Reliability modelling of uninterruptible power supply systems using reliability block diagram method

M.K. Rahmat, S. Jovanovic

Research output: Contribution to journalArticle


The aim of this paper is to investigate the reliability parameters prediction method for the Uninterruptible Power Supply (UPS) systems using the Reliability Block Diagram (RBD) technique. In contrast with the existing UPS reliability prediction methods that requires more input data and computationally tedious, the new approach provides a useful and fast method to evaluate the system’s Failure rates (), Mean Time Between Failures (MTBF), Availability and Unavailability of the UPS systems. In this paper, reliability parameters obtained from five major AC UPS configurations (online with and without bypass, offline, line-interactive with buck/boost transformer and line-interactive with ferroresonant transformer) were compared and discussed in detail. Equations for calculating the MTBF and Unavailability are presented along with component reliability estimates. Sensitivity analysis on UPS components was performed to investigate the effect on the overall system reliability. Finally, to validate the results obtained from this RBD method, comparisons were made to the results from other reliability estimation method such as the Boolean Truth Table, Probability Tree, Fault Tree Analysis, Monte-Carlo Simulation method and Field Data estimation method.
Original languageEnglish
Pages (from-to)543-551
Number of pages9
JournalInternational Review of Electrical Engineering
Issue number4
Publication statusPublished - 2006


  • reliability modelling
  • uninterruptible power supply
  • reliability block diagram

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