UPS systems below 1000 VA are available in two basic designs: line-interactive or double-conversion on-line. This paper describes the advantages and disadvantages of each topology and addresses some common misconceptions about real-world application requirements. Most of the factors that go into deciding which UPS to purchase are visible and easily understood: battery back-up time, cost, size, manufacturer, number of outlets, manageability, etc. But there are also less visible factors that are not so easy to understand. One of the least understood, yet most discussed, is topology. The topology (internal design) of a UPS affects how it will operate in various environments.
