| 1. |
- Abd-Elrady, Emad, 1970-
(författare)
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Nonlinear Approaches to Periodic Signal Modeling
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Periodic signal modeling plays an important role in different fields. The unifying theme of this thesis is using nonlinear techniques to model periodic signals. The suggested techniques utilize the user pre-knowledge about the signal waveform. This gives these techniques an advantage as compared to others that do not consider such priors. The technique of Part I relies on the fact that a sine wave that is passed through a static nonlinear function produces a harmonic spectrum of overtones. Consequently, the estimated signal model can be parameterized as a known periodic function (with unknown frequency) in cascade with an unknown static nonlinearity. The unknown frequency and the parameters of the static nonlinearity are estimated simultaneously using the recursive prediction error method (RPEM). A treatment of the local convergence properties of the RPEM is provided. Also, an adaptive grid point algorithm is introduced to estimate the unknown frequency and the parameters of the static nonlinearity in a number of adaptively estimated grid points. This gives the RPEM more freedom to select the grid points and hence reduces modeling errors. Limit cycle oscillations problem are encountered in many applications. Therefore, mathematical modeling of limit cycles becomes an essential topic that helps to better understand and/or to avoid limit cycle oscillations in different fields. In Part II, a second-order nonlinear ODE is used to model the periodic signal as a limit cycle oscillation. The right hand side of the ODE model is parameterized using a polynomial function in the states, and then discretized to allow for the implementation of different identification algorithms. Hence, it is possible to obtain highly accurate models by only estimating a few parameters. In Part III, different user aspects for the two nonlinear approaches of the thesis are discussed. Finally, topics for future research are presented.
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| 13. |
- Brus, Linda, 1977-
(författare)
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Nonlinear Identification and Control with Solar Energy Applications
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nonlinear systems occur in industrial processes, economical systems, biotechnology and in many other areas. The thesis treats methods for system identification and control of such nonlinear systems, and applies the proposed methods to a solar heating/cooling plant. Two applications, an anaerobic digestion process and a domestic solar heating system are first used to illustrate properties of an existing nonlinear recursive prediction error identification algorithm. In both cases, the accuracy of the obtained nonlinear black-box models are comparable to the results of application specific grey-box models. Next a convergence analysis is performed, where conditions for convergence are formulated. The results, together with the examples, indicate the need of a method for providing initial parameters for the nonlinear prediction error algorithm. Such a method is then suggested and shown to increase the usefulness of the prediction error algorithm, significantly decreasing the risk for convergence to suboptimal minimum points. Next, the thesis treats model based control of systems with input signal dependent time delays. The approach taken is to develop a controller for systems with constant time delays, and embed it by input signal dependent resampling; the resampling acting as an interface between the system and the controller. Finally a solar collector field for combined cooling and heating of office buildings is used to illustrate the system identification and control strategies discussed earlier in the thesis, the control objective being to control the solar collector output temperature. The system has nonlinear dynamic behavior and large flow dependent time delays. The simulated evaluation using measured disturbances confirm that the controller works as intended. A significant reduction of the impact of variations in solar radiation on the collector outlet temperature is achieved, though the limited control range of the system itself prevents full exploitation of the proposed feedforward control. The methods and results contribute to a better utilization of solar power.
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| 14. |
- Brus, Linda
(författare)
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Recursive black-box identification of nonlinear state-space ODE models
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nonlinear system identification methods is a topic that has been gaining interest over the last years. One reason is the many application areas in controller design and system development. However, the problem of modeling nonlinear systems is complex and finding a general method that can be used for many different applications is difficult.This thesis treats recursive identification methods for identification of systems that can be described by nonlinear ordinary differential equations. The general model structure enables application to a wide range of processes. It is also suitable for usage in combination with many nonlinear controller design methods.The first two papers of the thesis illustrates how a recursive prediction error method (RPEM) can be used for identification of an anaerobic digestion process and a solar heating system. In the former case the model complexity is significantly reduced compared to a semi-physical model of the system, without loosing much in model performance. In the latter case it is shown that it is possible to reach convergence even for a small data set, and that the resulting model is of comparable quality as a previously published grey-box model of the same system.The third paper consists of a convergence analysis of the studied RPEM. The analysis exploits averaging analysis using an associated ordinary differential equation, and formulates conditions for convergence to a minimum of the criterion function. Convergence to a true parameter set is also illustrated by an example.The fourth, and last, paper of this thesis addresses the problem of finding suitable initial parameters e.g. for the RPEM. With a potentially non-convex criterion function the choice of initial parameters becomes decisive for whether the algorithm converges to the global optimum, or a local one. The suggested initialization algorithm is a Kalman filter based method. Experiments using a simulated example show that the Kalman based method can, under beneficial circumstances, be used for initialization of the RPEM. The result is further supported by successful identification experiments of a laboratory scale cascaded tanks process, where the Kalman based method was used for initialization.
