ADVANCED POSITION AND SPEED CONTROL TECHNIQUES FOR INDUCTION MOTORS

Abstract

The high performance electric motors for precise rotor position and/or rotor speed control are important in industrial applications. The performance of an electric motor depends on the motor dynamics as well as the control strategies. Of all the available electric motor types, the induction motor is the most widely used and is often viewed as the workhorse of modern industry. Induction motors have many advantages compared to other types of electrical motors. They are simple in structure, reliable and inexpensive. They do not have brushes like DC motors and do not require periodic maintenance, and their compact structure is insensitive to environmental conditions. However, it is known that the control of an induction motor is relatively difficult compared to other kinds of motors, such as DC motors. In fact, the induction motor presents a nonlinear and complex mathematical model, rotor variables are rarely measurable and its parameters vary with operating conditions. The search for simple control methods similar to those used for DC motors, has led to the so-called vector control or field oriented control methods. By using these techniques, the induction motors have proved to outperform the DC ones. In field oriented control, imperfect knowledge of the rotor resistance degrades the steady state and transient responses of the drive because the decoupling between torque and rotor flux is lost. This led to an interest in development of so-called robust control methods which seek to solve these problems. The specific contributions of this thesis are: first, a simple new sliding mode control method for rotor position and rotor speed control of induction motor is presented. This technique is shown to reduce chattering and accelerate reaching phase. Feedback linearization control method is one of the most widely used nonlinear approaches to the control problem, which has attracted a great deal of research interest in recent years. However, there are also a number of ii important limitations associated with the feedback linearization control approach. To overcome the above shortages and achieve accurate control performance of rotor speed control of induction motor, a robust control scheme is designed by employing sliding mode control and feedback linearization control. Also, to achieve accurate control performance of rotor position control of the induction motor, a newly designed control optimal method is presented. The proposed controller is designed via combining sliding mode control and linear quadratic regulator. This new controller technique fully matches the merits of the easy design of the linear quadratic regulator method and the strong robustness of the sliding mode control. Finally, a novel proposed control scheme based on adaptive inverse control strategy is implemented for the control of rotor position and rotor speed of the induction motor. The effectiveness of various advanced control methods, supported by many different simulation results, is studied. The robustness of the different controllers against induction motor parameters variation is also verified.