Internal Model Control Research Articles

IMC-based tuning of PIDA controllers: a comparison with PID control

In this paper we evaluate the performance achieved by a tuning methodology based on Internal Model Control for a Proportional-Integral-Derivative-Acceleration (PIDA) controller. In particular, we compare the results obtained for the set-point and load disturbance step responses with those achieved with a Proportional-Integral-Derivative (PID) controller tuned by applying the well-known SIMC and AMIGO tuning rules. Different high-order processes are considered: self-regulating, distributed lag and non self-regulating. It is shown that, in general, the use of the double derivative (acceleration) action allows the integrated absolute error to be decreased without a decrement of the robustness and with a moderate increment of the control effort.

Internal model control of cumene process using analytical rules and evolutionary computation

Cumene is a precursor for producing many organic chemicals and is thinner in paints and lacquers. Its production process involves one of the large-scale manufacturing processes with complex kinetics. Different classical control strategies have been implemented and compared in this process for the cumene reactor. As a system with large degrees of freedom, a novel approach for extracting the state space model from the COMSOL Multiphysics implementation of the system is adopted here. Internal Modern Control (IMC) based PI and PID controllers are derived for the system. The system is reduced to the FOPDT and SOPDT model structure to derive the controller setting using Skogestad half rules. The integral time is modified for excellent set point tracking and faster disturbance rejection. From the analysis, it can be stated that the PI controller suits more for this specific process. The particle swarm optimization (PSO) algorithm, an evolutionary computation technique, is also used to tune the PI settings. The PI controllers with IMC, Zeigler Nichols, and PSO tuning are compared, and it can be concluded that the PSO PI controller settles at 45 s without any oscillations and settles down faster for the disturbance of magnitude 0.5 applied at t = 800 s. However, it is computationally intensive compared to other controller strategies.

Application of Fractional-order PID controllers in a Greenhouse Climate Control System

A model-based Fractional Order Proportional-Integral-Derivative (FOPID) control design method is applied to a multivariable greenhouse climate control system. A multivariable transfer function model of the greenhouse system, obtained via model Identification experiment, provides plant’s model information for control design. The fractional controller is tuned using the conventional Biggest Log-modulus Tuning (BLT) method associated with integer order PID controllers. However, unlike the conventional PID case, the controller gains are first computed using internal model control design procedure. This produces preliminary values of controller parameters. The FOPID controller gains are further tuned using a single detuning factor (F) until a biggest log modulus of 2N dB is obtained where N is the number of loops in the MIMO system. Simulation studies, using MATLAB and Simulink, show that good compromise between performance and robustness is achievable for both temperature and humidity regulation in a greenhouse control application.

An Experimental Validation of Model Based Control Techniques for Interacting Nonlinear Systems

Model based controllers are those controllers that has gained significant attention in the arena of nonlinear process control. Conical tank is a nonlinear process whose nonlinearity increases when it interacts with another conical tank. Maintaining the level of an interacting nonlinear process operating with constraints is the control objective of this paper. Model Predictive Control (MPC) has the capability of handling constraints and exerts a control action with optimization. MPC is employed for this process and the experimental results obtained are subjected to time domain analysis and the performances are compared with the performance of Proportional’, ’Integral’, ’Derivative (PID) and Internal Model controller based PID (IMC’, ’PID) controller.

Developing the methodology for internal control of current assets in organizations of health resort industry

Subject. In organizations of health resort industry, current assets occupy a significant share in the balance-sheet total, which requires increased attention on the part of management and owners to the condition of these assets, their inflow, outflow, and consumption efficiency. Unified methodological approaches to continuous control over current assets optimize the amount of material resources consumed, thus reducing the cost of services provided by the sanatorium and health resort complex, and increasing the profitability of industry organizations. Objectives. The study aims to formulate an effective model of internal control over current assets for business entities of the sanatorium and health resort complex, considering the general digitalization of organization's business processes. Methods. We employ interviewing and observation, analytical, statistical, computational and graphical methods. Results. We determined that positive dynamics of the industry does not allow for building positive development forecasts due to a number of macroeconomic problems, as well as management, planning and economic, accounting and analytical, personnel and legal problems. Owners and management of the industry organizations face the challenge of searching for in-house reserves for effective business management and continuous control of inventory representing a significant share in the balance sheet currency. Conclusions. The offered methodology for internal control of current assets will ensure ongoing monitoring of business risks and financial stability of business entities in the industry.

