Power Generation and Automatic Control

Ancillary services for TSOs by means of platform based usage of dispersed flexibility in the cellular system of the future

• Investigation and analysis of flexibility potentials for congestion management and modelling of influencing factors on flexibility options and flexibility platform
• Scenario definition and simulation of an integrated model in order to use flexibility options for platform-based congestion management in the prospective cellular system together with assessing the possibilities of coupling market and grid

Topic and objectives

The project fleXells is designed to reveal the possibilities of providing system services for transmission system operators by platform-based utilization of dispersed flexibility options in the prospective cellular system.

The superior goal of this research project is the analysis of flexibility potentials from distribution systems and its accessibility for transmission and distribution system operators’ congestion management within the context of cellular concepts. The following essentials are emphasized:

• Determination and optimization of residual potentials after subtraction of not usable and not available potentials of flexibility options.
• Exploitation and connection of these potentials to energy market on one side as well as grids on the other side via a platform solution.
• Considering special features of aggregated virtual power plants and their operation strategies for the evaluation and utilization of residual flexibility potential.

FleXells is strongly linked to the national joint research project "C/sells". The integration of superior concepts, i.e. the cellular approach, the so-called “grid traffic light” as an important tool for safe and secure system operation and a platform solution for congestion management by flexibility options (“flexibility platform”) is focused.

Keywords

congestion management, flexibility potential, platform solution, virtual power plant

Related Publications

• Müller B., Lens H., “Coordinated Dynamic Use of Dispersed Flexibility to Maximize the Time-Variant Aggregated Potential for Redispatch “accepted for IFAC World Congress 2020, Berlin.
• Müller B., Paret T., Lens H., „Redispatch Potential of Virtual Power Plants for Transmission Grid Congestion Management“, Proc. of International ETG-Congress; ETG Symposium, Esslingen, 2019.

Research Scientists

• Benjamin Müller, M.Sc.
• Daniel Scheifele, M.Sc.

Analysis of infrastructural options to integrate renewable energies in Germany and Europe considering security of supply

• Modeling of transmission grids in the context of energy system analysis
• Role of grid expansion as a flexibility option for integration of renewable energies

Topic and objectives

Iterative coupling between energy system and transmission grid models

• Coupling from energy system model to transmission grid model:
  The main requirement for this coupling direction is a full grid dataset, which contains both the electrical network parameters and the substation geocoordinates.
  In a first step, the regional active load and active generation time series that result from the energy system optimization are disaggregated. Then the disaggregated results are extended to an AC-network load case based on assumptions on reactive power consumption and generator voltage magnitude. Regionalized transmission line and generation expansion decision are also disaggregated and implemented in the network model.
• Coupling from transmission grid model to energy system model:
  In this coupling direction, aggregated network constraints are considered in the regionalized optimization problem. The restrictions ensure the safe Network operation, even during n-1 contingency cases. For this purpose, the space for the planning and operation decisions is restricted.
  Furthermore, cost functions for regional network expansion planning, which takes the nodal network topology and the topography into account, are derived. This results in realistic network expansion planning costs.

Integrative modeling approach

The investigation of an integrative modeling approach, which integrate energy system models with nodal transmission grid modeling, will be carried out subsequently.

Dynamic aspects

The analysis of the consideration of dynamic network aspects – such as frequency and voltage stability – as additional optimization constraints rounds off the scope of the project.

Keywords

transmission grid modelling, grid expansion, energy system analysis, power flow computation

Research Scientist

• Dipl.-Ing. Oussama Alaya

Regional combined heat and power plants in a changing energy system

• Dynamic modelling of biomass and waste incineration plants
• Flexibility potential analysis of existing plants
• Design of control strategies for regional cogeneration plants with sector coupling

Topic and objectives

Project Overview

As the share of volatile renewable energies in the German energy landscape increases, challenges arise to guarantee grid stability and security of supply. By increased sector coupling in combined heat and power (CHP) plants, the joint research project KWK 4.0, coordinated by the Chair of Energy Process Engineering of TU Dresden, aims to address these challenges and to expand the business model of CHP plants. The possibilities offered by system-internal storage, P2G, P2L and P2H as well as others are being investigated, while taking into account regional parameters such as population density and amount of renewables installed in the region of the specific CHP plant.

CHP Flexibility and Control

In this project, the Power Generation and Automatic Control department at IFK of the University of Stuttgart is responsible for researching control mechanisms in regional CHP plants and proposing control strategies for the synergetic CHP concepts. The main focus lies with increased flexibility of the plants, both by optimal usage of available sector coupling and storage in the plants, as by modifications to existing CHP plants, which can be achieved through changes to the control and/or the installation itself. Control strategies that were developed to increase the flexibility of large thermal power plants as well as new control strategies will be examined.

Keywords

Cogeneration, CHP, Power plant flexibility, energy storage, P2X, Dynamic simulation

Research Scientist

• Johannes Lips, M.Sc.

