Journals – Stephan Trenn

34.	Hossain, Sumon; Trenn, Stephan Midpoint based balanced truncation for switched linear systems with known switching signal Journal Article In: IEEE Transactions on Automatic Control, vol. 69, no. 1, 2024, (2023 early access). Abstract \| Links \| BibTeX @article{HossTren24, title = {Midpoint based balanced truncation for switched linear systems with known switching signal}, author = {Sumon Hossain and Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2023/05/Preprint-HT230508.pdf, Preprint}, doi = {10.1109/TAC.2023.3269721}, year = {2024}, date = {2024-01-01}, urldate = {2024-01-01}, journal = {IEEE Transactions on Automatic Control}, volume = {69}, number = {1}, abstract = {We propose a novel model reduction approach for switched linear systems with known switching signal. The class of considered systems encompasses switched systems with mode-dependent state-dimension as well as impulsive systems. Our method is based on a suitable definition of (time-varying) reachability and observability Gramians and we show that these Gramians satisfy precise interpretations in terms of input and output energy. Based on balancing the midpoint Gramians, we propose a piecewise-constant projection based model reduction resulting in a switched linear system of smaller size.}, note = {2023 early access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We propose a novel model reduction approach for switched linear systems with known switching signal. The class of considered systems encompasses switched systems with mode-dependent state-dimension as well as impulsive systems. Our method is based on a suitable definition of (time-varying) reachability and observability Gramians and we show that these Gramians satisfy precise interpretations in terms of input and output energy. Based on balancing the midpoint Gramians, we propose a piecewise-constant projection based model reduction resulting in a switched linear system of smaller size. Close Preprint doi:10.1109/TAC.2023.3269721 Close
33.	Hossain, Sumon; Trenn, Stephan Reduced realization for switched linear systems with known mode sequence Journal Article In: Automatica, vol. 154, no. 111065, pp. 1-9, 2023, (open access). Abstract \| Links \| BibTeX @article{HossTren23a, title = {Reduced realization for switched linear systems with known mode sequence}, author = {Sumon Hossain and Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2023/03/Preprint-HT230322.pdf, Preprint https://doi.org/10.5281/zenodo.6410136, Matlab sources}, doi = {10.1016/j.automatica.2023.111065}, year = {2023}, date = {2023-03-22}, urldate = {2023-03-22}, journal = {Automatica}, volume = {154}, number = {111065}, pages = {1-9}, abstract = {We consider switched linear systems with mode-dependent state-dimensions and/or state jumps and propose a method to obtain a switched system of reduced size with identical input-output behavior. Our approach is based in considering time-dependent reachability and unobservability spaces as well as suitable extended reachability and restricted unobservability spaces together with the notion of a weak Kalman decomposition. A key feature of our approach is that only the mode sequence of the switching signal needs to be known and not the exact switching times. However, the size of a minimal realization will in general depend on the mode durations, hence it cannot be expected that our method always leads to minimal realization. Nevertheless, we show that our method is optimal in the sense that a repeated application doesn’t lead to a further reduction and we also highlight a practically relevant special case, where minimality is achieved.}, note = {open access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We consider switched linear systems with mode-dependent state-dimensions and/or state jumps and propose a method to obtain a switched system of reduced size with identical input-output behavior. Our approach is based in considering time-dependent reachability and unobservability spaces as well as suitable extended reachability and restricted unobservability spaces together with the notion of a weak Kalman decomposition. A key feature of our approach is that only the mode sequence of the switching signal needs to be known and not the exact switching times. However, the size of a minimal realization will in general depend on the mode durations, hence it cannot be expected that our method always leads to minimal realization. Nevertheless, we show that our method is optimal in the sense that a repeated application doesn’t lead to a further reduction and we also highlight a practically relevant special case, where minimality is achieved. Close Preprint Matlab sources doi:10.1016/j.automatica.2023.111065 Close
32.	Yin, Hao; Jayawardhana, Bayu; Trenn, Stephan On contraction analysis of switched systems with mixed contracting-noncontracting modes via mode-dependent average dwell time Journal Article In: IEEE Transactions on Automatic Control, 2023, (early access). Abstract \| Links \| BibTeX @article{YinJaya23, title = {On contraction analysis of switched systems with mixed contracting-noncontracting modes via mode-dependent average dwell time}, author = {Hao Yin and Bayu Jayawardhana and Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2022/04/Preprint-YJT221110.pdf, Preprint}, doi = {10.1109/TAC.2023.3237492}, year = {2023}, date = {2023-01-16}, urldate = {2022-11-10}, journal = {IEEE Transactions on Automatic Control}, abstract = {This paper studies contraction analysis of switched systems that are composed of a mixture of contracting and non- contracting modes. The first result pertains to the equivalence of the contraction of a switched system and the uniform global ex- ponential stability of its variational system. Based on this equiva- lence property, sufficient conditions for a mode-dependent average dwell/leave-time based switching law to be contractive are estab- lished. Correspondingly, LMI conditions are derived that allow for numerical validation of contraction property of nonlinear switched systems, which include those with all non-contracting modes.}, note = {early access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper studies contraction analysis of switched systems that are composed of a mixture of contracting and non- contracting modes. The first result pertains to the equivalence of the contraction of a switched system and the uniform global ex- ponential stability of its variational system. Based on this equiva- lence property, sufficient conditions for a mode-dependent average dwell/leave-time based switching law to be contractive are estab- lished. Correspondingly, LMI conditions are derived that allow for numerical validation of contraction property of nonlinear switched systems, which include those with all non-contracting modes. Close Preprint doi:10.1109/TAC.2023.3237492 Close
31.	Chen, Yahao; Trenn, Stephan Impulse-free jump solutions of nonlinear differential-algebraic equations Journal Article In: Nonlinear Analysis: Hybrid Systems, vol. 46, no. 101238, pp. 1-17, 2022. Abstract \| Links \| BibTeX @article{ChenTren22a, title = {Impulse-free jump solutions of nonlinear differential-algebraic equations}, author = {Yahao Chen and Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2022/03/Preprint-CT220312.pdf, Preprint}, doi = {10.1016/j.nahs.2022.101238}, year = {2022}, date = {2022-11-01}, urldate = {2022-11-01}, journal = {Nonlinear Analysis: Hybrid Systems}, volume = {46}, number = {101238}, pages = {1-17}, abstract = {In this paper, we propose a novel notion called impulse-free jump solution for nonlinear differential-algebraic equations (DAEs) of the form E(x)x' = F(x) with inconsistent initial values. The term “impulse-free” means that there are no Dirac impulses caused by jumps from inconsistent initial values, i.e., the directions of jumps stay in ker E(x). We find that the existence and uniqueness of impulse-free jumps are closely related to the notion of geometric index-1 and the involutivity of the distribution defined by ker E(x). Moreover, a singular perturbed system approximation is proposed for nonlinear DAEs; we show that solutions of the perturbed system approximate both impulse-free jump solutions and C1-solutions of nonlinear DAEs. Finally, we show by some examples that our results of impulse-free jumps are useful for the problems like consistent initializations of nonlinear DAEs and transient behavior simulations of electric circuits.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we propose a novel notion called impulse-free jump solution for nonlinear differential-algebraic equations (DAEs) of the form E(x)x' = F(x) with inconsistent initial values. The term “impulse-free” means that there are no Dirac impulses caused by jumps from inconsistent initial values, i.e., the directions of jumps stay in ker E(x). We find that the existence and uniqueness of impulse-free jumps are closely related to the notion of geometric index-1 and the involutivity of the distribution defined by ker E(x). Moreover, a singular perturbed system approximation is proposed for nonlinear DAEs; we show that solutions of the perturbed system approximate both impulse-free jump solutions and C1-solutions of nonlinear DAEs. Finally, we show by some examples that our results of impulse-free jumps are useful for the problems like consistent initializations of nonlinear DAEs and transient behavior simulations of electric circuits. Close Preprint doi:10.1016/j.nahs.2022.101238 Close
