Dynamic UPS Drive Model for Low-Power Applications

In this paper, a drive model for a low-power rotary UPS system is described. Traditionally static UPS systems are preferred for low-power applications, although rotary UPS systems offer some interesting advantages. A comparison between both types is made to highlight these advantages. Three drive models are presented, with their advantages and disadvantages and a comparison is made to determine the most interesting model, considering both technical and economical aspects. The drive model based on a doubly-fed induction machine (DFIM) is further investigated by simulation as well as using an experimental setup. A case study investigating the inverter power rating as a function of the DFIM´s stator power is included. The inverter control schemes are described in detail and the operation of the UPS system is illustrated, both in grid-connected mode and in islanding operation