Fraunhofer-Institut für Angewandte Informationstechnik FIT

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  • Publication
    Centralized Model Predictive Control for Transient Frequency Control in Islanded Inverter-Based Microgrids
    ( 2023)
    Heins, T.
    ;
    Josevski, M.
    ;
    Gurumurthy, S.
    ;
    Monti, Antonello
    Grid-forming inverters can establish frequency and voltage regulation in autonomous microgrids by themselves without relying on the external grid and as such are significant enablers for the integration of inverter-interfaced renewable energy sources. The most prominent grid-forming strategies, the droop-based techniques, cannot provide an error-free frequency regulation after a step-wise disturbance and thus are completed by the secondary integral action. In this paper, we propose a model predictive control for fast frequency response in an AC, purely inverter-based microgrid operating in islanded mode. The controller acts as a secondary control unit and adjusts the control actions of the underlying droop controllers leading to an error-free frequency transient control. The controller has been designed leveraging the concept of frequency divider - a simple analytical formulation that estimates the frequency at every system bus. The proposed control is successful in providing a fast frequency response, i.e., it assures a system-wide error-free frequency regulation under different operating circumstances including load changes and varying X/R-ratios. Numerical simulations are carried out in the WSCC 9-Bus and IEEE 39-Bus systems to verify the performance of the proposed method during transients and a comparison with respect to the more common secondary frequency control is given.
  • Publication
    IoT Middleware Platforms for Smart Energy Systems
    ( 2022)
    Alfalouji, Q.
    ;
    Schranz, T.
    ;
    Kümpel, A.
    ;
    Schraven, M.
    ;
    Storek, T.
    ;
    Groß, Stephan
    ;
    Monti, Antonello
    ;
    Müller, D.
    ;
    Schweiger, G.
    Middleware platforms are key technology in any Internet of Things (IoT) system, considering their role in managing the intermediary communications between devices and applications. In the energy sector, it has been shown that IoT devices enable the integration of all network assets to one large distributed system. This comes with significant benefits, such as improving energy efficiency, boosting the generation of renewable energy, reducing maintenance costs and increasing comfort. Various existing IoT middlware solutions encounter several problems that limit their performance, such as vendor locks. Hence, this paper presents a literature review and an expert survey on IoT middleware platforms in energy systems, in order to provide a set of tools and functionalities to be supported by any future efficient, flexible and interoperable IoT middleware considering the market needs. The analysis of the results shows that experts currently use the IoT middleware mainly to deploy services such as visualization, monitoring and benchmarking of energy consumption, and energy optimization is considered as a future application to target. Likewise, non-functional requirements, such as security and privacy, play vital roles in the IoT platforms' performances.
  • Publication
    Comparative Assessment of Shifted Frequency Modeling in Transient Stability Analysis using the Open Source Simulator DPsim
    ( 2022)
    Nakti, Ghassen
    ;
    Dinkelbach, Jan
    ;
    Mirz, Markus
    ;
    Monti, Antonello
    Modern power systems introduce new dynamics, which may require the appropriate selection of the modeling method for each type of dynamic simulation. In this paper, electromagnetic transient (EMT), Root Mean Square (RMS), and Shifted Frequency Analysis (SFA) modeling are compared in the scope of the dynamic simulation of transient stability analysis. The comparison is carried out by analyzing the accuracy of the simulation results as a function of the simulation step size. The evaluation is conducted for classic and low inertia systems for the accuracy of rotor angle transients and the critical clearing time, being the variables of interest in transient stability analysis. The real-time open source simulator DPsim is employed. The main advantage presented by DPsim, is the possibility to run the same simulation scenario with the same solver, but in three different modeling domains. This powerful feature enables a systematic comparison between the modeling methods. With respect to transient stability analysis, the results of the comparative analysis support the usage of SFA, both for classic and low inertia systems. SFA incorporate more dynamics than RMS simulation into the models, while at the same time allowing larger step sizes than EMT simulation.
  • Publication
    SMU Open-Source Platform for Synchronized Measurements
    ( 2022)
    Carducci, C.G.C.
    ;
    Pau, Marco
    ;
    Cazal, C.
    ;
    Ponci, F.
    ;
    Monti, Antonello
    The ramping trend of cheap and performant single board computers (SBC) is growingly offering unprecedented opportunities in various domains, taking advantage of the widespread support and flexibility offered by an operating system (OS) environment. Unfortunately, data acquisition systems implemented in an OS environment are traditionally considered not to be suitable for reliable industrial applications. Such a position is supported by the lack of hardware interrupt handling and deterministic control of timed operations. In this study, the authors fill this gap by proposing an innovative and versatile SBC-based open-source platform for CPU-independent data acquisition. The synchronized measurement unit (SMU) is a high-accuracy device able to perform multichannel simultaneous sampling up to 200 kS/s with sub-microsecond synchronization precision to a GPS time reference. It exhibits very low offset and gain errors, with a minimum bandwidth beyond 20 kHz, SNR levels above 90 dB and THD as low as -110 dB. These features make the SMU particularly attractive for the power system domain, where synchronized measurements are increasingly required for the geographically distributed monitoring of grid operating conditions and power quality phenomena. We present the characterization of the SMU in terms of measurement and time synchronization accuracy, proving that this device, while low-cost, guarantees performance compliant with the requirements for synchrophasor-based applications in power systems.