Question1: The speed of a dc motor is controlled by a DC-DC converter. The dc supply voltage is 80V. The armature circuit resistance is Ra=0.3 Ohm and armature inductance is La=8mH. The motor constant Ka=0.07V/rpm. The motor drives a constant torque load requiring an average armature current of 20A. Assuming that the motor current is continuous, compute

a. The range of speed control

b. Range of duty cycle

Solution:

a. The average value of armature voltage is given by

Minimum speed is zero at which E_b=0

The duty ratio is given by

Maximum speed corresponds to D=1, at which Va=Vdc=80V

The back emf at maximum speed is

The maximum speed is

Hence, the range of speed control is 0rpm to 1057.14 rpm