Railcab (Neue Bahntechnik Paderborn)

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The RailCab system is a novel transportation system that allows comfortable journeys on rails while at the same time satisfying the desire for individual mobility, with no distinction being made between local and long-distance  traffic. The RailCabs can transport passengers or goods directly to their destination without the need for reloading or changing trains. The  vehicles run on demand, not according to schedule. They can be ordered and configured via telecommunication services.

Linear drives enable a direct transformation of electric energy into a linear mechanical motion. Furthermore, mechanical losses can be reduced by elimination of gear or bearing. Linear direct drives are used in precise and minimal friction transportation of material and passengers and are also applied in materials handling as well as in installation engineering and machine tool building.The department investigates different types of linear drives, especially for the use as traction drives within the scope of the research project "Neue Bahntechnik Paderborn" (NBP) [1]. The central point is the linear doubly-fed asynchronous motor. Both the primary part and the  secondary part of  this motor contain three-phase windings.

Fig. 1: Passenger and freight RailCabs in a convoy                                           Fig. 2: Linear doubly-fed asynchronous motor

The doubly-fed motor enables contactless energy transfer to the on-board power supply system at asynchronous mode according to the transformative principle, thus the vehicle does not need to be supplied with power by conductor rails or catenaries. However, motor control is more difficult.
The losses can be minimized by adjusting a phase displacement of 90° between secondary and primary currents. Since secondary and primary current controllers are locally distributed and the phase of the other motor component cannot be measured by usual position measurement devices, special synchronization strategies are required. Thus, besides encoderless processes, also magnetic field measurements are studied [2], [3].
As a further motor topology, a linear induction motor is studied, which features a passive reaction plate consisting of a conducting material (copper, aluminium) as well as ferromagnetic material for magnetic couplings, instead of an active stator.

                                       Fig. 3: Linear induction Motor

As usual for an induction motor, due to relative velocity of the exciting magnetic field, eddy currents occur in the reaction plate, which are used for force generation. Hence only the vehicle is equipped with three-phase windings; thus a contactless transfer of energy is not possible. However, the motor's advantages are the costs and the simple control strategy.

Further research works focus on linear switched reluctance motors (LSRM), which are mentioned in another research topic.

In 2003 a test track was constructed on a scale of 1:2.5 (see Fig. 4) within the scope of the research project "Neue Bahntechnik Paderborn" (NBP). This test track is equipped with the linear doubly-fed asynchronous motor, which was described before. Additionally, the test facility features sections which are equipped with a passive reaction plate (induction motor).

                                          Fig. 4: NBP test track in scale 1:2.5

In the department we also study the control of longitudinal dynamics for railway vehicles, in addition to motor control. Linear motors make it possible to control vehicles accurately according to the intended operational profile, because the vehicles can be accelerated and decelerated independently of the wheel-rail contact and thus of weather conditions and material properties. This provides the basis for convoy operation, which enables a reduction of energy demand and increases the track capacity. The RailCabs can form convoys without mechanical coupling, preferably during drive operation, with a small separation distance [4]. Apart from distance control, this also requires strategies for bringing together and separating convoys safely [5], [6].

Additional central topics in this field are the control and communication system and the safety technology for the test plant [7]. In addition to the coordination of every single vehicle, which is necessary for controlling the longitudinal dynamics, a communication connection is needed for the linear doubly-fed motor in order to exchange reference values between the vehicles and the track-sided information processing. Furthermore, a synchronization of the rectifiers, which are distributed along the track, is necessary. The data exchange between vehicle and track takes place via a wireless network which is integrated in the control structure of the linear motor. A bus system is used for track communication to guarantee continuous switching of the rectifiers under real-time conditions [8]. The structure of the control and communication system is shown in Fig. 5.

                          Fig. 5: Structure of control and communication system

A further part of research at the test plant is the operating point control of the linear motor. The adjustment of power flows is accomplished via motor current control of the secondary and primary of the linear doubly-fed motor. Additionally to the major adjustment of the thrust, the degrees of freedom for transfer of energy have to be taken into account. If several vehicles are operated on a common section of the primary, a collective operating point has to be found for the track-sided motor part via the inter-vehicular communication. The operating point assignment inside the convoy happens in direct connection to the vehicles' energy management.      



C. Henke, C. Rustemeier, T. Schneider, J. Böcker, A. Trächtler
RailCab – Ein Schienenverkehrssystem mit autonomen, Linearmotor getriebenen Einzelfahrzeugen
Internationaler ETG-Kongress 2007 – Kundennutzen durch neue Technologien in der Bahntechnik, Karlsruhe, Deutschland, 2007
T. Schneider, B. Schulz, C. Henke, J. Böcker
Redundante Positionserfassung für ein spurgeführtes linearmotorgetriebenes Bahnfahrzeug
Workshop Entwurf mechatronischer Systeme (EMS), Heinz-Nixdorf-Institut, Universität Paderborn, Deutschland, 2006
A. Pottharst, C. Henke, T. Schneider, J. Böcker, H. Grotstollen
Drive Control and Position Measurement of RailCab Vehicles Driven by Linear Motors
Int. Symposium on Instrumentation and Control Technology (ISICT), Beijing, China, 2006
C. Henke, H. Vöcking, J. Böcker, N. Fröhleke, A. Trächtler
Convoy Operation of Linear Motor Driven Railway Vehicles
The Fifth International, Symposium on Linear Drives for Industry Applications (LDIA), Kobe-Awaji, Japan, 2005

C. Henke, M. Tichy, T. Schneider, J. Böcker, W. Schäfer
Organization and Control of Autonomous Railway Convoys
9th International Symposium on Advanced Vehicle Control, Kobe, Japan, 2008

C. Henke, N. Fröhleke, J. Böcker
Advanced Convoy Control Strategy for Autonomously Driven Railway Vehicles
IEEE Conf. on Intelligent Transportation Systems, Toronto, Canada, 2006

C. Henke, M. Tichy, T. Schneider, J. Böcker, W. Schäfer
System Architecture and Risk Management for Autonomous Railway Convoys
2nd Annual IEEE International Systems Conference, Montreal, Canada, 2008

A. Pottharst, H. Grotstollen
Radio Based Control of a Linear Motor for the NBP Railway System
ISICT 2003, 5th International Symposium on Instrumentation and Control Technology, Beijing, China, 2003

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