M.R. Katebi

Predictive Control Design for Large Scale Systems

Abstract The design of model-based Generalised Predictive Controller (GPC) for large scale systems is reported. A two-level decentralised Kalman filter is devised using the MAP approach. An optimal co-ordination strategy is developed for this filtering solution. This filter provides an output predictor for the GPC control design formulation. A two-level optimisation strategy is then employed to decompose the global GPC problem with the input/output constraints. The GPC solution for each subprocess is independently found at the lower level. This solution is sent to a higher level to update the values of an optimal co-ordinator. This procedure is repeated until an optimal solution is found. Simulation results demonstrate the improvements achieved by using the technique.

Predictive PID control: a new algorithm

This paper deals with the design of PID controllers, which have similar features to the model-based predictive controller. A PID type control structure is defined which includes prediction of the output and the recalculation of new set point using the future set point data. The optimal values of the PID gains are calculated using the values of gains calculated by an unconstrained generalised predictive control algorithm. It is also shown that the system stability can be reached for general second and third order systems. Simulation studies demonstrate the performance of the proposed controller, and the results are compared with conventional and generalised predictive control solutions.

PID controller optimisation for fin roll stabilisation

The classical ship roll control PID design method is based on a single performance criterion. This paper extends this method to a nonlinear constrained optimisation, which includes all the controller performance and stability design criteria. The classic PID design method is first introduced before going on to discuss the set of controller design specifications. It is then shown how these specifications are incorporated into the optimised design. The optimal method is then applied to the design of controllers for three separate ships, which present particular problems for the classical design method. Conclusions are then drawn from the results obtained.

Robust Control of a Hot Strip Mill Looper

Abstract A multivariable controller for the looper of a hot strip mill to control the tension and mass flow of the strip is presented. The looper is an arm pushing against the strip between stands in a tandem mill to keep the strip tension constant and to isolate the interactions of the adjacent stands. The controller is designed using H-infinity to decouple the tension and angle and also to infer the unmeasured tension. The performance and robustness of this design is demonstrated using a non-linear simulation of a hot strip mill.

Evaluation of Fin Roll Stabiliser Controller Design

Abstract The control of ship roll motion using fins or rudders has been extensively studied in the last decade. Many different control design techniques have been investigated but very few have found application in practice. The majority of fin stabilisation control systems are still based on PID controllers. The objective of this paper is to identify the benefits of advanced control design techniques and possible advantages, which they might have over their classical counterparts. Three control design techniques namely, classical PID, optimised PID and H ∞ controllers are compared and frequency and time domain performance indices are calculated to demonstrate the advantages and disadvantages of each method.

A Comparison of Stability and Performance Robustness of Multivariable PID Tuning Methods

Abstract Despite the wide popularity of SISO tuning methods, the number of manual tuning methods for MIMO systems is limited. The MIMO control loops are usually tuned sequentially using scalar techniques. Often this is not effective since tuning one loop may detune other loops in the system. Sequential tuning methods are partially open loop, and this is not easily accepted by the plant operators. The objective of this paper is to review and compare the robustness of MIMO PID tuning methods. The study is based on a widely used model of a distillation column and simulation results are presented to demonstrate the performance of the tuning methods.

Guidance Controller Design for Autonomous Underwater Vehicles

Abstract This paper is concerned with the development of the guidance controller for Autonomous Underwater Vehicles (AUVs). A three-layer controller architecture is proposed to enhance the autonomy of the vehicle. At the bottom layer, the local feedback controllers are designed using H ∞ /H 2 control design technique to directly drive the actuators. A 4-degree-of-freedom controller is used to incorporate the sensor and actuator faults and to account for the interaction between the regulation and the diagnostic module. Predictive Control (PC) design technique is employed at the middle layer (guidance) to optimally manoeuvre the AUV along a desired trajectory. Simulation results are presented to demonstrate the performance of the proposed technique.

ℋ︁∞ adaptive controllers for auto‐pilot applications

The design of an H∞ adaptive controller for auto-pilot control applications is considered. The method is based on interpolation between several fixed controllers designed at different operating speeds. The cost functions are chosen for a worst-case design simplifying the control law calculation. The robustness of the adaptive controller to changes in ship speed are illustrated by means of non-linear simulation results.

State-space adaptive H∞ controller with application to a ship control system

This paper is concerned with the design of a state-space H∞ self-tuning surface ship auto-pilot. A state-space approach is employed for the on-line recursive identification which lends itself readily to the H∞ problem formulation. To improve the robustness properties of the identification scheme, vector variable forgetting factor and UD factorisation of the covariance matrix are used. Two different methods for the controller design are described and conditions are given that allow suspension of parameter estimation and controller updating. Both approaches are used to design controllers that are robust to changes in ship speed and sea-states. The benefits of an advanced control design and the advantages of self-tuning capabilities are illustrated by means of non-linear simulations.

H∞ Robust Autopilot Design

Abstract A design of an autopilot for the manoeuvring of a surface ship is considered using an H ∞ standard optimisation technique. The approach is applied to design robust controllers that guarantee the stability and performance robustness with respect to changes in ship speed and sea-states. The benefits of an advanced control design and the advantage of adding adaptive features are illustrated by a simulated design example.