Modeling Voltage Source Converters for Harmonic Power Flow Studies

Voltage source converter (VSC) based devices have become widely accepted by the power industry in recent years as a result of renewable energy initiatives and other developments. Due to their nonlinear v~i characteristics, it is essential to understand and model the harmonic impact of VSC devices in a power system. In response to such a need, this paper proposes a rigorous harmonic model of VSC devices suitable for harmonic power flow studies of large-scale power systems. Through detailed mathematical derivations, this research has shown that the model takes the form of a coupled frequency-dependent impedance matrix. Formulas to compute the impedance elements have been established. The results show that the impedance is independent of the harmonic voltages experienced by the VSC device, and thus it can be easily integrated into existing harmonic power flow tools. The accuracy of the model, as well as its usefulness for harmonic power flow studies, have been verified using EMT simulations.