FREQUENCY AND VOLTAGE RESPONSES OF GAS-FIRED DISTRIBUTED GENERATION SYSTEM TO LOAD

Abstract

Research has shown that addition of loads to a distributed generation (DG) system operating either in stand-alone mode (SAM) or grid-connected mode (GCM) has impacts on its operations. This paper analyzed the voltage and frequency responses of the DG when operated in stand-alone and grid-connected modes under load variations. Mathematical equations showing the characteristics of the DG under varying loads with the two modes were developed. The equations were modeled using MATLAB in Simulink environment. By applying gradual and sudden loads using 2MW DG and an 11kV distribution grid network, the frequency and voltage responses under the two modes were calculated. The results showed that with gradual load addition from 10 to 100 % loading, the output frequency varied from 49.72 to 49.27 Hz (-0.56 to -1.46 %) for SAM while it varied for GCM from 49.90 to 49.44 Hz (-0.20 to -1.12 %). Output voltage varied from 376 to 232.9 V (-6.0 to -41.78 %) for 10 to 100 % load respectively for SAM while it varied from 387.7 to 268.3 V (-3.08 to -32.93 %) for GCM. For sudden load additions, the output frequency variation was between 49.39 to 49.25 Hz (-1.22 to -1.5 %) for 25 to 100 % load for SAM while that of GCM was between 49.51 to 49.43 Hz (-0.98 to -1.14 %); voltage variation was 271.7 to 190 V (-32.08 to -52.5 %) for 25 to 100 % load respectively for SAM while that of GCM was 294.2 to 219.9V(-26.45% to -45.03%). The results revealed that the frequency with gradual and sudden load additions for SAM and GCM varied outside the operational limit of 49.75-50.25 Hz () except in the case of 10 % load under gradual load addition in GCM. However, the frequency and voltage variation are less in GCM than SAM with gradual and sudden load additions