Frequency Dynamics of the Northern European AC/DC Power System: A Look-Ahead Study

Abstract

In many power systems, the increased penetration of inverter-based renewable generation will cause a decrease in kinetic energy storage, leading to higher frequency excursions after a power disturbance. This is the case of the future Nordic Power System (NPS). The look-ahead study reported in this paper shows that the chosen units participating in Frequency Containment Reserves (FCR) cannot keep the frequency above the prescribed threshold following the outage of the largest plant. This analysis relies on a detailed model of the Northern European grid. The latter is compared to the classical singlemass equivalent, and the impact of voltage-dependent loads is assessed in some detail. Next, the paper focuses on emergency power control of the HVDC links that connect the NPS to the rest of the European grid, which can supplement or even replace part of the FCR. The proper tuning of that control is discussed. Finally, the analysis is extended to the HVDC links connecting the future North Sea Wind Power Hub under two configurations, namely low and zero inertia. The impact of outages in the latter sub-system is also assessed. The material to simulate the system with industrial software is made publicly available.

Distributed HVDC Emergency Power Control; case study Nordic Power System

“…The studies performed in this work are applied to the Northern European AC/DC power system test case, with the full system description regarding the NPS, HVDC links, neighboring system equivalents, and the North Sea Wind Power Hub (NSWPH) given in [18]. Those descriptions relate to the modeling details, which are carefully chosen to serve the studies of frequency control assessment in the current and near-future scenarios for the NPS.…”

“…Those descriptions relate to the modeling details, which are carefully chosen to serve the studies of frequency control assessment in the current and near-future scenarios for the NPS. This manuscript provides only the changes to the model given in [18] and the most essential properties needed to follow the context of work. Since all components are represented by generic models and no proprietary information is involved, the model has been made publicly available and can be accessed at [27] and used through the DigSilent PowerFactory 2020 software [28] (or newer).…”

“…The focus of interest is the NPS response for the largest N-1 power disturbance, the trip of nuclear power plant Oskarshamn 3, marked with an orange "X" sign over a generator in Fig 2 . This is a dimensioning incident for the FCR study in the NPS, and it creates a power step disturbance of 1450 MW and 103 MVAr with a kinetic energy loss of 3.29 GWs. The response constraints are defined such that the maximum allowed IFD and Steady-State Frequency Deviation (SSFD) are 0.9 Hz and 0.4 Hz, respectively [18]. Other disturbances, indicated with the blue "X" signs in Fig.…”

“…To highlight the challenges in the frequency control, the inertia constant of non-hydro generation is reduced by half compared to the model given in [18] 4 . In that way, the total kinetic energy of the system is E k =104.8 GWs, which is slightly smaller than the minimum inertia scenario ever recorded in the NPS [29] -110 GWs.…”

“…The analysis in [18] illustrated the impact of voltage controllers and the importance of detailed large-scale systems for accurate FCR assessment. It is shown how excluding voltage dynamics, implying the change to total loads and losses response, can lead to incorrect IFDs values.…”