The application of a new PID autotuning method for the steam/water loop in large scale ships

In large scale ships, the most used controllers for the steam/water loop are still the proportional-integral-derivative (PID) controllers. However, the tuning rules for the PID parameters are based on empirical knowledge and the performance for the loops is not satisfying. In order to improve the control performance of the steam/water loop, the application of a recently developed PID autotuning method is studied. Firstly, a 'forbidden region' on the Nyquist plane can be obtained based on user-defined performance requirements such as robustness or gain margin and phase margin. Secondly, the dynamic of the system can be obtained with a sine test around the operation point. Finally, the PID controller's parameters can be obtained by locating the frequency response of the controlled system at the edge of the 'forbidden region'. To verify the effectiveness of the new PID autotuning method, comparisons are presented with other PID autotuning methods, as well as the model predictive control. The results show the superiority of the new PID autotuning method

Decoupling Controller Design Based on Gain and Phase Margin Specifications for a Coupled Tank System Model

The objective of a multi-variable control involves maintaining various control variables at independent set points. The interactions present in the system affects more than one controlled variables because of the manipulated variable. Decouplers are designed to reduce the interactions in between the loops in to achieve a satisfactory responses when there is presence of non-minimum phase zeros,multiple time delays and large uncertainty. The dynamic and static decoupling are the two types of decoupling strategies. In this thesis, these control strategies are discussed. In practice, there exists certain process unmodelled dynamics. Hence, there is a necessity to examine the robust stability of a system to check whether the control system stability is ascertained in presence of these unmodelled dynamics. This thesis deals with designing a controller along with decoupler to achieve the desired performance of a TITO system. At first, a decoupler is being designed from the plant matrix. Then, a first order plus dead time model is obtained for each of the decoupled process on the basis of the frequency response fitting. After getting the FOPDT model a decentralized PI/PID controller for each reduced order decoupled model is designed to obtain desired gain and phase margins. The present technique is applied to a coupled tank system. The characteristics like non-minimum phase and non-linear characteristics make the control of coupled tank liquid level system, a standout amongst the most difficult benchmark control problems. The main objective of the coupled tank system is to maintain a desired level of liquid in the two tanks independent of each other when the water enters the tank and when the water flows out. The coupling impact here in this framework is a coupling switch that permits stream of water in the tank at higher level to a tank at lower level. Lastly, robust stability of the control system is analyzed in the presence of various process uncertainties like additive uncertainty and multiplicative uncertainties. The stability analysis is examined using the small gain theorem or the spectral radius criterion. The robust stability of the coupled tank system is also determined

Nonlinear predictive control applied to steam/water loop in large scale ships

In steam/water loop for large scale ships, there are mainly five sub-loops posing different dynamics in the complete process. When optimization is involved, it is necessary to select different prediction horizons for each loop. In this work, the effect of prediction horizon for Multiple-Input Multiple-Output (MIMO) system is studied. Firstly, Nonlinear Extended Prediction Self-Adaptive Controller (NEPSAC) is designed for the steam/water loop system. Secondly, different prediction horizons are simulated within the NEPSAC algorithm. Based on simulation results, we conclude that specific tuning of prediction horizons based on loop’s dynamic outperforms the case when a trade-off is made and a single valued prediction horizon is used for all the loops

An extended approach of inverted decoupling

This paper presents an extension of the inverted decoupling approach that allows for more flexibility in choosing the transfer functions of the decoupled apparent process. In addition, the expressions of the inverted decoupling are presented for general n × n processes, highlighting that the complexity of the decoupler elements is independent of the system size. The realizability conditions are stated in order to select a proper configuration, and the different possible cases for each configuration are shown. Comparisons with other works demonstrate the effectiveness of this methodology, through the use of several simulation examples and an experimental lab process

Adaptive Signal Processing Strategy for a Wind Farm System Fault Accommodation

In order to improve the availability of offshore wind farms, thus avoiding unplanned operation and maintenance costs, which can be high for offshore installations, the accommodation of faults in their earlier occurrence is fundamental. This paper addresses the design of an active fault tolerant control scheme that is applied to a wind park benchmark of nine wind turbines, based on their nonlinear models, as well as the wind and interactions between the wind turbines in the wind farm. Note that, due to the structure of the system and its control strategy, it can be considered as a fault tolerant cooperative control problem of an autonomous plant. The controller accommodation scheme provides the on-line estimate of the fault signals generated by nonlinear filters exploiting the nonlinear geometric approach to obtain estimates decoupled from both model uncertainty and the interactions among the turbines. This paper proposes also a data-driven approach to provide these disturbance terms in analytical forms, which are subsequently used for designing the nonlinear filters for fault estimation. This feature of the work, followed by the simpler solution relying on a data-driven approach, can represent the key point when on-line implementations are considered for a viable application of the proposed scheme

Distillation Column Control Strategies; IMC & IMC Based PID Controller

Distillation column is a multi-input multi-output system, used especially in petrochemical industries. It is a multi-variable control system, used to separate various components of a mixture. It is a highly interacting system. So the objective of this project is to control the compositions of top and bottom products. The performance analysis of controlling different compositions has been found out using different control strategies i.e. PID controller as well as IMC controller. It is found out that the performance analysis of IMC controller is better than that of the PID controller. The project emphasizes mainly on the tuning of the IMC controller. For that, different models of the process have been taken and the responses have been found out. Some empirical relationships have been derived between the tuning parameters and the process response characteristics. Based on this relationships, an empirical formula has been derived between the tuning parameter and the process parameters. That has been tested for an unknown process and verified in order to get the desired response characteristics

Compensation of distributed delays in integrated communication and control systems

The concept, analysis, implementation, and verification of a method for compensating delays that are distributed between the sensors, controller, and actuators within a control loop are discussed. With the objective of mitigating the detrimental effects of these network induced delays, a predictor-controller algorithm was formulated and analyzed. Robustness of the delay compensation algorithm was investigated relative to parametric uncertainties in plant modeling. The delay compensator was experimentally verified on an IEEE 802.4 network testbed for velocity control of a DC servomotor

Decoupling Level Flow Process Control

This Final Year Research Project (FYRP) which entitled "Decoupling Level Flow Process Control" is purposely done to model level and flow process using step test and several set of experiments. Data extracted from the experiments were used to build process models and were simulated in the MATLAB simulink since it is the most appropriate software that can model the process. In order to achieve themain objectives of the project which is to design the decoupler as well as reducing or eliminating the interactions, some calculation involves in the decoupler design stage. As a requirement to the project, some modifications have been done on the equipment involved. From the experimental works, transfer function for level process, flow process and interaction between level and flow process could be obtained, hi the simulation, the trial is divided into three parts namely openloop process, closed loop with PIDprocess and closed loop withPID plus a decoupler process. All the responses were analyzed to compare the effectiveness of the decoupler. Based on the result, it is shown that the level will deviate in a great amount if step change is applied in an open loop process. However, the deviation decreases as the conventional PID controller is introduced in the process. As expected, with the presence of decoupler, the result will bebetter since the decoupler helps the controlled variable to be as close as possible to the desired set point. It is also observed that the performance of the decoupler is better as the flow rate increases as well as at higher gain of the interaction process; in other words, the decoupler works best for strong interaction process. The objectives specified for this project have been successfully achieved within the time constraint given. Further research could be made to observe the performance of the decoupler in the industries