Relocated internal model control based cascade control strategy for stable and unstable systems with delay

To control unstable and stable plants a new series cascade control structure (SCCS) is proposed. The proposed SCCS incorporates two or three controllers (setpoint tracking controller, secondary disturbance rejection controller and stabilising controller for only unstable plants). Internal model control scheme (IMCS) augmented with integration of square error (ISE) minimisation along with robustness considerations are applied to design the secondary loop disturbance rejection controller. In contrast, relocated IMCS augmented with ISE minimisation is applied for the outer loop or setpoint tracking controller. Routh Hurwitz stability criteria and maximum sensitivity considerations are used to design the proportional-derivative (PD) controller, which stabilises the unstable plant. It is important to note that the suggested SCCS only needs four controller parameters to be tuned, which is less than the recently reported techniques. Robust stability analysis of the proposed SCCS is performed in the presence of uncertainty. The simulation results depict that the suggested approach imparts pre-eminent improvement in closed-loop performance such as faster setpoint tracking and better disturbance rejection for nominal and perturbed plants.

Research on Secure State Estimation and Recovery Control for CPS under Stealthy Attacks

As the application of cyber-physical systems (CPSs) becomes more and more widespread, its security is becoming a focus of attention. Currently, there has been much research on the security defense of the physical layer of the CPS. However, most of the research only focuses on one of the aspects, for example, attack detection, security state estimation, or recovery control. Obviously, the effectiveness of security defense targeting only one aspect is limited. Therefore, in this paper, a set of security defense processes is proposed for the case that a CPS containing multiple sensors is subject to three kinds of stealthy attacks (i.e., zero-dynamics attack, covert attack, and replay attack). Firstly, the existing attack detection method based on improved residuals is used to detect stealthy attacks. Secondly, based on the detection results, an optimal state estimation method based on improved Kalman filtering is proposed to estimate the actual state of the system. Then, based on the optimal state, internal model control (IMC) is introduced to complete the recovery control of the system. Finally, the proposed methods are integrated to give a complete security defense process, and the simulation is verified for three kinds of stealthy attacks. The simulation results show that the proposed methods are effective.

Internal control models: Historical transformations and development prospects

Subject. This article examines the issue of transformation of the system and models of internal control as a guarantor of the economic security of organizations, regions and countries in the historical aspect and in relation to global changes in the world economy. Objectives. The article aims to determine further ways of development of internal control models and their conceptual foundations, taking into account the realities of the time. Methods. For the study, we used case and chronological analyses, and data systematization. Results. The article finds that internal control models are subject to continuous transformation, taking into account external economic influences and the development of automation tools. This unlocks the process synergies, in other words, more complex processes taking place in the economy and crisis phenomena that affect the conditions for the functioning of companies, make it necessary to look for internal reserves to ensure the continuity of the activities of an economic entity through constant control of risks and the search for options for their minimization. Conclusions and Relevance. The article concludes that the most popular models of internal control are those that are based on a process-oriented approach and continuous analysis of business processes of an economic entity, with further processing of the information obtained and transformation into a system-oriented model of internal control aimed at finding internal reserves. The results of the study can be used in the theory and practice of internal control, as well as for further scientific developments and practical application.

