Abstract

The squirrel-cage induction machine is very attractive for small and medium power generation schemes because of its low cost, robustness and high power density (W/kg). However, the magnitude and the frequency of the generated voltage depend upon the rotor speed, the amount of capacitive excitation, and the load in stand-alone systems with unregulated prime movers. A common approach for providing regulated voltage and frequency to the load is the use of an asynchronous link (ac-dc-ac) power electronic converter. The main disadvantage of this scheme is that the two series connected ac-dc converters have to be rated at least to the rated generator output power. This thesis investigates the use of a single reduced rating ac-dc converter, or voltage source inverter (VSI), connected to the stator of a self-excited induction generator (SEIG) for regulating purposes. Reactive power control is used to regulate the voltage magnitude while active power control, made possible by using a battery bank at the dc side of the VSI, regulates the voltage frequency. An experimental set-up is implemented for the proposed scheme operating with unregulated micro hydro and wind turbines, implemented on a prime mover emulator. The experimental results are in agreement with the simulation results, theoretical analysis and design specifications