Variable frequency converter based voltage and frequency regulation of induction generator for stand-alone system application

Self-Excited Induction Generators (SEIG) exhibit a poor voltage and frequency regulation when subjected to load and speed changes. The proposed variable frequency converter (VFC) based Induction generator can provide constant frequency and almost constant voltage feeding ac loads in stand-alone systems without requiring fixed excitation capacitor and a special designed power electronics circuit. The system is designed using off-the-shelf products likes squirrel cage induction machine, an industrial VFC, a dump-resistor, a small LC-filter and a battery for starting up the system. The open loop vector mode operation of VFC provides constant V/f ratio except at low speed to keep the flux constant under varying load conditions. An external dumping load resistor is connected across the DC chopper to regulate varying consumer load. The proposed method has been carried out on a 50 Hz Induction machine with output power of 5.5kW and rated voltage of 400V in delta connection. The experimental result reveals that the proposed induction machine operation as Induction generator (IG) can be effectively used in a rural area to supply ac load with constant voltage and frequency with rated power delivery.