| 1. |
- Abera, Bethlehem, et al.
(författare)
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An Overview of Biogas Plants in Ethiopia and Sweden: What Ethiopia Can Learn from Sweden
- 2023
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Ingår i: 2023 IEEE PES/IAS PowerAfrica, PowerAfrica 2023.
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Konferensbidrag (refereegranskat)abstract
- To promote the development of Ethiopia's biogas sector, this paper gives an overview and status of biogas in Ethiopia and Sweden, highlights the challenges impeding the expansion of biogas technology in Ethiopia, and tries to suggest lessons Ethiopia can learn from Sweden. Currently, Ethiopia has over 36,000 digesters installed, while Sweden has 281. The challenges to the expansion of biogas in Ethiopia stated in this paper include a lack of stated policy to include biogas as part of the energy system, a lack of research and development facilities dedicated to biogas, higher investment costs, the inefficiency of digesters, a lack of cooperation among stakeholders, and a lack of a comprehensive database on the subject. We recommend that Ethiopia learn from Sweden about developing a dedicated policy and roadmap, developing a national competence center like Sweden's Biogas Research Center, improving production and efficiency, considering multiple feedstocks, and appropriate waste collection, segregation, and allocation.
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| 2. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Automatically adjusting light spectrum for optimal short term photosynthetic rate
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of light emitting diods (LEDs) as greenhouse illumination is increasingly common. When each LED color is individually dimmable both light spectrum and light intensity can be tuned, which opens up for optimisation of photosynthesis through automatic control of light quality and quantity. However, this requires a non-destructive biological growth signal that can be measured fast, remotely and preferably without interacting with the plants. A potential candidate signal is steady-state chlorophyll a fluorescence gain at 740 nm, defined as dF740/dq, i.e. the difference in fluorescence at 740 nm divided by the difference in incident light quanta caused by a (small) change in intensity of each individual LED color in the lamp (Ahlman et al., 2017). By automatically adjusting the spectrum, to aim for equal fluorescence gains for all LED colors (Wik et al., 2014), the instant photosynthetic rate can be optimised given a preset electric power input to the lamp. When implementing such a controller though, constraints on the spectral distribution are needed to minimise a negative impact on plant morphology.
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| 3. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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LED spectrum optimisation using steady-state fluorescence gains
- 2016
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Ingår i: Acta Horticulturae. - 0567-7572. - 9789462611092 ; 1134, s. 367-374
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Tidskriftsartikel (refereegranskat)abstract
- The use of light emitting diodes (LEDs) in greenhouses entails the possibility to control the light in a better way, since both spectrum and light intensity can be adjusted. We aim at developing a method to automatically find the optimal spectrum in terms of energy consumption and plant growth. Previous work shows that chlorophyll fluorescence (ChlF) at 740 nm strongly correlates with the photosynthetic rate (carbon dioxide uptake rate) and that the net efficiency of a LED group therefore is coupled to the fluorescence gain w.r.t. energy consumption, i.e., the slope of a curve depicting steady-state ChlF versus applied power to the LED group. In the present work we compare the fluorescence gains for six different LED types (wavelength peaks from 400 to 660 nm) and six different species: tomato, cucumber, basil, lettuce (two species) and dill. We also compare two different kinds of experiments: steadystate experiments, waiting for the fluorescence to reach a steady state at a few incident light intensities, and ramp experiments, where the light intensity is increased slowly. The ramp experiment gives essentially the same information as the steady-state experiment, but was found to slightly overestimate the gains of the blue LEDs. Being aware of this, it should be possible to initially use the faster (ramp) method in order to find the right light composition, possibly using steady-state experiments for a few LED colours to fine tune the lamp. The relative order of the fluorescence gains among the tested LED groups is similar, but not identical, for all species tested. LED660 has the highest fluorescence gain w.r.t. incident photon flux density, and LED400 and/or LED530 have the lowest. However, the important quantity is in fact the fluorescence gain w.r.t. applied electrical power. If the individual electrical efficiencies of the LEDs change the most efficient power split on the different LEDs might change.
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| 4. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Light spectrum optimization for plant growth using biological feedback
- 2018
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Ingår i: EasyChair Preprints. - : EasyChair. - 2516-2314.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of light emitting diods (LEDs) as greenhouse illumination is increasingly common. When each LED color is individually dimmable both light spectrum and light intensity can be tuned, which opens up for optimisation of photosynthesis through automatic control of light quality and quantity. However, this requires a non-destructive biological growth signal that can be measured fast, remotely and preferably without interacting with the plants. A potential candidate signal is steady-state chlorophyll a fluorescence gain at 740 nm, defined as dF740/dq, i.e. the difference in fluorescence at 740 nm divided by the difference in incident light quanta caused by a (small) change in intensity of each individual LED color in the lamp (Ahlman et al., 2017). By automatically adjusting the spectrum, to aim for equal fluorescence gains for all LED colors (Wik et al., 2014), the instant photosynthetic rate can be optimised given a preset electric power input to the lamp. When implementing such a controller though, constraints on the spectral distribution are needed to minimise a negative impact on plant morphology. In this study measurements were conducted (on cucumber and lettuce) under different background light, and at each setting excitation signals were sequentially added by each of six different LED colors (peak wavelength at 400, 420, 450, 530, 630 and 660 nm). The corresponding changes in steady-state fluorescence were measured with a spectrometer and the fluorescence gain (dF740/dq) was calculated for each LED color and at each background light setting. These fluorescence gains were compared in order to evaluate the different LEDs' relative effect on photosynthesis under each of the different background light settings.
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| 5. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Relation between Changes in Photosynthetic Rate and Changes in Canopy Level Chlorophyll Fluorescence Generated by Light Excitation of Different Led Colours in Various Background Light
- 2019
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- Using light emitting diodes (LEDs) for greenhouse illumination enables the use of automatic control, since both light quality and quantity can be tuned. Potential candidate signals when using biological feedback for light optimisation are steady-state chlorophyll a fluorescence gains at 740 nm, defined as the difference in steady-state fluorescence at 740 nm divided by the difference in incident light quanta caused by (a small) excitation of different LED colours. In this study, experiments were conducted under various background light (quality and quantity) to evaluate if these fluorescence gains change relative to each other. The light regimes investigated were intensities in the range 160-1000 molm-2s-1, and a spectral distribution ranging from 50% to 100% red light. No significant changes in the mutual relation of the fluorescence gains for the investigated LED colours (400, 420, 450, 530, 630 and 660 nm), could be observed when the background light quality was changed. However, changes were noticed as function of light quantity. When passing the photosynthesis saturate intensity level, no further changes in the mutual fluorescence gains could be observed.
