A New VSC-HVDC Model for Power Flows Using the Newton-Raphson Method

The paper presents a new model of the VSC-HVDC aimed at power flow solutions using the Newton-Raphson method. Each converter station is made up of the series connection of a voltage source converter (VSC) and its connecting transformer which is assumed to be a tap-changing (LTC) transformer. The new model represents a paradigm shift in the way the fundamental frequency, positive sequence modeling of VSC-HVDC links are represented, where the VSCs are not treated as idealized, controllable voltage sources but rather as compound transformer devices to which certain control properties of PWM-based inverters may be linked—just as DC-to-DC converters have been linked, conceptually speaking, to step-up and step-down transformers. The VSC model, and by extension that of the VSC-HVDC, takes into account, in aggregated form, the phase-shifting and scaling nature of the PWM control. It also takes into account the VSC inductive and capacitive reactive power design limits, switching losses and ohmic losses.