Definition

A static UPS system is a circuit which ensures a continuous power supply to the load irrespective of outages, spikes, brownouts, or other disturbances from the normal incoming mains supply. It is achieved by using solid-state circuitry which employs a battery or possibly kinetic energy as the alternative energy source.

Background

The development of static UPS clearly was dependent on the availability of solid-state switching devices. The earliest conversion systems available in 1960 for dc to ac were no more than mechanical vibrators with ratings no higher than 500 VA used for radio/communications applications. The advent of power transistors enabled the first true static inverters to be built, applications in the early years being communication and instrumenation. Thyristors then became available and, gradually, ratings of modules increased. It should be remembered in these early days that switching devices suffered from wandering characteristics due to operating temperature and aging. In time these problems were solved. By approximately 1960 computers began to require UPS systems

From inception to todays designs we have seen dramatic improvements, efficiency originally at 80 to 81 percent compares with claimed efficiencies of up to 98 percent for present designs. The size of systems also has reduced considerably, modern designs are now some 60 percent less in proportion. Maintenance costs are much reduced and reliability figures now quoted are some 10 years mean time between failure for a single module. Note this figure does not allow for battery reliability. Figures for a multimodule parallel redundant system...