Active flutter suppression of nonlinear fin-actuator system via inverse system and immersion and invariance method

Structural nonlinearities such as freeplay will affect the stability and even flight safety of the fin-actuator system. There is a lack of a practical method for designing Active Flutter Suppression (AFS) control laws for nonlinear fin-actuator systems. A design method for the AFS controller of the nonlinear all-movable fin-electromechanical actuator system is established by combining the inverse system and the Immersion and Invariance (I&I) theory. First, the composite control law combining the inverse system principle and internal model control is used to offset the nonlinearity and dynamics of the actuator, so that its driving torque can follow the ideal signal. Then, the ideal torque of the actuator is designed employing the I&I theory. The unfavorable oscillation of the fin is suppressed by making the output torque of the actuator track the ideal signal. The simulation results reveal that the proposed AFS method can increase the flutter speed of the nonlinear fin-actuator system with freeplay, and a set of controller parameters is also applicable for wider freeplay within a certain range. The power required for the actuator does not exceed the power that can be provided by the commonly used aviation actuator. This method can also resist a certain level of noise and external disturbance.

The closed-loop control method based on dual-port adaptive internal model control for fine image stabilization of space telescopes.

In view of the complex working environment of space astronomical telescopes, the influence of various disturbance sources on the imaging quality cannot be ignored. This paper focuses on compensating for the space telescope line-of-sight (LOS) deviation and suppressing the low-frequency disturbance problem in astronomical observation. A closed-loop control method based on dual-port adaptive internal model control (AIMC) for the fine image stabilization system (FISS) was proposed. To be specific, the fine guidance sensor (FGS) as the high-precision detection unit of the FISS calculates the telescope LOS deviation and sends it to the controller unit in real time. The controller unit drives the large-aperture fast steering mirror (FSM), which performs high-precision two-dimensional rotation to compensate for the telescope LOS deviation, according to the dual-port AIMC control algorithm. Moreover, the dual-port AIMC control method adds an AIMC loop on the basis of the feedback loop and adjusts the filter parameters adaptively according to the target angular velocity of the FSM, achieving higher disturbance suppression capability. The experimental results verify that the control method proposed can effectively compensate for the LOS deviation and suppress the composite frequency disturbance. In the 0-8Hz frequency band, the power spectral density integral values of the star centroid deviation in the X and Y directions of the FGS are, respectively, suppressed by 97.38% and 98.38%.

Suspension Flux Internal Model Control of Single-Winding Bearingless Flux-Switching Permanent Magnet Motor

A suspension flux internal model control method is proposed to address the problem of the strong coupling of a single-winding bearingless flux-switching permanent magnet motor leading to a significant ripple of the rotor radial displacement. Firstly, based on air-gap magnetic field modulation theory, the stator flux equation considering rotor dynamic eccentricity is established to reveal the relationship between the eccentric rotor and the magnetic field. Secondly, according to the dynamic characteristics of the motor and the variation law of the air-gap magnetic field, the suspension-plane flux is substituted into the rotor dynamic model, and the suspension flux-dynamics internal model and corresponding output are constructed, respectively. Finally, a complete control strategy is established, and the rotor is stably suspended by PWM control. The simulation and experimental results show that the proposed method has better steady-state and dynamic performance than traditional PID control, and the maximum radial displacement ripples of the rotor are reduced by 53% and 50% in steady-state and dynamic operation.

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.

Experimentally validated frequency shifted internal model cascade control strategy for magnetic levitation system

Magnetic levitation systems (MLS) provide friction-less, dependable, quick, and affordable operations in a variety of real life applications. One of the often-employed control strategies for the MLS is traditional cascade control, which uses internal model control (IMC)-based proportional–integral–derivative (PID) and proportional–integral (PI) controllers in its primary and secondary loops, respectively. Though this control structure succeeds in achieving levitation, it falls short in terms of set point tracking and disturbance rejection performance. To overcome this limitation, a bi-loop frequency shifted IMC proportional–derivative (FSIMC-PD) strategy is used in the primary loop retaining the conventional IMC-based PI controller in the secondary loop. Routh stability constraints are used to build the PD controller for stabilizing the MLS. Once the MLS is stabilized, an FSIMC-based PID controller for reference tracking is designed for the outer loop. In addition to simulation-based performance comparison of IMC-based PID-PI cascade scheme and the proposed scheme, experimental validation is also carried out on a laboratory scaled MLS setup. Furthermore, performance evaluation based on metrics like the integral of absolute error, integral of square error, integral of time weighted absolute error, total variation of the control signal and its maximum value are also carried out to vindicate the effectiveness of the suggested design. Robust stability analysis is carried out in addition to Nyquist stability considerations to vindicate that the FSIMC-based design is capable of yielding stable closed-loop response amid uncertainties in plant model parameters.

