| 1. |
- Agredano Torres, Manuel, et al.
(författare)
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Decentralized Dynamic Power Sharing Control for Frequency Regulation Using Hybrid Hydrogen Electrolyzer Systems
- 2024
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Ingår i: IEEE Transactions on Sustainable Energy. - : Institute of Electrical and Electronics Engineers (IEEE). - 1949-3029 .- 1949-3037. ; 15:3, s. 1847-1858
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen electrolyzers are promising tools for frequency regulation of future power systems with high penetration of renewable energies and low inertia. This is due to both the increasing demand for hydrogen and their flexibility as controllable load. The two main electrolyzer technologies are Alkaline Electrolyzers (AELs) and Proton Exchange Membrane Electrolyzers (PEMELs). However, they have trade-offs: dynamic response speed for AELs, and cost for PEMELs. This paper proposes the combination of both technologies into a Hybrid Hydrogen Electrolyzer System (HHES) to obtain a fast response for frequency regulation with reduced costs. A decentralized dynamic power sharing control strategy is proposed where PEMELs respond to the fast component of the frequency deviation, and AELs respond to the slow component, without the requirement of communication. The proposed decentralized approach facilitates a high reliability and scalability of the system, what is essential for expansion of hydrogen production. The effectiveness of the proposed strategy is validated in simulations and experimental results.
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| 2. |
- Anggraini, Dita, et al.
(författare)
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Electric Vehicle Charging Considering Grid Limitation in Residential Areas
- 2024
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Ingår i: 2024 IEEE Transportation Electrification Conference and Expo, ITEC 2024. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- The growing adoption of electric vehicles (EVs) has introduced substantial challenges to the grid. Uncontrolled EV charging may lead to grid overloading, voltage instability, increased power losses, accelerated aging of distribution transformers, and risk of outages. Therefore, a strategic approach is required to tackle the adverse impacts of uncontrolled EV charging to the grid. A promising approach is using EV batteries collectively as a flexible load. Residential areas have the most pronounced EV flexibility potential due to the significant length of uninterrupted parking. In this paper, models of EV charging in residential areas are formulated, followed by Monte Carlo simulations. Three charging models are developed: uncontrolled charging, controlled charging without considering grid limitation and controlled charging considering grid limitation. An optimization problem based on quadratic programming is used in the controlled charging. A residential area based on the IEEE European LV test feeder adopting the deregulated Swedish electricity market is taken as a case study for the simulation. The case study findings indicate that incorporating grid limitation into controlled charging strategies can prevent grid overload and significantly reduce charging and battery degradation costs. In this case study, controlled charging can reduce the charging costs to approximately 42% compared to uncontrolled charging. Considering the battery degradation costs, controlled charging costs are 24% lower than uncontrolled charging. It is possible to postpone the costly grid reinforcement by applying strategic EV charging scheduling. The methods and outcomes pave the way for developing, testing, and implementing business models to manage the grid impacts of growing EV charging.
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| 3. |
- Blom, Evelin, et al.
(författare)
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Single-level reduction of the hydropower area Equivalent bilevel problem for fast computation
- 2024
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 225
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Tidskriftsartikel (refereegranskat)abstract
- For inclusion in large-scale power system models, various aggregations and simplifications in the modeling of relevant actors are needed. This paper focuses on reduced models of hydropower, so called area Equivalent models. They use a simplified topology but are not a direct aggregation of the real hydropower system. Instead, the area Equivalent is constructed to mimic the simulated power production of a more detailed hydropower reference model. Here, this goal is fulfilled by formulating a bilevel problem minimizing the difference in simulated power production between the area Equivalent and its reference. Solving this can be computationally heavy. Thus, for a fast solution of this bilevel problem, a single-level reduction is done, which is then solved using two methods. The first method includes McCormick envelopes to form a linear single-level problem. Second is a modified Benders with a relaxed sub-problem to handle the non-convex single-level. These are then also compared to Particle Swarm Optimization. Moreover, six new upper-level objective functions are investigated for a case study of hydropower in northern Sweden. The method using McCormick envelopes is fast (2–5 min), but the area Equivalent shows lower average performance. The modified Benders finds a solution in 5–31 min with good performance.
