15EE53
Visvesvaraya Technological University, Belagavi
MODEL QUESTION PAPER
5th Semester, B.E. (CBCS) EE
Course: 15EE53 Power Electronics
Time: 3 hours Max. Marks: 80
Note: Answer Five full questions selecting any one full question from each Module.
Module-1
1 a. Explain in brief, the different types of power electronic converter circuits and also
specify the form of input and output with waveforms.
b. If a single-phase full-wave rectifier with center-tapped transformer has a purely
resistive load of determine the efficiency, the RF, the TUF and the
input power factor PF.
OR
2 a. What is power electronics? Mention its industrial applications.
b. Explain the function of a freewheeling diode, in a switched RL load circuit. Draw
the circuit diagram and waveforms.
c. Compare the advantages and disadvantages of bridge rectifier and rectifier with
centre-tapped transformer.
Module-2
3 a. Explain the isolation of gate drive using pulse transformers and optocouplers
b. With the help of waveforms, explain the switching characteristics of a BJT.
OR
4 a. Draw the circuit diagram for an IGBT and explain its typical output
characteristics.
b. The bipolar transistor is specified to have βF in the range of 8 to 40. The load
resistance is RC 15 Ω. The dc supply voltage is VCC 150 V and the input voltage to
the base circuit is VB 8 V. If VCE 1.0 VBE(sat) 1.5 V and RB 1.047
determine the ODF, the forced β and the power loss in the transistor PT.
Module-3
5 a. With a neat sketch describe the two-transistor model of a thyristor and obtain the
expression for anode current.
b. Ten thyristors are used in a string to withstand a dc voltage of Vs 15 kV. The
maximum leakage current and recovery charge differences of thyristors are 10 mA
and 150μC, respectively. Each thyristor has a voltage-sharing resistance of R 56 kΩ
and capacitance of C1 0.5μF. Determine the maximum steady-state voltage
sharing VDS(max), the steady-state voltage derating factor, the maximum transient
voltage sharing VDT(max), and the transient voltage derating factor.
OR
6 a. Explain the VI characteristics of SCR with a neat graph.
b. Briefly explain the following:
(i)LASCR GTO TRIAC

C. A thyristor carries a current as shown in Figure
=120 Hz. Determine the average ON state current
7 a. With the help of suitable diagrams, explain the working of a single phase dual
converter.
b. A single-phase ac voltage controller in Figure
and the rms input voltage is
Determine the rms value of output voltage
rms input current Is.
8 a. Draw the circuit diagram of a three phase bidirectional controller for a resistive load
and show the waveforms for Input line voltages, Input phase voltages,
Thyristor gate pulses, and Output phase voltage at a firing angle of 60
b. A three-phase full-wave converter is operated from a three
208-V, 60-Hz supply and the load resistance is
average output voltage of 50% of the maximum possible output voltage, calculate
the delay angle the rms and average output currents, the
thyristor currents, the rectification efficiency.
9 a. Explain the principle of step
output voltage.
b. The single-phase full
input voltage is Vs
frequency, and the output power
c. What are the main differences between voltage
10 a. Draw the circuit diagram for a four quadrant
b. Explain 120° conduction mode of operation in a three
circuit and neat waveforms.
6 The switching frequency is
IT.
Fig 6
Module-4
7 has a resistive load of
Vs 120 60 Hz. The delay angle of thyristor
Vo, the input PF, and
Fig. 7
OR
three-phase
R 10 Ω. If it is required to obtain an
Module-5
step-up chopper and derive an expression for the average
full-bridge inverter has a resistive load of R 2.4
48 V. Determine the rms output voltage at the fundamental
Po.
voltage-source and current-source inverters?
OR
converter and explain its working
three-phase inverter along with

. fs


R 10 Ω
T1 is α
the

60°
Y-connected
. rms and average


Ω and the dc