advanced simulation technologies
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Performance and efficiency are top priorities when designing motors
for electric powertrains. At the same time, electric motor development
for the automotive industry is faced with increasingly complex requirements
regarding maximum power density and changing operating loads.
In order to meet the opposing development goals of efficiency and performance,
the components of the electric motor must be designed in such
a way that they can be operated at overload for a limited period of time.
A deep understanding of the thermal behavior of all motor components
is required to prevent failure due to overheating in circumstances such as
these. Thermal simulation is therefore a core task in the development of
electric motors. This begins with the precise calculation of the electrical
and mechanical losses that act as heat sources. Heat flows and temperature
distributions in the motor’s structures must be taken into account as
well as heat removal by the cooling medium.
The starting point of any detailed electric motor analysis is an electromagnetic
calculation. Our recognized simulation software AVL FIRE™ M
offers the possibility to model the stator and rotor for different types of
electric motors and to use this model to perform an electromagnetic field
calculation.
Electrical losses are then calculated from the distribution of current density
and magnetic flux density. In combination with mechanical and ventilation
losses, this results in the distribution of the power dissipation densities,
which serve as heat sources in the thermal analysis.
In order to keep the local temperatures in the windings and magnets within
the material limits, different cooling concepts are investigated. Cooling
water jackets in the stator housing are widely used. However, recently also
oil splash cooling of the end windings and direct oil cooling in the entire
winding area are becoming increasingly popular, especially for electric
motors integrated in the gearbox.
For the thermal calculation, a multi-domain model is created, which includes
the regions of the cooling media as well as the structural components. It
allows the simultaneous calculation of the transient flow of gases and
liquids, the heat transfer between fluids and structural components and the
heat transport in solids. FIRE M supports the fast generation of such a
model with its fully automatic polyhedral mesh generator. The thermal
calculation provides the detailed three-dimensional temperature field of
the model and thus helps to discover weaknesses of the cooling concept.
Since operating temperatures vary in different locations, this can also influence
the electromagnetic behavior of the electric motor. So an exact analysis
requires a tight coupling of electromagnetic and thermal calculations.
An automated interface in the software facilitates this step and saves time
for the calculation engineer.
Due to the typically long simulation times needed for 3D calculations, such
a model is not suitable for a thermal simulation of a complete drive cycle.
Therefore, we have developed a workflow that creates an AVL CRUISE™ M
system simulation model out of the 3D equivalent in just a few steps. The
input parameters are adjusted on the basis of the results of the 3D model.
The model calibrated in this way also allows the temperature of all relevant
electric motor components to be calculated quickly, but still accurately for
the complete range of different operating conditions. Due to its real-time
capability, the system model is not only suitable for the office, but also for
hardware-in-the-loop and testbed use.
The result of our efforts is a fully comprehensive and detailed modelling
solution for the development of electric motors that supports optimum
performance while also promoting component durability at all levels of
operation.