The doctoral thesis is dedicated to the elaboration of modular uninterruptible power supply system that utilizes versatile power module (VPM). The novelty of the work and difference from many existent modules of UPS is in multifunction of the VPM. Existent UPS modules allow only to increase power or to add module for system redundancy for higher reliability. The VPMs allows connection of alternative energy sources and storages like supercapacitor, flywheels, fuel-cells, photovoltaic panel, wind-turbines and etc. At the given moment on the market there are many different types of UPS systems. Some of them are not expandable at all. Some of them can be parallel for higher power and reliability increase. Some of them utilize alternative storage like supercapacitors and flywheels. Most advanced UPS system even switches between operation modes (“online” mode or ”line-interactive” mode) for higher efficiency or higher protection. The modular UPS system that is researched in the thesis combines most features of the UPS systems mentioned above. It allows: - To build stand alone converters like invertors, active rectifiers, DC/DC converters; - To build different UPS topologies like “standby UPS”, “on-line UPS”, “DC-UPS”; - To utilize different energy storages like supercapacitor, flywheels; - To utilize different energy sources like photovoltaic panels, wind-turbines, fuel-cells; - To build UPS systems for remote places with alternative primary energy source where does not available power grid; - Power converters that are built with VPM can be easily rebuild to any another system. The first chapter describes grid problems. There are given short UPS topologies description. Energy sources and storages which can be utilized in UPS systems are described as well. At the end of the first chapter there are given the reasons of modular system utilization. In the second chapter VPM development stages are given. In the third chapter development of Matlab-simulink model of VPM and its control algorithms are described. The forth chapter considers the proof of possibility of usage of VPM for UPS systems assembly by means of simulations and experiments. In the last chapter price of VPM and UPS system that are built with VPM are calculated. The thesis, written in English, contains: 190 pages, introduction, 5 chapters, conclusions, 190 figures, 72 formulas, 29 tables, 68 references and 4 appendixes.