Frequency Modulation - Power Electronics - Past Exam Paper, Exams of Power Electronics

Download Frequency Modulation - Power Electronics - Past Exam Paper and more Exams Power Electronics in PDF only on Docsity! EE411 Power Electronics Page 1 of 3 Semester II Examinations 2010 / 2011 Exam Code(s) 4BN Exam(s) B.E. Degree (Electronic Engineering) Module Code(s) EE411 Module(s) Power Electronics Paper No. 1 External Examiner(s) Professor G. W. Irwin Internal Examiner(s) Professor G. Ó Laighin Professor W.G. Hurley Instructions: Answer 3 questions from 4. All questions will be marked equally (20 marks). Duration 2 hrs No. of Pages 3 Discipline Electrical and Electronic Engineering Requirements None EE411 Power Electronics Page 2 of 3 Question 1 Describe, with the aid of a sketch, the operation of a PWM Bipolar Inverter. Explain how the output is generated and show the switching sequence. [6 marks] The dc source supplying an inverter with a bipolar PWM output is 120 V. The load is an R-L series combination with R=32 Ω and L=24 mH. The output has a fundamental frequency of 50 Hz. (a) Specify the amplitude modulation ratio to provide an output of 68 Vrms at the fundamental frequency; [4 marks] (b) If the frequency modulation ratio is 15 and the amplitude of the 13th, 15th, 17th, harmonics of voltage are 0.22, 0.82 and 0.22 respectively of the dc supply voltage, estimate the THD of the voltage and current waveforms; [7 marks] (c) Explain the advantage of a unipolar inverter over the biplolar configuration. [3 marks] Question 2 Figure 1 shows the circuit diagram for a six-step three-phase inverter. Sketch the line-line voltage vAB and the phase voltage vAN. [6 marks] (a) Show the switching sequence to produce these waveforms; [4 marks] (b) Calculate the amplitude of the fifth harmonic of the line-line voltage if the d.c. input voltage is 100V; [4 marks] (c) The Y connected load has R=5 Ω and L=70 mH, determine the range of the rms value of the fundamental frequency component of the load current as the frequency is varied from 25 Hz to 50 Hz. . [6 marks] Figure 1