SAFETY ASSESSMENT OF DOUBLE TWO-OUT-OF-TWO REDUNDANT LCU SYSTEM
Author(s):
Yanbiao Yang, Yanwen Zhan
This is an open access article distributed under the Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
Abstract
In addressing the issues of multiple common-cause failures and data uncertainty in safety assessments of subway Logic Control Units (LCU), this study investigates the redundancy structure and safety assessment methods of LCU. The double two-out-of-two redundancy structure is implemented for the hardware redundancy design of the LCU, and the Markov method is applied for its safety evaluation. System states within the Markov model are defined based on the hardware structure and redundancy strategy. To address the deficiency of the β factor model in common-cause failures, which does not account for multiple commoncause failures, structural factors are introduced for optimization. Separate Markov models for independent and common-cause failures are developed. To address parameter uncertainty within the Markov model, the Monte Carlo method is utilized for sampling these uncertain parameters, subsequently establishing LCU safety assessment model that accounts for common-cause failures under parameter uncertainty. Simulation results show that considering multiple common-cause failures results in a more conservative safety assessment for the LCU; both the fault coverage rate and the common-cause failure of undetectable faults significantly influence the LCU’s safety; the safety assessment results of the LCU under parameter uncertainty, considering common-cause failures, is rated at SIL3. The findings of this research provide a theoretical basis for the development and safety assessment of high-performance LCU.
KEYWORDS:
Logic control unit, double 2-out-of-2 redundant, safety, common cause failures，data uncertainty