Fault Tolerant Actuation of a Railway Track Switch: a Simulation Study

Track switches (also known as “point” or “turnout”) are essential to the railway system and provide route flexibility by allowing vehicles to move between tracks on the network. However, the single actuators in the current switch technology mean that a single actuator fault will result in the failure of the switch (and the concomitant delays to trains waiting to pass the switch). This paper focuses on providing redundant actuation through an approach known as High Redundancy Actuation (HRA), which might allow track switches to remain operational after failure in actuator elements. The paper also proposes the use of closed-loop control (track switches are usually operated open-loop). In the paper, we introduce a model of a C-type switch and validate it against results from a previous paper. This model is then used combined with an HRA of nine elements (3x3). Two closed-loop controllers are then proposed for each of the single actuator and the HRA actuator system. The findings indicate that closed-loop control on its own has some benefits. However, when combined with HRA, the resulting system is able to tolerate a number of faults in the actuator subsystems, creating an effective graceful degradation rather than the sudden failure with a traditional single actuator.