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Tampere University of Technology — DEE-34106 Converter dynamics and EMC 9.5.2016
Electrical Engineering

Teuvo Suntio

Ouestion 1.

Ouestion 2.

Programmable calculator allowed 5 guestions/ & 6 pts
Onnen ö

Fig. 1 shows an ideal PWM shunt regulator widely applied in space application. The
MOSFET is turned on during the off-time. Solve the transfer functions representing the
dynamics of the converter according to

a Sh 5
Wa: ”
14180 S 0... ;

d

Each correct transfer function will give 1 pt.

 

Fig.1 — Ideal PWM shunt regulator.

Two different control-to-output-voltage transfer functions are of the form

L o
(1+5/0,)1+5/0,)

and

a 1+5/o, (3)
= (1—5/0,)A+5/0,)

where 0, =27-10'*4, 07, 27.10 =! , 97, =27.10%4 and K=10.
s s s

a) Which one of G/, indicates unstable system and why? (2 pts)

b) Can you stabilize the unstable system by control design and how? (2 pts)

c) Does the stable system contain any control design limitation? Justify your answer (2 pts).

103)

 
 

 

Tampere University of Technology —DEE-34106 Converter dynamics and EMC 9.5.2016
Electrical Engineering

Teuvo Suntio Programmable calculator allowed 5 guestions/ 4 6 pts

Ouestion 3. — Fig. 3 shows G,,,(a) and the corresponding final loop gain Z,, (b). a) What type of
controller is used in the design (P, 1, PI, or PID). Justify your answer (2 pts). b) Is the closed-
loop converter stable? Justify your answer (1 pts), and c) What kind of controller would suit
better for this purpose and how its zeros and poles should be placed (3 pts).

Open-Loop Bode

Magnitude (dB)

Phase (deg)

   

P.M.:16.4 dog

 
 
    

 

10" 10? 10 10! 10 105
Freguency (Hz)
(a)
Closed-Loop Bode
xi 100
G 50
o
5 o
E
=
o
= -50' os: 16.508
Freg: 1.13e+003 Hz
Stable loop i

100

45
5 %
= 135
3
E 19018 14000 Nt
% PM:ST9 -

225 LUHESST i i

10! 10? 10? 10* 10 108
Freguency (Hz)
(9)

Fig. 3 — Buck converter: (a) G.,,» and (b) Lou

20)

 
Tampere University of Technology —DEE-34106 Converter dynamies and EMC 9.5.2016

Electrical Engineering
Teuvo Suntio Programmable calculator allowed 5 guestions/ ä 6 pts

Ouestion 4. — Fig. 4 shows the measured input impedances of a buck converter eguipped with an input LC
filter. The output impedance of the LC filter in Fig. 4 shows the typical freguency-domain
behaviour of a parallel resonant circuit.

a) Estimate the output-voltage-loop crossover freguency based on the freguency-domain
behaviour of the closed-loop and open-loop input impedances in Fig. 4 (2pts).

b) Is the converter-LC-filter system stable? Justify your answer based on the impedance
behaviour in Fig. 4 (2 pts).

c) What is the approximate value of the converter ideal input impedance (Z;,..) according
to Fig. 4. Justify your answer (2 pts).

 

v Nw &
5085

Magnitude (dB0)

 
 

 

 

Phase (deg)

 

Freguency (Hz)

Fig.4 — The measured input impedances of a buck converter.

Ouestion 5. — Fig. 5 shows the typical input filter structure of the voltage-fed converters, which is
characterized by four transfer functions. Compute those transfer functions by utilizing only
circuit theory. Each correct transfer functions will give 1 pts and the identification of the
correct set would give 2 pts. Only the named method would give the points. 1f other
technigues are used then the outcome would be zero.

 

 

Fig. 5 Input LC filter

3(3)