Novel approaches to ensure redundant rectifier system's reliability performance

Reliability performance of a DC UPS system having redundant (n+1) rectifiers and battery back-up of several hours can be theoretically very high. Emergence of digitalized implementation of supervisory and control functions can significantly reduce or even totally destroy the naturally high reliability performance. It has turned out in many field occasions that the reliability performance of a system is especially in danger when the vital system parameters such as overvoltage shut down limit and boost or equalizing charge voltages are reconfigured or when manual repair or replacement work is carried out. This paper describes the methodology to analyze the availability and reliability performance based on Markov chains. Methods and ways are introduced and discussed by which the digitalized implementation of supervisory and control functions can be made more reliable by utilizing fuzzy logic based linguistic variables.