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The robust control of the crude oil outlet temperature uniformity in a heating furnace of a petroleum refinery is addressed. A reliable dynamic model of the nominal process has been attained using a system identification procedure based on real-time data. This procedure yields a second order model with a dominant time-delay. A PI controller embedded in a modified Smith predictor structure is therefore proposed. Sensitivity and robustness properties of this control system are analytically obtained. Based on that, a tuning procedure is developed for this control system which has lower sensitivity to disturbances than the standard Smith predictor while guaranteeing the system stability when plant parameters change. Simulations are carried out of the proposed control system and other well-known linear advanced process control systems. The comparison of the obtained results shows the superior performance of our control system in most cases, both in rejecting a variety of disturbances and in maintaining the closed-loop stability when the process parameters change. • Temperature uniformity of the crude oil flowrate is improved by a modified SP control. • A sensitivity analysis of this modified SP controller is carried out. • A method to tune the parameters of this modified SP controller is proposed. • Stability robustness of this modified SP controller is assessed. • Simulations prove that this SP rejects disturbances better than others. [ABSTRACT FROM AUTHOR]

The fast and accurate tracking of periodic and arbitrary reference trajectories is the principal goal in many nanopositioning applications. Flexure-based piezoelectric stack driven nanopositioners are widely employed in applications where accurate mechanical displacements at these nanometer scales are required. The performance of these nanopositioners is limited by the presence of lightly damped resonances in their dynamic response and actuator nonlinearities. Closed-loop control techniques incorporating both damping and tracking are typically used to address these limitations. However, most tracking schemes employed use a first-order integrator where a triangular trajectory commonly used in nanopositioning applications necessitates a double integral for zero-error tracking. The phase margin of the damped system combined with the hardware-induced delay deem the implementation of a double-integrator unstable. To overcome this limitation, this paper presents the design, analysis and application of a new control scheme based on the structure of the traditional Two-Degrees-of-Freedom PID controller (2DOF-PID). The proposed controller replaces the integral action of the traditional 2DOF-PID with a double integral action (2DOF-PI 2 D). Despite its simplicity, the proposed controller delivers superior tracking performance compared to traditional combined damping and tracking control schemes based on well-reported designs such as positive position feedback (PPF), Integral resonant control (IRC), and Positive Velocity and Position Feedback (PVPF). The stability of the control system is analyzed in the presence of a time delay in the system. Experimental results validating the efficacy of the proposed chattering-free control of a piezo-driven nanopositioning system are included. • Nanopositioners are typically used to track signals minimizing the distortion. • Applications where the main goal is to remove the tracking error are usually neglected. • A new control scheme easy to design and implement is proposed to improve the tracking performance. • Improvements in the tracking performance even in the presence of time delays is demonstrated. [ABSTRACT FROM AUTHOR]

The control of robots that interact with the environment is an open area of research. Two applications that benefit from this study are: the control of the force exerted by a robot on an object, which allows the robot to perform complex tasks like assembly operations, and the control of collisions, which allows the robot safely collaborate with humans. Robot control is difficult in these cases because: (1) bouncing between free and constrained motion appears that may cause instability, (2) switching between free motion (position) controller and constrained motion (force) controller is required being the switching instants difficult to know and (3) robot control must be robust since the mechanical impedance of the environment is unknown. Robots with flexible links may alleviate these drawbacks. Previous research on flexible robots proved stability of a P D controller that fed back the motor position when contacting an unknown environment, but force control was not achieved. This paper proposes a control system that combines a fractional-order D tip position controller with a feedforward force control. It attains higher stability robustness and higher phase margin than a P D controller, which is the integer-order controller of similar complexity. This controller outperforms previous controllers: (1) it achieves force control with nearly zero steady state error, (2) this control is robust to uncertainties in the environment and motor friction, (3) it guarantees stability (like others) but it also guarantees a higher value of the phase margin, i.e., a higher damping, and a more efficient vibration cancellation, and (4) it effectively removes bouncing. Experimental results prove the effectiveness of this new controller. • New results on the force control of a single-link flexible manipulator, which is of interest in several robotic applications. • A fractional-order controller combined with a collision detection mechanism has been designed and implemented. • This methodology combines the obtention of a fractional-order robust controller to cope with unknown environment mechanical impedance. • Experimental validation of the proposed methodology. [ABSTRACT FROM AUTHOR]

