@article{schmidtke2023resilience, abstract = {System performance of distributed control systems and networked computing systems is strongly dependent of the underlying communication topology. This paper considers the rarely studied problem of how the topology can maintain resilience by reconfiguration in case that agents leave or join the network during online operation. Existing optimization-based approaches which reconfigure the entire network can typically not be used in this case, since the computational burden for online application is too high. Thus, this paper proposes a novel combined offline-online scheme which optimizes the topology for high convergence rate (of e.g. consensus problems) while providing guarantees for the robustness against agent failures. In the offline part, an optimization of the entire topology is carried out using novel constraints to prepare resilience of the online procedure. For the latter, the proposed scheme guarantees that robustness is maintained for joining agents and if a specified number of agents leave the network. In simulation, the proposed scheme is compared to existing approaches and the advantages of the online-offline procedure are demonstrated.}, author = {Schmidtke, V. and Liu, Z. and Stursberg, O.}, interhash = {0abe187591fec2338fcd8444f871f26b}, intrahash = {bc27d938e96e278f41adfc2c8380395f}, journal = {62nd IEEE Conference on Decision and Control}, pages = {3474-3479}, title = {Resilience of Time-Varying Communication Graphs for Consensus of Changing Sets of Computing Agents}, url = {https://css.paperplaza.net/images/temp/CDC/files/1515.pdf}, year = 2023 } @article{mast2023unified, abstract = {This letter introduces a novel method to address communication delay and communication frequency in distributed state estimation using a unified structure. Starting from a general type of delay, which can be time-varying, unknown, and different for each channel, two estimation strategies are proposed which use either a unified upper-bound of the delay in all channels, or a sender specific upper-bound in order to improve the performance. The strategies guarantee convergence of the estimation error, and they can be applied to study how communication frequency (or asynchronous communication) affects the convergence rate of the estimation. Thus, the task of determining a necessary communication frequency for obtaining specified performance of distributed estimation is considered, and this task is approached as a special case of the one tailored to delay. Effectiveness of the techniques is confirmed by numerical examples for both types of tasks.}, author = {Mast, J. and Liu, Z. and Wang, Z. and Stursberg, O.}, doi = {10.1109/LCSYS.2023.3289436}, interhash = {f816b1a861633a81056194bb4ec02e25}, intrahash = {7e0a204513f7487c07524a24a8538699}, journal = {IEEE Control Systems Letters}, pages = {2755-2760}, title = {A Unified Approach to Communication Delay and Communication Frequency in Distributed State Estimation of Linear Systems}, url = {https://ieeexplore.ieee.org/document/10163931}, volume = {Volume 7}, year = 2023 } @article{schmidtke2023model, abstract = {Processes of additive manufacturing by 3D-printing are typically operated by only using constant references for feed motion and laser power. For adapting properties of workpieces to desired geometries, the control towards changing reference signals is an enabling factor, though. With a focus on temperature control, this paper proposes a scheme of model predictive control for 3D-printing with consideration of constraints and arbitrary references. Starting from partial differential equations to model heat propagation over the geometry, prediction models and optimization problems are formulated as a local part of a more detailed simulation model of the complete workpiece. For laser velocity and power as manipulated variables, optimization problems involving integer variables are solved. Simulation results show how spatial temperature profiles can be adjusted by the proposed approach.}, author = {Schmidtke, V. and Rüger, M. and Stursberg, O.}, interhash = {658f10dec823a4cb915d001250144032}, intrahash = {c6ba819c84bd01ac43debe3b41a6bb4c}, journal = {Proc. of the 2023 European Control Conference}, pages = {496-501}, title = {Model Predictive Control of PDEs for Temperature Control in 3D-Printing Processes.