an investigation of dual stator winding induction machines

integral and a new stretch-turn operator have been used to ensure the operation at very
low speed. Another sensorless scheme has been proposed in [10.41], in which the error of
q-axis current is used to feed a PI control and the output of this PI control is the estimated
slip frequency. Then the estimated rotor speed is obtained by subtracting the estimated
slip from the synchronous speed. The sliding-mode control and variable-structure control
have been adopted into the MRAS system to offer robust performance and overcome the
parameters uncertainties [10.42-10.47]. The induction machine sensorless control using
the Luenberger observer have been found in [10.48-10.49].
It is also found that in addition to the emergence of new approaches, some “new”
techniques have been applied into the old approaches to yield better results. For example,
the Phase Locked Loop (PLL) technique is combined with a low-pass filter to obtain
better flux estimation results from the simple voltage model approach [10.50]. In [10.51],
the MRAS scheme and the saliency-based flux orientation are used at different speed
ranges and the combination scheme offers the synergetic effect between these two
methods. The MRAS adaptive scheme has also been applied to study the induction
generator and wound-rotor induction machine in wind energy applications [10.52-10.54].
The magnetic structure method is based on using second order effects due to the
physical structure of the machine [1.11]. The third harmonic voltages due to the
saturation effects were used to estimate the flux angle in [10.55]. Another technique that
uses the effect of the rotor slots to track position has been presented by Lorenz. This
method achieves zero speed estimation by using high frequency excitations adding to the
main signals. The high frequency injection method, which is based on saturation induced
saliency, has been proposed in [10.56-10.58]. It is claimed that the local saturation due to
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