The design of sophisticated control systems have led in the past ten years to the necessity of satisfying more than one design criterion. Thus, it is natural to think that those criteria can be met in an optimal manner. If several criteria have simultaneously to be optimized, one is in presence of a multi-objective optimization problem. In this paper, many efforts to design the most popular control strategies, i.e. PID and MPC, by using multi-objective optimization techniques are reviewed. Both control strategies have dissimilar optimization characteristics and therefore, they can be considered as representative of two different multi-objective optimization problems, which are described including definitions, possible solutions, algorithms and available software implementations.

Modern multi-megawatt wind turbines are currently designed as pitch-regulated machines, i.e., machines that use the rotation of the blades (pitching) in order to adjust the aerodynamic torque, such that the power is maintained constantly throughout a wide range of wind speeds when they exceed the design value (rated wind speed). Thus, pitch control is essential for optimal performance. However, the pitching activity is not for free. It introduces vibrations to the tower and blades and generates fatigue loads. Hence, pitch control requires a compromise between wind turbine performance and safety. In the past two decades, many approaches have been proposed to achieve different objectives and to overcome the problems of a wind energy converter using pitch control. The present work summarizes control strategies for problem of wind turbines, which are solved by using different approaches of pitch control. The emphasis is placed on the bibliographic information, but the merits and demerits of the approaches are also included in the presentation of the topics. Finally, very large wind turbines have to simultaneously satisfy several control objectives. Thus, approaches like collective and individual pitch control, tower and blade damping control, and pitch actuator control must coexist in an integrated control system.

Optimization techniques have been a crucial tool for designing control systems and for tuning controllers. The always increasing quality requirements for new products and consequently the natural advance in control system design have lead to the introduction of more than one design criterion, which will require in turn more sophisticated techniques to solve such Multi-Objective Optimization (MOO) problems. Thus, many examples of using MOO techniques in control have appeared in the literature. In this paper, several optimal control design problems are analyzed from the MOO point of view. Moreover, some suggestions about how standard control design techniques can be extended to introduce multi-objective optimization are given.

Reverse osmosis (RO) has become an important process for desalting water. It requires an efficient control system to maintain costs at acceptable level and therefore dynamic models are essential. Although it is possible to find in the literature steady-state models and some dynamic models obtained by parameter identification, there are no reports about lumped parameter dynamic models for control purposes obtained by application of physical laws. Such models are useful not only to design model-based control systems but also for the implementation of fault tolerant systems based on fault detection and isolation (FDI) methods, as well as to analyze transient characteristics of the plant. In this paper, models from the literature are shortly analyzed and a simple lumped parameter model for control purposes, which is derived from physical laws, is proposed. Moreover, a block-oriented library for MATLAB/SIMULINKtrade is presented, so that different plant configurations can be implemented as block diagram to simulate the system and to test control algorithms.