German startup promises 25% range increase with low voltage 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.
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.
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.
For demonstration purposes, Volabo has already built 5 prototypes and is now busy integrating its e-drive in demo cars. The new motor concept has already been benchmarked against industry leading e-drives and enabled a 25% increase in driving range at equivalent battery capacity, or allowed a 30% reduction of battery capacity for the same range (through the cascading effects of lighter e-drive weight, lower power losses and reduced battery weight in the vehicle).
Backed by research, Volabo claims the ISCAD reduces losses in common driving cycles by more than 50 % compared to reference drives based on induction machines.
270mm long and 253mm in diameter, the prototype ISCAD delivers over 300kW at a safe-to-touch 48V battery voltage, removing the need for costly high-voltage shielding and making this e-drive inherently safe for maintenance personnel or even in the event of a heavy car crash.
Next, the 20-staff strong company wants to design optimized power electronics to further leverage the efficiency gains of its e-drive. The startup is looking for investors or strategic partners to build its first series of products.
Volabo – www.volabo.com