Dependability analysis of UPS architectures for the Italian railway signaling system

Continuous power supply in railway systems is vital to guar- antee dependable accomplishment of energy-supported critical opera- tions. With reference to the Italian railway infrastructure, this paper focuses on the railroad signaling system, used to control the movement of railway traffic, where Uninterruptable Power Supply systems (UPS) for Safety and Signalling are employed. Fault tolerant UPS architectures are adopted to cope with unpredictable fault events occurring at UPS level, potentially resulting in safety/availability violations. This paper proposes a stochastic model-based analysis to support the comparison between different UPS redundant architectures in terms of dependability attributes, primarily reliability and availability indicators. The analysis results can be fruitfully exploited by a designer to set up the most effec- tive UPS configuration, able to satisfy dependability requirements, while also accounting for possible saving in energy consumption.