Internal Model Control Tuning Research Articles

A Study of PI Controller Tuning Methods Using the Internal Model Control Guide for a Ship Central Cooling System as a Multi-Input, Single-Output System

Since the variable-speed seawater pump and the three-way valve of a ship’s central cooling system are forms of feedback from the same output signal, these controllers may cause interference when they are not coordinated. Therefore, studying an efficient control tuning method for a central cooling water system is necessary. In this study, a central cooling water system is modeled using Matlab Simulink by utilizing an actual operation dataset, and unknown parameters are estimated for fine-tuning. The simulation model is then verified using the second operating dataset. Additionally, transfer functions are developed for the freshwater output temperature against the three-way valve openness input and the electrical power frequency input to the seawater pump motor, supposing that the two systems are independent. Then, the two PI controllers are tuned using internal model control (IMC) filters. Moreover, the modified internal model control tuning method is suggested, using the character of the central cooling system, which has a large time constant for the heat exchanger system with the seawater pump and a small time constant for the three-way valve system. This method simplifies the tuning of the two combined PI controllers, enhancing the seawater pump’s overall efficiency and the three-way valve’s operation. This study presents the proposed tuning methods based on the IMC filter and modified IMC guide, which confirmed the simple determination of the gain values of the PI controller with the efficient control of the rotational speed of the seawater pump and the three-way valve with reasonable control of the freshwater outlet temperature.

Disturbance rejection using IMC tuned PID controller with improved filter

<p>IMC-PID controllers supply exceptional set point tracking but slow<br />disturbance refutation, because of introduction of slow process pole<br />introduced by the conventional filter. Disturbance rejection is important in<br />many industrial applications over set point tracking. An enhanced IMC filter<br />cascaded with PID controller with Internal Model Control Tuning System<br />(IMC-PID) is presented right now for efficient disruption rejection and<br />reliable first order process operation with time delay (FOPTD). The optional<br />filter does away with the sluggish dominant pole. The present learning shows<br />that the recommended IMC filter provide excellent trouble rejection<br />irrespective of where the trouble enters the procedure and provide high-<br />quality robustness to duplicate deviation in surroundings of accepting in<br />difference with other method cited in the text. Reenactment study was led to<br />show the feasibility of the suggested approach on processes with different 0/r ratios by measuring the controller parameters while retaining the same<br />robustness as regards maximal sensitivity. His efficiency of the closed loops<br />was assessed utilizing integral error parameters. Viz. ISE, ITAE, IAE. The<br />recommended filter provides excellent response pro lag dominant processes.</p>

Dynamic analysis and decentralised control system design for diphenyl carbonate reactive distillation process

ABSTRACT Reactive distillation (RD), a process intensified technique, involves integrating reaction and separation in a single unit. High non-linearities associated with the RD process constrict the control degrees of freedom and set the key challenge in designing a robust control system. In the present work, the design is optimised for reactive distillation–diphenyl carbonate and a decentralised feedback control configuration is applied to carry out the control studies. A comparative decentralised control performance is studied for different transfer function models obtained by using analytical and optimisation-based process identification techniques. The controller parameters obtained from the simple internal model control tuning relations are applied to (i) the linear transfer function model and (ii) non-linear plant model. Set-point tracking and load rejection studies are carried out to compare the performance of different models and investigate the non-linear model’s controller performance.

Modified Smith predictor‐based all‐proportional‐derivative control for second‐order delay‐dominated integrating processes

AbstractAn all‐proportional‐derivative (PD) control‐based modified Smith predictor design is reported here for second‐order delay‐dominated integrating processes. The proposed control structure is realized with two PD controllers along with a first‐order filter towards achieving the desired closed‐loop response. To eliminate the tuning complexity, reported internal model control (IMC) scheme suggests a single tuning parameter λ (i.e. closed‐loop time constant) to tune both the PD controllers along with the filter present in the modified Smith predictor designing. The forward path PD controller parameters are obtained as per the IMC tuning guideline suggested for servo tracking, whereas the feedback path PD controller is realized based on Routh stability analysis with a goal towards improved regulatory responses. The first‐order filter present in the feedback path helps to ensure robust closed‐loop performance. Considerable performance enhancement is observed during set point tracking by the proposed scheme where no overshoot is observed even with smaller rise time. In addition, smooth and reasonably quick load rejection behaviour is also found during a regulatory response. Superiority of the proposed scheme is also substantiated in comparison with others' reported dead‐time compensating techniques in terms of closed‐loop performance indices as well as stability margins.