30.	Lee, Jin Gyu; Trenn, Stephan; Shim, Hyungbo Synchronization with prescribed transient behavior: Heterogeneous multi-agent systems under funnel coupling Journal Article In: Automatica, vol. 141, no. 110276, pp. 13, 2022, (open access). Abstract \| Links \| BibTeX @article{LeeTren22, title = {Synchronization with prescribed transient behavior: Heterogeneous multi-agent systems under funnel coupling}, author = {Jin Gyu Lee and Stephan Trenn and Hyungbo Shim}, url = {https://stephantrenn.net/wp-content/uploads/2022/08/LeeTren22.pdf, Paper https://arxiv.org/abs/2012.14580, Extended ArXiv-version}, doi = {10.1016/j.automatica.2022.110276}, year = {2022}, date = {2022-07-01}, urldate = {2022-07-01}, journal = {Automatica}, volume = {141}, number = {110276}, pages = {13}, abstract = {In this paper, we introduce a nonlinear time-varying coupling law, which can be designed in a fully decentralized manner and achieves approximate synchronization with arbitrary precision, under only mild assumptions on the individual vector fields and the underlying (undirected) graph structure. The proposed coupling law is motivated by the so-called funnel control method studied in adaptive control under the observation that arbitrary precision synchronization can be achieved for heterogeneous multi-agent systems by a high-gain coupling; consequently we call our novel synchronization method ‘(node-wise) funnel coupling.’ By adjusting the conventional proof technique in the funnel control study, we are even able to obtain asymptotic synchronization with the same funnel coupling law. Moreover, the emergent collective behavior that arises for a heterogeneous multi-agent system when enforcing arbitrary precision synchronization by the proposed funnel coupling law, is analyzed in this paper. In particular, we introduce a single scalar dynamics called ‘emergent dynamics’ which describes the emergent synchronized behavior of the multi-agent system under funnel coupling. Characterization of the emergent dynamics is important because, for instance, one can design the emergent dynamics first such that the solution trajectory behaves as desired, and then, provide a design guideline to each agent so that the constructed vector fields yield the desired emergent dynamics. We illustrate this idea via the example of a distributed median solver based on funnel coupling.}, note = {open access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we introduce a nonlinear time-varying coupling law, which can be designed in a fully decentralized manner and achieves approximate synchronization with arbitrary precision, under only mild assumptions on the individual vector fields and the underlying (undirected) graph structure. The proposed coupling law is motivated by the so-called funnel control method studied in adaptive control under the observation that arbitrary precision synchronization can be achieved for heterogeneous multi-agent systems by a high-gain coupling; consequently we call our novel synchronization method ‘(node-wise) funnel coupling.’ By adjusting the conventional proof technique in the funnel control study, we are even able to obtain asymptotic synchronization with the same funnel coupling law. Moreover, the emergent collective behavior that arises for a heterogeneous multi-agent system when enforcing arbitrary precision synchronization by the proposed funnel coupling law, is analyzed in this paper. In particular, we introduce a single scalar dynamics called ‘emergent dynamics’ which describes the emergent synchronized behavior of the multi-agent system under funnel coupling. Characterization of the emergent dynamics is important because, for instance, one can design the emergent dynamics first such that the solution trajectory behaves as desired, and then, provide a design guideline to each agent so that the constructed vector fields yield the desired emergent dynamics. We illustrate this idea via the example of a distributed median solver based on funnel coupling. Close Paper Extended ArXiv-version doi:10.1016/j.automatica.2022.110276 Close
29.	Berger, Thomas; Ilchmann, Achim; Trenn, Stephan Quasi feedback forms for differential-algebraic systems Journal Article In: IMA Journal of Mathematical Control and Information, vol. 39, iss. 2, pp. 533-563, 2022, (open access, published online October 2021). Abstract \| Links \| BibTeX @article{BergIlch22, title = {Quasi feedback forms for differential-algebraic systems}, author = {Thomas Berger and Achim Ilchmann and Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2023/01/BergIlch22.pdf, Paper https://arxiv.org/abs/2102.12713, arXiv:2102.12713}, doi = {10.1093/imamci/dnab030}, year = {2022}, date = {2022-06-01}, urldate = {2022-06-01}, journal = {IMA Journal of Mathematical Control and Information}, volume = {39}, issue = {2}, pages = {533-563}, abstract = {We investigate feedback forms for linear time-invariant systems described by differential-algebraic equations. Feedback forms are representatives of certain equivalence classes. For example state space transformations, invertible transformations from the left, and proportional state feedback constitute an equivalence relation. The representative of such an equivalence class, which we call proportional feedback form for the above example, allows to read off relevant system theoretic properties. Our main contribution is to derive a quasi proportional feedback form. This form is advantageous since it provides some geometric insight and is simple to compute, but still allows to read off the relevant structural properties of the control system. We also derive a quasi proportional and derivative feedback form. Similar advantages hold.}, note = {open access, published online October 2021}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We investigate feedback forms for linear time-invariant systems described by differential-algebraic equations. Feedback forms are representatives of certain equivalence classes. For example state space transformations, invertible transformations from the left, and proportional state feedback constitute an equivalence relation. The representative of such an equivalence class, which we call proportional feedback form for the above example, allows to read off relevant system theoretic properties. Our main contribution is to derive a quasi proportional feedback form. This form is advantageous since it provides some geometric insight and is simple to compute, but still allows to read off the relevant structural properties of the control system. We also derive a quasi proportional and derivative feedback form. Similar advantages hold. Close Paper arXiv:2102.12713 doi:10.1093/imamci/dnab030 Close
28.	Mostacciuolo, Elisa; Trenn, Stephan; Vasca, Francesco A smooth model for periodically switched descriptor systems Journal Article In: Automatica, vol. 136, no. 110082, pp. 1-8, 2022, (open access). Abstract \| Links \| BibTeX @article{MostTren22, title = {A smooth model for periodically switched descriptor systems}, author = {Elisa Mostacciuolo and Stephan Trenn and Francesco Vasca}, url = {https://stephantrenn.net/wp-content/uploads/2021/04/Preprint-MTV210921.pdf, Preprint}, doi = {10.1016/j.automatica.2021.110082}, year = {2022}, date = {2022-02-01}, urldate = {2021-09-21}, journal = {Automatica}, volume = {136}, number = {110082}, pages = {1-8}, abstract = {Switched descriptor systems characterized by a repetitive finite sequence of modes can exhibit state discontinuities at the switching time instants. The amplitudes of these discontinuities depend on the consistency projectors of the modes. A switched ordinary differential equations model whose continuous state evolution approximates the state of the original system is proposed. Sufficient conditions based on linear matrix inequalities on the modes projectors ensure that the approximation error is of linear order of the switching period. The theoretical findings are applied to a switched capacitor circuit and numerical results illustrate the practical usefulness of the proposed model.}, note = {open access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Switched descriptor systems characterized by a repetitive finite sequence of modes can exhibit state discontinuities at the switching time instants. The amplitudes of these discontinuities depend on the consistency projectors of the modes. A switched ordinary differential equations model whose continuous state evolution approximates the state of the original system is proposed. Sufficient conditions based on linear matrix inequalities on the modes projectors ensure that the approximation error is of linear order of the switching period. The theoretical findings are applied to a switched capacitor circuit and numerical results illustrate the practical usefulness of the proposed model. Close Preprint doi:10.1016/j.automatica.2021.110082 Close
27.	Trenn, Stephan Distributional restriction impossible to define Journal Article In: Examples and Counterexamples, vol. 1, no. 100023, pp. 1-4, 2021, (open access). Abstract \| Links \| BibTeX @article{Tren21, title = {Distributional restriction impossible to define}, author = {Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2020/09/Preprint-Tre200901.pdf, Preprint}, doi = {10.1016/j.exco.2021.100023}, year = {2021}, date = {2021-11-30}, urldate = {2021-11-30}, journal = {Examples and Counterexamples}, volume = {1}, number = {100023}, pages = {1-4}, abstract = {A counterexample is presented showing that it is not possible to define a restriction for distributions.}, note = {open access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close A counterexample is presented showing that it is not possible to define a restriction for distributions. Close Preprint doi:10.1016/j.exco.2021.100023 Close