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| 4. |
- Khodadadi, Abolfazl
(författare)
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Electricity Market Design Strategies for Hydro-dominated Power Systems : Exploring Optimal Bidding, Planning, and Strategic Operation through Various Market Design Strategies
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The existing wholesale power markets in Nordic countries play a vital role in ensuring the planned balance between supply and demand. However, these markets do not guarantee real-time operational security of the power system. This responsibility falls on the transmission system operator (TSO), who balances consumption and generation in real-time to maintain a secure state.To address these issues, a series of research studies have been performed in this thesis to delve into the intricacies of Nordic balancing markets and propose strategies to enhance their efficiency and effectiveness. These studies have been conducted around the hydropower units as the main generation sources in the Nordic electricity markets. These studies recognize the potential benefits of versatile balancing markets and increased trade of flexible resources with Continental Europe. Additionally, the research results shed light on the optimal bidding strategies for hydropower plants (HPPs) in the day-ahead energy and manual frequency restoration reserve (mFRR) markets. HPPs play a crucial role as a flexible energy source, and their participation in these markets requires careful planning and decision-making. The studies consider various factors such as market rules, mFRR capacity market, future electricity prices, and the impact of active-time duration of balancing energy market offers on revenue generation. This inclusion provides a more realistic revenue portfolio for the operators based on the possibility of not being dispatched in the balancing market. Furthermore, the research explores the concept of flexible stochastic scheduling strategies in hydropower-dominated energy markets. By considering day-ahead energy markets, mFRR markets, and the interaction between different market setups. These strategies provide the necessary flexibility for both the planning and operational stages. The aim is to maximize the profits of the hydropower units while addressing the opportunity cost of saving water and meeting the mFRR capacity requirements imposed by the TSO. Participation in new market setups is an increasingly interesting framework for the operator after the recent introduction of those markets and the results of this section help them to form more profitable decision-making frameworks for their assets. Moreover, the optimal strategic portfolio assessment of HPPs in a multi-settlement market is discussed. Recognizing the increasing electricity prices and the growing penetration of renewable energy resources, these studies leverage bilevel programming problems to model the strategic behavior of HPPs in day-ahead and frequency containment reserve markets. The proposed approaches aim to enhance decision-making processes, promote market efficiency, and enable effective asset management in a dynamic and evolving energy landscape to make more informed multi-market trading decisions. Also, the research examines the dimensioning of frequency restoration reserves in a multi-area power system, specifically focusing on the Nordic case study. By adopting a sequential dimensioning methodology and employing chance-constrained optimization, the studies allocate reserves based on system needs, optimize line flows, and reduce total reserve requirements. The results highlight the potential for sharing reserves among bidding zones in the Nordic synchronous area, contributing to a more efficient and coordinated power system operation.Lastly, a thorough investigation has been performed to assess the effectiveness of the current contract-for-difference contracts as the main support schemes for the development of new renewable energy assets. Case studies have been conducted to demonstrate quantitatively the pros and cons of different proposals and provide new hints for policy-makers about their future decisions.
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| 5. |
- Nordström, Henrik, et al.
