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This paper provides an assessment of the effect from virtual inertia provided by an HVDC converter terminal on the Nordic power system. The analysis is based on results from Power-Hardware-in-the-Loop (P-HiL) tests with a laboratory-scale Modular Multilevel Converter (MMC) representing an HVDC terminal interfaced with a real-time phasor simulation of the Nordic grid. The applied control method for providing virtual inertia is utilizing the derivative of the locally measured grid frequency to adapt the power reference for the studied converter terminal. The power injection provided by the converter and the resulting impact on the frequency dynamics of the power system are investigated as a function of the emulated inertia constant and the frequency droop gain. The results demonstrate how the HVDC converter can effectively support the dynamic response of the power system when exposed to large load transients by improving the frequency nadir and reducing the Rate-of-Change-of-Frequency (ROCOF).

This paper presents a method to locate the source of forced oscillations in power grids caused by maloperation of turbine-governor systems. The transfer function between the grid frequency and the output active power is first estimated for each generator in normal operation condition. The turbinegovernor acting as the source of the forced oscillations is then detected by identifying rather large mismatches between the predicted output of its estimated transfer function and actual measurements from the grid. The proposed approach can locate both single and concurrent sources of forced oscillations. The method requires synchronized measurements of the grid frequency and the active power of the generator, preferably from PMU measurements. Results from simulations of the Nordic 44 grid model, which emulates the Nordic power system, demonstrate the validity of the proposed method.

This paper presents a platform for testing wide area monitoring system (WAMS) applications in real time with a Hardware-in-the-Loop (HIL) approach. The power grid dynamics are emulated by performing real-time phasor simulations. Voltage and current phasors can be streamed to external systems based on the standard IEEE C37.118-2011, recreating synthetic synchrophasors. Moreover, phasors can be transformed into timedomain quasi-sinusoidal signals and transferred via a low-latency fiber optic connection to a 200 kW high-bandwidth grid emulator. The grid emulator can amplify the voltage and current signals, allowing Power Hardware-in-the-Loop (P-HIL) testing of physical hardware components. A graphical user interface has been developed to facilitate the interactions with the real time simulation and for better visualizing the power system dynamics. Two WAMS applications for assessing voltage stability margins and for detection of power oscillation are implemented and tested as examples. These examples demonstrate that the framework is a suitable platform to test WAMS applications in power systems

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