26.	Chen, Yahao; Trenn, Stephan; Respondek, Witold Normal forms and internal regularization of nonlinear differential-algebraic control systems Journal Article In: International Journal of Robust and Nonlinear Control, vol. 2021, no. 31, pp. 6562-6584, 2021, (open access). Abstract \| Links \| BibTeX @article{ChenTren21d, title = {Normal forms and internal regularization of nonlinear differential-algebraic control systems}, author = {Yahao Chen and Stephan Trenn and Witold Respondek}, url = {https://stephantrenn.net/wp-content/uploads/2021/06/ChenTren21d.pdf, Paper}, doi = {10.1002/rnc.5623}, year = {2021}, date = {2021-04-13}, urldate = {2021-04-13}, journal = {International Journal of Robust and Nonlinear Control}, volume = {2021}, number = {31}, pages = {6562-6584}, abstract = {In this paper, we propose two normal forms for nonlinear differential-algebraic control systems (DACSs) under external feedback equivalence, using a notion called maximal controlled invariant submanifold. The two normal forms simplify the system structures and facilitate understanding the various roles of variables for nonlinear DACSs. Moreover, we study when a given nonlinear DACS is internally regularizable, i.e., when there exists a state feedback transforming the DACS into a differential-algebraic equation (DAE) with internal regularity, the latter notion is closely related to the existence and uniqueness of solutions of DAEs. We also revise a commonly used method in DAE solution theory, called the geometric reduction method. We apply this method to DACSs and formulate it as an algorithm, which is used to construct maximal controlled invariant submanifolds and to find internal regularization feedbacks. Two examples of mechanical systems are used to illustrate the proposed normal forms and to show how to internally regularize DACSs.}, note = {open access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we propose two normal forms for nonlinear differential-algebraic control systems (DACSs) under external feedback equivalence, using a notion called maximal controlled invariant submanifold. The two normal forms simplify the system structures and facilitate understanding the various roles of variables for nonlinear DACSs. Moreover, we study when a given nonlinear DACS is internally regularizable, i.e., when there exists a state feedback transforming the DACS into a differential-algebraic equation (DAE) with internal regularity, the latter notion is closely related to the existence and uniqueness of solutions of DAEs. We also revise a commonly used method in DAE solution theory, called the geometric reduction method. We apply this method to DACSs and formulate it as an algorithm, which is used to construct maximal controlled invariant submanifolds and to find internal regularization feedbacks. Two examples of mechanical systems are used to illustrate the proposed normal forms and to show how to internally regularize DACSs. Close Paper doi:10.1002/rnc.5623 Close
25.	Iervolino, Raffaele; Trenn, Stephan; Vasca, Francesco Asymptotic stability of piecewise affine systems with Filippov solutions via discontinuous piecewise Lyapunov functions Journal Article In: IEEE Transactions on Automatic Control, vol. 66, no. 4, pp. 1513-1528, 2021. Abstract \| Links \| BibTeX @article{IervTren21, title = {Asymptotic stability of piecewise affine systems with Filippov solutions via discontinuous piecewise Lyapunov functions}, author = {Raffaele Iervolino and Stephan Trenn and Francesco Vasca}, url = {https://stephantrenn.net/wp-content/uploads/2020/02/Preprint-ITV200204.pdf, Preprint}, doi = {10.1109/TAC.2020.2996597}, year = {2021}, date = {2021-04-01}, urldate = {2021-04-01}, journal = {IEEE Transactions on Automatic Control}, volume = {66}, number = {4}, pages = {1513-1528}, abstract = {Asymptotic stability of continuous-time piecewise affine systems defined over a polyhedral partition of the state space, with possible discontinuous vector field on the boundaries, is considered. In the first part of the paper the feasible Filippov solution concept is introduced by characterizing single-mode Caratheodory, sliding mode and forward Zeno behaviors. Then, a global asymptotic stability result through a (possibly discontinuous) piecewise Lyapunov function is presented. The sufficient conditions are based on pointwise classifications of the trajectories which allow the identification of crossing, unreachable and Caratheodory boundaries. It is shown that the sign and jump conditions of the stability theorem can be expressed in terms of linear matrix inequalities by particularizing to piecewise quadratic Lyapunov functions and using the cone-copositivity approach. Several examples illustrate the theoretical arguments and the effectiveness of the stability result.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Asymptotic stability of continuous-time piecewise affine systems defined over a polyhedral partition of the state space, with possible discontinuous vector field on the boundaries, is considered. In the first part of the paper the feasible Filippov solution concept is introduced by characterizing single-mode Caratheodory, sliding mode and forward Zeno behaviors. Then, a global asymptotic stability result through a (possibly discontinuous) piecewise Lyapunov function is presented. The sufficient conditions are based on pointwise classifications of the trajectories which allow the identification of crossing, unreachable and Caratheodory boundaries. It is shown that the sign and jump conditions of the stability theorem can be expressed in terms of linear matrix inequalities by particularizing to piecewise quadratic Lyapunov functions and using the cone-copositivity approach. Several examples illustrate the theoretical arguments and the effectiveness of the stability result. Close Preprint doi:10.1109/TAC.2020.2996597 Close
24.	Wijnbergen, Paul; Trenn, Stephan Impulse-free interval-stabilization of switched differential algebraic equations Journal Article In: Systems & Control Letters, vol. 149, pp. 104870.1-10, 2021, (Open Access.). Abstract \| Links \| BibTeX @article{WijnTren21a, title = {Impulse-free interval-stabilization of switched differential algebraic equations}, author = {Paul Wijnbergen and Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2021/01/24-SCL149-104870.pdf, Paper}, doi = {10.1016/j.sysconle.2020.104870}, year = {2021}, date = {2021-01-23}, urldate = {2021-01-23}, journal = {Systems & Control Letters}, volume = {149}, pages = {104870.1-10}, abstract = {In this paper stabilization of switched differential algebraic equations is considered, where Dirac impulses in both the input and the state trajectory are to be avoided during the stabilization process. First it is shown that stabilizability of a switched DAE and the existence of impulse-free solutions are merely necessary conditions for impulse-free stabilizability. Then necessary and sufficient conditions for the existence of impulse-free solutions are given, which motivate the definition of (impulse-free) interval-stabilization on a finite interval. Under a uniformity assumption, which can be verified for a broad class of switched systems, stabilizability on an infinite interval can be concluded based on interval-stabilizability. As a result a characterization of impulse-free interval stabilizability is given and as a corollary we provide a novel impulse-free null-controllability characterization. Finally, the results are compared to results on interval-stabilizability where Dirac impulses are allowed in the input and state trajectory. }, note = {Open Access.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper stabilization of switched differential algebraic equations is considered, where Dirac impulses in both the input and the state trajectory are to be avoided during the stabilization process. First it is shown that stabilizability of a switched DAE and the existence of impulse-free solutions are merely necessary conditions for impulse-free stabilizability. Then necessary and sufficient conditions for the existence of impulse-free solutions are given, which motivate the definition of (impulse-free) interval-stabilization on a finite interval. Under a uniformity assumption, which can be verified for a broad class of switched systems, stabilizability on an infinite interval can be concluded based on interval-stabilizability. As a result a characterization of impulse-free interval stabilizability is given and as a corollary we provide a novel impulse-free null-controllability characterization. Finally, the results are compared to results on interval-stabilizability where Dirac impulses are allowed in the input and state trajectory. Close Paper doi:10.1016/j.sysconle.2020.104870 Close
23.	Borsche, Raul; Kocoglu, Damla; Trenn, Stephan A distributional solution framework for linear hyperbolic PDEs coupled to switched DAEs Journal Article In: Mathematics of Control, Signals, and Systems (MCSS), vol. 32, pp. 455-487, 2020, (Open Access). Abstract \| Links \| BibTeX @article{BorsKoco20, title = {A distributional solution framework for linear hyperbolic PDEs coupled to switched DAEs}, author = {Raul Borsche and Damla Kocoglu and Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2020/11/23-MCSS2020.pdf, Paper}, doi = {10.1007/s00498-020-00267-7}, year = {2020}, date = {2020-11-18}, urldate = {2020-11-18}, journal = {Mathematics of Control, Signals, and Systems (MCSS)}, volume = {32}, pages = {455-487}, abstract = {A distributional solution framework is developed for systems consisting of linear hyperbolic partial differential equations (PDEs) and switched differential-algebraic equations (DAEs) which are coupled via boundary conditions. The unique solvability is then characterize in terms of a switched delay DAE. The theory is illustrated with an example of electric power lines modeled by the telegraph equations which are coupled via a switching transformer where simulations confirm the predicted impulsive solutions.}, note = {Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close A distributional solution framework is developed for systems consisting of linear hyperbolic partial differential equations (PDEs) and switched differential-algebraic equations (DAEs) which are coupled via boundary conditions. The unique solvability is then characterize in terms of a switched delay DAE. The theory is illustrated with an example of electric power lines modeled by the telegraph equations which are coupled via a switching transformer where simulations confirm the predicted impulsive solutions. Close Paper doi:10.1007/s00498-020-00267-7 Close
