TY - GEN A1 - Schiffer, Johannes A1 - Krishna, Ajay A1 - Hans, Christian A. A1 - Raisch, Jörg A1 - Kral, Thomas T1 - Steady State Evaluation of Distributed Secondary Frequency Control Strategies for Microgrids in the Presence of Clock Drifts T2 - 25th Mediterranean Conference on Control and Automation N2 - Secondary frequency control, i.e., the task of restoring the network frequency to its nominal value following a disturbance, is an important control objective in microgrids. In the present paper, we compare distributed secondary control strategies with regard to their behaviour under the explicit consideration of clock drifts. In particular we show that, if not considered in the tuning procedure, the presence of clock drifts may impair an accurate frequency restoration and power sharing. As a consequence, we derive tuning criteria such that zero steady state frequency deviation and power sharing is achieved even in the presence of clock drifts. Furthermore, the effects of clock drifts of the individual inverters on the different control strategies are discussed analytically and in a numerical case study. Y1 - 2017 UR - http://eprints.whiterose.ac.uk/115991/ U6 - https://doi.org/10.1109/MED.2017.7984168 SN - 2473-3504 SP - 508 EP - 515 ER - TY - GEN A1 - Schiffer, Johannes A1 - Ojo, Yemi T1 - Towards a Time-Domain Modeling Framework for Small-Signal Analysis of Unbalanced Microgrids T2 - IEEE PowerTech 2017, Manchester, UK, 2017 N2 - Small-signal analysis is one of the most frequently used techniques to assess the operating conditions of power systems. Typically, this analysis is conducted by employing a phasor-based model of the power network derived under the assumption of balanced operating conditions. However, distribution networks and, amongst these, microgrids are often unbalanced. Hence, their analysis requires the development of tools and methods valid under such conditions. Motivated by this, we propose a modeling approach for generic nonlinear and unbalanced three-phase microgrids, which allows to derive a small-signal model in a standard fashion. The approach is based on a time-domain decomposition of the electrical waveforms in positive and negative synchronous reference frames. The efficacy of the approach is demonstrated via application to an exemplary unbalanced microgrid. Y1 - 2017 UR - http://eprints.whiterose.ac.uk/114880/ U6 - https://doi.org/https://doi.org/10.1109/PTC.2017.7981013 ER - TY - GEN A1 - Gustavo-Escobedo, Juan A1 - Moreno, Jaime A. A1 - Schiffer, Johannes T1 - Finite-Time Estimation of Time-Varying Frequency Signals in Low-Inertia Power Systems T2 - 8th European Control Conference (ECC) N2 - The ongoing and unprecedented transformation of power systems leads to a reduction in the number of conventional power plants, which are the classical actuators of the grid. In addition, this development results in a decreasing system inertia, which is expected to yield faster frequency dynamics. Therefore power-electronics-interfaced units have to take over system control tasks and, in particular, frequency control. For this purpose, accurate and fast estimation algorithms for time-varying frequency signals are needed. Motivated by this fact, we propose a time-varying parameter estimator and a tuning criterion, which for sufficiently small initial estimation errors allows to reconstruct the time-varying frequency signal of a symmetric three-phase waveform in finite time. The proposed estimator is derived by using a time-varying version of the super twisting algorithm and its performance is illustrated via numerical examples. KW - Power Systems, Frequency Signals, Finite-Time Estimation Y1 - 2019 U6 - https://doi.org/10.23919/ECC.2019.8795926 SP - 2108 EP - 2114 ER - TY - GEN A1 - Schiffer, Johannes A1 - Efimov, Denis A1 - Ortega, Romeo T1 - Global synchronization analysis of droop-controlled microgrids—A multivariable cell structure approach T2 - Automatica N2 - The microgrid concept represents a promising approach to facilitate the large-scale integration of renewable energy sources. Motivated by this, the problem of global synchronization in droop-controlled microgrids with radial topology is considered. To this end, at first a necessary and sufficient condition for existence of equilibria is established in terms of the droop gains and the network parameters. Then, the local stability properties of the equilibria are characterized. Subsequently, sufficient conditions for almost global synchronization are derived by means of the multivariable cell structure approach recently proposed in Efimov and Schiffer (2019). The latter is an extension of the powerful cell structure principle developed by Leonov and Noldus to nonlinear systems that are periodic with respect to several state variables and possess multiple invariant solutions. The analysis is illustrated via numerical examples. KW - Global synchronization KW - controlled microgrids Y1 - 2019 UR - https://www.sciencedirect.com/science/article/pii/S000510981930411X U6 - https://doi.org/10.1016/j.automatica.2019.108550 SN - 0005-1098 IS - 109 ER - TY - GEN A1 - Krishna, Ajay A1 - Schiffer, Johannes A1 - Monshizadeh, Nima A1 - Raisch, Jörg T1 - A consensus-based voltage control for reactive power sharing and PCC voltage regulation in microgrids with parallel-connected inverters T2 - European Control Conference 2019, Naples, Italy N2 - We consider small-scale power systems consisting of several inverter-interfaced units connected in parallel to a common bus, the point of common coupling (PCC), and sharing a joint load. This is a frequently encountered configuration in microgrid applications. In such a setting, two important control objectives are reactive power sharing and voltage regulation at the PCC. In this paper, we first show that the nonlinear equilibrium equations corresponding to the aforementioned objectives admit a unique positive solution. Then, we propose a consensus-based distributed voltage controller which renders this desired unique solution locally asymptotically stable. Finally, control performance is illustrated via a simulation example. Y1 - 2019 SN - 978-3-907144-00-8 SN - 978-3-907144-01-5 SN - 978-1-7281-1314-2 U6 - https://doi.org/10.23919/ECC.2019.8795924 CY - Neapel ER - TY - GEN A1 - Alghamdi, Sultan A1 - Smith, Nathan A1 - Aristidou, Petros A1 - Schiffer, Johannes T1 - Delay-Robust Distributed Secondary Frequency Control: A Case Study T2 - IEEE PES PowerTech Conference 2019, Milano, Italy N2 - With the purpose of enabling a low-carbon future, power systems worldwide are undergoing major transformations. These developments require new advanced control and operation approaches to ensure a stable and efficient system operation. Distributed consensus-based algorithms are a promising option to provide the necessary flexibility and scalability to cope with these challenges and have, thus, been widely investigated in the literature. Yet, most available results are limited to scenarios with reduced-order models and ideal communication. Motivated by this, we perform a case study using a detailed dynamic model of the well-known Nordic test system equipped with a consensus-based distributed secondary frequency controller. Our main objectives are to analyse the robustness of the closed-loop system with respect to unmodelled (voltage and higher-order generator) dynamics as well as communication delays. To facilitate the later property, we employ robust-stability conditions in the control design. Then, the performance of the proposed controller is assessed through detailed dynamic simulations covering several disturbances leading to large frequency and voltage excursions. Y1 - 2019 SN - 978-1-5386-4722-6 SN - 978-1-5386-4723-3 U6 - https://doi.org/10.1109/PTC.2019.8810821 CY - Milano ER - TY - GEN A1 - Efimov, Denis A1 - Schiffer, Johannes T1 - On boundedness of solutions of state periodic systems: a multivariable cell structure approach T2 - IEEE Transactions on Automatic