EEE 405: Power Electronics First Semester Examination

Power electronics paper built on thyristors and converters. Covers the construction and working of the silicon controlled rectifier with its schematic and symbol, the terminologies of transformer utilisation factor, peak inverse voltage and ripple factor, and the definitions of latching current, holding current and break-over voltage. Works the two methods of turning an SCR on, the snubber circuit in a thyristor connection, silicon controlled rectifiers in the speed control of a d.c. shunt motor and the minimum gate pulse duration needed to latch a rectifier into a resistive-inductive circuit. Continues with the triac and diac, their working and industrial use, the transistor against the SCR and electronic against mechanical switches, why power electronic controllers are efficient and what pushed the gate turn-off thyristor, and the average current of a thyristor triggered thirty degrees after the zero crossing. Closes on step-down choppers, inverters and cycloconverters with their applications, the freewheeling diode in a bridge converter, the limitations of uncontrolled rectification, the boost converter, the diode sequence of a three-phase bridge rectifier, the on-line uninterruptible power supply, firing and conduction angle from gate current and forward breakdown voltage, voltage and current source inverters with pulse width modulation, and a single-phase full-wave semiconverter charging a battery.