| 1. |
- Bengtsson, Fredrik, 1989, et al.
(författare)
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Finding feedforward configurations using gramian based interaction measures
- 2021
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Ingår i: Modeling, Identification and Control. - : Norwegian Society of Automatic Control. - 1890-1328 .- 0332-7353. ; 42:1, s. 27-35
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Tidskriftsartikel (refereegranskat)abstract
- A sparse control structure can be seen as a decentralised controller that is expanded to include feedforward or MIMO blocks. Here, use of the gramian based interaction measures to determine a sparse control structure with feedforward is examined. A modification to the method used today is proposed and it is demonstrated that it results in a considerable improvement. Furthermore, recently proposed modifications to scaling gramian based measures are expanded to also cover sparse control structures. We show that the method that yields the best result is when two different scaling methods are combined, using one to design a decentralized controller and another to find feedforward connections.
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| 2. |
- Fransson, Carl-Magnus, 1976, et al.
(författare)
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Non-conservative robust control: Optimized and constrained sensitivity functions
- 2009
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Ingår i: IEEE Transactions on Control Systems Technology. - 1063-6536 .- 1558-0865. ; 17:2, s. 298-308
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Tidskriftsartikel (refereegranskat)abstract
- An automated procedure for optimization of proportional–integral–derivative (PID)-type controller parametersfor single-input, single-output (SISO) plants with explicit modeluncertainty is presented. Robustness to the uncertainties is guaranteedby the use of Horowitz–Sidi bounds, which are used asconstraints when low-frequency performance is optimized in anonconvex but smooth optimization problem. In the optimization(and hence the parameter tuning), separate criteria are formulatedfor low-, mid-, and high-frequency (HF) closed-loop properties.The tradeoff between stability margins, control signals, HF robustness,and low-frequency performance is clarified, and the finalparameter choice is facilitated. We use a combination of globaland local optimization algorithms in the TOMLAB optimizationenvironment and obtain robust convergence without relying ongood initial estimates for the controller parameters. The methodis applied to a controller structure comparison for a plant with anuncertain mechanical resonance and a plant with uncertain timedelay and time constants. For a given control activity, stabilitymargin, and HF robustness, it is shown that a PID controller witha second-order filter and an controller based on loop-shapingachieve approximately the same low-frequency performance.
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| 3. |
- Halvarsson, Björn, et al.
(författare)
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A New Input/Output Pairing Strategy based on Linear Quadratic Gaussian Control
- 2009
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Ingår i: Proc. 7th IEEE International Conference on Control and Automation, Dec. 9-11, Christchurch, New Zealand. - Piscataway, NJ : IEEE. - 9781424447060 ; , s. 978-982
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Konferensbidrag (refereegranskat)abstract
- In this paper a new input/output pairing strategy based on linear quadratic Gaussian control (LQG) is suggested. The strategy is used to compare the expected performance of decentralized control structures in some illustrative examples. The pairing suggestions are compared with the recommendations previously obtained using other interaction measures such as the Relative Gain Array (RGA). The new strategy gives suitable pairing recommendations and is easy to interpret.
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| 4. |
- Halvarsson, Björn, et al.
(författare)
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New Input-Output Pairing Strategies Based on Linear Quadratic Gaussian Control
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Two input-output pairing strategies based on linear quadratic Gaussian (LQG) control are suggested. In the first strategy, denoted linear quadratic interaction index (LQII), input-output pairing suggestions are found from a minimization of the output signal variance. This index not only guides to what pairing should be tried, it also gives a direct measure of how much better a full MIMO controller can perform. The second proposed interaction measure, denoted integrating linear quadratic index array (ILQIA), focuses more on the low frequency behaviour of the considered plant, such as load disturbances. The strategies are used to compare the expected performance of decentralized control structures in some illustrative examples. The pairing suggestions are compared with the recommendations previously obtained using other interaction measures such as the relative gain array (RGA), the Hankel interaction index array (HIIA) and the participation matrix (PM). The new strategies are easy to interpret and give suitable pairing recommendations where other methods may fail.
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| 5. |
- Hedegärd, Marcus, 1979, et al.
(författare)
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An online method for estimation of degradable substrate and biomass in an aerated activated sludge process
- 2011
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 45:19, s. 6308-6320
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Tidskriftsartikel (refereegranskat)abstract
- The activated sludge process for degradation of organic matter is one of the main processes commonly used in biological wastewater treatment, and aeration in that process stands for a large part of the energy consumed in a plant. Hence, there have been many attempts to improve the operation of the activated sludge process using mathematical models of the process. The advanced models used has in general their origin in IWA (former IAWQ) activated sludge model no 1 (ASM1). Unfortunately, optimization w.r.t. discharge and economy is limited for municipal wastewater treatment plants because several of the most important variables; heterotrophic biomass, readily biodegradable soluble substrate, and slowly biodegradable substrate cannot be reliably measured online because of their complexity hiding behind their notation. With the predenitrifying WWTP in Göteborg having post nitrification in trickling filters as an example, we resolve this problem by deriving an observer that estimates these concentrations in the aerobic parts based on only the commonly available online measurements of oxygen, water flows, TSS concentration and supplied air. Based on control theory analysis and simulations it is concluded that estimation does not work for an activated sludge process with aeration in one stirred tank alone, but when the activated sludge process can be described by at least two tanks in series, with oxygen measurements in each tank, the estimates converge. A sensitivity analysis with respect to deviations in model parameters reveals that the derived estimator is also fairly robust to model errors.
