Three of a kind [UPS topologies, IEC standard]

With uninterruptible power supplies now used in critical applications across every industrial sector, a standard terminology to describe types and performance measures has become essential. The author outlines how the international standards community has responded to this need by introducing IEC 62040-3 which distinguishes three types of UPS topology: passive standby, line interactive, and double conversion. These three topologies are described. For low power ratings (less than 2 kVA) all three topologies, as defined by the standards, are used. For medium to high power ratings, the case for the passive standby and the line interactive is, at best, marginal, in spite of their significantly lower cost. The vast majority of sales to medium to high-power rating applications are represented by double conversion UPSs (95% from a few kVA upwards; 98% above 10 kVA). The dominance of the double-conversion topology is attributable to its almost total lack of weaknesses, combined with the capacity to meet the needs of sensitive loads at these power ratings-a consequence of UPS being connected in series with the utility power sources.