SwePub - sökning: L773:2405 8963

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1.	Abdalmoaty, Mohamed, 1986-, et al. (författare) On Re-Weighting, Regularization Selection, and Transient in Nuclear Norm Based Identification 2015 Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; 48:28, s. 92-97 Tidskriftsartikel (refereegranskat)abstract In this contribution, we consider the classical problem of estimating an Output Error model given a set of input-output measurements. First, we develop a regularization method based on the re-weighted nuclear norm heuristic. We show that the re-weighting improves the estimate in terms of better fit. Second, we suggest an implementation method that helps in eliminating the regularization parameters from the problem by introducing a constant based on a validation criterion. Finally, we develop a method for considering the effect of the transient when the initial conditions are unknown. A simple numerical example is used to demonstrate the proposed method in comparison to classical and another recent method based on the nuclear norm heuristic.
2.	Chistiakova, Tatiana, et al. (författare) Nonlinear system identification of the dissolved oxygen to effluent ammonia dynamics in an activated sludge process 2017 Ingår i: IFAC-PapersOnLine. - : Elsevier B.V.. - 2405-8963. ; 50:1, s. 3917-3922 Tidskriftsartikel (refereegranskat)abstract Aeration of biological reactors in wastewater treatment plants is important to obtain a high removal of soluble organic matter as well as for nitrification but requires a significant use of energy. It is hence of importance to control the aeration rate, for example, by ammonium feedback control. The goal of this paper is to model the dynamics from the set point of an existing dissolved oxygen controller to effluent ammonia using two types of system identification methods for a Hammerstein model, including a newly developed recursive variant. The models are estimated and evaluated using noise corrupted data from a complex mechanistic model (Activated Sludge Model no.1). The performance of the estimated nonlinear models are compared with an estimated linear model and it is shown that the nonlinear models give a significantly better fit to the data. The resulting models may be used for adaptive control (using the recursive Hammerstein variant), gain-scheduling control, L2 stability analysis, and model based fault detection.
3.	Abdalmoaty, Mohamed, 1986-, et al. (författare) Continuous Time-Delay Estimation From Sampled Measurements 2023 Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; 56:2, s. 6982-6987 Tidskriftsartikel (refereegranskat)abstract An algorithm for continuous time-delay estimation from sampled output data and a known input of finite energy is presented. The continuous time-delay modeling allows for the estimation of subsample delays. The proposed estimation algorithm consists of two steps. First, the continuous Laguerre spectrum of the output (delayed) signal is estimated from discretetime (sampled) noisy measurements. Second, an estimate of the delay value is obtained via a Laguerre domain model using a continuous-time description of the input. The second step of the algorithm is shown to be intrinsically biased, the bias sources are established, and the bias itself is modeled. The proposed delay estimation approach is compared in a Monte-Carlo simulation with state-of-the-art methods implemented in time, frequency, and Laguerre domain demonstrating comparable or higher accuracy in the considered scenario.
4.	Abdalmoaty, Mohamed, 1986-, et al. (författare) Privacy and Security in Network Controlled Systems via Dynamic Masking 2023 Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; 56:2, s. 991-996 Tidskriftsartikel (refereegranskat)abstract In this paper, we propose a new architecture to enhance the privacy and security of networked control systems against malicious adversaries. We consider an adversary which first learns the system using system identification techniques (privacy), and then performs a data injection attack (security). In particular, we consider an adversary conducting zero-dynamics attacks (ZDA) which maximizes the performance cost of the system whilst staying undetected. Using the proposed architecture, we show that it is possible to (i) introduce significant bias in the system estimates obtained by the adversary: thus providing privacy, and (ii) efficiently detect attacks when the adversary performs a ZDA using the identified system: thus providing security. Through numerical simulations, we illustrate the efficacy of the proposed architecture
5.	Abdalmoaty, Mohamed R., 1986-, et al. (författare) Application of a Linear PEM Estimator to a Stochastic Wiener-Hammerstein Benchmark Problem⁎ 2018 Ingår i: IFAC-PapersOnLine. - : Elsevier B.V.. - 2405-8963. ; 51:15, s. 784-789 Tidskriftsartikel (refereegranskat)abstract The estimation problem of stochastic Wiener-Hammerstein models is recognized to be challenging, mainly due to the analytical intractability of the likelihood function. In this contribution, we apply a computationally attractive prediction error method estimator to a real-data stochastic Wiener-Hammerstein benchmark problem. The estimator is defined using a deterministic predictor that is nonlinear in the input. The prediction error method results in tractable expressions, and Monte Carlo approximations are not necessary. This allows us to tackle several issues considered challenging from the perspective of the current mainstream approach. Under mild conditions, the estimator can be shown to be consistent and asymptotically normal. The results of the method applied to the benchmark data are presented and discussed.
