Reduced parts single-phase series-parallel UPS systems with active filter capabilities

Three different topologies of single-phase series-parallel uninterruptible power supplies (UPS) are discussed in this paper. The first topology is a conventional four-leg system. The two other topologies consist of two or three legs instead of four legs. All three systems have the effective capability of line current conditioning as well as load voltage regulation. Control methods and analysis of all three systems for different functions and operating modes are discussed. Simulation and experimental results are also presented to verify the theoretical analysis.