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Ho, Du
Publications (2 of 2) Show all publications
Ho, D. & Enqvist, M. (2018). On the equivalence of inverse and forward IV estimators with application to quadcopter modeling. In: 18th IFAC Symposium on System Identification (SYSID), Proceedings: . Paper presented at 18th IFAC Symposium on System Identification (SYSID), Stockholm, Sweden, July 9-11, 2018 (pp. 951-956). Elsevier, 51(15)
Open this publication in new window or tab >>On the equivalence of inverse and forward IV estimators with application to quadcopter modeling
2018 (English)In: 18th IFAC Symposium on System Identification (SYSID), Proceedings, Elsevier, 2018, Vol. 51, no 15, p. 951-956Conference paper, Published paper (Refereed)
Abstract [en]

This paper concerns the estimation of a dynamic model from two measured signals when it is not clear which signal should be used as input to the model. In this case, both a forward and an inverse model can be estimated. Here, a basic instrumental variable approach is used and it is shown that the forward and inverse model estimators give identical parameter estimates provided that corresponding model structures have been used. Furthermore, it is shown that this scenario occurs when properties of a quadcopter are estimated from accelerometer and gyro signals and, hence, that it does not matter which signal is used as input.

Place, publisher, year, edition, pages
Elsevier, 2018
Series
IFAC papers online
National Category
Engineering and Technology Control Engineering
Identifiers
urn:nbn:se:liu:diva-152269 (URN)10.1016/j.ifacol.2018.09.071 (DOI)000446599200161 ()
Conference
18th IFAC Symposium on System Identification (SYSID), Stockholm, Sweden, July 9-11, 2018
Note

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 642153.

Available from: 2018-10-24 Created: 2018-10-24 Last updated: 2018-10-30Bibliographically approved
Ho, D. (2018). Some results on closed-loop identification of quadcopters. (Licentiate dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Some results on closed-loop identification of quadcopters
2018 (English)Licentiate thesis, monograph (Other academic)
Abstract [en]

In recent years, the quadcopter has become a popular platform both in research activities and in industrial development. Its success is due to its increased performance and capabilities, where modeling and control synthesis play essential roles. These techniques have been used for stabilizing the quadcopter in different flight conditions such as hovering and climbing. The performance of the control system depends on parameters of the quadcopter which are often unknown and need to be estimated. The common approach to determine such parameters is to rely on accurate measurements from external sources, i.e., a motion capture system. In this work, only measurements from low-cost onboard sensors are used. This approach and the fact that the measurements are collected in closed-loop present additional challenges.

First, a general overview of the quadcopter is given and a detailed dynamic model is presented, taking into account intricate aerodynamic phenomena. By projecting this model onto the vertical axis, a nonlinear vertical submodel of the quadcopter is obtained. The Instrumental Variable (IV) method is used to estimate the parameters of the submodel using real data. The result shows that adding an extra term in the thrust equation is essential.

In a second contribution, a sensor-to-sensor estimation problem is studied, where only measurements from an onboard Inertial Measurement Unit (IMU) are used. The roll submodel is derived by linearizing the general model of the quadcopter along its main frame. A comparison is carried out based on simulated and experimental data. It shows that the IV method provides accurate estimates of the parameters of the roll submodel whereas some other common approaches are not able to do this.

In a sensor-to-sensor modeling approach, it is sometimes not obvious which signals to select as input and output. In this case, several common methods give different results when estimating the forward and inverse models. However, it is shown that the IV method will give identical results when estimating the forward and inverse models of a single-input single-output (SISO) system using finite data. Furthermore, this result is illustrated experimentally when the goal is to determine the center of gravity of a quadcopter.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 98
Series
Linköping Studies in Science and Technology. Licentiate Thesis, ISSN 0280-7971 ; 1826
National Category
Engineering and Technology Control Engineering
Identifiers
urn:nbn:se:liu:diva-152701 (URN)10.3384/lic.diva-152701 (DOI)9789176851661 (ISBN)
Presentation
2018-11-30, Ada Lovelace, B-huset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Funder
EU, Horizon 2020
Note

This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 642153.

Available from: 2018-11-21 Created: 2018-11-15 Last updated: 2019-10-12Bibliographically approved
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