ECE349F 2018 INTRODUCTIONTOENERGYSYSTEMS...
ECE349F_2018_INTRODUCTIONTOENERGYSYSTEMS_E.pdf-UNIVERSITY OF TORONTO DEPARTMENT OF ELECTRICAL
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ECE349F 2018 INTRODUCTIONTOENERGYSY...
ECE349F_2018_INTRODUCTIONTOENERGYSYSTEMS_E.pdf-UNIVERSITY OF TORONTO DEPARTMENT OF ELECTRICAL
##### Page 1
UNIVERSITY OF TORONTO
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
FINAL EXAMINATION
9:30am
-
12:00, December 15, 2018
ECE 349
-
Introduction to Energy Systems
EXAM TYPE: C (single aid sheet, both sides, any 8
1
/
2
x 11 paper)
NON-PROGRAMMABLE CALCULATORS ONLY
EXAMINER:
Prof. Peter Lehn
STUDENT NAME:
STUDENT NUMBER:
Mark
Question 1
Question 2
Question 3
Question 4
Question
5
Total
Page 1 of 11

##### Page 2
L
[20 Marks]
1. Shown below is a simple full-bridge diode rectifier with RL load, connected to a 60 Hz grid with
voltage vs(t)=100sin(377t). If the inductance is sufficiently large, the dc side current into the load is
nearly ripple-free and can be approximated is constant at
'DC.
The grid sees the rectifier as a load on
the ac utility network. The measured current into the diode rectifier is plotted below and has a peak
value of bA. The rectifier and inductor are lossless.
/OA
a.
Find the average power delivered to the dc resistor R (value of R unknown).
The grid sees the rectifier as a load on the ac system. Find the displacement factor of this
Find the power factor of this rectifier load.
The largest harmonic drawn from the utility network is the third harmonic. Find the third
harmonic current drawn from the utility.
Page 2 of 11

##### Page 3
[20 Marks]
2. Shown below is a 2 quadrant chopper that is used to drive a large electromagnet, modeled by a series
RL. The electromagnet has an inductance of 1 H and has winding resistance of
5
ohms. The duty
cycle of the 2 quadrant chopper is D=0.3 and its switching frequency is 1 kHz. V
0
=1000V.
ILL
-f
L -VZ
Complete the following sketches. Assume continuous conduction mode, as will be verified in
part (c). Give symbolic expressions for the maximum and minimum values for the
inductor voltage and
the slopes
of the inductor current waveform.
i
t
2
Page 3 of 11

##### Page 4
b. Here we will define the "output voltage" of this system to be
VR,
as shown, and the input
voltage to be
VG.
Use the small ripple assumption and volt-seconds balance
to determine
the input-output voltage ratio,
VR/Vo,
of this converter. Alternate solution methods will not be
considered as I am looking for your methodology in applying the small ripple tools to systems
where no output capacitor exists.
Find the average inductor current and the peak-to-peak inductor current ripple.
Based on the waveforms above, can you identify any unnecessary power electronic devices
within this circuit that you might be able to eliminate for cost-cutting reasons?
e.
If you do eliminate any power electronic devices, what functionality does my system lose?
In other words, what practical feature might you be able to advertise on your electromagnet
product if you keep all the switching devices in place. What potentially useful feature do you
lose when pursuing the cost cutting exercise as outlined in part (b).
Page 4 of 11

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