Download Boost Converter - 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 2012 / 2013 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 Explain the following terms: distortion factor, displacement factor, power factor. [4 marks] In a half-wave phase controlled rectifier with a free wheeling diode (shown in Figure 1) and a highly inductive load, the source is 240Vrms at 50 Hz and the load resistance is 8 Ω, assuming the firing angle α=0. (a) Sketch the output voltage, the source current and the current through the freewheeling diode; [4 marks] (b) Calculate the power absorbed by the load; [4 marks] (c) Calculate the power factor as seen by the source; [4 marks] (d) How would the operation of the circuit change if the free wheeling diode were replaced by an SCR fired π radians after the rectifying SCR is fired. Derive an expression for the average load voltage in this case. [4 marks] D Vsin ωt Id Figure 1 Question 2 Draw the circuit for a PWM Boost regulator, and explain its operation. [6 marks] What is the difference between active and passive power factor correction? [6 marks] Describe in detail, with the aid of circuit diagrams, typical waveforms and a block diagram how the boost converter may be used in the power factor correction of a power supply. [8 marks] Question 3 Describe three advantages of using a transformer in a switch mode power supply. [4 marks] Draw the circuit and associated waveforms for a flyback converter and explain its operation. [6 marks] A flyback converter operates at 50 kHz, 100V input with an output voltage of 500 V and 1000 W and with a turns ratio of 1:4. Calculate (a) the value of the output capacitance so that the output voltage ripple is 10 V; [4 marks] (b) the value of the primary inductance so that the input current ripple is 0.5 A; [4 marks] (c) the corresponding value of the output inductance for (b) [2 marks] Vsin ωt Id D