6.	Abdalmoaty, Mohamed R., 1986-, et al. (författare) Identification of a Class of Nonlinear Dynamical Networks⁎ 2018 Ingår i: IFAC-PapersOnLine. - : Elsevier B.V.. - 2405-8963. ; 51:15, s. 868-873 Tidskriftsartikel (refereegranskat)abstract Identification of dynamic networks has attracted considerable interest recently. So far the main focus has been on linear time-invariant networks. Meanwhile, most real-life systems exhibit nonlinear behaviors; consider, for example, two stochastic linear time-invariant systems connected in series, each of which has a nonlinearity at its output. The estimation problem in this case is recognized to be challenging, due to the analytical intractability of both the likelihood function and the optimal one-step ahead predictors of the measured nodes. In this contribution, we introduce a relatively simple prediction error method that may be used for the estimation of nonlinear dynamical networks. The estimator is defined using a deterministic predictor that is nonlinear in the known signals. The estimation problem can be defined using closed-form analytical expressions in several non-trivial cases, and Monte Carlo approximations are not necessarily required. We show, that this is the case for some block-oriented networks with no feedback loops and where all the nonlinear modules are polynomials. Consequently, the proposed method can be applied in situations considered challenging by current approaches. The performance of the estimation method is illustrated on a numerical simulation example.
7.	Abdalmoaty, Mohamed, 1986-, et al. (författare) Simulated Pseudo Maximum Likelihood Identification of Nonlinear Models 2017 Ingår i: The 20th IFAC World Congress. - : Elsevier. ; 50:1, s. 14058-14063 Konferensbidrag (refereegranskat)abstract Nonlinear stochastic parametric models are widely used in various fields. However, for these models, the problem of maximum likelihood identification is very challenging due to the intractability of the likelihood function. Recently, several methods have been developed to approximate the analytically intractable likelihood function and compute either the maximum likelihood or a Bayesian estimator. These methods, albeit asymptotically optimal, are computationally expensive. In this contribution, we present a simulation-based pseudo likelihood estimator for nonlinear stochastic models. It relies only on the first two moments of the model, which are easy to approximate using Monte-Carlo simulations on the model. The resulting estimator is consistent and asymptotically normal. We show that the pseudo maximum likelihood estimator, based on a multivariate normal family, solves a prediction error minimization problem using a parameterized norm and an implicit linear predictor. In the light of this interpretation, we compare with the predictor defined by an ensemble Kalman filter. Although not identical, simulations indicate a close relationship. The performance of the simulated pseudo maximum likelihood method is illustrated in three examples. They include a challenging state-space model of dimension 100 with one output and 2 unknown parameters, as well as an application-motivated model with 5 states, 2 outputs and 5 unknown parameters.