}, year = 2023 } @article{nils2023design, abstract = {In the context of studying periodic processes, this paper investigates first under which conditions switching affine systems in the plane generate stable limit cycles. Based on these conditions, a design methodology is proposed by which the phase portraits of the switching systems are determined to obtain globally stable limit cycles from simple specifications, such as given amplitudes and frequencies of desired oscillations. As an application, the paper finally shows that an oscillator model can be derived with a small effort from data measured for an unknown oscillating system.}, author = {Hanke, N. and Stursberg, O.}, interhash = {b0002ee0dc7915c0c83e73daf93efbe5}, intrahash = {f27c450409a949e0162b4f716bcb8daf}, journal = {Proc. of the 2023 European Control Conference}, pages = {2251-2256}, title = {On the Design of Limit Cycles of Planar Switching Affine Systems.}, url = {https://www.researchgate.net/publication/369623446_On_the_Design_of_Limit_Cycles_of_Planar_Switching_Affine_Systems}, year = 2023 } @article{markolf2023dnnapproximations, abstract = {This work focuses on deep artificial feed-forward neural networks as parametric function approximators in optimal control of discrete-time nonlinear but affine-in-control systems subject to polytopic constraints on the continuous states and control inputs. The neural networks are either considered as approximators of optimal control laws or as approximators of the corresponding cost functions. In both cases, an approach is developed for determining the approximated optimal control inputs without violating the constraints. A simple approximate policy iteration algorithm exploiting both approaches is finally presented and illustrated for a numerical example.}, author = {Markolf, L. and Stursberg, O.}, doi = {https://doi.org/10.1016/j.ifacol.2023.10.1847}, interhash = {40afba055d6501778d4623935307c810}, intrahash = {0cee2eecb50fa6092733f62495d05bbd}, journal = {Proc. of the 22nd IFAC World Congress}, pages = {1516-1521}, title = {DNN-Approximations of Control Laws for Nonlinear Systems with Polytopic Constraints.}, year = 2023 } @article{markolf2023tailored, abstract = {This work considers the synthesis of state feedback controllers established as deep artificial feed-forward neural networks for the control of discrete-time nonlinear but input-affine systems. The idea is to design output layers of particular structure to guarantee the satisfaction of state constraints in form of control-invariant ellipsoids. Since an analytical expression can be derived for the resulting neural network controller, the latter can be stored and evaluated efficiently. Moreover, the proposed output layer guarantees the satisfaction of the considered state constraints for each specification of the parameter vector. Numerical examples are provided for illustration and evaluation of the approach, in which the approximation of a nonlinear model predictive control law is considered as application.}, author = {Markolf, L. and Stursberg, O.}, doi = {https://doi.org/10.23919/ACC55779.2023.10156344}, interhash = {6685ae9192053ea3c4d62090da11864f}, intrahash = {532f519a9f08a43ebd6bc977b570681a}, journal = {Proceedings of the 2023 Annual American Control Conference (ACC)}, pages = {1881-1888}, title = {Tailored Output Layers of Neural Networks for Satisfaction of State Constraints in Nonlinear Control Systems}, year = 2023 } @article{wang2023distributed, abstract = {This paper proposes a two-step distributed interval estimation method for continuous-time linear time-invariant (LTI) systems subject to unknown but bounded disturbance and measurement noise. First, a network of local observers is designed to obtain point-wise estimation. Second, interval estimation is obtained based on the point-wise estimation and peak-to-peak analysis. The conditions of the observer design and the peak-to-peak analysis are formulated as linear matrix inequalities, which can be solved efficiently. Compared with the distributed interval observers designed using the monotone system theory, the proposed method has less restrictive design conditions and hence broader application scopes. Moreover, the parameter matrices in the proposed method can be optimized to obtain tight interval estimation. A numerical simulation is given to illustrate the performance of the proposed method.