Schematic representation of the integrated drive system

From the idea to implementation

Integrated electric drive system moves from Bergische Universität to industrialization

A new, integrated drive system for electric and hybrid vehicles is creating promising prospects for electromobility. Scientists at the Chair of Sensor Technology and Metrological Systems at the University of Wuppertal, led by Prof. Dr.-Ing. S. Butzmann, have rethought the classic design of electric drive systems and for the first time developed a system that integrates all three main components - battery, electronics and motor - into one component.

The all-electric drive system is now being further developed for market launch in a spin-off company.

E-drive with competitive advantage

Electric drives consist of an energy storage unit (usually a high-voltage battery), a pulse inverter and control system, and a motor designed as a 3-phase synchronous or asynchronous machine. These components are usually installed separately in the vehicle and connected to each other by cables. In many cases, this is supplemented by a DC/DC converter that connects the high-voltage on-board network with the vehicle's 12V on-board network.
"The high voltages in the powertrain are both a blessing and a curse," explains Prof. Butzmann. On the one hand, he says, they are necessary to keep the currents and thus the cable cross-sections, weight and costs low for a given power output; on the other hand, they require elaborate insulation and safety measures. In addition, in the event of a fire, the high-voltage system must first be shut down before the firefighting work can begin, i.e., the battery must be disconnected from the vehicle's electrical system. In passenger cars, for example, this is now almost always done automatically in the event of an accident, but all these measures, such as disconnect relays, are still associated with considerable costs.
The aim of the work at the Chair of Sensors and Measuring Systems at the University of Wuppertal was therefore to develop a low-voltage drive system that can also provide higher power and yet does not require the additional protective measures described above.
This goal is achieved by using a multiphase motor in which each individual phase is operated with a touch-safe voltage of less than 60V. Here, the scaling of the power is not done by the voltage but by the number of phases used. Such motors have been known from the literature for some time, but have so far found little use because of the high cabling effort to the individual phases.
The idea of the BUW scientists was now to spatially combine the electronics, the battery and the motor in order to avoid exactly this wiring. To do this, the battery cells are arranged around the motor and the power electronics are attached to the front of the drive in such a way that they are directly connected to both the battery cells and the motor connections. Cable connections between the battery, inverter and motor can thus be dispensed with completely. The high-current printed circuit boards required for this were manufactured in-house at the institute using a specially developed technology.

Due to the increased number of motor phases, the number of electronic components required has also increased, but the power components now used (MOSFETs) in particular are considerably cheaper than the IGBTs normally used in HV systems, so that the costs for the power electronics have remained largely the same. On the other hand, considerable cost savings can be achieved by eliminating the HV protection measures that were previously necessary and by eliminating the wiring.

In addition, the system's inherent modularity and redundancy mean that an overall system failure can be avoided in the event of a component defect. If one functional unit fails, the remaining units continue to operate and there is only a loss of performance. Due to the compact design and the use of the chassis potential as reference mass for the drive train, there are also considerable advantages with regard to electromagnetic compatibility.
A demonstrator of the electric drive with an 8kWh battery has been built at the Bergische Universität Wuppertal and delivers 60kW of power. The complete drive has a diameter and a length of about 40cm each. Such a system could be used in a wide variety of applications such as hybrid or plug-in hybrid vehicles.
Use in fully electric passenger cars is also conceivable in principle with an expansion battery. Here, however, the problem of the charging interface must first be solved, where fast charging is not possible without high voltages. "We are pursuing various promising approaches here as part of a doctorate to be able to charge our system, which is actually designed for low voltages, with high voltages as well and still retain the cost advantages," says Prof. Butzmann. However, the obvious solution of using a DC/DC converter for this purpose was ruled out for cost reasons.

Broad patenting and rapid marketing

In order to comprehensively secure the rights to the two inventions on which the all-electric drive is based, the University of Wuppertal, with the support of PROvendis, has applied for international patents, which are now about to be granted.

In order to drive forward the further development and marketing of the drive system, investors were quickly found who provided a medium, eight-figure sum in the establishment of a company for the further development, production and marketing of the new drive system. Here, too, PROvendis provided active support in drawing up the contract.

Start-up with vision

"We develop state-of-the-art system solutions that change the way we get around," says Achim Fedyna, formerly vice president of technology at Bosch Mahle Turbosystems and now managing director at the newly founded stoba e-Systems.

The start-up's ambitions are big. In the meantime, a now 50-strong, highly motivated team is intensively driving forward the development of the drive system and the company.
Additional impetus is provided by the positive feedback from numerous presentation and discussion rounds with potential customers. In parallel to the actual system development, an interesting preliminary study project has already been won with a major OEM in the automotive industry.
In addition, interested parties range from municipal vehicle manufacturers, manufacturers of all-terrain vehicles, construction machinery and industrial trucks to classic/oldtimer vehicles in which the combustion engine is to be replaced by an electric drive.
To this end, stoba e-Systems was already able to present a concept study with a fully electrified Mercedes Pagoda - a sporty and elegant classic vehicle from 1963 - at the "Retro Classics, Fair for Driving Culture" in the spring of this year.
The vehicle is ready to drive with the new electric drive system and is meeting with great interest from manufacturers of electromobility and industrial solutions from Germany and abroad.

Mercedes Pagoda with fully integrated electric drive system.
(left: H. Schweden, Bergische Universität Wuppertal; right: M. Fischer, stoba e-systems)

The next generation of drives is currently being developed at stoba e-systems. At the same time, the construction of the test benches and the production planning are already taking place.
In order to gain an even higher development speed, another development office has been opened in Wuppertal in addition to the location in Weinstadt. "The constellation is ideal. By working at the chair, the students learn the necessary skills with which they can then fully contribute and prove themselves directly in a highly professional research and development environment," says Professor Butzmann. In this way, two employees have already been placed in the new company in the last two months, who are now helping to actually bring the integrated electric drive system to the road.

Prof. Dr. Stefan Karl Butzmann
Tel. 0202 / 439 1814

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