(författare)
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Continuous power imbalance assessment from multi-area economic dispatch models
- 2024
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Ingår i: Renewable energy. - : Elsevier Ltd. - 0960-1481 .- 1879-0682. ; 225
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Tidskriftsartikel (refereegranskat)abstract
- To be able to efficiently maintain a continuous balance between supply and demand in power systems with high shares of variable renewable energy (VRE) sources, a variety of studies related to the topic are needed. A fundamental input parameter for such studies is an assessment of the power system's physical needs for balancing power, in form of power imbalances. This article presents a new model for simulating physical power imbalances with a 1-minute time resolution based on multi-area economic dispatch simulations. Compared to existing models with the same purpose, the new model includes the combination of simulating power imbalances with 1-minute time resolution, simulating forecast uncertainty, simulating the continuous behaviour of all power system components and simulating the transmission for netting of power imbalances between balancing areas. By applying the model to a case study of the Nordic synchronous power system in year 2045, the impact of including these features in the model is highlighted. Case study results also show that the size and pattern of power imbalances much depends on the characteristics of a balancing area, in terms of electricity demand, available generation technologies and interconnections to other balancing areas.
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| 6. |
- Söder, Lennart, 1956-
(författare)
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Angående Svenska Kraftnäts metod: ”Effekttillräcklighet enligt statisk metod” : Uppdaterade parametrar, konsekvenser och kommentarer
- 2024
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Svenska kraftnät använder metoden ”Effekttillräcklighet enligt statisk metod”. Vad denna egentligen beräknar är:Hur mycket effekt behöver importeras:· Under den timmen med den högsta elförbrukning som kan inträffa under ett normalår eller under den mest extrema timmen vart 10:e eller 20:e år (dvs en mycket ovanlig situation). · om: Vindkraften producerar på en nivå som överskrids under 91 procent av tiden· om: Kärnkraften producerar på en genomsnittlig nivå (90%), vilken är den nivå som underskrids under ca 35-42 procent av tiden. Dvs under 58-65 procent av tiden är tillgänglig effekt högre.· om: Även andra kraftslag producerar på en given procent av installerad effekt.Detta innebär (med de värden de använder) att det är cirka 4 procent sannolikhet att såväl kärnkraften som vindkraften skulle ge lägre effekt än det som antas, och detta vid den mest extrema timmen under 10 eller 20 år. Och frågan är inte ”effektbrist” utan ”behov av import” vid dessa mycket osannolika enstaka timmar. Det som studerats i denna rapport är inverkan av en mer rimlig ansats av vilka tillgänglighetsdata man ska använda för vindkraft för att den ska ge samma effektbidrag (samma sannolikhet) som kärnkraft. Resultatet är att vindkraftens ”tillgänglighetsfaktor” bör ändras från ca 9-11 procent till ca 27 procent. Detta kommer därmed, med denna metod, minska ”effekt-bristen” (dvs underskottet enligt den statiska metoden). Med ca 18000 MW vindkraft som totalt förväntas finnas installeras inom de närmaste åren så innebär en tillgänglighetsfaktor om 27.6% istället för den använda nivån 9% en ”effektförstärkning” om 3300 MW. Detta sätt att räkna innebär att man fortsätter anta 90% tillgänglighet för kärnkraften och använder samma percentil för vindkraft och kärnkraft. Med antagande om att 2014-2023 är en representativ period så blir ”effektbidraget” för vindkraft ca 100 MW/TWh och för kärnkraft ca 124 MW/TWh.Men denna metod är fortfarande lite märklig då den inte alls beräknar ”effektbrist”, den studerar enbart den extremaste timmen och beaktar inte alls explicit kombinerade sannolikheter för möjlig import etc. Detta kommenterade Svenska Kraftnät redan 2019: ”Denna metod har vissa begränsningar: bara topplasttimmen undersöks, och flöden mellan elområden och länder, samt utländska produktionsresurser beaktas inte. Därför inkluderas nu en probabilistisk metod, som belyser effekttillräckligheten i Sverige på ett annat sätt. Denna typ av modellering för att mäta risken för effekt-brist används på flera håll i världen, bl.a. av ENTSO-E, och det är sannolikt att en sådan metod framöver blir viktigare framöver även för Svenska kraftnät.”Rekommendationen är att inte alls använda den ”statiska metoden”, då a) Den inte alls beaktar sannolikheter, samt kombinationer av olika händelser, på ett rimligt sätt. Detta innebär att resultaten ofta misstolkas. b) Metoden indikerar ökat behov av import samtidigt som den faktiska importen tvärtom minskat. Detta i sin tur beror just på de antaganden man gjort. Om man använder samma percentil för vindkraften som faktiskt används för kärnkraften, får man inte alls denna minskade tillräcklighet, eller ökande importbehov.c) Den ”probabilistiska metoden” är numer standard i EU. Den ger en helt rimlig beskrivning av olika möjligheter och utmaningar. Svenska Kraftnät använder denna metod idag. De rekommendationer som kommit från Energimarknadsinspektionen samt de beslut som tagits av regeringen bygger också helt på denna metod.
