Interactive Tool for Frequency Domain Tuning of PID Controllers

This paper presents an interactive tool focused on the study of proportional-integral-derivative (PID) controllers. Nowadays, PID control loops are extensively used in industrial applications. However, it is reported that many of them are badly tuned. From an educational point of view, it is essential for undergraduate students in control engineering to understand the importance of tuning a control loop correctly. For this reason, the tool provides different PID tuning methods in the frequency domain for stable open-loop time-delay-free processes. The different designs can be compared interactively by the user, allowing them to understand concepts about stability, robustness, and performance in PID control loops. A survey and a comparative study were performed to evaluate the effectiveness of the proposed tool

Performance index for closed-loop controls

Control performance assessment is becoming increasingly important, as processes are wanted to be as efficient as possible. Performance assessment measures can indicate how well the controllers are functioning, and what can be done to improve their performance. They can be used as an aid in tuning the controller, as well as to monitor the control performance during process operation. The aim of this thesis is to present methods developed for control performance assessment, and evaluate the usability of these methods in assessing the performance of marine engine controls. After presenting the theory, a method to assess the engine control performance is developed. The factors needed to be taken into account regarding the specific processes are discussed. The developed algorithms are then evaluated first with a basic process model and PID control function. Once the functionality is tested, the methods are evaluated with an engine model. Finally, the performance assessment methods are evaluated on an actual engine. Their usability and limitations are discussed, and further actions to be taken are presented. This thesis provides an overview on the present performance assessment methods avail-able, discusses their practical implementation, and their usefulness in marine engine control performance evaluation. However, it is only a start to developing a functioning engine control performance assessment tool. Further developing is still needed. More tests on the actual engine process controls need to be done, to verify the functionality of the methods in different situations. Also, a simplified result from the performance assessment tool should be provided to have one clear value to indicate the whole engine control performance

Stiction Quantification: A Robust Methodology for Valve Monitoring and Maintenance Scheduling

Valve stiction is one of the most common causes of poor performance in control loops. This paper presents a procedure which allows stiction quantification. The technique permits one to estimate the unknown real stem position, and moreover, it does not need any process knowledge and requires only the data normally registered in industrial plants. It is pointed out that the real problem consists of the lack of knowledge about the true value of stiction. A general methodology is proposed to discard data for which quantification is very likely to give wrong indications and to restrict its application to appropriate cases. Simulations show that several sources of perturbations can be eliminated, thus improving the reliability of stiction evaluation. Results are confirmed by application to industrial data: a significant number of valves are analyzed for repeated acquisitions before and after plant shutdown. The proposed procedure seems to be a valid methodology to monitor valve stiction and to schedule and check valve maintenance

Multi-input multi-output proportional integral derivative controller tuning based on improved particle swarm optimization

The PID controller is regarded as a dependable and reliable controller for process industry systems. Many researchers have devoted time and attention to PID controller tuning and they all agree that PID controllers are very important for control systems. A PID equation is very sensitive; its parameters must always be varied following the specific application to increase performance, such as by increasing the system’s responsiveness. PID controllers still have many problems despite their importance for control systems in industries. The problem of big overshoot on the conventional gain tuning is one of the serious problems. Researchers use the PSO algorithm to try and overcome those problems. The tuning of the MIMO PID controller based on the PSO algorithm shows many disadvantages such as high-quality control with a short settle time, steady-state error, and periodical step response. The traditional PSO algorithm is very sensitive and it sometimes affects the quality of good PID controller tuning. This research has proposed a new equation for improving the PSO algorithm. The proposed algorithm is the combination of linearly decreasing inertia weight and chaotic inertia weight, after which a control factor was introduced as an exponential factor. This was very useful for simulations as it is adjustable. The Matlab simulation results of the experiments show that the simulations as it is adjustable. The Matlab simulation results of the experiments show that the new proposed equation converges faster and it gives the best fitness compared to linear inertia weight and oscillating inertia weight and other old equations. The MIMO PID controller system that consists of four plants was tuned based on the new proposed equation for the PSO algorithm (LCPSO). The optimized results show the best rise time, settling time, time delays, and steady-state compared to the systems that are tuned using the old equations. The exploration was directed at considering the impact of using the PSO calculation as an instrument for MIMO PID tuning. The results obtained in the examination reveal that the PSO tuning output improved reactions and can be applied to various system models in the measure control industry. The results for the MIMO PID controller tuned using PSO were assessed using integral square error (ISE), integral absolute error (IAE), and the integral of time expanded by absolute error (ITAE). The five well-known benchmark functions were also used to endorse the feasibility of the improved PSO and excellent results in terms of convergence and best fitness were attained.Electrical and Mining EngineeringM. Tech. (Electrical Engineering

