Control of squirrel cage induction generator in an oscillating point absorber based wave energy conversion system

This paper presents operation and control of a Squirrel Cage Induction Generator (SCIG) to generate power from an oscillating point absorber based wave energy conversion (WEC) system. The oscillating point absorber buoy is assumed to be connected with the SCIG through a rack and pinion gear arrangement, thus converting the linear motion of the buoy to rotary motion of the generator. Proper gear ratio is assumed to amplify the low speed of the buoy to the standard rpm of the rotary generator. An equivalent mechanical model of the buoy is presented. The SCIG is controlled with indirect field oriented control (IFOC) method to extract power from the buoy. It is assumed that the SCIG is operated below its rated speed and the air gap flux is maintained at its rated value in all operating conditions. The torque component of the current is varied in proportion with the buoy speed to harvest variable power from the buoy. The system control is validated through simulation in MATLAB-Simulink platform and corresponding results are presented. A discussion on the peak to average power generation ratio and its impact on the machine rating is also provided.