Philadelphia University
Student Name:
Faculty of Engineering
Student Number:
Dept. of Electrical Engineering
First Exam, First Semester: 2011/2012
Course Title: Power Electronics +Drives
Course No: (610581)+(640324)
Date:21 /11/2011
Time Allowed: 1 Hour
Lecturer:
No. of Pages: 2
Dr. Mohammed Tawfeeq
Question 1:
(8 Marks)
Objectives: Understanding the characteristics of power semiconductor devices.
Mark the correct answer:
1. The latching and holding currents are terms applicable to:
(a) Thyristor
(b) BJT
(c) IGBT Transistor (d) MOSFET (d) None of the above
2. The conditions which must be satisfied to turn on the thyristor with its current is
more than its latching current are:
(a) The anode is positive and the cathode is negative and a positive current pulse is
applied to the gate.
(b) The anode is negative the cathode is positive and a positive current pulse is
applied to the gate.
(c) The cathode is positive and the anode is negative and negative current pulse is
applied to the gate.
(d) The anode is positive and the cathode is negative and a negative voltage pulse is
applied to the gate.
3. For a certain applications of power supply a power semiconductor switch is
required to operate with 300V, 200A load and switching frequency of 150 kHz .The
power switching device suitable for this task is:
(a) Thyristor
(b) Diode
(c) IGBT
(d) MOSFET
4. The supply voltage for a single –phase full-wave uncontrolled rectifier is
vs = 240√2 sin314t. The rectifier is loaded with resistive load R= 100 ohms. The DC
power absorbed by the load is:
1
(a) 1073W (b) 576.7W (c) 467.22 W (d) 990.56 W
(e) 8908 W
5. In a 3-phase full-wave uncontrolled rectifier, if per phase input voltage is 200 V,
then the average output voltage is
(a) 467.82 V
is correct.
(b) 233.9 V
(c) 405.12 V
(d) 202.56 V (e) none of these
6. Each diode of a hexa-phase uncontrolled diode rectifier conducts for:
(a) 60°
(b) 120°
(c) 180°
(d) 90°.
7. In a 3-phase full-wave uncontrolled bridge rectifier, if per phase peak input voltage
is Vm, then the average output voltage is given by
(a) Vm/2π
(b) √3Vm/2π
(d) 3 √3Vm/π
(c) 3√3Vm/2π
8. A thyristor (SCR) has a latching current of 100mA s connected between a DC
source of 200V and a purely inductive load of L= 0.2H. The minimum width of the
gate pulse current required to turn on this SCR is:
(a) 50 ms
(b) 50 µs
(c) 100 µs
(d) 40ms
(e) 60 µs
Question 2:
(12 Mark)
Objectives: Understanding the principles of single-phase AC-DC converter.
A single-phase uncontrolled full-wave rectifier shown in Fig.1 (a) has a source of 120
V r.m.s at 50 Hz, and is feeding a resistive load with R = 30 Ω.It is required to:
(a)Sketch the appropriate load voltage and load current waveforms
(b) Determine the average load voltage and current.
(c) Determine the r.m.s load voltage and current.
(d) Determine the a.c and d.c powers absorbed by the load.
(e) If the four diodes of the rectifier bridge are replaced by
Fig.1 (a)
Four thyristors as shown in Fig.1(b). Calculate the Average
Output voltage, dc current , and the dc power when the
triggering angle is α = 30º .
Fig.1(b)
2
3
4
5