CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Application No. 19160279.6, having a filing date of Mar. 1, 2019, the entire contents of which are hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to a manufacturing method for a segmented stator or rotor of an electrical machine, i.e. a stator or a rotor including a plurality of stator segments circumferentially joined together. More particularly the following relates to such a stator or rotor.

BACKGROUND

In large electrical machines, segmentation of the stator and/or the rotor structure is required to ease manufacturing and transportation. This is in particular required for stators or rotors where a winding is provided. Due to manufacturing tolerances and limitations as well as to ease assembly, tolerance circumferential gaps are typically designed between segments.

The presence of the segment circumferential gaps can lead to differences in the electromagnetic performance compared to a single stator and often leads to issues with undesirable torque harmonics and output power harmonics of the electrical machine, which can lead to high levels of vibration and acoustic noise as well as losses and complicated control. It is therefore important to control the shape and dimensions of the circumferential gaps in order to minimize the detrimental effect on the performance introduced by the segmentation.

For electrical machines with half teeth at the circumferential ends of the segments (typically integral slot electrical machines with distributed windings), the segment circumferential gaps can be controlled in shape and dimensions by conveniently shaping and dimensioning the half teeth. This has no detrimental effects on the area of slot used for housing the copper windings and therefore the torque and output power of the electrical machine is not affected.

For electrical machines where a half slot is present at each circumferential end of a segment (typically fractional slot machines with concentrated windings), the slot cannot be modified, for example by decreasing them in width, as this would reduce the area for the windings. A reduction in winding area would increase the resistance in this particular coil and therefore increase the loss. By having an imbalance in losses between the coils, a hot spot would be expected to form in the circumferential end coil, thus limiting the operating point of the whole machine from a thermal perspective.

SUMMARY

An aspect relates to a new method of manufacturing a stator or a rotor of an electrical machine, for controlling the shape and dimensions of the circumferential gaps in segmented stators or rotors having half slots at the circumferential ends of the segments, in order to minimize the detrimental effects above described.

According to embodiments of the invention, there is provided a method of manufacturing a stator or a rotor of an electrical machine, the stator or rotor including a plurality of segments circumferentially joined together in such a way that a circumferential gap is interposed between two circumferentially adjacent stator segments.

According to embodiments of the present invention, the presence of the circumferential protrusion leads to a reduction in certain cogging and loaded torque harmonics, as well as in the voltage and power harmonics. Each segment includes a segment body circumferentially extending about a longitudinal axis of the stator segment between a first circumferential end and a second circumferential end. The segmented body includes: a plurality of teeth protruding from a yoke of the segment body, the plurality of teeth being circumferentially distributed between two end teeth of the plurality of teeth, the plurality of teeth comprising at least one intermediate tooth circumferentially comprised between the end teeth,

a plurality of slots, circumferentially interposed between the teeth of the stator, the plurality of slots being circumferentially distributed between two end slots, each end slot being circumferentially comprised between a respective end tooth and a respective circumferential end, the plurality of slots comprising at least an intermediate slot circumferentially comprised between the two end slots, the plurality of slots, the method including the steps of:

modelling a plurality of model segments circumferentially joined together in such a way that two circumferentially adjacent model segments contacts each other at respective circumferential interfaces, the plurality of model segments including a plurality of model teeth interposed between a plurality of slot,

manufacturing the segmented body in such a way that at least the two end slots are circumferentially shifted away from the circumferential interfaces of the respective model segment for creating respective gap portions of the circumferential gap, the sum of the circumferentially shifts of the at least the two end slots being equal to the sum of the circumferential extensions of the gap portions,

circumferentially joining the plurality of segments together in such a way that two gap portions of two adjacent segments forms the respective circumferential gap.

According to embodiments of the invention, in the step manufacturing the segmented body each slot is circumferentially shifted away from the respective circumferential interface of the respective model segment which is closer to the slot, the sum of the circumferentially shifts of the slots being equal to the sum of the circumferential extensions of the gap portions.

According to an embodiment of the invention, each tooth circumferentially extends between two respective side faces and in the step of manufacturing and in the step of manufacturing the segmented body the circumferential widths of the end teeth are reduced on both sides faces and the end teeth are circumferential shifted away from the respective circumferential interface in order that the slots widths are kept equal to the model slots, the sum of the reduction of the circumferential widths and of the shifts of the end teeth being equal to the sum of the circumferential extensions of the gap portions.

With reference to known embodiments where the tooth thicknesses are reduced and all the teeth are consequently shifted, this embodiment limits the change in coil pitch to magnet pitch ratio, therefore limiting the levels of torque and power harmonics (particularly the second and the fourth harmonic).

According to another embodiment of the invention, each tooth circumferentially extends between two respective side faces and in the step of manufacturing the segmented body the circumferential width of each end tooth is reduced by circumferentially shifting away from the respective circumferential interface the respective side face being closer to the respective circumferential interface, the sum of the circumferentially shifts of the side faces being equal to the sum of the circumferential extensions of the gap portions

This embodiment limits the levels of torque and power harmonics (particularly the second and the fourth harmonic) at the same time limiting the modification to be performed on the segment with respect to the model segment.

According to a further embodiment of the invention, the method includes the further step of dividing each model segments in two halves, each half model segment circumferentially extending between a respective circumferential interface and a circumferential middle section intermediate between the two circumferential interfaces, each slot of each half model segment being shifted by shifting a side face of a respective tooth, the side face being oriented towards the respective circumferential interface.

This embodiment further limits the levels of torque and power harmonics (particularly the second and the fourth harmonic) with respect to the one previously described.

The aspects defined above and further aspects of embodiments of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The embodiments of the invention will be described in more detail hereinafter with reference to examples of embodiment but to which embodiments of the invention is not limited.

