Influence of Induction Motor-Equivalent-Circuit Selection on Harmonic Power Quality Assessment in Industrial Power Supply System
Abstract
As the share of nonlinear loads in the power supply systems of industrial enterprises increases, the importance of accurately estimating higher harmonics through modeling grows both in operation and in design. In this case, all network elements and loads are represented by their corresponding models or equivalent circuits (ECs), and the simulation results depend on the modeling assumptions adopted for these circuits. This paper investigates equivalent circuits of an induction motor under higher-harmonic conditions. Laboratory tests were carried out for 1.5 and 5.5 kW squirrel-cage induction motors operating under distorted supply voltage and at different shaft loads. The experimentally obtained impedance characteristics were compared with those calculated using the T-type and parallel resistive–inductive equivalent circuits. The selected induction motor models were then used in a comprehensive simulation of a typical industrial enterprise power supply system, and power quality indices were evaluated for different total motor capacities. The experimental results obtained for the 1.5 and 5.5 kW motors up to the 19th harmonic were extrapolated, as an engineering assumption, to the 160 kW motor and to the harmonic range up to the 49th order. The obtained results demonstrate significant qualitative and quantitative differences, indicating that the choice of the induction motor-equivalent circuit can substantially influence harmonic power quality assessment.