Abstract This paper presents the grid connected mode of a 3 kVA single-phase uniterruptible power supply (UPS), with features of low frequency operation, high efficiency and unit power factor of the input. The input stage of the proposed UPS is composed by a power factor correction rectifier based on classical boost converter, which is used to supply the dc bus. The output stage is composed by a multilevel inverter, which is based on a low frequency full-bridge converter associate to a multiple winding transformer with one primary coil and several secondary coils. Each secondary coil is used to produces the partial alternating voltage and the series combination of the output coils are used to generating the complete output voltage. The theoretical analysis, design example, as well as experimental results of the proposed UPS system are presented in this paper.
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