8.	Adaldo, Antonio, et al. (författare) Hybrid coverage and inspection control for anisotropic mobile sensor teams 2017 Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; 50:1, s. 613-618 Tidskriftsartikel (refereegranskat)abstract In this paper, we present an algorithm for pose control of a team of mobile sensors for coverage and inspection applications. The region to cover is abstracted into a finite set of landmarks, and each sensor is responsible to cover some of the landmarks. The sensors progressively improve their coverage by adjusting their poses and by transferring the ownership of some landmarks to each other. Inter-sensor communication is pairwise and intermittent. The sensor team is formally modeled as a multi-agent hybrid system, and an invariance argument formally shows that the team reaches an equilibrium configuration, while a global coverage measure is improving monotonically. A numerical simulation corroborates the theoretical results.
9.	Ahlberg, Sofie, et al. (författare) Mixed-Initiative Control Synthesis: Estimating an Unknown Task Based on Human Control Input 2020 Ingår i: Proceedings of the 3rd IFAC Workshop on Cyber-Physical & Human Systems. - : Elsevier BV. Konferensbidrag (refereegranskat)abstract In this paper we consider a mobile platform controlled by two entities; an autonomousagent and a human user. The human aims for the mobile platform to complete a task, whichwe will denote as the human task, and will impose a control input accordingly, while not beingaware of any other tasks the system should or must execute. The autonomous agent will in turnplan its control input taking in consideration all safety requirements which must be met, sometask which should be completed as much as possible (denoted as the robot task), as well aswhat it believes the human task is based on previous human control input. A framework for theautonomous agent and a mixed initiative controller are designed to guarantee the satisfaction ofthe safety requirements while both the human and robot tasks are violated as little as possible.The framework includes an estimation algorithm of the human task which will improve witheach cycle, eventually converging to a task which is similar to the actual human task. Hence, theautonomous agent will eventually be able to find the optimal plan considering all tasks and thehuman will have no need to interfere again. The process is illustrated with a simulated example
10.	Ahlén, Anders, et al. (författare) Event-Based Transmission Scheduling and LQG Control Over a Packet Dropping Link 2017 Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; 50:1, s. 8945-8950, s. 8945-8950 Tidskriftsartikel (refereegranskat)abstract This paper studies a joint transmission scheduling and controller design problem, which minimizes a linear combination of the control cost and expected energy usage of the sensor. Assuming that the sensor transmission decisions are event-based and determined using the random estimation error covariance information available to the controller, we show a separation in the design of the transmission scheduler and controller. The optimal controller is given as the solution to an LQG-type problem, while the optimal transmission policy is a threshold policy on the estimation error covariance at the controller.
11.	Ahmadi, Alireza, et al. (författare) Optimum failure management strategy for periodically inspected units with imperfect maintenance 2016 Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 49:12, s. 799-804 Tidskriftsartikel (refereegranskat)abstract The aim of this paper is to develop a reliability-based cost model for periodically inspected units subject to hidden functions, with imperfect restoration (overhaul) action after a certain number of inspections. In the model, effectiveness of the consecutive restoration actions is considered, and possible alternative maintenance strategies are identified and compared. The method is based on the Total Cost and identifies the optimum interval and frequency of inspections, as well as restoration that minimize the total life cycle cost. In the proposed model, repair due to failures found by inspection is considered as minimal repair, and restoration/overhaul action is considered as normal repair. The result also shows that for a specific value of restoration effectiveness (θ0), when θ> θ0, the behavior of alternatives tends to as-bad-as-old and for θ< θ0 tends to an as-good-as-new. It is also observed that when the cost of accident is high it is needed to perform inspections at smaller intervals.
12.	Ahmadi, Shervin Parvini, et al. (författare) A Distributed Second-Order Augmented Lagrangian Method for Distributed Model Predictive Control 2021 Ingår i: IFAC PAPERSONLINE. - : ELSEVIER. - 2405-8963. ; , s. 192-199 Konferensbidrag (refereegranskat)abstract In this paper we present a distributed second-order augmented Lagrangian method for distributed model predictive control. We distribute the computations for search direction, step size, and termination criteria over what is known as the clique tree of the problem and calculate each of them using message passing. The algorithm converges to its centralized counterpart and it requires fewer communications between sub-systems as compared to algorithms such as the alternating direction method of multipliers. Results from a simulation study confirm the efficiency of the framework. Copyright (C) 2021 The Authors.
