Exam text content

 

Tampere University of Technology — DEE-33116 Power Electronics Converters — 12.12.2016
Electrical Engineering

Jenni Rekola Programmable calculator allowed 5 guestions/ä 6 p
Answers in English or in Finnish allowed

1. A simplified ideal single-phase diode rectifier circuit is shown in Fig. 1.

230Vrms »
50Hz a

 

Fig. 1. Full-bridge diode rectifier loaded by a current sink

a) Sketch the waveform of the output voltage vo as a function of time

b) Calculate the average output voltage value

c) Sketch the waveform of the input current as a function of time

d) Calculate the rms-value of the input current

e) What should be the maximum peak repetitive reverse voltage rating of the diode if 1.5 safety margin
is used?

f) Whatis the power factor of the rectifier? Hint: in the ideal converter Pin= Pout

2. Ideal boost converter is shown in Fig. 2.

Output voltage is 32V and input voltage is 12V. The power is 200W and the inductance value is
0.5mH. Assume that the capacitor voltage ripple is negligible.

a) Whatis the duty ratio of the converter?

b) Whatisthe average inductor current?

c) Sketch the inductor current waveform

d) Whatis the average capacitor current?

e) Whatis the average transistor current?

f) What should be the switching freguency that the peak-to-peak ripple in the inductor current
would be 20 %?

 

 

Fig 2. Idealboost converter

1G)
Tampere University of Technology —DEE-33116 Power Electronics Converters — 12.12.2016

Electrical Engineering

Jenni Rekola Programmable calculator allowed 5 guestions/ä 6 p
Answers in English or in Finnish allowed

3. Compare the characteristics of thyristor (SCR), MOSFET and IGBT

a) Which of these have the highest switching freguency?

b) Which of these have the highest current capability?

c) Which of these reguire always antiparallel-connected diode?

d) Which of these cause voltage notching? What it means?

e) Which of these cause so called tailing current phenomena? What it means?
9) Whichofthese is presented in Fig. 3.?

 

Fig 3. Transistor

4. The single-phase inverter is used in the solar power system shown in Fig. 4a and the output
voltage waveform is shown in Fig. 4b.

a) What is the inverter bridge topology used in the solar power system according to the output
voltage waveform?

b) Draw the inverter bridge

c) Whatis the switching freguency of the transistors?

d) How large DC voltage is produced by the solar power plant?

e) Why inductor and capacitor are connected between the inverter bridge and the load?

f) Why the DC capacitor is connected in front of the inverter?

 

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Tampere University of Technology —DEE-33116 Power Electronics Converters — 12.12.2016

Electrical Engineering
Jenni Rekola Programmable calculator allowed 5 guestions/ ä 6 p
Answers in English or in Finnish allowed

Voltage (V)
&
=

  

 

 

 

i rit. Kt L iti
012345 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (ms)

b)
Fig. 4. a) Solar power system and b) inverter bridge voltage Voridse

 

5. Space-vector modulation
Three-phase inverter is shown in Fig. 5a. Suppose, that the DC voltage is 540V.

a) Whatis the length of the active vectors (Fig. 6b)? (1p)

Sa

; Ja 5 =
b) The instantaneous reference voltage of the inverter is v"! =150 V-e 1 . Which active
vectors are used to produce the reguired output voltage (vectors shown in Fig. 6b)? (1p)

c) Present the switching seguence reguired to produce the above mentioned reference
voltage. The conventional space-vector pulse-width modulation SV-PWM method is

used. (2p)

d) What is the maximum output voltage with the analyzed inverter in the linear modulation
region when SV-PWM modulation method is used? (2p)

The complex space vector of three-phase variable is defined as

2x

2=3(n,+am+a'x). where a=e"3 : (1)

 

Fig. 5. a) Three-phase inverter b) vector diagram

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