Yokogawa power analyzers are playing a key part in tests designed to optimize the efficiency of a new generation of motors for electric vehicles being developed by German drives specialist FEAAM.
The new motors are being developed in cooperation with the Institute for Electrical Drives & Actuators of the Universität der Bundeswehr (University of the Federal Armed Forces) in Neubiberg, near Munich.
The developments are part of a research project to examine ways of increasing the efficiency of induction motors with the aim of challenging two perceived limitations that are hampering the market acceptance of electric cars: namely, the short range and the high purchase price.
The research project is looking at the components of the drive train, and is basing its tests on driving cycles: the same concept that is used in efficiency and emissions tests on internal combustion engines. An important element of this approach is that the results do not depend on the efficiency at maximum load conditions, but on the efficiency at partial load operation.
A promising approach for the optimization of the electric motor efficiency is the concept of asynchronous motors with concentrated windings. Unlike a conventional induction motor with distributed winding, where the coils are wound around multiple lamination teeth, the windings use only a single tooth. Although the technique has been known about for some time, it has not previously been practically applied because of the interfering harmonics that can occur.
In the joint research project, FEAAM and the university team analyzed the magnetic fields in the motor precisely by a combination of simulation and practical experiments. As a result, they were able to devise various measures to suppress unwanted harmonics. The closer these harmonics are to the working wave, the more they can interfere with the motor’s operation, causing electrical losses or acoustic noise.
The damping of the harmonics is achieved by a special winding technique in which adjacent tooth coils are wound in opposing directions. With the correct configuration of the number of wires in each coil, the harmonics can be reduced. In the research project, the structure of the coils is first simulated using mathematical models, and the effects are then verified by measurements.
The University’s Institute for Electrical Drives & Actuators has several test facilities for electric motors with an output of up to 220 kW and a peak torque of 2,000 Nm. The test benches are designed for four-quadrant operation, and are equipped with high-precision speed and torque-measuring devices, power analyzers, and oscilloscopes. They are used for student projects as well as research and collaborative work with industry.
The development process took about two years, and has also pursued the aims of simultaneous optimization of ease of manufacturing, low production costs, and achieving a high efficiency at partial load conditions.
The end result is of interest for the automotive industry and other industrial sectors. There are now several patent applications, and the first prototypes have been developed for industrial partners. The prototype of the new induction motor is equivalent to a conventional traction motor for an electric car and has a power of about 50 kW.