Control N2 - Many dynamical systems are periodic with respect to several state variables. This periodicity typically leads to the coexistence of multiple invariant solutions (equilibria or limit cycles). As a consequence, while there are many classical techniques for analysis of boundedness and stability of such systems, most of these only permit to establish local properties. Motivated by this, a new sufficient criterion for global boundedness of solutions of such a class of nonlinear systems is presented. The proposed method is inspired by the cell structure approach developed by Leonov and Noldus and characterized by two main advances. First, the conventional cell structure framework is extended to the case of dynamics, which are periodic with respect to multiple states. Second, by introducing the notion of a Leonov function, the usual definiteness requirements of standard Lyapunov functions are relaxed to sign-indefinite functions. Furthermore, it is shown that under (mild) additional conditions the existence of a Leonov function also ensures input-to-state stability, i.e., robustness with respect to exogenous perturbations. The performance of the proposed approach is demonstrated via the global analysis of boundedness of trajectories for a nonlinear system. Y1 - 2019 U6 - https://doi.org/10.1109/TAC.2019.2892395 SN - 0018-9286 SN - 1558-2523 VL - 64 IS - 10 SP - 4094 EP - 4104 ER - TY - GEN A1 - Krishna, Ajay A1 - Schiffer, Johannes A1 - Raisch, Jörg T1 - Distributed Secondary Frequency Control in Microgrids: Robustness and Steady-State Performance in the Presence of Clock Drifts T2 - European Journal of Control N2 - Microgrids are distributed systems with high share of inverter-interfaced renewable energy sources where stable and reliable system operation is realized by suitably controlling the inverters. In this work, we focus on secondary frequency control, which is an important ancillary service provided by the inverters. In the literature on secondary frequency control, the effect of clock drifts has often been neglected. However, clock drifts are practically unavoidable parameter uncertainties in inverter-based microgrids and we show that the most commonly employed distributed secondary frequency controllers exhibit performance deteriorations when taking clock drifts explicitly into consideration. Motivated by this, we propose a novel alternative control law called generalized distributed averaging integral (GDAI) control, which achieves the secondary control objectives of steady-state accurate frequency restoration and proportional power sharing in the presence of clock drifts. In addition, we derive a sufficient tuning criterion in the form of a set of linear matrix inequalities (LMIs) which guarantees robust stability of the closed-loop equilibrium point in the presence of uncertain clock drifts. Finally, our analysis is validated extensively via simulation with comprehensive comparisons to other related distributed control approaches. Y1 - 2020 U6 - https://doi.org/10.1016/j.ejcon.2019.08.003 SN - 0947-3580 VL - 51 SP - 135 EP - 145 ER - TY - GEN A1 - Schiffer, Johannes A1 - Aristidou, Petros A1 - Ortega, Romeo T1 - Online Estimation of Power System Inertia Using Dynamic Regressor Extension and Mixing T2 - IEEE Transactions on Power Systems N2 - The increasing penetration of power-electronic-interfaced devices is expected to have a significant effect on the overall system inertia and a crucial impact on the system dynamics. In future, the reduction of inertia will have drastic consequences on protection and real-time control and will play a crucial role in the system operation. Therefore, in a highly deregulated and uncertain environment, it is necessary for transmission system operators to be able to monitor the system inertia in real time. We address this problem by developing and validating an online inertia estimation algorithm. The estimator is derived using the recently proposed dynamic regressor and mixing procedure. The performance of the estimator is demonstrated via several test cases using the 1013-machine ENTSO-E dynamic model. Y1 - 2019 U6 - https://doi.org/10.1109/TPWRS.2019.2915249 SN - 1558-0679 SN - 0885-8950 VL - 34 IS - 6 SP - 4993 EP - 5001 ER - TY - GEN A1 - Alghamdi, Sultan A1 - Markovic, Uros A1 - Stanojev, Ognjen A1 - Schiffer, Johannes A1 - Hug, Gabriela A1 - Aristidou, Petros T1 - Wide-area oscillation damping in low-inertia grids under time-varying communication delays T2 - ScienceDirect N2 - Wide-Area Control (WAC) can be efficiently used for oscillation damping in power systems. However, to implement a WAC, a communication network is required to transmit signals between the generation units and the control center. In turn, this makes WAC vulnerable to time-varying communication delays that, if not appropriately considered in the control design, can destabilize the system. Moreover, with the increasing integration of renewable energy resources into the grid, usually interfaced via power electronics, power system dynamics are becoming drastically faster and making WAC more vulnerable to communication delays. In this paper, we propose a design procedure for a delay-robust wide-area oscillation damping controller for low-inertia systems. Its performance is illustrated on the well-known Kundur two-area system. The results indicate that the obtained WAC successfully improves the oscillation damping while ensuring robustness against time-varying communication delays. KW - Low-inertia systems KW - Oscillation damping KW - Time-varying communication delay KW - Wide-area control Y1 - 2020 U6 - https://doi.org/10.1016/j.epsr.2020.106629 SN - 0378-7796 VL - 189 ER - TY - GEN A1 - Matveev, Alexey S. A1 - Machado, Juan Eduardo A1 - Ortega, Romeo A1 - Schiffer, Johannes A1 - Pyrkin, Anton T1 - A Tool for Analysis of Existence of Equilibria and Voltage Stability in Power Systems with Constant Power Loads T2 - IEEE Transactions on Automatic Control N2 - It is well known that constant power loads in power systems have a destabilizing effect. Their growing presence in modern installations significantly aggravates this issue, hence, motivating the development of new methods to analyze their effect in ac and dc power systems. Formally, this problem can be cast as the analysis of solutions of a set of nonlinear algebraic equations of the form f(x) = 0, where f : R n → R n , to which we associate the differential equation x = f(x). By invoking advanced concepts of dynamical systems theory and effectively exploiting its monotonicity, the following properties are established: First, prove that, if there are equilibria, there is a distinguished one that is stable and attractive, and give conditions such that it is unique. Second, give a simple online procedure to decide whether equilibria exist or not and to compute the distinguished one. Third, prove that the method is also applicable for the case when the parameters of the system are not exactly known. It is shown how the proposed tool can be applied to the analysis of long-term voltage stability in ac power systems, and to the study of existence of equilibria of multiterminal high-voltage dc systems and dc microgrids. Y1 - 2020 U6 - https://doi.org/10.1109/TAC.2020.2965028 SN - 0018-9286 SN - 1558-2523 VL - 65 IS - 11 SP - 4726 EP - 4740 ER - TY - GEN A1 - Alghamdi, Sultan A1 - Markovic, Uros A1 - Stanojev, Ognjen A1 - Schiffer, Johannes A1 - Hug, Gabriela A1 - Aristidou, Petros T1 - Wide-Area Oscillation Damping in Low-Inertia Grids under Time-Varying Communication Delays T2 - 21st Power Systems Computation Conference, Porto, Portugal — June 29 – July 3, 2020 N2 - Wide-Area Control (WAC) can be efficiently used for oscillation damping in power systems. However, to implement a WAC, a communication network is required to transmit signals between the generation units and the control center. In turn, this makes WAC vulnerable to time-varying communication delays that, if not appropriately