The concept is simple: instead of sending the current through three phases into the motor, the number of phases is simply increased so that the current load is divided between the many phases and thus does not exceed the current carrying capacity per phase. Advances in power electronics made this possible years ago. "But the real hurdle for us was something else. For decades, even experts have been firmly convinced based on their experience in the field of overhead grids: High power can only be transmitted effectively at high voltage. But this is a fallacy if the power is to be transmitted over short distances - like in a car," said Prof. Dieter Gerling in an interview with Markt&Technik.

His chair at the Bundeswehr University in Neubiberg gave rise to Volabo, which was founded by two of his former colleagues - Florian Bachheibl and Adrian Patzak - in 2016. Prof. Gerling was able to show that his concept works in principle with an initial prototype back in 2014/15. Then things went from strength to strength - in 2016, the second prototype already reached an output of 150 kW. Here, however, the power electronics were still installed externally. The third prototype followed in 2017, in which the power electronics could be integrated into the motor itself for the first time, and in spring 2019 Volabo succeeded in reducing the size of the power electronics by more than half again. The result is a motor that reaches 110 kW with a length of just 33 cm, including the associated electronics, i.e. the inverter with control unit. "We were able to integrate it into the front axle of a Touran without any problems," says Adrian Patzak happily. In addition, a second car built with a partner is already running with the Volabo drive.

"So we can demonstrate live that the old mantra 'high power only works with high voltage' is not true," says Prof. Gerling. After all, there are only short distances to cover from the battery to the motor in the car, so currents of 1000 A, 4000 A and beyond can easily be transmitted without high line losses.

Pasi Pennanen and Vesa Lehtinnen, founders of the Finnish company Toroidion, thought the same thing. They had nothing less in mind than to develop an electric racing car that could win the 24 Hours of Le Mans. They equipped the first prototype with four motors - one for each wheel - with a total output of 1 MW and a 48 V power supply. They also split the motor into many phases, through which relatively small currents then flow. Toroidion has also developed the appropriate power management electronics and batteries (only the cells are supplied) for its drive system. According to Pennanen, the range of the sports car reaches 650 km with a 65 kWh battery.

The low voltage supply of 48 V, which will establish itself as the standard for future generations of cars, offers numerous advantages. All the complex protective measures that are required for the motor voltages between 400 and 800 V that are common in electric cars today can be dispensed with. No specially trained employees or special safety precautions are required either for the construction, maintenance or repair of 48 V cars.

Safety with e-cars

Prof. Dieter Gerling, Voalbo: "We can show live that the old mantra 'high power only works with high voltage' is not true in cars."

© Thomas Benz/just imagine

Most importantly, rescue teams also have safe access to the car in the event of an accident and can rescue injured people. "I wouldn't be surprised if a discussion similar to the Dieselgate scandal develops around the lack of safety for e-cars, which could severely damage e-mobility as a whole," Pasi Pennanen told Markt&Technik.

Another major advantage: the low supply voltage means that relatively inexpensive power semiconductors can be used, eliminating the need for protective circuits.
This has also convinced Continental. The company has built its new, six-phase 48 V motor on the basis of "plugged windings (hairpin)". Specifically, these are fixed wires that are inserted into slots in the stator and then welded together. The 6-phase motor achieves peak outputs of up to 30 kW and can be integrated into various topologies (P2, P3, P4) of a hybrid vehicle. In Continental's demo vehicle, the motor is located between the combustion engine and transmission - in a so-called P2 topology. This enables purely electric driving at speeds of up to 90 km/h, especially in inner-city areas. The efficiency of the electric drive increases by 10% compared to conventional 48 V systems. This halves the losses in the electric drive during the recuperation process. Overall, this results in fuel savings of 20 % compared to the corresponding combustion engine.

A major additional advantage: manufacturing the coils is very expensive, replacing them with plug-in windings drastically reduces costs. "Together with the battery and the power electronics, we have created a system that can replace a high-voltage full hybrid system in an economically viable way," explained Stefan Lauer, Project Manager at Powertrain Technology and Innovation at Continental, to Markt&Technik. At the moment, the first step has been completed with pre-development, and pre-series projects are planned. If there is interest, series production could start in around four years' time. According to him, there is no lack of interest: "Practically all OEMs are currently taking a very close look at 48 V technology. Our motor also fits very well in hybrid vehicles from an economic point of view." Continental is currently investigating whether the 48 V motors would also be suitable for use in plug-in hybrids.

Volabo has taken the coil-less principle to the extreme. The "Intelligent Stator Cage Drive" - ISCAD for short - consists only of aluminum rods that form the phases. Because the phases and the associated power electronics form the basic modules from which different motor types for different cable classes can be constructed, these modules can be produced cost-effectively in large quantities.

"But we don't just replace the coils, which in itself significantly reduces production costs, we also create new functionalities," explains Dieter Gerling. This is because the phases can be switched on and off as required. When accelerating, all phases can be switched on; if the car is rolling along on level ground, only a few phases are required and the others can be switched off. This further increases efficiency.

No permanent magnets

Vesa Lehtinnen and Pasi Pennanen founded Toroidion and have already demonstrated a 1 MW sports car based on four 48 V motors.

© Toroidion

Thanks to this effect and the equally efficient power electronics, Volabo can dispense with permanent magnets, which previously gave motors the high efficiency required for use in cars and were therefore generally indispensable. However, permanent magnets are expensive, and the extent to which the rare earths (neodymium and disprosium) required for this will be available cannot yet be predicted, as the largest deposits by far are found in China. "Our motors, on the other hand, consist only of iron and aluminum, both of which are inexpensive and highly available," says Patzak.

In addition, the large winding heads are no longer needed in the coil-less motors, as Gerling explains: "This is a key reason why we were able to integrate the line electronics and the motor, including all the electronics, is therefore no larger than motors from other manufacturers without electronics." At the same time, the losses in the motor are reduced and material can be saved.

In the meantime, word has apparently gotten around that high motor performance can also be achieved with low voltages in the car. In any case, Volabo was able to finance itself in the first three years of its existence purely through project business relating to ISCAD. This alone shows how sought-after the technology is - "rather unusual for a start-up", says Gerling.

"The next step is now industrialization; we need to find production partners and investors." That is not a problem either, "we practically skipped the first round of financing with the help of the project business and are starting on the second one straight away." Now it is important to obtain the relevant certifications and qualifications as quickly as possible. The first series production could start in one and a half to two years.
Charging the 48 V battery on three-phase systems up to 12 kW is not a problem. For charging at fast charging stations, a DC/DC converter would have to be integrated into the cars. According to Gerling, this means a little more effort and cost for this device, but it still pays off in the overall system due to the many other advantages. But he also has an idea here: inductive high-performance charging. Because charging takes place via the magnetic field, the transmission is voltage-independent. However, charging over greater distances of 10 to 20 cm would be ineffective.

However, if the ground station were to be movably mounted and automatically moved to a distance of approx. 1 mm from the car, then all batteries could be charged very effectively - whether 48 V, 400 V or 800 V. "Then only one charging infrastructure would be required for all the different vehicles. Because the charging network is still being developed, we are now at exactly the right time," Gerling is convinced. This could even allow Volabo to build up a second mainstay. The founders have optimistically given the start-up the Latin name Volabo (I will fly). Gerling is convinced that the company is about to take off.