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

Abstract

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.

Coupling of AC Grids via VSC-HVDC Interconnections for Oscillation Damping Based on Differential and Common Power Control

“…Block diagram of (a) a differential power controller emulating the effect of a mechanical friction, and (b) the dc-voltage controller based on the common power concept. Centralised implementation [29].…”

“…The differential power p ∆ is associated to the active power exchange between grids, if losses and energy stored in the LCL filters of the terminals are neglected. As first introduced in [29], the differential power can be controlled to provide an effect equivalent to that of a mechanical friction between the ac networks. With this aim, the following expression is defined:…”

“…This paper introduces a controller for VSC-HVDC links that introduces virtual electro-mechanical friction between two power systems. As introduced in [24], the design of the proposed control strategy is based on equivalent swing equation models representing the interconnected power systems. Frequency support as well as damping of frequency oscillations at both sides of the HVDC link is inherently provided by the control strategy.…”

“…Based on the general concepts introduced in [24], this paper addresses the controller implementation in detail, and shows that the proposed approach allows a straightforward implementation of the virtual friction control with no need of communication between the HVDC converter terminals. Furthermore, the POD capability of the proposed controller is analytically evaluated by using a simplified model of the two ac networks connected via the HVDC-link.…”