considered in the control design, can destabilize the system. Moreover, with the increasing integration of renewable energy resources into the grid, usually interfaced via power electronics, the power system dynamics becoming drastically faster and making WAC more vulnerable to communication delays. In this paper, we propose a design procedure for a delay-robust wide-area oscillation damping controller for low-inertia systems. Its performance is illustrated on the well-known Kundur two-area system. The results indicate that the obtained WAC successfully improves the oscillation damping while ensuring robustness against time-varying communication delays. Y1 - 2020 UR - https://www-docs.b-tu.de/fg-regelungssysteme/public/Publications/Widearea_oscillation.pdf ER - TY - GEN A1 - Alghamdi, Sultan A1 - Schiffer, Johannes A1 - Fridman, Emilia T1 - Synthesizing Sparse and Delay-Robust Distributed Secondary Frequency Controllers for Microgrids T2 - IEEE Transactions on Control Systems Technology N2 - Consensus-based control schemes experience increasing popularity in the context of secondary frequency control in microgrids. Fundamental aspects in their practical implementation are the design of the communication topology as well as robustness with respect to both time-varying communication delays and exogenous disturbances. Motivated by this, we propose a design procedure for a consensus-based secondary frequency controller that ensures robustness with respect to heterogeneous fast-varying communication delays and simultaneously provides the option to trade off the L₂-gain performance against the number of required communication links. Our design criterion is equilibrium-independent and based on the Lyapunov-Krasovskii method for interval time-varying delays together with the descriptor method. The efficacy of the proposed approach is demonstrated by using numerical experiments on the CIGRE benchmark medium-voltage distribution network. Y1 - 2020 U6 - https://doi.org/10.1109/TCST.2020.2977300 SN - 1558-0865 SN - 1063-6536 VL - 29 IS - 2 SP - 691 EP - 703 ER - TY - GEN A1 - Bobtsov, Alexey A1 - Ortega, Romeo A1 - Nikolaev, Nikolay A1 - Schiffer, Johannes T1 - A Globally Convergent State Observer for Multimachine Power Systems with Lossy Lines T2 - 21st IFAC World Congress, Berlin, Germany, Jul. 11-17, 2020 N2 - We present the first solution to the problem of estimation of the state of multimachinepower systems with lossy transmission lines. We consider the classical three-dimensional “flux-decay” model of the power system and assume that the active and reactive power as wellas the rotor angle and excitation voltage at each generator is available for measurement—ascenario that is feasible with current technology. The design of the observer relies on two recentdevelopments proposed by the authors: a parameter estimation based approach to the problemof state estimation and the use of the dynamic regressor extension and mixing technique toestimate these parameters. Thanks to the combination of these techniques it is possible toovercome the problem of lack of persistent excitation that stymies the application of standardobserver designs. Simulation results illustrate the performance of the proposed observer. Y1 - 2020 UR - https://www-docs.b-tu.de/fg-regelungssysteme/public/Publications/Globally_convergent.pdf UR - https://arxiv.org/abs/2005.01482 ER - TY - GEN A1 - Rueda-Escobedo, Juan G. A1 - Tang, Shiqing A1 - Schiffer, Johannes T1 - A Performance Comparison of PLL Algorithms in Low-Inertia Power Systems Using an Observer-Based Framework T2 - 21st IFAC World Congress, Berlin, Germany, Jul. 11-17, 2020 N2 - Phase-locked loop (PLL) implementations are critical components for the control and operation of grid-connected converters. Hence, they have to exhibit a highly reliable behavior under a wide range of operating conditions. Available implementations and performance analyses mainly focus on the impact of unbalances and harmonics. However, in converter-dominated low-inertia power systems an additional important type of perturbation will arise from fast variations in the grid frequency. Motivated by this, we show that the structure of several popular PLL implementations is closely related to that of high-gain observers and, by using this framework, provide a tuning criterion for the PLL gains that mitigates the impact of the rate of change of the frequency (RoCoF) on the estimation performance. This criterion is then used to conduct a numerical comparison of four popular PLL implementations under three distorted conditions: unbalances, harmonics and frequency variations. KW - Phase-locked loop implementations; Frequency estimation;High-gain observers; Electric power systems; Low-inertia systems; Inverter-based applications Y1 - 2020 UR - https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwj-3Nvqy6zuAhVCi1wKHSFhAWcQFjAAegQIBhAC&url=https%3A%2F%2Fwww-docs.b-tu.de%2Ffg-regelungssysteme%2Fpublic%2FPublications%2FA%2520performance%2520comparison%2520of%2520PLL%2520implementations%2520in%2520low%2520lnertia%2520power%2520systems%2520using%2520an%2520observer-based%2520framework.pdf&usg=AOvVaw0N4TiSh9cu9DeyVoOhNZpf ER - TY - GEN A1 - Machado, Juan Eduardo A1 - Schiffer, Johannes T1 - A Passivity-Inspired Design of Power-Voltage Droop for DC Microgrids with Electrical Network Dynamics T2 - 59th IEEE Conference on Decision and Control (CDC), Jeju Island, Republic of Korea, Dec. 14-18, 2020 N2 - We propose a design procedure for a power-voltage droop controller in structure-preserving DC microgrids under explicit consideration of the electrical network dynamics. Differently from most related literature, the system’s controlled output is taken as the power—not the current—injection at each generation unit, yielding a nonlinear closed-loop system. This makes the output regulation problem non-trivial, yet far more appealing in a practical setting than the usual linear current-voltage droop control. Our approach is inspired by passivity-based control design in the sense that we exploit the natural port-Hamiltonian representation of the system dynamics and its associated shifted Hamiltonian to derive a control law together with sufficient conditions on the tuning gains that guarantee global asymptotic stability. The analysis is illustrated via detailed simulations, where accurate power sharing is manifested among the distributed generation units in the presence of load variations. Y1 - 2020 UR - https://www-docs.b-tu.de/fg-regelungssysteme/public/Publications/2020%20A%20Passivity-Inspired%20Design%20of%20Power-Voltage%20Droop%20for%20DC%20Microgrids%20with%20Electrical%20Network%20Dynamics.pdf ER - TY - GEN A1 - Rueda-Escobedo, Juan G. A1 - Schiffer, Johannes T1 - Data-Driven Internal Model Control of Second-Order Discrete Volterra Systems T2 - 59th IEEE Conference on Decision and Control (CDC), Jeju Island, Republic of Korea, Dec. 14-18, 2020 N2 - The increase in system complexity paired with a growing availability of operational data has motivated a change in the traditional control design paradigm. Instead of modeling the system by first principles and then proceeding with a (model-based) control design, the data-driven control paradigm proposes to directly characterize the controller from data. By exploiting a fundamental result of Willems and collaborators, this approach has been successfully applied to linear systems, yielding data-based formulas for many classical linear controllers. In the present paper, the data-driven approach is extended to a class of nonlinear systems, namely second-order discrete Volterra systems. Two main contributions are made for this class of systems. At first, we show that - under a necessary and sufficient condition on the input data excitation - a data-based system representation can be derived from input-output data and used to replace an explicit system model. That is, the fundamental result of Willems et al.is extended to this class of systems. Subsequently