Utkal V. Mehta

Identification of a class of Wiener and Hammerstein-type nonlinear processes with monotonic static gains

In this paper a non-iterative approach to identifying Wiener and Hammerstein models, including model structure and parameters, is proposed. A single symmetrical relay test is conducted to determine the structure and then the parameters of the block-oriented nonlinear model possessing a static nonlinearity and a linear process in cascade. The static nonlinearity block is represented by a memoryless and monotonic function and the linear process by a second order transfer function model. A relay with hysteresis induces the limit cycle output signal and one cycle data of the output signal is used to identify the block-oriented nonlinear model. The proposed identification method is simple and gives better performance than previous methods for processes with static nonlinearity.

On-line identification of cascade control systems based on half limit cycle data

An on-line identification procedure is presented for cascade control systems in which both inner and outer loop process dynamics are modelled simultaneously by performing a single experiment. Departing from the conventional relay autotuning method where the controller is replaced by a relay, the proposed method is carried out on-line without breaking the closed-loop control. Exact analytical expressions are derived for process model parameters in terms of a few critical parameters of half period data of limit cycle output. Simulation examples are included to demonstrate the effectiveness of the proposed method.

On-line relay test for automatic tuning of PI controllers for stable processes

The applicability of the basic relay tuning method is extended by a robust on-line method to tune proportional–integral controllers without breaking the closed-loop control. A relay is connected in parallel to the controller to induce self-oscillation and then simple measurements are made only on the half period of limit cycle output to obtain a first-order plus dead time model of the process dynamics. A non-iterative optimum tuning formulae is developed in order to reduce the control signal variations. The simulation and experimental studies are presented to validate the design method.

FPAA-Based PI controller for DC servo position control system

In this paper, the real-time application is implemented for a DC servo position control system using Field Programmable Analog Array (FPAA) technology. An automatic tuning technique based on relay feedback is successfully implemented for obtaining the dynamics of a plant. A non-iterative tuning formulae is used in order to reduce the control efforts and to obtain the desired position. Results of real-time hardware-in-the-loop evaluation, obtained when running the on-line relay feedback test together with initial PI settings and improved response with updated settings, are reported.

On-line identification and control methods for PID controllers

The aim of this paper is to present a method for on-line tuning of PID controller for stable processes. Without breaking closed-loop control, an explicit process model is developed from a single relay test and then controller gains are re-tuned non-iteratively to improve the performance. An explicit tuning rules are derived with special emphasis on minimizing the control efforts. Examples are given to illustrate the simplicity and superiority of the proposed method compared with some existing ones.

Deformation Study of Sintered Iron–Carbon–Silicon–Copper Steel Compacts during Cold Forging

Cylindrical preforms of 0.4 initial aspect ratio with 86 ± 1% initial theoretical density has been prepared for iron–0.8%carbon–1%silicon with 0.4% and 1.2% copper added steel preforms through classical powder metallurgy route. These preforms are then subjected to secondary deformation such as cold upsetting to evaluate the deformation characteristics. The cold upsetting is carried out in an incremental step of 0.04 MN under two different frictional media using 100 tons capacity hydraulic press. Plasticity theories have been portrayed for various stresses, strains and Poissons ratio under triaxial condition. The results revealed that the compositional effect on deformation is quite evident under dry friction condition than at graphite employed lubricant condition; on the other hand, both the friction condition shows a phenomenal effect on densification characteristics. Further, it is found that increase of copper content and frictional condition proportionally increases axial and hoop stress but there is a nil effect on mean stress.

Comparative study of constraint optimizations for automatic voltage regulator

A notable literature is available on optimal design of PID parameters using various evolutionary algorithms. The proper selection of an optimization algorithm is significantly important in finding the robust solution for a given optimization problem. Two most powerful optimization techniques are cuckoo optimization algorithm (COA) and particle swarm optimization (PSO). In this paper, a tight constraint is developed to ensure the less variation in the control input signal and at the same time the overall dynamic performance is not compromised for automatic voltage regulator (AVR) system. Then, using two metaheuristic search algorithms the optimal tune techniques are implemented by imposing the performance index. The presented performance index performs well in the presence of the uncertainties in system parameters. A result is discussed in the simulation study.

Stabilizing relay experiment for modeling of unstable processes with large time delay

Relay experiment can be used to identify exact model parameters of an unstable first-order plus dead time transfer function when a limit cycle exists. This article deals with unstable processes with large time delay where the relay test is not applicable. For these processes, the conventional relay method does not induce a stable limit cycle at the output. A method to overcome the problems with inducing a sustained limit cycle output is discussed by deriving a suitable stabilizer for a feedback control. Then, a non-iterative estimation technique is given to identify the unknown parameters of a first-order mathematical model.

Modelling of Integrating Processes with Time Delay Using a Relay Response Curve

Abstract This paper presents a technique to identify integrating processes based on time domain analysis of the relay response curve. Explicit analytical expressions are provided for first- and second-order integrating process models in terms of a few critical point data. Models with up to three parameters are estimated by means of a single symmetrical relay experiment without solving any nonlinear equations. The procedure requires less time for the autotuning test as it uses only half-output limit cycle data. Simulation examples illustrate the simplicity of the presented method.

Fast Fourier transform for estimating process frequency response

This paper discusses the online technique to estimate the process frequency response without breaking the closed-loop control. The extended method of relay feedback using fast Fourier transform (FFT) is measured input and output responses without disconnecting the controller from the loop, which significantly reduces the time required for the autotuning test. The method utilizes step response information and one period of limit cycle oscillation that induced under tight continuous closed-loop control. The frequency domain identification method is useful for certain critical applications where it is dangerous for the control loop to be broken for tuning purposes. Simulation examples are included to illustrate the efficacy of the proposed method.