Single loop feedback control is commonly used in process control. The main drawback of single loop feedback control is its less effectiveness in rejecting the external disturbances. In order to improve speed of disturbance rejection and stability of closed-loop system, cascade control was studied and analyzed. To design the cascade control, first-order plus deadtime (FOPDT) models of both inner and outer loop were developed and applied for both sequential and simultaneous tuning methods. For sequential tuning, an IMC-based tuning was used whereas for simultaneous tuning method, Multiscale and Enhanced Cascade Control tunings were chosen. Relative performance of various controller settings for single and cascade control were compared. Moreover, recommendation for optimized tuning used “Step Response Checker” from System Design Toolbox was also elaborated and tested. Performance results were evaluated through Minimum Integral Error measurement. The effectiveness of the tuning methods was compared and evaluated using a lab-scale air flow rig.

Improved Cascade Control Tuning for Temperature Control System

This paper presents the digital realization of the fractional‐order PI (FOPI) controller fractional integrator element using the improved constant phase approximation method. A new pole‐zero rationalization approach is proposed within the bandwidth of the Bode phase plot. The voltage source inverter fed induction motor fractional‐order model has been identified. A novel mathematical FOPI controller design procedure for the identified FO plant model has been proposed. The designed FOPI controller fractional integrator element is implemented using the constant phase approximation method. A detailed comparative performance study of the proposed approximation method with the existing Charef, Oustaloup, and refined Oustaloup methods has been carried out using the Bode, Nyquist, and Nichols plots. The proposed FOPI controller is placed in the speed feedback loop of the rotor field‐oriented control algorithm of IM. To confirm the proposed FOPI controller approximation method's robustness, a hardware study is carried out on the laboratory hardware‐in‐loop (HIL) platform. In addition, variation in the number of pole‐zero pair's effect on the speed tracking performance, robustness against parameter and load variations are also analyzed.

Improved constant phase fractional order approximation method for induction motor FOPI speed controller

In this paper the Proportional integral controllers based on Internal Model Control principles tuning technique for a pure integrating process with dead time is designed. The performance of these controllers with different closed loop time constants is analyzed and compared for its set point tracking capability. The controller with best performance for the selected time constant is decided. Every tuning procedure is centered on process model. The understanding of the operator who knows how the plant responds to the different inputs is the simplest model. Neglecting model uncertainty leads controllers unstable in the real world operations. The input is to be decided according to their importance. Finally the design specifications are given for good performance(1). A process model is a set of equations including the necessary input data to solve the equations that allows us to predict the behaviour of a chemical process system(2).The process whose model to be prepared may be with time delay or without time delay. The processes with time delay are the complex processes which are difficult to analyze .The delay time in the process is due to the transportation lag i.e. delay is always present with movement and due to the location of the sensors. The delay in the process may also be caused due to the delay in any part of the system. The delay in the process creates a serious problem in the designing process control system. The system with time delay are difficult to analyze and can be classified as first order plus dead time (FOPDT),second order plus dead time (SOPDT) and integral plus dead time (IPDT). The time delay present in the process can be approximated by different approximating techniques like Taylor's approximation, Pade's approximation etc. �

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Set point tracking capability analysis for an industrial ipdt process model

Combustion control system is a typical system with large time delays and complex couplings. The traditional PID control approach is a classical method often used. However, control performances of PID are unsatisfied such as overshoot and switch time. Internal model control (IMC) is a new control strategy with controller design based on process mathematical model. IMC is widely applied in combustion system because of its outstanding control performance and the simplicity of design. In this paper, an IMC structure is established firstly. Then, adaptive weight particle swarm optimization (AWPSO) algorithm is used in optimizing parameters of IMC and PID with the control evaluation index based on integral of time-weighted absolute value of the error (ITAE). Finally, these adjusted parameters are applied in process object. Result shows that the proposed approach can achieve better control performance than PID.

Design of internal model controller based on ITAE index and its application in boiler combustion control system

Single Board Heater System, a Single Input-Single Output temperature control system, comprises of a heater, fan and a temperature sensor. The amount of current passing through the coil decides the temperature of the thin metal plate. This control problem is designed as the development of suitable model for the system, designing of model-based controllers using the models developed and subsequently the evaluation of their performance. In the proposed work, the data-driven model is identified through step and PRBS tests. The mathematical models are used to identify dynamic characteristics of the system and a controller can then be developed based on these characteristics. The identified models of SBHS are utilized here to design Direct Synthesis PID Controllers, IMC-PID Controller and Modified Dahlin Controller on embedded platform of LabVIEW and analyzed afterwards with MATLAB. The performance measures like stability, time response measures, set-point tracking, disturbance rejection and integral errors are evaluated on developed controllers for comparison in this paper.

Performance Evaluation of Model-based Controllers for Data-driven Models of Temperature Control System employing Embedded Platform

Classical Proportional Integral Derivative(PID) controller
remains the most popular approach for industrial process
control. Poor tuning of PID controller can lead to mechanical
wear associated with excessive control activity, poor control
performance and even poor quality products. In this paper, we
design procedure for the internal model control(IMC) approach
for tuning of conventional PID controller with proper tuning
rules. Furthermore, with help of analytical rule of step test
obtaining the effective first order time delay model of the process.
A simulation example of continuous stirred tank reactor is used
in which the IMC based PID tuning method implemented and
the step response of the closed loop system is compared with
classical tuning methods like Ziegler-Nichols and Cohen-Coon.

Ankit K. Shah

Papers

Performance analysis of IMC based PID controllertuning on approximated process model