Target tracking and source seeking using unmanned aerial vehicles with input constraints
The potential applications of unmanned aerial vehicles (UAVs) in both military and civilian fields have spurred the research on UAV control. Although great progresses in this area have been made by researchers worldwide, practical and theoretical challenges are still abundant. This thesis f...
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| Format: | Theses and Dissertations |
| Language: | English |
| Published: |
2014
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| Online Access: | https://hdl.handle.net/10356/59961 |
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| Institution: | Nanyang Technological University |
| Language: | English |
| Summary: | The potential applications of unmanned aerial vehicles (UAVs) in both military
and civilian fields have spurred the research on UAV control. Although great progresses
in this area have been made by researchers worldwide, practical and theoretical
challenges are still abundant. This thesis focuses on the problems of target
tracking and source seeking using UAVs subject to input constraints.
Ground target tracking is an important application of UAVs. Due to UAV inherent
motion constraints, the fixed-wing UAV generally can not stay on top of the ground
target. Standoff tracking is one possible solution to target tracking. In the first part
of the thesis, a single UAV is used to achieve moving ground target tracking. A
guidance law is introduced to generate a desired relative course for the UAV. Based
on the desired relative course, a saturated heading rate controller is proposed to
achieve standoff target tracking. A rigorous global stability proof of the system with
the proposed controller is provided. As the ground target velocity may be unknown,
a bounded adaptive observer is designed to estimate the unknown constant target
velocity and background wind.
Ground target could be friendly or adversarial. For adversarial target tracking or
hazardous target tracking, safety and tracking performance are two critical issues
for the UAV. In order to achieve adversarial target tracking, the initial condition
of the UAV is analyzed, and two types of tracking scenarios are defined: exposure
avoidance and minimum exposure time. A bang-bang controller is proposed to achieve target tracking in both scenarios.
Advances in sensing, communication and control systems make it possible for multiple
UAVs to carry out missions cooperatively. A circular formation strategy for
target tracking is proposed in this thesis. Firstly, a guidance law based heading rate
controller is designed for circular tracking. A notion called temporal phase is introduced
for multi-UAV cooperation. Based on the temporal separation, a bounded
variable airspeed controller is developed to achieve equal temporal separation.
Source seeking is a potential application of multi-UAV cooperation. In the past
decades, single vehicle is successfully used for source seeking. However, the time
cost and extreme movement are two challenging issues to be addressed. Cooperation
of multiple UAVs makes it possible to attain better source seeking performance.
This thesis proposes a leader-follower formation strategy for source seeking. Based
on the measurement of all UAVs, the scalar field gradient at the leader location is
estimated using least-squares method. After that, an adaptive observer is designed
to estimate the source velocity. By using the estimated gradient and source velocity,
a heading rate controller for the leader is developed to achieve level tracking.
Then, heading rate controller for follower UAVs is also proposed to achieve circular
formation around the leader.
Finally, conclusions and some recommendations are presented. |
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