ECE 4411 Introduction to DC Machines Advantages –Adjustable speed –Develop rated torque at all speeds –Higher torque than an equivalent AC machine Uses –Robots –Automotive –Railroads

ECE 4412 Elementary 2-pole DC motor Poles created by DC current in the field winding or by a permanent magnet

ECE 4413 Flux through the “window” of a 1-turn armature coil as a function of position

ECE 4414 Voltage induced in the armature coil

ECE 4415 Flux Distribution and Induced Voltage The induced voltage is AC

ECE 4416

7 Average Value of one-half cycle

ECE 4418 Rectify the other half-cycle Ea

ECE 4419 Express in r/min

ECE 44110

ECE Commutation / Mechanical Rectification “Neutral” position –Coil shorted by the brushes –No armature voltage generated – coil sides not cutting any flux –No current

ECE Commutation (continued) Brushes contact the armature conductor CCW rotation Coils sides cut flux Current in A as shown Current in B as shown

ECE Commutation (continued) “Neutral” position –As before, coil shorted by the brushes –No armature voltage generated – coil sides not cutting any flux –No current

ECE Commutation (continued) Brushes contact the armature conductor CCW rotation Coils sides cut flux Current in B as shown Current in A as shown Currents are in the same direction as before!