Two-port network equivalent of VSC-HVDC for power flow studies

Abstract

This paper presents a novel harmonic domain (HD) approach that computes a two-port network equivalent of a switching converter for power flow studies. The equivalent stems from the harmonic domain admittance matrix (HDAM) of a switching converter which accounts for harmonics interaction. Power flow studies, involving switching converters, require modifying the Jacobian matrix via calculation and incorporation of the partial derivative terms corresponding to the switched part within the iterative solution process. The proposed approach is readily applicable to modern power systems involving electronic converters. Also, it avoids calculating partial derivative terms of the switching converter by including it as a simple, yet an effective, equivalent two-port network, i.e., by just modifying the admittance matrix within the iterative power-flow solution process. This paper demonstrates that the procedure to obtain the PI equivalent is general for any linear time-periodic system and does not rely on library components when embedded into a commercial software tool.The proposed approach is validated by two test networks which involve High-Voltage Direct Current (HVDC) systems. The obtained results are compared, in terms of accuracy, with those given by the Power System Computer-Aided Design/Electromagnetic Transients including Direct Current (PSCAD/EMTDC) software tool, which involves the detailed system model, once steady-state is reached. Also, the results of the proposed approach are verified against those obtained from a dedicated power flow software tool, i.e., Power System Simulator for Engineering (PSS/E).