Schriftenreihe .;technologiekompetenz Verkehr in

CURRENT STATE OF TECHNOLOGY
The great potential for electric vehicles derives from the
possibility of reducing dependency on fossil fuels and
significantly increasing the efficiency of the drivetrain. Electric
drives have a far higher level of efficiency than drivetrains with a
conventional combustion engine. Given the current state of the
technology, however, these key advantages are set against
certain disadvantages, such as poor range, high initial cost and
safety aspects of the energy storage systems (table 1).
Constraints imposed by the requirements of the electric vehicle
concept, especially regarding the battery storage system,
prevented the entering of this technology into the mass market
so far. The outcome of past electric vehicle developments
mainly resulted in special applications not suitable for the mass
market. Current applications range from scooters over vehicles
for handicapped people to micro cars with restricted space and
drive range. All of these are more or less only suitable for
special tasks and needs, not being able to compete in the
dominant vehicle segments with large sale figures. The trend
nevertheless shows that manufacturers are trying to enter the
mass market with competitive electric vehicles. Although
manufacturers are quite cautious with forecasts at the moment,
customers can expect competitive electric or partially electric
vehicles in the forthcoming years. Fleet demonstrations like for
instance those in London, Berlin or Munich as well as larger
scale projects like the project „better place“ will support the
market introduction of electric vehicles with considerably higher
sales figures.
Advantages of electric vehicles
• CO 2-neutral system by using renewable energy
• High energy efficiency
• Low operating costs
• Low-noise propulsion system
• Existing power supply grid
• No emission of pollutants at the place of vehicle operation
Table 1: Advantages and requirements for future-proof electric vehicles
TECHNOLOGICAL CHALLENGES
ELECTRIC VEHICLES
The main focus in the development of EVs remains in
maximising range, performance and safety, while minimising
weight and cost. To that end, it is necessary on the one hand to
consider the electrical drive, comprising the electric machine,
the converter, the controller and the energy storage unit, as a
total system and to develop highly optimised individual
components in accordance with these system requirements.
Often the individual components are configured for maximum
performance, with the ability of the individual components to
cope with overload mostly not being taken into consideration,
generally resulting in over-dimensioning, higher costs and
greater weight in the overall system. For that reason, in order to
achieve ideally configured components, the overall system in
the vehicle including all relevant components and their reciprocal
dependencies needs to be considered as the starting point in
developing the individual components. On this basis, a key step
can also be taken towards optimising energy management and
the control system.
The core component of an electric vehicle is the energy storage
system, since it defines the range and performance of the
vehicle, but, at the same time, it is the biggest challenge for
further improvements of the overall vehicle.
In recent years, nickel-metal hydride (Ni-MH) and above all new
lithium-ion (Li-ion) cells have established themselves as very
high-performance batteries which already possess sufficient
energy density and are thus ready for series applications (figure
2). At the same time, further improvements in Li-ion batteries
are needed with regard to weight, costs and especially safety, in
order to establish them as an alternative technology for hybrid
and electric vehicles.
Requirements of electric vehicles for broad market penetration
• Ensuring adequate drive range
• Safety of the energy storage system
• Widespread availability of the charging infrastructure
• Acceptable charging times for the energy storage system
• Innovative design
• Use of renewable energy resources to provide electrical energy
• Reduction of high initial cost for energy storage device
19