22.	Anh, Pham Ky; Linh, Pham Thi; Thuan, Do Duc; Trenn, Stephan Stability analysis for switched discrete-time linear singular systems Journal Article In: Automatica, vol. 119, no. 109100, 2020. Abstract \| Links \| BibTeX @article{AnhLinh20, title = {Stability analysis for switched discrete-time linear singular systems}, author = {Pham Ky Anh and Pham Thi Linh and Do Duc Thuan and Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2020/02/Preprint-ALTT200515.pdf, Preprint}, doi = {10.1016/j.automatica.2020.109100}, year = {2020}, date = {2020-09-01}, urldate = {2020-09-01}, journal = {Automatica}, volume = {119}, number = {109100}, abstract = {The stability of arbitrarily switched discrete-time linear singular (SDLS) systems is studied. Our analysis builds on the recently introduced one-step-map for SDLS systems of index-1. We first provide a sufficient stability conditions in terms of Lyapunov functions. Furthermore, we generalize the notion of joint spectral radius of a finite set of matrix pairs, which allows us to fully characterize exponential stability.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The stability of arbitrarily switched discrete-time linear singular (SDLS) systems is studied. Our analysis builds on the recently introduced one-step-map for SDLS systems of index-1. We first provide a sufficient stability conditions in terms of Lyapunov functions. Furthermore, we generalize the notion of joint spectral radius of a finite set of matrix pairs, which allows us to fully characterize exponential stability. Close Preprint doi:10.1016/j.automatica.2020.109100 Close
21.	Patil, Deepak; Tesi, Pietro; Trenn, Stephan Indiscernible topological variations in DAE networks Journal Article In: Automatica, vol. 101, pp. 280-289, 2019. Abstract \| Links \| BibTeX @article{PatiTesi19, title = {Indiscernible topological variations in DAE networks}, author = {Deepak Patil and Pietro Tesi and Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2019/01/Preprint-PTT181205.pdf, Preprint}, doi = {10.1016/j.automatica.2018.12.012}, year = {2019}, date = {2019-03-01}, journal = {Automatica}, volume = {101}, pages = {280-289}, abstract = {A problem of characterizing conditions under which a topological change in a network of differential algebraic equations (DAEs) can go undetected is considered. It is shown that initial conditions for which topological changes are indiscernible belong to a generalized eigenspace shared by the nominal system and the system resulting from a topological change. A condition in terms of eigenvectors of the nominal system is derived to check for existence of possibly indiscernible topological changes. For homogenous networks this condition simplifies to the existence of an eigenvector of the Laplacian of network having equal components. Lastly, a rank condition is derived which can be used to check if a topological change preserves regularity of the nominal network.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close A problem of characterizing conditions under which a topological change in a network of differential algebraic equations (DAEs) can go undetected is considered. It is shown that initial conditions for which topological changes are indiscernible belong to a generalized eigenspace shared by the nominal system and the system resulting from a topological change. A condition in terms of eigenvectors of the nominal system is derived to check for existence of possibly indiscernible topological changes. For homogenous networks this condition simplifies to the existence of an eigenvector of the Laplacian of network having equal components. Lastly, a rank condition is derived which can be used to check if a topological change preserves regularity of the nominal network. Close Preprint doi:10.1016/j.automatica.2018.12.012 Close
20.	Tanwani, Aneel; Trenn, Stephan Detectability and observer design for switched differential algebraic equations Journal Article In: Automatica, vol. 99, pp. 289-300, 2019. Abstract \| Links \| BibTeX @article{TanwTren19, title = {Detectability and observer design for switched differential algebraic equations}, author = {Aneel Tanwani and Stephan Trenn}, url = {https://stephantrenn.net/wp-content/uploads/2018/09/Preprint-TT180917.pdf, Preprint}, doi = {10.1016/j.automatica.2018.10.043}, year = {2019}, date = {2019-01-01}, journal = {Automatica}, volume = {99}, pages = {289-300}, abstract = {This paper studies detectability for switched linear differential–algebraic equations (DAEs) and its application to the synthesis of observers, which generate asymptotically converging state estimates. Equating detectability to asymptotic stability of zero-output-constrained state trajectories, and building on our work on interval-wise observability, we propose the notion of interval-wise detectability: If the output of the system is constrained to be identically zero over an interval, then the norm of the corresponding state trajectories scales down by a certain factor at the end of that interval. Conditions are provided under which the interval-wise detectability leads to asymptotic stability of zero-output-constrained state trajectories. An application is demonstrated in designing state estimators. Decomposing the state into observable and unobservable components, we show that if the observable component of the system is reset appropriately and persistently, then the estimation error converges to zero asymptotically under the interval-wise detectability assumption.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper studies detectability for switched linear differential–algebraic equations (DAEs) and its application to the synthesis of observers, which generate asymptotically converging state estimates. Equating detectability to asymptotic stability of zero-output-constrained state trajectories, and building on our work on interval-wise observability, we propose the notion of interval-wise detectability: If the output of the system is constrained to be identically zero over an interval, then the norm of the corresponding state trajectories scales down by a certain factor at the end of that interval. Conditions are provided under which the interval-wise detectability leads to asymptotic stability of zero-output-constrained state trajectories. An application is demonstrated in designing state estimators. Decomposing the state into observable and unobservable components, we show that if the observable component of the system is reset appropriately and persistently, then the estimation error converges to zero asymptotically under the interval-wise detectability assumption. Close Preprint doi:10.1016/j.automatica.2018.10.043 Close
19.	Küsters, Ferdinand; Trenn, Stephan Switch observability for switched linear systems Journal Article In: Automatica, vol. 87, pp. 121-127, 2018. Abstract \| Links \| BibTeX @article{KustTren18, title = {Switch observability for switched linear systems}, author = {Ferdinand Küsters and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/10/Preprint-KT170808.pdf, Preprint}, doi = {https://doi.org/10.1016/j.automatica.2017.09.024}, year = {2018}, date = {2018-01-01}, journal = {Automatica}, volume = {87}, pages = {121-127}, abstract = {Mode observability of switched systems requires observability of each individual mode. We consider other concepts of observability that do not have this requirement: Switching time observability and switch observability. The latter notion is based on the assumption that at least one switch occurs. These concepts are analyzed and characterized both for homogeneous and inhomogeneous systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Mode observability of switched systems requires observability of each individual mode. We consider other concepts of observability that do not have this requirement: Switching time observability and switch observability. The latter notion is based on the assumption that at least one switch occurs. These concepts are analyzed and characterized both for homogeneous and inhomogeneous systems. Close Preprint doi:https://doi.org/10.1016/j.automatica.2017.09.024 Close
18.	Mostacciuolo, Elisa; Trenn, Stephan; Vasca, Francesco Averaging for switched DAEs: convergence, partial averaging and stability Journal Article In: Automatica, vol. 82, pp. 145–157, 2017. Abstract \| Links \| BibTeX @article{MostTren17, title = {Averaging for switched DAEs: convergence, partial averaging and stability}, author = {Elisa Mostacciuolo and Stephan Trenn and Francesco Vasca}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-MTV170407.pdf, Preprint}, doi = {10.1016/j.automatica.2017.04.036}, year = {2017}, date = {2017-08-01}, journal = {Automatica}, volume = {82}, pages = {145--157}, abstract = {Averaging is a useful technique to simplify the analysis of switched systems. In this paper we present averaging results for the class of systems described by switched differential algebraic equations (DAEs). Conditions on the consistency projectors are given which guarantee convergence towards a non-switched averaged system. A consequence of this result is the possibility to stabilize switched DAEs via fast switching. We also study partial averaging in case the consistency projectors do not satisfy the conditions for convergence; the averaged system is then still a switched system, but is simpler than the original. The practical interest of the theoretical averaging results is demonstrated through the analysis of the dynamics of a switched electrical circuit.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Averaging is a useful technique to simplify the analysis of switched systems. In this paper we present averaging results for the class of systems described by switched differential algebraic equations (DAEs). Conditions on the consistency projectors are given which guarantee convergence towards a non-switched averaged system. A consequence of this result is the possibility to stabilize switched DAEs via fast switching. We also study partial averaging in case the consistency projectors do not satisfy the conditions for convergence; the averaged system is then still a switched system, but is simpler than the original. The practical interest of the theoretical averaging results is demonstrated through the analysis of the dynamics of a switched electrical circuit. Close Preprint doi:10.1016/j.automatica.2017.04.036 Close
