The Impact of the Load Side Parameters on PC Cluster's Harmonics Emission

Harmonics current emission from personal computers (PCs) is of special interest to power quality researchers, due to their wide spread application and the fact that they are usually concentrated in large groups (clusters). The input current total harmonic distortion (THDI) dependence on number of connected PCs in a cluster (NPC) is affected by network parameters and load side parameters of each cluster's PC simultaneously. As the impact of grid parameters on the THDI=f(NPC) dependence is analyzed in the author's previous papers, special emphasis is given on the impact of the DC side smoothing capacitor (C) in PCs power supply unit. For engineering application it is convenient to present the THDI=f(NPC) function with simple mathematical expressions which include these effects. In the paper authors are proposing an improved mathematical expression to presents impact of load side (DC capacitance) parameters. To achieve this goal, results of the measurements of harmonic emission from a large computer center with 167 clustered PCs and the computer simulation for even larger number of PCs are used.