| 1. |
- Agner, Felix, et al.
(författare)
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Anti-windup coordination strategy around a fair equilibrium in resource sharing networks
- 2023
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Ingår i: IEEE Control Systems Letters. - 2475-1456.
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Tidskriftsartikel (refereegranskat)abstract
- We coordinate interconnected agents where the control input of eachagent is limited by the control input of others. In that sense, the sys-tems have to share a limited resource over a network. Such problems canarise in different areas and it is here motivated by a district heating ex-ample. When the shared resource is insufficient for the combined needof all systems, the resource will have to be shared in an optimal fash-ion. In this scenario, we want the systems to automatically converge toan optimal equilibrium. The contribution of this paper is the proposalof a control architecture where each separate system is controlled by alocal PI controller. The controllers are then coordinated through a globalrank-one anti-windup signal. It is shown that the equilibrium of the pro-posed closed-loop system minimizes the infinity-norm of stationary statedeviations. A proof of linear-domain passivity is given, and a numericalexample highlights the benefits of the proposed method with respect tothe state-of-the-art.
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| 2. |
- Alisic, Rijad, et al.
(författare)
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Model-Free Undetectable Attacks on Linear Systems Using LWE-Based Encryption
- 2023
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Ingår i: IEEE Control Systems Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2475-1456. ; 7, s. 1249-1254
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Tidskriftsartikel (refereegranskat)abstract
- We show that the homomorphic property, a desired property in encrypted control, can lead to failure in the cyber defense of a dynamical control system from undetectable attacks, even though individual signal sequences remain unknown to the attacker. We consider an encryption method based on the Learning with Errors (LWE) problem and demonstrate how model-free undetectable attacks on linear systems over integers can be computed from sampled inputs and outputs that are encrypted. Previous work has shown that computing such attacks is possible on nonencrypted systems. Applying this earlier work to our scenario, with minor modifications, typically amplifies the error in encrypted messages unless a short vector problem is solved. Given that an attacker obtains a short vector, we derive the probability that the attack is detected and show how it explicitly depends on the encryption parameters. Finally, we simulate an attack obtained by our method on an encrypted linear system over integers and conduct an analysis of the probability that the attack will be detected.
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| 3. |
- Arnström, Daniel, et al.
(författare)
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A Linear Programming Method Based on Proximal-Point Iterations With Applications to Multi-Parametric Programming
- 2022
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Ingår i: IEEE Control Systems Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2475-1456. ; 6, s. 2066-2071
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Tidskriftsartikel (refereegranskat)abstract
- We propose a linear programming method that is based on active-set changes and proximal-point iterations. The method solves a sequence of least-distance problems using a warm-started quadratic programming solver that can reuse internal matrix factorizations from the previously solved least-distance problem. We show that the proposed method terminates in a finite number of iterations and that it outperforms state-of-the-art LP solvers in scenarios where an extensive number of small/medium scale LPs need to be solved rapidly, occurring in, for example, multi-parametric programming algorithms. In particular, we show how the proposed method can accelerate operations such as redundancy removal, computation of Chebyshev centers and solving linear feasibility problems.
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| 4. |
- Arnström, Daniel, et al.
(författare)
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Complexity Certification of Proximal-Point Methods for Numerically Stable Quadratic Programming
- 2021
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Ingår i: IEEE Control Systems Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2475-1456. ; 5:4, s. 1381-1386
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Tidskriftsartikel (refereegranskat)abstract
- When solving a quadratic program (QP), one can improve the numerical stability of any QP solver by performing proximal-point outer iterations, resulting in solving a sequence of better conditioned QPs. In this letter we present a method which, for a given multi-parametric quadratic program (mpQP) and any polyhedral set of parameters, determines which sequences of QPs will have to be solved when using outer proximal-point iterations. By knowing this sequence, bounds on the worst-case complexity of the method can be obtained, which is of importance in, for example, real-time model predictive control (MPC) applications. Moreover, we combine the proposed method with previous work on complexity certification for active-set methods to obtain a more detailed certification of the proximal-point methods complexity, namely the total number of inner iterations.
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| 5. |
- Arnström, Daniel, et al.
(författare)
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Exact Complexity Certification of a Nonnegative Least-Squares Method for Quadratic Programming
- 2020
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Ingår i: IEEE Control Systems Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2475-1456. ; 4:4, s. 1036-1041
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Tidskriftsartikel (refereegranskat)abstract
- In this letter we propose a method to exactly certify the complexity of an active-set method which is based on reformulating strictly convex quadratic programs to nonnegative least-squares problems. The exact complexity of the method is determined by proving the correspondence between the method and a standard primal active-set method for quadratic programming applied to the dual of the quadratic program to be solved. Once this correspondence has been established, a complexity certification method which has already been established for the primal active-set method is used to also certify the complexity of the nonnegative least-squares method. The usefulness of the proposed method is illustrated on a multi-parametric quadratic program originating from model predictive control of an inverted pendulum.
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| 6. |
- Aspeel, Antoine, et al.