17.	Tanwani, Aneel; Trenn, Stephan Determinability and state estimation for switched differential–algebraic equations Journal Article In: Automatica, vol. 76, pp. 17–31, 2017, ISSN: 0005-1098. Abstract \| Links \| BibTeX @article{TanwTren17, title = {Determinability and state estimation for switched differential–algebraic equations}, author = {Aneel Tanwani and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-TT160919.pdf, Preprint}, doi = {10.1016/j.automatica.2016.10.024}, issn = {0005-1098}, year = {2017}, date = {2017-02-01}, journal = {Automatica}, volume = {76}, pages = {17--31}, abstract = {The problem of state reconstruction and estimation is considered for a class of switched dynamical systems whose subsystems are modeled using linear differential–algebraic equations (DAEs). Since this system class imposes time-varying dynamic and static (in the form of algebraic constraints) relations on the evolution of state trajectories, an appropriate notion of observability is presented which accommodates these phenomena. Based on this notion, we first derive a formula for the reconstruction of the state of the system where we explicitly obtain an injective mapping from the output to the state. In practice, such a mapping may be difficult to realize numerically and hence a class of estimators is proposed which ensures that the state estimate converges asymptotically to the real state of the system.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The problem of state reconstruction and estimation is considered for a class of switched dynamical systems whose subsystems are modeled using linear differential–algebraic equations (DAEs). Since this system class imposes time-varying dynamic and static (in the form of algebraic constraints) relations on the evolution of state trajectories, an appropriate notion of observability is presented which accommodates these phenomena. Based on this notion, we first derive a formula for the reconstruction of the state of the system where we explicitly obtain an injective mapping from the output to the state. In practice, such a mapping may be difficult to realize numerically and hence a class of estimators is proposed which ensures that the state estimate converges asymptotically to the real state of the system. Close Preprint doi:10.1016/j.automatica.2016.10.024 Close
16.	Gross, Tjorben B.; Trenn, Stephan; Wirsen, Andreas Solvability and stability of a power system DAE model Journal Article In: Syst. Control Lett., vol. 97, pp. 12–17, 2016. Abstract \| Links \| BibTeX @article{GrosTren16, title = {Solvability and stability of a power system DAE model}, author = {Tjorben B. Gross and Stephan Trenn and Andreas Wirsen}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-GTW160816.pdf, Preprint}, doi = {10.1016/j.sysconle.2016.08.003}, year = {2016}, date = {2016-11-01}, journal = {Syst. Control Lett.}, volume = {97}, pages = {12--17}, abstract = {The dynamic model of a power system is the combination of the power flow equations and the dynamic description of the generators (the swing equations) resulting in a differential–algebraic equation (DAE). For general DAEs solvability is not guaranteed in general, in the linear case the coefficient matrices have to satisfy a certain regularity condition. We derive a solvability characterization for the linearized power system DAE solely in terms of the network topology. As an extension to previous result we allow for higher order generator dynamics. Furthermore, we show that any solvable power system DAE is automatically of index one, which means that it is also numerically well posed. Finally, we show that any solvable power system DAE is stable but not asymptotically stable.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The dynamic model of a power system is the combination of the power flow equations and the dynamic description of the generators (the swing equations) resulting in a differential–algebraic equation (DAE). For general DAEs solvability is not guaranteed in general, in the linear case the coefficient matrices have to satisfy a certain regularity condition. We derive a solvability characterization for the linearized power system DAE solely in terms of the network topology. As an extension to previous result we allow for higher order generator dynamics. Furthermore, we show that any solvable power system DAE is automatically of index one, which means that it is also numerically well posed. Finally, we show that any solvable power system DAE is stable but not asymptotically stable. Close Preprint doi:10.1016/j.sysconle.2016.08.003 Close
15.	Küsters, Ferdinand; Trenn, Stephan Duality of switched DAEs Journal Article In: Math. Control Signals Syst., vol. 28, no. 3, pp. 25, 2016. Abstract \| Links \| BibTeX @article{KustTren16a, title = {Duality of switched DAEs}, author = {Ferdinand Küsters and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-KT160627.pdf, Preprint}, doi = {10.1007/s00498-016-0177-2}, year = {2016}, date = {2016-07-01}, journal = {Math. Control Signals Syst.}, volume = {28}, number = {3}, pages = {25}, abstract = {We present and discuss the definition of the adjoint and dual of a switched differential-algebraic equation (DAE). For a proper duality definition, it is necessary to extend the class of switched DAEs to allow for additional impact terms. For this switched DAE with impacts, we derive controllability/reachability/determinability/observability characterizations for a given switching signal. Based on this characterizations, we prove duality between controllability/reachability and determinability/observability for switched DAEs.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We present and discuss the definition of the adjoint and dual of a switched differential-algebraic equation (DAE). For a proper duality definition, it is necessary to extend the class of switched DAEs to allow for additional impact terms. For this switched DAE with impacts, we derive controllability/reachability/determinability/observability characterizations for a given switching signal. Based on this characterizations, we prove duality between controllability/reachability and determinability/observability for switched DAEs. Close Preprint doi:10.1007/s00498-016-0177-2 Close
14.	Küsters, Ferdinand; Ruppert, Markus G. -M.; Trenn, Stephan Controllability of switched differential-algebraic equations Journal Article In: Syst. Control Lett., vol. 78, no. 0, pp. 32 - 39, 2015, ISSN: 0167-6911. Abstract \| Links \| BibTeX @article{KustRupp15, title = {Controllability of switched differential-algebraic equations}, author = {Ferdinand Küsters and Markus G.-M. Ruppert and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-KRT150122.pdf, Preprint}, doi = {10.1016/j.sysconle.2015.01.011}, issn = {0167-6911}, year = {2015}, date = {2015-01-01}, journal = {Syst. Control Lett.}, volume = {78}, number = {0}, pages = {32 - 39}, abstract = {We study controllability of switched differential–algebraic equations. We are able to establish a controllability characterization where we assume that the switching signal is known. The characterization takes into account possible jumps induced by the switches. It turns out that controllability not only depends on the actual switching sequence but also on the duration between the switching times.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We study controllability of switched differential–algebraic equations. We are able to establish a controllability characterization where we assume that the switching signal is known. The characterization takes into account possible jumps induced by the switches. It turns out that controllability not only depends on the actual switching sequence but also on the duration between the switching times. Close Preprint doi:10.1016/j.sysconle.2015.01.011 Close
13.	Berger, Thomas; Trenn, Stephan Kalman controllability decompositions for differential-algebraic systems Journal Article In: Syst. Control Lett., vol. 71, pp. 54–61, 2014, ISSN: 0167-6911. Abstract \| Links \| BibTeX @article{BergTren14, title = {Kalman controllability decompositions for differential-algebraic systems}, author = {Thomas Berger and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-BT140603.pdf, Preprint}, doi = {10.1016/j.sysconle.2014.06.004}, issn = {0167-6911}, year = {2014}, date = {2014-01-01}, journal = {Syst. Control Lett.}, volume = {71}, pages = {54--61}, abstract = {We study linear differential-algebraic control systems and investigate decompositions with respect to controllability properties. We show that the augmented Wong sequences can be exploited for a transformation of the system into a Kalman controllability decomposition (KCD). The KCD decouples the system into a completely controllable part, an uncontrollable part given by an ordinary differential equation and an inconsistent part, which is behaviorally controllable but contains no completely controllable part. This decomposition improves a known KCD from a behavioral point of view. We conclude the paper with some features of the KCD in the case of regular systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We study linear differential-algebraic control systems and investigate decompositions with respect to controllability properties. We show that the augmented Wong sequences can be exploited for a transformation of the system into a Kalman controllability decomposition (KCD). The KCD decouples the system into a completely controllable part, an uncontrollable part given by an ordinary differential equation and an inconsistent part, which is behaviorally controllable but contains no completely controllable part. This decomposition improves a known KCD from a behavioral point of view. We conclude the paper with some features of the KCD in the case of regular systems. Close Preprint doi:10.1016/j.sysconle.2014.06.004 Close
