The unit is driven by three phases at up to 400 V. Using transducers in each phase, current and voltage are measured. In this way, asymmetry can be identified. In addition to efficiency measurements, a recording of torque/speed characteristics takes place, and this is used for the optimization of the mathematical models. As the rotor resistance, and thus also the losses, increases with increasing temperature, it is held constant using a cooling liquid and is monitored using a thermal imaging camera.
In addition, measurements with different driving cycles are taken. The power and efficiency measurements are performed with the WT1600, WT1800, and WT3000 power analysers from Yokogawa. The measured values, including torque and speed and the resulting efficiency, are automatically transferred into an Excel spreadsheet.
"We have several generations of Yokogawa power meters in use, and we are very satisfied with their operability and the test results," comments Prof. Dr.-Ing. Dieter Gerling from the University. "It is particularly important that we obtain very accurate efficiency in the region, over 97 percent, and we have found that we can rely fully on these instruments."
Because of the easier production and the higher efficiency at partial load conditions, the new induction motor brings advantages both in terms of acquisition costs as well as the driving range of electric vehicles.
The new winding technology also opens up new advantages in production. The stamped sheet metal parts for the stator can be individually wound and then simply plugged together into a motor. This contrasts with the situation in a conventional induction motor, where the plates are assembled first, and then the winding is applied in a much more complicated fashion. Owing to this complicated production process and the associated high costs of this type of motor, the previous approach would not be ideally suited to the production of several million units per year typically found in the automotive industry.
"Previously, electric motors in this power range were produced by medium-sized companies in quantities of a few thousand per year", says Prof. Gerling. "In the automotive industry, we are looking at quite different numbers, which means that costs become much more significant.
"This industry has a lot of experience in cost management. In principle, this, of course, also applies to power electronics and battery technology."
In addition to the electric motor, the FEAAM and University teams have also dealt with the optimization of the power electronics circuitry and the motor control systems. Again, there are already proposals for optimizing the efficiency at partial load operation. In addition, the powered electric wiring systems in vehicles and airplanes are being investigated.
With electric motors, little attention has been paid to efficiency or weight issues, but this situation has changed with the advent of electric mobility. In particular, the high production volumes inherent in the automotive industry should lead to massive cost reductions. The team at the Universitšt der Bundeswehr is convinced that the future belongs to vehicles equipped with electric drive trains.
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This story orginally appeared on EE Times Europe.