Direct control strategy for PMSMs in railway traction applications
DIRECTORS: Javi Poza, Amaia López de Heredia UNIVERSITY: Mondragon Unibertsitatea
The application of electrical motors in railway traction systems has evolved significantly in the last decades. The first employed traction machines were direct current motors (dc motor), which were finally replaced in the early 70’s by alternating current (ac) asynchronous motors due to the improvements in power electronic converters. The asynchronous motors allow an easy implementation because they do not present the maintenance problems of dc machines (as they do not have brushes).
Neverthelles, currently Permanent Magnet Synchronous Machines (PMSMs) are being presented as the new industrial trend for this type of application due to their god performance characteristics: high power to weight ratio, high torque at low sped, direct-drive capacity, higher efficiency, etc. Following the innovative trend of leading industrial companies (Alstom, Skoda Electric, Melco, Mitsubishi, etc.) that already use PMSM motors for railway rolling stock and motivated by the need of more technological knowledge about the control of this type of machines, this thesis studies and analyses different advanced control strategies employed in PMSMs.
Being the main objective of this thesis the final proposal of an efficient and reliable control strategy that can fulfill the application requirements. In this thesis the direct control strategy (DSC) is presented as a suitable new approach for the control of PMSM based railway traction applications. Based on an already implemented robust induction machine direct torque controller, firstly the required modifications for a PMSM have been defined and implemented in order to correctly adapt the controller to the peculiarities of PMSMs, for example, its own permanent flux.
The developed DSC control strategy has been thoroughly analysed and finally validated during this thesis, not only by numerical simulations but also with experimental tests in a 10 kW laboratory test-bench with a full scale PMSM traction prototype. In addition, a deep comparison study has also been realised with a traditional vector control strategy used in this type of application. Several improvements have also been analysed in order to enhance the proposed control strategy. For example, the variation of machine internal parameters, such as stator resistance, stator inductances or permanent magnet flux due to external parameters variations as temperature or stator current have demonstrated that a correct parameterization is essential in order to achieve a robust control. Therefore, two permanent magnet flux online estimation algorithms, a reduced order Extended Kalman Filter (EKF) and a Q-feedback based estimation method, have been developed, studied and compared both in simulation and experimentally.
As a summary, this thesis has experimentally validated the proposal of an enhanced, fast and robust direct torque and flux control strategy with excellent performance characteristics for PMSMs in railway traction applications.