Auszug | eb - Elektrische Bahnen 6 | 2021

245 Vehicle Technology Science 119 (2021) Heft 6 Direct drive for electric traction – a review on advantages and drawbacks Andreas Binder, Björn Deusinger, Darmstadt Permanent magnet synchronous machines are well suited as direct drives, where the gear is omitted. An overall efficiency improvement is possible as well as a noise and a total mass reduction. Some companies prefer as a first stage only to replace the cage induction machine by a permanent magnet machine at high speed, using still the gear. Chance, pros and contras for the direct drive as a possible drive system for future train generations are shortly reviewed in this paper. Direktantriebe für die elektrische Traktion – Ein Überblick über Vor- und Nachteile Permanentmagneterregte Synchronmaschinen eignen sich gut als Direktantriebe, bei denen kein Getriebe benötigt wird. Eine Gesamtwirkungsgradverbesserung ist ebenso möglich wie eine Ge- räusch- und eine Gesamtmassenreduzierung. Einige Unternehmen ziehen es vor, im ersten Schritt nur die Käfigläufer-Asynchronmaschine durch eine Permanentmagnet-Synchronmaschine mit hoher Drehzahl zu ersetzen, wobei weiterhin ein Getriebe verwendet wird. Chancen, Vor- und Nachteile des Direktantriebs als mögliches Antriebssystem für zukünftige Zuggenerationen werden in diesem Beitrag kurz beleuchtet. Commande directe pour la traction électrique – un aperçu des avantages et des inconvénients Les machines synchrones à aimant permanent sont bien adaptées comme commande directe de moteur, pour lesquelles la transmission mécanique n’est plus utile. Une amélioration globale de l’effi- cacité est possible, ainsi que la réduction du bruit émis et de la masse totale. Quelques compagnies préfèrent, en première étape, remplacer uniquement la machine à cage à induction par une machine à aimant permanent à grande vitesse, en continuant d’utiliser le couplage mécanique. Les opportu- nités, les pours, les contres de la transmission directe utilisée comme système de transmission pour les futures générations de trains sont brièvement abordés dans cet article. 1 Introduction With the advent of rare-earth permanent-magnet systems and its broad application in industrial motor drives over 20 years ago there was also a strong movement to apply permanent-magnet synchro- nous motors (PMSMs), fed by IGBT fast-switching inverter drive systems, for electric traction. The dom- inating variable-speed drive system for locomotives, for electric multiple units, and for street cars and commuter trains (metros) is the cage induction mo- tor, operating at elevated speed to reduce motor torque and size. A (often single-stage) gear and a flexible coupling to the wheel-set reduce the speed to the necessary wheel-set rotational speed. This ro- bust and well-suited system for integration in the wheel-set with its limited space was investigated concerning the improvement of efficiency by replac- ing the induction machine with the permanent- magnet synchronous machine (PMSM), and even more, by completely skipping the gear. Thus several companies and research facilities investigated direct drive rotating systems, based on PMSMs of various types in combination with different designs to omit the gear. Different prototypes were built and tested, and some concepts were put into practical operation especially for the smaller sized drive systems in street cars. Now, about 15 years after that hype, a review on the practical experience with direct drives and their impact on the further development of AC trac- tion systems until now may answer the question: Was this hype on direct drives a misleading direction of innovation or has there been technological poten- tial, which so far still waits to be fully utilized? The special section of direct drive systems with linear mo- tors, e.g. for wheeled people movers or magnetically levitated lightweight vehicles, will not be treated here. Focusing on rotating electrical motors in gear- less traction systems, a review on the technical de- velopment and technical experience of the last about 15 years, based on published material shall give an insight on pros and cons of direct drive technology and its impact on nowadays traction drive systems. Authors are aware that there may be additional ma- terial available, so they regard this paper not as a complete survey on direct drive development and solutions, but as a contribution to highlight, why af- ter the direct drive hype 10…15 years ago the more