The concept of System-Adaptive Approach (SAA) as a new approach to ensuring business continuity

Subject. This article deals with the issues of the current concept of internal control at enterprises and organizations. Objectives. The article aims to derive a qualitatively new paradigm that meets the current challenges that companies have to deal with, by revealing the evolution of internal control models, as well as taking into account the accumulated world experience of risk orientation, and also determine the role assigned to such a structure as internal audit, based on the author-developed concept of the system-adaptive approach (SAA). Methods. For the study, we used case-study and chronological analyses, historical approach, scientific abstraction, comparison, and generalization. Results. The article identifies a qualitatively new nature of modern threats faced by companies, and presents a paradigm of the author-developed system-adaptive approach, which can help adapt to risks and carry out effective re-engineering of business processes. Conclusions and Relevance. The concept of the system-adaptive approach, as a new approach as opposed to the risk-oriented one, is designed to adapt the activities of organizations to the challenges that they have to involuntarily accept through correctly placed accents. The results summarized in the article can be successfully implemented in the theory and practice of internal control, used in the construction of an integrated risk management system, be a reliable basis for improving the approaches practiced in internal audit, and also serve as a solid foundation for further scientific research.

Hammerstein–Wiener Model Identification for Oil-in-Water Separation Dynamics in a De-Oiling Hydrocyclone System

To reduce the environmental impact of offshore oil and gas, the hydrocarbon discharge regulations tend to become more stringent. One way to reduce the oil discharge is to improve the control systems by introducing new oil-in-water (OiW) sensing technologies and advanced control. De-oiling hydrocyclones are commonly used in offshore facilities for produced water treatment (PWT), but obtaining valid control-oriented models of hydrocyclones has proven challenging. Existing control-oriented models are often based on droplet trajectory analysis. While it has been demonstrated that these models can fit steady-state separation efficiency data, the dynamics of these models have either not been validated experimentally or only describe part of the dynamics. In addition to the inlet OiW concentration, they require the droplet size distribution to be measured, which complicates model validation as well as implementation. This work presents an approach to obtain validated nonlinear models of the discharge concentration, separation efficiency, and discharge rate, which do not require the droplet size distribution to be measured. An exhaustive search approach is used to identify control-oriented polynomial-type Hammerstein–Wiener (HW) models of de-oiling hydrocyclones based on concentration measurements from online OiW monitors. To demonstrate the effectiveness of this modeling approach, a PI controller is designed using the Skogestad internal model control (SIMC) tuning rules to control the discharge OiW concentration directly. The identification experiment emulates an offshore PWT system with installed OiW monitors, which is realistic with the legislative incentive to include online OiW discharge measurements. The proposed approach could enable the application of OiW-based control on existing offshore PWT facilities, resulting in improved de-oiling performance and reduced oil discharge.

