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Institute
Due to the increasing share of volatile renewable energy sources, like photovoltaics (PV) and wind energy in nearly Zero Energy Buildings (nZEB), there is an increasing need for demand-side management (DSM) or demand response (DR) programs to balance the production and consumption in the grid. The flexibility that can be obtained for smart grids from such DR methods is not limited to appliances like water heaters or dishwashers but can also be achieved with space heating and air-conditioning. In such an interdisciplinary investigation, often one part is simplified, in this case, typically either the thermal models or the implemented DR strategy are very detailed. In this work, a detailed thermal model of a control center is obtained and calibrated in IDA ICE building-modelling software with measurements from a test site in Germany. Afterward, several price-based load matching algorithms are applied to the model to see the possible flexibility exploitation with the thermal capacity of this small building. Not all investigated algorithms show good performance but some of them show promising results. Thus, this model can be used for DR methods and should be extended to work with more DSM strategies and provide ancillary services.
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.
In the future more and more conventional power plants, which provide ancillary services such as provision of reactive power for voltage control and primary control power (active power) for frequency control to the transmission system and thus secure the energy supply, are going to be replaced by renewable energy sources. Due to this fact new concepts for providing these services by renewable power sources will be necessary in the future to maintain stability of the network operation. This refers to the delivery of active and reactive power by distributed generation (DG) and distributed storage (DS). Beyond that DG and DS can be found nowadays in households or also called nanogrids. This research work presents a concept of a nanogrid that can provide ancillary services to the distribution grid in the low voltage level and transfer reactive power as well as primary control power to higher voltage levels by upscaling, which means the connection of many nanogrids. The implementation of the concept is done in a real system and also in a simulation environment that uses simplified mathematical models.
This research work presents an operation mechanism for supplying a scheduled value of reactive power at the medium voltage (MV) side of the distribution transformer by a group of interlinked nanogrids in the low voltage level (LV), which are part of a topological power plant (TPP). The operation mechanism takes into account the self-consumption of the nanogrid and network constraints, such as the permissible voltage band for each node and the loading of the transformer as well as cables. Furthermore, the minimization of active power losses within the TPP is taken into consideration while the scheduled reactive power at the MV side should be accomplished.
The massive development and implementation of small- and medium-scale generation units within the distribution grids result in novel needs and options for ancillary services. The project DeCAS develops solutions for the coordinated activation of ancillary cross-voltage-level services considering the different objective functions of individual voltage levels. This study aims to analyse, define and describe common requirements focusing on a technical, stakeholder and market perspective.