Mitigation of harmonic interactions by the VSC-HVDC converter in variable networks

System stability can be affected by the interaction between the converter control and the network resonances. Current installations of VSC-HVDC converters have experienced instability issues due to this interaction and have triggered questions in industry and research such as the suitable methods to evaluate the interferences, the necessary models in order to determine them and the techniques to mitigate the effects. This paper first explains how to study the phenomena and to determine the frequency range of interactions. Several active damping techniques to mitigate the arising oscillations in networks with multiple and variable resonances are proposed. The techniques are implemented by means of different control loops and making use of the different control variables from measurements. Results from time-domain simulations show the satisfactory behaviour of the proposed controls.