Harmonic Analysis of Grid-Connected PV Systems by Applying Discrete-Time Companion-Circuits

This article describes the application of a time-domain (TD) procedure based on companion-circuits analysis (CCA) combined with a Newton method of extrapolation to the Limit Cycle (based on a Numerical Differentiation (ND) process). The particular application is aimed at the dynamic and periodic steady state solution of single-phase distributed generation systems with PV units under harmonic distortion conditions. Fundamentally, the applied methodology is based on the representation of linear elements, using Norton equivalents and non-linear elements as discrete variable resistance. The application determines a set of discrete differential equations obtained by nodal analysis. The associated case study is related to the evaluation of harmonic distortion, in terms of individual and total harmonic distortion (THD) at the point of common coupling (PCC) between the PV system and the electrical system. The results obtained have been validated against the PSCAD/EMTDC® simulator.