Exam text content

Tampere University of Technology —DEE-33116 Power Electronics Converters — 22.3.2017

Electrical Engineering

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

1. The grid phase-voltage and grid current are shown in Fig. 1

a) Whatis the rectifier topology used in the system according to the grid current waveform shown
in Fig. 1?

b) Draw the rectifier topology used in the system according to the grid current waveform shown in
Fig. 1

c) Sketch the waveform of the output DC voltage as a function of time

d) Calculate the average output voltage value

e) What should be the maximum peak repetitive reverse voltage rating of the power semiconductor
switching components used in the rectifier if 1.5 safety margin is used?

f) Whatis the lowest freguency of the produced grid current harmonic component?

 

o 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Fig. 1. Measured grid phase voltage (amplitude *100) and grid current (amplitude*10)

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

Input voltage is 12V and output voltage is 48V. The power is SOOW. Assume that the capacitor
voltage ripple is negligible.

a) What is the average capacitor current?

b) What is the average diode current?

c) Sketch the diode current waveform

d) Whatis the average transistor current?

e) What is the average input current?

f) The switching freguency is 10 kHz. How large inductor is needed to achieve 20 % peak-to-peak
ripple in the inductor current?

1(4)

 

 

 
Tampere University of Technology —DEE-33116 Power Electronics Converters — 22.3.2017
Electrical Engineering
Jenni Rekola Programmable calculator allowed 5 guestions/ ä 6 p

Answers in English or in Finnish allowed

 

Fig 2. Ideal boost converter

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 are used in conventional welding machines (hitsauskone in Finnish)?
d) Which of these are used in mobile phone chargers? '

e) Which of these needs antiparallel connected diode? Why?

9) Which of these 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's the inverter bridge topology used in the solar power system according to the output
voltage waveform? Draw the inverter bridge.

b) What is the switching freguency of the transistors?

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

d) What is the maximum output voltage rms value if conventional sinusoidal PWM modulation
method is used in linear modulation region?

e) What should be the PWM modulation index if the load is designed to be grid connected (230
Vrms) and the DC voltage is the same as in Fig. 4b?

f) Whatis the lowest freguency of the produced output current harmonic component?

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Tampere University of Technology — DEE-33116 Power Electronics Converters — 22.3.2017

Electrical Engineering

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

 

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 Voriage

5. Space-vector modulation
Three-phase inverter is shown in Fig. Sa. Suppose that the DC voltage is 560V.
a) What is the length of the active vectors (Fig. 5b)? (1p)
b) The instantaneous reference voltage of the inverter is v =150 vei - Present the
switching seguence reguired to produce the reference voltage (vectors shown in Fig. 5b).

The conventional space-vector pulse-width modulation SV-PWM method is used. (2p)

c) What is the maximum output voltage with the analyzed inverter in the linear modulation
region when SV-PWM modulation method is used? (1p)

d) What are the advantages of SV-PWM modulation method compared to conventional
sinusoidal PWM modulation method? (2p)

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

2 ja
(x,+ax,+a X); where = a=e 3

(1)

VIP

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Tampere University of Technology —DEE-33116 Power Electronics Converters — 22.3.2017

Electrical Engineering

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

 

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

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