| 1. |
- Agredano Torres, Manuel, et al.
(author)
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Decentralized Dynamic Power Sharing Control for Frequency Regulation Using Hybrid Hydrogen Electrolyzer Systems
- 2024
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In: 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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Journal article (peer-reviewed)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. |
- Agredano Torres, Manuel, et al.
(author)
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Dynamic power allocation control for frequency regulation using hybrid electrolyzer systems
- 2023
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In: 2023 IEEE Applied Power Electronics Conference And Exposition, APEC. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 2991-2998
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Conference paper (peer-reviewed)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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| 3. |
- Astero, Poria, 1984-, et al.
(author)
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Improvement of RES hosting capacity using a central energy storage system
- 2017
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In: 2017 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538619537 ; , s. 1-6
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Conference paper (peer-reviewed)abstract
- High penetration of renewable energy sources (RESs) in distribution systems leads to reverse active power and voltage rise in low voltage (LV) grids, which limits the hosting capacity. Energy storage systems (ESSs) have been used to improve the hosting capacity by decreasing the reverse active power in some literature. ESSs can still improve the hosting capacity more by providing reactive power. The reactive power shows a little effect in existing researches, because they have mostly simulate LV grids without modeling transformers. However, the high reactance of the transformer magnifies the effectiveness of the reactive power control even more than the active power in some buses. This paper develops an optimal method for placement, sizing, and active and reactive power control of a central ESS to improve the hosting capacity. The simulation results in highly RES penetrated grids at Germany show the effectiveness of the proposed method.
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| 4. |
- Astero, Poria, 1984-, et al.
(author)
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Improving Hosting Capacity of Rooftop PVs by Quadratic Control of an LV-Central BSS
- 2017
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In: IEEE Transactions on Smart Grid. - : Institute of Electrical and Electronics Engineers (IEEE). - 1949-3053 .- 1949-3061. ; PP:99, s. 1-1
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Journal article (peer-reviewed)abstract
- High integration of rooftop photovoltaic (PV) plants in distribution systems leads to new technical challenges: reverse-active power and voltage rise in low-voltage (LV) and medium-voltage (MV) grids. These challenges limit the maximum amount of power can be produced by PVs in LV and MV grids, called the hosting capacity (HC). Battery storage systems (BSSs) have been used in many studies to decrease the reverse power and improve the HC by controlling the active power. However, the influence of a central BSS on the HC can be greatly improved by using a quadratic power control, simultaneous active and reactive power control, and by selecting of the optimal battery size, the converter size, and the place of the central BSS. The effectiveness of the quadratic power control was not seen in previous works due to the fact that grids with one level of voltage without modeling of MV/LV transformers were simulated. This paper develops a method to select the optimal size of the battery and converter unit as well as the optimal place of an LV-central BSS having an optimal quadratic power control. The simulation results show considerable effects of the optimal selection of an LV-central BSS on the HC improvement.
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| 5. |
- Astero, Poria, 1984-, et al.
(author)
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Improving PV Dynamic Hosting Capacity Using Adaptive Controller for STATCOMs
- 2019
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In: IEEE transactions on energy conversion. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8969 .- 1558-0059. ; 34:1, s. 415-425
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Journal article (peer-reviewed)abstract
- High penetrations of renewable energy sources (RES) in distribution grids lead to new challenges in voltage regulation. These challenges are not just limited to the steady-state voltage rise, but they are extended to rapid voltage changes due to wind speed variations and moving clouds, casting shadows on photovoltaic panels. According to EN50160 in low-voltage (LV) grids, the steady-state voltage should not exceed 1.1 pu (static characteristic), and rapid voltage changes should be kept less than 0.05 pu (dynamic characteristic). These two characteristics may limit the maximum amount of RES that can be installed in LV grids, called, respectively, the static hosting capacity (SHC) and dynamic hosting capacity (DHC). Although existing research just evaluated SHC in distribution grids, high-penetrated RES grids can be faced with such large voltage changes, which cause a smaller DHC than the SHC. This paper studies both SHC and DHC in distribution grids and proposes an adaptive controller for static synchronous compensators to regulate the steady-state and dynamic voltage while avoiding the unnecessary increase in the reactive power. The simulation results in some German distribution grids show considerable effects of the proposed adaptive controller on improving both SHC and DHC.
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| 6. |
- Astero, Poria, 1984-, et al.
(author)
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Improving PV Hosting Capacity of Distribution Grids Considering Dynamic Voltage Characteristic
- 2018
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In: 2018 POWER SYSTEMS COMPUTATION CONFERENCE (PSCC). - : Institute of Electrical and Electronics Engineers (IEEE).
