H Bridge - Power Electronics - Exam, Exams of Power Electronics

Download H Bridge - Power Electronics - Exam and more Exams Power Electronics in PDF only on Docsity! Cork Institute of Technology Bachelor of Engineering (Honours) in Electronic Engineering- Award (NFQ Level 8) Summer 2006 Power Electronics (Elective) (Time 2 hours) Answer any three questions Examiners: Prof. G. Hurley Dr. S. Foley Dr. N. Barry Q1. Consider a H bridge dc to variable ac output inverter (i) If the load is highly inductive, show the voltage and current waveforms of the load, indicating clearly which devices are conducting the current at each stage of the inverter. [10 marks] (ii) If the output ac voltage is at its maximum (that is the firing angle )0=α Show that the rms current flowing in any switch is given as I V fLrms s= 4 3 in standard notation [10 marks] (iii) What is the peak current flowing through the switches, if the voltage source is 48V, L the inductance is 200µ H and the frequency of switching is 20kHz? [5 marks] Q2. Consider the buck circuit with a zero voltage resonant switching circuit, as shown below, Fig.Q2. (i) Describe the operation using the various modes of operation, starting with the switch opened, showing relevant waveforms. [10 marks] (ii) Show that the minimum off time of the switch is given as t t t t LC LCV CI V I C L s s min sin= + + = + + − 1 2 3 1 0 0 π [10 marks] (iii) What is the peak voltage on the switch capacitor for the circuit in fig. Q2? [5 marks]