Study On Some Methods For Robust Control Of Induction Motor Drive

In this dissertation, researches are focused on high performance induction motor drive system. Aimed to solve the control problems of nonlinearity coupling of electrical variables, model parameter uncertainty and external disturbance existing in induction motor, in-depth theory analysis, simulations are performed concerning the rotor flux observer, the close-loop controllers in the system. Robust control performance with quick response is obtained.Parameter uncertainty and exogenous disturbances in the system, which is called linear parameter-varying system, is studied in the dissertation. State space equation of parameter variation is described by polytope matrixes. Based on the equivalence between H₂/H_∞norm condition and linear matrix inequality, the robust of the system is obtained. Meanwhile on the basis of robust weighted function method, the controller is designed. Then input signal can be effectively tracked and external disturbance is outstandingly restrained. The relationship of subsection and changing rate of parameter between stability and L₂-gain of system is introduced and analyzed. Experiment and simulation results show the robust of the system is obtained and the method designed is valid.The variation of the stator resistance during operation degrades the performance of the flux observer at low speed segment. A new approach to the design of robust rotor flux observer of induction motor is presented. A polytope technique is introduced in the paper. Polytopic self-scheduled output feedback controller with limiting point disposition in linear parameter-varying system is acquired. The induction motor is regarded as a linear parameter-varying system of which the flux observer is a controller. The rotor speed and the stator resistance are considered variable parameters especially. Based on robust control theory, a flux observer, which is of H_∞performance and good dynamic characteristics, is designed with a linear matrix inequality approach. Meanwhile the adverse influence of external disturbances such as measurement noises is suppressed. Simulation results demonstrate the validity of the flux observer designed. The performance of flux observer based on above method is improved to a great degree.Passivity-based control(PBC) theory to the control of induction motor is introduced. First the passivity of motor rotor flux subsystem is proved. Workless force has no influence on the energy balance equation and the asymptotic stability. Then it is discussed that the system can stably track the reference rotor flux without rotor flux observer. The controller developed is an indirect field-oriented one. At last an adaptive PBC strategy is proposed with regard to the rotor resistance change. The design of the control law is globally defined without singularity. Simulink example demonstrates the torque, rotor flux magnitude and rotor speed can be asymptotically tracked.Based on the equipollence relationship of passivity and stability and direct project tlieorem, an nonlinear adaptive L2-gain robust controller is designed. It is a novel approach which is applied to the control of induction motor. Aimed at the uncertainty of rotor resistance and load torque, adjustable parameters corresponding to uncertain ones are introduced. According to direct project theorem, the adaptive control law is acquired by adjusting parameters on-line. Meanwhile the L₂-gain algorithm is adopted as passivity analyzed. The designed control scheme ensures the total system is not only robust to rotor resistance and load torque, but also restrains external disturbance. So the dynamic quality of closed loop system is guaranteed. The correctness of the design method is verified by numerical simulations.Induction motor is a nonlinear system with complicated coupling. On the basis of quadratic optimal control theory, the method of the track adjuster is designed. At first, three linearization and decoupling control methods of induction motor rotor field-orient control are compared in the paper. By selecting rotor flux rotorΦ=φ_rα² +φ_rβ², a new method is designed to make rotor flux and speed decoupled into two independent subsystems and realized the complete linearization using feedback control. The design of the control law is globally defined without decoupling singularity. At last, the control of system can be performed to asymptotically track rotor flux and speed using the linear quadratic optimal control theory. The computations are simple and allow more insight and understanding. Simulink example denotes the system possesses good dynamic and static performance.Aimed at solve the control problems of uncertainty existing in nonlinear system, the robust stability and robust tracking control law based on Lyapunov theory is introduced in the paper. The mathematical model of this system is divided the nominal and uncertainty subsystems. Nonlinear feedback compensation to realize the expectative objective is designed. Then theory above is applied to control problem of a rotor field-oriented induction motor, because of the rotor resistance is subjected to variability and hard to be measured, which more or less deteriorate the performance. Simulation results show the feasibility of the method. The designed scheme guarantees rotor flux and speed to track stably their reference even if the rotor resistance varies from its nominal value.