Revisiting the simplified internal model control tuning rules for low‐order controllers: feedforward controller

In this work, the load disturbance rejection problem is studied. Specifically, the feedforward compensators are considered to reduce the effect of the disturbance in the process' performance. The authors propose simple tuning rules that can be easily applied to a wide range of processes improving the response against the disturbance. The improvement of the proposed method is measured through different performance indices in several simulation examples.

Fuzzy rule-based auto-tuned internal model controller for real-time experimentation on temperature and level processes

Recently, internal model control (IMC) technique has been widely employed for various industrial close-loop control applications. Rewarding feature of IMC controller is that we need to tune only one parameter λ (close-loop time constant) for achieving the desired close-loop response. But, finding an appropriate value of λ is not an easy task. From the basic behaviour of IMC-based close-loop responses, it is found that when the process variable is moving very fast towards the desired value, relatively larger value of λ (smooth control) is required to reduce the possible oscillations. In contrary, smaller value of λ (tight control) is preferred when the process response is quickly moving away from the set point to restrict its further deviation. Hence, to mitigate the limitation of conventional IMC tuning with a fixed λ, a fuzzy rule-based auto-tuning scheme is proposed here for IMC-proportional integral derivative (IMC-PID) controller and its performance is validated through real-time experimentation on temperature and level control loops.

Controller Design and Control Structure Analysis for a Novel Oil–Water Multi-Pipe Separator

To enable more efficient production of hydrocarbons on the seabed in waters where traditional separator equipment is infeasible, the offshore oil and gas industry is leaning towards more compact separation equipment. A novel multi-pipe separator concept, designed to meet the challenges of subsea separation, has been developed at the Department of Geoscience and Petroleum at the Norwegian University of Science and Technology. In this initial study, a control structure analysis for the novel separator concept, based on step-response experiments, is presented. Proportional-integral controllers and model reference adaptive controllers are designed for the different control loops. The proportional-integral controllers are tuned based on the well-established simple internal model control tuning rules. Both control methods are implemented and tested on a prototype of the separator concept. Different measurements are controlled, and results show that the performance of the separator under varying inlet conditions can be improved with proper selection of control inputs and measurements.

Modeling of turbine follow control with internal model control tuning method based on hysys

The power plant is one of the several industries whose product are used by consumers directly. The power plant requires an appropriate control strategy based on real-plant to maintain electricity production,. Turbine Follow Control (TFC) is one of the several control strategies for keeping electricity production. TFC is a control strategy that used to control throttle pressure based on Advanced Regulatory Control (ARC) concept. When there is a change of load on the generator, the error signal will be received by the indicator control. The error signal is used to respond fuel arrangement to maintain the main steam production. Furthermore, the changes of main steam production indicated by the pressure indicator control. It will be responded by the turbine governor valve to carry out a follow-up response in maintaining the main steam towards the turbine. The actual response is given in the form of the percentage of valve. This paper has been modeled TFC strategy using Internal Model Control (IMC) tuning method and First Order Plus Dead Time (FOPDT) approach for getting good control response based on HYSYS. In addition, IMC tuning response in this paper also depends on the ± 5% from setpoint test. From modeling of TFC based on HYSYS, the simulation shows that TFC is precise control strategy to handle the changes of load on the generator with integral absolute error value are 102,087.7 for +5% from setpoint test and 122,947.1 for -5% from setpoint test.

