For a high efficiency grade

The highest prescribed energy efficiency class IE4 for electric motors according to the ecodesign requirement (VO2019/1781) presents manufacturers with challenges in terms of efficiency. Asynchronous machines can only achieve this efficiency class with increased development and cost expenditure. Electric motor specialist BEN Buchele is currently testing the use of synchronous reluctance machines, which have a better efficiency and can therefore be a good alternative when a high efficiency class is required.

Asynchronous machines are reliable all-round motors for many applications and are not considered the workhorse of electric motors for nothing: robust, low-maintenance, durable. Their disadvantage is a lower efficiency compared to other machine topologies, primarily in the partial load range. Synchronous reluctance machines, on the other hand, have a better efficiency because there are very low losses in the rotor.

The mode of operation of the synchronous reluctance machine is based on the reluctance force: the system always strives for the lowest magnetic resistance (reluctance) and thus triggers the rotary movement. While the rotor of the asynchronous machine runs asynchronously to the rotating field of the stator, the rotor of the synchronous reluctance machine rotates synchronously to the stator magnetic field. As a result, there are hardly any magnetization losses, which is very advantageous for achieving IE4.

It should be noted with the synchronous reluctance machine that, unlike the asynchronous machine, it cannot be started up from the mains; this requires converter operation. In comparison to earlier times, when the use of a converter was complex and costly, converter operation is now common practice and investment costs are amortized through the energy costs saved.

Research project on automotive test benches

The fact that the use of a synchronous reluctance machine is very promising for achieving better efficiency is shown by a research project for automotive test benches in which BEN Buchele is currently developing and testing a synchronous reluctance machine. The blow-out speed in a cross-flow airflow blower for airflow simulations was to be increased from 160 km/h to 180 km/h - with the same size of the motor (160) and the design for energy efficiency class IE4.

More power usually requires more installation space, which was limited. An energy-efficient, compact and powerful drive solution was therefore required, for which BEN Buchele brought the synchronous reluctance machine into play. "The initial test results of the prototype are promising," says Bastian Kohlmann, Research & Development at BEN Buchele. "So far, efficiency, design points, torque and speed have been achieved as intended. This makes us confident for further drive projects with synchronous reluctance machines."

Synchronous reluctance machines are suitable wherever high efficiency with a small, compact size is important in S1 operation. Possible applications include pumps, compressors, turbines or fans.