Literature distinguishes two types of FOC technique, the Direct- and the Indirect-FOC control (IFOC). In the case of
the Direct FOC control the rotor flux is directly estimated using the measurements of the terminal voltages and
currents. In the case of the IFOC control the slip is estimated using the motor model in FOC condition and the rotor flux
angle is recalculated from the integration of estimated slip and measured rotor speeds. In case of induction machines,
the indirect method is based on reconstruction (estimation)approaches employing terminal quantities such as voltage
and currents in a motor model to calculate the flux position.IFOC does not have inherent low-speed problems and is
therefore preferred in most applications.