Magnetizing rotor flux determination using a time-discrete voltage source inverter

In the paper, a possible approach for sensorless determination of the magnetizing rotor flux frequency of the induction machine (IM) in rotor field frame is described. Field oriented speed control of the IM requires information on the exact position and magnitude of the magnetizing rotor flux vector. With sensorless control this can be evaluated by measuring stator voltages and currents provided that the certain IM parameters are known. The power stage of the drive consists of a conventional three phase time-discrete inverter with a supplemented LC filter. The role of the filter is active output voltage shaping, since its output voltage (also IM stator voltage) is attained trough an impressed filter capacitor current. Assuming a cosine capacitor current reference, the output of the filter is of sinusoidal shape. As a consequence of easily measured stator voltage, magnetizing rotor flux frequency and thus rotor speed are calculated from instantaneous values of stator voltages and currents.