Schriftenreihe .;technologiekompetenz Verkehr in

ELECTRIC DRIVES
A comparison of the key characteristics of AIM and PMSM,
together with their main advantages and drawbacks, is given in
table 1. It can clearly be seen that the key advantage of the
PMSM is its high power density and, as a consequence, lower
weight to compensate for different drawbacks like complex
assembly or control. By using the latest permanent magnet
materials and by taking account of these materials in the motor
design process, further optimisation can be achieved in terms of
the power density of the PMSM.
By comparison, the power of the AIM can be increased for
example by using copper rotors with copper bars and soldered
rotor end rings. Compared to traditional cast aluminium rotors,
this offers advantages in terms of the electrical behaviour of the
machine due to reduced losses and higher efficiency.
In the system analysis, different aspects need to be taken into
consideration to select the most appropriate machine type, such
as:
> Power requirement (continuous output, peak power, speed,
torque)
> Weight or power density
> Available space (highly integrated solution)
> Cost
> Environmental conditions (cooling, weather-proof, dirt)
> Availability and cost of materials
> Manufacturing (standardisation versus special-purpose
solutions)
> Reliability, especially in relation to robustness and monitoring
> Suitability for series application
This wide-ranging of conditions requires a comprehensive
development for the electric machine. The design process,
looking at electrical and thermal behaviour, the choice of an
appropriate cooling system, and the packaging of the entire
electric drive, is essential to realise a highly integrated and
optimised electric machine for automotive applications.
32 Austrian Technological Expertise in Transport
POWER ELECTRONICS
The power electronics connect the electric machine to the
energy storage system. Since the electrical energy storage
provides direct current or direct voltage, the power electronics
have to convert this into alternating current or alternating voltage
according to the requirements of the electric machine. This
allows the power electronics to influence the speed and torque
of the electric machine, therefore playing an essential role in
optimising the electric drive.
To convert direct current into alternating current, the
semiconductors on the power electronics perform a large
number of switching processes, consequently resulting in
additional losses. Reducing these losses (switching and on-state
losses) is one of the key issues in developing high-efficiency
solutions. Research and development is required to integrate
the latest low-loss semiconductors. In addition, optimised and
innovative control procedures for power electronics and the
electric motor offer the potential to further improve efficiency.