An assisted speed-sensorless control of induction motor drives for railways applications

The paper deals with controlled induction motor for traction units of railways vehicles. Based on a conventional speed-sensorless vector-control of induction motor drives, some numerical investigations are carried out in order to verify the suitability of an open-loop observer in the context of railway traction applications with their specific requirements. In particular, the attention is focused on the control in the re-powering phase (e.g. after a coasting operation) and during an uphill start of the train with a steep slope; both of them usually are critical situations. Among the large amount of data available on-board of a modern railway vehicle, the propulsion control can use the speed signal usually delivered on the Ethernet bus in order to facilitate the re-synchronization of the inverter commands. Also the possible use of a low-accuracy speed detection is considered in order to improve the drive performance specifically in these operating conditions, where sensorless speed-identification is definitely incorrect. These speed estimations allow to improve the drive dynamic performance, avoiding at the same time the activation of protections against over-currents or over-voltages.