B. M. Patre

Decentralized PI/PID controllers based on gain and phase margin specifications for TITO processes.

In this paper, a decentralized PI/PID controller design method based on gain and phase margin specifications for two-input-two-output (TITO) interactive processes is proposed. The decouplers are designed for systems to minimize the interaction between the loops, and the first order plus dead time (FOPDT) model is achieved for each decoupled subsystem based on the frequency response fitting. An independent PI/PID controller is designed for each reduced order decoupled subsystem to obtain the desired gain and phase margins, and the performance is verified on the original interactive system to show the effectiveness of the proposed design method for the general class of TITO systems. Simulation examples are incorporated to validate the usefulness of the presented algorithm. An experimentation is performed on the Level-Temperature reactor process to show the practical applicability of the proposed method for the interactive system.

Discrete sliding mode control for robust tracking of higher order delay time systems with experimental application

In this paper, a discrete time sliding mode controller (DSMC) is proposed for higher order plus delay time (HOPDT) processes. A sliding mode surface is selected as a function of system states and error and the tuning parameters of sliding mode controller are determined using dominant pole placement strategy. The condition for the existence of stable sliding mode is obtained by using Lyapunov function. The proposed method is applicable to HOPDT processes with oscillatory and integrating behavior, open loop instability or non-minimum phase characteristics and works satisfactory under the effect of parametric uncertainty. The method does not require reduced order model and provides simple way to design the controllers. The simulation and experimentation results show that the proposed method ensures desired tracking dynamics.

Design of Single-Input Fuzzy Logic Controller for Spatial Control of Advanced Heavy Water Reactor

In large nuclear reactors, such as the Advanced Heavy Water Reactor (AHWR), the spatial oscillations in the neutron flux distribution due to xenon reactivity feedback need to be properly controlled; otherwise, power density and rate of change of power at some locations in the reactor core may exceed limits of fuel failure due to “flux tilting.” Further, situations, such as online refueling, might cause transient variations in the flux shape from the nominal flux shape. For analysis and control of spatial oscillations in AHWR, it is necessary to design a suitable control strategy, which will be able to stabilize these oscillations. In this paper, a simplified scheme to design a fuzzy logic controller for spatial control of AHWR, known as the single-input fuzzy logic controller (SIFLC) is proposed. The SIFLC reduces the conventional two-input fuzzy logic controller (CFLC) to a single-input FLC. The SIFLC offers a significant reduction in rule inferences and simplifies the tuning of control parameters. The SIFLC requires less execution time compared to CFLC for the control of spatial oscillations in AHWR. Through the dynamic simulations, it is observed that the designed SIFLC is able to suppress spatial oscillations developed in AHWR and the performance is found to be better compared to the recently proposed approach in the literature.

Task Space Control of an Autonomous Underwater Vehicle Manipulator System by Robust Single-Input Fuzzy Logic Control Scheme

In this paper, a robust single-input fuzzy logic control Robust Single Input Fuzzy Logic Controller (RSIFLC) scheme is proposed and applied for task-space trajectory control of an autonomous underwater vehicle manipulator system (AUVMS) employed for underwater manipulation tasks. The effectiveness of the proposed control scheme is numerically demonstrated on a planar underwater vehicle manipulator system [consisting of an underwater vehicle and a two link rotary (2R) serial planar manipulator]. The actuator and sensor dynamics of the system are also incorporated in the dynamical model of an AUVMS. The proposed control law consists of a feedforward term to exaggerate the control activity with immoderation from the known desired acceleration vector and an estimated perturbed term to compensate for the unknown effects namely external disturbances and unmodeled dynamics as a first part and a single-input fuzzy logic control as a feedback portion to enhance the overall closed-loop stability of the system as a second part. The primary objective of the proposed control scheme is to track the given end-effector task space trajectory despite of external disturbances, system uncertainties, and internal noises associated with the AUVMS. To show the efficacy of the proposed control scheme, comparison is made with conventional fuzzy logic control (CFLC), sliding mode control (SMC), and proportional–integral–derivative (PID) controllers. Simulation results confirmed that with the proposed control scheme, the AUVMS can successfully track the given desired spatial trajectory and gives better and robust control performance.

