High power UPS system using transistorized inverters

To achieve higher output current in uninterruptible power supplies (UPS), either single transistors or complete inverters must be connected in parallel. The author gives a solution for doing both. An inverter module having 18 transistors (three in parallel for each switch) works together with 1,2,3,4, . . . modules of the same kind. Using a special power-independent control loop, the number of parallel-working inverters is not limited. The B42 UPS makes practical use of this concept forming 330 and 500 kVA units containing two and three of these inverters. Higher-power units, such as 800 kVA with five parallel-working inverters, have been successfully tested in the laboratory