Predicting the net harmonic currents produced by large numbers of distributed single-phase computer loads

Abstract

In this paper we use the results of simulations to predict the net harmonic currents produced by large numbers of single-phase desktop computers in a facility, such as a commercial office building. We take into account attenuation due to system impedance and voltage distortion, as well as diversity in harmonic current phase angles due to variations in power and circuit parameters. Using experimental and published data we establish ranges of circuit parameters for an equivalent 120 V, 100 W base computer unit and branch circuit, update our computer modeling code (described in previous papers) to iteratively handle the interaction between current and voltage harmonics, and use the code to predict the net harmonic injection currents at the point of common coupling (PCC) represented by a shared transformer connected to a stiff power system. The key contributions of this paper are: providing estimates of the net harmonic current injection due to distributed single-phase computer loads in Amps/kW, as well as in percent of fundamental current, for a wide range of system loading and voltage distortion conditions; and illustrating that the reduction in harmonic currents due to phase angle diversity (expressed in Amps/kW) is relatively independent of system loading, whereas the reduction due to attenuation increases significantly with system loading. >