arXiv subjects

Danilo Obradovic

Publications and source records attributed to Danilo Obradovic.

3 recordsLinked to original sources

arXiv2022

Distributed HVDC Emergency Power Control; case study Nordic Power System

Frequency Containment Reserves might be insufficient to provide an appropriate response in the presence of large disturbances and low inertia scenarios. As a solution, this work assesses the supplementary droop frequency-based Emergency Power Control (EPC) from HVDC interconnections, applied in the detailed Nordic Power System model. EPC distribution and factors that determine the EPC performance of an HVDC link are the focus of interest. The main criteria are the maximum Instantaneous Frequency Deviation and used EPC power. The presented methodology is motivated based on the theoretical observation concerning linearized system representation. However, the assessed and proposed properties of interest, such as provided EPC active and reactive power, their ratio, and energy of total loads and losses in the system due to the EPC, concern highly nonlinear system behavior. Finally, based on the obtained study, remarks on the pragmatical importance of the EPC distribution to the frequency nadir limitation are provided.

eess.SY↗

arXiv2021

Frequency dynamics of the Northern European AC/DC power system: a look-ahead study

A large share of renewable energy sources integrated into the national grids and an increased interconnection capacity with asynchronous networks, are the main contributors in reducing the kinetic energy storage in the Nordic Power System. Challenges arise to operate system after a loss of generation and to minimize the offshore systems interaction with onshore grids. To assess the associated challenges, a novel dynamic model was developed under the phasor approximation to represent the future Northern European Power System, including High Voltage Direct Current (HVDC) links and future offshore energy islands in the North Sea. First, the future frequency response is provided for two large disturbances to highlight the benefit of the developed model and point out potential future frequency issues. Consequently, further actions are investigated to better utilize the existing frequency containment reserves or to partially replace them using emergency droop-based power control of HVDC links. Lastly, the offshore grid interaction and frequency support to the Nordic network is investigated, and the dynamic response is compared for zero- and low-inertia designs of the offshore energy islands. The simulations were performed using industrial software, and the associated material is made publicly available.

eess.SY↗

arXiv2020

Market Integration of HVDC Lines: Cost Savings from Loss Allocation and Redispatching

In the Nordic region, many interconnectors are formed by HVDC links, as Scandinavia, Continental Europe and the Baltic region are non-synchronous AC systems. This paper presents two cost benefit analyses on the utilization of HVDC interconnectors in the Nordic countries: in the first we investigate the utilization of HVDC interconnectors for reserve procurement and, in the second, we assess the implementation of implicit grid losses on HVDC interconnectors in the day-ahead market. The first analysis is motivated by real events in 2018 where the inertia of the Nordic system dropped below a critical level and the most critical generating unit, a nuclear power plant in Sweden, was redispatched to guarantee the security of the system. In order to guarantee system security while reducing the costs of preventive actions, in summer 2020 new frequency products were introduced in the Nordic system: the Fast Frequency Reserves (FFR). HVDC lines, however, can perform similar tasks at lower costs. In our analysis, we are, thus, investigating the cost savings of using HVDC lines for frequency support using their Emergency Power Control (EPC) functionality, instead of redispatching or FFR. The second analysis is based on the proposition of Nordic Transmission System Operators (TSOs) to introduce linear HVDC loss factors in the market clearing. With our analysis, we show that linear loss factors can unfairly penalize one HVDC line over the other, and this can reduce social benefits and jeopardize revenues of merchant HVDC lines. In this regard, we propose piecewise-linear loss factors: a simple-to-implement but highly-effective solution. Moreover, we demonstrate how the introduction of HVDC loss factors is a partial solution, since it disproportionally increases the AC losses. Our results show that the additional inclusion of AC loss factors can eliminate this problem.

math.OC↗