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hw7 - Assuming that the current into the machine varies...

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EE321 Spring 2010 Homework 7 Problem 1 – Buck converter operation Consider the example on page 55 of the lecture notes. Suppose the dc voltage is changed to 125 V and the speed to 400 rad/s. Find the average armature current, the average switch current, the converter efficiency, the motor efficiency, and the system efficiency. Also, find the conduction loss in the transistor and the conduction loss is the diode. Problem 2 – Power calculation error Let’s investigate our approximation that the average power into the motor is ˆ ˆ a a v i . Suppose the dc voltage is 100 V, the forward switch voltage drop is 2 V, and the forward diode drop is 1 V. Suppose the peak armature current is 10 A, and the minimum armature current is 9 A. Further suppose the duty cycle is 0.8.
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Unformatted text preview: Assuming that the current into the machine varies linearly, what is the true input power into the machine. What is the input power if we approximate it by a a v i . Problem 3 Current Ripple Consider problem 1. Suppose it is desired that the peak-to-peak torque ripple is 10% of the average torque. Assuming that 2 . = aa L mH, what should the switching frequency be? Problem 4 Combined Performance Consider the example on page 66-68 of the lecture notes. Consider the case of a duty cycle of 0.5. Plot the torque-speed curve on one figure. Superimpose plots of the average power into the converter, the average power into the motor, and the average mechanical power in another figure. Consider speeds from 0-150 rad/s....
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