Exam text content

Tampere University of Technology —DEE-33116 Power Electronics Converters

12.3.2018

Electrical Engineering

Jenni Rekola

Programmable calculator allowed
Answers in English or in Finnish allowed

5 guestions/ a 6 p

1. Rectifier

The grid line-to-line voltage (Un), DC voltage (U2) and DC current (12) are shown in Fig. 1

2)
b)
o)
d)
e)

n

What is the used rectifier topology according to the DC voltage waveform shown in Fig. 1?
Draw the used rectifier topology

Sketch the waveform of the grid current as a function of time

Calculate the average output voltage value

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?

What is the lowest freguency of the produced grid current harmonic component?

 

600

 

 

400

 

200 ft /

-200

UV), Ua(V) and 1a(A)*10

-400

 

 

600
18

 

1802 1804 1806 1808 181 1812 1814 1816 1818 182
t(s)

Fig. 1. Grid line-to-line voltage (Un), DC voltage (Ua) and DC current (12)

2. Ideal boost converter

Ideal boost converter is shown in Fig. 2a and the input current waveform is shown in Fig. 2b.

Input

voltage is 200V. Assume that the capacitor voltage ripple is negligible.

a) What is the average input current?
b) What is the average out;
c) What is the inductance L value?

d) What is the average capacitor current?
e) What is the average diode current?
f) Sketch the diode current waveform

put voltage?

 

T T T

Current (4)

 

 

 

 

 

 

i i H i
00201 0.0202 00203 00204 00205

 

 

Fig 2.

103)

Time (seconds)

b)

a) Ideal boost converter and b) input current
Tampere University of Technology —DEE-33116 Power Electronics Converters — 12.3.2018
Electrical Engineering
Jenni Rekola Programmable calculator allowed 5 guestions/ ä 6 p

Answers in English or in Finnish allowed

3. The freguency converter

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

2)

b)
9)
d)
e)

What is the rms value of the maximum fundamental-freguency line voltage that can be produced
to the motor terminals with conventional SPWM operating in linear range? Assume that the
converter is connected to the Finnish utility grid (rms value of the line voltage is 400 V at 50
Hz), the rectifier has large output capacitor, and L =0 H.

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

Is it possible to supply the regenerative power of the motor back to the grid by using this circuit?
Why the capacitor Cac is connected to the circuit?

Why the diodes are connected antiparalle! with the IGBTs?

Why the inductance L is connected in the grid side?

 

 

4. Single-phase inverter

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. The peak amplitude of triangular waveform (Vu) is SV and the
reference voltage is 4.5 V. The DC voltage value is 560V.

a) What is 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) What is the modulation index of the inverter?

d) What is the maximum output voltage rms value in linear modulation region?

e) What should be the 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?

 
Tampere University of Technology —DEE-33116 Power Electronics Converters — 12.3.2018

Electrical Engineering

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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

5. Space-vector modulation

Three-phase inverter is shown in Fig. 5a and the corresponding space vector sectors (i.e.,
hexagon) in Fig. Sb. Assume that dc-link voltage eguals 560 V.

a) What is the length of the active vectors?

b) How many active switching states and zero switching states can be produced by the
converter presented in Fig. 5?

c) Present the switching seguence of the inverter bridge when a conventional space-vector
pulse-width modulation (SV-PWM) algorithm is used and the reference voltage eguals

7
vi =200 V-e'*.(2p)

d) What is the maximum output voltage with the analyzed inverter in the linear modulation
region when SV-PWM modulation method is used?
e) What are the advantages of SV-PWM compared to conventional PWM method?

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

2n

2 3
2=3(a + an + x). where a=e"" ; (1)

   

labo)

 

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