Modeling and Analysis of Homopolar Motors and Generators

The dc homopolar motor converts electrical energy into mechanical rotational energy using the Lorentz force. The same machine can be operated in reverse to convert mechanical energy into dc electrical energy. To better understand homopolar motors and their suitability for use in various applications, a computer model was created using PSpice. Forces opposing the motor rotation include back voltage, eddy currents, moment of inertia, and sliding contact friction and are analyzed in detail. Forces and torques are discussed and calculated analytically. The capabilities of the homopolar machine operating as both a motor and a generator are considered. Using current research from the University of Missouri on helical guns and railguns, which utilize similar electromagnetic forces for linear acceleration, the maximum efficiency of the homopolar motor during transient start-up phase is examined. The measured homopolar motor efficiency in this paper asymptotically approaches 50% and is determined by several variables. Experimental data are collected and used to compare the simulation results and verify the accuracy of motor performance. Sensitivity analysis and the estimated maximum machine efficiency obtained from simulation are presented.