Manuel Beschi

On the presence of equilibrium points in PI control systems with send-on-delta sampling

This paper deals with the presence of equilibrium points and limit-cycles in a PI control system with send-on-delta sampling. In particular, sufficient conditions on the controller parameters for the existence of equilibrium points are given. These conditions can be usefully exploited for the tuning of the event-based PI controller parameters, thus making the overall design easier. Simulation results are provided as illustrative examples.

Event-Based PI Plus Feedforward Control Strategies for a Distributed Solar Collector Field

This brief deals with the application of an event-based proportional-integral (PI) plus feedforward control strategy to a distributed solar collector field. In particular, a symmetric send-on-delta strategy is considered and an event-based feedforward action to compensate for the disturbance represented by changes in the solar radiation is added to the PI control law. Furthermore, we propose a simple strategy, based on the describing function technique, to estimate the model parameters for tuning the controller. The obtained experimental results show that the proposed control strategy permits to obtain a very significant reduction of the events with only a slight decrement of the control performance.

Constrained Temperature Control of a Solar Furnace

A new constrained control strategy for a solar furnace is proposed in this paper with the goal of attaining a minimum-time transition between two values of the temperature subject to constraints on both the saturation and slew rate level of the process input. In the case of set-point step-shape signals, the strategy basically consists in implementing a (model-based) feedforward control law with maximum positive and negative velocity phases in order to obtain a minimum-time transition with no overshoot. In the case of ramp-shape set-point signals (addressing the output slew-rate constraint), the suitable feedforward control law is obtained by also inverting the dynamics of the system. Implementation issues are discussed. Simulation and real experimental results demonstrate the effectiveness of the methodology.

The generalised isodamping approach for robust fractional PID controllers design

ABSTRACT In this paper, we present a novel methodology to design fractional-order proportional-integral-derivative controllers. Based on the description of the controlled system by means of a family of linear models parameterised with respect to a free variable that describes the real process operating point, we design the controller by solving a constrained min–max optimisation problem where the maximum sensitivity has to be minimised. Among the imposed constraints, the most important one is the new generalised isodamping condition, that defines the invariancy of the phase margin with respect to the free parameter variations. It is also shown that the well-known classical isodamping condition is a special case of the new technique proposed in this paper. Simulation results show the effectiveness of the proposed technique and the superiority of the fractional-order controller compared to its integer counterpart.

Stability analysis of symmetric send-on-delta event-based control systems

In this paper we present a methodology for the stability analysis of a particular type of event-based control system. In particular, a symmetric send-on-delta technique is employed to generate the events and any single-input-single-output linear time-invariant process is considered. The devised procedure allows the user to find the interval of values of the DC gain of the loop transfer function which ensures that limit cycles do not occur. The technique can be usefully employed to find the range of parameters of an event-based PI controller that ensures the absence of limit cycles in the system. Simulation results show the effectiveness of the methodology.

Friction modeling with temperature effects for industrial robot manipulators

In this paper we present a new friction model for industrial robot manipulators that takes into account temperature effects. In particular, after having shown that friction might change very significantly during robot operations, two solutions based on a polynomial description of the joint friction are proposed and compared. In both cases the models proposed do not need a measurement of the joint temperature, but just of the environmental temperature, so as to be easily applied in industry. Experimental results demonstrate the effectiveness of the applied methodology.

Symmetric Send-On-Delta PI Control of a Greenhouse System

Abstract This paper deals with a symmetric send-on-delta PI control strategy for controlling the internal temperature of a greenhouse. It is shown that, by properly designing the control system, the disturbances represented by the soil temperature, the solar radiation, the wind velocity, and the outside temperature can be effectively compensated with a limited number of events. The role of the design parameters is outlined and simulation results demonstrate the efficacy of the methodology by comparing it with previously proposed techniques.

On the Stability of an Event-based PI Controller for FOPDT processes

Abstract This paper deals with the stability of an event-based proportional-integral controller. In particular, necessary and sufficient conditions on the controller parameters for the existence of equilibrium points without limit cycles are given for a first-order-plus-dead-time process. Practical issues related to the controller implementation are also addressed. The presented conditions enable a simpler tuning of the controller. Simulation and experimental results are provided as illustrative examples.

An Interactive Software Tool for the Study of Event-based PI Controller

Abstract The paper describes an interactive tool focused on the study of a new family of event-based PI controller. Most research in control engineering considers periodic or time-driven control systems. Event-based control is particularly a very promising alternative when systems with reduced computation and communication capacities are considered. For event-driven controllers it is the occurrence of an event, instead of the autonomous progression of the time what decides when the signal sampling should be made. The tool has been developed using Sysquake, a Matlab-like language with fast execution and excellent facilities for interactive graphics. The highly visual and strongly coupled nature of event based control system is very amenable to interactive tools. The tool presented in this paper enables to discover a myriad of important properties of these systems.

Control Strategies for Disturbance Rejection in a Solar Furnace

Abstract This paper addresses the temperature control problem in a solar furnace. In particular, two control strategies for the rejection of disturbances (represented by the variation of the input energy provided by the Sun, mainly because of passing clouds) are proposed. The first one is based on Generalised Predictive Control, where a nonlinear model is employed for free response prediction while a linearised model is used for the computation of the forced response. The second one is a constrained control strategy where the process input and output constraints are taken into account explicitly. In both cases an adaptation of the most significant process parameter is performed. Simulation results show the effectiveness of the methodologies.