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Unformatted text preview: EE321 Spring 03 Exam 2 Neatly print your full name: There are 15 questions on the exam. 1.) Consider the multi-stack variable reluctance stepper motor we discussed in class. In this machine, the absence of mutual inductance is because (a) the mutual flux cancels out, (b) the phases are on different stators, (c) the windings are orthogonal to each other, or (d) the Pauli exclusion principle (5 pts). 2.) A 3-phase variable reluctance stepper motor has 5 = b L mH and a TP = 4 / π . Suppose that it is desired to operate the machine in single step mode (one phase on at a time). Suppose that the load torque can vary between –0.1 and 0.1 Nm. The minimum value of phase current that needs to be used (rounded to 3 decimal places) (a) cannot be determined from the information given, (b) is 2.34 A, (c) is 3.16 A, (d) is 4.47 A, or (e) is none of the above. (8 pts) 3.) With a certain combination of phases being on, with certain currents, the torque of a variable reluctance stepper motor may be expressed: ) 8 / 8 cos( 5 π θ − = r e T The load torque is such that 2 . = r θ is an equilibrium point. The load torque is not a function of position. Is this equilibrium point (a) stable or (b) unstable ? (7 pts) 4.) Why do variable reluctance stepper motors always have at least three phases ? (a) it minimizes the number of wires to the device, (b) you need at least three phases...
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This note was uploaded on 02/19/2012 for the course ECE 321 taught by Professor Staff during the Spring '08 term at Purdue.
- Spring '08