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| 6. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Stress Detection Using Proximal Sensing of Chlorophyll Fluorescence on the Canopy Level
- 2021
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Ingår i: AgriEngineering. - : MDPI AG. - 2624-7402. ; 3:3, s. 648-668
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Tidskriftsartikel (refereegranskat)abstract
- Chlorophyll fluorescence is interesting for phenotyping applications as it is rich in biological information and can be measured remotely and non-destructively. There are several techniques for measuring and analysing this signal. However, the standard methods use rather extreme conditions, e.g., saturating light and dark adaption, which are difficult to accommodate in the field or in a greenhouse and, hence, limit their use for high-throughput phenotyping. In this article, we use a different approach, extracting plant health information from the dynamics of the chlorophyll fluorescence induced by a weak light excitation and no dark adaption, to classify plants as healthy or unhealthy. To evaluate the method, we scanned over a number of species (lettuce, lemon balm, tomato, basil, and strawberries) exposed to either abiotic stress (drought and salt) or biotic stress factors (root infection using Pythium ultimum and leaf infection using Powdery mildew Podosphaera aphanis ). Our conclusions are that, for abiotic stress, the proposed method was very successful, while, for powdery mildew, a method with spatial resolution would be desirable due to the nature of the infection, i.e., point-wise spread. Pythium infection on the roots is not visually detectable in the same way as powdery mildew; however, it affects the whole plant, making the method an interesting option for Pythium detection. However, further research is necessary to determine the limit of infection needed to detect the stress with the proposed method.
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| 7. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Using chlorophyll a fluorescence gains to optimize LED light spectrum for short term photosynthesis
- 2017
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Ingår i: Computers and Electronics in Agriculture. - : Elsevier BV. - 0168-1699. ; 142, s. 224-234
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Tidskriftsartikel (refereegranskat)abstract
- When changing from the traditional high pressure sodium (HPS) lamps to light emitting diode (LED) lamps there is a quite unexplored energy saving potential in the fact that they are far better suited for control, since both spectrum and light intensity can be adjusted. This work aims at finding a way to automatically adjust the spectrum of a LED lamp, equipped with several different types of LEDs, to maximize plant growth by feedback of a remote online measure correlated with growth.A series of experiments were conducted on basil plants in order to examine whether remotely sensed steady-state chlorophyll fluorescence (F740) can be used for this purpose, and if its derivatives (fluorescence gains) w.r.t. applied powers change relative to each other for different light intensities and spectraA strong correlation between F740 and photosynthetic rate was indeed found. However, the order (w.r.t. LED type) of the fluorescence gains was only moderately affected by the light intensities and spectra investigated. The gain was highest w.r.t. red light (630 nm), though, when taking the electrical efficiencies of individual LED types into consideration, blue LEDs (450 nm) were equally, or even more efficient than the red onesAn online controller to regulate optimal spectrum for basil appears to be unnecessary. However, the fluorescence gains could be used to adapt to changes in the efficiencies when crops and operating conditions change, or when the diodes degrade. The method also shows promise as a tool to find optimal light intensity levels as well as identifying plant stress.
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| 8. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Using Fluorescence as Control Parameter to Decide Optimal Light Spectrum for Plant Growth
- 2015
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Ingår i: Proceedings 19th Nordic Process Control Workshop, Hurtigruta, Norway, Jan 2015. ; , s. 9:1-4.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modern greenhouses having lighting systems are large consumers of electricity. In Europe alone, the lighting consumption is estimated to 150 TWh per year. High pressure sodium (HPS) lamps are still dominating and the illumination is in general controlled manually by on/off control. Changing to light emitting diodes (LED) gives the possibility of adapting the spectrum (i.e. changing the power split to diodes of different colours) and to gradually changing the intensity, which implies an energy saving potential. The optimal spectrum might depend on a number of factors, for example plant species, required characteristics and energy use effciency on the diodes.Using LEDs with different blue to red (B:R) ratios, as a supplement to sunlight, have been investigated for growing of cucumber seedling [Hernández and Kubota, 2014] and tomato seedling [Hernández and Kubota, 2012]. Their conclusion was that 100% red LED is preferred, indicating that the blue light in the sunlight is sufficient (B:R in sunlight is about 4:3 on photons=m2=s basis [ASTM, 2012].
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| 9. |
- Bengtsson, Fredrik, 1989, et al.
(författare)
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A multiple input, multiple output model generator
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- When new methods of design and analysis are introduced in the control engineering field, it is scientificallyimportant to compare the new results with existing methods. Often this requires application of the methodson examples, and for this purpose benchmark processes are introduced. However, in many areas of controlengineering research the number of examples is limited to a relatively few examples, and in particular so whenmulti-input multi-output (MIMO) systems are considered. For a thorough assessment of a method, however, aslarge number of relevant models as possible should be used. As a remedy we propose a framework for generatinglinear multiple input, multiple output models based on predefined system properties, such as model type, size,stability, time constants, delays etc.
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| 10. |
- Bengtsson, Fredrik, 1989, et al.
(författare)
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A new method of scaling the gramian based input-output pairing methods for improved results
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A key problem in the application of process control systems is to decide which inputs should control which outputs. There are multiple ways to solve this problem, among them using gramian based measures, which include the Hankel interaction index array, the participation matrix and the Σ2 method. These methods take into account system dynamics as opposed to many other methods which only consider the steady-state system. However, the gramian based methods have issues with input and output scaling. Generally, this is resolved by scaling all inputs and outputs to have equal range. We will, however, demonstrate how this can result in an incorrect pairing. Further, we examine scaling of the gramian based measures, using either row or column sums, or by utilizing the Sinkhorn-Knopp algorithm instead. Then, to more systematically analyze the benefits of the scaling schemes, a multiple input multiple output model generator is used to test the different schemes on a large number of systems. This, along with implementation of automatic controller tuning, allows for a statistical comparison of the scaling methods. This assessment shows considerable benefits to be gained from the alternative scaling of the gramian based measures, especially when using the Sinkhorn-Knopp algorithm. The use of this method also has the advantage that the results are completely independent of the original scaling of the inputs and outputs.
