To realise a high-dynamic controlled operation of induction machines the flux position has to be estimated during 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 applied. To determine the flux position at zero speed without shaft sensor it is thus necessary to use parasitic, non-fundamental wave effects of standard induction machines, such as spatial saturation, slotting, or other anisotropy. These effects are not evident in normal operation but can be exploited using the high frequency or transient electrical behaviour of the machine. All sensorless zero speed schemes currently published 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 measured and the flux and/or rotor position signal estimated using special algorithms and signal processing techniques. However, it turned out in the past that the shape of the lamination and especially the slot geometry have strong influence on the high frequency/transient electrical response of the machine. 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. The presented investigation is thus focused on the influence of the lamination geometry on the resulting signals of a sensorless control scheme. The sensorless control method applied is usually denoted as INFORM-method in literature and is based on a transient excitation with voltage pulses. In the transient electrical current response of the machine there are always all saliencies present. The two most prominent saliencies are caused by saturation and slotting. Their modulations in the control signals have to be extracted and separated in order to obtain the flux or the rotor position of the machine. Currently the interaction of the saliencies limits the practical application of these methods. To investigate the mentioned influence, measurements have been performed on five machines with different lamination geometry. By comparing the extracted saliencies of these machines, the influence of slot design on the sensorless control signals is depicted. Thus the magnitudes of the two saliencies can be influenced by a proper adjustment of the geometry. This association is shown for the saturation saliency in Fig. 1. Depending if the flux or rotor position is to be used for the machine control the corresponding saliency can be boosted and the others attenuated. This results in a more reliable extraction and separation of the saliencies and a more robust control.
| Filename: | EPE Journal 13-3 - 7 - Paper Wolbank |
| Filesize: | 75.72 KB |
