| 1. |
- Andreasson, Hannes, et al.
(författare)
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Utilizing discrete event simulation to support conceptual development of production systems
- 2019
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Ingår i: Proceedings - Winter Simulation Conference. - 0891-7736. ; 2019, s. 2073-2084
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Konferensbidrag (refereegranskat)abstract
- Discrete Event Simulation (DES) is a well-reputed tool for analyzing production systems. However, the development of new production system concepts introduces challenges from uncertainties, frequent concept changes, and limited input data. This paper investigates how DES should be applied in this context and proposes an adapted simulation project methodology that sets out to deal with the identified challenges. Key adaptations include parallel and iterative methodology steps, and close involvement of the simulation team in the development of the new concept. The proposed methodology has been applied and evaluated in an industrial case study during the development of a new production system concept. The findings show that the methodology can reduce the impact of the identified challenges and provide valuable feedback which contributes to the development of both the simulation model and the production system concept. Further, an evaluation of investments in new technology can be better facilitated.
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| 2. |
- Andreasson, Jakob, et al.
(författare)
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Saturated ablation in metal hydrides and acceleration of protons and deuterons to keV energies with a soft-x-ray laser
- 2011
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 83:1, s. 016403-
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Tidskriftsartikel (refereegranskat)abstract
- Studies of materials under extreme conditions have relevance to a broad area of research, including planetary physics, fusion research, materials science, and structural biology with x-ray lasers. We study such extreme conditions and experimentally probe the interaction between ultrashort soft x-ray pulses and solid targets (metals and their deuterides) at the FLASH free-electron laser where power densities exceeding 1017 W/cm2 were reached. Time-of-flight ion spectrometry and crater analysis were used to characterize the interaction. The results show the onset of saturation in the ablation process at power densities above 1016 W/cm2. This effect can be linked to a transiently induced x-ray transparency in the solid by the femtosecond x-ray pulse at high power densities. The measured kinetic energies of protons and deuterons ejected from the surface reach several keV and concur with predictions from plasma-expansion models. Simulations of the interactions were performed with a nonlocal thermodynamic equilibrium code with radiation transfer. These calculations return critical depths similar to the observed crater depths and capture the transient surface transparency at higher power densities.
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| 3. |
- Andréasson, Kristofer, et al.
(författare)
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Mycophenolate mofetil for systemic sclerosis : drug exposure exhibits considerable inter-individual variation-a prospective, observational study
- 2020
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Ingår i: Arthritis Research & Therapy. - : BMC. - 1478-6362 .- 1478-6354. ; 22
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Mycophenolate mofetil (MMF) is an established therapy for systemic sclerosis (SSc), but its pharmacokinetics in this disease remains unexplored. We have investigated drug exposure in MMF-treated patients with SSc in relation to clinical features of the disease and common concomitant drugs.Methods: This study was predefined to include 35 MMF-treated SSc patients who were using MMF at a fixed dose of 0.5, 1.0 or 1.5g twice daily since at least 3months. The 12-h drug exposure of the active MMF metabolite mycophenolic acid (MPA) was estimated by repeated analysis of plasma MPA over a 6-h period. This 12-h drug exposure was dose normalised to a daily intake of 3g MMF (MPA_AUC(3g)) in order to compare subjects using MMF at different doses. Drug exposure was analysed in reference to the clinical characteristics including body weight, renal function, autoantibodies, intestinal dysbiosis, intestinal inflammation assessed by faecal (F)-calprotectin, intestinal symptoms assessed by the University of California Los Angeles Scleroderma Trial Consortium Gastrointestinal Tract Instrument 2.0 and concomitant drug usage including proton-pump inhibitors (PPI).Results:Thirty-four out of 35 study participants completed the study. The mean daily MMF dose was 2.1g. Drug exposure expressed as MPA_AUC(3g) varied up to 8-fold between patients (median 115, range 27-226mg h/L).MPA_AUC(3g) was inversely related to body weight (r(s)=-0.58, p<0.001) and renal function (r(s)=-0.34, p=0.054). Anti-topoisomerase-1 antibodies and male sex were associated with lower MPA_AUC(3g) (87 vs 123 and 71 vs 141; p=0.008 and p=0.015, respectively). MPA_AUC(3g) was inversely related to the intestinal abundance of lactobacilli and to F-calprotectin (r(s)=-0.54, p=0.004; r(s)=-0.36, p=0.034), but not to gastrointestinal symptoms. MPA_AUC(3g) was inversely related to PPI usage (r(s)=-0.45, p=0.007). We found no association between MPA_AUC(3g) and disease subtype, disease duration or disease activity.Conclusion: MMF-treated SSc patients exhibit considerable inter-individual variation in drug exposure, and lower MPA levels were primarily found in PPI users with poor prognostic factors. Body weight, renal function, sex, serology, gastrointestinal manifestations and/or measuring individual MPA exposure should be considered when using MMF for SSc.
