Date & Time: June 17th, 9:00-10:00
Location: Seminar Room M 3170-73 at Dept. of Automatic Control, LTH
Author: Ask Hällström
Title:  On the advantages of heterogeneity in bidirectional control of platoons
Supervisor: Richard Pates
Examiner: Anders Rantzer

Abstract:

The control of large and complex systems is a difficult but important topic. In applications centralized control, in which all measurements about a system are used to compute control actions, is often preferable, since it allows for a better overview of the system and more precise control. However in large networks, where the complexity of implementing a centralized controller becomes too difficult or when information cannot easily be shared between network members, decentralized controllers are needed. This however can result in unwanted behaviors emerging, such as oscillations or even instability.

This project explores how to use heterogeneity in the control design to reduce these problematic behaviors for networks with a string topology, for example platoons of self driving cars. Inspired by impedance matching in transmission lines, where a load impedance can be added at the end of a transmission line to remove reflected waves, the primary objective of this thesis is to find a method for designing controllers for the last platoon member to remove reflecting oscillations.
 

The main result is a theorem on how to design such control laws. This result shows that if the control law for the last member is designed in a particular way, the sensitivity functions in the platoon can be made independent of the number of platoon members. The result also yields a formula for what the resulting transfer functions will look like, which can be used to inform design. Questions of stability are answered and compared to the homogeneous case, and the new method proves to be able to stabilize a larger class of processes no matter the length of the platoon. This holds even for open loop unstable processes, which cannot be stabilized in a decentralized fashion using homogeneous control. Finally simulations on a model of cars in a platoon was used to illustrate teh properties of the heterogeneous control design on a more practical example. These showed that the heterogeneous control approach could indeed improve the reference tracking and disturbance rejection of such systems.