Maria Letizia Corradini

A Quasi-Sliding Mode Approach for Robust Control and Speed Estimation of PM Synchronous Motors

This paper presents a discrete-time variable-structure-based control and a speed estimator designed for a permanent-magnet synchronous motor (PMSM). A cascade control scheme is proposed which provides accurate speed tracking performance. In this control scheme the speed estimator is a robust digital differentiator that provides the first derivative of the encoder position measurement. The analysis of the control stability is given and the ultimate boundedness of the speed tracking error is proved. The control scheme is experimentally tested on a commercial PMSM drive. Reported experimental evidence shows that the proposed solution produces good speed trajectory tracking performance and it is robust in the presence of disturbances affecting the system.

A discrete adaptive variable-structure controller for MIMO systems, and its application to an underwater ROV

This paper addresses discrete-time variable structure control for multiple input-multiple output (MIMO) systems. Two control algorithms are presented, obtained extending to the multivariable case two control techniques previously proposed by the authors (1995) for single input-single output (SISO) systems. Both techniques consist of variable structure control laws cascaded to a generalized minimum variance controller. The former algorithm refers to a completely known system, while the latter has been designed to deal with parameter uncertainties in the plant. In this case, the connection with a MIMO online parameter estimator has been considered. Proofs are provided about the convergence of the proposed control laws. The presented algorithms have been applied to the problem of position and orientation control of an underwater remotely operated vehicle (ROV) used in the exploitation of combustible gas deposits at great water depths. Resulting performances have been tested by simulation, modeling the ROV with a nonlinear differential equations system. Results have been discussed and compared with recent literature.

Actuator Failure Identification and Compensation Through Sliding Modes

The actuator failure compensation problem is addressed in this brief. It is considered an uncertain linear plant, which is supposed to undergo unknown failures causing the plant input components to be stuck at some uncertain but bounded time functions. A sliding-mode-based control policy is presented, guaranteeing the detection of the fault and the identification of the failed component by means of a suitable test input. Once the failed component has been identified, the control law is reconfigured, redistributing the control activity among the controllers still working. The proposed controller has been tested by simulation on a benchmark problem

Brief paper: Linear unstable plants with saturating actuators: Robust stabilization by a time varying sliding surface

This paper proposes the use of a time-varying sliding surface for the robust stabilization of linear uncertain SISO plants with saturating actuators. A constructive procedure for its design is also proposed, and stability of the closed loop system is proved in the null controllable region. The proposed technique does not require plant stability, and can manage any bounded disturbance term satisfying the matching condition. Theoretical results have been validated by simulation using the missile roll angle control problem.

Technical communique: Robust quantized feedback stabilization of linear systems

This paper investigates the feedback stabilization problem for SISO linear uncertain control systems with saturating quantized measurements. In the fixed quantization sensitivity framework, we propose a time varying control law able to effectively account for the presence of saturation, which is often the main source of instability, designed using sliding mode techniques. Such controller is proved able to stabilize the plant both in the presence and in the absence of quantization.

Control of mobile robots with uncertainties in the dynamical model: a discrete time sliding mode approach with experimental results

Abstract In this note the trajectory tracking problem for a wheeled mobile base has been addressed, considering the presence of uncertainties in the dynamical model. The proposed solution is based on discrete sliding mode control, in order to ensure both robustness and implementability of the controller. The asymptotic boundedness of the tracking errors has been theoretically proved. The proposed discrete time algorithm has been experimentally tested, performing the experiments on the LABMATE vehicle available at the Robotics Lab of the University of Ancona, and compared with a kinematic controller proposed in the literature.

An Actuator Failure Tolerant Control Scheme for an Underwater Remotely Operated Vehicle

This paper proposes an actuator fault-tolerant control scheme, composed of the usual modules performing detection, isolation, accommodation, designed for a class of nonlinear systems, and then applied to an underwater remotely operated vehicle (ROV) used for inspection purposes. Detection is in charge of a residual generation module, while a sliding-mode-based approach has been used both for ROV control and fault isolation, after the application of an input decoupling nonlinear state transformation to the ROV model. Finally, control reconfiguration is performed exploiting the inherent redundancy of actuators. An extensive simulation study has been also performed, supporting the effectiveness of the proposed approach.

Neural Networks Based Control of Mobile Robots: Development and Experimental Validation

The paper proposes a neural networks approach to the solution of the tracking problem for mobile robots. Neural networks based controllers are investigated in order to exploit the nonlinear approximation capabilities of the nets for modeling the kinematic behavior of the vehicle and for reducing unmodeled tracking errors contributions. The training of the nets and the control performances analysis have been done in a real experimental setup. The proposed solutions are implemented on a PC-based control architecture for the real-time control of the LabMate mobile base and are compared with classical kinematic control schemes. Experimental results are satisfactory in terms of tracking errors and computational efforts.

Robust Control of Variable-Speed Wind Turbines Based on an Aerodynamic Torque Observer

This paper focuses on a robust power generation control strategy for a variable-speed wind energy conversion system based on a permanent magnet synchronous generator. The proposed control strategy combines a robust observer of the aerodynamic torque with a sliding mode-based field-oriented control strategy. The robust vanishing of the observation error and the tracking error is proved. Reported numerical simulations show that the proposed control policy is effective in terms of optimal power extraction and it is robust with respect to uncertainties affecting the system.

Robust stabilization of a mobile robot violating the nonholonomic constraint via quasi-sliding modes

The stabilization problem for a wheeled mobile base has been addressed, considering the presence of disturbances violating the nonholonomic constraint. The proposed solution is based on discrete time sliding mode control, in order to ensure both robustness and implementability. The controller is shown to drive the robot to a bounded neighborhood of the origin. Simulation results have been reported, demonstrating the effectiveness of the proposed control law.