a data-driven internal model control formula for output-tracking is derived. The approach is illustrated via two simulation examples Y1 - 2020 UR - https://www-docs.b-tu.de/fg-regelungssysteme/public/Publications/2020%20RuedaSchiffer%20Data-Driven%20Internal%20Model%20Control%20of%20Second-Order%20Discrete%20Volterra%20Systems.pdf ER - TY - GEN A1 - Rojas, Michael A1 - Rueda-Escobedo, Juan G. A1 - Espinosa-Pérez, Gerardo A1 - Schiffer, Johannes T1 - Observer-Based Excitation Control for Transient Stabilization of the Single Machine Infinite Bus System T2 - 59th IEEE Conference on Decision and Control (CDC), Jeju Island, Republic of Korea, Dec. 14-18, 2020 N2 - The availability of excitation controllers to enhance transient stability has regained significant relevance in recent years, due to the unprecedented ongoing changes in power systems. Yet, the practical deployment of many reported control schemes is hampered by the fact that their implementation requires the measurement of the full state vector. Our main contribution is to address this fundamental obstacle by proposing an observer-based excitation controller using modern phasor measurement technology. For this purpose, a linear time-varying observer scheme for the generator frequency and the internal voltage is derived. This observer is then combined with a classical passivity-based excitation controller. Stability of the resulting nonlinear observer-based closed-loop system is shown by deriving an ISS-based separation principle. The performance of the proposed approach is demonstrated via simulation example. Y1 - 2020 UR - https://www-docs.b-tu.de/fg-regelungssysteme/public/Publications/2020%20RojasRuedaEspinosaSchiffer%20Observer-Based%20Excitation%20Control%20for%20Transient%20Stabilization%20of%20the%20Single%20Machine%20Infinite%20Bus%20System.pdf ER - TY - GEN A1 - Lorenz-Meyer, Nicolai A1 - Bobtsov, Alexey A1 - Ortega, Romeo A1 - Nikolaev, Nikolay A1 - Schiffer, Johannes T1 - PMU-Based Decentralized Mixed Algebraic and Dynamic State Observation in Multi-Machine Power Systems T2 - IET Generation, Transmission & Distribution N2 - We propose a novel decentralized mixed algebraic and dynamic state observation method for multi-machine power systems with unknown inputs and equipped with Phasor Measurement Units (PMUs). More specifically, we prove that for the third-order flux-decay model of a synchronous generator, the local PMU measurements give enough information to reconstruct algebraically the load angle and the quadrature-axis internal voltage. Due to the algebraic structure a high numerical efficiency is achieved, which makes the method applicable to large scale power systems. Also, we prove that the relative shaft speed can be globally estimated combining a classical Immersion and Invariance (I&I) observer with—the recently introduced—dynamic regressor and mixing (DREM) parameter estimator. This adaptive observer ensures global convergence under weak excitation assumptions that are verified in applications. The proposed method does not require the measurement of exogenous inputs signals such as the field voltage and the mechanical torque nor the knowledge of mechanical subsystem parameters. Y1 - 2020 UR - https://ietresearch.onlinelibrary.wiley.com/doi/10.1049/iet-gtd.2020.1275 U6 - https://doi.org/10.1049/iet-gtd.2020.1275 SN - 1751-8695 SN - 1751-8687 VL - 14 IS - 25 SP - 6267 EP - 6275 ER - TY - GEN A1 - Metzkow, Renè A1 - Rueda-Escobedo, Juan G. A1 - Döring, Daniela A1 - Schiffer, Johannes T1 - An Internal Model Approach to Robust Current Control of IPMSM Drives with Respect to Unknown and Varying Inductances T1 - Ein interner Modellansatz zur robusten Stromregelung von IPMSM-Antrieben unter Berücksichtigung von unbekannten und variierenden Induktivitäten T2 - IFAC PapersOnLine N2 - Interior permanent magnet synchronous machines (IPMSMs) are well-suited for high-performance applications, such as traction drives in hybrid and electric vehicles. Yet a major challenge to fully exploit their potential is the fact that their self and cross-coupling inductances vary significantly across the operation range. In addition, this variation is difficult to characterize and complicates the design of provably stabilizing and robust controls. Motivated by this, by using an IPMSM model with current dependant inductances together with the internal model principle, a nonlinear current control scheme is derived that renders the equilibrium point of the closed-loop system exponentially stable. Both the control and the stability result only require the knowledge of an upper bound of the gradient of the inductances as well as lower and upper bounds on the inductance values themselves, while their actual evolution can be completely unknown. This is a major advantage compared to existing (PI-based) current control approaches, as it makes costly practices to determine the inductance variations unnecessary. The efficacy of the proposed control scheme is demonstrated in a simulation example. Y1 - 2020 UR - https://www.sciencedirect.com/science/article/pii/S2405896320314154 U6 - https://doi.org/10.1016/j.ifacol.2020.12.1046 SN - 2405-8963 VL - 53 IS - 2 SP - 14185 EP - 14191 ER - TY - GEN A1 - Bai, Handong A1 - Zhang, Hongwai A1 - Cai, He A1 - Schiffer, Johannes T1 - Voltage regulation and current sharing for multi-bus DC microgrids: A compromised design approach T2 - Automatica N2 - It is well known that accurate current sharing and voltage regulation are both important, yet conflicting control objectives in multi-bus DC microgrids. In this paper a distributed control scheme is proposed, which simultaneously considers these two control objectives via a trade-off factor. This factor permits to adjust the degree of compromise between accurate voltage regulation and current sharing. At the same time, the voltage of a critical node can be precisely regulated. A sufficient condition for closed-loop stability is given and it is shown that the control parameters can always be chosen, such that stability is guaranteed. In addition, the steady state voltage and current deviations relative to their rated values are quantified via suitable metrics. For a given topology and settings of a DC microgrid, a sufficient condition for the existence of the trade-off factor is provided. The results are illustrated by simulation examples. Y1 - 2022 UR - https://www.sciencedirect.com/science/article/pii/S0005109822001893 U6 - https://doi.org/10.1016/j.automatica.2022.110340 SN - 0005-1098 VL - 142 ER - TY - GEN A1 - Bobtsov, Alexey A1 - Ortega, Romeo A1 - Nikolaev, Nikolay A1 - Lorenz-Meyer, Nicolai A1 - Schiffer, Johannes T1 - State Observation of Power Systems Equipped with Phasor Measurement Units: The Case of Fourth Order Flux-Decay Model T2 - IEEE Transactions on Automatic Control N2 - The problem of effective use of phasor measurement units (PMUs) to enhance power systems awareness and security is a topic of key interest. The central question to solve is how to use these new measurements to reconstruct the state of the system. In this article, we provide the first solution to the problem of (globally convergent) state estimation of multimachine power systems equipped with PMUs and described by the fourth-order flux-decay model. This article is a significant extension of our previous result, where this problem was solved for the simpler third-order model, for which it is possible to recover algebraically part of the unknown state. Unfortunately, this property is lost in the more accurate fourth-order model, and we are confronted with the problem of estimating the full state vector. The design of the observer relies on two recent developments proposed by the authors, a parameter estimation based approach to the problem of state estimation and the use of the dynamic regressor extension and mixing (DREM) technique to estimate these parameters. The use of DREM allows us to overcome the problem of lack of persistent excitation that