Discrete-Time Sliding Mode Spatial Control of Advanced Heavy Water Reactor

This brief presents the design of a discrete-time sliding mode control (DSMC) for spatial power stabilization of advanced heavy water reactor (AHWR). Mathematical model of AHWR is represented by 90 first-order nonlinear differential equations with 18 outputs and five inputs. The linear model is obtained by linearizing nonlinear equations over the rated power. This linear model is found to be highly ill conditioned and is possessing three-time-scale property. Initially, the linear model is transformed into block diagonal form to separate slow, fast 1, and fast 2 subsystems and then DSMC is designed using slow subsystem alone since fast 1 and fast 2 subsystems are stable. The proposed DSMC strategy is designed using the constant plus proportional rate reaching law with matched disturbance. Finally, the nonlinear multivariable model of AHWR is simulated with the designed controller and the results are generated under different transients. The efficacy of the proposed DSMC is demonstrated with the comparison of prevalent controllers in the literature and the performance is evaluated under the same transient levels.

Decentralized PID controller for TITO systems using characteristic ratio assignment with an experimental application

This paper presents a decentralized PID controller design method for two input two output (TITO) systems with time delay using characteristic ratio assignment (CRA) method. The ability of CRA method to design controller for desired transient response has been explored for TITO systems. The design methodology uses an ideal decoupler to reduce the interaction. Each decoupled subsystem is reduced to first order plus dead time (FOPDT) model to design independent diagonal controllers. Based on specified overshoot and settling time, the controller parameters are computed using CRA method. To verify performance of the proposed controller, two benchmark simulation examples are presented. To demonstrate applicability of the proposed controller, experimentation is performed on real life interacting coupled tank level system.

Periodic Output Feedback for Spatial Control of AHWR: A Three-Time-Scale Approach

This paper presents a novel technique of designing Periodic Output Feedback (POF) based controller for three-timescale systems. This design method is investigated for spatial control of Advanced Heavy Water Reactor (AHWR). The numerically ill-conditioned system of AHWR is first decomposed into three subsystems, namely, slow, fast1 and fast 2 by direct block-diagonalization and then a composite controller is designed which provides an output injection gain. This output injection gain has been used to compute POF gain, which is then applied to the vectorized nonlinear model of AHWR to achieve spatial control. This controller is tested via simulations carried out under different transient conditions and the results of simulation are presented.

Discrete sliding mode controller with reaching phase elimination for TITO systems

Sliding mode control (SMC) is emerged as a powerful robust controller for the process control application. However, it does not posses robustness properties during reaching phase and suffers from chattering, which is undesirable. In this paper, a chatter free discrete sliding mode controller (DSMC) with reaching phase elimination is proposed. The issue of existence of reaching phase due to physical constraints such as saturation of actuating devices is also addressed. The two-input-two-output (TITO) system is decoupled into two single-input-single-output (SISO) systems using ideal decoupler. The DSMCs are separately designed for two decoupled SISO systems. The stability is ensured via Lyapunov approach. Simulation study and experimentation on real life interacting two tank liquid level system are included to demonstrate effectiveness and applicability of the proposed controller.

Multirate output feedback based controllers for non-linear inverted pendulum system

Multirate output feedback (MROF) techniques have attracted the interest of many researchers for the design of controller, as these methods are based on output feedback and are at the same time capable of assigning arbitrary dynamical characteristics to the closed loop system. Fast output sampling (FOS) is a kind of MROF, in which the states of the system can be computed from the output of the system. In this paper, different techniques of FOS based controllers are investigated for non-linear system of inverted pendulum (IP). Control laws are designed using linear model of IP system. The first control law is constructed based on past output observations. In second control law, past output observations alongwith past input is used for design purpose. However, in third case, discrete-time sliding mode control (DSMC) in combination with FOS feedback, presented in second control law, is formulated. Simulations have been carried out using non-linear model of IP system developed in MatLab/Simulink environment. From simulations it is observed that, the performance of FOS feedback based DSMC is comparatively better than other control techniques.

Non-singular terminal sliding mode control for robust trajectory tracking control of an autonomous underwater vehicle

The nonlinear trajectory tracking control design of an autonomous underwater vehicle (AUV) is a challenging task because of highly uncertain nature of ocean environment, time varying nonlinear vehicle dynamics and poorly known hydrodynamic coefficients of the vehicle. This paper addresses a trajectory tracking control problem for a class of nonlinear, highly coupled with motion in six degrees-of-freedom (DOF) AUV. The robust tracking control is achieved by designing an non-singular terminal sliding mode control (NTSMC) for complete nonlinear model of an AUV. The proposed control scheme assures finite time convergence of the systems states due to addition of a nonlinear term into linear sliding surface results in nonlinear sliding mode called terminal sliding mode (TSM). In addition, the problem of singularity associated with conventional terminal sliding mode control (TSMC) is overcome by the proposed control scheme. Numerical simulations on an experimental AUV is performed for complex reference trajectory to test the efficacy of the controller. Also the proposed NTSMC is capable of handling the hydrodynamic parameter uncertainties, unidentified disturbances like ocean current and measurement sensor noises.