High-output-voltage single-phase UPS based on series connection of low-output-voltage modular UPS

Critical loads are usually provided by sources of uninterruptible power supply (UPS). Such devices have output voltages equivalent to levels found in commercial power grids. However, when high output voltages are required there is still no standard solution to achieve the desired level of voltage. This paper presents a proposal for developing a high-output-voltage single-phase UPS. This proposal is based on the series connection of several single-phase modules, which are compact, commercially available and of low cost, making this an attractive solution for use in industry. In this context, this paper introduces some principles regarding the series connection of UPS, which translates into the serial connection of voltage source inverters (VSIs). Furthermore, the study provides the experimental verification of the proposed system through the development of a prototype of 660V and 15kVA, obtained from the connection of three single-phase modules of 220V and 5kVA.