EEE 405: Power Electronics First Semester Examination

Power electronics paper. Defines power electronics, the firing circuit of a thyristor, commutation and its different methods, and the freewheeling diode and its uses, then the parameters of a power supply: rectifier efficiency, voltage regulation, peak inverse voltage, transformer turns ratio and ripple factor with its importance. Explains what each section of the block diagram does in converting an alternating mains input to a regulated direct output, and reads voltage regulation and minimum load resistance off a regulation curve. Separates a rectifier from a converter and half wave from full wave, gives the advantages of a three-phase over a single-phase rectifier, and describes the full-wave diode rectifier with its waveforms. Works a centre-tap full-wave rectifier with 15 ohms forward resistance per diode, a 141.4 sine omega t secondary and a 1.5 kilo-ohm load through average current, ripple factor, output power, input power and efficiency. Compares the transistor with the SCR as a switch, lists the limitations of uncontrolled rectification, uses an SCR to control the speed of an alternating-current shunt motor, and reads the thyristor voltage-current characteristic for latching and holding current, including the minimum gate pulse duration needed to turn on a series resistance-inductance circuit. Closes on the current source inverter, its principle and 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 load voltage of a step-up chopper from its pulse width and non-conduction time.