The Research On Speed Sensorless Vector Control System For Induction Motor Drives

In recent years, the rapid development of power electronics technology, computertechnology and vector control technology provides a great technical support for theachievement of high performance AC drive system. Induction motor has a wide range ofapplications in industrial drive system because of the advantages of simple structure, easymanufacturing and less repair work. In order to overcome all sorts of shortcomings thatinstallation speed sensor brings in practical application, researching on the technology ofspeed sensor-less vector control has important theoretical and practical meanings.First of all, brief analysis of research status and development of induction motor speedsensor-less vector control system are provided in this paper. At the same time, the advantagesand disadvantages of different speed identification scheme on the basis of the structure ofvector control system which use speed sensor are summarized. Then, with the methods ofvector control, the paper conducts a deep analysis in dynamic mathematical model ofinduction motor, therefore, coordinate transformation can be inferred via the mathematicalmode of induction motor in different coordinates. And choose the method of rotor magneticfield directional mode to realize the decoupling characteristics of flux and electromagnetismtorque. As an important part of the vector control system, the principle of SVPWM isanalyzed, and the details of modeling processes are given. All of the above provide atheoretical foundation for the study of speed-sensorless control system of induction motor.In many scenarios of speed estimation, the method of model reference adaptivesystem(MRAS) is relatively mature not only in theoretical but also in practical applications.So this paper choose this method to estimate the rotor speed, and uses Popov stability theoremto ensure the stability of the system, then establish the induction motor speed sensorlessvector control system based on MRAS. By analyzing the defects of the traditional MRASusing PI controller, this paper presents a novel Sliding-Mode Mode Reference AdaptiveSystem based on approach law, and gives a detailed mathematical derivation. This method hasrobust ability to external noise disturbance, and has a good effect on chattering reduction.Above all, it has no need to use the complex gain adjustment. Meanwhile, there is a hugedifference between the continuous-time systems and discrete-time system, so it's necessary toanalyze the discrete-time systems of reaching law theory, and gives the solution of theadaptive sliding mode controller, which can solve the contradiction between speed and thechattering problem. In this way, it's more conducive to the engineering design andimplementation. Based on theoretical analysis, the simulations of speed sensor-less vector control systemon the basis of model reference adaptive system are realized in MATLAB/Simulink, and thesimulation results are discussed and compared, these results also prove the accuracy of theidentification algorithm and the good dynamic characteristics.