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| 4. |
- Andreasson, Martin, et al.
(författare)
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Coherence in Synchronizing Power Networks with Distributed Integral Control
- 2017
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Ingår i: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017. - : IEEE. - 9781509028733 ; , s. 6683-6688
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Konferensbidrag (refereegranskat)abstract
- We consider frequency control of synchronous generator networks and study transient performance under both primary and secondary frequency control. We model random step changes in power loads and evaluate performance in terms of expected deviations from a synchronous frequency over the synchronization transient; what can be thought of as lack of frequency coherence. We compare a standard droop control strategy to two secondary proportional integral (PI) controllers: centralized averaging PI control (CAPI) and distributed averaging PI control (DAPI). We show that the performance of a power system with DAPI control is always superior to that of a CAPI controlled system, which in turn has the same transient performance as standard droop control. Furthermore, for a large class of network graphs, performance scales unfavorably with network size with CAPI and droop control, which is not the case with DAPI control. We discuss optimal tuning of the DAPI controller and describe how internodal alignment of the integral states affects performance. Our results are demonstrated through simulations of the Nordic power grid.
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| 5. |
- Andreasson, Martin, 1987-, et al.
(författare)
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Control of MTDC Transmission Systems under Local Information
- 2014
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Ingår i: Decision and Control (CDC), 2014 IEEE 53rd Annual Conference on. - : IEEE conference proceedings. - 9781479977468 ; , s. 1335-1340
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Konferensbidrag (refereegranskat)abstract
- High-voltage direct current (HVDC) is a commonly used technology for long-distance electric power transmission, mainly due to its low resistive losses. In this paper a distributed controller for multi-terminal high-voltage direct current (MTDC) transmission systems is considered. Sufficient conditions for when the proposed controller renders the closed-loop system asymptotically stable are provided. Provided that the closed loop system is asymptotically stable, it is shown that in steady-state a weighted average of the deviations from the nominal voltages is zero. Furthermore, a quadratic cost of the current injections is minimized asymptotically.
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| 6. |
- Andreasson, Martin, 1987-
(författare)
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Control of Multi-Agent Systems with Applications to Distributed Frequency Control Power Systems
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multi-agent systems are interconnected control systems with many application domains. The first part of this thesis considers nonlinear multi-agent systems, where the control input can be decoupled into a product of a nonlinear gain function depending only on the agent's own state, and a nonlinear interaction function depending on the relative states of the agent's neighbors. We prove stability of the overall system, and explicitly characterize the equilibrium state for agents with both single- and double-integrator dynamics.Disturbances may seriously degrade the performance of multi-agent systems. Even constant disturbances will in general cause the agents to diverge, rather than to converge, for many control protocols. In the second part of this thesis we introduce distributed proportional-integral controllers to attenuate constant disturbances in multi-agent systems with first- and second-order dynamics. We derive explicit stability criteria based on the integral gain of the controllers.Lastly, this thesis presents both centralized and distributed frequency controllers for electrical power transmission systems. Based on the theory developed for multi-agent systems, a decentralized controller regulating the system frequencies under load changes is proposed. An optimal distributed frequency controller is also proposed, which in addition to regulating the frequencies to the nominal frequency, minimizes the cost of power generation.
