Impedance in voltage-current relations description of the power system PCC - experimental investigations of the accuracy of the LTI system model

The paper presents experimental verification of the quality of LTI power grid model valid for the frequency range of 8 kHz. The single PCC was investigated so the paper is the local, university grid investigations oriented, however concerns two general important problems: one is the absolute accuracy of real grid impedance measurements to which no direct reference data are accessible, the second is the validity of the LTI model, which is used for description of the complex structure composed of nonlinear and switched power installations. The LTI models form very interesting and useful approximation of the complex reality and have meaningful time and frequency domain interpretation. When used for power grids they deal with their Norton/Thevenin equivalent models. Two components of such a model: impedance and system side sources describe the grid and are discussed in the paper. Rich experimental data were referenced to the structural model of the grid so the paper gives evaluative information on the quality of ad-choc grid modeling. Interesting, incremental method for the estimation of absolute impedance errors was proposed and used for improvement of the implemented DSP. Time varying nature of the investigated grid impedance was presented, and system errors with implementation of LTI model to such a time-varying PCC description are discussed.