Silvia Pettinari

On the adoption of a fractional-order sliding surface for the robust control of integer-order LTI plants

This paper investigates the possible adoption of a fractional order sliding surface for the robust control of perturbed integer-order LTI systems. It is proved that the standard approach used in Sliding Model Control (SMC) cannot be used and a substantial redesign of the control policy is needed. A novel control strategy is discussed, ensuring that the sliding manifold is hit at an infinite sequence of time instants becoming denser as time grows. Interesting asymptotic properties are derived relatively to the closed loop response in the presence of a wide class of disturbances. It is also proved that the chattering phenomenon may be remarkably alleviated. A careful simulation study is reported using an electromechanical system taken from the literature, which includes also a comparative analysis of performances with respect to standard SMC and second-order SMC.

An actuator failure tolerant robust control approach for an underwater Remotely Operated Vehicle

This paper proposes an actuator failure tolerant robust control scheme for underwater Remotely Operated Vehicles (ROVs). A reduced order observer has been introduced first, for estimating the ROV velocities. In order to solve the control problem for the ROV positions, a sliding mode control law has been developed using the available position measurements and the velocity estimates provided by the observer. A thruster failure is shown to be detectable simply checking the presence of any deviation of the observed sliding surfaces. Moreover, an isolation policy for the failed thruster is proposed. Finally, control reconfiguration is performed exploiting the inherent redundancy of actuators. An extensive simulation study has been performed, supporting the effectiveness of the proposed approach.

Detection of scramjet unstart in a hypersonic vehicle model

An observer-based strategy for the detection of engine unstart in a scramjet-powered hypersonic vehicle model is presented in this paper. The occurrence of engine unstart, which is regarded as an actuator fault, causes a transition from an operational vehicle mode in which the engine is controllable to a mode where the vehicle is effectively unpowered. Since this transition is accompanied by an abrupt change in model parameters, the vehicle dynamics is modeled as a switching system. A simple algorithm is derived that detects the occurrence of the transition from “started” to “unstarted” mode by processing only the flight control system data, without relying on engine data or measurement of the airflow across the isolator, which facilitate integration with existing control architectures. The method is shown to possess a certain degree of robustness with respect to perturbation on model parameters. Simulation results show the effectiveness of the proposed approach.

Speed Estimation and Fault Detection for PMSM via Quasi Sliding Modes

Abstract The paper presents a cascade control scheme for Permanent Magnet Synchronous Motors (PMSMs) based on a novel reduced order state observer which provides accurate speed tracking performance. The asymptotic vanishing of both the observation error and the speed tracking error is proven. The observer design allows a residual signal to be defined, able to detect faults using Parks vector currents. The performance of the proposed solution is evaluated by simulation using the model of a commercial PMSM drive.

On dynamic input allocation for fat plants subject to multi-sinusoidal exogenous inputs

In this paper, a previously proposed dynamic input allocation approach, essentially geared towards optimizing the steady state response for closed loop systems subject to constant exogenous signals, is revisited and extended in order to deal with periodic exogenous signals with known frequency content.

Robust FDI filters and fault sensitivity analysis in continuous-time descriptor systems

This paper addresses the robust (in the disturbance de-coupling sense) design problem of fault detection and isolation observers for uncertain continuous-time linear descriptor systems. In the considered set-up, the only available signal is the output variable. A bank of disturbance-decoupled filters are designed to distinguish actuator from sensor faults. A fault sensitivity analysis is discussed for three different classes of faults affecting both the actuators and the sensors.

Hybrid control design for fault accommodation in sampled-data systems

This paper addresses a fault accommodation problem for hybrid systems resulting from quantization of continuous linear systems; only the output signal has been assumed to be measurable. A control reconfiguration technique is developed in order to adjust the system dynamics by correcting the effects of generalized drift-like actuator faults.

A Lyapunov-based diagnosis signal for fault detection robust tracking problem of a class of sampled-data systems

This paper addresses a novel Lyapunov-based diagnosis signal design for the Robust Fault Detection of a class of Sampled Data systems whose output vector has to follow an assigned reference. The only signal available for measurements is the output variable. A simulation study on a vehicle suspension system is also reported.

Robust control of hybrid plants in the presence of quantization errors

In this paper, the hybrid system consisting of the interconnection of an uncertain continuous-time plant and of a digital controller is considered. The plant is supposed to be affected by matched uncertainties belonging to a wide class. It is also assumed the presence of an A/D converter with bounded quantization errors. A robust controller based on quasi-sliding modes is designed using quantized state information. The behavior of the solutions of the system is investigated, with reference also to the bounds on the quantization size.

Fault tolerant control allocation for fractional-order systems

In this paper a new fault tolerant control strategy for commensurate Fractional Order time invariant systems is proposed, where only measured system outputs are supposed to be available. The output-feedback Fault Tolerant Control/Control Allocation procedure introduced by Edwards et al. [18] is extended to commensurate Fractional-Order uncertain systems. Both the parametric uncertainty of the system matrix and an extra disturbance term are considered. The policy ensures closed-loop stability throughout the entire closed-loop response of the system even in the presence of actuator reduction in the effectiveness. This is accomplished by incorporating ideas of Fractional Sliding Mode Control, Unknown Input Observers and a fixed Control Allocation method. A convex representation of the problem is created in order to get the controller and observer gains.