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Conference paper (peer-reviewed)abstract
- Since the penetration of renewable energy sources is rapidly increasing in distribution grids, the hosting capacity (HC) of distribution systems becomes the main concern. According to EN 50160, in LV grids, the mean value of voltage cannot exceed 1.1 pu (static characteristic) and voltage rapid changes should be kept less than 0.05 pu (dynamic characteristic). Existing researches evaluated the HC of distribution grids just based on the static characteristic. However, wind speed variations and rapid moving cloud, casting shadow on solar panels, can cause rapid voltage changes in LV grids. This paper studies the rapid voltage change by modeling the moving cloud shadow and compares the HC from perspective of both dynamic and static characteristic, which is not done before. Since voltage dynamic characteristic could be more restrictive than the static characteristic, as shown in a German distribution grid, a static synchronous compensator (STATCOM) is proposed and controlled to regulate dynamic voltage profile and to improve the HC.
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| 7. |
- Astero, Poria, 1984-, et al.
(author)
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Transactive Demand Side Management Programs in Smart Grids with High Penetration of EVs
- 2017
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In: Energies. - : MDPI AG. - 1996-1073. ; 10:10
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Journal article (peer-reviewed)abstract
- Due to environmental concerns, economic issues, and emerging new loads, such as electrical vehicles (EVs), the importance of demand side management (DSM) programs has increased in recent years. DSM programs using a dynamic real-time pricing (RTP) method can help to adaptively control the electricity consumption. However, the existing RTP methods, particularly when they consider the EVs and the power system constraints, have many limitations, such as computational complexity and the need for centralized control. Therefore, a new transactive DSM program is proposed in this paper using an imperfect competition model with high EV penetration levels. In particular, a heuristic two-stage iterative method, considering the influence of decisions made independently by customers to minimize their own costs, is developed to find the market equilibrium quickly in a distributed manner. Simulations in the IEEE 37-bus system with 1141 customers and 670 EVs are performed to demonstrate the effectiveness of the proposed method. The results show that the proposed method can better manage the EVs and elastic appliances than the existing methods in terms of power constraints and cost. Also, the proposed method can solve the optimization problem quick enough to run in real-time.
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| 8. |
- Biel, Martin
(author)
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Distributed Stochastic Programming with Applications to Large-Scale Hydropower Operations
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Stochastic programming is a subfield of mathematical programming concerned with optimization problems subjected to uncertainty. Many engineering problems with random elements can be accurately modeled as a stochastic program. In particular, decision problems associated with hydropower operations motivate the application of stochastic programming. When complex decision-support problems are considered, the corresponding stochastic programming models often grow too large to store and solve on a single computer. This warrants a need for parallel approaches to enable efficient treatment of large-scale stochastic programs in a distributed environment. In this thesis, we develop mathematical and computational tools to efficiently store and solve distributed stochastic programs. First, we present a software framework for stochastic programming implemented in the Julia programming language. A key feature of the framework is the support for distributing stochastic programs in memory. Moreover, the framework includes a large set of structure-exploiting algorithms for solving stochastic programming problems. These algorithms are based on the classical L-shaped, progressive-hedging, and quasi-gradient algorithms and can be run in parallel on distributed stochastic programs. The distributed performance of our software framework is improved by exploring algorithmic innovations and software patterns. We present the architecture of the framework and highlight key implementation details. Finally, we provide illustrative examples of stochastic programming functionality and benchmarks on large-scale problems. Then, we pursue further algorithmic improvements to the distributed L-shaped algorithm. Specifically, we consider the use of dynamic cut aggregation. We develop theoretical results on convergence and complexity and then showcase performance improvements in numerical experiments. We suggest several aggregation schemes that are based on parameterized selection rules. In brief, cut aggregation can bring major performance improvements to L-shaped algorithms in distributed settings. Next, we consider a fast smoothing scheme for large-scale stochastic programming. We derive a smooth approximation of the subproblems in the quasi-gradient algorithm. This allows us to utilize modern acceleration methods for gradient descent. We derive problem-dependent approximation bounds and convergence properties and note a trade-off between accuracy and speed. We then pose a hybrid procedure that is both fast and accurate and show that it is competitive with the L-shaped method on large-scale benchmarks. Finally, we consider applications to hydropower operations. We consider three case studies in the Swedish river Skellefteälven. The day-ahead planning problem involves specifying optimal order volumes in a deregulated electricity market, without knowledge of the next-day market price, and then optimizing the hydropower production. We provide a detailed introduction to the day-ahead model and explain how it can be implemented in our framework. Using a sample-based algorithm that internally relies on our structure-exploiting solvers, we obtain tight confidence intervals around the optimal solution of the day-ahead problem. We then consider a maintenance scheduling problem as a variation of the day-ahead problem. Last, we consider a capacity expansion problem with a long planning horizon.
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| 9. |
- Blom, Evelin, et al.
(author)
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Accurate model reduction of large hydropower systems with associated adaptive inflow
- 2022
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In: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 200, s. 1059-1067
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Journal article (peer-reviewed)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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| 10. |
- Blom, Evelin, et al.
(author)
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Comparison of Different Computational Methods and Formulations for Hydropower Equivalents
- 2022
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In: 2022 7th IEEE International Energy Conference (EnergyCon).
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Conference paper (peer-reviewed)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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