stymies the application of standard parameter estimation designs. Simulation results illustrate the latter fact and show the improved performance of the proposed observer with respect to a locally stable gradient-descent-based observer. Y1 - 2022 UR - https://doi.org/10.1109/TAC.2021.3073887 U6 - https://doi.org/10.1109/TAC.2021.3073887 SN - 0018-9286 SN - 1558-2523 VL - 67 IS - 4 SP - 2123 EP - 2130 ER - TY - GEN A1 - Ortega, Romeo A1 - Bobtsov, Alexey A1 - Nikolaev, Nikolay A1 - Schiffer, Johannes A1 - Dochain, Denis T1 - Generalized parameter estimation-based observers: Application to power systems and chemical–biological reactors T2 - Automatica N2 - In this paper we propose a new state observer design technique for nonlinear systems. It consists of an extension of the recently introduced parameter estimation-based observer, which is applicable for systems verifying a particular algebraic constraint. In contrast to the previous observer, the new one avoids the need of implementing an open loop integration that may stymie its practical application. We give two versions of this observer, one that ensures asymptotic convergence and the second one that achieves convergence in finite time. In both cases, the required excitation conditions are strictly weaker than the classical persistent of excitation assumption. It is shown that the proposed technique is applicable to the practically important examples of multimachine power systems and chemical–biological reactors. KW - Estimation parameters KW - Nonlinear systems KW - Observers KW - Time-invariant systems KW - Power systems Y1 - 2021 UR - https://www.sciencedirect.com/science/article/pii/S0005109821001552?via%3Dihub#! U6 - https://doi.org/10.1016/j.automatica.2021.109635 SN - 0005-1098 IS - 129 ER - TY - GEN A1 - Rueda-Escobedo, Juan G. A1 - Fridman, Emilia A1 - Schiffer, Johannes T1 - Data-Driven Control for Linear Discrete-Time Delay Systems T2 - IEEE Transactions on Automatic Control N2 - The increasing ease of obtaining and processing data together with the growth in system complexity has sparked the interest in moving from conventional model-based control design toward data-driven concepts. Since in many engineering applications time delays naturally arise and are often a source of instability, we contribute to the data-driven control field by introducing data-based formulas for state feedback control design in linear discrete-time time-delay systems with uncertain delays. With the proposed approach, the problems of system stabilization as well as of guaranteed cost and H∞ control design are treated in a unified manner. Extensions to determine the system delays and to ensure robustness in the event of noisy data are also provided KW - Data-driven control KW - delay systems KW - robust control KW - sampled data control Y1 - 2022 UR - https://ieeexplore.ieee.org/document/9484756 U6 - https://doi.org/10.1109/TAC.2021.3096896 SN - 1558-2523 VL - 67 IS - 7 SP - 3321 EP - 3336 ER - TY - GEN A1 - Krishna, Ajay A1 - Schiffer, Johannes T1 - A Port-Hamiltonian Approach to Modeling and Control of an Electro-Thermal Microgrid T2 - IFAC-PapersOnLine N2 - We address the problems of modeling and controlling multi-energy microgrids (meMGs) composed of an electrical and a thermal system, which are connected via heat pumps (HPs). At first, we model the individual subsystems in a port-Hamiltonian (pH) framework. Then, by exploiting the structural properties of pH systems, we interconnect the subsystems in a passive manner and show that the overall meMG is shifted passive with respect to the control input-output mapping. We then use this property to propose a distributed passivity based-control (PBC) that addresses frequency and temperature regulation by utilizing the resources in the meMG in a proportional fashion and renders the closed-loop equilibrium asymptotically stable. KW - Passivity-based control KW - port-Hamiltonian systems KW - multi-energy microgrid KW - district heating systems KW - distributed control Y1 - 2021 UR - https://www.sciencedirect.com/science/article/pii/S2405896321021169 U6 - https://doi.org/10.1016/j.ifacol.2021.11.092 SN - 2405-8963 VL - 54 IS - 19 SP - 287 EP - 293 ER - TY - GEN A1 - Rueda-Escobedo, Juan G. A1 - Moreno, Jaime A. A1 - Schiffer, Johannes T1 - L2-Gain Tuning for the Gradient Descent Algorithm in the Presence of Disturbances T2 - 2022 European Control Conference (ECC) N2 - Due to its simplicity and inexpensive computation, the gradient descent algorithm is one of the most used tools in adaptive control and system identification. Although it has been studied for decades, little has been achieved in terms of tuning methods in the presence of disturbances. One of the main difficulties in its analysis is the time-varying nature of the algorithm. In this work, we contribute in such direction by providing LMI tools for tuning the gradient descent algorithm gain such that a guaranteed upper bound on the L2 -gain with respect to parameter variations and measurement noise is achieved. Two academic examples are provided to illustrate the efficient application of the method. KW - Upper bound KW - Gain measurement KW - Minimization KW - robustness KW - system identification KW - noise measurement Y1 - 2022 UR - https://ieeexplore.ieee.org/document/9838051 SN - 978-3-9071-4407-7 U6 - https://doi.org/10.23919/ECC55457.2022.9838051 SP - 1610 EP - 1616 PB - IEEE CY - Piscataway ER - TY - GEN A1 - Jaramillo-Cajica, Ismael A1 - Schiffer, Johannes T1 - A Dwell-Time Approach for Grid-Aware Operation of a Distributed Generator in an Islanded DC Microgrid T2 - 2022 European Control Conference (ECC) N2 - We propose a switched control law for a DC-DC Buck converter that enables a grid-aware operation of a distributed generator (DG) in a low-voltage islanded DC microgrid (MG). The qualifier grid-aware means that the DG adjusts its operation mode in dependency of the MG status. The resulting closed-loop system is a switched system, in which the subsystems possess different equilibrium points. By means of a time- and state-dependent switching logic together with dwell-time stability analysis methods, we derive sufficient stability criteria that ensure the existence of a unique and globally exponentially stable equilibrium point of the resulting closed-loop switched system. The performance of the proposed control is illustrated via a numerical example. KW - Switched systems KW - Low voltage KW - Buck converters KW - Stability criteria KW - Switches KW - Microgrids Y1 - 2022 UR - https://ieeexplore.ieee.org/document/9838354 SN - 978-3-9071-4407-7 U6 - https://doi.org/10.23919/ECC55457.2022.9838354 SP - 1079 EP - 1084 PB - IEEE CY - Piscataway ER - TY - GEN A1 - Mendoza-Avila, Jesus A1 - Efimov, Denis A1 - Mercado-Uribe, Angel A1 - Schiffer, Johannes T1 - On Relaxed Conditions of Integral ISS for Multistable Periodic Systems T2 - Proceedings of the 2021 61st IEEE Conference on Decision and Control (CDC) N2 - A novel characterization of the integral Inputto- State Stability (iISS) property is introduced for multistable systems whose dynamics are periodic with respect to a part of the state. First, the concepts of iISS-Leonov functions and output smooth dissipativity are introduced, then their equivalence to the properties of bounded-energy-bounded-state and global attractiveness of solutions in the absence of disturbances are proven. The proposed approach permits to relax the usual requirements of positive definiteness and periodicity of the iISSLyapunov functions. Moreover, the usefulness of the theoretical results is illustrated by a robustness analysis of a nonlinear pendulum with a constant bias input and an unbounded statedependent input coefficient. Y1 - 2022 UR - https://hal.archives-ouvertes.fr/hal-03778051/ ER - TY - GEN A1 - Rueda-Escobedo, Juan G. A1 - Moreno, Jaime A. A1 - Schiffer, Johannes T1 - Design and Tuning of the Super-Twisting-Based Synchronous Reference Frame Phase-Locked-Loop T2 - 2022 IEEE 