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| 7. |
- Andreasson, Martin, et al.
(författare)
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Coordinated frequency control through MTDC transmission systems
- 2015
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Ingår i: IFAC Proceedings. - : Elsevier. ; , s. 106-111
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Konferensbidrag (refereegranskat)abstract
- In this paper we propose a distributed dynamic controller for sharing frequency control reserves of asynchronous AC systems connected through a multi-terminal HVDC (MTDC) grid. We derive sufficient stability conditions, which guarantee that the frequencies of the AC systems converge to the nominal frequency. Simultaneously, the global quadratic cost of power generation is minimized, resulting in an optimal distribution of generation control reserves. The proposed controller also regulates the voltages of the MTDC grid, asymptotically minimizing a quadratic cost function of the deviations from the nominal voltages. The proposed controller is tested on a high-order dynamic model of a power system consisting of asynchronous AC grids, modelled as IEEE 14 bus networks, connected through a six-terminal HVDC grid. The performance of the controller is successfully evaluated through simulation.
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| 8. |
- Andreasson, Martin, et al.
(författare)
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Correlated Failures of Power Systems : Analysis of the Nordic Grid
- 2011
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Ingår i: Preprints of Workshop on Foundations of Dependable and Secure Cyber-Physical Systems.
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Konferensbidrag (refereegranskat)abstract
- In this work we have analyzed the effectsof correlated failures of power lines on the total systemload shed. The total system load shed is determined bysolving the optimal load shedding problem, which is thesystem operator’s best response to a system failure.We haveintroduced a Monte Carlo based simulation framework forestimating the statistics of the system load shed as a functionof stochastic network parameters, and provide explicitguarantees on the sampling accuracy. This framework hasbeen applied to a 470 bus model of the Nordic power systemand a correlated Bernoulli failure model. It has been foundthat increased correlations between Bernoulli failures ofpower lines can dramatically increase the expected valueas well as the variance of the system load shed.
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| 9. |
- Andreasson, Martin, et al.
(författare)
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Distributed Control of Networked Dynamical Systems : Static Feedback, Integral Action and Consensus
- 2014
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Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 59:7, s. 1750-1764
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Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes distributed control protocols for first- and second-order networked dynamical systems. We propose a class of nonlinear consensus controllers where the input of each agent can be written as a product of a nonlinear gain, and a sum of nonlinear interaction functions. By using integral Lyapunov functions, we prove the stability of the proposed control protocols, and explicitly characterize the equilibrium set. We also propose a distributed proportional-integral (PI) controller for networked dynamical systems. The PI controllers successfully attenuate constant disturbances in the network. We prove that agents with single-integrator dynamics are stable for any integral gain, and give an explicit tight upper bound on the integral gain for when the system is stable for agents with double-integrator dynamics. Throughout the paper we highlight some possible applications of the proposed controllers by realistic simulations of autonomous satellites, power systems and building temperature control.
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| 10. |
- Andreasson, Martin, 1987-, et al.
(författare)
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Distributed controllers for multiterminal HVDC transmission systems
- 2017
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Ingår i: IEEE Transactions on Control of Network Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 2325-5870. ; 4:3, s. 564-574
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Tidskriftsartikel (refereegranskat)abstract
- High-voltage direct current (HVDC) is a commonly used technology for long-distance electric power transmission, mainly due to its low resistive losses. In this paper the voltagedroop method (VDM) is reviewed, and three novel distributed controllers for multi-terminal HVDC (MTDC) transmission systems are proposed. Sufficient conditions for when the proposed controllers render the closed-loop system asymptotically stable are provided. These conditions give insight into suitable controller architecture, e.g., that the communication graph should be identical with the graph of the MTDC system, including edge weights. Provided that the closed-loop systems are asymptotically stable, it is shown that the voltages asymptotically converge to within predefined bounds. Furthermore, a quadratic cost of the injected currents is asymptotically minimized. The proposed controllers are evaluated on a four-bus MTDC system.
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