Speed Estimation Method Of Sensorless Vector Control Of Induction Motor

Sensorless vector control system of induction motor is not only an important aspect but also a hotspot of investigation in modern AC drive. The key problem is that how we can get the speed of motor accurately.Speed estimation utilized in this paper is based on the way of full order flux observer. The observer makes use of motor parameters to estimate speed, but these parameters (stator and rotor resistance, magnetizing inductance) will vary because of the change of environmental temperature, iron loss and main flux saturation. So parameter variation will lead to the error of estimation, the purpose of this paper is to study the influence and the compensation of parameter variation.Firstly, this paper has discussed the impact of variable parameter variation on speed estimation in the case of idealized motor model and found that the effect of stator resistance can be ignored but the effect of rotor resistance is so large enough that we have to consider the way of compensation which is on-line estimation in common. By using rotor resistance and rotor speed adaptive schemes, rotor resistance variation is compensated effectively which has been proven by simulation.In the past, the establishment of dynamic mathematical model neglected iron loss generally, but iron loss exists truly. After establishing induction motor simulation model with iron loss, this paper has investigated effect of iron loss and proposed two schemes to compensate estimated error due to iron : one modified the structure of controller, the other modified the structure of observer, both schemes eliminated the detuning effect of iron.In order to validate the theoretical investigation, experimental motor sampled signal (the voltage and the current) is conversion to digital quantity and given to observer for estimating speed. The comparative results of estimated speed and actual speed show that both are in good agreement.