61st Conference on Decision and Control (CDC) ; December 6-9, 2022, Cancun, Mexico N2 - The worldwide transition to climate-friendly energy systems entails the substitution of conventional energy generation based on synchronous generators by renewable energy sources based on power electronics. As a consequence, the overall inertia of the grid decreases, resulting in high volatility of the frequency and posing new challenges for the estimation of the latter quantity. To address this problematic, in the present paper a phase-locked-loop (PLL) based on the super-twisting algorithm is considered for the estimation of the phase angle and time-varying frequency of a symmetric three-phase signal. A rigorous proof of the algorithm’s exact convergence in the presence of a fast-varying frequency together with tuning rules for its gains are derived by means of Lyapunov theory. Additionally, an estimate of the region of attraction is provided. The effectiveness of the proposed tuning method is illustrated in numerical simulations, while comparing its performance against a standard synchronous reference frame PLL. Y1 - 2022 UR - https://css.paperplaza.net/conferences/conferences/CDC22/program/CDC22_ContentListWeb_3.html ER - TY - GEN A1 - Syed, Wasif H. A1 - Machado, Juan E. A1 - Schiffer, Johannes T1 - Distributed Adaptive Control for a DC Power Distribution System of a Series-Hybrid-Electric Propulsion System of a Commuter Aircraft T2 - 2024 American Control Conference (ACC) Y1 - 2024 U6 - https://doi.org/10.23919/ACC60939.2024.10644618 SP - 2598 EP - 2603 PB - IEEE ER - TY - GEN A1 - Rueda-Escobedo, Juan G. A1 - Metzkow, René A1 - Schiffer, Johannes T1 - Robust current control of IPMSM drives under uncertain and varying inductances T2 - Automatica N2 - Interior permanent magnet synchronous machines (IPMSMs) are gaining popularity in e-mobility applications due to their wide constant power speed range when compared with other electric motors. The high-performance of IPMSMs is due to the pronounced degree of magnetic saliency, which originates from embedding their magnets inside the rotor. Yet, this feature complicates their control since it increases nonlinear phenomena such as cross-magnetization and saturation. This results in pronounced variations of the machine inductances, which are highly dependent on the machine current. This behaviour is of particular relevance in e-mobility applications, where a highly dynamic operation of the machine is required. In contrast to most existing current control approaches, where precise inductance knowledge is required, we address this challenge by deriving a controller that exploits the machine dynamics to achieve exponential current tracking in the presence of unknown and varying inductances. By interpreting the flux linkage as a modelled disturbance, we propose a dynamic compensator based on the internal model principle. As a by-product, the method provides an estimate of the flux linkage. The gain in performance compared to the standard PI controller is illustrated in simulation. Y1 - 2023 U6 - https://doi.org/10.1016/j.automatica.2023.110998 SN - 0005-1098 VL - 152 ER - TY - GEN A1 - Schiffer, Johannes A1 - Efimov, Denis T1 - Strong and Weak Leonov Functions for Global Boundedness of State Periodic Systems T2 - IEEE Transactions on Automatic Control N2 - We present new results for the analysis of global boundedness of state periodic systems. Thereby, we address both the case of systems, whose dynamics is periodic with respect to a part of the state vector, and the case of systems, whose dynamics is periodic with respect to all state variables. To derive the results, the notion of strong Leonov functions is introduced. The main results are complemented by a number of relaxations based on the concept of weak Leonov functions. Y1 - 2023 U6 - https://doi.org/10.1109/TAC.2023.3251903 SN - 0018-9286 SN - 1558-2523 VL - 68 IS - 12 SP - 7958 EP - 7965 ER - TY - GEN A1 - Mercado-Uribe, Angel A1 - Mendoza-Ávila, Jesús A1 - Efimov, Denis A1 - Schiffer, Johannes T1 - A Leonov Function for Almost Global Synchronization Conditions in Acyclic Networks of Heterogeneous Kuramoto Oscillators T2 - IFAC-PapersOnLine N2 - Sufficient conditions for almost global synchronization in acyclic networks of Kuramoto oscillators with heterogeneous coupling strengths and natural frequencies are presented. The result is established by employing the recently developed Leonov function framework for systems whose dynamics are periodic for all state variables. The synchronization property is accompanied by necessary and sufficient conditions to guarantee the existence of equilibria. The implications of these conditions on the network topology, the oscillator's coupling strengths and natural frequencies are discussed. Finally, the results are illustrated via a numerical example. Y1 - 2023 U6 - https://doi.org/10.1016/j.ifacol.2023.10.248 SN - 2405-8963 VL - 56 IS - 2 SP - 9505 EP - 9510 ER - TY - GEN A1 - Mendoza-Avila, Jesus A1 - Mercado-Uribe, Angel A1 - Efimov, Denis A1 - Schiffer, Johannes T1 - Design of controls for ISS and Integral ISS Stabilization of Multistable State Periodic Systems T2 - IFAC-PapersOnLine Y1 - 2023 U6 - https://doi.org/https://doi.org/10.1016/j.ifacol.2023.10.936 VL - 56 IS - 2 SP - 4472 EP - 4477 ER - TY - GEN A1 - Würfel, Hans A1 - Lorenz-Meyer, Nicolai A1 - Schiffer, Johannes T1 - Experimentally Validated Reduced-Order Models for Grid-Connected Inverters Using Balanced Residualization T2 - 2023 8th IEEE Workshop on the Electronic Grid (eGRID), Karlsruhe, Germany, 16-18 October 2023 Y1 - 2023 SN - 979-8-3503-2700-7 U6 - https://doi.org/10.1109/eGrid58358.2023.10380931 CY - Karlsruhe ER - TY - GEN A1 - Gernandt, Hannes A1 - Krenzlin, Franziska A1 - Hagemann, Willem A1 - Schiffer, Johannes T1 - Data-based modeling for optimizing the operation of seasonal underground storages T2 - Der Geothermiekongress 2023 : 17.-19. Oktober 2023 in Essen : Tagungsband N2 - Underground thermal energy storages (UTES) are essential for decarbonizing the existing heating networks. To accurately simulate the storage and the connected heat supply system, typically detailed numerical models of the UTES and the heat supply system are required. In a co-simulation these models must be coupled, which is often time-consuming and has therefore not been used to operate systems in real-time. In this contribution, we present a method that leads to a data-based surrogate model of low complexity, which can then be directly integrated in the operational optimization. To illustrate the method, we derive a surrogate model from a Feflow model of a borehole thermal energy storage (BTES) as a particular type of UTES and integrate the surrogate model into a supply system that is optimized for electrical energy consumption using the Python toolbox Pyomo. Y1 - 2023 UR - https://www.der-geothermiekongress.de/tagungsbaende/tagungsband-2023 UR - https://www.der-geothermiekongress.de/Tagungsband2023/www.conftool.net/geothermiekongress2023/index.php/Gernandt-Datenbasierte_Modellierung_f%c3%bcr_den_optimalen_Systembetrieb_von_saisonalen_Untergrundspeichern-248_LongVersion30ee.pdf?page=downloadPaper&ismobile=false&filename=Gernandt-Datenbasierte_Modellierung_f%C3%BCr_den_optimalen_Systembetrieb_von_saisonalen_Untergrundspeichern-248_LongVersion.pdf&form_id=248&form_version=final CY - Essen ER - TY - GEN A1 - Zurita-Bustamante, Erik W. A1 - Rueda-Escobedo, Juan G. A1 - Schiffer, Johannes T1 - Passivity-Based Conditions for Asymptotic Stability of Speed Control for Three-Phase and Dual Three-Phase Permanent Magnet Synchronous Motors T2 - 62nd IEEE Conference on Decision and Control (CDC), 2023 Y1 - 2023 SN - 979-8-3503-0124-3 SN - 979-8-3503-0123-6 U6 - https://doi.org/10.1109/CDC49753.2023.10383817 SN - 2576-2370 ER - TY - GEN A1 - Mendoza-Avila, Jesus A1 - Efimov, Denis A1 - Mercado-Uribe, Angel A1 - Schiffer, Johannes T1 - Design of Controls for Boundedness of Trajectories of Multistable