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- Blom, Evelin
(author)
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Hydropower Area Equivalents : Reduced Models for Efficient Simulation of Large-Scale Hydropower Systems
- 2023
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Doctoral thesis (other academic/artistic)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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| 2. |
- Shinde, Priyanka, 1993-
(author)
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Efficient Trading in the Short-term Electricity Markets for Integration of Renewable Energy Sources : Multistage Stochastic and Agent-based Modeling Approaches for Continuous Intraday Electricity Market
- 2023
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Doctoral thesis (other academic/artistic)abstract
- This thesis investigates the role of different short-term electricity market design aspects that can facilitate better coordination of resources within the power system. The work also emphasizes on better cross-border integration of the short-term markets to improve the market liquidity, competition, social welfare, and flexibility in the system, which is essential for facilitating the integration of renewable sources. Apart from the policy design issues, the thesis also focuses on developing several mathematical models to support algorithmic trading decisions in short-term markets with various sources of stochasticities. The models proposed in this thesis enable improved trading decisions closer to real-time both for the production and consumption portfolio. The work presented in this thesis encompasses the short-term electricity markets with a primary focus on intraday electricity markets. The contributions of this work are in two directions, one is from the perspective of the trader in the intraday market. In this direction of the work, the aim was to develop optimization models to support algorithmic decision-making for generation and consumption portfolios. To this end, multistage stochastic programming problems have been developed to model cross-border continuous intraday (CID) trading for a price-taking virtual power plant with hydropower, wind power, and thermal power assets. The order clearing in the CID market is enabled by the two presented models, namely the Immediate Order Clearing and the Partial Order Clearing models. Further advancements in the multistage model has been achieved by proposing a bilevel model to tackle the problem of unit commitment of thermal power plant in the continuous intraday market. The lower level of the model accounts for the continuous market clearing considering for the minimum generation level of the thermal power plant. In this model, the virtual power plant is able to post its own prices in the intraday market. The resulting multistage stochastic programming problem with integer variables is tackled by Stochastic Dual Dynamic integer Programming algorithm.For the consumption portfolio, the participation of an electric vehicle aggregator in the intraday and balancing market is modeled as a multistage stochastic programming problem. Intraday markets allow the electric vehicle aggregator to trade furtherbased on their updated forecasts of consumption and price development in the market. The response of the electric vehicle aggregator to the prices in the market helps the power system tobetter manage the imbalances that might be injected by the intermittent generation sources. The algorithmic contribution in this work includes the deployment of randomized progressive hedging which was found to be faster than the conventional progressive hedging algorithm. Furthermore, the performance was accelerated by a parallel randomized progressive hedging algorithm and an asynchronous version of the randomized progressive hedging algorithm is leveraged to speed up the multistage model of electric vehicle aggregator trading.The other direction of the work is from the point-of-view of policymakers where an open-source agent-based model is proposed to model the cross-border continuous intraday electricity market. In this model, the trading behavior of different agents, including renewable, thermal power producers, storage, and consumers, in a cross-border Continuous Intraday market is simulated. The continuous market clearing is performed by a market operator agent. Two capacity calculation methods, Available Transfer Capacity, and Flow-based Market Coupling are availed to compute the cross-border transmission capacities. The agents are enabled to trade for multiple delivery products simultaneously in the CID market. Furthermore, the agents can choose between two different trading strategies, naive and modified trader adaptive aggressiveness, to decide the price-volume curves they post in the CID market. To simulate a realistic trading behavior, a user-defined parameter, switch, is introduced for the storage and thermal agents to allow them to choose the time-instant in the trading timeline when the traders can switch from trading towards increasing their profits to considering their ramping constraints in the CID market. The role of better forecasts of imbalance prices in deciding order prices and thereby the transaction prices in the CID market is also discussed.Ultimately, a forward-looking mechanism is proposed for the system operator to dispatch generators to activate their up- and down-regulation bids on the basis of having lowest expected costs, taking into account both their production costs and potential deviations from nominated outputs. The proposed method has been mathematically applied to compare three imbalance pricing models.
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