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| 7. |
- Söder, Lennart, 1956-
(författare)
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ELPRISETS VOLATILITET : En kort analys
- 2024
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Rapport (populärvet., debatt m.m.)abstract
- Volatilitet i elkostnader har alltid funnits och kommer alltid att finnas eftersom ett rationellt elsystembestår av en kombination av olika kraftverk. Vid hög tillgång på produktion och låg efterfrågan blirmarginalkostnaden låg, och på motsvarande sätt blir marginalkostnaden signifikant högre vid högefterfrågan och låg tillgång på kraftverk med låga driftkostnader.Den liberala elmarknaden som finns i hela Europa innebär att elpriset sätts efter dennaproduktionskostnad. Detta ger ett volatilt elpris, vilket ger incitament till flexibilitet samt ger ocksåsignaler till marknaden att investera i det som ger störst nytta för elsystemet. De kunder somefterfrågar ett stabilt elpris kan ha kontrakt med någon aktör som tar pris-risken. Detta kommer attske till en kostnad, då ingen aktör erbjuder denna tjänst gratis, men många kunder är beredda att tadenna kostnad.Sammanfattningsvis kan följande sägas om prisvolatiliteten:1) Det är av stort värde för elmarknaden att det finns finansiella verktyg att hanteraelprisvariationer för de aktörer som så önskar. Det är bra att någon myndighet har till uppgift attstudera detta.2) Prisvolatiliteten, mätt som standardavvikelse på elpriset i Euro/MWh har dock varit lägre iSverige jämfört med, t ex, Tyskland, Frankrike och Nederländerna under 2022-2023.3) Prisvolatilitet gynnar flexibilitet. Den konsument som kan vara flexibel, t ex ladda sin elbil vid lågefterfrågan, får därmed ett lägre elpris.4) En troligen central fråga gällande volatilitet är prisvariationer mellan olika år. För framtidenerbjuder då sol+vind den lägsta volatiliteten (plus/minus 4.4 procent baserat på data frånSvenska Kraftnät för tidsperioden 1982-2006) jämfört med faktisk kärnkraft (plus-minus 9.2 procent baserat på data från Energimyndigheten för tidsperioden 1996-2022).5) Det finns en tyvärr spridd missuppfattning att kärnkraft automatiskt skulle minska prisvolatiliteten.Kärnkrafts-landet Frankrike hade såväl 2022 som 2023 en högre volatilitet änSverige, mätt som standardavvikelse för elpris per timme i Euro/MWh. I Finland ökadeprisvolatiliteten när deras nya kärnkraftverk kom igång den 16 april 2023.
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| 8. |
- Agredano Torres, Manuel, et al.
(författare)
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Dynamic power allocation control for frequency regulation using hybrid electrolyzer systems
- 2023
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Ingår i: 2023 IEEE Applied Power Electronics Conference And Exposition, APEC. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 2991-2998
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Konferensbidrag (refereegranskat)abstract
- The increase in hydrogen production to support the energy transition in different sectors, such as the steel industry, leads to the utilization of large scale electrolyzers. These electrolyzers have the ability to become a fundamental tool for grid stability providing grid services, especially frequency regulation, for power grids with a high share of renewable energy sources. Alkaline electrolyzers (AELs) have low cost and long lifetime, but their slow dynamics make them unsuitable for fast frequency regulation, especially in case of contingencies. Proton Exchange Membrane electrolyzers (PEMELs) have fast dynamic response to provide grid services, but they have higher costs. This paper proposes a dynamic power allocation control strategy for hybrid electrolyzer systems to provide frequency regulation with reduced cost, making use of advantages of AELs and PEMELs. Simulations and experiments are conducted to verify the proposed control strategy.
