John J. Martinez

Multisensor switching control strategy with fault tolerance guarantees

In this paper we propose a novel fault tolerant multisensor switching strategy for feedback control. Each sensor of the proposed multisensor scheme has an associated state estimator which, together with a state feedback gain, is able to individually stabilise the closed-loop system. At each instant of time, the switching strategy selects the sensor-estimator pair that provides the best closed-loop performance, as measured by a control-performance criterion. We establish closed-loop stability of the resulting switching scheme under normal (fault-free) operating conditions. More importantly, we show that closed-loop stability is preserved in the presence of faulty sensors if a set of conditions on the system parameters (such as bounds on the sensor noises, maximum and minimum values of the reference signal, etc.) is satisfied. This result enhances and broadens the applicability of the proposed multisensor scheme since it provides guaranteed properties such as fault tolerance and robust closed-loop stability under sensor fault. The results are applied to the problem of automotive longitudinal control.

A multi-observer switching strategy for fault-tolerant control of a quadrotor helicopter

This paper deals with fault tolerant control of the attitude of a four-rotor helicopter (quadrotor). A set of non-linear estimators/observers is implemented to estimate the attitude of the quadrotor. Each estimator has been designed in order to be sensitive to faults in all sensors but one. The attitude estimate that exhibits the smaller error when compared to the attitude computed from the mechanical model is selected to feed the controller. Thus the strategy proposed selects, at each instant, the estimator/observer that minimizes a suitable switching criterion. Simulations of the controlled system, under various scenarios, illustrate that the proposed switching strategy is able to maintain performance levels and to preserve stability under the occurrence of sensor failures.

Adaptive Suppression of Multiple Time-Varying Unknown Vibrations Using an Inertial Actuator

An active vibration control system using an inertial actuator for suppression of multiple unknown and/or time-varying vibrations will be presented. The objective is to minimize the residual force by applying an appropriate control effort through the inertial actuator. The system does not use any additional transducer for getting in real-time information upon the disturbances. A direct feedback adaptive regulation scheme for the suppression of multiple unknown and/or time-varying vibrations will be used and evaluated in real time. It uses the internal model principle and the Youla-Kucera parametrization. In the Appendix, a comparison with an alternative indirect adaptive regulation scheme is presented.

Design and Tuning of Reduced Order H-Infinity Feedforward Compensators for Active Vibration Control

This brief presents a procedure for design and tuning of reduced orders H∞ feedforward compensators for active vibration control systems subject to wide band disturbances. The procedure takes in account the inherent “positive” feedback coupling between the compensator system and the measurement of the image of the disturbance. It also takes advantage of the availability of reliable models obtained by system identification. A controller order reduction technique is proposed for reducing the complexity of the nominal H∞ controller without degrading the performance. Experimental results obtained on an active vibration control system for a flexible mechanical structure will illustrate the procedure.

Robust fault detection for vehicle lateral dynamics

This paper investigates the problem of fault detection and isolation (FDI) for vehicle lateral dynamics. The system under consideration is a Linear Parameter Varying (LPV) model, where the scheduling parameter is related to the vehicle speed. The heart of the proposed approach relies in synthesizing robust residuals for some specified working speed. The robustness guaranties the validity between each working points. Synthesis of robust residuals is inspired from the well-known parity-space method but extended for uncertain systems. The final fault detector is reconstructed by switching from the different residuals according to the speed. An applicative illustration is presented to detect a sensor fault on a vehicle lateral dynamic system. The measurements have been provided by the MIPS laboratory in collaboration within the French INOVE project.

Vehicle yaw control via coordinated use of steering/braking systems

Abstract The aim of this paper is to present a novel methodology that deals with steering/braking coordination task for vehicle yaw control. For steerability enhancement, only active steering control is involved. However, when the vehicle reaches the handling limits, both steering and braking collaborate together to ensure vehicle stability. Judging the vehicle stability region is deduced from the phase-plane of the sideslip angle and its time derivative. The coordination of the steering/braking actuators is achieved through a suitable gain scheduled LPV (Linear Parameter Varying) controller. The controller is synthesized within the LMI (Linear Matrix Inequalities) framework, while warranting H ∞ performances. The simulation results show the effectiveness of the proposed control scheme when the vehicle is subject to various driving situations.

Gain-scheduled LPV/H ∞ controller based on direct yaw moment and active steering for vehicle handling improvements

This paper deals with the design of a control scheme that integrates braking and front steering to enhance the vehicle yaw stability and the lateral vehicle dynamics. The proposed VDSC (Vehicle Dynamic Stability Controller) allows control of the yaw rate and obtains good response for the sideslip angle. Besides, this controller takes into account the braking actuator limitations (i.e braking only the rear wheels) and limits the use of the steering actuator only in the linear vehicle handling region (stability region). To reach these objectives, an original parameter dependent LPV controller structure with consistent performances weights is designed. The solution of the problem is obtained within the LMI framework, while warranting H∞ performances. To prevent tires longitudinal slip due to brake forces generated by the controller, an ABS strategy is included in the control scheme. Computer simulations, carried out on a complex full vehicle model subject to critical driving situations, confirm the effectiveness of the proposed control system and the overall improvements in vehicle handling and stability.

Lyapunov event-triggered control: a new event strategy based on the control

Event-triggered control is a sampling strategy that updates the control value only when some events occur. An event is usually generated by an event-function that indicates if the control signal must be updated or not. If one excepts self-triggered implementation, event-triggered control requires the evaluation of the event function at each time instant. Unfortunately, in the literature of nonlinear system event-based control, computing the event function is more resource consuming than computing the control itself. Moreover, it requires the knowledge of a Lyapunov function that is not necessarily available. The purpose of this paper is to propose for affine nonlinear systems a new strategy for the choice of the event function that only requires the computation of the control. This reduces the complexity of computing the event and avoids to know the Lyapunov function.

Fault tolerant control with additive compensation for faults in an automotive damper

A novel Fault-Tolerant Controller is proposed for an automotive suspension system based on a Quarter of Vehicle (QoV) model. The design is divided in a robust Linear Parameter-Varying controller used to isolate vibrations from external disturbances and in a compensation mechanism used to accommodate actuator faults. The compensation mechanism is based on a robust fault detection and estimation scheme that reconstructs a fault on the semi-active damper; this information is used to reduce the failure effect into the vertical dynamics to achieve good control performances. Validations have been made over a QoV model in CarSimTM. Results show the effectiveness of the fault-tolerant semi-active damper versus an uncontrolled damper; the improvement is 50.4% in comfort and 42.4% in road holding, by avoiding biases in the damper deflection.

Invariant set approach to actuator fault tolerant control

We present a new actuator fault-tolerant control strategy based on the separation of sets that characterise healthy system operation from sets that characterise faulty operation. The new scheme is an extension of a similar strategy recently proposed by the authors. In the present paper we propose a new criterion for fault detection and isolation that leads to less conservative conditions for fault tolerant closed-loop stability. These new conditions employ discrete-time models for the plant, reference system and observers and allow for quicker fault detection and consequent reconfiguration of the controller.