German startup promises 25% range increase with low voltage e-drives

November 20, 2018 //By Julien Happich
German startup promises 25% range increase with low voltage e-drives
Founded in 2016, German startup Volabo GmbH based in Ottobrunn near Munich has secured over 30 patents worldwide to redefine e-drives.

The company's Intelligent Stator Cage Drive (ISCAD) of which a prototype could be seen at electronica is built without expensive and difficult to manufacture copper windings and magnets.

Taking out the stator, solid aluminium bars
short-circuited at the back.

Instead, both the rotor and the stator of the ISCAD are made of plain aluminium bars, the die-cast stator cage in particular, consists of thick solid bars short-circuited at the back with a large ring. The die-cast construction of the stator is both economical, lightweight, and boasts a high slot fill factor, up to 100% or about 2.5 times higher than for conventional distributed windings, according to a 2014 IEEE proceeding titled "Low Costs and High Efficiency Asynchronous Machine with Stator Cage Winding" published by researchers from Universitaet der Bundeswehr Muenchen.

At the front, each stator bar (60 or them) is controlled individually by a half-bridge MOSFET switches, fed with a low voltage (48V) high phase current.

Fitting into a wheel, Volabo's ISCAD explained.

Through this discrete stator bar control, 60 phases are individually fed to the ISCAD, allowing the precise shaping of the air gap magnetomotive force (MMF) or even changing the number of pole-pairs of the motor during operation.

"Being able to energize each conductor (slot) separately gives a great variety of possible modes of operations such as, changing the number of pole-pairs, generating several pole-pairs simultaneously, controlling the amplitude and frequency of corresponding pole-pairs separately, changing the number of active phases, and so on" the authors write.

This kind of electrical gearbox can be used to optimize drive efficiency in the total operating area, fitting motor torque and speed to the conditions at the wheels, the researchers explain in the paper. In essence, the e-drive's mechanics are simple and its operation can be re-configured on-the-fly through software and electronics. What's more, the ISCAD's very construction eases heat dissipation and efficient cooling could be carried out by simply affixing a cooler channel to the stator end-ring lateral side.

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