Multi-degree-of-freedom Internal Model Control for Optoelectronic Stabilized Platform Based on Sliding Mode Friction Compensation

Multi-degree-of-freedom Internal Model Control for Optoelectronic Stabilized Platform Based on Sliding Mode Friction Compensation

Harmonic Disturbance Compensation of a System With Long Dead-Time, Design and Experimental Validation

An internal model control scheme is proposed to compensate both a long dead-time of a system and a harmonic disturbance. The controller is based on an inversion of the first-order model used to approximate the system dynamics together with an input delay. Two other components of the controller consist of a filter and an additional delay by which the harmonic modes are targeted via adjusting the control loop gain and phase shift. The design of the filter-delay pair is fully analytical and the implementation of the scheme is straightforward. The main attention is paid to the complete compensation of a single-harmonic disturbance. Besides, an extension of the scheme is proposed to target a double harmonic disturbance. Increased attention is paid to the robustness aspects of the schemes. Outstanding performance in terms of harmonic disturbance compensation of the proposed schemes is demonstrated on a series of laboratory experiments.

Modified modeling and internal model control method of thrust ripples in PMLSMs for ultraprecision air-bearing linear feed systems

With the aim of attenuating thrust ripples in ultraprecision air-bearing linear feed systems, a simple and effective internal model control (IMC) system is herein presented based on a modified modeling and identification method of permanent magnet linear synchronous motors (PMLSMs). First, flux linkage equations were used to describe the volt–ampere characteristics of PMLSMs and provide a thrust expression in a differential form based on the principle of virtual work. Then, an analytical formula was obtained through derivation based on the condition of field-oriented control. On this basis, an IMC compensator was designed using an inverse model to attenuate nonlinear thrust effects, and an extended Kalman filter (EKF) was adopted to estimate the actual current in an analog linear amplifier. The boundedness of the nonlinear system was analyzed based on the convergence condition; furthermore, the stability of the proposed IMC compensator with EKF could be guaranteed. Then, an accurate model and thrust parameters were obtained using an identification experiment on an air-bearing linear platform driven by a linear analog amplifier. To demonstrate the coupling effect of current on thrust and confirm the effectiveness of the proposed method, both simulations and experiments were performed at a uniform velocity under extra loads of different weights; then, an extended state observer (ESO) was introduced as a comparative method. Finally, the results of the following error indicated that the proposed method demonstrated improved performance in terms of overcoming the influence of nonlinearity and that it results in smooth velocities in steady states.

A robust inventory management in dynamic supply chains using an adaptive model-free control

As a complex and nonlinear systems characterized by inherent delays, supply chains call for more robust and efficient strategies for their dynamic management. Given the inherent modeling challenges that often fail to capture their dynamic behavior, this paper examines the application of model-free control, as introduced by Fliess and Join, to address supply chain management (SCM) issues. The proposed control framework integrates the principles of model-free control, further enriched by recent advancements in time series analysis for delay compensation and customer demand forecasting. The primary objective, in addition to ensuring effective supply chain control, is to mitigate the intriguing bullwhip effect, where the system model is assumed unknown, and the delay is constant yet unknown. To substantiate this approach’s effectiveness, we present several convincing computer simulations using real-world examples and compare the results with the internal model control strategy.

Generalized optimal 3-degree of freedom parallel cascade control strategy for stable, unstable and integrating chemical processes

To control stable, unstable and integrating chemical processes, a new three-degree of freedom (3DOF) decoupled parallel cascade control architecture (PCCA) is proposed. The proposed PCCA assimilates two/three controllers (secondary disturbance rejection controller, stabilizing controller for only unstable/integrating plants and set-point tracking controller). Internal model control approach (IMCA) augmented with integral of squared error (ISE) minimization and robustness considerations are adopted to design both the secondary loop disturbance rejection controller and the outer-loop set-point tracking controller with the satisfactory performance-robustness tradeoff. Maximum sensitivity constraints and Routh-Hurwitz stability criteria are applied to design the proportional-derivative (PD) controller which stabilizes the unstable and integrating primary plant. It is worth mentioning that the suggested decoupled 3DOF PCCA requires tuning of only two/three controller parameters which are less when compared to recently reported strategies. Robust stability of the suggested 3DOF PCCA is studied in the presence of uncertainty. The simulation results epitomize that the suggested methodology imparts pre-eminent enhancement in closed-loop performance (faster setpoint following and disturbance elimination) for both nominal as well as perturbed plants.