12.	Liberzon, Daniel; Trenn, Stephan The bang-bang funnel controller for uncertain nonlinear systems with arbitrary relative degree Journal Article In: IEEE Trans. Autom. Control, vol. 58, no. 12, pp. 3126–3141, 2013. Abstract \| Links \| BibTeX @article{LibeTren13b, title = {The bang-bang funnel controller for uncertain nonlinear systems with arbitrary relative degree}, author = {Daniel Liberzon and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-LT130702.pdf, Preprint}, doi = {10.1109/TAC.2013.2277631}, year = {2013}, date = {2013-08-16}, journal = {IEEE Trans. Autom. Control}, volume = {58}, number = {12}, pages = {3126--3141}, abstract = {The paper considers output tracking control of uncertain nonlinear systems with arbitrary known relative degree and known sign of the high frequency gain. The tracking objective is formulated in terms of a time-varying bound-a funnel-around a given reference signal. The proposed controller is bang-bang with two control values. The controller switching logic handles arbitrarily high relative degree in an inductive manner with the help of auxiliary derivative funnels. We formulate a set of feasibility assumptions under which the controller maintains the tracking error within the funnel. Furthermore, we prove that under mild additional assumptions the considered system class satisfies these feasibility assumptions if the selected control values are sufficiently large in magnitude. Finally, we study the effect of time delays in the feedback loop and we are able to show that also in this case the proposed bang-bang funnel controller works under slightly adjusted feasibility assumptions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close The paper considers output tracking control of uncertain nonlinear systems with arbitrary known relative degree and known sign of the high frequency gain. The tracking objective is formulated in terms of a time-varying bound-a funnel-around a given reference signal. The proposed controller is bang-bang with two control values. The controller switching logic handles arbitrarily high relative degree in an inductive manner with the help of auxiliary derivative funnels. We formulate a set of feasibility assumptions under which the controller maintains the tracking error within the funnel. Furthermore, we prove that under mild additional assumptions the considered system class satisfies these feasibility assumptions if the selected control values are sufficiently large in magnitude. Finally, we study the effect of time delays in the feedback loop and we are able to show that also in this case the proposed bang-bang funnel controller works under slightly adjusted feasibility assumptions. Close Preprint doi:10.1109/TAC.2013.2277631 Close
11.	Hackl, Christoph M.; Hopfe, Norman; Ilchmann, Achim; Mueller, Markus; Trenn, Stephan Funnel control for systems with relative degree two Journal Article In: SIAM J. Control Optim., vol. 51, no. 2, pp. 965–995, 2013. Abstract \| Links \| BibTeX @article{HackHopf13, title = {Funnel control for systems with relative degree two}, author = {Christoph M. Hackl and Norman Hopfe and Achim Ilchmann and Markus Mueller and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/HackHopf13.pdf, Paper}, doi = {10.1137/100799903 }, year = {2013}, date = {2013-03-19}, journal = {SIAM J. Control Optim.}, volume = {51}, number = {2}, pages = {965--995}, abstract = {Tracking of reference signals y_ref(.) by the output y(.) of linear (as well as a considerably large class of nonlinear) single-input, single-output systems is considered. The system is assumed to have strict relative degree two with (weakly) stable zero dynamics. The control objective is tracking of the error e=y-y_ref and its derivative e' within two prespecified performance funnels, respectively. This is achieved by the so-called funnel controller u(t) = -k_0(t)^2 e(t) - k_1(t) e'(t), where the simple proportional error feedback has gain functions k_0 and k_1 designed in such a way to preclude contact of e and e' with the funnel boundaries, respectively. The funnel controller also ensures boundedness of all signals. We also show that the same funnel controller (i) is applicable to relative degree one systems, (ii) allows for input constraints provided a feasibility condition (formulated in terms of the system data, the saturation bounds, the funnel data, bounds on the reference signal, and the initial state) holds, (iii) is robust in terms of the gap metric: if a system is sufficiently close to a system with relative degree two, stable zero dynamics, and positive high-frequency gain, but does not necessarily have these properties, then for small initial values the funnel controller also achieves the control objective. Finally, we illustrate the theoretical results by experimental results: the funnel controller is applied to a rotatory mechanical system for position control.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Tracking of reference signals y_ref(.) by the output y(.) of linear (as well as a considerably large class of nonlinear) single-input, single-output systems is considered. The system is assumed to have strict relative degree two with (weakly) stable zero dynamics. The control objective is tracking of the error e=y-y_ref and its derivative e' within two prespecified performance funnels, respectively. This is achieved by the so-called funnel controller u(t) = -k_0(t)^2 e(t) - k_1(t) e'(t), where the simple proportional error feedback has gain functions k_0 and k_1 designed in such a way to preclude contact of e and e' with the funnel boundaries, respectively. The funnel controller also ensures boundedness of all signals. We also show that the same funnel controller (i) is applicable to relative degree one systems, (ii) allows for input constraints provided a feasibility condition (formulated in terms of the system data, the saturation bounds, the funnel data, bounds on the reference signal, and the initial state) holds, (iii) is robust in terms of the gap metric: if a system is sufficiently close to a system with relative degree two, stable zero dynamics, and positive high-frequency gain, but does not necessarily have these properties, then for small initial values the funnel controller also achieves the control objective. Finally, we illustrate the theoretical results by experimental results: the funnel controller is applied to a rotatory mechanical system for position control. Close Paper doi:10.1137/100799903 Close
10.	Berger, Thomas; Trenn, Stephan Addition to ``The quasi-Kronecker form for matrix pencils'' Journal Article In: SIAM J. Matrix Anal. & Appl., vol. 34, no. 1, pp. 94–101, 2013. Abstract \| Links \| BibTeX @article{BergTren13, title = {Addition to ``The quasi-Kronecker form for matrix pencils''}, author = {Thomas Berger and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/BergTren13.pdf, Paper}, doi = {10.1137/120883244}, year = {2013}, date = {2013-02-11}, journal = {SIAM J. Matrix Anal. & Appl.}, volume = {34}, number = {1}, pages = {94--101}, abstract = {We refine a result concerning singular matrix pencils and the Wong sequences. In our recent paper [T. Berger and S. Trenn, SIAM J. Matrix Anal. Appl., 33 (2012), pp. 336--368] we have shown that the Wong sequences are sufficient to obtain a quasi-Kronecker form. However, we applied the Wong sequences again on the regular part to decouple the regular matrix pencil corresponding to the finite and infinite eigenvalues. The current paper is an addition to [T. Berger and S. Trenn, SIAM J. Matrix Anal. Appl., 33 (2012), pp. 336--368], which shows that the decoupling of the regular part can be done already with the help of the Wong sequences of the original matrix pencil. Furthermore, we show that the complete Kronecker canonical form can be obtained with the help of the Wong sequences.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We refine a result concerning singular matrix pencils and the Wong sequences. In our recent paper [T. Berger and S. Trenn, SIAM J. Matrix Anal. Appl., 33 (2012), pp. 336--368] we have shown that the Wong sequences are sufficient to obtain a quasi-Kronecker form. However, we applied the Wong sequences again on the regular part to decouple the regular matrix pencil corresponding to the finite and infinite eigenvalues. The current paper is an addition to [T. Berger and S. Trenn, SIAM J. Matrix Anal. Appl., 33 (2012), pp. 336--368], which shows that the decoupling of the regular part can be done already with the help of the Wong sequences of the original matrix pencil. Furthermore, we show that the complete Kronecker canonical form can be obtained with the help of the Wong sequences. Close Paper doi:10.1137/120883244 Close
9.	Berger, Thomas; Trenn, Stephan The quasi-Kronecker form for matrix pencils Journal Article In: SIAM J. Matrix Anal. & Appl., vol. 33, no. 2, pp. 336–368, 2012. Abstract \| Links \| BibTeX @article{BergTren12, title = {The quasi-Kronecker form for matrix pencils}, author = {Thomas Berger and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/BergTren12.pdf, Paper}, doi = {10.1137/110826278}, year = {2012}, date = {2012-05-03}, journal = {SIAM J. Matrix Anal. & Appl.}, volume = {33}, number = {2}, pages = {336--368}, abstract = {We study singular matrix pencils and show that the so-called Wong sequences yield a quasi-Kronecker form. This form decouples the matrix pencil into an underdetermined part, a regular part, and an overdetermined part. This decoupling is sufficient to fully characterize the solution behavior of the differential-algebraic equations associated with the matrix pencil. Furthermore, we show that the minimal indices of the pencil can be determined with only the Wong sequences and that the Kronecker canonical form is a simple corollary of our result; hence, in passing, we also provide a new proof for the Kronecker canonical form. The results are illustrated with an example given by a simple electrical circuit.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We study singular matrix pencils and show that the so-called Wong sequences yield a quasi-Kronecker form. This form decouples the matrix pencil into an underdetermined part, a regular part, and an overdetermined part. This decoupling is sufficient to fully characterize the solution behavior of the differential-algebraic equations associated with the matrix pencil. Furthermore, we show that the minimal indices of the pencil can be determined with only the Wong sequences and that the Kronecker canonical form is a simple corollary of our result; hence, in passing, we also provide a new proof for the Kronecker canonical form. The results are illustrated with an example given by a simple electrical circuit. Close Paper doi:10.1137/110826278 Close
