Harmonic‐Amplitude Modulation Strategy for PtP‐VSC‐HVDC Links Providing Frequency Support

ABSTRACT This paper presents a communication‐free frequency support strategy for point‐to‐point voltage source converter high‐voltage direct‐current (PtP‐VSC‐HVDC) links. The proposed strategy is conceived as a harmonic‐amplitude modulation (HAM), where the frequency deviation experienced by one power system is described as an instantaneous bi‐dimensional trajectory problem, which is analysed using Green's theorem. The trajectory analysis allows to express the level of frequency deviation experienced by a disturbed AC network as a geometrical problem. This is used to generate the necessary active power adjustment command for the PtP‐VSC‐HVDC link depending on the severity of the power imbalance in the affected AC network. The novel HAM strategy introduces a fixed‐frequency AC voltage waveform into the reference of the DC voltage to facilitate the active power adjustment through the PtP‐VSC‐HVDC. Numerical simulations show that the HAM strategy effectively helps to bind the maximum frequency deviations during extreme emergency conditions, such as a network splitting (AC network separation) events in synchronously coupled multi‐area power systems.