S. Di Gennaro

Output stabilization of flexible spacecraft with active vibration suppression

Addressed here is the problem of designing a dynamic controller capable of performing rest-to-rest maneuvers for flexible spacecraft, by using attitude measures. This controller does not need the knowledge of modal variables and spacecraft angular velocity. The absence of measurements of these variables is compensated by appropriate dynamics of the controller, which supplies their estimates. The Lyapunov technique is applied in the design of this dynamic controller. Possible source of instability of the controlled system in real cases are the influence of the flexibility on the rigid motion, the presence of disturbances acting on the structure, and parameter variations. In order to attenuate their effects and to damp out undesirable vibrations affecting the spacecraft attitude, distributed piezoelectric actuators are used. In fact, in presence of disturbances and/or parameter variation the proposed controller ensures an approximate solution of the control problem.

Hybrid Control of Induction Motors via Sampled Closed Representations

In this paper, a controller for induction motors is proposed. A continuous feedback is first applied to obtain a discrete-time model in closed form. Then, on the basis of these exact sampled dynamics, a discrete-time controller ensuring speed and flux modulus reference tracking is determined, making use of the sliding mode technique. The resulting controller is hence hybrid, in the sense that it contains both continuous and discrete-time terms. It is shown how to implement such a hybrid controller using the so-called exponential holder, which is the only device to be implemented analogically, together with an analog integrator. Moreover, a discrete-time reduced-order observer is designed for rotor fluxes and load torque estimation. The performance of the proposed controller is finally studied by simulation and experimental tests.

Output attitude tracking for flexible spacecraft

In this work a class of nonlinear controllers has been derived for spacecraft with flexible appendages. The control aim is to track a given desired attitude. First, a static controller based on the measure of the whole state is determined. Then, a dynamic controller is designed; this controller does not use measures from the modal variables, and the variables measured are the parameters describing the attitude and the spacecraft angular velocity. Finally, it is shown that a relaxed version of the tracking problem can be solved when the only measured variable is the spacecraft angular velocity. Simulations show the performances of such control schemes.

On regulation under sampling

The paper deals with linear and nonlinear regulation under sampling. It is shown that digital solutions exist under assumptions which are closely related to the existence of robust solutions to the continuous problem. Approximated solutions are computed starting from the continuous ones.

Nonlinear regulation for a class of discrete-time systems

Abstract This paper deals with nonlinear discrete-time regulation for multi-input, multi-output plants. Conditions involving solvability of nonlinear transcendental equations are set. Following the approach recently developed by Isidori and Byrnes (1990) for continuous time systems, the existence of solutions to the posed problem is proved by investigating the properties of the zero dynamics. Finally a condition is given for the existence of an arbitrary approximation of the nonlinear solution.

Passive attitude control of flexible spacecraft from quaternion measurements

In this work, we propose a dynamic controller for a spacecraft with flexible appendages and based on attitude measurements. This control ensures the asymptotic fulfillment of the objectives in the case of rest-to-rest maneuvers when a failure occurs on the accelerometer sensors, so that the angular velocity is not available for feedback. Also, it is assumed that the modal variables describing the flexible elements are not measured. This is a lower level controller and is to be selected at the higher level by a supervisor when an emergency situation is detected.In this work, we propose a dynamic controller for a spacecraft with flexible appendages and based on attitude measurements. This control ensures the asymptotic fulfillment of the objectives in the case of rest-to-rest maneuvers when a failure occurs on the accelerometer sensors, so that the angular velocity is not available for feedback. Also, it is assumed that the modal variables describing the flexible elements are not measured. This is a lower level controller and is to be selected at the higher level by a supervisor when an emergency situation is detected.

Discrete time sliding mode control with application to induction motors

This work deals with a sliding mode control scheme for discrete time nonlinear systems. The control law synthesis problem is subdivided into a finite number of subproblems of lower complexity, which can be solved independently. The sliding mode controller is designed to force the system to track a desired reference and to eliminate unwanted disturbances, compensating at the same time matched and unmatched parameter variations. Then, an observer is designed to eliminate the need of the state in the controller implementation. This design technique is illustrated determining a dynamic discrete time controller for induction motors.

Individual cylinder characteristic estimation for a spark injection engine

Engine control policies are mostly based on the assumption that all injectors have the same behavior independent of location and aging. In reality, injectors do vary and age. To contain variations around a nominal value, tight tolerances are imposed on the manufacturing process. Even if the manufacturing process is tightly controlled, the air-to-fuel (A/F) ratio needed to satisfy emission constraints is difficult to achieve due to aging and even slight mismatch among different injectors. To devise control policies that take into account behavior differences among injectors, we need to estimate injector characteristics from measurements that are taken on the engine during its life time. In this paper, we present an estimation technique for injector characteristics based on a set of measurements that can be carried out using the sensors present in the car, i.e., intake manifold pressure, crank-shaft speed, throttle-valve plate angle, injection timings and exhaust A/F ratio, which is measured by a single UEGO sensor placed at the exhaust pipe output.

Adaptive robust tracking for flexible spacecraft in presence of disturbances

The paper deals with trajectory tracking for a flexible spacecraft, subject to a gravity-gradient disturbance, under parameter uncertainties. The controls are gas jets and reaction wheels, and the measured variables describe the attitude and angular velocity of the rigid part. The flexible dynamics is treated as an additional disturbance acting on a rigid structure. First, an adaptive control is designed with only the gravity-gradient disturbance acting on the spacecraft; second, it is proved to be effective also in the presence of disturbance due to the flexibility, provided that appropriate robustness conditions on the controller gains are satisfied. These conditions use partial knowledge of the parameters describing the elastic dynamics. Simulations show the good performance of such control scheme and demonstrate its applicability even in the presence of input saturation.The paper deals with trajectory tracking for a flexible spacecraft, subject to a gravity-gradient disturbance, under parameter uncertainties. The controls are gas jets and reaction wheels, and the measured variables describe the attitude and angular velocity of the rigid part. The flexible dynamics is treated as an additional disturbance acting on a rigid structure. First, an adaptive control is designed with only the gravity-gradient disturbance acting on the spacecraft; second, it is proved to be effective also in the presence of disturbance due to the flexibility, provided that appropriate robustness conditions on the controller gains are satisfied. These conditions use partial knowledge of the parameters describing the elastic dynamics. Simulations show the good performance of such control scheme and demonstrate its applicability even in the presence of input saturation.

Nonlinear Digital Scheme for Attitude Tracking

The paper deals with asymptotic tracking of a reference attitude trajectory for rigid spacecraft. Based on differential equations that describe the error dynamics with respect to a given reference trajectory, the design procedure is formulated as a stabilization problem. Both gas-jet and reaction-wheel control modes are considered. Under mild smoothness assumptions on the reference trajectory, a nonlinear digital controller is proposed based on a multirate control strategy. Simulation results show the effectiveness of the proposed digital control scheme.