Speed Control With Low Armature Loss for Very Small Sensorless Brushed DC Motors

A method for speed control of brushed dc motors is presented. It is particularly applicable to motors with armatures of less than 1 cm³. Motors with very small armatures are difficult to control using the usual pulsewidth-modulation (PWM) approach and are apt to overheat if so driven. The technique regulates speed via the back electromotive force but does not require current-discontinuous drives. Armature heating in small motors under PWM drive is explained and quantified. The method is verified through simulation and measurement. Control is improved, and armature losses are minimized. The method can expect to find application in miniature mechatronic equipment.