8.	Liberzon, Daniel; Trenn, Stephan Switched nonlinear differential algebraic equations: Solution theory, Lyapunov functions, and stability Journal Article In: Automatica, vol. 48, no. 5, pp. 954–963, 2012. Abstract \| Links \| BibTeX @article{LibeTren12, title = {Switched nonlinear differential algebraic equations: Solution theory, Lyapunov functions, and stability}, author = {Daniel Liberzon and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-LT111011.pdf, Preprint}, doi = {10.1016/j.automatica.2012.02.041}, year = {2012}, date = {2012-05-01}, journal = {Automatica}, volume = {48}, number = {5}, pages = {954--963}, abstract = {We study switched nonlinear differential algebraic equations (DAEs) with respect to existence and nature of solutions as well as stability. We utilize piecewise-smooth distributions introduced in earlier work for linear switched DAEs to establish a solution framework for switched nonlinear DAEs. In particular, we allow induced jumps in the solutions. To study stability, we first generalize Lyapunov’s direct method to non-switched DAEs and afterwards obtain Lyapunov criteria for asymptotic stability of switched DAEs. Developing appropriate generalizations of the concepts of a common Lyapunov function and multiple Lyapunov functions for DAEs, we derive sufficient conditions for asymptotic stability under arbitrary switching and under sufficiently slow average dwell-time switching, respectively.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close We study switched nonlinear differential algebraic equations (DAEs) with respect to existence and nature of solutions as well as stability. We utilize piecewise-smooth distributions introduced in earlier work for linear switched DAEs to establish a solution framework for switched nonlinear DAEs. In particular, we allow induced jumps in the solutions. To study stability, we first generalize Lyapunov’s direct method to non-switched DAEs and afterwards obtain Lyapunov criteria for asymptotic stability of switched DAEs. Developing appropriate generalizations of the concepts of a common Lyapunov function and multiple Lyapunov functions for DAEs, we derive sufficient conditions for asymptotic stability under arbitrary switching and under sufficiently slow average dwell-time switching, respectively. Close Preprint doi:10.1016/j.automatica.2012.02.041 Close
7.	Berger, Thomas; Ilchmann, Achim; Trenn, Stephan The quasi-Weierstraß form for regular matrix pencils Journal Article In: Linear Algebra Appl., vol. 436, no. 10, pp. 4052–4069, 2012, (published online February 2010). Abstract \| Links \| BibTeX @article{BergIlch12a, title = {The quasi-Weierstraß form for regular matrix pencils}, author = {Thomas Berger and Achim Ilchmann and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-BIT091017.pdf, Preprint http://dx.doi.org/10.1016/S0024-3795(11)00688-4, Corrections (see Paragraph 6 of Note to Editors)}, doi = {10.1016/j.laa.2009.12.036}, year = {2012}, date = {2012-01-01}, journal = {Linear Algebra Appl.}, volume = {436}, number = {10}, pages = {4052--4069}, abstract = {Regular linear matrix pencils A- E d in K^{n x n}[d], where K=Q, R or C, and the associated differential algebraic equation (DAE) E x' = A x are studied. The Wong sequences of subspaces are investigate and invoked to decompose the K^n into V* + W, where any bases of the linear spaces V and W* transform the matrix pencil into the Quasi-Weierstraß form. The Quasi-Weierstraß form of the matrix pencil decouples the original DAE into the underlying ODE and the pure DAE or, in other words, decouples the set of initial values into the set of consistent initial values V* and ``pure'' inconsistent initial values W* - {0}. Furthermore, V* and W* are spanned by the generalized eigenvectors at the finite and infinite eigenvalues, resp. The Quasi-Weierstraß form is used to show how chains of generalized eigenvectors at finite and infinite eigenvalues of A- E d lead to the well-known Weierstraß form. So the latter can be viewed as a generalized Jordan form. Finally, it is shown how eigenvector chains constitute a basis for the solution space of E x' = A x.}, note = {published online February 2010}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Regular linear matrix pencils A- E d in K^{n x n}[d], where K=Q, R or C, and the associated differential algebraic equation (DAE) E x' = A x are studied. The Wong sequences of subspaces are investigate and invoked to decompose the K^n into V* + W, where any bases of the linear spaces V and W* transform the matrix pencil into the Quasi-Weierstraß form. The Quasi-Weierstraß form of the matrix pencil decouples the original DAE into the underlying ODE and the pure DAE or, in other words, decouples the set of initial values into the set of consistent initial values V* and ``pure'' inconsistent initial values W* - {0}. Furthermore, V* and W* are spanned by the generalized eigenvectors at the finite and infinite eigenvalues, resp. The Quasi-Weierstraß form is used to show how chains of generalized eigenvectors at finite and infinite eigenvalues of A- E d lead to the well-known Weierstraß form. So the latter can be viewed as a generalized Jordan form. Finally, it is shown how eigenvector chains constitute a basis for the solution space of E x' = A x. Close Preprint Corrections (see Paragraph 6 of Note to Editors) doi:10.1016/j.laa.2009.12.036 Close
6.	Trenn, Stephan Regularity of distributional differential algebraic equations Journal Article In: Math. Control Signals Syst., vol. 21, no. 3, pp. 229–264, 2009. Abstract \| Links \| BibTeX @article{Tren09b, title = {Regularity of distributional differential algebraic equations}, author = {Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-Tre090806.pdf, Preprint}, doi = {10.1007/s00498-009-0045-4}, year = {2009}, date = {2009-12-01}, journal = {Math. Control Signals Syst.}, volume = {21}, number = {3}, pages = {229--264}, abstract = {Time-varying differential algebraic equations (DAEs) of the form E x' = A x + f are considered. The solutions x and the inhomogeneities f are assumed to be distributions (generalized functions). As a new approach, distributional entries in the time-varying coefficient matrices E and A are allowed as well. Since a multiplication for general distributions is not possible, the smaller space of piecewise-smooth distributions is introduced. This space consists of distributions which could be written as the sum of a piecewise-smooth function and locally finite Dirac impulses and derivatives of Dirac impulses. A restriction can be defined for the space of piecewise-smooth distributions, this restriction is used to study DAEs with inconsistent initial values; basically, it is assumed that some past trajectory for x is given and the DAE is activated at some initial time. If this initial trajectory problem has a unique solution for all initial trajectories and all inhomogeneities, then the DAE is called regular. This generalizes the regularity for classical DAEs (i.e. a DAE with constant coefficients). Sufficient and necessary conditions for the regularity of distributional DAEs are given.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Time-varying differential algebraic equations (DAEs) of the form E x' = A x + f are considered. The solutions x and the inhomogeneities f are assumed to be distributions (generalized functions). As a new approach, distributional entries in the time-varying coefficient matrices E and A are allowed as well. Since a multiplication for general distributions is not possible, the smaller space of piecewise-smooth distributions is introduced. This space consists of distributions which could be written as the sum of a piecewise-smooth function and locally finite Dirac impulses and derivatives of Dirac impulses. A restriction can be defined for the space of piecewise-smooth distributions, this restriction is used to study DAEs with inconsistent initial values; basically, it is assumed that some past trajectory for x is given and the DAE is activated at some initial time. If this initial trajectory problem has a unique solution for all initial trajectories and all inhomogeneities, then the DAE is called regular. This generalizes the regularity for classical DAEs (i.e. a DAE with constant coefficients). Sufficient and necessary conditions for the regularity of distributional DAEs are given. Close Preprint doi:10.1007/s00498-009-0045-4 Close
5.	Trenn, Stephan A normal form for pure differential algebraic systems Journal Article In: Linear Algebra Appl., vol. 430, no. 4, pp. 1070 – 1084, 2009. Abstract \| Links \| BibTeX @article{Tren09a, title = {A normal form for pure differential algebraic systems}, author = {Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-Tre081215.pdf, Preprint}, doi = {10.1016/j.laa.2008.10.004}, year = {2009}, date = {2009-01-01}, journal = {Linear Algebra Appl.}, volume = {430}, number = {4}, pages = {1070 -- 1084}, abstract = {In this paper linear time-invariant differential algebraic equations (DAEs) are studied; the focus is on pure DAEs which are DAEs without an ordinary differential equation (ODE) part. A normal form for pure DAEs is given which is similar to the Byrnes–Isidori normal form for ODEs. Furthermore, the normal form exhibits a Kalman-like decomposition into impulse-controllable- and impulse-observable states. This leads to a characterization of impulse-controllability and observability.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper linear time-invariant differential algebraic equations (DAEs) are studied; the focus is on pure DAEs which are DAEs without an ordinary differential equation (ODE) part. A normal form for pure DAEs is given which is similar to the Byrnes–Isidori normal form for ODEs. Furthermore, the normal form exhibits a Kalman-like decomposition into impulse-controllable- and impulse-observable states. This leads to a characterization of impulse-controllability and observability. Close Preprint doi:10.1016/j.laa.2008.10.004 Close