13.	Alegret, Guillem, et al. (författare) Modeling of a Large Marine Two-Stroke Diesel Engine with Cylinder Bypass Valve and EGR System 2015 Ingår i: 10th IFAC Conference on Manoeuvring and Control of Marine Craft MCMC 2015: Copenhagen, 24–26 August 2015. - : IFAC Papers Online. ; , s. 273-278 Konferensbidrag (refereegranskat)abstract A nonlinear mean value engine model (MVEM) of a two-stroke turbocharged marine diesel engine is developed, parameterized and validated against measurement data. The goal is to have a computationally fast and accurate engine model that captures the main dynamics and can be used in the development of control systems for the newly introduced EGR system. The tuning procedure used is explained, and the result is a six-state MVEM with seven control inputs that capture the main system dynamics.
14.	Alisic, Rijad, et al. (författare) Modeling and Stability of Prosumer Heat Networks 2019 Ingår i: IFAC PAPERSONLINE. - : ELSEVIER. - 2405-8963. ; , s. 235-240 Konferensbidrag (refereegranskat)abstract The energy sector is going through a large transformation due to public demands of renewable energy sources. However, a major issue is that these energy sources are intermittent. If designed correctly, district heating systems can naturally contain energy storing units, for example by storing heat in the isolated pipes that make up the heat grid. Additionally, this makes it easier to reuse and transport already generated heat to other users. This paper proposes a mathematical model of such a grid, where excess energy can be retracted from one user and distributed to other users using a network of heat pumps. In some cases, one can balance residual heat production with the heat consumption, temporarily eliminating the need for a centralized heating plant. Existence conditions for stable steady states of such a network with general topology are given. Finally, energy optimal stable steady states are obtained through convex optimization.
15.	Aljanaideh, Khaled F., et al. (författare) New Features in the System Identification Toolbox - Rapprochements with Machine Learning 2021 Ingår i: IFAC PAPERSONLINE. - : ELSEVIER. - 2405-8963. ; , s. 369-373 Konferensbidrag (refereegranskat)abstract The R2021b release of the System Identification ToolboxTM for MATLAB contains new features that enable the use of machine learning techniques for nonlinear system identification. With this release it is possible to build nonlinear ARX models with regression tree ensemble and Gaussian process regression mapping functions. The release contains several other enhancements including, but not limited to, (a) online state estimation using the extended Kalman filter and the unscented Kalman filter with code generation capability; (b) improved handling of initial conditions for transfer functions and polynomial models; (c) a new architecture of nonlinear black-box models that streamlines regressor handling, reduces memory footprint and improves numerical accuracy; and (d) easy incorporation of identification apps in teaching tools and interactive examples by leveraging the Live Editor tasks of MATLAB. Copyright (C) 2021 The Authors.
16.	Altaf, Faisal, 1982, et al. (författare) Electro-thermal Control of Modular Battery using Model Predictive Control with Control Projections 2015 Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 48:15, s. 368-375 Konferensbidrag (refereegranskat)abstract This paper proposes a novel model predictive control algorithm to achieve voltage regulation and simultaneous thermal and SOC balancing of a modular battery using limited future load information. The modular battery is based on multilevel converter (MLC), which provides a large redundancy in voltage synthesis and extra degree-of-freedom in control. The proposed algorithm is based on orthogonal decomposition of controller into two components, one for voltage control and the other for balancing control. The voltage control decisions are made using a simple minimum norm problem whereas the balancing control decisions are made in two stages. The first stage computes a balancing control policy based on an unconstrained LQ problem and the second stage enforces constraint on control actions via projection on a time-varying control constraint polytope. The control algorithm shows promising performance in a simulation study of a four cell modular battery. The performance and the simplicity of the control algorithm make it attractive for real-time implementation in large battery packs.