Abstract By exploiting the co-located sensor-actuator arrangement in typical flexure-based piezoelectric stack actuated nanopositioners, the polezero interlacing exhibited by their axial frequency response can be transformed to a zero-pole interlacing by adding a constant feed-through term. The Integral Resonant Control (IRC) utilizes this unique property to add substantial damping to the dominant resonant mode by the use of a simple integrator implemented in closed loop. IRC used in conjunction with an integral tracking scheme, effectively reduces positioning errors introduced by modelling inaccuracies or parameter uncertainties. Over the past few years, successful application of the IRC control technique to nanopositioning systems has demonstrated performance robustness, easy tunability and versatility. The main drawback has been the relatively small positioning bandwidth achievable. This paper proposes a fractional order implementation of the classical integral tracking scheme employed in tandem with the IRC scheme to deliver damping and tracking. The fractional order integrator introduces an additional design parameter which allows desired pole-placement, resulting in superior closed loop bandwidth. Simulations and experimental results are presented to validate the theory. A 250% improvement in the achievable positioning bandwidth is observed with proposed fractional order scheme. Highlights • New results on the application of fractional-order controllers to nanopositioners. • Design of a fractional-order IRC control scheme and application to a nanopositioner. • Expansion of the available bandwidth beyond the resonant frequency of the plant. • Experimental validation and robustness analysis of the proposed controller. [ABSTRACT FROM AUTHOR]

Abstract This article addresses the control of a laboratory hydraulic canal prototype that has fractional order dynamics and a time delay. Controlling this prototype is relevant since its dynamics closely resembles the dynamics of real main irrigation canals. Moreover, the dynamics of hydraulic canals vary largely when the operation regime changes since they are strongly nonlinear systems. All this makes difficult to design adequate controllers. The controller proposed in this article looks for a good time response to step commands. The design criterium for this controller is minimizing the integral performance index ISE. Then a new methodology to control fractional order processes with a time delay, based on the Wiener-Hopf control and the Padé approximation of the time delay, is developed. Moreover, in order to improve the robustness of the control system, a gain scheduling fractional order controller is proposed. Experiments show the adequate performance of the proposed controller. Highlights • New results on the application of control of a laboratory hydraulic canal prototype that has fractional order dynamics. • Extension of the Wiener-Hopf design method to the case of fractional order processes with time delay. • Propose of a gain scheduling fractional order controller based on the controller previously designed. • Experimental validation and robustness analysis of the proposed controller. [ABSTRACT FROM AUTHOR]

This work presents a position control for a two degree of freedom flexible-beam made of a composite material, whose aim is to control the tip of the flexible-beam by decreasing the vibration when the beam moves. A mechatronic unit that uses a multi-axis force/torque sensor has been specially designed and we propose to control the system by using a reduced dynamic model. The control method makes use of an inner-loop to control the position of two servo-motors, by means of PID regulators, and an outer-loop that cancels the tip vibration. Moreover, the closed-loop motor dynamics has been reduced by using a series connection of filters that invert its dynamics. The motor controllers have proved to be fast and precise, and cancel the non-modelled components of the motor friction without the need for a previous estimation. The flexible-beam vibration has been controlled by implementing an input-state feedback linearisation which includes compensation terms for the nonlinear beam dynamics, a linear feedback control law and a full state estimator. The experimental validation of the complete control method showed a significant trajectory tracking of the tip, while vibrations were prevented. [ABSTRACT FROM AUTHOR]

The Incremental Conductance (IncCond) algorithm based on direct control mode is one of the highest Maximum Power Point Tracking (MPPT) algorithms ensuring multiple performances compared to some other classical methods. Unfortunately, these performances can deteriorate, especially in the case of sudden changes in weather conditions and load variation., Preventing these drawbacks will form the basis of a new IncCond-MPPT scheme based on indirect control mode in which a smooth electrical power response generated by photovoltaic (PV) panels is well ensured, regardless of quick changes in solar irradiance, absolute temperature and load variation. The proposed MPPT approach uses two stages of control. The first one is used to provide the reference PV-module voltage. The second control loop is formulated as a transfer function that is then controlled using an appropriate Integral controller. Its integral gain is well tuned by applying the Routh's stability criterion on the characteristic equation of the obtained closed loop transfer function. This allows providing the proposed new guideline, which represents the main contribution of this paper. The proposed IncCond-MPPT scheme is compared with the standard one in terms of MPP tracking accuracy and electrical power ratio, which exceeds 97 %, where quick changes of weather conditions and load variations are considered. [ABSTRACT FROM AUTHOR]