Control of a polyphase induction generator/induction motor power conversion system completely isolated from the utility

Two squirrel cage induction machines interconnected via a 20 kHz parallel resonant high frequency (HF) AC link and associated switching pulse density modulated (PDM) power converters are investigated, one operating as a generator and the other as a motor. No capacitors are used for the excitation of the generator or motor. Instead, the real power of the generator is controlled so as to maintain the proper link voltage and match the power between the input and output, Current regulated PDM converters operating via field oriented controllers are used to control both machines. A zero voltage switching technique is utilized with the associated PDM converters. Low harmonic distortion waveforms have been obtained both at the input and output due to the high 40 kHz switching frequency. Link voltage build-up and excitation of the generator by an initial charging circuit, power matching between input and output, and peak link voltage regulation techniques are investigated. Both computer simulations and experimental results demonstrate the feasibility of the proposed system