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| 11. |
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| 12. |
- 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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| 13. |
- Bengtsson, Fredrik, 1989, et al.
(författare)
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LQG Control for Systems with Random Unbounded Communication Delay
- 2016
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Ingår i: Proceedings of the 55th IEEE Conference on Decision and Control (CDC 2016); Las Vegas; United States; 12-14 December 2016. - 0743-1546. - 9781509018376 ; , s. Art no 7798406, Pages 1048-1055
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Konferensbidrag (refereegranskat)abstract
- In this paper LQG control over unreliable communication links is examined. That is to say, the communication channels between the controller and the actuators and between the sensors and the controller are unreliable. This is of growing importance as networked control systems and use of wireless communication in control are becoming increasingly common. A proposed approach is to use tree codes to turn lossy channels into ones with a random delay. The problem of how to optimize LQG control in this case is examined, and it is found that to optimize LQG control previous control signals must also be used. Only the situation where communication between the components is done with acknowledgments is examined. An optimal solution is derived for finite horizon discrete hold-input LQG control for this case. The solution is compared with standard LQG control in simulations, which demonstrate that a significant improvement in the cost can be achieved when the probability of delay is high.
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| 14. |
- Bengtsson, Fredrik, 1989, et al.
(författare)
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Modeling of tensile index using uncertain data sets
- 2020
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Ingår i: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 2000-0669 .- 0283-2631. ; 35:2, s. 231-242
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this investigation is to analyze and model tensile index. Two approaches are used, one based on training and validation data, while the other novel approach tests models using all possible combinations of data points. This approach is focused on small data sets which have here been obtained from nineteen pulp samples at different refining conditions in a full-scale TMP production line with a CD-76 refiner as a primary stage. From each pulp sample twenty handsheet strips for tensile index measurements were performed. Initially, specific energy and the external variables (dilution water feed rates and plate gaps) are used as predictors in a modeling approach based on an adjusted R 2 {R^{2}} approach. Thereafter, the resulting models are compared with a combination of specific energy and internal variables (primarily consistencies) obtained from temperature measurements inside the refining zones using a soft sensor concept. It is found that specific energy and internal variables as predictors outperform the external variables when estimating tensile index.
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| 15. |
- Bengtsson, Fredrik, 1989, et al.
(författare)
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On the modeling of pulp properties in CTMP processes
- 2021
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Ingår i: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 2000-0669 .- 0283-2631. ; 36:2, s. 234-248
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Tidskriftsartikel (refereegranskat)abstract
- The goal of this paper is to model the pulp properties fiber length, shives width and freeness. This will be done utilizing specific energy, flat zone inlet consistency and the internal variables, consistencies and fiber residence times estimated from refining zone soft sensors. The models are designed using more than 3600 hours of data from a RGP82CD refiner. The pulp properties are sampled using a measurement device positioned after the latency chest. Such measurements are noisy and irregularly sampled which opens for a number of challenges to overcome in modeling procedures. In this paper it is shown that the models for shives width and fiber length are capable of predicting most of the major dynamics. However, for freeness no reliable linear models can be derived. When estimating fiber length, the specific energy together with flat zone inlet consistency, fiber residence times and the consistency in the conical zone were the dominant inputs. For shives width it was found that a similar set of inputs resulted in the best models, except that the consistencies during normal process conditions did not significantly influence shives width. Furthermore, fiber residence times were shown to have considerably more pronounced impact on fiber length compared with shives width estimates.
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| 16. |
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| 17. |
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| 18. |
- Bengtsson, Fredrik, 1989, et al.
(författare)
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Resolving issues of scaling for gramian-based input–output pairing methods
- 2022
-
Ingår i: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; 95:3, s. 679-691
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Tidskriftsartikel (refereegranskat)abstract
- A key problem in process control is to decide which inputs should control which outputs. There are multiple ways to solve this problem, among them using gramian-based measures, which include the Hankel interaction index array, the participation matrix and the (Formula presented.) method. The gramian-based measures, however, have issues with input and output scaling. Generally, this is resolved by scaling all inputs and outputs to have equal range. However, we demonstrate how this can result in an incorrect pairing and examine alternative methods of scaling the gramian-based measures, using either row or column sums or by utilising the Sinkhorn-Knopp algorithm. To systematically analyse the benefits of the scaling schemes, a multiple-input multiple-output model generator is used to test the different schemes on a large number of systems. This assessment shows considerable benefits to be gained from the alternative scaling of the gramian-based measures, especially when using the Sinkhorn-Knopp algorithm.
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| 19. |
- Bengtsson, Fredrik, 1989, et al.
(författare)
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Stochastic optimal control over unreliable communication links
- 2022
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098. ; 142
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper LQG control over unreliable communication links is derived. That is to say, the communication channels between the controller and the actuators and between the sensors and the controller are unreliable. This is of growing importance as networked control systems and use of wireless communication in control are becoming increasingly common. The problem of how to optimize LQG control in this case is examined in the situation where communication between the components is done with acknowledgments. Previous solutions to finite horizon discrete time hold-input LQG control for this case do not fully utilize the available information. Here a new solution is presented which resolves this limitation. The solution is linear and covers communication channels subject to both packet losses and delays. The new control scheme is compared with previous solutions for LQG control in simulations, which demonstrates that a significant improvement in the cost can be achieved by fully utilizing the available information.
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| 20. |
- Bånkestad, Daniel, et al.
