fi Department of Electrical, Computer
1 & Biomedical Engineering
Fa ity OF = = (v & :l| ter topal Do W i
MIDTERM
ELE754 Power Electronics
Duration: 3 hours Instructor:
Date: October 14, 2025 Dr. D. Xu
INSTRUCTIONS:
1. Close-book test. The formula sheets are attached as the last two pages. You may
detach the formula sheets. The formula sheets will not be marked. DO NOT write
your answers on the formula sheets.
2. Answer all questions. Show details of derivation steps. Marks will be lost if there
IS no appropriate units.
3. If doubt exists as to the interpretation of any question, you are urged to submit
with the answer paper a clear statement of any assumptions made.
4. All the ac voltages and currents are rms values unless noted otherwise.
Read the question carefully! Part of questions may or may not be related.
i
6. Total 9 pages including cover page (this page)
Marks (total 80):
Ql. {fiOPWT"O”)
Q2.
Q3.
Q4.
Student Name:
Student Number:
, Midterm ELE754 Power Electronics October 14, 2025
Questions 1 (25%) DC-DC Switching Converters
A 240W buck converter with voltage feedback controller is shown in Figure 1. The dc input voltage 1s
48V. The inductance L is 6.8uH. The switching frequency and duty cycle is adjusted by the controller to
keep the output voltage constant at reference voltage V,, =12V in steady state. The full power rating is
240W. The converter is always operating in critical mode in load power range from 24W ~240W. The
duty cycle is then adjusted when the load power is below 24W. Answer the following questions when
the converter is operating in steady state.
v, D CT v § R,
Controller 4—&+V
+ ref
Figure 1 Buck converter with voltage feedback controller
I.1) Find the switching frequency range at specified load range.
79 o )~ 240 W in Critiesf ;m/e, . 2/ s
T
=1L =1 = ,.L/’f_@(,
1 ) ?) = =
lg= R
Where 17145—" 9%
R
A'f" ”’()W
eT
-*U"T:D_ -20/\/Tip:JQA/T: _:ff),zwffpff;g;‘ag%
33 086 s = 330, S5
1.2) Find the minimum capacitance if the required ripple voltage is less than 100mV at full load.
5% 0
A‘f !M{/ (00(6? C/!ff_r"og mooe ;> ceM
/)Vo B,
ELC ((——'D)
o/5 _— W
;?Z—-—T/{/,,?)).Z; = /00;2/!(/
N = (siMf-
Page | of 8
1 & Biomedical Engineering
Fa ity OF = = (v & :l| ter topal Do W i
MIDTERM
ELE754 Power Electronics
Duration: 3 hours Instructor:
Date: October 14, 2025 Dr. D. Xu
INSTRUCTIONS:
1. Close-book test. The formula sheets are attached as the last two pages. You may
detach the formula sheets. The formula sheets will not be marked. DO NOT write
your answers on the formula sheets.
2. Answer all questions. Show details of derivation steps. Marks will be lost if there
IS no appropriate units.
3. If doubt exists as to the interpretation of any question, you are urged to submit
with the answer paper a clear statement of any assumptions made.
4. All the ac voltages and currents are rms values unless noted otherwise.
Read the question carefully! Part of questions may or may not be related.
i
6. Total 9 pages including cover page (this page)
Marks (total 80):
Ql. {fiOPWT"O”)
Q2.
Q3.
Q4.
Student Name:
Student Number:
, Midterm ELE754 Power Electronics October 14, 2025
Questions 1 (25%) DC-DC Switching Converters
A 240W buck converter with voltage feedback controller is shown in Figure 1. The dc input voltage 1s
48V. The inductance L is 6.8uH. The switching frequency and duty cycle is adjusted by the controller to
keep the output voltage constant at reference voltage V,, =12V in steady state. The full power rating is
240W. The converter is always operating in critical mode in load power range from 24W ~240W. The
duty cycle is then adjusted when the load power is below 24W. Answer the following questions when
the converter is operating in steady state.
v, D CT v § R,
Controller 4—&+V
+ ref
Figure 1 Buck converter with voltage feedback controller
I.1) Find the switching frequency range at specified load range.
79 o )~ 240 W in Critiesf ;m/e, . 2/ s
T
=1L =1 = ,.L/’f_@(,
1 ) ?) = =
lg= R
Where 17145—" 9%
R
A'f" ”’()W
eT
-*U"T:D_ -20/\/Tip:JQA/T: _:ff),zwffpff;g;‘ag%
33 086 s = 330, S5
1.2) Find the minimum capacitance if the required ripple voltage is less than 100mV at full load.
5% 0
A‘f !M{/ (00(6? C/!ff_r"og mooe ;> ceM
/)Vo B,
ELC ((——'D)
o/5 _— W
;?Z—-—T/{/,,?)).Z; = /00;2/!(/
N = (siMf-
Page | of 8
