Exam text content

 

 

Tampere University of Technology — DEE-33116 Power Electronics Converters 8.12.2015

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

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

Assume that the supply voltage is sinusoidal (RMS value 230V at 50 Hz). Suppose the components
to be ideal (power losses are not taken into account). 1; =10A.
i

 

 

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

a) Sketch the waveform of the output voltage as a function of the supply voltage electrical angle ot
b) Calculate the average output voltage value

c) Sketch the waveform of the input current as a function of the supply voltage electrical angle ot
d) Calculate the rms-value of the input current

e) What should be the voltage rating of the diode if 1.5 safety margin is supposed to be used?

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

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

Input voltage is 24V and output voltage is 12V. The power is 100W and the inductance value is
1mH. Assume that the capacitor voltage ripple is negligible.

a) What is the average inductor current?

b) What is the average diode current?

c) Whatis the average transistor current?

d) Whatis the average input current?

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

f) Sketch the diode current waveform with maximum and minimum values. The switching
freguency is 10 kHz.

 

Fig 2. Ideal buck-converter

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Tampere University of Technology DEE-33116 Power Electronics Converters 8.12.2015
Electrical Engineering

Jenni Rekola Programmable calculator allowed 5 guestions/ ä 6 p

Answers in English or in Finnish allowed

3. Explain shortly the meaning of the following terms

a)
19)
o)
d)
o)
n

As-balance
Vs-balance

dead time

reverse recovery
Distortion power D
tail current

4. The single-phase inverter is used in the UPS-system shown in Fig. 3a and the output voltage
waveform is shown in Fig. 3b.

a)
0
o)
d)

e)
n

Name the used inverter

Draw the used inverter

What is the switching freguency of the transistors?

What is the minimum battery voltage to produce 230 Vrms to the load (all components are
supposed to be ideal)?

Why inductor and capacitor are connected between the inverter and the load?

How the value of the reguired inductor and capacitor can be defined? (Answer shortly)

L Load

   
  

Voltage (V)

 

8 9 10 11 12 13 14 15 16 17 18 19 2
Time (ms)

b)
Fig. 3. a) UPS and b) output voltage vo

5. Compare the following modulation methods: PWM, PWM with 34 harmonic injection, space
vector modulation and six-step modulation

a) Which method produces maximum output voltage amplitude?

b) Which method enables control of switching losses without changing the switching
freguency?

c) Which method minimized the switching losses?

d) Which method does not enable the control of the output voltage amplitude?

€) Which method is possible to use with three-phase inverters?

f) Which method produces harmonies to the output voltage at the lowest freguencies?

Multiple modulation methods might be a correct answer to one guestion. In this case, mention all of them.

2(2)