}, author = {Wang, Z. and Zhang, J. and Liu, Z. and Han, W. and Shen, M.}, doi = {https://doi.org/10.1016/j.ifacol.2023.10.1139}, interhash = {f6fb551cb2f60cfe76c8ce178ac4155e}, intrahash = {b20bdb6717492430c621ce150ebdecae}, journal = {Proc. of the 22nd IFAC World Congress}, number = {Issue 2}, pages = {8500-8505}, title = {Distributed Interval Estimation for Continuous-Time Linear Systems: A Two-Step Method.}, url = {https://www.sciencedirect.com/science/article/pii/S2405896323015422}, volume = {Volume 56}, year = 2023 } @article{trummel2023optimal, abstract = {This paper proposes a novel method to achieve and preserve synchronization for a set of connected heterogeneous Van der Pol oscillators. Unlike the state-of-the-art synchronization methods, in which a large coupling gain is applied to couple any pair of connected oscillators, the proposed method first casts the whole synchronization process into two phases. The first one considers the period from the beginning to the first instant of synchronization, while the second phase covers the following time in which synchronization must be preserved. It is shown that a large coupling gain is adopted for the first phase, while the averaged coupling gain to preserve the synchronization in the second phase can be reduced significantly by using an offline optimized coupling law. Efficiency and performance of this method are confirmed by a set of numerical tests with different graphs and system dynamics.}, author = {Trummel, T. and Liu, Z. and Stursberg, O.}, interhash = {defce06ba08637d912d3dc38b394bf1d}, intrahash = {703b06b751b1a76901ab8df97f9b9efc}, journal = {IFAC-PapersOnLine}, number = {Issue 2}, pages = {9475-9480}, title = {On Optimal Synchronization of Diffusively Coupled Heterogeneous Van Der Pol Oscillators}, url = {https://www.researchgate.net/publication/369592584_On_Optimal_Synchronization_of_Diffusively_Coupled_Heterogeneous_Van_der_Pol_Oscillators}, volume = {Volume 56}, year = 2023 } @article{flus2023distributed, abstract = {This paper proposes a method to control a class of multi-agent systems with uncertainties modeled as stochastic processes with arbitrary probability distributions. The considered control problem is to lead a formation of agents through a space which is partially obstructed by obstacles. The proposed solution is to use a hierarchically structured approach of distributed stochastic model predictive control (DSMPC). The approach combines elements of formation reference structures, leader-follower concepts, and successive convexification (SC) for collision avoidance. To consider the stochastic uncertainties, over-approximated probabilistic reachable sets (PRS) are computed based on Chebyshev's inequality. The nominal (expected) agent behavior is optimized within the DSMPC such that (probabilistic) constraints are satisfied in a distributed way. For the overall approach, closed-loop stability of the distributed control concept is investigated and an illustrating example is provided.}, author = {Flüs, P. and Stursberg, O.}, doi = {https://doi.org/10.1016/j.ifacol.2023.10.890}, interhash = {62aa14ef15ed5d70f97cc177c44c8cac}, intrahash = {2cd0138f1a4936e5143c16df439c6588}, journal = {Proc. of the 22nd IFAC World Congress}, number = {Issue 2}, pages = {10155-10161}, title = {Distributed MPC of Uncertain Multi-Agent Systems Considering Formations and Obstacles}, url = {https://www.sciencedirect.com/science/article/pii/S2405896323012715}, volume = {Volume 56}, year = 2023 } @article{hahn2023reference, abstract = {This paper addresses model predictive control of a class of linear systems subject to additive stochastic disturbances and constraints. The underlying stochastic optimal control problem combines inverse cumulative distribution functions with ellipsoid-in-polyhedron formulations to reduce the conservatism induced by constraint satisfaction. By use of terminal constraints and time-varying weights within the cost functional, the presented control scheme satisfies criteria for mean-square stability and can be adapted to reference-tracking problems for arbitrary reference signals.}, author = {Hahn, J. and Stursberg, O.