Control algorithms for a two tank liquid level system: An experimental study

The liquid level control in the coupled tank system (CTS) is a classical benchmark control problem. The dynamics of CTS resembles with that of many real systems such as distillation column, boiler process, oil refineries in petrochemical industries and many more. It is a most challenging benchmark control problem owing to its non linear and non-minimum phase characteristics. Furthermore, its physical constraints are also pose complexity in its control design. The thesis provides the description of a CTS along with its hardware setup used for carrying out research work. Usually, system identification is a procedure to obtain the mathematical model of a physical system from the experimental input-output data of the system. The entire process of identifying a system from input and output data broadly consists of six steps. It begins with an experimental design followed by data collection and data preprocessing, next a suitable model structure is selected, then the parameters of the model are estimated and finally the model is validated using the experimental data. The present work is aimed at utilizing the existing as well as developing new tools of system identification for obtaining a suitable model for the studied coupled tank apparatus. Based on the identified model, control algorithms are developed in order to maintain constant liquid levels in the presence of disturbances which is arising due to sudden opening of the valve in the tanks. A lot of research works have been directed in the past several years to develop the control strategies for a CTS. But, few works have been reported for validating the developed control strategies through the experimental setup. Thus, there lies a good opportunity to develop some advanced controllers and to implement them in real-time on the experimental set-up of a CTS in the laboratory

Air-conditioning system design for optimum control performance in Hong Kong

Studies on design for control optimization of air-conditioning (a/c) system for better performance in Hong Kong are reported in this thesis. Typical plant configuration data was collected from an in-depth survey of a/c systems and control used in Hong Kong. Control performance has been used for the first time as an objective for optimizing a/c system designs. The study investigates and illustrates that optimization of a/c systems for application in the Hong Kong by simulation is promising and flexible. The accuracy of simulation is enhanced by using the survey data. The survey shows that some a/c control systems and their control strategies are not well considered in the design stage and their operation and set-up are not properly addressed. Hence, there exists optimization opportunities in the a/c system design and control strategies for a/c systems used in Hong Kong. Parameters affecting the control performance of a/c systems were investigated by carrying out experiments. Identified parameters are the objective function of optimization, controller settings, control valve and drive and, in case of direct digital control, sampling rate. The influence of these factors on the control performance is an essential consideration for the entire optimization process. Strategies in applying the findings in optimizing an a/c system for control performance by simulation were developed and suggested. This study provides platform for further simulation study of optimization in both methodologies and control strategies for a/c system design and operation

Sviluppo di tecniche di monitoraggio delle prestazioni di processi chimici controllati

La tesi proposta tratta del monitoraggio delle prestazioni dei controllori in processi chimici. Diverse sono le cause di malfunzionamento: da valvole con attrito, a regolatori sintonizzati impropriamente alla propagazione di disturbi negli impianti. Con questa tesi si vuole illustrare una metodologia per individuare le cause di mancata prestazione in modo da poterle classificare ed intraprendere le necessarie contromisure. In particolare é stato approfondito il problema della sintonizzazione dei regolatori ed è stata proposta una tecnica di identificazione basata sullo studio dei disturbi, evitando quindi ulteriori sollecitazioni agli impianti per variazioni di set-point. Inoltre è stato affrontato il problema dell’attrito sulle valvole utilizzando diverse tecniche di individuazione automatica originali e già presentetate in letteratura. Il tutto è stato organizzato in un software sviluppato in ambiente Matlab