State Periodic Systems T2 - 62nd IEEE Conference on Decision and Control (CDC), 2023 Y1 - 2023 SN - 979-8-3503-0124-3 SN - 979-8-3503-0123-6 U6 - https://doi.org/10.1109/CDC49753.2023.10383528 SN - 2576-2370 ER - TY - GEN A1 - Mercado-Uribe, Angel A1 - Mendoza-Ávila, Jesús A1 - Efimov, Denis A1 - Schiffer, Johannes T1 - A Control Leonov Function Guaranteeing Global ISS of Two Coupled Synchronverters T2 - 62nd IEEE Conference on Decision and Control (CDC), 2023 Y1 - 2023 SN - 979-8-3503-0124-3 SN - 979-8-3503-0123-6 U6 - https://doi.org/10.1109/CDC49753.2023.10383811 SN - 2576-2370 ER - TY - GEN A1 - Jaramillo-Cajica, Ismael A1 - Mercado-Uribe, Angel A1 - Schiffer, Johannes T1 - Coordinated Control of Load Tap Changer Transformers for Voltage Regulation and Voltage Hunting Prevention: A Switched Systems Approach T2 - 62nd IEEE Conference on Decision and Control (CDC), 2023 Y1 - 2023 SN - 979-8-3503-0124-3 SN - 979-8-3503-0123-6 U6 - https://doi.org/10.1109/CDC49753.2023.10383763 SN - 2576-2370 ER - TY - GEN A1 - Mathew, Riya A1 - Rueda-Escobedo, Juan G. A1 - Schiffer, Johannes T1 - Robust Design of Phase-Locked Loops in Grid-Connected Power Converters T2 - European Journal of Control Y1 - 2024 U6 - https://doi.org/10.1016/j.ejcon.2024.101055 ET - Volume 80 ER - TY - GEN A1 - Lorenz-Meyer, Nicolai A1 - Würfel, Hans A1 - Schiffer, Johannes T1 - Consensus + Innovations approach for online distributed multi-area inertia estimation T2 - 2024 IEEE PES Innovative Smart Grid Technologies Europe (ISGT EUROPE) N2 - The reduction of overall system inertia in modern power systems due to the increasing deployment of distributed energy resources is generally recognized as a major issue for system stability. Consequently, real-time monitoring of system inertia is critical to ensure a reliable and cost-effective system operation. Large-scale power systems are typically managed by multiple transmission system operators, making it difficult to have a central entity with access to global measurement data, which is usually required for estimating the overall system inertia. We address this problem by proposing a fully distributed inertia estimation algorithm with rigorous analytical convergence guarantees. This method requires only peer-to-peer sharing of local parameter estimates between neighboring control areas, eliminating the need for a centralized collection of real-time measurements. We robustify the algorithm in the presence of typical power system disturbances and demonstrate its performance in simulations based on the well-known New England IEEE 39-bus system. Y1 - 2024 U6 - https://doi.org/10.1109/ISGTEUROPE62998.2024.10863379 SP - 1 EP - 6 PB - IEEE CY - New York ER - TY - GEN A1 - Mercado-Uribe, Angel A1 - Mendoza-Ávila, Jesús A1 - Efimov, Denis A1 - Schiffer, Johannes T1 - Sufficient conditions for global boundedness of solutions for two coupled synchronverters T2 - 2024 IEEE 63rd Conference on Decision and Control (CDC) N2 - This paper analyzes two synchronverters connected in parallel to a common capacitive-resistive load through resistive-inductive power lines. This system is conceptualized as a microgrid with two renewable energy sources controlled using the synchronverter algorithm. It is modeled as an interconnection of three port-Hamiltonian systems, and the dq-coordinates model is derived by averaging the frequencies. Applying the recent Leonov function theory, sufficient conditions to guarantee the global boundedness of the whole system’s trajectories are provided. This is necessary to reach the global synchronization of microgrids. Additionally, a numerical example illustrates the potential resonance behavior of the microgrid. Y1 - 2024 U6 - https://doi.org/10.1109/CDC56724.2024.10886006 SP - 2785 EP - 2790 PB - IEEE CY - New York ER - TY - BOOK A1 - Parisio, Alessandra A1 - Schiffer, Johannes A1 - Hans, Christian A. ED - Parisio, Alessandra ED - Schiffer, Johannes ED - Hans, Christian A. T1 - System level control and optimisation of microgrids N2 - Microgrids are essential components of next-generation energy grids. A microgrid is a local, integrated energy system comprising interconnected loads and distributed energy resources; they can represent urban or rural districts, islands or local communities. Microgrids can operate in parallel with the main grid or independently in an intentional island mode. When on-site generation is included, intelligent buildings can also function as microgrids. Efficient optimization and control algorithms are crucial for ensuring optimal microgrid performance, making them a continuous focus of research and development in the field of power systems. The next-generation energy grid and urban environment need to be smart and sustainable to deal with the growing energy demand and achieve environmental goals. In this context, the role of local energy systems at the distribution level, which can represent urban or rural districts, islands or local communities, is crucial. System Level Control and Optimisation of Microgrids offers a comprehensive and systematic review of developments in this field. The chapters cover topics such as modelling of integrated energy systems and district heating systems, dynamics and control of grid-connected microgrids, frequency regulation, distributed optimization for energy grids, integration of distributed energy resources, transactive energy management for multi-energy microgrids, and laboratory validation. Real-world examples are provided through case studies based on the EUREF Energy Workshop and fog computing-based decentralized energy management. This book presents a wide range of perspectives from academia and industry on the challenges and solutions in microgrid optimization and control. It serves as a thorough resource for engineers and academics in the control and power systems fields, as well as for graduate students in related disciplines. Advanced control and optimization techniques for microgrids are discussed in depth, with examples and case studies demonstrating their practical application in shaping the future of energy systems. Y1 - 2024 SN - 9781785618758 U6 - https://doi.org/10.1049/PBPO149E PB - The Institution of Engineering and Technology CY - London ER - TY - GEN A1 - Krenzlin, Franziska A1 - Hagemann, Willem A1 - Gernandt, Hannes A1 - Schiffer, Johannes T1 - Data-driven modeling of borehole thermal energy storage (BTES) for operational optimization of renewable heat production systems T2 - 37th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems (ECOS 2024) N2 - The utilization of underground thermal energy storage (UTES) systems, such as borehole thermal energy storage (BTES) systems plays a crucial role in the decarbonization of district heating. To ensure high performance and operation efficiency under the condition of a robust system operation, heat supply systems require advanced control and operation strategies including the operation of the thermal storage systems. The focus of our operational optimization lies on the heat production side, comprising a BTES and diverse heat sources, buffer storage systems and heat pumps. We utilize a nonlinear model of the heating network that explicitly integrates mass flows and temperatures instead of solely relying on heat flow considerations. The advantage of this more detailed consideration is that realistic constraints on temperatures and mass flows can be easily incorporated into the model. A major challenge in such realistic modeling is the correct representation of the temperature dynamics of thermal storage components, especially when the storage parameters are unknown and only limited input-output data are available. In this work, we propose a novel method leading to a reduced surrogate model of the BTES temperature dynamics that can be directly included in the optimization or control algorithms. The resulting data-based surrogate model captures the fundamental dynamics while being deployable to operational