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

Abstract

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.

A novel VSC-HVDC link model for dynamic power system simulations

“…2 depicts the equivalent circuit of the VSC corresponding to the inverter station; a similar topology can be formulated for the rectifier station. Its steady-state representation relies on an ideal phase-shifting transformer with complex taps, a series impedance on its AC side as well as an equivalent variable shunt susceptance B eqI , and a shunt resistor on its DC side [15].…”

“…Since the objective is to regulate the voltage magnitude at both AC sides of the VSC-HVDC while keeping the DC voltage fixed, V vI , V vR and E DCI are not part of the set of state variables that need to be computed. Thus, Â vR , m aR , Â vI , m aI , E DCR , R , I , B eqR and B eqI , constitute the set of state variables that must be calculated by solving (7)- (15) with the rest of the equations arising from the network. To guarantee that each VSC operates within feasible operating limits, a limit checking of the modulation ratio and terminal current must take place, that is, m a ≤ 1 and I ≤ I nom .…”

A simplified algorithm to solve optimal power flows in hybrid VSC-based AC/DC systems

“…Regarding the modelling approach used, OPF algorithms for hybrid AC/DC systems published so far can be classified into two types, that will be referred in this paper as type-1 [4]- [14] and type-2 [3], [17], [22]- [24] models. Both approaches differ in the way in which VSC stations and DC grids are modelled.…”

A Load Flow Analysis for AC/DC Hybrid Distribution Network Incorporated with Distributed Energy Resources for Different Grid Scenarios

“…The difference between the approaches is the applied procedure for the integration of AC and DC network equations. A comprehensive multi-terminal VSC-HVDC newton power flow model suitable for different VSC interconnection configurations was presented in [27][28][29]. In [29], VSCs are treated as compound transformer devices that take into account their inductive and capacitive power design limits along with switching and ohmic losses.…”

“…A comprehensive multi-terminal VSC-HVDC newton power flow model suitable for different VSC interconnection configurations was presented in [27][28][29]. In [29], VSCs are treated as compound transformer devices that take into account their inductive and capacitive power design limits along with switching and ohmic losses. In another study, a steady-state VSC-MTDC model includes DC grids with arbitrary topologies considering converter transformer losses [25], unlike [30], where an approximate solution is obtained by neglecting converter losses and losses in the phase reactor.…”