}, doi = {https://doi.org/10.1016/j.ifacol.2023.10.1057}, interhash = {593a63dbd657431e96daf77e254c3fab}, intrahash = {85b51c4012a40e108c91329908c89917}, journal = {Proc. of the 22nd IFAC World Congress}, number = 2, pages = {10421-10427}, title = {Reference Tracking for Constrained Uncertain Linear Systems by Stochastic MPC}, url = {https://www.sciencedirect.com/science/article/pii/S2405896323014593}, volume = 56, year = 2023 } @article{liu2023modelbased, abstract = {This paper aims at applying optimal control principles to investigate optimal vaccination strategies in different phases of a pandemic. Background of the study is that many countries have started their vaccination procedures against the COVID-19 disease in the beginning of 2021, but supply shortages for the vaccines prevented that everyone could be vaccinated immediately. At the beginning of 2022, in contrast, the vaccine supply was ample, but the effectiveness of different existing vaccines to avoid infection by new virus variants was in doubt, as well as the acceptance of booster doses decreased over time. To account for these effects, two formulations of optimization tasks based on different epidemic models are proposed in this paper. The solution of these tasks determines optimal distribution strategies for available vaccines, and optimized vaccination schemes to reduce the need of booster doses for later phase. Effectiveness of these strategies compared with other popular strategies (as applied in practice) is demonstrated through a series of simulations.}, author = {Liu, Z. and Omayrat, M. and Stursberg, O.}, doi = {https://doi.org/10.1007/978-3-031-26474-0_10}, interhash = {64379a5dc8b3aa7f0676017a4bdcd4e0}, intrahash = {1da828f875982b375525e3bdf6a0de98}, issn = {978-3-031-26473-3}, journal = {Informatics in Control, Automation and Robotics. ICINCO 2021. Lecture Notes in Electrical Engineering}, pages = {185–208}, title = {Model-Based Optimization of Vaccination Strategies in Different Phases of Pandemic Virus Spread}, url = {https://link.springer.com/chapter/10.1007/978-3-031-26474-0_10}, volume = 1006, year = 2023 } @article{markolf2022recedinghorizon, abstract = {This work studies receding-horizon control of discrete-time switched linear systems subject to polytopic constraints for the continuous states and inputs. The objective is to approximate the optimal receding-horizon control strategy for cases in which the online computation is intractable due to the necessity of solving mixed-integer quadratic programs in each discrete time instant. The proposed approach builds upon an approximated optimal finite-horizon control law in closed-loop form with guaranteed constraint satisfaction. The paper derives the properties of recursive feasibility and asymptotic stability for the proposed approach. A numerical example is provided for illustration and evaluation of the approach.}, author = {Markolf, Lukas and Stursberg, Olaf}, doi = {https://doi.org/10.1007/s42979-022-01442-0}, interhash = {7ca72057978a6df9f5d9212801dc9844}, intrahash = {3c78e858a562a35db3a3946a4b4927f8}, journal = {SN Computer Science}, number = 62, title = {Receding-Horizon Control of Constrained Switched Systems with Neural Networks as Parametric Function Approximators}, url = {https://link.springer.com/article/10.1007/s42979-022-01442-0#author-information}, volume = 4, year = 2022 } @article{HAHN2022276, abstract = {The paper addresses modeling, stability analysis, and control of a class of networked control systems, in which the communication network, and thus the probability for successful transmission of sensor data, varies over time. This variation is modeled probabilistically by Markov chains with time-varying transition probabilities. The offline synthesis of output feedback controllers for this system class is addressed with focus on criteria for mean square stability.}, author = {Hahn, Jannik and Stursberg, Olaf}, doi = {https://doi.org/10.1016/j.ifacol.2022.07.272}, interhash = {ac0b613875ab9a30e4cbbce3f47e27c4}, intrahash = {31d461ab25f5c0d364c353335cd1eca2}, issn = {2405-8963}, journal = {IFAC-PapersOnLine}, note = {9th IFAC Conference on Networked Systems NECSYS 2022}, number = 13, pages = {276-281}, title = {On Stability of Network Control Systems with Switching Transmission Probabilities}, url = {https://www.sciencedirect.com/science/article/pii/S2405896322006632}, volume = 55, year = 2022 } @article{liu2022mixedinteger, author = {Liu, Zonglin and Stursberg, Olaf}, interhash = {8054c7ab75ddce2643a68f64a053cb8b}, intrahash = {262c9fec0ca6ece862b38782e5b2e74d}, journal = {61st IEEE Conference on Decision and Control (CDC)}, title = {Distributed Solution of Mixed-Integer Programs by ADMM with Closed Duality Gap}, year = 2022 } @article{liu2022efficient, abstract = {This letter considers a class of fault detection problems for discrete-time piecewise-affine (PWA) systems. Inspired by the state-of-the-art of set-membership methods to estimate the state of PWA systems, a novel detection method based on zonotopes and over-approximation of sets is proposed to overcome high computational complexity caused by unknown discrete states. The efficiency and high accuracy of detection of the new method is confirmed through both theoretical analysis and numerical examples.}, author = {Liu, Xinyang and Liu, Zonglin and Wang, Zhenhua and Stursberg, Olaf}, doi = {10.1109/LCSYS.2022.3185166}, interhash = {576c0e66da3b03b2e767d83362f43178}, intrahash = {ba5edad69e35753352f9ffb8b014fc88}, journal = {IEEE Control Systems Letters}, pages = {3361-3366}, title = {Efficient Fault Detection for Discrete-Time PWA Systems,}, url = {https://ieeexplore.ieee.org/document/9802655}, volume = 6, year = 2022 } @article{liu2022distributed, abstract = {This paper considers the consensus of mixed-integer linear programming (MILP) problems as occurring in distributed control and machine learning of multi-agent networks. Unlike existing work on consensus problems, in which the agents only have to agree on the continuous part of their decision variables, this paper proposes a new method to enable them to also agree on the integer part. This mixed-integer setting may arise from distributed control problems of hybrid dynamical systems, or distributed machine learning problems using support vector machines. It is shown in this paper that the consensus of mixed-integer variables is guaranteed to be achieved by a tailored series of continuous consensus problems.}, author = {Liu, Zonglin and Stursberg, Olaf}, doi = {10.23919/ECC55457.2022.9838543}, interhash = {c5f89f21cda5c594e2d3f009be7689b0}, intrahash = {cb10e97079aa0ab9c8bba753e653713b}, journal = {2022 European Control Conference (ECC)}, pages = {2196-2202}, title = {Distributed Optimization for Mixed-Integer Consensus in Multi-Agent Networks}, url = {https://ieeexplore.ieee.org/document/9838543}, year = 2022 } @article{hahn2022using, abstract = {In order to enhance the performance of cyber-physical systems, this paper proposes the integrated design of distributed controllers for distributed plants together with the control of the communication network. Conventional design methods use static interfaces between both entities and therefore rely on worst-case estimations of communication delay, often leading to conservative behavior of the overall system. By contrast, the present approach establishes a robust distributed model-predictive control scheme, in which the local subsystem controllers operate under the assumption of a variable communication schedule that is predicted by a network controller. Using appropriate models for the communication network, the network controller applies a predictive network policy for scheduling the communication among the subsystem controllers across the network. Given the resulting time-varying predictions of the age of information, the paper shows under which conditions the subsystem controllers can robustly stabilize the distributed system. To illustrate the approach, the paper also reports on the application to a vehicle platooning scenario.}, author = {Hahn, Jannik and Schoeffauer, Richard and Wunder, Gerhard and Stursberg, Olaf}, interhash = {b8f81d790e7dbaf062682b07d9693097}, intrahash = {722234043e1ade4663b8ed0ebfd8813d}, journal = {IEEE Transactions on Control of Network Systems}, number = 2, pages = {742-752}, title = {Using AoI Forecasts in Communicating and Robust Distributed Model-Predictive Control}, url = {https://ieeexplore.ieee.org/abstract/document/9599512}, volume = 9, year = 2022 } @article{hahn2022uncertain, abstract = {This paper addresses finite-time horizon optimal control of control structures with shared communication network. To cope with the uncertainties, induced by network imperfections and exogenous disturbances at the same time, an optimization-based control scheme is proposed. It uses a disturbance feedback and the Age of Information (AoI), a receiver-based measure of communication delays, as central aspects. The disturbance feedback is an extension of the control law used for balanced stochastic optimal control. Balanced optimality is understood as a compromise between minimizing expected deviations from the reference and the minimization of the uncertainty of future states. Time-varying state constraints as well as time-invariant input constraints are considered, and the controllers are synthesized by semi-definite programming.