optimization and system control algorithms. In particular, we employ a Python-based operational optimization process of a theoretical system setup using Pyomo. In conclusion, the presented storage modeling approach is a first step towards a broad variety of system configurations including different UTES types. Y1 - 2024 U6 - https://doi.org/10.52202/077185-0157 SP - 1831 EP - 1841 PB - ECOS 2024 CY - Zografos, Greece ER - TY - GEN A1 - Mercado-Uribe, Angel A1 - Mendoza-Avila, Jesus A1 - Efimov, Denis A1 - Schiffer, Johannes T1 - Conditions for global synchronization in networks of heterogeneous Kuramoto oscillators T2 - Automatica N2 - The Kuramoto model is essential for studying synchronization. In this work, we present sufficient conditions for global synchronization in networks of heterogeneous Kuramoto oscillators in the absence of homoclinic and heteroclinic cycles. The result is established by constructing a suitable Leonov function candidate for the Kuramoto model, which provides sufficient conditions for almost global synchronization in networks with acyclic and meshed topologies. The synchronization property is accompanied by necessary and sufficient conditions to guarantee the existence of equilibria, which are satisfied if the conditions for synchronization hold. The implications of the main conditions and their relationship with the network topology and parameters are discussed. Finally, the results are illustrated via a numerical example. Y1 - 2025 U6 - https://doi.org/10.1016/j.automatica.2025.112180 SN - 0005-1098 VL - 175 SP - 1 EP - 11 PB - Elsevier BV CY - Amsterdam ER - TY - CHAP A1 - Schiffer, Johannes A1 - Simpson-Porco, John W. A1 - Parisio, Alessandra T1 - Control in Low-Inertia Power and Integrated Energy Systems T2 - Reference Module in Materials Science and Materials Engineering N2 - Driven by global efforts to mitigate the climate crisis, power systems are undergoing unprecedented changes. An important factor in this energy transition is the replacement of large-scale conventional fossil fuel-driven synchronous generators by renewable-driven inverter-based generation. This substitution entails a large reduction of the overall power system inertia, leading to faster and more volatile dynamics. Such power systems are therefore termed low-inertia power systems. In the present chapter, key properties and aspects for modeling, control and operation of this kind of future power systems are introduced, with a focus on automatic frequency control, dynamic state estimation and grid-synchronization of inverter-based resources. As moving beyond decarbonization of only the electricity sector is viewed as essential for the successful development of climate-neutral societies, the exposition is complemented by identifying current trends in integrated energy systems. These novel energy system architectures are characterized by integration of diverse energy vectors, such as electricity, heat, transportation, and (hydrogen) gas, in a holistic manner. Overall, the chapter places a control-theoretic lens on these societal-scale sustainability challenges. Y1 - 2024 SN - 9780128035818 U6 - https://doi.org/10.1016/B978-0-443-14081-5.00068-4 N1 - Kostenpflichtiger Zugang. PB - Elsevier ER - TY - GEN A1 - Jaramillo-Cajica, Ismael A1 - Schiffer, Johannes T1 - A dwell-time approach for decentralized grid-aware operation of islanded DC microgrids T2 - Automatica N2 - In islanded microgrid (MG) applications, renewable-based distributed generation units (DGUs) are commonly operated in grid-feeding mode, while storage-based DGUs assume the grid-forming responsibilities. This results in limited controllable power reserves, which may pose severe threats to the overall system stability. Motivated by this, we consider the problem of designing a more flexible grid-aware control scheme for enlarging the actuation power of a DC MG. That is, existing DGUs are able to adopt different operation modes by switching among two decentralized passivity-based subsystem control laws in dependency of their node status. To this purpose, we design a time- and state-dependent switching logic that coordinates the DGU mode transitions and ensures that the closed-loop interconnected MG possesses a unique equilibrium point. Then, we derive sufficient tuning conditions on the control parameters that ensure global exponential stability of this equilibrium by adopting a multiple Lyapunov functions approach that exploits the passive interconnection properties of the MG together with dwell-time methods for switched systems. The advantageous performance of the proposed strategy is illustrated via a numerical example. Y1 - 2024 U6 - https://doi.org/10.1016/j.automatica.2023.111461 SN - 0005-1098 VL - 160 SP - 1 EP - 11 PB - Elsevier BV ER - TY - GEN A1 - Reimann, Ansgar A1 - Rose, Max A1 - Küpper, Jan A1 - Schiffer, Johannes T1 - Nonlinear system identification and predictive control for waste heat recovery with heat pumps T2 - IFAC-PapersOnLine N2 - The utilization of low-temperature waste heat, particularly from electrolyzers, in district heating networks via heat pumps presents a promising approach to accelerate the decarbonization of the heat sector. However, managing the electrolyzer’s specific temperature requirements and dynamic waste heat output, while simultaneously meeting the district heating network’s variable temperature demands, requires the implementation of an advanced control system for the heat pump cycle. For this, model predictive control is a promising approach since it not only ensures the satisfaction of constraints, but also facilitates a direct optimization of the heat pump’s operational efficiency. Nevertheless, model predictive control requires a dynamic heat pump model. In this context, first-principles models are often used. However, they are very complex and difficult to parameterize for real heat pumps. Therefore, in the present paper, a data-based system identification is carried out to obtain a reduced-order heat pump model from a high-fidelity first-principles simulation model. Based on the identified model, a predictive controller is implemented. The effectiveness of the obtained controller for operating the first-principles model is demonstrated in a numerical case study. Y1 - 2024 U6 - https://doi.org/10.1016/j.ifacol.2024.07.103 SN - 2405-8963 VL - 58 IS - 2 SP - 130 EP - 135 PB - Elsevier BV ER - TY - GEN A1 - Herrmann, Ulrike A1 - Plietzsch, Anton A1 - Rose, Max A1 - Gernandt, Hannes A1 - Schiffer, Johannes T1 - A predictive operation management scheme for hydrogen networks based on the method of characteristics T2 - 2024 European Control Conference (ECC) N2 - As future hydrogen networks will be strongly linked to the electricity system via electrolysers and hydrogen power plants, challenges will arise for their operation. A suitable response to phenomena, such as rapidly changing boundary conditions and unbalanced supply and demand, requires the implementation of operational concepts based on transient pipe models. The transient pipe flow can be described by the isothermal Euler equations, which we discretize using an explicit Method Of Characteristics. Based on this, we develop a nonlinear space-time discretized network model that incorporates various other components, including hydrogen storage facilities, active elements such as valves and compressor stations, as well as electrolyzers and fuel cells. This network model serves as the foundation for the development of a tailored economic model predictive control algorithm designed for fast timescales. The algorithm enables controlled pressure changes within specified bounds in response to changes in supply and demand while simultaneously minimizing fast pressure fluctuations in the pipelines. Through a detailed case study, we demonstrate the algorithm's proficiency in addressing these transient operation challenges. Y1 - 2024 U6 - https://doi.org/10.23919/ECC64448.2024.10591107 SP - 1084 EP - 1089 PB - IEEE ER -