Modeling and speed control of an induction motor using sliding mode technique

A new method to control the speed and rotor flux of an induction motor drive using the sliding-mode control technique is presented in this research work. The control algorithm maintains robust drive performance in the presence of load disturbances and drastic motor parameter variations, i.e., change of the rotor and stator resistance up to 100% of the nominal value. In the first chapter, the concept of variable structure control as applied to electrical drives is explained and compared with the traditional and classical approach of linear controllers. The main feature of variable structure control, namely sliding-mode, is explained and the key stages of the design using variable structure control are presented.;Several mathematical models of the induction motor used in the research are derived in the second chapter. Beginning with Park's equations, a model in terms of the stator current and rotor flux derived by Izosimov is presented in differential equations form. Using Izosimov's model, a new state variable model is derived and its per-unit representation is obtained.;Fundamental concepts of variable structure control to be used in the derivation of the control algorithm are presented in the third chapter. The control algorithm is derived and Lyapunov direct method is used to demonstrate stability of the system. A controller with three different levels of voltage is obtained to preserve instantaneous balanced condition of the stator voltages. Assurance of the boundedness of the control effort, necessary for the sliding-mode practical application, is included.;The fourth chapter presents the design of a two-level voltage controller. To minimize the unbalanced currents an additional switching function is included. Direct measurements of the rotor flux are avoided through measurements of stator currents. A new control law in terms of the phase voltages is presented. Computer simulations are presented at the end of Chapters 3 and 4 to demonstrate the robustness of these new controllers.;The details of the derivation of the models of the induction motor are given in Appendices A, B and C.