Closed-loop step response for tuning PID-fractional-order-filter controllers

Analytical methods are usually applied for tuning fractional controllers. The present paper proposes an empirical method for tuning a new type of fractional controller known as PID-Fractional-Order-Filter (FOF-PID). Indeed, the setpoint overshoot method, initially introduced by Shamsuzzoha and Skogestad, has been adapted for tuning FOF-PID controller. Based on simulations for a range of first order with time delay processes, correlations have been derived to obtain PID-FOF controller parameters similar to those obtained by the Internal Model Control (IMC) tuning rule. The setpoint overshoot method requires only one closed-loop step response experiment using a proportional controller (P-controller). To highlight the potential of this method, simulation results have been compared with those obtained with the IMC method as well as other pertinent techniques. Various case studies have also been considered. The comparison has revealed that the proposed tuning method performs as good as the IMC. Moreover, it might offer a number of advantages over the IMC tuning rule. For instance, the parameters of the fractional controller are directly obtained from the setpoint closed-loop response data without the need of any model of the plant to be controlled.

Design of RCGA-based PID controller for two-input two-output system

Proportional-integral-derivative (PID) controllers are widely used in industrial sites. Most tuning methods for PID controllers use an empirical and experimental approach; thus, the experience and intuition of a designer greatly affect the tuning of the controller. The representative methods include the closed-loop tuning method of Ziegler-Nichols (Z-N), the C-C tuning method, and the Internal Model Control tuning method. There has been considerable research on the tuning of PID controllers for single-input single-output systems but very little for multi-input multi-output systems. It is more difficult to design PID controllers for multi-input multi-output systems than for single-input single-output systems because there are interactive control loops that affect each other. This paper presents a tuning method for the PID controller for a two-input two-output system. The proposed method uses a real-coded genetic algorithm (RCGA) as an optimization tool, which optimizes the PID controller parameters for minimizing the given objective function. Three types of objective functions are selected for the RCGA, and each PID controller parameter is determined accordingly. The performance of the proposed method is compared with that of the Z-N method, and the validity of the proposed method is examined.

Design and Simulation of Internal Model Controller for a Real Time Nonlinear Process

Background/Objectives: PID controllers are one of the first solutions often considered in the control of process industries. It has always been very difficult to treat the level anomalies n the real time processes. Particularly the non linear systems and processes have been a challenge in relation with their dynamics and flow properties. Methods/Statistical analysis: Dual Spherical Tank Liquid Level System (DSTLLS) has the characteristics of nonlinearity due to the dynamic behaviour and area of cross section of tank. One of the major problems in process industries is to control of liquid level for Second Order System Plus Delay (SOSPD) system because the presence of time delay in the system can lead to destabilization of the system. This simulation aims at portraying the performance of the designed Internal Model Control (IMC) PID Controller. Using the black box modelling technique the SOSPD is mathematically modelled experimentally, assuming the system to be a Single Input Single Output (SISO) model. Findings: The aim of this paper is to design a PID controller using IMC tuning method for a (DSTLLS) whose modelling has been done in real time. This simulation briefly explains about stabilizing problem for SOSPD system using an IMC PID controller. The designed controller performance is analysed in terms of performance indices like Integral Squared Error (ISE) and Integral Absolute Error (IAE) and time domain specifications like Rise time, Settling time and Peak time. Conclusion: The validation of the performance of the designed controller is performed under MATLAB environment. There can different controllers which can be also experimented on the same mathematical model for different configurations of the system, namely MISO and MIMO.

Design of Cascaded IMC-PID Controller with Improved Filter for Disturbance Rejection

IMC-PID controllers provide good set point tracking but sluggish disturbance rejection, because of introduction of slow process pole by the conventional filter. In many industrial applications disturbance rejection is important than set point tracking. In this paper PID controller with Internal model control tuning method (IMC-PID) with an improved IMC filter is presented for effective disturbance rejection and robust operation of first order process with time delay (FOPTD). The suggested filter eliminates the slow dominant pole. The present study illustrates that the suggested IMC filter provides good disturbance rejection irrespective of where the disturbance enters the process and provides good robustness to model mismatch in terms of sensitivity in comparison with other methods cited in the literature. Simulation study was performed on processes with different θ/τ ratios to show the effectiveness of suggested method by calculating the controller parameters to have same robustness in terms of maximum sensitivity. The closed loop performance was tested using integral error criteria Viz. IAE, ISE, ITAE. The suggested IMC filter provides good disturbance rejection response for process having θ/τ ＜1.

