In conventional power systems inertia and damping of synchronous generators, generator control systems as well as the power system topology define conditions for low-frequency electro-mechanical oscillations. Such oscillations in a Wide-Area-Network may lead to blackouts in power systems affecting one or several regions/countries. Different Power Oscillation Damping methods have been used to improve the system damping and are currently applied in High Voltage Direct Current (HVDC) applications. The expected increase of HVDC link deployment in Europe will lead to the creation of large and meshed hybrid ac and dc grids resulting in improved network capacity and network resilience. However, in order to operate the system two main challenges will arise: the availability of Wide Area Measurements and the Real-Time management of POD parameters for all active network components.
An alternative control solution for HVDC links has been proposed and developed by IMDEA Energy researchers from Electrical Systems Unit in collaboration with SINTEF, Norway, and is based on a novel Virtual Friction Method, VFM*. A HVDC link with the proposed VFM introduces a damping effect in the power flow equivalent to a mechanical friction between the generators connected to the ac grids at the two terminals. Such coupling effect of the VFM inherently improves the damping across the whole power system and, at the same time, simplifies the configuration of network stability parameters. Moreover, the VFM offers the regulation of system damping and effectively and rapidly attenuates poorly damped frequency oscillations observed at either terminal of the HVDC link.
The proposed control algorithm does not require any time critical measurements or communication links between the HVDC converter terminals - HVDC link uses only local measurements at its terminal (namely the local frequency, power and DC-link voltage). The VFM implementation on a HVDC link is straightforward and does not require any hardware modifications.
(*) Rodriguez-Cabero, A., Roldan-Perez, J., Prodanovic, M., Suul, J.A., D'Arco, S. “Coupling of AC Grids via VSC-HVDC Interconnections for Oscillation Damping Based on Differential and Common Power Control”, (2020) IEEE Transactions on Power Electronics, 35 (6), art. no. 8894842, pp. 6548-6558. https://doi.org/10.1109/TPEL.2019.2952656
More information: Milan Prodanovic, Head of the Electrical Systems Unit email@example.com
a) Two network areas with their inertia and damping coefficient connected by using VFM, b) equivalent mechanical representation depicting the coupling by using the virtual friction (Bω)
Frequency deviations in two network areas showing the oscillation damping in each area with and without the VFM.