17.	Altaf, Faisal, 1982, et al. (författare) Evaluating the Potential for Cell Balancing Using a Cascaded Multi-Level Converter Using Convex Optimization 2012 Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. - 9783902823168 ; 3, s. 100-107 Konferensbidrag (refereegranskat)abstract The modeling and design of an active battery cell balancing system using Multi- Level Converter (MLC) for EV/HEV/PHEV is studied. The MLC allows to independently switch ON/OFF each battery cell in a battery pack . This extra degree-of-freedom (DoF) can be exploited to optimally use each cell in order to balance among them the temperature and state-of- charge (SoC). This study has shown that the constrained convex optimization based control policy, exploiting the extra DoF of MLC, gives significant benefit in terms of reduction in temperature and SoC deviations, especially under parameter variations, compared to uniformly using all the cells. Thus, the MLC has promising potential to offer extra benefit of achieving cell balancing while being simultaneously used as a motor driver.
18.	Altaf, Faisal, 1982, et al. (författare) Feasibility Issues of using Three-Phase Multilevel Converter based Cell Balancer in Battery Management System for xEVs 2013 Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. - 9783902823434 ; 46, s. 390-397 Konferensbidrag (refereegranskat)abstract The use of a three-phase multilevel converter (MLC) as an integrated cell balancer and motor driver is investigated for three-phase AC applications in EVs/HEVs/PHEVs. The paper analyzed an issue of additional battery losses caused by the flow of reactive and/or harmonic power from each power cell of the three-phase MLC battery system. The paper also investigates the size of shunt capacitor required for compensation of the losses to acceptable level. This study concludes that the size of the required capacitor is too big for the vehicle application unless some other active compensation is used as well. Another practical way to employ the MLC as a cell balancer is to use it in a cascaded connection with the conventional three-phase two-level voltage source inverter however it may not be a cost-effective solution either due to high component count.
19.	Altaf, Faisal, 1982, et al. (författare) Gain-Scheduled Control of Modular Battery for Thermal and SOC Balancing 2016 Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 49:11, s. 62-69 Konferensbidrag (refereegranskat)abstract This paper proposes a simple constrained proportional controller with gain scheduling for simultaneous thermal and state-of-charge (SOC) balancing of a multilevel converter based modular battery. The proposed balancing controller is devised by investigating structural properties of constrained linear quadratic (LQ) model predictive controller (MPC) introduced in our earlier study. This investigation reveals a particular factorization of time-varying control gain matrices, which leads to approximation of matrix gains as scalar gains under the assumption of small parametric variations among battery cells. The gains are scheduled in load current for nominal cells. This special structure enables the identification of two dominant operational modes of the balancing controller: SOC balancing mode in low to medium load current range and thermal balancing mode in high current range. This study also proposes a simple algorithm for control projection on constraint polytope. The proposed balancing controller is tested in simulations for a modular battery with four significantly mismatched cells. The performance is comparable to MPC, which uses true battery parameters. The performance and the simplicity of the controller make it attractive for real-time implementation in large battery packs.
20.	Andersson, Alina, et al. (författare) Robustness of the Moore-Greitzer Compressor Model's Surge Subsystem with New Dynamic Output Feedback Controllers 2014. - 3 Ingår i: 19th IFAC World Congress. - : Elsevier. - 2405-8963. - 9783902823625 ; 47, s. 3690-3695 Konferensbidrag (refereegranskat)abstract This work presents an extension of a design procedure for dynamic output feedback design for systems with nonlinearities satisfying quadratic constraints. In this work we used an axial gas compressor model described by the 3-state Moore-Greitzer compressor model (MG) that has some challenges for output feedback control design (Planovsky and Nikolaev 1990), (Rubanova 2013). The more general constraints for the investigation of the robustness with respect to parametric uncertainties and measurement noise are shown.