}, author = {Hahn, Jannik and Stursberg, Olaf}, interhash = {55098abf737e2aa2724deb40bbcf439a}, intrahash = {f5e3f2da4e0df8c8c5cf0bd63f1b38ef}, journal = {at - Automatisierungstechnik}, pages = {343–354}, title = {Uncertain AoI in stochastic optimal control of constrained LTI systems}, url = {https://doi.org/10.1515/auto-2021-0125}, volume = {70(4)}, year = 2022 } @inproceedings{KrollSSCI2011TSK, abstract = {Models are commonly derived and their performance is assessed wrt. minimal prediction error on a closed data set. However, if no perfect model can be used, the degrees of freedom in modeling should be used to adjust the model to application-specific metrics. For model-based controller design, control-oriented performance metrics (e.g. performance wrt. to control-critical properties) are important, but not primarily prediction (i.e. prognosis- and simulation-oriented) ones. This motivates the derivation of control-specific models. The contribution introduces structured and quantitative measures on "model suitability for control" for the class of affine dynamic Takagi-Sugeno models. A method is suggested that derives control-specific dynamic models from a physical model given as a set of nonlinear differential equations. Within a case study, the proposed method demonstrates its significance: Using control-specific models improves control performance metrics such as set-point tracking quality, stability region and energy efficiency.}, address = {Paris, France}, author = {Kroll, Andreas and Dürrbaum, Axel}, booktitle = {CICA 2011 IEEE Symposium on Computational Intelligence in Control and Automation}, interhash = {29ee47b9b69180a8af57a3cdf81281e0}, intrahash = {18d0b3bec62d3810613f240dc19df603}, language = {english}, month = {April 11-15}, mrtnote = {peer, FuzzyIdControl, talk:Dürrbaum}, organization = {IEEE Symposium Series on Computational Intelligence}, pages = {23 -- 30}, title = {On Control-specific Derivation of Affine Takagi-Sugeno Models from Physical Models: Assessment Criteria and Modeling Procedure}, url = {http://www.ieee-ssci.org/}, year = 2011 } @article{flues2022control, abstract = {This paper introduces a method to control a class of jump Markov linear systems with uncertain initialization of the continuous state and affected by disturbances. Both types of uncertainties are modeled as stochastic processes with arbitrarily chosen probability distributions, for which however, the expected values and (co-)variances are known. The paper elaborates on the control task of steering the uncertain system into a target set by use of continuous controls, while chance constraints have to be satisfied for all possible state sequences of the Markov chain. The proposed approach uses a stochastic model predictive control approach on moving finite-time horizons with tailored constraints to achieve the control goal with prescribed confidence. Key steps of the procedure are (i) to over-approximate probabilistic reachable sets by use of the Chebyshev inequality, and (ii) to embed a tightened version of the original constraints into the optimization problem, in order to obtain a control strategy satisfying the specifications. Convergence of the probabilistic reachable sets is attained by suitable bounding of the state covariance matrices for arbitrary Markov chain sequences. The paper presents the main steps of the solution approach, discusses its properties, and illustrates the principle for a numeric example.}, author = {Flues, Patrick and Stursberg, Olaf}, interhash = {0be2d10d9ec347bd8582da795c2e1407}, intrahash = {a56d21f778d779295e4327de226c03d6}, journal = {Frontiers of Control Eng.}, title = {Control of Jump Markov Uncertain Linear Systems With General Probability Distributions}, url = {https://www.frontiersin.org/articles/10.3389/fcteg.2022.806543/full}, volume = {Vol 3.}, year = 2022 }