Date of Graduation

2015

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Jay Wilhelm

Committee Co-Chair

Marvin Cheng

Committee Member

Mario Perhinschi

Abstract

Behavior monitors typically collect data, and consequently spend energy, at fixed intervals. For devices that utilize energy harvesting, a fixed data collection interval may result in inefficient battery usage due to variability in available solar radiation. Work was performed for a system capable of adjusting a data collection rate, proportional to changes in battery charge, such that data obtained was maximized without sacrificing battery energy sustainability. Energy consumption, of an actual behavior monitor, was modeled to aid in design and evaluation of a changeable data collection rate system. Model validation was performed by comparing simulated to empirical data for battery charge over time. Proportional Integral Derivative (PID) control was used that changed the rate at which data was collected such that error was minimized between battery State Of Charge (SOC) and a reference point. Gain scheduling was incorporated as a mechanism to resist change in data collection rate caused by fluctuation in available SOC. Gain parameters for a discrete, time domain, PID controller were tuned using a manual, trial and error method. Results of tuning showed improved performance with the absence of Integral control. The system was evaluated by performing simulations for change in available solar energy. Results showed that data collection adjusted to changes in available energy and as a consequence, SOC remained within +/-5% of a reference point.

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