Utilization of Self-Excited Three-Phase Induction Generator System

Abstract

In this paper the analysis of a three phase self-excited induction generator system under transient and steady states with various load conditions are presented. In rare area where assumed no national grid is present, but hydro or wind energy may be available a cheap prime mover, such as micro hydro or wind turbine may be applied, which has fluctuating speed. In order to obtain self-excitation, a voltage source inverter based on sinusoidal pulse width modulation strategy has been proposed. The generated voltage and frequency are regulated by adjusting modulation index value. The value of modulation index depends also on the DC voltage level obtained from batteries or solar panels. The proposed system has been also examined without main dc power source , but with the existence of bank capacitor located at the dc link side of the inverter, in this case the generated active power should be equal to/or greater than the required active load power. DC chopper load has thus been utilized to absorb the extra active power, this will control the DC voltage across the capacitor while modulation index will control the system AC output voltage. The generated voltage waveform contains harmonic orders around and higher than the switching frequency, therefore three-phase high passive filter has been used to eliminate the harmonics effects. As a result the machine terminal voltage and frequency values are regulated and maintained constant for different types of loads at different prime mover speed cases. In all these cases, total harmonic distortion values are within the standard values.