| 1. |
- Blom, Evelin, et al.
(författare)
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Accurate model reduction of large hydropower systems with associated adaptive inflow
- 2022
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 200, s. 1059-1067
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Tidskriftsartikel (refereegranskat)abstract
- Simulation of sizeable hydro-thermal power systems, such as Northern Europe or larger, requires several extensive simplifications and model reductions to decrease simulation time. Such reductions for hydrosystem sare often called Equivalent models. Their purpose is to mimic a more detailed hydropower model whiled ecreasing computation time. Both aspects are vital for accurate and useable simulation results. Here, different Equivalent models for hydropower have been developed together with a new function for adaptive Equivalentinflow based on local inflows to the detailed system. The models were computed via a bilevel optimization problem factoring in the novel adaptive inflow. Based on this, the new function for adaptive inflow was calculated using regression. The Equivalents have then been evaluated in a case study of hydropower systems in Northern Sweden regarding accuracy in hourly and total power generation, revenue estimation, and relative computation time. For all Equivalents, the computation time is decreased by >96%. Further, the Equivalents demonstrate improved performances in hourly and total power production and revenue estimations. The best hourly power difference was 9.2%, and the best revenue estimation was 5.9%. Especially notable is the low total power production difference of <0.5% compared to the more detailed model.
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| 2. |
- Blom, Evelin, et al.
(författare)
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Comparison of Different Computational Methods and Formulations for Hydropower Equivalents
- 2022
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Ingår i: 2022 7th IEEE International Energy Conference (EnergyCon).
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Konferensbidrag (refereegranskat)abstract
- Simplified models of hydropower systems are necessary for simulation of large power systems, long-term analysis, and future studies. One common simplification has been to aggregate all hydropower within an area based on historical data. Another option is to use mathematical so-caned hydropower Equivalents. Here, hydropower Equivalents represent an optimized model reduction of a more Detailed model depicting the complete hydropower system within a specific area. These Equivalents are computed based on a bilevel optimization problem formulation. In this paper, the impact different Equivalent model constraints have on the performance is analyzed via a novel investigation of new model formulations. Moreover, recent solution methods and a baseline aggregation of the hydropower from statistics are compared and evaluated for the first time. All bilevel Equivalents show a significantly better performance than the baseline aggregation; the accuracy in hourly power generation relative to the Detailed model is almost twice as high for all bilevel Eqmvalents.
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| 3. |
- Blom, Evelin, et al.
(författare)
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Computation of Multi-Scenario Hydropower Equivalents Using Particle Swarm Optimization
- 2020
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Ingår i: Proceedings - 2020 IEEE International Conference on Environment and Electrical Engineering and 2020 IEEE Industrial and Commercial Power Systems Europe, EEEIC / I and CPS Europe 2020. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- Simulation of large hydro-thermal power systems requires several extensive simplifications and model reductions. For hydropower systems with several interconnected power stations, these reductions can be particularly challenging and are denoted Equivalent models. The purpose of the Equivalent model is to mimic a more detailed hydropower model, while decreasing computation time, to be used in larger power system models. In this paper different Equivalent models for hydropower systems have been computed with a novel approach using a Particle swarm optimization-algorithm and are evaluated with respect to accuracy in hourly and total power generation as well as computation time. For each of the Equivalent models, computation time is decreased with over 99.99 % and the difference in power production is less than 11% compared to a more detailed model.
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| 4. |
- 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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| 5. |
- Blom, Evelin
(författare)
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Including Hydropower in Large Scale Power System Models
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Hydropower is the most used renewable energy technology with over 4000 TWh electricity generated worldwide in 2017, corresponding to almost 16% of the total electricity generation. In the Nordic countries, hydropower provides an even larger share of the electricity generation with about 50% of the total electricity generation coming from hydro. In other words, hydropower plays a significant role in power systems worldwide in general and in the Nordic power system in particular. Typically the hydropower included in larger power system models are simplified to reduce computation time. These simplifications can be denoted as a hydropower Equivalent which aims to mimic the behaviour of a more detailed description of the hydropower system.Here some of the most common power system models of the Nordic system are summarized including a shorter description specifically describing the modelling of hydropower. The models included are Apollo developed by Sweco, Balmorel which is an open-source alternative, EMPS created by Sintef and BID3 developed by Pöyry.All four models utilizes so called hydropower Equivalents with one or two stations per geographical area. In BID and EMPS the inflow is divided into regulated and unregulated inflow and only include one hydropower station and associated reservoir per area. Apollo and Balmorel on the other hand include two hydropower stations per area, one regulated, with an associated reservoir, and one unregulated.
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| 6. |
- Blom, Evelin, et al.
(författare)
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Optimal Segmented Efficiency In Hydrosystem Area Equivalents To Capture Real Production Peaks
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Ingår i: Energy Systems, Springer Verlag. - 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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| 7. |
- 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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| 8. |
- Blom, Evelin, et al.
(författare)
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Performance of multi-scenario equivalent hydropower models
- 2020
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Ingår i: Electric power systems research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 187
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Tidskriftsartikel (refereegranskat)abstract
- Simulations and analysis of large hydro-thermal power systems easily become computationally heavy without simplifications of the system at hand. Hydropower, in particular, presents a challenge as complex river systems add a large amount of variables and linked constraints to the analysis. A possible simplification is to use aggregated Equivalent models for different parts of the hydrosystem which give similar results, with respect to e.g. power production, as a more detailed description of the Original system. In this paper, novel linear multi-scenario Equivalent models for hourly simulations of nonlinear hydropower systems are developed and their performance investigated. The new models consider multiple scenarios for inflow, price and start resp. end content in the reservoirs as well as reserves for balancing capacity. The performance analysis is based on case studies over Swedish hydropower systems located in the electricity trading area SE1. The average relative error in power production is 9-15% and the computation time is reduced from 9 hours to between 0.4 and 36 seconds.
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| 9. |
- Blom, Evelin, et al.
(författare)
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Sensitivity Analysis of Hydropower Equivalent Parameters With Fast Identification Using PSO
- 2022
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Ingår i: 2022 14th IEEE PES Asia-Pacific Power and Energy Engineering Conference (APPEEC). - : IEEE.
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Konferensbidrag (refereegranskat)abstract
- Hydropower system Equivalents are fictive model reductions of a more detailed hydropower model of all individual hydropower stations within an area. The system Equivalent only has one or a few stations and can significantly reduce the computational effort compared to the detailed system. The aim is to at the same time maintain accuracy in power production. To achieve this a bilevel problem formulation can be utilized. In this bilevel problem, the optimal system Equivalent parameter values are calculated. However, this computation can be very time-consuming and the problem formulation is very complex. Moreover, which of the parameters are most important for overall Equivalent performance and accuracy is unknown. To get a better understanding of the system Equivalent model parameters and their connection to performance, this paper performs a sensitivity analysis and develops a method to determine the parameter importance. Based on these results methods to reduce the computational time of the bilevel problem can be devised, with an example given here. It is shown that the most important parameter is the maximum discharge limit.
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| 10. |
- Blom, Evelin, et al.
(författare)
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Single-Level Reduction of the Hydropower Area Equivalent Bilevel Problem for Fast Computation
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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 and assets are needed. This paper focuses on simplified reduced models of hydropower, or 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 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 compared to Particle Swarm Optimization. Moreover, six new upper-level objectives are investigated and compared based on a case study of the hydropower in northern Sweden. The method using McCrmick-envelopes is very 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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