Optimization of permanent magnet brushless machine for biomechanical energy harvesting applications

Cylindrical permanent magnet brushless machines are used in the biomechanical energy conversion device, mounted in a backpack, to harvest energy from center-of-mass motion during human walking. Optimization of motor constant, indicating torque efficiency, is studied. The optimal ratio of the stator bore diameter to the stator outer diameter, the so-called split ratio, is determined analytically to maximize the motor constant per-unit volume of the machine. The influence of winding disposition, tooth-tips and end-windings are taken into account appropriately. The optimization procedure is implemented using a 40 W brushless dc machine.