An 1100-W, 150-V, 3000-r/min permanent-magnet dc motor is to be operated from a current source inverter so as to provide direct control of the motor torque. The motor torque constant is K_m = 0.465 V/ (rad/sec); its armature resistance is 1.37Ω. The motor rotational loss at a speed of 3000 r/min is 87 W. Assume that the rotational loss can be represented by a constant loss torque as the motor speed varies.

a. Calculate the rated armature current of this motor. What is the corresponding mechanical torque in N · m?

b. The current source supplies a current of 6.2 A to the motor armature, and the motor speed is measured to be 2670 r/min. Calculate the load torque and power.

c. Assume the load torque of part (b) to vary linearly with speed and the motor and load to have a combined inertia of 2.28 x 10^-3 kg · m². Calculate the motor speed as a function of time if the armature current is suddenly increased to 7.0 A.