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| 6. |
- Hedegärd, Marcus, 1979, et al.
(författare)
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Observer design for the activated sludge process
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The activated sludge process for degradation of organic matter is one of the main processes commonly used in biological wastewater treatment, and aeration in that process stands for a large part of the energy consumed in a plant. Hence, there has been many attempts to optimize the operation of the activated sludge process, which requires a model of the process. The advanced models used has in general their origin in IWA (former IAWQ) activated sludge model no 1 (ASM1). Unfortunately, feasible optimization is limited because several of the most important variables; bacterial biomass, readily biodegradable soluble substrate, and slowly biodegradable particulate substrate cannot be reliably measured online because of their complexity hiding behind their notation. One way to resolve this problem is to estimate these concentrations using an observer and other online measurements at hand. One of the developed methods is an Extended Kalman Filter (EKF) that estimates the relevant concentrations in the ASM1 based on oxygen measurements, and supplied air. For faster convergence, measurements of totally suspended solids in the influent flows are included in the algorithm. It is concluded that estimation does not work for one stirred tank alone, but when the activated sludge process is described by several tanks in series with oxygen measurements in each of them, the estimates converge. The filter has more interesting convergence properties, and to explain these observability properties are investigated. For an implementation of the observer it is necessary to estimate the oxygen transfer function and methods for this are evaluated and further developed. One of these and the EKF were evaluated for a real wastewater plant. The observer is not convergent for this, which among others can be explained by the many uncertainties regarding the model. The optimization problem is considered briefly and is solved for one control variable, and results based on real data are presented.
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| 7. |
- Kianfar, Roozbeh, 1984, et al.
(författare)
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Automated Controller Design using Linear Quantitative Feedback Theory for Nonlinear systems
- 2010
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Ingår i: Reglermöte 2010.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A method to design simple linear controllers for mildly nonlinear systems is presented. In order to design thedesired controller we approximate the behavior of the nonlinear system with a set of linear systems which are derived through linearizations. Classical local linearization is carried out around stationary points but in order to have a better approximation of the nonlinear system selected non-stationary points are taken into account as well. This set of linear models are considered as an uncertainty description for a nominal plant. Quantitative Feedback theory (QFT) may be used to guarantee specification to be fulfilled for all linear models in such an uncertainty set. Traditionally QFT design is carried out in a Nichols diagram by loop shaping of the nominal linear plant. This task highly depends on the experience of the designer and is difficult for unstable systems. In order to facilitate this task an optimization algorithm based on Genetic algorithm is used to automatically synthesize a fixed structure controller. For illustration and evaluation the method is succesfully applied to a Wiener system and a nonlinear Bioreactor benchmark problem.
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| 8. |
- Li, Yang, 1984, et al.
(författare)
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Control-Oriented Modeling of All-Solid-State Batteries Using Physics-Based Equivalent Circuits
- 2022
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Ingår i: IEEE Transactions on Transportation Electrification. - 2332-7782. ; 8:2, s. 2080-2092
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Tidskriftsartikel (refereegranskat)abstract
- Considered as one of the ultimate energy storage technologies for electrified transportation, the emerging all-solid-state batteries (ASSBs) have attracted immense attention due to their superior thermal stability, increased power and energy densities, and prolonged cycle life. To achieve the expected high performance, practical applications of ASSBs require accurate and computationally efficient models for the design and implementation of many onboard management algorithms, so that the ASSB safety, health, and cycling performance can be optimized under a wide range of operating conditions. A control-oriented modeling framework is thus established in this work by systematically simplifying a rigorous partial differential equation (PDE) based model of the ASSBs developed from underlying electrochemical principles. Specifically, partial fraction expansion and moment matching are used to obtain ordinary differential equation based reduced-order models (ROMs). By expressing the models in a canonical circuit form, excellent properties for control design such as structural simplicity and full observability are revealed. Compared to the original PDE model, the developed ROMs have demonstrated high fidelity at significantly improved computational efficiency. Extensive comparisons have also been conducted to verify its superiority to the prevailing models due to the consideration of concentration-dependent diffusion and migration. Such ROMs can thus be used for advanced control design in future intelligent management systems of ASSBs.
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| 9. |
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| 10. |
- Rutquist, Per, 1976, et al.
(författare)
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Finite-time state-constrained optimal control for input-affine systems with actuator noise
- 2011
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Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. - 9783902661937 ; 18:PART 1, s. 5915-5919
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Konferensbidrag (refereegranskat)abstract
- Abstract: We show that a linearizing transformation of the Hamilton-Jacobi-Bellman (HJB) equation can be applied to certain finite-time problem such that the time dependence can be separated and also has a simple analytical solution. The remaining state dependence is the solution to a linear eigenvalue problem that may have an analytical solution or is readily solved numerically. The efficiency of the method is illustrated by an inventory control problem.
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