Sensorless Torque Control of a DFIG connected to a DC Link

This paper presents a frequency regulation system and a sensorless method for the direct estimation of the slip position of the wound-rotor induction machine connected to a DC link, performing a torque control. Since the stator is connected to the DC link through a diode bridge, it is also necessary to implement the stator frequency regulation. Connecting the DFIG to a DC link using a diode bridge on the stator brings considerable benefits, because only a dc/ac power electronic inverter is required. In this system the magnetizing current is necessarily fed by the rotor: this makes the considered sensorless method particularly appropriate, because, under mismatched parameters, it gives small estimation errors. Simulation and experimental results are presented matching and showing good performances.