An Observer for Sensorless DFIM Drives Based on the Natural Fifth Harmonic of the Line Voltage, without Stator Current Measurement

This paper proposes an observer for the sensorless control of Doubly Fed Induction Machines which is based on the effect of a natural signal injection in the stator windings due to the fifth harmonic of the line voltage. A method to extract the rotor position and speed only from the rotor current and stator voltage measurements is developed: as a novelty the stator current measurement and the anisotropies in the machine design are not required. A phase-locked loop is used in order to track the harmonic current component which is induced in the rotor by the fifth line voltage harmonic and whose speed and position are directly related to the rotor speed and position. The tuning of the observer parameters is discussed together with the effect of the other line voltage harmonics. The paper is completed by the experimental validation of the observer performances.