Advanced Motion Control in Induction Motor Systems - Modelling, Analysis and Control

Using a unified notation, this thesis collects and discusses the most important steps and issues in the design of estimation and control algorithms for induction motors. It contains many estimation and control algorithms. Their stability is analyzed and their performance is illustrated by simulations and experiments on the same induction motor. An intense and challenging collective research effort is carefully documented and analyzed, with the aim of providing and clarifying the basic intuition and tools required in the analysis and design of nonlinear feedback control algorithms. This material should be of specific interest to engineers who are engaged in the design of control algorithms for electric motors and, more generally, to a broader audience interested in nonlinear control design. In fact, induction motor dynamics are surprisingly rich and their control is challenging even for engineers with a strong nonlinear control background. The induction motor is an excellent source of projects and examples that can be physically and experimentally tested. This thesis is divided into three main parts. The first part is devoted to the modeling issues and the basic assumptions are discussed; the structural properties of models such as observability are also analyzed. In particular the continuous and the discrete time models are explored, and subsequently more complex models are presented, where the basic assumptions of the simplified model are relaxed, i.e. saturation effects. Also a less common version of the induction motor is presented: the Linear Induction Motor (LIM). The LIM, differently from the Rotating Induction Motor (RIM), offers a direct linear motion without the need for any gearbox for the motion transformation (from rotating to linear), and this option has been the key issue for their study in motion control systems. Moreover, this simplification in the mechanical coupling results in a more complex model of the motor itself. The second part is devoted to the estimation of state variables. Novel rotor flux observers with an arbitrary rate of convergence are presented. Particular importance is placed on speed-sensorless output feedback controls which are based only on stator current measurements. For this purpose different types of estimators are designed, i.e Kalman filter, adaptive and robust observers, etc. All the estimation algorithms are validated by experiments. In the third part the output feedback controls based on rotor speed, stator current, and stator voltage measurements are presented; some algorithms incorporate flux and speed-observers to improve performance. All the control schemes are experimentally validated for the same motor with similar references to illustrate their performance, so that they can be compared. Advantages and drawbacks of each scheme are pointed out. Finally the last part explains some aspects of the experimental implementation and validation of the algorithm. Tests which validate the motor model and the parameters used are also presented. This thesis is not be a complete treatment of the control motion systems with induction motors, since many basic parts are omitted (only the references are given), and for this reasons it is only suitable in a skilled reader in this field, who is interested in the recent developments in control of induction motors. This thesis contains the work on the motion control systems with induction motors that has been done in the three years of my PhD period. It summarizes the 8 papers on the most important international journals in this field (Transaction on Industrial Electronics, Transaction on Industry Application, Automatica and Control Engineering Practice) and the 7 papers on international conferences of which I have been the Author.