DC motor equivalent circuit

For permanent magnet DC motors or separately
excited DC motors , the equivalent circuit is shown in the figure
. The back electromotive force Ea can be regarded as a variable
voltage source, which is proportional to the motor speed n
. The electromagnetic torque T and the armature current
are also proportional to each other. The armature resistance R is usually small and has a certain current limiting effect when
the motor is starting and stalled .
Armature inductance L. It has an impact on the dynamic performance. When the motor
is driven in a switching mode, for example, in a pulse width modulation mode, it has a smoothing effect on the current pulsation
.