(författare)
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Growth tracking of basil by proximal remote sensing of chlorophyll fluorescence in growth chamber and greenhouse environments
- 2016
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Ingår i: Computers and Electronics in Agriculture. - : Elsevier BV. - 0168-1699. ; 128, s. 77-86
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Tidskriftsartikel (refereegranskat)abstract
- Remote sensing is a promising tool for plant phenotyping and precision farming, as it allows for non-invasive, fast and automated measurements of relevant plant traits with spatial and temporal resolution. The simplest and most used remote sensing application in the field is to use reflectance vegetation indices, based on the optical properties of chlorophyll, as indicators of variables of interest. However, the applicability is limited by their sensitivity to environmental conditions and canopy structure. Another remotely sensed signal related to chlorophyll is chlorophyll fluorescence. Compared to reflectance it is plant specific and directly linked to plant physiological processes; but it is also weak, which complicates its use for in-field applications. This study evaluates the performance of an active proximal remote sensing system utilizing the chlorophyll fluorescence ratio method, measuring the ratio of red fluorescence to far-red fluorescence (termed SFR), for the assessment of growth and biomass as an alternative or complement to reflectance vegetation indices. Basil plants were subject to chlorophyll fluorescence and weight measurements periodically throughout commercial growth cycles, both in a laboratory and commercial greenhouse environment. In the laboratory, SFR showed a strong linear relationship with dry weight on logarithmic scales. Further characterization of the method indicated that it is independent of background light and the same growth dynamics is obtained irrespective of point in time during chlorophyll fluorescence induction. The same trend that was observed in the laboratory was also observed in the greenhouse, but varying background light from the sun and from supplemental lighting added complexity that needs to be addressed in further studies. To our knowledge, the strong link between SFR and biomass, both in a closed environment and greenhouse setting, has not so clearly been demonstrated on canopy level before. Owing to the simplicity of the method, being relatively cheap and fast, it has potential for commercial applications.
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| 21. |
- Cai, Yao, 1996, et al.
(författare)
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Fast Charging Control of Lithium-Ion Batteries: Effects of Input, Model, and Parameter Uncertainties
- 2022
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Ingår i: 2022 European Control Conference, ECC 2022. ; , s. 1647-1653
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Konferensbidrag (refereegranskat)abstract
- The foundation of advanced battery management is computationally efficient control-oriented models that can capture the key battery characteristics. The selection of an appropriate battery model is usually focused on model order, whereas the effects of input and parameter uncertainties are often overlooked. This work aims to pinpoint the minimum model complexity for health-conscious fast charging control of lithiumion batteries in relation to sensor biases and parameter errors. Starting from a high-fidelity physics-based model that describes both the normal intercalation reaction and the dominant side reactions, Padé approximation and the finite volume method are employed for model simplification, with the number of control volumes as a tuning parameter. For given requirements on modeling accuracy, extensive model-based simulations are conducted to find the simplest models, based on which the effects of current sensor biases and parameter errors are systematically studied. The results show that relatively loworder models can be well qualified for the control of voltage, state of charge, and temperature. On the other hand, high-order models are necessary for health management, particularly during fast charging, and the choice of the safety margin should also take the current sensor biases into consideration. Furthermore, when the parameters have a certain extent of uncertainties, increasing the model order will not provide improvement in model accuracy.
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| 22. |
- Cai, Yao, 1996, et al.
(författare)
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Safety margin for Li-plating-free fast-charging of Li-ion batteries considering parameter uncertainty
- 2024
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Ingår i: 8th IEEE Conference on Control Technology and Applications (CCTA).
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Konferensbidrag (refereegranskat)abstract
- The widespread adoption of electric vehicles has led to increasing concerns about range anxiety. Fast charging of the lithium-ion battery is an important part of addressing this problem. However, a higher charging rate also tends to cause more rapid degradation and shorter battery life. Therefore, how to charge as fast as possible while not leading to excessive aging has become an important research topic. This paper introduces a single particle model-based inversion-based fast charging method with a calculated safety margin. The inversion-based fast-charging method relies a lot on the accuracy of the model parameters that cannot be identified precisely due to inevitable differences between the model and the plant. Provided with the range of parameter uncertainty, a theoretical Li-plating safety margin is calculated with which lithium-plating can be completely avoided. Simulation results demonstrate the effectiveness of the proposed algorithm.
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| 23. |
- Carstensen, Anna-Maria, 1982, et al.
(författare)
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Exploring the dynamics of remotely detected fluorescence transients from basil as a potential feedback for lighting control in greenhouses
- 2016
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Ingår i: Acta Horticulturae. - 0567-7572. - 9789462611092 ; 1134, s. 375-383
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Tidskriftsartikel (refereegranskat)abstract
- Optimizing artificial lighting control in industrial scale greenhouses has a potential for increased crop yields, energy savings and production timing. One possible component in controlling greenhouse lighting is continuous and accurate measurement of plant photosynthetic performance. A widely used tool for measuring photosynthetic performance non-invasively is chlorophyll fluorescence. For the purpose of automatic control, remote sensing of fluorescence is favourable, since it provides an aggregated measure for a large canopy area. However, adaptation of traditional fluorescence methodologies to remote sensing is problematic since they are based on the analysis of fluorescence intensities and therefore sensitive to distance and morphology. Other problems with using traditional methods remotely in a greenhouse are a need for dark adaption and use of saturating light. This paper presents a novel concept for the detection of photosynthetic performance based on the dynamics of remotely sensed light induced fluorescence signals. The dynamics of the fluorescence signal is insensitive to distance and morphology and hence provide a good basis for remote detection of photosynthetic performance. Through experiments we have explored how the dynamics of the time-varying fluorescence signal from basil plants was affected by light intensity, light acclimation and light induced stress. This was done by first identifying a dynamic model by transient analysis and then applying frequency analysis on the model. We conclude that the capacity of basil plants to use a certain light intensity was reflected by how fast and how complex the dynamics are. These results show that an identified resonance peak frequency is a potential indicator of plants' ability to adapt to light, which could be a valuable feedback signal for lighting control in greenhouses.
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| 24. |
- Carstensen, Anna-Maria, 1982, et al.
