Browsing by Author "Cole, Daniel G."

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    Design of, and initial experiments with, a MIMO plate control testbed
    Cole, Daniel G. (Virginia Tech, 1992-09-01)
    This work discusses the design of, and initial experiments with, a MIMO plate control testbed. This structure will be used as a development and standard comparison site for AVC and ASAC and is an extension of previous SIMO control investigations which used accelerometers and shakers. This portion of the development process of the MIMO plate control testbed is concerned with actuator and sensor materials and architecture, modeling approaches and requirements, and initial control experiments. The piezoelectric sensors and actuators are arranged on the plate to control the first five vibration modes. The sensors measure plate positions using a high impedance signal conditioning amplifier. The sixteen-channel design implements a band-pass filter to eliminate low- and high-frequency noise. The power amplification scheme chosen for the actuators uses low-gain amplifiers (~2.5 V/V) in series with a transformer (24:1) to deliver high voltages (up to 150 V) to the actuators. Low-pass smoothing filters (200 Hz cutoff) were added on the control inputs to reduce the high frequency content of the zero-order-held digital control signal. Initial methods for system identification of piezostructures are presented. Parametric frequency response approaches (modal analysis) were used and the model achieved is compared with measured data and purely analytic models. The empirical model was used in initial SIMO control experiments to demonstrate the testbed closed-loop performance. A LQG controller was implemented and produced 6 dB of suppression for the second mode for a 110 Hz disturbance.
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    Harmonic and Narrowband Disturbance Rejection for Linear Time-Periodic Plants
    Cole, Daniel G. (Virginia Tech, 1998-10-19)
    This research investigates the harmonic and narrowband disturbance rejection problem for linear time-periodic (LTP) systems. The consequence of disturbances on LTP systems is similar to their linear time-invariant (LTI) counterparts, but is complicated by the interaction of the disturbance and plant acting at different frequencies, which manifests itself in the modulation of the disturbance signal. The result, for an m-periodic plant and disturbance containing a single tone, is that the output contains m tones. Using various disturbance rejection architectures, harmonic and narrowband disturbance rejection is investigated for linear time-periodic plants. Included are classical and multivariable feedback controllers, fixed-gain feedforward designs using finite impulse response (FIR) filters and H-infinity synthesis tools, and adaptive feedforward controllers. The objective of time-periodic, narrowband, disturbance rejection seeks to place a zero in the controlled system's disturbance path and align the zero direction, defined by the null space of the controlled system at the disturbance frequency, with the disturbance. In this research, constraints on controlled system infinity-norms specify nominal performance and robust stability objectives. Periodic controllers are found using existing LTI H-infinity control theory, and causality is satisfied using two techniques which can be added easily to H-infinity solvers: loop-shifting and Q-parameterization. The resulting controllers are high-gain, narrowband-pass, periodic filters; the closed-loop sensitivity has a zero at the disturbance frequency, and the disturbance is in the sensitivity's null space. It is also shown that classical designs do not achieve the same performance levels as periodic controllers. Similar developments are made using the feedforward disturbance rejection architecture. Objectives are given which minimize the weighted infinity-norm of the controlled system. Such feedforward controllers achieve perfect disturbance rejection. A multivariable equivalent of the tapped-delay line is used in the description of periodic FIR filters. In addition, periodic FIR filters are made adaptive using an algorithm similar to filtered-X least mean square (LMS) but modified for periodic systems.