Reliability analysis and calculation for the most common modular UPS system architectures

A modular UPS system is generally presented as having a much higher level of availability than a monolithic, double conversion, on-line UPS system. However, there are different types of modular UPS systems available on the market, with varying degrees of reliability and availability. To represent the strengths and weaknesses of each architecture and accurately compare them to one another, a detailed reliability model must be built. This paper presents a rational methodology to define and analyse each modular UPS system, and to identify its mode of operation and possible failure conditions. This methodology is then applied to the most common modular UPS architectures present on the market, highlighting the advantages and disadvantages of each, and making the differentiation between ordinary, good and excellent modular UPS system designs possible.