(författare)
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Greenhouse Illumination Control
- 2010
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Ingår i: 15th Nordic Process Control Workshop, Lund.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Illumination of European greenhouses consumes electricity equivalent to 1.5 times the electricity production in Sweden. This amount could be reduced by approximately 75% by improving the illumination. Today HPS lamps (High pressure sodium lamps) are used. The spectrum of the HPS lamp fits poorly with the action spectrum of the photosynthesis, why most of the illumination cannot be used. By combining LEDs of different wavelengths, a spectrum closer to the action spectrum of the photosynthesis can be achieved. Experiments carried out with Heliospectra HB LED-lamp on the crop basil showed 40% improved efficiency compared to HPS lamps. Further improvements are possible, since the LED-lamp allows the intensity of each wavelength-band to be adjusted to the varying needs of plants. A plant’s need, and its efficiency in using light, can be measured through plant fluorescence and reflectance. The aim of this project is to derive mathematical models that correlate plant growth with reflectance and illumination, and fluorescence with physiological state of the plant and plant stress. These models will then be used for a control system for the LED-lamp with which the plants are able to modulate their own light environment. Expected results are decreased energy use, predictable harvest and higher crop quality.Reflectance and growth rateReflectance from plants has showed a general relationship to chlorophyll content in leafs, leaf area index and plant hight. Estimates of green biomass has been done from remote sensing of reflectance from satellites as well as on ground level through the use of reflectance indices. These indices, for example the NDVI, are based on relations between the reflectance of the wavelengths that are the least and the most sensitive to chlorophyll content. Since plant reflectance is sensitive to chlorophyll content it is reasonable to assume that it can be correlated also to growth rate. By remote (at about one meter distance) and on leaf measurements of plant reflectance and measurements of dry matter content in plants we hope to find a correlation between growth rate and plant reflectance. The relationship between growth rate and reflectance is then to be used for non destructive determination of biomass content and prediction of time for harvest.Fluorescence and plant stressFluorescence measurements contains information about the physiological state of plants. The physiological state of a plant is affected by access to specific wavelengths of light (especially 680 and 700 nm), CO2, water and nutrients. Unbalanced access to these growth factors blocks the transfer of absorbed light energy and causes deexcitation of chlorophyll molecules, which gives rise to fluorescence. Hence fluorescence intensity can be used to measure if the plants are stressed due to lack of any of these parameters.From fluorescence measurements it can also be determined whether the plants are exposed to damaging light intensities. Damaging light intensities causes break down of chlorophyll.
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| 25. |
- Carstensen, Anna-Maria, 1982, et al.
(författare)
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Method and system for growth status determination of a plant
- 2015
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The present invention relates to a method fordetermining a growth status of a plant comprisingchlorophyll, the method comprising the steps of:illuminating the plant (102) with input lightincluding a light intensity modulation component(205, 206, 207, 208); detecting light emitted fromthe plant; determining (S702) an offset lightintensity (204) surrounding the plant, the offset lightintensity being a static component of the input light;determining (S718) a phase and a gain between theinput light and the detected light, determining(S720) a growth status of the plant based on apredetermined relationship between input light anddetected light, and on the phase and the gain. Theinvention also relates to a corresponding system andto a computer program product.
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| 26. |
- Carstensen, Anna-Maria, 1982, et al.
(författare)
-
Remote detection of light tolerance in Basil through frequency and transient analysis of light induced fluorescence
- 2016
-
Ingår i: Computers and Electronics in Agriculture. - : Elsevier BV. - 0168-1699. ; 127, s. 289-301
-
Tidskriftsartikel (refereegranskat)abstract
- © 2016 Elsevier B.V.Artificial lighting control in industrial scale greenhouses has a large potential for increased crop yields, energy savings and timing in greenhouse production. One key component in controlling greenhouse lighting is continuous and accurate measurement of plant performance. This paper presents a novel concept for remote detection of plant performance based on the dynamics of chlorophyll fluorescence (CF) signals induced by a LED-lamp. The dynamic properties of the CF is studied through fitting a linear dynamic model to CF data. The hypothesis is that changes in photochemistry affects the fluorescence dynamics and can therefore be detected as changes in the model parameters and properties. The dynamics was studied in experiments using a sinusoidal varying light intensity (period 60 s) or step changes (step length 300 s). Experiments were performed in a controlled light environment on Basil plants acclimated to different light intensities. It is concluded that the capacity to use a certain light intensity is reflected by how fast and how complex the dynamics are. In particular, the results show that optimal model order is a potential indicator of light tolerance in plants that could be a valuable feedback signal for lighting control in greenhouses.
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| 27. |
- Carstensen, Anna-Maria, 1982, et al.
(författare)
-
Remote light stress detection for greenhouse LED lighting control
- 2015
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Ingår i: Proceedings 19th Nordic Process Control Workshop. ; , s. 20:1-6
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The illumination in greenhouses is in general still controlled manually by on/off control because of the type of lamps (High Pressure Sodium) that are traditionally used. With High Brightness LEDs being introduced on the market today, sufficiently high power for greenhouse grown crops can be achieved, which opens up for advanced lighting control since both light spectrum and intensity can be controlled then. For the growers, maximizing production in order to meet customer demand and economically optimize the production, often imply a high light intensity and a high level of artificial light complementing the natural sunlight. However, a too high intensity causes light stress and a photo inhibition that can significantly reduce the photosynthetic yield and hence, production. A key issue to address is therefore to detect when this level is reached. Here we present new results on how to diagnose the plants remotely based on transient and frequency analysis, system identification and frequency function properties.
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| 28. |
- Clendinning, Kirk, et al.
(författare)
-
Method for controlling a growth cycle for growing plants using state oriented control
- 2013
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The present invention relates to a method for controlling a growth cycle for growing plants. Such a method may be implemented in a greenhouse, a walk-in chamber or a growth cabinet. The invention also relates to a corresponding system, use of the system and a computer program product. The invention allows for improvements in operating a greenhouse, such as in relation to reduced energy consumption and increased predictability of the growth process.
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| 29. |
- Eriksson, Karin, 1976, et al.
(författare)
-
Pre-study on the establishment of a research collaboration between industrial energy systems and process control at Chalmers
- 2013
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the project described in this report has been to create a platform for collaboration between the research areas of industrial energy systems and process control at Chalmers. The authors of this report, belonging to the division of Heat and Power Technology, the Automatic control group and to CIT Industriell Energi, are convinced that a close collaboration between these areas could generate benefits for the process industry including •Improved efficiency with respect to energy•Improved opportunities to ensure satisfying operability•Improved process stability and product uniformity•Intensified utilization of available process equipment•Increased profitabilityIn accordance with the project scope, an inventory of relevant academic literature and of past and ongoing activities within the relevant research community has been conducted. Firstly, this inventory recognizes that researchers at Lehigh University (US), NTNU (Norway) and Carnegie Mellon University (US) have been strongly involved in the establishment of a research field commonly referred to as Integrated design and control. It is found that the research questions that are in the interest of the project partners largely can be attributed to this field. Other related labels used, and investigated as part of the project, are plant-wide control and heat exchanger network control. In a specific section of the report, definitions of important terms like operability, controllability and flexibility are given and commented on. Secondly, international research groups of special interest that has been identified are presented. In this category, I2C2 at University of Auckland and CAPEC at Technical University of Denmark can be mentioned. Relevant publications of the above mentioned research groups and their associates have been studied and are commented on in the report. Special emphasize has been put on review papers and on recent publications. Furthermore, the project has mapped the competences, experience and interest of the project partners. On this basis, the following keywords were identified:•Retrofit•Bio-based processes•Pulp and paper industry•Real life case studies•Industrial co-operation•Economic evaluation•Simulation•Scale up challengesThis list was used during discussions on research questions and project ideas for future collaboration. This project has provided the partners an opportunity to obtain deeper insight into each other’s knowledge and experiences, and, moreover, research areas of common interest have been recognized. To further develop the collaboration, the next step seems to imply joint participation in specific research projects. Research questions of interest and ideas for future projects are presented in the full report. This relates to the prevailing possibilities to apply for research grant - an issue that is addressed lastly in this report. In relation to this it should be noted that there is a program on Industrial Process Automation, supported by Vinnova, the Swedish Energy Agency and Formas, that is soon to be launched. A strategy for monitoring calls from this program as well as other relevant programs was formulated. As a result of the work in this project, it has also been possible to formulate proposals for two specific PhD-student projects within the Preem-Chalmers cooperation. These proposals take the outcome of this project into account and include opportunities to further develop the collaboration between industrial energy systems and process control at Chalmers.
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| 30. |
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| 31. |
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| 32. |
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| 33. |
- Fransson, Carl-Magnus, 1976, et al.
(författare)
-
Non-conservative robust control: Optimized and constrained sensitivity functions
- 2009
-
Ingår i: IEEE Transactions on Control Systems Technology. - 1063-6536 .- 1558-0865. ; 17:2, s. 298-308
-
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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| 34. |
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| 35. |
- Fridholm, Björn, et al.
(författare)
-
Estimating power capability of aged lithium-ion batteries in presence of communication delays
- 2018
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 383, s. 24-33
-
Tidskriftsartikel (refereegranskat)abstract
- Efficient control of electrified powertrains requires accurate estimation of the power capability of the battery for the next few seconds into the future. When implemented in a vehicle, the power estimation is part of a control loop that may contain several networked controllers which introduces time delays that may jeopardize stability. In this article, we present and evaluate an adaptive power estimation method that robustly can handle uncertain health status and time delays. A theoretical analysis shows that stability of the closed loop system can be lost if the resistance of the model is under-estimated. Stability can, however, be restored by filtering the estimated power at the expense of slightly reduced bandwidth of the signal. The adaptive algorithm is experimentally validated in lab tests using an aged lithium-ion cell subject to a high power load profile in temperatures from −20 to +25 °C. The upper voltage limit was set to 4.15 V and the lower voltage limit to 2.6 V, where significant non-linearities are occurring and the validity of the model is limited. After an initial transient when the model parameters are adapted, the prediction accuracy is within ±2% of the actually available power.
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| 36. |
- Fridholm, Björn, et al.
(författare)
-
Kalman filter for adaptive learning of look-up tables with application to automotive battery resistance estimation
- 2016
-
Ingår i: Control Engineering Practice. - : Elsevier BV. - 0967-0661 .- 1873-6939. ; 48, s. 78-86
-
Tidskriftsartikel (refereegranskat)abstract
- In online automotive applications, look-up tables are often used to model nonlinearities in component models that are to be valid over large operating ranges. If the component characteristics change with ageing or wear, these look-up tables must be updated online. Here, a method is presented where a Kalman filter is used to update the entire look-up table based on local estimation at the current operating conditions. The method is based on the idea that the parameter changes observed as a component ages are caused by physical phenomena having effect over a larger part of the operating range that may have been excited. This means that ageing patterns at different operating points are correlated, and these correlations are used to drive a random walk process that models the parameter changes. To demonstrate properties of the method, it is applied to estimate the ohmic resistance of a lithium-ion battery. In simulations the complete look-up table is successfully updated without problems of drift, even in parts of the operating range that are almost never excited. The method is also robust to uncertainties, both in the ageing model and in initial parameter estimates.
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| 37. |
- Fridholm, Björn, et al.
(författare)
-
Robust recursive impedance estimation for automotive lithium-ion batteries
- 2016
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 304, s. 33-41
-
Tidskriftsartikel (refereegranskat)abstract
- Recursive algorithms, such as recursive least squares (RLS) or Kalman filters, are commonly used in battery management systems to estimate the electrical impedance of the battery cell. However, these algorithms can in some cases run into problems with bias and even divergence of the estimates. This article illuminates problems that can arise in the online estimation using recursive methods, and lists modifications to handle these issues. An algorithm is also proposed that estimates the impedance by separating the problem in two parts; one estimating the ohmic resistance with an RLS approach, and another one where the dynamic effects are estimated using an adaptive Kalman filter (AKF) that is novel in the battery field. The algorithm produces robust estimates of ohmic resistance and time constant of the battery cell in closed loop with SoC estimation, as demonstrated by both in simulations and with experimental data from a lithium-ion battery cell.
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| 38. |
- Fridholm, Björn, et al.
(författare)
-
Robustness comparison of battery state of charge observers for automotive applications
- 2014
-
Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - : IFAC Secretariat. - 1474-6670. - 9783902823625 ; , s. 2138-2146
-
Konferensbidrag (refereegranskat)abstract
- This paper compares the robustness of three different battery State of Charge (SoC) estimation algorithms: the Extended Kalman Filter (EKF), the Unscented Kalman Filter (UKF) and the H∞ filter. Their performance when subject to disturbances such as parameter uncertainties, different sensor noise characteristics and sensitivity to tuning of the filter are examined. Simulations show that the appropriate choice of observer algorithm will depend on battery chemistry as well as on the intended application. For batteries with a strong correlation between SoC and OCV, the UKF is robust to disturbances such as sensor bias. The H∞ observer shows performance on par with the UKF but the variability of the estimation errors are larger. The EKF is a good all-round choice.
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| 39. |
- Halvarsson, Björn, et al.
(författare)
-
A New Input/Output Pairing Strategy based on Linear Quadratic Gaussian Control
- 2009
-
Ingår i: Proc. 7th IEEE International Conference on Control and Automation, Dec. 9-11, Christchurch, New Zealand. - Piscataway, NJ : IEEE. - 9781424447060 ; , s. 978-982
-
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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| 40. |
- Halvarsson, Björn, et al.
(författare)
-
New Input-Output Pairing Strategies Based on Linear Quadratic Gaussian Control
- 2011
-
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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| 41. |
- Han, Weiji, 1987, et al.
(författare)
-
Analysis and Estimation of the Maximum Switch Current during Battery System Reconfiguration
- 2022
-
Ingår i: IEEE Transactions on Industrial Electronics. - 0278-0046 .- 1557-9948. ; 69:6, s. 5931-5941
-
Tidskriftsartikel (refereegranskat)abstract
- Batteries are interconnected in series and/or parallel to meet wide-range power or energy demands in various industrial applications. To pursue the benefits of multiple connection structures in one system, reconfigurable battery systems (RBSs) have recently emerged for safe and efficient operation, extended energy storage and delivery, etc. Switches are the essential elements to enable the battery system reconfiguration, but selecting appropriate switches for RBS designs has not been systematically investigated. To bridge this gap, analytical expressions are derived in this paper to estimate the maximum switch current and its upper limit to facilitate the selection of RBS switches. An RBS prototype based on H-bridges is set up and experimental results verify the effectiveness and advantage of the proposed estimation method. These analytical expressions, relying only on resistances of batteries and switches, are readily applicable to practical RBS design and much more efficient than conducting numerous circuit experiments, simulation tests, or circuit analyses, especially for large-scale systems. Moreover, the analysis framework and estimation method proposed for series-parallel mutual conversion can be adaptively extended to other complex system reconfigurations to facilitate various RBS designs.
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| 42. |
- Han, Weiji, 1987, et al.
(författare)
-
Near-Fastest Battery Balancing by Cell/Module Reconfiguration
- 2019
-
Ingår i: IEEE Transactions on Smart Grid. - 1949-3053 .- 1949-3061. ; 10:6, s. 6954-6964
-
Tidskriftsartikel (refereegranskat)abstract
- Charge imbalance is a very common issue in multi-cell/module/pack battery systems due to manufacturing variations, inconsistent charging/discharging, and uneven thermal distribution. As a consequence, the deliverable charge capacity, battery lifespan, and system reliability may all decrease over time. To tackle this issue, various external circuit designs can be attached for charge balance, and the internal battery cell/module/pack connection can also significantly affect the charge balance performance. This paper focuses on minimizing the battery charge equalization (BCE) time by battery cell/module reconfiguration. Specifically, for the reconfigurable module-based BCE system, we propose reconfiguration algorithms for fast charge equalization under different levels of system reconfigurability. For battery systems allowing module reconfiguration and intra-module cell reconfiguration, the proposed module-based bounded reconfiguration algorithm can reach or get very close to the minimum BCE times obtained by exhaustive search. When the reconfigurability level is extended by allowing inter-module cell reconfiguration, the proposed module-based complete reconfiguration algorithm can achieve similar optimality to that of the genetic algorithm (GA). Moreover, as compared to the circuit experiments, exhaustive search, and GA, the proposed algorithms take much less computational time. The optimality and computational efficiency of the proposed algorithms are demonstrated by both circuit and numerical experiments.
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| 43. |
- Han, Weiji, 1987, et al.
(författare)
-
Next-Generation Battery Management Systems: Dynamic Reconfiguration
- 2020
-
Ingår i: IEEE Industrial Electronics Magazine. - 1941-0115 .- 1932-4529. ; 14:4, s. 20-31
-
Tidskriftsartikel (refereegranskat)abstract
- Batteries are widely applied to the energy storage and power supply in portable electronics, transportation, power systems, communication networks, etc. They are particularly demanded in the emerging technologies of vehicle electrification and renewable energy integration for a green and sustainable society. To meet various voltage, power, and energy requirements in large-scale applications, multiple battery cells have to be connected in series and/or parallel. While battery technology has advanced significantly in the past decade, existing battery management systems (BMSs) mainly focus on state monitoring and control of battery systems packed in fixed configurations. In fixed configurations, though, the battery system performance is in principle limited by the weakest cells, which can leave large parts severely underutilized. Allowing dynamic reconfiguration of battery cells, on the other hand, allows individual and flexible manipulation of the battery system at cell, module, and pack levels, which may open up a new paradigm for battery management. Following this trend, this paper provides an overview of next-generation BMSs featuring dynamic reconfiguration. Motivated by numerous potential benefits of reconfigurable battery systems (RBSs), the hardware designs, management principles, and optimization algorithms for RBSs are sequentially and systematically discussed. Theoretical and practical challenges during the design and implementation of RBSs are highlighted in the end to stimulate future research and development.
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| 44. |
- Han, Weiji, 1987, et al.
(författare)
-
Sensitivity Analysis of the Battery System State of Power
- 2022
-
Ingår i: IEEE Transactions on Transportation Electrification. - 2332-7782. ; 8:1, s. 976-989
-
Tidskriftsartikel (refereegranskat)abstract
- In battery-powered applications, it is necessary to estimate the battery system’s maximum allowed current/power for a certain future time horizon, commonly referred to as the system’s state of power (SoP). Battery system SoP is sensitive to multiple factors, such as battery state of health, state of charge, temperature, and their imbalances in multi-battery systems. Analyzing such sensitivities is important for selecting appropriate system components and connection structure during the system design as well as for predicting substantial SoP changes to proactively guide the online power control. However, such sensitivity analyses are challenging since the SoP is not directly expressed in terms of these factors and the SoP expression can become significantly complicated for interconnected heterogeneous battery cells. To address these challenges, qualitative and quantitative sensitivity analyses are first conducted for both series and parallel battery systems by deriving approximate expressions for the maximum system currents constrained by different operating limits. Some critical insights, commonly overlooked in industrial practices, have been revealed for improving the system SoPs. To pursue reliable analysis results, exact system SoPs are evaluated based on an accurate estimation method along with battery modeling parameters identified through experiments. Experimental tests are also performed to demonstrate some analysis results.
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| 45. |
- Han, Weiji, 1987, et al.
(författare)
-
State of Power Prediction for Battery Systems with Parallel-Connected Units
- 2022
-
Ingår i: IEEE Transactions on Transportation Electrification. - 2332-7782. ; 8:1, s. 925-935
-
Tidskriftsartikel (refereegranskat)abstract
- To meet the ever-increasing demand for energy storage and power supply, battery systems are being vastly applied to, e.g., grid-level energy storage and automotive traction electrification. In pursuit of safe, efficient, and cost-effective operation, it is critical to predict the maximum acceptable battery power on the fly, commonly referred to as the battery system’s state of power (SoP). As compared to the SoP prediction at the battery cell level, predicting the SoP of a multi-battery system, especially including parallel-connected cells/modules/packs, is much more complicated and far less investigated. To solve this problem, a system-model-based SoP prediction method is first proposed in this paper. Specifically, based on the formulated system model and generic state-space representation, the challenge of non-monotonic system state evolution, arising from the dynamic parallel current distribution, is identified and systematically addressed by the proposed method. As demonstrated by tests on a battery system set up with experimentally verified parameter values, the proposed method outperforms the commonly applied cell-SoP based methods for providing a more accurate and reliable prediction of the battery system SoP. Moreover, the proposed prediction framework presented in generic forms can be readily applied to other system structures.
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| 46. |
- Hedegärd, Marcus, 1979, et al.
(författare)
-
Adaptive Hysteresis Compensation Using Reduced Memory Sequences
- 2017
-
Ingår i: IEEE/ASME Transactions on Mechatronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 1083-4435 .- 1941-014X. ; 22:5, s. 2296-2307
-
Tidskriftsartikel (refereegranskat)abstract
- Hysteresis in sensors and actuators can often be effectively compensated for by implementing an inverse hysteresis model in series with the sensor or the actuator. However, an apparent problem enters when the hysteresis characteristics vary over time in an unpredicted manner. Here, we derive an adaptive hysteresis compensation method for the case when we only have observations that are very sparse in time and magnitude. Contrary to previous methods it is based on reduced memory sequences and a preidentified initial model, which makes it possible to use only a few adaption parameters. In particular, we investigate the Preisach model (PM). Using a Bernstein polynomial basis for the PM, it is shown that invertibility translates into linear constraints, which ensures that the overall identification problem for the initial PM is convex. The dependence on PM initial conditions may have negative effects on hysteresis compensation and model adaptation. We give general conditions for losing this dependence and also an upper bound for the maximum error it may cause. The method is experimentally applied to a sensor for measurement of torque in a shaft. At times, the shaft is unloaded and consequently the torque can then be independently observed as being zero. This kind of problem leads to a nonlinear parameterization, but with very few parameters to update, which is successfully achieved using an extended Kalman filter. The method essentially removes the effects of hysteresis, fatigue, and aging for the intended use of the sensor.
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| 47. |
- Hedegärd, Marcus, 1979, et al.
(författare)
-
An online method for estimation of degradable substrate and biomass in an aerated activated sludge process
- 2011
-
Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 45:19, s. 6308-6320
-
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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| 48. |
- Hedegärd, Marcus, 1979, et al.
(författare)
-
Convex Identification of Minimal Function Bases for Cylinder Pressure by Using Pressure Values as Basis Weights
- 2019
-
Ingår i: IEEE Transactions on Control Systems Technology. - 1063-6536 .- 1558-0865. ; 27:1, s. 346-354
-
Tidskriftsartikel (refereegranskat)abstract
- Estimating cylinder individual pressures using flywheel angular measurements is difficult, foremost because several input signals must be estimated from one single measurement signal. Since the pressures cannot vary arbitrary, estimation can still be possible, but it leaves little room for robustness. To take most use of data and models, it is suggested here to parameterize pressures using a function basis. For a general physics-based engine model, it is shown how the information content in the angular measurement is limited, implying that only a few parameters per cylinder can be estimated. If small deviations in the combustion are to be identified, a very parameter efficient basis is, therefore, needed. By showing that the basis can be chosen such that its weights are pressures at distinct angles, a convex optimization problem to determine optimal basis functions is derived. The method is applied to extensive cylinder pressure data for a six-cylinder diesel engine in a case study with induced combustion faults. The result is that only three to four free parameters per cylinder are needed to achieve a close fit, and a provided analysis suggests that this may enable the design of robust estimators.
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| 49. |
- Hedegärd, Marcus, 1979, et al.
(författare)
-
Convex identification of models for asymmetric hysteresis
- 2014
-
Ingår i: American Control Conference. - 0743-1619. - 9781479932726 ; , s. 4753-4758
-
Konferensbidrag (refereegranskat)abstract
- The generalized Prandtl-Ishlinskii model (GPI) of hysteresis has a wide applicability, partly because of its capability of modelling highly asymmetric hysteresis. A disadvantage of the GPI models compared to, for example the Modified Prandtl-Ishlinskii models, has been that they have had to be identified using parametric non convex methods. Recently though, a method for non-parametric convex identification for an extended and more general GPI model was described, giving all model functions. Here, the method, which was based on input discrete equations, is briefly presented in terms of the corresponding input continuous equations. This extended model corresponds to a Preisach model and an explicit expression for this relation is derived. The method is directly applicable to data consisting of first order reversal curves, but in an application to an electrical substation equipment, it is shown that other kinds of data can also be used. The method gives significantly closer fit to this data than previous studies, and it demonstrates that non-equal left and right envelope functions are optimal.
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| 50. |
- Hedegärd, Marcus, 1979, et al.
(författare)
-
Non-parametric convex identification of extended generalized Prandtl–Ishlinskii models
- 2014
-
Ingår i: Automatica. - : Elsevier BV. - 0005-1098. ; 50:2, s. 465-474
-
Tidskriftsartikel (refereegranskat)abstract
- The Generalized Prandtl–Ishlinskii model (GPI) of hysteresis has wide applicability, partly because of its capability to model asymmetric hysteresis. It is characterized by three unknown functions. Today, GPI models are typically identified through trial and error by ad hoc methods, presuming parameterized expressions for these functions and then using nonlinear least squares to determine the parameters, with concurrent problems of convergence, a dependence on the initial parameter guess, and local minima. Except for the aggregated hysteresis input–output fit the result gives no information as to whether the functions chosen are appropriate or not. Here we present a method to circumvent these problems for a more general class of hysteresis models. First, we introduce an extended GPI model (XGPI), where an additional memoryless function is placed in parallel to the GPI model. This further widens the applicability, allowing, for example, arbitrary orientation of the hysteresis loop. For such models it is shown how its four separate mappings can be identified by convex optimization. Appropriate single-valued functions can then be fitted individually to the resulting mappings and, if necessary, the function parameters found can be fine-tuned using nonlinear least squares on input–output data. The method is applied to simulated data and experimental data from a magnetoelastic torque sensor, and the results are favorably compared to the results of another commonly used hysteresis model.
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