EEE 405: Power Electronics First Semester Examination

Power electronics paper. Explains the drawbacks of a mechanical switch in an electrical circuit and the advantages of electronic switches, whether a diode can be used for three-phase rectification with its circuit and working, the power diode from its voltage-current characteristic, the two-resistor model of a thyristor, the advantages of a thyristor over a transistor, and the applications where direct current cannot replace alternating current. Determines the minimum capacitance that keeps a 100 volts per millisecond dv/dt rating from causing erratic turn-on when power is switched onto an eight ohm load from a 400 volt supply. Continues with why a heat sink is required when connecting a thyristor, commutation and its different methods, the clamping circuit and how it works, the purpose of filters in a rectifier circuit, the methods of improving input power factor with rectifier circuits and the best among them, and four-quadrant operation with a dual converter and its application. Defines ripple factor with its expression derived, rectifier efficiency, latching current and breakover voltage, then the advantages of reactive power, the necessity of a regulated power supply and the limitations of uncontrolled rectification, with a single-phase full-wave semiconverter charging a 24 volt battery through a 5 ohm limit resistor at a firing angle of forty-five degrees from a 50 volt input. Closes on the current source inverter and its industrial applications against the voltage source type, the conventional on-line uninterruptible power supply, the oscillation period and resonant frequency of a series inverter, the dual converter, the direct-current chopper and its industrial uses, cycloconverter types and configurations, and the speed of a 220 volt shunt motor running at 1500 revolutions per minute on no load when fed through a type A chopper drawing 20 amperes at a ratio of zero point six.