Armstorfer, Andreas
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The increasing share of distributed energy resources gives rise to new opportunities for deploying innovative business models and coordination schemes within sustainable energy systems. Different concepts entail different implications at socioeconomic, technical and institutional level. Hence, their thorough assessment is key to understanding their actual potential as enablers of the energy transition. Considering this background, we focus on local energy markets as an increasingly discussed approach for coordinating distributed energy systems and introduce a simulative framework for enabling a multi-regional assessment of this concept. Local energy markets bear the potential for increasing the active participation of end consumers, which could increase their acceptance for energy projects in general and their returns on investment, as well as for reducing the peak load on increasingly congested electrical grids by enhancing local energy balancing. We evaluate these hypotheses for twelve representative German regions, for which we formulate assumptions regarding the energy demand as well as the shares of distributed energy resources that are consistently aligned with an overall European energy scenario envisaging a rapid growth of electric vehicles in Germany. For this purpose, we enhance an existing framework for the assessment of local energy markets in order to be able to include the flexibility of the electric mobility sector in local trade activities. The simulation results show that local energy markets have a significant impact on energy systems: First, local trading increases the economic benefits over all participants, who would otherwise only be able to use their generation for self-consumption or direct marketing in central energy markets. Second, local energy balancing increases on average by 60%over all regions. Third, infrastructural relief of the overlaying transmission grids can be accomplished by reducing the yearly peak load at the point of common coupling by 39%on average and at the most by 97%. Furthermore, we find that including electric vehicles in local market activities does not alter but rather reinforces these effects.
The paper presents an approach for modelling a Battery Energy Storage System (BESS). This approach consists of four stages. In the first stage a detailed model is developed taking into consideration all the electrical details of the original system. In stage two the detailed model will be validated using real measurements. In the third stage the complexity of the detailed model is reduced resulting in a simplified model which is able to represent the relevant electrical dynamics of the original system and to decrease the simulation time significantly. In the last stage the simplified model is validated by a comparison with simulation results of the detailed model.
Microgrids play an important role in the energy transition. The change from few centralized power plants to thousands of small renewable and volatile energy resources requires, but also enables new grid control strategies.
The full potential of microgrids is deployed by the extension of island grid operation.
This leads to an increased reliability and resilience of the distribution of electrical energy.
Further, the island capability of microgrids can support a greater grid area in case of failures in higher voltage levels by a temporary disconnection from the main grid and later by resynchronization in the frame of a cellular approach.
For the modeling and control of microgrids in island operation, this thesis delivers mathematical models for typical assets verified by specifc measurements at an existing microgrid (Microgrid Campus Wildpoldsried - MCW) with island capability.
Further, the interaction of inverter-based assets, such as battery storage systems in grid forming, but also in grid support mode, and photovoltaic systems as well as rotating generation units by using droop control, is investigated by simulation; the results are confirmed by measurements at the MCW.
Based on these verified simulation models, further control strategies for the microgrid are developed and analyzed by simulation. This includes a centralized approach for a microgrid controller, including active and reactive power management, strategies for black start and resynchronization as well as energy scheduling for the battery storage systems.
Further, also a failsafe control strategy for active and reactive power sharing between distributed generation, battery storage systems and rotating generation units is investigated for systems without communication system (e.g., temporarily caused by a failure or permanent to reduce installation and maintenance costs). All investigations were performed under consideration of the practical application in real grids. This includes existing rules like VDE AR-N4105 for the distributed generation and the DIN EN50160 for voltage quality on the one hand, but also communication dead times caused by Ethernet-based communication links, protocol converters and control platforms.
Therefore, this thesis provides insightful methods for the planning, dimensioning and analysis of islanded microgrids.
Transactive energy approaches entail the paradigm shifts needed for a successful energy transition towards cleaner energy systems. In the research project pebbles, one such approach aims at developing a Blockchain-based platform for enabling both local energy markets directly accessible to prosumers and distribution grid services. The present paper describes the project’s goal, scope and preliminary findings laying the focus on the conceptual groundwork for the development of a prototypical platform.
Microgrids with a high penetration of distributed generation (DG) in combination with energy storage systems (ESS), but also in combination with fuel-driven generation units (gensets) can be operated in on-grid mode, but also in off-grid mode (island operation). For grid restoration in island mode, a black start strategy is needed. This scientific work deals with a black start concept for island grids with a high amount of non-controllable DG units and non-controllable loads which is investigated by mathematical modeling and simulation for different scenarios. The assumed underlying control behavior of the DG units is described in the German application guide VDE-AR-N 4105. The corresponding mathematical modeling is presented and a verification by specific measurements is presented.
Microgrids can be operated in on-grid mode, but also in off-grid mode (island operation). In off-grid mode, grid forming units have to ensure the grid's voltage and frequency stability. For more than one grid forming unit, the active and reactive power sharing has to be handled. This paper presents a method for voltage and reactive power control for systems without a superordinated control system or a communication link between the grid forming units. A failsafe concept is included, that means that a stable operation is given also in case that one grid forming unit is disconnected.
Local energy markets (LEM) represent a user-centric approach to provide direct market access to prosumers able to compensate selected inadequacies associated with the current design of central energy markets. This paper presents four LEM design options and introduces the specific configurations for both an auction-based and a central coordinator approach. While both approaches aim at maximizing welfare, they differ with regard to the role assumed for the LEM participants and coordinator. Finally, exemplary results are discussed for a test case.
The paper presents the dynamic modeling and stability analysis of Low Voltage (LV) microgrids in island operation using simplified electrical models for Distributed Generations (DGs). These simplified models are used to simulate electrical (excluding switching) as well as control dynamics for each DG to setup and facilitate system level simulations. The paper focuses on the operation of components in grid forming mode using a droop based primary control. This approach is applied on a real microgrid which is set up within the IREN2 research project framework. The demonstrator incorporates a Li-Ion based Battery Energy Storage System (BESS), a plant oil driven generator as well as a BESS emulator. First, a brief overview of the detailed model for each DG including its simplification is discussed. Next, the microgrid is set up using simplified models for transient simulations and the comparison with real measurements is shown for different microgrid topologies. Later, overall microgrid stability i.e., various instability aspects in LV island grids are discussed. In this regard, an analytical method based on Eigenvalue analysis for identification of stability limits for relevant electrical and control parameters and under various loading conditions is presented. Finally, the complete microgrid model is simulated for potential instable conditions and a comparison with the analytical solution is shown.
The research work presents an approach to set-up simplified mathematical models of microgrid components based on detailed models. The verification is done by a comparison with measurement results of a real system. Using simplified models allows an accurate analysis and optimization of the dynamic behavior of existing as well as planned microgrids. The paper shows simulation and measurement results for different combinations of microgrid components in island mode operation.
Mathematical modeling and dynamic behavior of a Lithium-Ion battery system for microgrid application
(2016)
This paper deals with the analysis and simulation of a stationary battery system for microgrid application, where the system structure including battery cells, inverters, filters, transformers, control system and a simplified grid model is described and modeled mathematically. For the simulation of the whole system the software PSCADTM is used. In the first part several equivalent circuit models for Lithium-Ion cells will be compared in order to model the dynamic behavior of the battery system. Particularly the evaluation of the effect of the model's complexity on the dynamics of the entire system will be investigated. In the second part, the dependency of state of charge (SOC), temperature and aging effects of the Lithium-Ion cells on electrical system quantities will be shown. It is also investigated the fact that a high frequency battery model has to be taken into account to describe the cells' dynamics if an inverter with Pulse Width Modulation is used.