Virtual Friction Control for Power System Oscillation Damping with VSC-HVDC Links

This paper presents a technique for damping of oscillations in ac grids by control of VSC-HVDC links. The effect of the proposed controller is equivalent to a mechanical friction between two asynchronous networks (modelled as rotating masses) interconnected by the HVDC link. Therefore, the dynamics of the ac grids will be coupled, and the virtual friction gain can be utilised to effectively damp frequency oscillations in any of the ac networks. A centralised and a decentralised implementation of the proposed controller are presented. It is shown that both implementations of the virtual friction-based damping can effectively attenuate poorly damped frequency oscillations in both of the interconnected ac grids and that the decentralised implementation can ensure damping without relying on fast communication between the HVDC terminals. The impact of the proposed controller on the stability of the two grids is analysed with a simplified system model, and the performance is experimentally validated by a scaled laboratory setup