Simultaneous automatic tuning of cascade control systems from closed-loop step response data

This study presents a novel automatic tuning method for cascade control systems in which both primary and secondary controllers are tuned simultaneously using a single closed-loop step test. The proposed technique identifies the required process information with the help of B-spline series representation for the step responses. The two proportional–integral–derivative (PID) controllers are then tuned using an internal model control (IMC) approach. Considering the rationale of cascade control, the secondary controller is designed for faster disturbance attenuation. Without requiring an additional experiment, the primary controller is designed based on an identified process model that accurately accounts for inner loop dynamics. Finally, this study includes robustness considerations in the controller tuning process, and develops explicit guidelines for the selection of the IMC tuning parameters, completing the automatic tuning procedure for cascade control systems. The proposed method is robust to measurement noise because of the filtering property of the B-splines, and can provide superior control performance for both set-point tracking and disturbance rejection. Simulation examples demonstrate the effectiveness of the proposed automatic tuning method.

Multi-objective optimization of cascade controller in combined biological nitrogen and phosphorus removal wastewater treatment plant

The multi-objective genetic algorithm (MOGA), aiming at determining the optimal set points for controllers existed in the supervisory control layer, is developed to enhance the treatment performance of a combined biological nitrogen and phosphorus removal wastewater treatment process (i.e. an anaerobic-anoxic-oxic process). Firstly, a cascade ammonia controller that consists of a primary proportional-integral (PI) controller and a secondary PI controller is set up and tuned using the internal model control tuning rule. The primary controller is used to control the ammonia concentration in the effluent and the secondary controller is used to control the dissolved oxygen concentration in the last reactor. This cascade controller could lead to better set point tracking and disturbance rejection control performance. Then, the multi-objective optimization (MOO) of the effluent ammonia controller set point and the nitrate controller set point in the fourth reactor is performed using the MOGA. The two conflicting optimization objectives are (1) effluent quality index which is a function of various main effluent loads and (2) energy consumption which is the sum of aeration energy consumption and pumping energy consumption. The MOO results indicate that the optimal set points for the effluent ammonia concentration and the nitrate concentration in the fourth reactor are both about 1.1g N/m3. The cascade controller with the optimal set points has the capability of enhancing the effluent quality and the energy-saving performance simultaneously.

Performance-based parameter tuning method of model-driven PID control systems

In this paper, performance-based parameter tuning method of model-driven Two-Degree-of-Freedom PID (MD TDOF PID) control system has been proposed to enhance the control performances of a process. Known for its ability of stabilizing the unstable processes, fast tracking to the change of set points and rejecting disturbance, the MD TDOF PID has gained research interest recently. The tuning methods for the reported MD TDOF PID are based on internal model control (IMC) method instead of optimizing the performance indices. In this paper, an Integral of Time Absolute Error (ITAE) zero-position-error optimal tuning and noise effect minimizing method is proposed for tuning two parameters in MD TDOF PID control system to achieve the desired regulating and disturbance rejection performance. The comparison with Two-Degree-of-Freedom control scheme by modified smith predictor (TDOF CS MSP) and the designed MD TDOF PID tuned by the IMC tuning method demonstrates the effectiveness of the proposed tuning method.

Imc Tuned Pid Governor Controller for Hydro Power Plant with Water Hammer Effect

In the present paper a PID governor controller with Internal Model Control (IMC) tuning method for the hydro electric power plant including water hammer effect is presented. The IMC has a single tuning parameter to adjust the performance and robustness of the controller. The proposed tuning method is very efficient in controlling the overshoot, stability and the dynamics of the speed-governing system of the hydro electric power plant supplying an isolated/grid connected load. The results of the proposed IMC tuning method have been compared in the midst of controller with singular frequency (SF) based tuning and Ziegler-Nichols (Z-N) closed loop tuning. A remarkable improvement in stability of the system has been observed with IMC tuning justifying its applicability. Simulated results given in the paper show the feasibility and versatility of the IMC tuning technique in hydro power plant in the presence of water hammer effect.

