Research On A Method Of Speed Estimation For Induction Motor

With the development of AC speed regulation system, made by field oriented control, speed sensorless vector control of induction motor did greater effects on enhancing the reliability and simplification, and as a research focus, its key point is how to obtain motor speed accurately.Researching on speed sensorless vector control system of induction motor based on slip frequency control, this paper designed improved model reference adaptive system for speed estimation, and proved the stability and convergence of this method.As stator and rotor parameters of induction motor vary due to running state change during motor running, especially diversification of stator resistance and rotor resistance has obvious influences on speed estimation and vector control system. Therefore, in order to estimate speed more accurately, blocks of stator resistance and rotor resistance online identification were designed. These two blocks also used MRAS, and to reduce influences of the identified stator resistance's fluctuation to speed estimation during given speed negative step, a stator resistance selector was designed; Meanwhile, a slight AC component was added to excitation current to decoupling speed estimation and rotor resistance.Based on above-mentioned theoretical analysis, speed sensorless vector control system of induction motor with stator and rotor resistance identification was set up under MATLAB/Simulink. Simulating resistances'actual variation in accordance with law, simulations of system with parameters identification and system without parameters identification were presented, and did them again with another motor parameters. Simulation results show the speed estimation system with stator and rotor resistance identification can estimate motor speed accurately, so it proves the system has robustness to parameters variation, and it also elevates the static and dynamic performance of vector control system.In order to validate the simulation investigation, test for motor start and run were done. The sampled stator voltages and currents were conversion to digital quantity and given to speed estimation system for estimating speed, then contrast it with the actual measured motor speed. The experimental results show the estimated speed can trace the actual speed, and the system has stable performance.