Harmonic Distortion - Power Electronics - Past Exam Paper, Exams of Power Electronics

Download Harmonic Distortion - Power Electronics - Past Exam Paper and more Exams Power Electronics in PDF only on Docsity! EE411 Power Electronics Page 1 of 3 Semester I Examinations 2011 / 2012 Exam Code(s) 4BN Exam(s) B.E. Degree (Electronic Engineering) Module Code(s) EE411 Module(s) Power Electronics Paper No. I External Examiner(s) Professor G. Irwin Internal Examiner(s) Professor G. Ó Laighin Professor W.G. Hurley Instructions: Answer three questions from four. All questions will be marked equally (20 marks). Duration 2 hrs No. of Pages 3 Department(s) Electrical and Electronic Engineering Requirements None EE411 Power Electronics Page 2 of 3 Question 1 Establish the relationship between Distortion Factor and Total Harmonic Distortion (THD). [4 marks] Figure 1 shows a half wave bridge rectifier with a capacitive filter. Calculate (a) the peak diode current; [6 marks] (b) the RMS value of the source current; [3 marks] (c) the power factor of the source; [4 marks] (d) the total harmonic distortion (THD) of the source. [3 marks] + - 340sin314t D 10,000μF 20Ω Figure 1 Question 2 Draw the circuit for a PWM Buck regulator, and explain its operation. [8 marks] Design a backup power supply for a personal computer. Use a 12 V battery and a Buck converter to provide the backup energy source. The computer’s power needs may be modelled as a 2.5 Ω resistor. The microprocessor specifications call for a 5 V supply with 3%± allowable fluctuations. Set the switching frequency to be 500 kHz. Assume ideal components. Calculate (a) the duty cycle and the conduction time of the controlled switch; [6 marks] (b) the value of the inductance to give a ripple %5± of the load current; [3 marks] (c) the value of the capacitance to give a 3%± voltage ripple [3 marks] Question 3 What are the principle advantages of a resonant topology over a switching PWM topology in dc-dc converters? [4 marks] Figure 2 shows a zero-current switching, quasi-resonant converter (ZCS-QRC) (a) Explain in detail, the four distinct modes of operation of the circuit; [8 marks] (b) Sketch the resonant inductor current and the resonant capacitor voltage over a full cycle; [4 marks]