Identification and Controller Tuning of Cascade Control Systems Based on Closed-Loop Step Responses

This paper presents a new automatic tuning method for cascade control systems based on a single closed-loop step test. The proposed method identifies the required process information with the help of B-spline series expansions for the step responses. The two PID controllers are then tuned using an internal model control (IMC) approach. The secondary controller is designed for enhanced disturbance rejection, and the primary controller is designed, without requiring an additional test, based on an identified process model that accurately accounts for the inner loop dynamics. The desired levels of system robustness explicitly guide the selection of the IMC tuning parameters. The proposed method is robust to measurement noises because of the filtering property of the B-splines, and can provide satisfactory control performance. Simulation examples confirm the effectiveness of the proposed method.

Improved Controller Performance of Selected Hybrid SOFC-GT Plant Signals Based on Practical Control Schemes

This paper compares and demonstrates the efficacy of implementing two practical single input single output multiloop control schemes on the dynamic performance of selected signals of a solid oxide fuel cell gas turbine (SOFC-GT) hybrid simulation facility. The hybrid plant located at the U.S. Department of Energy National Energy Technology Laboratory in Morgantown, WV is capable of simulating the interaction between a 350 kW solid oxide fuel cell and a 120 kW gas turbine using a hardware in the loop configuration. Previous studies have shown that the thermal management of coal based SOFC-GT hybrid systems is accomplished by the careful control of the cathode air stream within the fuel cell (FC). Decoupled centralized and dynamic decentralized control schemes are tested for one critical airflow bypass loop to regulate cathode FC airflow and modulation of turbine electric load to maintain synchronous turbine speed during system transients. Improvements to the studied multivariate architectures include: feed-forward control for disturbance rejection, antiwindup compensation for actuator saturation, gain scheduling for adaptive operation, bumpless transfer for manual to auto switching, and adequate filter design for the inclusion of derivative action. Controller gain tuning is accomplished by Skogestad’s internal model control tuning rules derived from empirical first order plus delay time transfer function models of the hybrid facility. Avoidance of strong input-output coupling interactions is achieved via relative gain array, Niederlinski index, and decomposed relative interaction analysis, following recent methodologies in proportional integral derivative control theory for multivariable processes.

Performance Assessment of PID Control Loops based on IMC Tuning Rule

AbstractIn industrial feedback control loops, setpoint changes are often in the form of step, ramp or other general types, and controllers are usually restricted to the PID form. This paper establishes the lower bounds of integrated absolute errors (IAEs), based on the widely-used internal model control (IMC) principle, from closed-loop responses subject to these setpoint changes. Taking the lower bound as a benchmark, an IMC-IAE-based index is proposed to assess the performance of PID controllers. Numerical and experimental examples, as well as an industrial case study, are provided to verify the lower bound as the performance benchmark, and to illustrate the effectiveness of using the proposed index for performance assessment of PID control loops.

Extension of IMC tuning correlations for non-self regulating (integrating) processes

The filter term of a PID with Filter controller reduces the impact of measurement noise on the derivative action of the controller. This impact is quantified by the controller output travel defined as the total movement of the controller output per unit time. Decreasing controller output travel is important to reduce wear in the final control element. Internal Model Control (IMC) tuning correlations are widely published for PI, PID, and PID with Filter controllers for self regulating processes. For non-self regulating (or integrating) processes, IMC tuning correlations are published for PI and PID controllers but not for PID with Filter controllers. The important contribution of this work is that it completes the set of IMC tuning correlations with an extension to the PID with Filter controller for non-self regulating processes. Other published correlations (not based upon the IMC framework) for PID with Filter controllers fix the filter time constant at one-tenth the derivative time regardless of the model of the process. In contrast, the novel IMC correlations presented in this paper calculate a filter time constant based upon the model of the process and the user’s choice for the closed-loop time constant. The set point tracking and disturbance rejection performance of the proposed IMC tunings is demonstrated using simulation studies and a bench-scale experimental system. The proposed IMC tunings are shown to perform as well as various PID correlations (with and without a filter term) while requiring considerably less controller action.