@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 }