Transfer Function of Armature Controlled D.C. Motor

 

Assumptions :

i) Flux is directly proportional to current through field winding,

ii) Torque produced is proportional to product of flux and armature current

.

iii) Back e.m.f is directly proportional to shaft velocity ɸ₁, as flux ω is constant.

      Apply Kirchhoff's law to armature circuit :

      Take Laplace transform

      Equating equations of T_m,

      Therefore can be represented in its block diagram form as in Fig.2.

Note : Field controlled d.c. motor is open loop while armature controlled is closed loop. Hence armature controlled d.c. motors are referred over field controlled type.