21.	Andersson, Carl R., et al. (författare) Learning deep autoregressive models for hierarchical data 2021 Ingår i: IFAC PapersOnLine. - : Elsevier. - 2405-8963. ; , s. 529-534 Konferensbidrag (refereegranskat)abstract We propose a model for hierarchical structured data as an extension to the stochastic temporal convolutional network. The proposed model combines an autoregressive model with a hierarchical variational autoencoder and downsampling to achieve superior computational complexity. We evaluate the proposed model on two different types of sequential data: speech and handwritten text. The results are promising with the proposed model achieving state-of-the-art performance.
22.	Andersson, Ingemar, 1969, et al. (författare) Detection of Combustion Properties in a Diesel Engine using Block Mounted Accelerometers 2014 Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - : Elsevier BV. - 2405-8963 .- 1474-6670. - 9783902823625 ; 19, s. 11866-11871 Konferensbidrag (refereegranskat)abstract Engine block mounted accelerometers was used for estimating combustion phasing parameters for a heavy duty diesel engine. Several sensor locations were evaluated for its sensitivity to combustion related vibrations and mechanical noise.One sensor-cylinder combination was selected for the evaluation of a simple algorithm to detect 10% and 50% burned mass fraction. The algorithm uses the accumulated accelerometer vibration energy as a base for extracting the 10% and 50% points respectively.The results show that the angular positions for 10% and 50% burned mass fraction can be estimated with precisions of 1.5 and 3 CAD respectively. It is also concluded that the early part of the accelerometer signal has a significant influence from a mechanical noise source related to the start of injection.
23.	Andersson, Sofie, et al. (författare) Control Synthesis for Multi-Agent Systems under Metric Interval Temporal Logic Specifications 2017 Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; , s. 2397-2402 Konferensbidrag (refereegranskat)abstract This paper presents a framework for automatic synthesis of a control sequence for multi-agent systems governed by continuous linear dynamics under timed constraints. First, the motion of the agents in the workspace is abstracted into individual Transition Systems (TS). Second, each agent is assigned with an individual formula given in Metric Interval Temporal Logic (MITL) and in parallel, the team of agents is assigned with a collaborative team formula. The proposed method is based on a correct-by-construction control synthesis method, and hence guarantees that the resulting closed-loop system will satisfy the desired specifications. The specifications considers boolean-valued properties under real-time bounds. Extended simulations has been performed in order to demonstrate the efficiency of the proposed methodology.
24.	Andreasson, Martin, et al. (författare) Coordinated frequency control through MTDC transmission systems 2015 Ingår i: IFAC Proceedings. - : Elsevier. ; , s. 106-111 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.
25.	Anistratov, Pavel, 1990-, et al. (författare) Autonomous-Vehicle Maneuver Planning Using Segmentation and the Alternating Augmented Lagrangian Method 2020 Ingår i: 21th IFAC World Congress Proceedings. - : Elsevier. ; 53:2, s. 15558-15565 Konferensbidrag (refereegranskat)abstract Segmenting a motion-planning problem into smaller subproblems could be beneficial in terms of computational complexity. This observation is used as a basis for a new sub-maneuver decomposition approach investigated in this paper in the context of optimal evasive maneuvers for autonomous ground vehicles. The recently published alternating augmented Lagrangianmethod is adopted and leveraged on, which turns out to fit the problem formulation with several attractive properties of the solution procedure. The decomposition is based on moving the coupling constraints between the sub-maneuvers into a separate coordination problem, which is possible to solve analytically. The remaining constraints and the objective function are decomposed into subproblems, one for each segment, which means that parallel computation is possible and benecial. The method is implemented and evaluated in a safety-critical double lane-change scenario. By using the solution of a low-complexity initialization problem and applying warm-start techniques in the optimization, a solution is possible to obtain after just a few alternating iterations using the developed approach. The resulting computational time is lower than solving one optimization problem for the full maneuver.

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