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09-02-2018 | Electric Vehicles | News | Article

Project Researches the Operation of Externally Excited Synchronous Motor

Author:
Patrick Schäfer

Will the current-excited synchronous motor become an alternative for the powertrain of electric vehicles? One project of Technische Hochschule Nürnberg is researching the safe operation of the electric motor. 

Permanent excitation synchronous motors or asynchronous motors are mainly used in electric mobility at present. While the former require complex electronics and rare-earth magnets, asynchronous motors have poorer efficiency and a lower power density.  

The as-yet rarely used externally excited synchronous motor type does not require rare-earth magnets, and has a high degree of efficiency. In this case, the disadvantage lies in the form of energy transferred via a slip ring system, where mechanical wear can occur and the resulting abrasion in the air gap can lead to high-voltage insulation problems. 

Contactless energy transfer solves a problem

Professor Dr.-Ing. Bernhard Wagner from the Faculty of Electrical Engineering, Precision Engineering, Information Technology at Technische Hochschule Nürnberg and his team are researching the optimisation of estimation methods for the state of the rotor. In a project completed in 2016, researchers developed a contactless energy transfer system that successfully eliminates the disadvantage of externally excited synchronous motors. 

However, the motor current can now no longer be measured directly. “We use mathematical models and calculation methods to estimate the rotor current and rotor resistance from other measured variables,” says Professor Bernhard Wagner, summarising the new technological approach. The rotor resistance shows the generation of heat in the rotor and should therefore act as a parameter for overheating protection. “The improvements in the estimation method are a further step forward that will increase the attractiveness of externally excited synchronous motors for the automotive industry. This can help to increase the competitiveness of the German automotive industry,” Wagner says.

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