A DOUBLY FED INDUCTION GENERATOR USING BACK-TO-BACK PWM CONVERTERS SUPPLYING AN ISOLATED LOAD FROM A VARIABLE-SPEED WIND TURBINE

A doubly fed induction generator (DFIG) designed to be driven at varia ble speed from a wind turbine and supplying an isolated load is presen ted. Two back-to-back PWM voltage-fed inverters connected between the stator and the rotor allow sub- and super-synchronous operation with l ow distortion currents. The load voltage is maintained at constant fre quency and its magnitude is regulated through control of the stator fl ux of the generator. An auxiliary load is connected in parallel with t he main load, and the auxiliary power is controlled to allow the DFIG to track the optimal wind turbine speed for maximum energy capture fro m the wind. An indirect stator-orientated vector control scheme is use d to control the DFIG and this results in constant load voltage and fr equency for variations in both load and wind speed. The techniques hav e been implemented and validated on a 7.5 kW experimental rig.