Uros Kalabic

Vehicle tracking control on piecewise-clothoidal trajectories by MPC with guaranteed error bounds

For control architectures of autonomous and semi-autonomous driving features, we design a vehicle steering controller with limited preview ensuring that the vehicle constraints are satisfied, and that any piecewise clothoidal trajectory, that is possibly generated by a path planner or supervisory algorithm and satisfies constraints on the desired yaw rate and the change of desired yaw rate, is tracked within a preassigned lateral error bound. The design is based on computing a non-maximal, yet polyhedral, robust control invariant (RCI) set for a system subject to bounded disturbances with state-dependent bounds, which also allows to determine the constraints describing the reference trajectories that can be followed. The RCI set is then enforced by model predictive control, where the cost function enforces additional objectives of the vehicle motion.

Geometric Mechanics Based Nonlinear Model Predictive Spacecraft Attitude Control with Reaction Wheels

This paper develops a nonlinear model predictive controller for constrained attitude maneuvering of a fully actuated spacecraft with reaction wheels. In the proposed control algorithm, a Lie group ...

Solution to the HJB equation for LQR-type problems on compact connected Lie groups

In this paper, we provide a solution to the HJB equation associated with LQR-type problems for fully-actuated left-invariant control systems on compact connected Lie groups. We obtain the corresponding algebraic/differential Riccati equation and in turn generalize some of the results in Berkane and Tayebi (2015) to a broader class of Lie groups. Closed-loop stability results are also derived.

Extended command governors for constraint enforcement in dual-stage processing machines

This manuscript presents a scheme for the constrained control of a dual-stage system used in precision manufacturing. The system consists of two stages, a fast and a slow stage, whose actuators have different bandwidths. The fast stage is primarily constrained in its range of operation, and the slow stage is primarily constrained in allowable velocity and acceleration. The constrained control is based on the extended command governor, which is a constraint-enforcement scheme used for closed-loop systems subject to state and control constraints. A method of dividing the motion between fast and slow stages is presented which is based on tracking a minimal-motion reference for the slow stage. The extended command governor scheme is modified to simultaneously ensure constraint-admissible tracking of the minimal-motion reference and machining of the desired manufacturing pattern. Numerical simulation results are reported, showing successful tracking and constraint enforcement.

Constraint-enforcing controller for both autonomous and assisted steering (Invited paper)

This paper considers the design of a controller and a constraint-enforcement scheme for application to dualmode, autonomous and manual steering systems. A tracking controller is designed to track a desired pinion angle during autonomous operation, and to provide assistive torque during manual operation. The tracking controller is designed using H∞ synthesis with tracking made possible via the solution to a full-information output regulation problem. A reference governor scheme is implemented in order to enforce constraints. Numerical simulations are presented corresponding to an aggressive step-steer maneuver in autonomous mode and show strict constraint enforcement.

Constrained attitude maneuvering of a spacecraft with reaction wheel assembly by Nonlinear Model Predictive Control

This paper develops a nonlinear model predictive controller for constrained attitude maneuvering of spacecraft actuated by a reaction wheel assembly. In the proposed control algorithm, a Lie group variational integrator is implemented for the prediction of discrete-time dynamics. The model predictive control problem is defined on SO(3) and converted to an optimal control problem over the prediction horizon. The numerical solver for this optimal control problem is implemented. The developed solver utilizes the Indirect Single Shooting Method to find a solution to the necessary conditions for optimality. The control constraints and exclusion zone constraints are handled using a penalty function approach. Simulation results on a spacecraft model are presented.

MPC on manifolds with an application to SE(3)

The paper considers formulations of constrained model predictive control (MPC) problems for systems with dynamics defined on smooth manifolds. Generalizations of conventional nonlinear MPC stabilization techniques based on the terminal set and terminal penalty approaches are presented based on recent work by the authors. The significance of the results includes the possibility of systematically generating globally stabilizing, discontinuous, time-invariant feedback laws in situations when smooth, or even continuous, globally stabilizing, time-invariant stabilizers do not exist. To illustrate the development of nonlinear MPC on manifolds, the paper considers an example of a system with dynamics evolving on SE(3). Such systems emerge in many applications, such as quadrotor and quadcopter flight control. In the example, the paper demonstrates semi-global stabilization properties of the nonlinear MPC feedback law.