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| 15. |
- Carlemalm, Catharina, et al.
(författare)
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Algorithms for time delay estimation using a low complexity exhaustive search
- 1999
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Ingår i: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 44:5, s. 1031-1037
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the problem of time-delay estimation. Two new algorithms for time-delay estimation are developed and analyzed. The suggested methods combine an exhaustive search with a low complexity. Consequently, the problems with local minima of gradient search algorithms are avoided. The receiver operating characteristics (ROC) are computed, and together with simulation results these verify the performance of the estimation schemes.
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| 19. |
- Chistiakova, Tatiana, et al.
(författare)
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Combined L2-stable feedback and feedforward aeration control in a wastewater treatment plant
- 2020
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Ingår i: IEEE Transactions on Control Systems Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-6536 .- 1558-0865. ; 28:3, s. 1017-1024
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Tidskriftsartikel (refereegranskat)abstract
- A nitrifying activated sludge process with ammonium feedback and inflow feedforward control is studied. The feedback and feedforward measurements are subject to time delay and the control loop includes a saturation. A Hammerstein-based model is therefore identified, including process delays and the nonlinearity. A Monod-type nonlinearity is used, as motivated by the oxygen injection efficiency reduction, with increasing dissolved oxygen concentration. The proposed feedback control strategy includes tuning of a linear lag compensator that has a limited low-frequency gain which allows global stability to be established with the Popov criterion. The feedforward controller attenuates the disturbance and provides an overall improvement of the control strategy. The performance of the combined feedback and feedforward aeration controller is evaluated with a benchmark model.
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| 20. |
- Chistiakova, Tatiana, et al.
(författare)
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Input–output stability design of an ammonium based aeration controller for wastewater treatment
- 2018
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Ingår i: 2018 Annual American Control Conference (ACC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538654286 - 9781538654279 - 9781538654293 ; , s. 2964-2971
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Konferensbidrag (refereegranskat)abstract
- Ammonium feedback is commonly used for controlling the aeration in wastewater treatment plants having biological nitrogen removal. The paper proposes the use of a PI controller tuning method based on a simplified identified model with Hammerstein structure. The Hammerstein model accounts for the delay of the process caused by the settler, the multiple bioreactors dynamics and the main nonlinear process effects. The controller tuning method exploits the Popov inequality for a pre-computation of (a subset of) the stability region of the closed loop system as a function of the PI-controller parameters, quantified in terms of the maximum loop delay of the system. The controller parameters are selected in the computed stability region. In the numerical study, the plant is identified as a Hammerstein model using a recently published method, here extended to identify multiple bioreactor tank dynamics. The identification data is obtained from a high fidelity simulator, which is also used for evaluation of the proposed controller tuning method. The results show that the proposed procedure results in a PI-controller tuning with predictable stability properties and a good performance.
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| 22. |
- Chistiakova, Tatiana, et al.
(författare)
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Nonlinear system identification of the dissolved oxygen to effluent ammonia dynamics in an activated sludge process
- 2017
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Ingår i: IFAC-PapersOnLine. - : Elsevier B.V.. - 2405-8963. ; 50:1, s. 3917-3922
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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.
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| 23. |
- Chistiakova, Tatiana, et al.
(författare)
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Nonlinear system identification of the dissolved oxygen to effluent ammonium dynamics in an activated sludge process
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)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 report is to model the dynamics from the set point of an existing dissolved oxygen controller to effluent ammonium 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 performances 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.
