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The module UPS can flexibly implement expansion of power system capacities. Furthermore, it can be used to build up parallel redundant system in order to improve the reliability of power system operation. To realize the module UPS, load sharing without interconnection among parallel connecting modules, as well as a small scale and lightweight topology is necessary. In this paper the three-arms converter and inverter is compared with the general full-bridge and half-bridge topology from a practical point of view, and chosen as the module UPS topology. The switching control approaches based on a pulse width modulation of the converter and inverter of the system are presented independently. The frequency and voltage droop concept is applied to parallel operation control to achieve load sharing. Two prototype 3 kVA modules are designed and implemented to confirm the effectiveness of the proposed approaches. Experimental results are shown that the three-arms UPS system has high power factor low distortion of output voltage and input current, and good load sharing characteristics.