Uninterruptible Power Supply Case Study

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Uninterruptible power supply (UPS) systems give continuous and reliable electrical power to loads in times of unexpected power failure. By connecting the UPS inverters in parallel, its capacity is expandable. Parallel operation of inverters has advantages, it increases system efficiency, provides redundancy and modularity. Parallel operation of inverters is difficulty due to the physical differences between the inverters and the load mismatch, circulation of current among the inverters takes place. Inverters when connected in parallel must satisfy basic requirements they are proper load current sharing between the inverters, doesn’t allow current circulation among the inverters and they are operated independently In this paper it mainly focuses on the control strategy for the parallel operation of the inverters and introduces …show more content…

The model of the inverter, of the input, Vpc, to output, IL, defined as Gi(s), is given by IL(s)/VPC(s)=((s.C+1/R0).n.Kinv)/(s2.L.C+S(L/R0)+1) (7) The closed-loop transfer function of the parallelism loop, ICLTF (s), is shown in Fig. 6 and is considered without simplification in the model of the inverter for the voltage loop. The transfer function defines the relation between the input IL and output V0. V0(s)/IL(s) =Gv(s)=1/(s.C+i/R0) (8) The model of the VSI, of the input, Vvc signal control, to the output, V0 voltage considering the inverter feeding a resistive load. The voltage controller selected was the Cv(s) =Kcv ((s+z1).(s+z2))/((s+p1).s)

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