Control of Eddy-Current Brakes
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Magnetic braking utilizing eddy currents is used in a wide range of applications. Eddy current braking is done by moving a magnet, either electronically controlled or permanently magnetized, relatively to an electrically conductive material. The existing literature is somewhat intricate and theoretical, and there is a need for bridging the gap between theory and practice. This thesis aims to facilitate practical research by implementing an eddy current braking testbed (ECBT), which enables torque measurement for model validation and also real-time torque control. The ECBT was made out of a large conductive disc spinning in the airgap of two electromagnets, mounted on a shaft that was fastened to a wooden base. A permanent magnet was also tested for comparison. The disc was driven by a DC motor and a chain drive, controlled by a PI-controller. Braking force measurements were done with the help of a force sensing mechanism that outputted an analog signal proportional to the braking force. The system was monitored and controlled with a microcontroller of the type Arduino Mega2560, running code produced in Simulink with the help of the Arduino Support Package made by MathWorks. Data was stored after each test and post-processed in Matlab. The final ECBT is to be considered as a first prototype of such a system, with some potential improvement areas. Deviations from theory were seen, something that is thought to be caused by a great deal of magnetic fringing in the air gap and possibly uncertainties in disc conductivity. Several interesting magnetic phenomena were encountered that must be considered when designing and controlling electromagnetic brakes. Finally, a torque control demonstration using a sliding mode controller showed the ECBT's ability to perform real-time torque control. The findings presented in this thesis highlight several important factors to consider when designing eddy current braking systems. The final system was made functional and it is the hope that this thesis may be an aid to future researchers doing work on electromagnetic braking.