Jan Tommy Gravdahl

Satellite Attitude Control by Quaternion-Based Backstepping

In this brief, a tracking controller is presented to stabilize the attitude of a micro satellite via integrator backstepping and quaternion feedback. The controller is shown to render the equilibrium points in the closed-loop system uniformly asymptotically stable. Simulations are performed using satellite parameters from the ESEO mission under the European Space Agencys SSETI project.

Brief paper: Spacecraft coordination control in 6DOF: Integrator backstepping vs passivity-based control

In this paper, we present three nonlinear control solutions for 6DOF spacecraft formation control, adopted from Euler-Lagrange system theory. The quaternion parametrization results in dual equilibrium points in the closed loop system, and the controllers are proved to render these uniformly asymptotically stable. We also present a theoretical comparison of the three control solutions, together with simulation results to visualize the performance of the controllers.

Centrifugal compressor surge and speed control

Previous work on stabilization of compressor surge is extended to include control of the angular velocity of the compressor. A low-order centrifugal compressor model is presented, where the states are mass flow, pressure rise, and rotational speed of the spool. Energy transfer considerations are used to develop a compressor characteristic. In order to stabilize equilibria to the left of the surge line, a close coupled valve is used in series with the compressor. Controllers for the valve pressure drop and spool speed are derived. Semiglobal exponential stability is proved using a Lyapunov argument.

A review on modelling, implementation, and control of snake robots

This paper provides an overview of previous literature on snake robot locomotion. In particular, the paper considers previous research efforts related to modelling of snake robots, physical development of these mechanisms, and finally control design efforts for snake locomotion. The review shows that the majority of literature on snake robots so far has focused on locomotion over flat surfaces, but that there is a growing trend towards locomotion in environments that are more challenging, i.e. environments that are more in line with realistic applications of these mechanisms.

Drive torque actuation in active surge control of centrifugal compressors

A novel approach to active surge control is presented for a centrifugal compressor driven by an electrical motor. The main idea of the paper is to use the drive itself for surge control. This eliminates the need for additional actuators, and has the potential of energy efficient operation. It is shown that previous unstable operating points to the left of the surge line can be made globally exponentially stable by using the rotational speed of the motor as control. It is then shown that stability and exponential convergence to a set follows when the torque of the drive is considered to be the control input. The proposed method is simulated on a compressor model using an approximation of a real compression system.

Modelling of UAV Formation Flight using 3D Potential Field

Abstract In this paper, we present a solution for formation flight and formation reconfiguration of unmanned aerial vehicles (UAVs). Based on a virtual leader approach, combined with an extended local potential field, the method is universal applicable by driving the vehicle’s auto pilot. The solution is verified, using a group of UAVs based on a simplified small scale helicopter, which is simulated in MATLAB TM /Simulink TM . As necessary for helicopters, the potential field approach is realized in 3D including obstacle and collision avoidance. The collision avoidance strategy could be used separately for the sense and avoid problem.

Spacecraft attitude control using explicit model predictive control

In this paper, an explicit model predictive controller for the attitude of a satellite is designed. Explicit solutions to constrained linear MPC problems can be computed by solving multi-parametric quadratic programs (mpQP), where the parameters are the components of the state vector. The solution to the mpQP is a piecewise affine (PWA) function, which can be evaluated at each sample to obtain the optimal control law. The on-line computation effort is restricted to a table-lookup, and the controller can be implemented on inexpensive hardware as fixed-point arithmetics can be used. This is useful for systems with limited power and CPU resources. An example of such systems is micro-satellites, which is the focus of this paper. In particular, the explicit MPC (eMPC) approach is applied to the SSETI/ESEO micro-satellite, initiated by the European Space Agency (esa). The theoretical results are supported by simulations.

Snake Robots: Modelling, Mechatronics, and Control

Snake Robots is a novel treatment of theoretical and practical topics related to snake robots: robotic mechanisms designed to move like biological snakes and able to operate in challenging environments in which human presence is either undesirable or impossible. Future applications of such robots include search and rescue, inspection and maintenance, and subsea operations. Locomotion in unstructured environments is a focus for this book. The text targets the disparate muddle of approaches to modelling, development and control of snake robots in current literature, giving a unified presentation of recent research results on snake robot locomotion to increase the readers basic understanding of these mechanisms and their motion dynamics and clarify the state of the art in the field. The book is a complete treatment of snake robotics, with topics ranging from mathematical modelling techniques, through mechatronic design and implementation, to control design strategies. The development of two snake robots is described and both are used to provide experimental validation of many of the theoretical results. Snake Robots is written in a clear and easily understandable manner which makes the material accessible by specialists in the field and non-experts alike. Numerous illustrative figures and images help readers to visualize the material. The book is particularly useful to new researchers taking on a topic related to snake robots because it provides an extensive overview of the snake robot literature and also represents a suitable starting point for research in this area.

Leader/Follower synchronization of satellite attitude without angular velocity measurements

In this paper we propose a Leader/Follower output feedback synchronization scheme for control of the attitude of two satellites when angular velocity measurements are not available. Nonlinear observers are used to estimate the angular velocities. The attitudes of the satellites are represented by unit quaternions, and the control design is based on vectorial observer backstepping. The analysis of the method shows that the rotation matrices representing the attitude errors between the follower and the leader, and between the leader and its reference attitude, converge to the identity matrix for any initial conditions. The control scheme is simulated to validate the results.

Group coordination and cooperative control

This volume contains the contributions to a Workshop on Group Coordination and Cooperative Control held in Tromso, Norway, 2006, to focus on control theoretic challenges raised by group coordination and cooperation, and lay a foundation for future research. The book covers a wide range of subjects within the area of group coordination and cooperative control, and forms a valuable and up-to-date text on the newer trends in group coordination and cooperative control.