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| 32. |
- Halvarsson, Susanne, et al.
(författare)
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Test statistics for low complexity change detection in dynamic systems based on averaged filter models
- 1996
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Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - Atlanta, GA, USA : IEEE. - 0780331923 ; , s. 2845-2848
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Konferensbidrag (refereegranskat)abstract
- This paper presents a new method to detect and discriminate between abrupt changes in dynamics and sudden changes in disturbance levels in dynamic systems. It is assumed that a normalized least mean square (NLMS) adaptive filter estimates the system. The detection method is based on the observation that the estimated taps behave differently in the two studied events. The convergence behavior of the taps is modeled using averaging theory, giving an exponential convergence behavior for each tap. Kalman filtering techniques, based on this model, are then used in order to design a new detection scheme.
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| 33. |
- Händel, Peter, 1962-, et al.
(författare)
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Performance analysis of a correlation based single tone frequency estimator
- 1995
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Ingår i: Signal Processing. - 0165-1684 .- 1872-7557. ; 44:2, s. 223-231
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Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes the frequency error variance of a low complexity single tone frequency estimator based on sample correlations of the input data. In the high SNR scenario it is analytically shown that the accuracy of a properly tuned algorithm is nearly optimal, i.e. nearly attains the Cramer-Rao lower bound. For low SNR the statistical efficiency of the algorithm is degraded, but it is analytically proven that for a large number of samples the error variance attains the lower bound for this class of estimators.
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| 35. |
- Kangas, Ari, et al.
(författare)
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Location coverage and sensitivity with A-GPS
- 2004
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Ingår i: Proc. 18th URSI International Symposium on Electromagnetic Theory. - Ghent, Belgium : URSI. ; , s. 361-363
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Konferensbidrag (refereegranskat)
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| 36. |
- Kangas, Ari, et al.
(författare)
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Positioning in LTE
- 2012
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Ingår i: Handbook of Position Location. - Hoboken, NJ : John Wiley & Sons. - 9780470943427 ; , s. 1081-1127
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Bokkapitel (refereegranskat)
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| 37. |
- Kangas, Ari, et al.
(författare)
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Positioning in LTE
- 2018. - 2nd
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Ingår i: Handbook of Position Location. - : IEEE Press. - 9781119434580
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Bokkapitel (refereegranskat)
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| 38. |
- Lagerqvist, Nina, et al.
(författare)
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Evaluation of 11 SARS-CoV-2 antibody tests by using samples from patients with defined IgG antibody titers
- 2021
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- We evaluated the performance of 11 SARS-CoV-2 antibody tests using a reference set of heat-inactivated samples from 278 unexposed persons and 258 COVID-19 patients, some of whom contributed serial samples. The reference set included samples with a variation in SARS-CoV-2 IgG antibody titers, as determined by an in-house immunofluorescence assay (IFA). The five evaluated rapid diagnostic tests had a specificity of 99.0% and a sensitivity that ranged from 56.3 to 81.6% and decreased with low IFA IgG titers. The specificity was > 99% for five out of six platform-based tests, and when assessed using samples collected ≥ 22 days after symptom onset, two assays had a sensitivity of > 96%. These two assays also detected samples with low IFA titers more frequently than the other assays. In conclusion, the evaluated antibody tests showed a heterogeneity in their performances and only a few tests performed well with samples having low IFA IgG titers, an important aspect for diagnostics and epidemiological investigations.
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| 48. |
- Martins da Silva, Margarida, et al.
(författare)
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An adaptive controller for propofol in anesthesia under synergistic remifentanil disturbances
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- An adaptive controller for propofol administration relying on a minimally parameterized SISO Wiener model for the depth of anesthesia is proposed. The exact linearization of this minimal Wiener structure using the continuous-time model parameters estimated online by an extended Kalman filter is a key point in the design. A linear quadratic Gaussian controller is developed for the exactly linearized system. The depth of anesthesia is considered to be measured by the bispectral index. Excellent results were obtained when the robustness of the proposed controller with respect to inter and intrapatient variability was assessed through simulations on a database of 500 patients. The closed-loop system showed good disturbance rejection properties when the synergistic effect of remifentanil in the depth of anesthesia was considered.
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