EE321 Spring 03
Exam 3
Neatly print your full name:
Work out problems completely – this won’t get you partial credit but will increase the
odds of getting the problem correct.
There are 11 questions on the exam.
Circle only one answer unless otherwise directed.
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(1)
A brushless dc machine has the following voltage equations:
dt
d
i
r
v
as
as
s
as
λ
+
=
dt
d
i
r
v
bs
bs
s
bs
λ
+
=
What are the corresponding equations in qd variables using the transformation
−
=
r
r
r
r
r
s
K
θ
θ
θ
θ
sin
cos
cos
sin
(10 pts)
(2)
In the analysis of the brushless dc machine, which of the following are reasons the
qd transformation is used (circle all that apply) (a) eliminates rotor position
dependence from the machine model, (b) eliminates rotor speed from the machine
model, (c) allows ac variables to be represented by dc variables, (d) makes the
control of the device more straightforward, (e) eliminates the need to consider the
permanent magnet. (10 pts)
(3)
A brushless dc machine is open circuited and spun at 900 rpm.
The aphase
voltage is given by
)
1
.
0
120
cos
360
+
(
=
t
v
as
π
π
The value of
m
λ
(a) cannot be determined since the number of poles is unknown,
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 Spring '08
 Staff
 Trigraph, Electric motor, Electric Motors, brushless dc machine

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