University Events

Description: TOPIC: Velocity Control of Piezoelectric Transducers with Class D Switching Power Amplifiers

Location; College of Engineering Conference Room, Textile's Building - Room 101E

ABSTRACT:
Velocity feedback control of underwater piezoelectric projectors in an array can mitigate the adverse effects of acoustic array interactions, improving beam patterns over a wide frequency band. This dissertation focuses on motional current monitoring as a method of velocity control based on earlier work, and is also applicable to velocity, acceleration, or displacement feedback in sensor arrays. The feedback stability and control loop outputs for motional current velocity control are constrained by the piezoelectric projector's electromechanical coupling coefficient, mechanical quality factor, and the accuracy of the estimate of the transducer's blocked electrical capacitance, which may vary due to environmental conditions. The steady state array equations dictating the array outputs for a single frequency continuous transmission is presented for velocity control systems, as are the conditions necessary for negative radiation impedance. It is shown that velocity control systems, regardless of the sensor types used, increases the risk for inducing negative radiation impedance which in some conditions can cause catastrophic amplifier failure. This risk increases with increased inter element acoustic coupling and higher feedback loop gain.

Velocity control of a piezoelectric load with a class D amplifier presents feedback stability challenges due to acquiring feedback after a high Q LC filter, which introduces a large gain and phase shift into the feedback loop. Post LC filter feedback is commonly used with Class D amplifiers when driving a voice coil load, but is rarely if ever used when driving an underwater piezoelectric load. Two different methods for stabilizing the feedback loop with a piezoelectric load are investigated, each with their own tradeoffs. A lossy damping network of a similar kind used in voice coil designs may be used, at the expense of resistive damping losses. Another approach is adding an inner feedback loop to synthetically dampen the filter resonance with current feedback, which requires multi-loop analysis to verify the stability of the inner and global feedback loop and the resulting outputs.

A prototype 8-layer amplifier board was designed, fabricated, and successfully tested with a 100V bus. An equivalent electrical circuit of a transducer was built to approximate the load that a candidate transducer for velocity control would present to the amplifier. The control loop parameters were then tuned to the measured parameters of the equivalent circuit to achieve motional current control. Measured feedback loop response, stability, and output levels all matched predicted levels within good tolerance.

Note: All ECE Graduate Students are ENCOURAGED to attend.
All interested parties are invited to attend. Open to the public.

Advisor: Dr. David A. Brown

Committee Members:
Dr. Yifei Li, Department of Electrical & Computer Engineering; Dr. Steven Nardone, Professor Emeritus, Department of Electrical and Computer Engineering; Dr. Boris Aronov, Adjunct Professor, Department of Electrical and Computer Engineering; Dr. Xiang Yan, Acoustic Research Engineer

*For further information, please contact Dr. David Brown via email at dbrown@umassd.edu