| Abstract |
To realise a high dynamic controlled operation of induction machines the flux position has to be
estimated during normal operation of the drive. Omitting the shaft sensor leads to a deterioration of the
performance at low fundamental frequencies if fundamental wave models of the machine are used. To
determine the flux position at zero speed without shaft sensor it is thus necessary to use parasitic nonfundamental
wave effects of standard induction machines, such as spatial saturation, slotting or
magnetic anisotropy.
These effects are not evident in normal operation but can be exploited using high frequencies.
Sensorless zero speed schemes thus make use of a high frequency or transient excitation of the
machine in addition to the fundamental wave, which are both impressed by the inverter. The machine
reaction on this high frequency excitation is then measured and the flux and/or rotor position signal
can be estimated by signal processing.
However, the shape of the lamination and especially the slot geometry have strong influence on the
high frequency behaviour. Before realising a sensorless controlled drive it is thus advantageous to
have a look at the design of the machine as not any design is suitable for a specific sensorless control
algorithm.
Usually either the flux or the rotor position can be extracted by exploiting the two most prominent
saliencies caused by saturation and slotting. To investigate the mentioned influence, measurements
have been performed and compared on machines designed with different slot geometry. Based on
these results, a deeper insight into the spatial distribution of the transient flux linkage and its influence
on the control signals is given. |
