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Tampere University of Technology —DEE-33116 Power Electronics Converters — 23.1.2018
Electrical Engineering
Jenni Rekola Programmable calculator allowed 5 guestions/ä 6 p
Answers in English or in Finnish allowed
Return the waveform template (p.4 of the exam)

1. Rectifier
The grid phase voltage (u) and grid current (i) are shown in Fig. 1

a) Whatis the used rectifier topology according to the DC voltage waveform shown in Fig. 1?

b) Draw the used rectifier topology

c) Sketch the waveform of the DC voltage as a function of time (use template in p. 4)

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?

 

4

 

 

 

 

 

4 4 4 1 4 4
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 01

Fig. 1. Measured grid phase voltage (amplitude *100) and grid current (amplitude*10)
2. Ideal boost converter

Ideal buck converter is shown in Fig. 2a and the input current waveform is shown in Fig. 2b. Input i
voltage is 100V. Assume that the capacitor voltage ripple is negligible.

a) What is the average input current? j

b) What is the average output voltage? 10 +-———
c) What is the inductance L value? |

d) What is the average capacitor current?

e) What is the average diode current? — »
£) Sketch the diode current waveform n H/

 

14)
Tampere University of Technology —DEE-33116 Power Electronics Converters — 23.1.2018

Electrical Engineering
Jenni Rekola Programmable calculator allowed 5 guestions/ä 6 p

Answers in English or in Finnish allowed
Return the waveform template (p.4 of the exam)

Input current (4)

   

 

o i i
0.025 00255 0025 00265 0027 00275 0026 00285 0029 00295 0.03
Time (seconds)

b)

Fig 2. a) Ideal buck converter and b) input current

3. The freguency converter

The freguency converter of a three-phase synchronous motor is shown in Fig. 3.

a)
b)
e)
d)
e)
fr

miahet

Why the resistor Rs and the switch Ss are connected to the circuit?
Why the capacitor Cac is connected to the circuit?

Why the diodes are connected antiparallel with the IGBTs?

Why the inductance L is connected in the grid side?

Is it possible to supply the regenerative power of the motor back to the grid by using this circuit? ——
Why the switch S» and an external resistor between b. and b. are connected to the circuit?

 

 

Fig 3. Schematic diagram of a conventional freguency converter

4. Single-phase inverter

The single-phase DC/DC converter and inverter is used in the solar power system shown in Fig. 4a.
The power-voltage characteristics of a PV module is shown in Fig. 4b.

9)
b)
9)
d)

e)

What is the minimum DC voltage udc-tinr if the system is grid connected (230 Vrms, SOHz) and
if two-level half-bridge inverter is used?

Why DC/DC converter is added between solar power panel and inverter?

What kind of DC/DC converter is reguired? Draw the converter.

What is the duty cycle of the DC/DC converter in the maximum power point in summer?
Minimum DC voltage is produced.

What is MPPT shown in Fig. 4a?

24)