1 of 2 PHILADELPHIA UNIVERSITY, SCHOOL OF ENGINEERING 2 nd Semester 2013/2014, Power electronics & Drives, 0640312 Mechatronics Engineering Department, Dr. Lutfi Al-Sharif Final Exam, 10/6/2014, 11:30-13:30 Name: Registration Number: 1. Three Phase Step-Wave Inverter (30 marks) The figure below shows a three-phase step-wave inverter, where each IGBT conducts continuously for 120º and is switched off for another 240º. a) Draw the switching waveforms for all six IGBTs (8 marks). b) Draw the waveform for the line voltage v RS . (8 marks). c) Draw the waveform for the line current, i R . (7 marks). d) If V DC is 100 V, and R is 10 Ω, find the rms value of the line current, i R (7 marks) Figure 1: Diagram for problem 1. 2. Single phase AC to AC converter (35 marks) a) Show that the formula for the rms output voltage of a single phase AC to AC converter shown below, as a function of the rms supply voltage Vs and the firing angle, α is: (15 marks). ( ) + − ⋅ = π α π α 2 2 sin 1 rms S rms L V V
1 of 2 PHILADELPHIA UNIVERSITY, SCHOOL OF ENGINEERING 2nd
Semester 2013/2014, Power electronics & Drives, 0640312
Mechatronics Engineering Department, Dr. Lutfi Al-Sharif Final
Exam, 10/6/2014, 11:30-13:30 Name: Registration Number: 1. Three
Phase Step-Wave Inverter (30 marks) The figure below shows a
three-phase step-wave inverter, where each IGBT conducts
continuously for 120 and is switched off for another 240. a) Draw
the switching waveforms for all six IGBTs (8 marks). b) Draw the
waveform for the line voltage vRS. (8 marks). c) Draw the waveform
for the line current, iR. (7 marks). d) If VDC is 100 V, and R is
10, find the rms value of the line current,iR (7 marks) Figure
1:Diagram for problem 1. 2. Single phase AC to AC converter (35
marks) a) Show that the formula for the rms output voltage of a
single phase AC to AC
convertershownbelow,asafunctionofthermssupplyvoltageVsandthe firing
angle, is: (15 marks). ( )+ =22 sin1rms S rms LV V 2 of 2 Figure
2:Diagram for problem 2. b)If the value of R is 200 , and the
supply voltage is 240 V rms, find the power factor of the system
when the firing angle is 30 degrees. (20 marks). 3. Power Factor
(35 marks) a)What is a non-linear load? (5 marks) b)Explain what
displacement power factor is and what causes it? (5 marks)
c)Explain what distortion power factor is and what causes it? (5
marks) d)A sinusoidal voltage source with an rms voltage of 220 V
at a frequency of 50 Hz supplies a non-linear load.The current
drawn contains harmonics. The details of the harmonic content of
the current are shown in the table below.The angle of each harmonic
is with respect to the supply voltage.Calculate the overall power
factor (15 marks). e)What is the frequency of the 7th harmonic? (5
marks) Assume that the voltage has an angle of zero degrees. The
rms of the current is 19.66 A. Harmonic numberRMS current (A)Angle
()Leading/lagging first harmonic (I1)18.40-16.5lagging third
harmonic (I3)5.22150leading fifth harmonic (I5)3.0260leading
seventh harmonic (I7)1.51-60lagging ninth harmonic
(I9)1.38170leading eleventh harmonic (I11)1.2160leading thirteenth
harmonic (I13)0.86-60lagging
