, piezoelectric and other electrostatic actuators have gained traction in a variety of small-scale electromechanical applications including mm- and cm-scale robotics and human-tactile feedback (haptics) due to improved force-displacement, more flexible geometries, and smaller size compared to conventional electro-magnetic actuators. However, electrostatic actuators (including piezoelectric devices) typically require high-voltage drive signals to achieve maximum benefit; the use of these devices in small electromechanical systems further motivates stringent size and weight constraints of the drive circuitry. Example system constraints in ‘micro’ robotic applications include a need for drive voltages of hundred volts to several kilovolts, volume << 1 cm³, and weight <<1g.

This proposal explores new topologies and integration strategies for the drive circuitry for small-scale, high-voltage electrostatic actuators. Specifically the proposal outlines a reconfigurable series-parallel switched-capacitor (SC) DC-DC converter that can both provide the needed voltage conversion (boost) from a low-voltage supply or battery and control the actuator drive voltage waveform. Importantly, the proposed system is both efficient and small size. The SC driver can be modelled as a pseudo-resonant system which can both provide and recover the reactive (CV²) power which dominates power flow in typical electrostatic loads. The proposal will provide an overview of past work in electrostatic drive systems, including hard-switching drivers and strategies which use predominantly magnetic-boost topologies. An overview of the switched-capacitor approach will be provided in order to outline advantages of the pseudo-resonant SC converter. Implementation details of several integrated-circuit (IC) prototypes will be presented including the need for scalable high-voltage level shifters, local voltage references, and embedded control. Future work which extends the concept to other applications, specifically gate drivers for modern power semiconductor devices will be discussed.