(författare)
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A Low-Rank Approach to Minimize Sensor-to-Actuator Communication in Finite-Horizon Output Feedback
- 2023
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Ingår i: IEEE Control Systems Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2475-1456. ; 7, s. 3609-3614
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Tidskriftsartikel (refereegranskat)abstract
- Many modern controllers are composed of different components that communicate in real-time over some network with limited resources. In this letter, we are interested in designing a controller that can be implemented with a minimum number of sensor-to-actuator messages, while satisfying safety constraints over a finite horizon. For finite horizon problems, a linear time-varying controller with memory can be represented as a block-lower-triangular matrix. We show that the rank of this matrix exactly captures the minimum number of messages needed to be sent from the sensors to actuators to implement such a controller. Moreover, we introduce a novel matrix factorization called causal factorization that gives the required implementation. Finally, we show that the rank of the controller is the same as the rank of the Youla parameter, enabling the Youla parametrization (or analogous parametrizations) to be used to design the controller, which reduces the overall design problem into a rank minimization one over a convex set. Finally, convex relaxations for rank are used to demonstrate that our approach leads to 20-50% less messages on a simulation than a benchmark method.
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| 7. |
- Atta, Khalid, et al.
(författare)
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On the Generalization and Stability Analysis of Pareto Seeking Control
- 2018
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Ingår i: IEEE Control Systems Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2475-1456. ; 2:1, s. 145-150
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, we address a multi-objective on-line optimization problem for unknown dynamical systems by providing a generalization of the Pareto seeking controller (PSC). The idea of the PSC is to drive the system to the Pareto front in the absence of knowledge of the values of the objectives or the input values to achieve Pareto optimality. Two special cases are presented, for two objectives and three objectives. A stability analysis is presented for the case of two objectives and two inputs, which shows that the controller practically drives the system into the neighborhood of the Pareto front, for any initial condition. Two simulation examples for the special cases are also presented
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| 8. |
- Bahraini, Masoud, 1991, et al.
(författare)
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Optimal Control Design for Perturbed Constrained Networked Control Systems
- 2021
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Ingår i: IEEE Control Systems Letters. - 2475-1456. ; 5:2, s. 553-558
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Tidskriftsartikel (refereegranskat)abstract
- This letter focuses on an optimal control design problem for a class of perturbed networked control systems where a number of systems, subject to state and input constraints, share a communication network with limited bandwidth. We first formulate an optimal control design problem with a constant feedback gain in order to minimize the communication demand for each system while guaranteeing satisfaction of state and input constraints; we show that this optimization problem is very hard to solve. Then, we formulate the same optimal control design problem with a non-constant feedback gain; we argue that this problem is less difficult and results in a lower, or equal, communication demand in comparison to the design with the constant feedback gain. We illustrate and compare these optimal control designs by a simple example.
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| 9. |
- Bai, Ting, et al.
(författare)
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Rollout-Based Charging Strategy for Electric Trucks With Hours-of-Service Regulations
- 2023
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Ingår i: IEEE Control Systems Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2475-1456. ; 7, s. 2167-2172
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Tidskriftsartikel (refereegranskat)abstract
- Freight drivers of electric trucks need to design charging strategies for where and how long to recharge the truck in order to complete delivery missions on time. Moreover, the charging strategies should be aligned with drivers' driving and rest time regulations, known as hours-of-service (HoS) regulations. This letter studies the optimal charging problems of electric trucks with delivery deadlines under HoS constraints. We assume that a collection of charging and rest stations is given along a pre-planned route with known detours and that the problem data are deterministic. The goal is to minimize the total cost associated with the charging and rest decisions during the entire trip. This problem is formulated as a mixed integer program with bilinear constraints, resulting in a high computational load when applying exact solution approaches. To obtain real-time solutions, we develop a rollout-based approximate scheme, which scales linearly with the number of stations while offering solid performance guarantees. We perform simulation studies over the Swedish road network based on realistic truck data. The results show that our rollout-based approach provides near-optimal solutions to the problem in various conditions while cutting the computational time drastically.
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| 10. |
- Batkovic, Ivo, 1992, et al.
(författare)
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A Robust Scenario MPC Approach for Uncertain Multi-Modal Obstacles
- 2021
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Ingår i: IEEE Control Systems Letters. - 2475-1456. ; 5:3, s. 947-952
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Tidskriftsartikel (refereegranskat)abstract
- Motion planning and control algorithms for autonomous vehicles need to be safe, and consider future movements of other road users to ensure collision-free trajectories. In this letter, we present a control scheme based on Model Predictive Control (MPC) with robust constraint satisfaction where the constraint uncertainty, stemming from the road users' behavior, is multimodal. The method combines ideas from tube-based and scenario-based MPC strategies in order to approximate the expected cost and to guarantee robust state and input constraint satisfaction. In particular, we design a feedback policy that is a function of the disturbance mode and allows the controller to take less conservative actions. The effectiveness of the proposed approach is illustrated through two numerical simulations, where we compare it against a standard robust MPC formulation.
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