Question

I can not seem to get the right answers. Thank you!

Given a 1/4 hp, separately excited, dc motor with the following parameters: K = 0.61, R, 15Ω, La-120mb. J = 0.005, and b = 0.0006. The armature voltage is controlled by a 120-V dc PWM source operating at 100 Hz 1. What is the armature current if the no-load speed is 1800 rpm when the armature supply is operated at a 100% duty cycle? 2. What is the no-load torque (loss torque)? 3. What is the electrical time constant of the armature? 4. What is the mechanical time constant of the unloaded motor? 5. A mechanical load of 0.5 N-m that requires a speed of 1500 RPM is connected to the motor shaft. Assume that the loss torque is constant (independent of shaft speed). What is the armature voltage and current? 6. If the motor is stopped, what is the maximum initial duty cycle if a 2.5A limit on the PWM device is not exceeded? 7. If you are controlling the shaft speed of the motor, but are not able to measure the shaft speed directly, how could you provide feedback of the speed to the controller using parameters, and voltage and current measurements? 8. Suppose that you are required to provide torque control rather than speed control. What value would you feedback to the controller?

Answer 1

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No- lood condi tior 1838.35 t 90 lt.