This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY 1 Modeling and Control of a Full-Scale Roller-Rig for the Analysis of Railway Braking Under Degraded Adhesion Conditions Benedetto Allotta, Member, IEEE, Roberto Conti, Enrico Meli, and Alessandro Ridolfi Abstract—Currently, braking on board subsystems such as wheel slide protection (WSP) devices almost totally control the longitudinal train dynamics. In particular, the vehicle safety highly depends on the study and the development of these systems, especially at high speeds and under degraded adhesion conditions. Usually, to save time and to avoid expensive on-track tests, the performances of braking subsystems are tested on full-scale roller-rigs. Nevertheless, the analysis of the subsystem behavior under degraded adhesion conditions is still limited to a few applications on roller-rigs because large slidings among the rollers and wheelsets produce severe wear of the rolling surfaces. This circumstance is not acceptable due to the effects on the maintenance costs (the rollers have to be turned or substituted), on the system dynamical stability and on the safety. In this paper, the modeling and control of an innovative hardware in the loop (HIL) architecture to test braking on board subsystems on full-scale roller-rigs is described. The new approach permits to reproduce on the roller-rig a generic wheel-rail adhesion pattern and, in particular, degraded adhesion conditions. The presented strategy is also followed by the innovative full-scale roller-rig of the Railway Research and Approval Center of Firenze-Osmannoro (Italy); the new roller- rig has been built by Trenitalia and is owned by SIMPRO. At this initial phase of the research activity, to effectively validate the proposed approach, a complete model of the HIL system has been developed. The complete numerical model is based on the real characteristics of the components provided by Trenitalia. The results coming from the simulation model have been compared with the experimental data provided by Trenitalia and relative to on-track tests performed in Velim, Czech Republic, with a UIC-Z1 coach equipped with a fully working WSP system. The preliminary validation performed with the HIL model highlights the good performance of the HIL strategy in reproducing on the roller-rig, the complex interaction between the degraded adhesion conditions and railway vehicle dynamics during the braking maneuver. Index Terms— Degraded adhesion conditions, hardware in the loop (HIL), railway braking, roller-rigs. I. I NTRODUCTION N OWADAYS, the longitudinal train dynamics is almost totally controlled by on board subsystems, such as wheel slide protection (WSP) braking devices. The study and the Manuscript received January 4, 2014; accepted April 13, 2014. Manuscript received in final form April 22, 2014. Recommended by Associate Editor F. Caccavale. The authors are with the Industrial Engineering Department, Florence University, Florence 50139, Italy (e-mail: benedetto.allotta@unifi.it; roberto.conti@unifi.it; enrico.meli@unifi.it; a.ridolfi@unifi.it). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TCST.2014.2320672 development of these systems are fundamental for the vehicle safety, especially at high speeds and under degraded adhesion conditions. On-track tests are currently quite expensive in terms of infrastructure and vehicle management. Therefore, to reduce these costs, full-scale roller-rigs are traditionally employed to investigate the performances of braking subsys- tems [1]–[4]. However, in the presence of degraded adhesion, the use of roller-rigs is still limited to few applications (see, for example, full-scale roller-rigs for the study of the wear [5], hardware in the loop (HIL) systems for WSP tests [8] and full-scale roller-rigs for locomotive tests [8]) because the high slidings between the rollers and wheelsets produce wear of the rolling surfaces. This circumstance is very dangerous and not acceptable: the flange wear can lead to the vehicle derailment while the tread wear can produce hunting instability of the vehicle [27]. Furthermore, the wheel flats may generate unsafe vibrations of the vehicle on the roller-rig. Finally, the wear of the rolling surfaces deeply affects the maintenance costs: the rollers have to be frequently turned or substituted. In this paper, the modeling and control of an innovative HIL architecture to test braking on board subsystems on full-scale roller-rigs is presented by the authors. The new strategy permits to reproduce on the roller-rig a generic wheel- rail adhesion pattern and, in particular, degraded adhesion conditions (characterized by adhesion coefficient values equal or less than 0.10 [31]). The control architecture, based on a robust sliding mode approach, performs a simulation of mechanical impedance by properly controlling the roller-rig motors (all the motors are independently controlled). More particularly, the roller motors are controlled to recreate, on the wheelsets, the same angular velocities, applied torques, and tangential efforts exchanged between the wheelsets and rails in the reality and calculated by a reference virtual railway vehicle model. The new control architecture allows the achievement of this goal by only controlling the roller motors and without having sliding (and consequently wear) between the wheelsets and rollers. In fact, since the real adhesion coefficient between the rollers and wheelsets surfaces is far higher than the simulated one (greater than 0.40), negligible sliding occurs and almost pure rolling conditions are always present between them. Some initial and partial results have been obtained in [9]. The major novelties of the presented work mainly concern the two following aspects. 1) The Motor Controllers (Able to Reproduce on the Roller- Rig the Same Dynamical Behavior of the Virtual Train 1063-6536 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.