Multi-parameter mathematical model for determination of PC cluster total harmonic distortion of input current

Abstract

Purpose – Low power devices with switched-mode power supply represent harmonic generating apparatus in widespread use nowadays. The influence of personal computers (PCs), which affect the supply voltage, is considered. Harmonic level due to simultaneous PC operation is quantified by the total harmonic distortion of input current (THD I ). The purpose of this paper is to propose a multi-parameter mathematical model for the THD I calculation. The model is convenient for practical engineering application. Design/methodology/approach – The model is derived using the measured and simulated data. The model coefficients are obtained in the least squares sense. Findings – Mathematical modeling of THD I is the least expensive and the most convenient solution for engineering application. The models proposed in the literature have many drawbacks, which motivated the authors to develop a more comprehensive solution. Grid stiffness, capacitance of PC power supply unit and PC cluster size represent the major parameters that affect THD I , and as such they are taken into account in the proposed model. The influence of other existing parameters from both line and load side is also discussed and the reasons for their omitting from the model are explained. The model considers various PC configurations within the cluster and it enables the THD I calculation for an arbitrary PC cluster size. Practical implications – Due to its comprehensiveness and mathematical simplicity, the model is suitable for practical use, and its accuracy is verified through conducted measurements presented in the paper. Originality/value – The proposed model is more comprehensive than the existing ones, and it overcomes their shortcomings. The THD I calculation is simplified to the level of applying basic arithmetic operations only, without jeopardizing the accuracy. The validity of the model is supported by additional measurements carried out in sites characterized by grid conditions quite different from that used for model developing.