Question

FQ5

4. Describe with aid of a block diagram the model for an rmature controlled DC motor.

Answer 1

Steady -state Operation of separation excited DC Motor: - Consider steady state model ia = armature current eb = back emf ea = armature terminal voltage wn = motor speed (rad/sec) T = motor torque Tf = static friction torque Ra = armature resistance La = armature inductance Tm = rotational interia Bm = vision friction \r\n Developed Torque T = KT.ia-Tf N-m T = motor torque KT = torque current. Tf = motor friction torque ia = armature current KVL in armature circuit Ra = ia.Ra + eb v Ra = armature voltage Rb = back emf Ra = armature resistance Back EMF Rb = Kc.wn V wm = shaft speed (rad/s) Rb = back emf Kc = back emf current Developed power P = wn.T w P = shaft power \r\n wn = KT.ea-(T-Tf) Ra/KT.Ke wm = ea-ia.Ra/Ke combining the previous equations gives: If the load torque is zero (T = 0) then the above equation (1) gives the no-load speed wnl = KT.Ra-(Tf) .Ra/KT.Ke Transfer function of armature controller DC motor: - write all variable on time functions write electrical equation and mechanical equations. use the electromechanical relationship to couple the two equations consider ea(+) and eb(+) of inputs and ia(t) an output. write KVL around armature. \r\n ea(t) = Ra. ia(t) + L.dia(t) /dt + eb(t) Mechanical Dynamics. T(t) = Tm. dwm(t) /dt + Bm.wm (t) Electromechanical equations: