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Nielsen, Lars
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Publications (10 of 82) Show all publications
Fors, V., Olofsson, B. & Nielsen, L. (2019). Attainable force volumes of optimal autonomous at-the-limit vehicle manoeuvres. Vehicle System Dynamics, 1-22
Open this publication in new window or tab >>Attainable force volumes of optimal autonomous at-the-limit vehicle manoeuvres
2019 (English)In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, p. 1-22Article in journal (Refereed) Epub ahead of print
Abstract [en]

With new developments in sensor technology, a new generation of vehicle dynamics controllers is developing, where the braking and steering strategies use more information, e.g. knowledge of road borders. The basis for vehicle-safety systems is how the forces from tyre–road interaction is vectored to achieve optimal total force and moment on the vehicle. To study this, the concept of attainable forces previously proposed in literature is adopted, and here a new visualisation technique is devised. It combines the novel concept of attainable force volumes with an interpretation of how the optimal solution develops within this volume. A specific finding is that for lane-keeping it is important to maximise the force in a certain direction, rather than to control the direction of the force vector, even though these two strategies are equivalent for the friction-limited particle model previously used in some literature for lane-keeping control design. More specifically, it is shown that the optimal behaviour develops on the boundary surface of the attainable force volume. Applied to lane-keeping control, this observation indicates a set of control principles similar to those analytically obtained for friction-limited particle models in earlier research, but result in vehicle behaviour close to the globally optimal solution also for more complex models and scenarios.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
Active safety, force vectoring, vehicle dynamics control, tyre–road interaction, vehicle manoeuvre strategy
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:liu:diva-156638 (URN)10.1080/00423114.2019.1608363 (DOI)000470461700001 ()2-s2.0-85064738528 (Scopus ID)
Note

Funding agencies: Swedish Government; Wallenberg AI, Autonomous Systems and Software Program (WASP) - Knut and Alice Wallenberg Foundation

Available from: 2019-05-02 Created: 2019-05-02 Last updated: 2019-07-03Bibliographically approved
Anistratov, P., Olofsson, B. & Nielsen, L. (2019). Efficient Motion Planning for Autonomous Vehicle Maneuvers Using Duality-Based Decomposition. In: Proceedings of the 9th IFAC International Symposium on Advances in Automotive Control, Orleans, June 23-27, 2019: . Paper presented at IFAC International Symposium on Advances in Automotive Control.
Open this publication in new window or tab >>Efficient Motion Planning for Autonomous Vehicle Maneuvers Using Duality-Based Decomposition
2019 (English)In: Proceedings of the 9th IFAC International Symposium on Advances in Automotive Control, Orleans, June 23-27, 2019, 2019Conference paper, Published paper (Refereed)
Abstract [en]

A method to decompose a motion-planning problem into several segments is presented. It is based on a modification of the original problem, such that certain variables at the splitting points are considered to be precomputed and thus fixedand the remaining variables are obtained by performing Lagrange relaxation. The resulting dual problem is split into several subproblems, allowing parallel computation. The method is formalized as a computational algorithm and evaluated in a safety critical double lane-change situation. The resulting maneuver has close-to-optimal behavior and, for certain initialization strategies, it is obtained in shorter computational time compared to computing the full maneuver in one step.

Keywords
trajectory and path planning, autonomous vehicles, duality-based decomposition, motion control, safety, intelligent transportation systems
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-159767 (URN)
Conference
IFAC International Symposium on Advances in Automotive Control
Available from: 2019-08-20 Created: 2019-08-20 Last updated: 2019-08-20
Fors, V., Olofsson, B. & Nielsen, L. (2018). Formulation and interpretation of optimal braking and steering patterns towards autonomous safety-critical manoeuvres. Vehicle System Dynamics, 57(8), 1206-1223
Open this publication in new window or tab >>Formulation and interpretation of optimal braking and steering patterns towards autonomous safety-critical manoeuvres
2018 (English)In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 57, no 8, p. 1206-1223Article in journal (Refereed) Published
Abstract [en]

Stability control of a vehicle in autonomous safety-critical at-the-limit manoeuvres is analysed from the perspective of lane keeping or lane changing, rather than that of yaw control as in traditional ESC systems. An optimal control formulation is developed, where the optimisation criterion is a linear combination of the initial and final velocity of the manoeuvre. Varying the interpolation parameter in this formulation turns out to result in an interesting family of optimal braking and steering patterns in stabilising manoeuvres. The two different strategies of optimal lane-keeping control and optimal yaw control are shown to be embedded in the formulation and result from the boundary values of the parameter. The results provide new insights and have the potential to be used for future safety systems that adapt the level of braking to the situation at hand, which is demonstrated through examples of how to exploit theresults.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
Keywords
Vehicle stability, yaw control, lane keeping, lane change, avoidance manoeuvre, at-the-limit
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:liu:diva-152896 (URN)10.1080/00423114.2018.1549331 (DOI)000470891200008 ()
Funder
Knut and Alice Wallenberg Foundation
Note

Funding agencies: Swedish Government (Sveriges Regering); Wallenberg AI, Autonomous Systems and Software Program (WASP) (Knut och Alice Wallenbergs Stiftelse) - Knut and Alice Wallenberg Foundation

Available from: 2018-11-27 Created: 2018-11-27 Last updated: 2019-07-15Bibliographically approved
Anistratov, P., Olofsson, B. & Nielsen, L. (2018). Lane-Deviation Penalty for Autonomous Avoidance Maneuvers. In: Proceedings of the 14th International Symposium on Advanced Vehicle Control, Beijing, July 16-20, 2018: . Paper presented at International Symposium on Advanced Vehicle Control, July 16-20, 2018, Beijing, China.
Open this publication in new window or tab >>Lane-Deviation Penalty for Autonomous Avoidance Maneuvers
2018 (English)In: Proceedings of the 14th International Symposium on Advanced Vehicle Control, Beijing, July 16-20, 2018, 2018Conference paper, Published paper (Refereed)
Abstract [en]

A formulation of an offline motion-planning method for avoidance maneuvers based on a lane-deviation penalty function is proposed,which aims to decrease the risk of a collision by minimizing the time when a vehicle is outside of its own driving lane in the case ofavoidance maneuvers. The penalty function is based on a logistic function. The method is illustrated by computing optimal maneuversfor a double lane-change scenario. The results are compared with minimum-time maneuvers and squared-error norm maneuvers. Thecomparison shows that the use of the considered penalty function requires fewer constraints and that the vehicle stays less time in theopposing lane. The similarity between the obtained trajectories for different problem configurations was noticed. This property couldbe used in the future for predicting an intermediate trajectory online from a sparse data set of maneuvers.

Keywords
aggressive maneuvers, vehicle automation and control, nonlinear optimization
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-152138 (URN)
Conference
International Symposium on Advanced Vehicle Control, July 16-20, 2018, Beijing, China
Available from: 2018-10-18 Created: 2018-10-18 Last updated: 2018-11-27
Anistratov, P., Olofsson, B. & Nielsen, L. (2018). Segmentation and Merging of Autonomous At-the-Limit Maneuversfor Ground Vehicles. In: Proceedings of the 14th International Symposium on Advanced Vehicle Control, Beijing, July 16-20, 2018: . Paper presented at International Symposium on Advanced Vehicle Control.
Open this publication in new window or tab >>Segmentation and Merging of Autonomous At-the-Limit Maneuversfor Ground Vehicles
2018 (English)In: Proceedings of the 14th International Symposium on Advanced Vehicle Control, Beijing, July 16-20, 2018, 2018Conference paper, Published paper (Refereed)
Abstract [en]

To decrease the complexity of motion-planning optimizations, a segmentation and merging strategy for maneuvers is proposed. Maneuvers that are at-the-limit of friction are of special interest since they appear in many critical situations. The segmentation pointsare used to set constraints for several smaller optimizations for parts of the full maneuver, which later are merged and compared withoptimizations of the full maneuver. The technique is illustrated for a double lane-change maneuver.

Keywords
vehicle automation and control, ground vehicle motion-planning, aggressive maneuvers
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-152222 (URN)
Conference
International Symposium on Advanced Vehicle Control
Available from: 2018-10-22 Created: 2018-10-22 Last updated: 2018-11-27
Fors, V., Olofsson, B. & Nielsen, L. (2018). Slip-Angle Feedback Control for Autonomous Safety-Critical Maneuvers At-the-Limit of Friction. In: Proceedings of the 14th International Symposium on Advanced Vehicle Control (AVEC’ 18): . Paper presented at International Symposium on Advanced Vehicle Control (AVEC).
Open this publication in new window or tab >>Slip-Angle Feedback Control for Autonomous Safety-Critical Maneuvers At-the-Limit of Friction
2018 (English)In: Proceedings of the 14th International Symposium on Advanced Vehicle Control (AVEC’ 18), 2018Conference paper, Published paper (Refereed)
Abstract [en]

From the basis of optimal control, a closed-loop controller for autonomous vehicle maneuvers at-the-limit of friction is developed.The controller exploits that the optimal solution tends to be close to the friction limit of the tires.This observation allows for simplifications that enable the use of a proportional feedback control in the control loop,which provides a smooth trajectory promising for realization in an actual control system.The controller is in comparison with an open-loop numerical optimal control solution shown to exhibit promising performance at low computational cost in a challenging turn scenario.

National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-149899 (URN)
Conference
International Symposium on Advanced Vehicle Control (AVEC)
Available from: 2018-07-30 Created: 2018-07-30 Last updated: 2018-11-27Bibliographically approved
Nyberg, P., Frisk, E. & Nielsen, L. (2017). Driving Cycle Equivalence and Transformation. IEEE Transactions on Vehicular Technology, 66(3), 1963-1974
Open this publication in new window or tab >>Driving Cycle Equivalence and Transformation
2017 (English)In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 66, no 3, p. 1963-1974Article in journal (Refereed) Published
Abstract [en]

There is a current strong trend where driving cycles are used extensively in vehicle design, especially for calibration and tuning of all powertrain systems for control and diagnosis. In such situations it is essential to capture real driving, and therefore using only a few driving cycles would lead to the risk that a test or a design would be tailored to details in a specific driving cycle. Consequently there are now widespread activities using techniques from statistics, big data and mission modeling to address these issues. For all such methods there is an important final step to calibrate a representative cycle to adhere to fair propulsion requirements on the driven wheels over a cycle. For this a general methodology has been developed, applicable to a wide range of problems involving driving cycle transformations. It is based on a definition of equivalence for driving cycles that loosely speaking defines being similar without being the same. Based on this, a set of algorithms are developed to transform a given driving cycle into an equivalent one, or into a cycle with given equivalence measure. The transformations are effectively handled as a nonlinear program that is solved using general purpose optimization techniques. The proposed method is general and a wide range of constraints can be used.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2017
Keywords
mean tractive force, nonlinear programming, numerical optimization, vehicle design, vehicle propulsion
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Computer Engineering
Identifiers
urn:nbn:se:liu:diva-118104 (URN)10.1109/TVT.2016.2582079 (DOI)000396401400006 ()
Note

Funding agencies|Swedish Hybrid Vehicle Centre; Linnaeus Center CADICS

At the time for thesis presentation publication was in status: Manuscript.

Available from: 2015-05-21 Created: 2015-05-21 Last updated: 2018-01-11Bibliographically approved
Fors, V., Olofsson, B. & Nielsen, L. (2017). Formulation and Interpretation of Optimal Braking Patterns in Autonomous Lane-Keeping Maneuvers. In: : . Paper presented at 2nd IAVSD Workshop on Dynamics of Road Vehicles. Berlin, Germany
Open this publication in new window or tab >>Formulation and Interpretation of Optimal Braking Patterns in Autonomous Lane-Keeping Maneuvers
2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The two perspectives of autonomous driving and new active safety in vehicles are complementary, and both hold promise to reduce the number of accidents and associated severe or fatal injuries. They both coincide in the recent interest in finding alternatives to traditional yaw-control systems that can utilize the full potential of the vehicle. By considering the control problem as that of lane-keeping, also at high speed and at-the-limit of tire friction, rather than that of yaw control, leads to the possibility of optimization-based active-braking systems with better performance than those existing today. Here, we investigate the optimal braking patterns in completely autonomous lane-keeping maneuvers resulting from a formulation where the optimization criterion used is an interpolation between the initial and final velocities of the maneuver. Varying the interpolation parameter, i.e., the relative weight between the initial and final velocity, results in different vehicle behavior. The analysis of these behaviors provides several new insights into stabilizing braking patterns for vehicles in at-the-limit maneuvers. Specifically, it is to be noted that the benefits of a lane-keeping strategy are immediate, both in terms of the maximum possible initial velocity and the velocity reduction. The formulation embeds the traditional yaw control and optimal lane-keeping as the end-point values of the interpolation parameter, and adds a continuous family of behaviors in between. This gives a new perspective for investigating the relation between traditional yaw control and optimal lane-keeping for autonomous vehicles.

Place, publisher, year, edition, pages
Berlin, Germany: , 2017
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-152756 (URN)
Conference
2nd IAVSD Workshop on Dynamics of Road Vehicles
Available from: 2018-11-20 Created: 2018-11-20 Last updated: 2018-11-27
Sundström, C., Frisk, E. & Nielsen, L. (2016). Diagnostic Method Combining the Lookup Tables and Fault Models Applied on a Hybrid Electric Vehicle. IEEE Transactions on Control Systems Technology, 24(3), 1109-1117
Open this publication in new window or tab >>Diagnostic Method Combining the Lookup Tables and Fault Models Applied on a Hybrid Electric Vehicle
2016 (English)In: IEEE Transactions on Control Systems Technology, ISSN 1063-6536, E-ISSN 1558-0865, Vol. 24, no 3, p. 1109-1117Article in journal (Refereed) Published
Abstract [en]

A common situation in industry is to store measurements for different operating points in the lookup tables, often called maps. They are used in many tasks, e.g., in control and estimation, and therefore considerable investments in engineering time are spent in measuring them which usually make them accurate descriptions of the fault-free system. They are thus well suited for fault detection, but, however, such a model cannot give fault isolation since only the fault free behavior is modeled. One way to handle this situation would be also to map all fault cases but that would require measurements for all faulty cases, which would be costly if at all possible. Instead, the main contribution here is a method to combine the lookup model with analytical fault models. This makes good use of all modeling efforts of the lookup model for the fault-free case, and combines it with fault models with reasonable modeling and calibration efforts, thus decreasing the engineering effort in the diagnosis design. The approach is exemplified by designing a diagnosis system monitoring the power electronics and the electric machine in a hybrid electric vehicle. An extensive simulation study clearly shows that the approach achieves both good fault detectability and isolability performance. A main point is that this is achieved without the need for neither measurements of a faulty system nor detailed physical modeling, thus saving considerable amounts of development time.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2016
Keywords
Electric machine; fault detection; fault diagnosis; fault isolation; hybrid electric vehicle (HEV); lookup table
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-128736 (URN)10.1109/TCST.2015.2480008 (DOI)000375273200032 ()
Available from: 2016-05-31 Created: 2016-05-30 Last updated: 2017-11-30
Nyberg, P., Frisk, E. & Nielsen, L. (2016). Using Real-World Driving Databases to Generate Driving Cycles with Equivalence Properties. IEEE Transactions on Vehicular Technology, 65(6), 4095-4105
Open this publication in new window or tab >>Using Real-World Driving Databases to Generate Driving Cycles with Equivalence Properties
2016 (English)In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 65, no 6, p. 4095-4105Article in journal (Refereed) Published
Abstract [en]

Due to the increasing complexity of vehicle design, understanding driver behavior and driving patterns is becoming increasingly more important. Therefore, a large amount of test driving is performed, which together with recordings of normal driving, results in large databases of recorded drives. A fundamental question is how to make best use of these data to devise driving cycles suitable in the development process of vehicles. One way is to generate driving cycles that are representative for the data or for a suitable subset of the data, e.g., regarding geographical location, driving distance, speed range, or many other possible selection variables. Further, to make a fair comparison on two such driving cycles possible, another fundamental requirement is that they should have similar excitation of the vehicle. A key contribution here is an algorithm that combines the two given objectives. A formulation with Markov processes is used to obtain a condensed and effective characterization of the database and to generate candidate driving cycles (CDCs). In addition to that is a method transforming a candidate to an equivalent driving cycle (EqDC) with desired excitation. The method is a general approach but is here based on the components of the mean tractive force (MTF), and this is motivated by a hardware-in-the-loop experiment showing the strong relevance of these MTF components regarding fuel consumption. The result is a new method that combines the generation of driving cycles using real-world driving cycles with the concept of EqDCs.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2016
Keywords
Drive cycle, equivalence measures, equivalent driving cycle (EqDC), mean tractive force (MTF), specific energy, test procedures, vehicle design, vehicle excitation, vehicle propulsion
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Computer Engineering
Identifiers
urn:nbn:se:liu:diva-118101 (URN)10.1109/TVT.2015.2502069 (DOI)000380068500022 ()
Note

Funding agencies|Swedish Hybrid Vehicle Centre; Linnaeus Center CADICS

At the time for thesis presentation publication was in status: Manuscript.

Available from: 2015-05-21 Created: 2015-05-21 Last updated: 2018-01-11Bibliographically approved
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