Evolution of power system dynamics due to the self-regulating effect

• Measurement-based determination of the selfregulating effect
• Development of dynamic distribution grid models

Project topic and objectives

Generation and consumption must be balanced in the electrical network at all times. Power imbalances that occur during operation are compensated on the one hand by automatic interventions by the grid control, and on the other hand there are system-inherent stabilization mechanisms, such as the inertia of the rotating masses of the synchronous generators and the selfregulating effect. However, the increase of converter-based power generation and power electronic consumers may lead to a fundamental change in these system-inherent stabilization mechanisms in the next few years. While the effects of the rotating masses on the overall system have already been the subject of various studies, the change in the network self-regulation effect has not yet been sufficiently investigated. The first goal of the project is therefore to measure the selfregulating effect. Subsequently, the developed models are used to carry out investigations of the dynamic behavior of the overall system to evaluate the effects of changes in the selfregulating effect on power system stability.

Keywords

Selfregulating effect, Measurement based load modelling, Active Distribution Networks

Related Publications

• G. Mitrentsis and H. Lens, “Unsupervised learning method for clustering dynamic behavior in the context of power systems,” accepted for IFAC World Congress 2020, Berlin.
• C. Schöll, J. Lehner, and H. Lens, “Importance and measurement-based determination of the selfregulating effect,” in 13. GMA/ETG-Fachtagung Netzregelung und Systemführung, Berlin, 2019.

Research Scientists

• Dipl.-Ing. Georgios Mitrentsis
• Christian Schöll, M.Sc.

Development and implementation of a methodology for monitoring the compliance with technical prequalification requirements for balancing reserves

• Development of a monitoring concept for the Balancing Reserve Power products FCR, aFRR and mFRR
• Development of a method for distributing the total power output to the offered products (scheduled power, FCR, aFRR, mFRR)

Project topic and objectives

Balancing Reserve Power (FCR, aFRR, mFRR) is used to compensate for power imbalances and to keep the frequency within the permitted operating limits. So far, Balancing Reserve Power has mainly been provided by large conventional power plants (e.g. coal-fired power plants and hydro pumped storage power plants). The monitoring of the delivery quality was carried out manually due to the small number of providers. As part of the energy transition, the Balancing Reserve Power market is also opened for smaller, decentralized units by adapting the regulations (e.g. shorter product periods and smaller minimum offers). As a result, the number of prequalified units (units eligible to participate in the Balancing Reserve Power market) has increased significantly and the range of technologies has diversified considerably.

Since this makes manual monitoring very complex, a concept for automated monitoring for the quality of Balancing Reserve Power provision is being developed within this project. Based on transfer functions that match the Balancing Reserve Power requirements, a tolerance channel for the provision is generated from the Balancing Reserve Power set point. Then the normalization of the tolerance channel results for each time step enables a clear presentation of the monitoring results in a diagram. To analyze the effects on different technologies, generic models for the different technologies (e.g. conventional power plants, batteries, electrolysers) are created and tested.

Moreover, a method for distributing the total power output to the offered products (schedule, FCR, aFRR, mFRR) is being developed to determine the power output data for the different Balancing Reserve Power products required for the monitoring. For this purpose, transfer functions for the reaction to set point changes of the respective product are estimated based on the transmitted data.

Keywords

Balancing Reserve Power, Monitoring

Related Publications

• Maucher, Philipp; Lens, Hendrik: “Dynamisches Monitoringverfahren für die Erbringung von Primärregelleistung (FCR).” for „KELI – Konferenz zur Elektro-, Leit- und Informationstechnik“ (accepted), Bremen, 2020.

Research Scientist

• Philipp Maucher, M.Sc.

Analysis of the stability of interconnected power systems by means of dynamic simulation with special consideration of the behavior of converter-based generation

• Development of grid-forming inverters
• Technically enable system operation with 100% renewable energies
• Investigation of the effects of inverters, both grid-following and grid-forming, on power system dynamics

Topic and objectives

The project deals with maintaining stability of the synchronous grid with a high share of frequency converter based generation. In the course of the continuing increase of renewable energy supply and the integration of electrical storage devices, the technological basis of the system changes fundamentally. The joint project goals are the development, analysis, implementation and testing of new approaches for the control of grid connected frequency converters, taking into account the current and future requirements on the stability and the robustness of the system.

The goal of the sub-project is to examine the influence of high shares of frequency converter based generation on the dynamic behaviour of the synchronous grid.  The evaluation of these simulations will yield qualitative results on power system stability.

Keywords

Grid-Forming Converters, Virtual Inertia, Power System Stability

Publications

• Schöll, and H. Lens (2020): “Impact of Current Limitation of Grid-forming Voltage Source Converters on Power System Stability,” accepted for IFAC World Congress 2020, Berlin.
• Schöll, J. Lehner, and H. Lens (2018): Impact of current-controlled voltage source converters on power system stability. In: Conference Proceedings: IFAC Symposium on Control of Power and Energy Systems - 10th CPES (Volume 51, Issue 28, 2018), S. 570–575. Available online: https://www.sciencedirect.com/science/article/pii/S2405896318334852.

Research Scientists

• Christian Schöll, M.Sc.