Variable speed field-oriented controlled induction generator

In this work, a new induction generator system (IG), to work with variable speed and load, is proposed. The objective is to make it work as a stand alone (not grid connected) generator to produce constant voltage and variable frequency AC current. The IG is based on a three-phase induction machine (IM) exited, simultaneously, by a capacitor bank and a field-oriented controlled inverter. The inverter manipulates the IG excitation currents to control the generated voltage. The capacitor bank is used to minimize the inverter current and to filter voltage harmonics. A laboratory set up was mounted to experimentally validate the proposal. This prototype is based on a 4 kW conventional squirrel cage IM. The inverter uses IGBTs and the controller was implemented using a conventional PC and adequate interfaces. Experimental results are presented to validate the proposed strategy. This system can be used in variable-speed micro wind or hydro power plants where the prime mover operates within a variable speed range to obtain a better efficiency.