4.	Trenn, Stephan Multilayer perceptrons: approximation order and necessary number of hidden units Journal Article In: IEEE Transactions on Neural Networks, vol. 19, no. 5, pp. 836–844, 2008, ISSN: 1045-9227. Abstract \| Links \| BibTeX @article{Tren08a, title = {Multilayer perceptrons: approximation order and necessary number of hidden units}, author = {Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-Tre071012.pdf, Preprint}, doi = {10.1109/TNN.2007.912306}, issn = {1045-9227}, year = {2008}, date = {2008-05-01}, journal = {IEEE Transactions on Neural Networks}, volume = {19}, number = {5}, pages = {836--844}, abstract = {This paper considers the approximation of sufficiently smooth multivariable functions with a multilayer perceptron (MLP). For a given approximation order, explicit formulas for the necessary number of hidden units and its distributions to the hidden layers of the MLP are derived. These formulas depend only on the number of input variables and on the desired approximation order. The concept of approximation order encompasses Kolmogorov-Gabor polynomials or discrete Volterra series, which are widely used in static and dynamic models of nonlinear systems. The results are obtained by considering structural properties of the Taylor polynomials of the function in question and of the MLP function.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close This paper considers the approximation of sufficiently smooth multivariable functions with a multilayer perceptron (MLP). For a given approximation order, explicit formulas for the necessary number of hidden units and its distributions to the hidden layers of the MLP are derived. These formulas depend only on the number of input variables and on the desired approximation order. The concept of approximation order encompasses Kolmogorov-Gabor polynomials or discrete Volterra series, which are widely used in static and dynamic models of nonlinear systems. The results are obtained by considering structural properties of the Taylor polynomials of the function in question and of the MLP function. Close Preprint doi:10.1109/TNN.2007.912306 Close
3.	Ilchmann, Achim; Sawodny, Oliver; Trenn, Stephan Pneumatic cylinders: modelling and feedback force-control Journal Article In: Int. J. Control, vol. 79, no. 6, pp. 650–661, 2006. Abstract \| Links \| BibTeX @article{IlchSawo06, title = {Pneumatic cylinders: modelling and feedback force-control}, author = {Achim Ilchmann and Oliver Sawodny and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-IST050502.pdf, Preprint}, doi = {10.1080/00207170600645875}, year = {2006}, date = {2006-01-01}, journal = {Int. J. Control}, volume = {79}, number = {6}, pages = {650--661}, abstract = {In this paper, we model, analyse, and control an experimental set-up of a servo pneumatic cylinder. The dynamic behaviour of pneumatic actuator systems is dominant by non-linear functions. First, a mathematical model for the pneumatic system is derived. Secondly, we investigate the mathematical properties of this model and show boundedness and positiveness of certain variables. Thirdly, we prove that a proportional output feedback controller with saturation achieves practical tracking a wide class of reference trajectories. We verify the theoretical results and the effectiveness of the control by experiments.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close In this paper, we model, analyse, and control an experimental set-up of a servo pneumatic cylinder. The dynamic behaviour of pneumatic actuator systems is dominant by non-linear functions. First, a mathematical model for the pneumatic system is derived. Secondly, we investigate the mathematical properties of this model and show boundedness and positiveness of certain variables. Thirdly, we prove that a proportional output feedback controller with saturation achieves practical tracking a wide class of reference trajectories. We verify the theoretical results and the effectiveness of the control by experiments. Close Preprint doi:10.1080/00207170600645875 Close
2.	Ilchmann, Achim; Ryan, Eugene P.; Trenn, Stephan Tracking control: performance funnels and prescribed transient behaviour Journal Article In: Syst. Control Lett., vol. 54, no. 7, pp. 655–670, 2005. Abstract \| Links \| BibTeX @article{IlchRyan05, title = {Tracking control: performance funnels and prescribed transient behaviour}, author = {Achim Ilchmann and Eugene P. Ryan and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-IRT041112.pdf, Preprint}, doi = {10.1016/j.sysconle.2004.11.005}, year = {2005}, date = {2005-01-01}, journal = {Syst. Control Lett.}, volume = {54}, number = {7}, pages = {655--670}, publisher = {Elsevier}, abstract = {Tracking of a reference signal (assumed bounded with essentially bounded derivative) is considered in a context of a class of nonlinear systems, with output y, described by functional differential equations (a generalization of the class of linear minimum-phase systems with positive high-frequency gain). The primary control objective is tracking with prescribed accuracy: given lambda >0 (arbitrarily small), determine a feedback strategy which ensures that, for every admissible system and reference signal, the tracking error e=y-r is ultimately smaller than lambda (that is, \|\|e(t)\|\| < lambda for all t sufficiently large). The second objective is guaranteed transient performance: the evolution of the tracking error should be contained in a prescribed performance funnel F. Adopting the simple non-adaptive feedback control structure u(t)=-k(t)e(t), it is shown that the above objectives can be attained if the gain is generated by the nonlinear, memoryless feedback k(t)=K_F(t,e(t)), where K_F is any continuous function exhibiting two specific properties, the first of which ensures that, if (t,e(t)) approaches the funnel boundary, then the gain attains values sufficiently large to preclude boundary contact, and the second of which obviates the need for large gain values away from the funnel boundary.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Tracking of a reference signal (assumed bounded with essentially bounded derivative) is considered in a context of a class of nonlinear systems, with output y, described by functional differential equations (a generalization of the class of linear minimum-phase systems with positive high-frequency gain). The primary control objective is tracking with prescribed accuracy: given lambda >0 (arbitrarily small), determine a feedback strategy which ensures that, for every admissible system and reference signal, the tracking error e=y-r is ultimately smaller than lambda (that is, \|\|e(t)\|\| < lambda for all t sufficiently large). The second objective is guaranteed transient performance: the evolution of the tracking error should be contained in a prescribed performance funnel F. Adopting the simple non-adaptive feedback control structure u(t)=-k(t)e(t), it is shown that the above objectives can be attained if the gain is generated by the nonlinear, memoryless feedback k(t)=K_F(t,e(t)), where K_F is any continuous function exhibiting two specific properties, the first of which ensures that, if (t,e(t)) approaches the funnel boundary, then the gain attains values sufficiently large to preclude boundary contact, and the second of which obviates the need for large gain values away from the funnel boundary. Close Preprint doi:10.1016/j.sysconle.2004.11.005 Close
1.	Ilchmann, Achim; Trenn, Stephan Input constrained funnel control with applications to chemical reactor models Journal Article In: Syst. Control Lett., vol. 53, no. 5, pp. 361–375, 2004. Abstract \| Links \| BibTeX @article{IlchTren04, title = {Input constrained funnel control with applications to chemical reactor models}, author = {Achim Ilchmann and Stephan Trenn}, url = {http://stephantrenn.net/wp-content/uploads/2017/09/Preprint-IT040715.pdf, Preprint}, doi = {10.1016/j.sysconle.2004.05.014}, year = {2004}, date = {2004-01-01}, journal = {Syst. Control Lett.}, volume = {53}, number = {5}, pages = {361--375}, publisher = {Elsevier}, abstract = {Error feedback control is considered for a class of exothermic chemical reactor models. The control objective is that the temperature T evolves within a prespecified performance envelope or ``funnel'' around the set point temperature T. A simple error feedback control with input constraints of the form u(t)=sat(-k(t)[T(t)-T] + u), u an offset, is introduced which achieves the objective in the presence of disturbances corrupting the measurement. The gain k(t) is a function of the error e(t)=T(t)-T* and its distance to the funnel boundary. The input constraints have to satisfy certain feasibility assumptions in terms of the model data and the operating point T.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Close Error feedback control is considered for a class of exothermic chemical reactor models. The control objective is that the temperature T evolves within a prespecified performance envelope or ``funnel'' around the set point temperature T. A simple error feedback control with input constraints of the form u(t)=sat(-k(t)[T(t)-T] + u), u* an offset, is introduced which achieves the objective in the presence of disturbances corrupting the measurement. The gain k(t) is a function of the error e(t)=T(t)-T* and its distance to the funnel boundary. The input constraints have to satisfy certain feasibility assumptions in terms of the model data and the operating point T*. Close Preprint doi:10.1016/j.sysconle.2004.05.014 Close