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| 9. |
- Blom, Evelin
(författare)
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Hydropower Area Equivalents : Reduced Models for Efficient Simulation of Large-Scale Hydropower Systems
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With over 4000 TWh yearly electricity production worldwide, hydropower plays an important role in many power systems. Unlike many other renewable energy sources, hydropower has a certain degree of controllability and high levels of flexibility over several time scales. This flexibility is estimated to be integral for the transition of the energy systems towards more variable renewable energies and thus reducing greenhouse gas emissions. Given the important role that hydropower currently plays and is expected to play in future power systems, accurate models of hydropower are vital. As hydropower electricity production is a non-convex function of the discharge with for example non-linear head dependencies and forbidden zones of operation, detailed models of real hydropower systems quickly become computationally heavy. Even linear models with high numbers of interconnected stations are often too complex for large-scale power system models. For this reason, reduced or aggregated models of hydropower are commonly used to simulate its operation in different power system models. Due to the temporal and spatial connections in many hydropower systems with large rivers, the aggregation of hydropower can pose significant challenges. This means that aggregation from historical data might not be good enough to accurately simulate the hydropower operation. However, accurate reduced models of hydropower are still needed for long-term current and future studies of energy systems worldwide. In this thesis, the basic assumption is that the simplified reduced hydropower model should mimic the real hydropower operation. Thus, instead of aggregating the existing hydropower stations within a certain geographical area, one computes a new hydropower area Equivalent model with the aim to match the simulated power production of a more Detailed model of the real hydro system in that area. In this work, the area Equivalent models are calculated by computing the model parameter values. Here, this is mainly done based on a bilevel optimization problem formulation. In this thesis, different methods to compute the area Equivalents are proposed together with different model formulations and bilevel problem formulations. These are all compared using case studies of Swedish hydropower systems. Moreover, a Baseline aggregation method is outlined and compared to the developed area Equivalents. The studies presented in this thesis highlight the potential trade-offs in the accuracy of the area Equivalent model. Some problem formulations give a higher accuracy in hourly power production, others in peak power production or total power production over the simulation period. All area Equivalents perform better than the Baseline aggregation. In general, the average error in hourly power production is reduced by 50% using the area Equivalent compared to the Baseline aggregation. Moreover, they all successfully reduce the simulation time compared to the reference Detailed model with over 96%.
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| 10. |
- Blom, Evelin, et al.
(författare)
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Optimal segmented efficiency in hydrosystem area equivalents to capture real production peaks
- 2023
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Ingår i: Energy Systems, Springer Verlag. - : Springer Nature. - 1868-3967 .- 1868-3975.
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Tidskriftsartikel (refereegranskat)abstract
- Modeling large energy systems requires different forms of simplifications and aggregations. This is especially true for large hydropower systems. One way to simplify the modeling of hydropower as a part of large scale energy systems is to utilize so-called Equivalent models. The hydropower Equivalent model is a simplified hydropower area model with only one (or a few stations) which aims to mimic the behavior of an Original more detailed model containing all stations in a specific area. However, one drawback has been that the Equivalent model fails to match the highest production peaks of the real Original system. Methods to increase the maximum peaks in the Equivalent model have so far resulted in overall lower performance, where the production during lower peaks instead would be overestimated. Thus, in this paper, a method for computing hydrosystem area Equivalent models that not only have good average performance but also can capture the production peaks of the real hydropower system is developed. The new method allows for optimal partition and efficiency of different segments in the hydropower marginal production function.
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