| 1. |
- Andersson, Malin, et al.
(author)
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Informative battery charging : integrating fast charging and optimal experiments
- 2023
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Conference paper (peer-reviewed)abstract
- This paper presents informative battery charging, a novel approach for battery model parameter estimation during fast charge. Our solution comprises three distinct contributions: first, we develop a semi-explicit solution to an optimal fast charging problem for equivalent circuit models with health-conscious voltage constraints; second, we design optimal experiments for battery model parameter estimation; and third, we suggest a strategy for how the fast charging and experimentation currents can be combined while still satisfying constraints and maintaining acceptable charging times. Numerical results show that model parameters can be identified with lower variance if an optimal experiment is added to the charging procedure.
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| 2. |
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| 3. |
- Taghavian, Hamed, 1992-, et al.
(author)
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Discrete-time SISO LTI Systems with Monotonic Closed-loop Step Responses : Analysis and Control Based on Impulse Response Models
- 2021
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In: IFAC papersonline. - : Elsevier BV. - 2405-8963. ; , s. 476-481
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Conference paper (peer-reviewed)abstract
- An explicit relation between the open- and closed-loop system responses is established directly in the time domain by means of Bell polynomials. This relation is used to derive necessary and sufficient conditions on the open-loop impulse response that guarantees that its closed-loop impulse response under unity feedback is non-negative in a given time range. Based on these conditions, a new design technique for PID controllers is presented that guarantees a monotonic closed-loop step response over a desired time interval. The results hold for any (possibly infinite-dimensional) discrete-time LTI system with a known impulse response. Numerical examples are provided to assess the contribution.
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| 4. |
- Taghavian, Hamed, 1992-, et al.
(author)
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External Positivity of Discrete-Time Linear Systems : Transfer Function Conditions and Output Feedback
- 2023
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In: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 68:11, s. 6649-6663
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Journal article (peer-reviewed)abstract
- This article develops an optimization-based synthesis procedure for fixed-order output-feedback controllers, ensuring a stable closed-loop system with a monotonic step response and rejection of persistent disturbances. This result is based on a unified set of external positivity conditions for discrete-time linear systems. The conditions are derived using an alternative technique for the inverse Z-transform of rational transfer functions based on Bell polynomials and a convenient recurrence relation for the impulse response. Our approach yields a necessary and sufficient condition expressed as polynomial inequalities in the transfer function coefficients. Under additional assumptions, we derive a sequence of weaker but numerically more tractable conditions, leading to an efficient controller synthesis procedure.
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| 5. |
- Taghavian, Hamed, 1992-, et al.
(author)
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Fixed-order controller synthesis for monotonic closed-loop responses : A linear programming approach
- 2020
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In: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963.
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Conference paper (peer-reviewed)abstract
- We consider the problem of synthesizing dynamic controllers to guarantee monotonic closed-loop step responses. Restricting our attention to controllers which yield positive closed-loop systems, we derive synthesis conditions that are linear in the controller parameters. A linear programming formulation that attempts to optimize the decay rate of the closed-loop system while ensuring asymptotic stability and monotonic step response is developed. An alternative approach which guarantees closed-loop stability and a near-monotonic response is also introduced. Several illustrative examples demonstrate the effectiveness of the approach.
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| 6. |
- Taghavian, Hamed, 1992-, et al.
(author)
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Logarithmically completely monotonic rational functions
- 2023
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In: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 155
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Journal article (peer-reviewed)abstract
- This paper studies the class of logarithmically completely monotonic (LCM) functions. These functions play an important role in characterizing externally positive linear systems which find applications in important control problems such as non-overshooting reference tracking. Conditions are proposed to ensure a rational function is LCM, a result that enables the known space of linear continuous-time externally positive systems to be enlarged and an efficient and optimal pole-placement procedure for the monotonic tracking controller synthesis problem to be developed. The presented conditions are shown to be less conservative than existing approaches whilst being computationally tractable.
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| 7. |
- Taghavian, Hamed, 1992-, et al.
(author)
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Non-Overshooting Tracking Controllers Based on Combinatorial Polynomials
- 2023
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In: 2023 62nd IEEE Conference on Decision and Control, CDC 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 677-684
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Conference paper (peer-reviewed)abstract
- This paper presents a technique for designing two-parameter compensators that stabilize a plant and provide offset-free tracking of set-points without overshooting or undershooting. We first represent the impulse response of linear systems using combinatorial polynomials, based on which a new set of conditions is derived for the system to be externally positive. This result is then used in control synthesis to achieve monotonic tracking. In contrast to the methods available in the literature, the proposed technique always gives a solution whenever the problem is feasible, can yield as small a settling time as desired, and provides the freedom to choose the closed-loop poles arbitrarily inside the unit circle, all obtained by low-degree controllers.
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| 8. |
- Taghavian, Hamed, 1992-, et al.
(author)
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Pole-placement for non-overshooting reference tracking
- 2021
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In: 2021 60TH IEEE CONFERENCE ON DECISION AND CONTROL (CDC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 414-421
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Conference paper (peer-reviewed)abstract
- We revisit the classical pole-placement controller design problem with the objective of ensuring non-overshooting and error-free reference tracking. To this end, we present a number of novel conditions for external positivity of discrete-time transfer functions which characterise this non-overshooting property. These conditions are both necessary and sufficient for first- and second-order systems, but only sufficient for higher-order systems. In addition, they have simple geometric interpretations in terms of allowed locations of the closed-loop poles. Based on these conditions, we propose a control design procedure that guarantees a stable closed-loop system with non-overshooting, error-free tracking of step changes in the reference.
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| 9. |
- Taghavian, Hamed, 1992-, et al.
(author)
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Preservation of external positivity in discretization of linear systems
- 2021
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In: European Journal of Control. - : Elsevier BV. - 0947-3580 .- 1435-5671. ; 62, s. 69-74
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Journal article (peer-reviewed)abstract
- We study the preservation of impulse response non-negativity, also known as external positivity, for general discretization methods. The results yield new subsets in the space of transfer function coefficients which ensure external positivity. Consequently, linear programming approaches for designing controllers ensuring monotonic step responses are derived for both continuous and discrete-time systems.
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| 10. |
- Taghavian, Hamed, 1992-, et al.
(author)
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Transient performance of linear systems through symmetric polynomials
- 2022
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In: 2022 IEEE 61ST CONFERENCE ON DECISION AND CONTROL (CDC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 4218-4223
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Conference paper (peer-reviewed)abstract
- Several time-domain constraints for linear systems are characterized using a new representation of the impulse response based on symmetric polynomials. This includes the induced infinity-norm, the peak response and external positivity - performance indices that are complicated to impose in existing LMI frameworks. Each index is described by a convex constraint, explicit in terms of the system poles. Despite their simplicity, numerical examples suggest that these constraints can provide relatively tight performance bounds.
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