Accurate inverter error compensation using self-tuning stator current estimation error in sensorless induction motor drives

Speed sensorless vector controlled induction motor drives have become very popular for motion-control applications due to their robustness. The performance of flux and speed observer is strongly influenced by the deadtime and inverter non-linear error at the low speed range. In most applications, the effect of deadtime can be offset by compensating the pulsewidth of PWM signal. However, the inverter non-linear error, such as voltage drop in switching devices, is difficult to compensate when the reconstructed phase voltage is utilized as the input of the observer, because it is not a fixed value. To solve the problem, in this paper the effect of non-linear error upon stator current estimation error is analyzed. A novel compensation method of non-linear error through the stator current estimation error is proposed. The proposed method separated the compensation of non-linear error from the deadtime compensation. Furthermore the nonlinear error can be identified directly off-line by the self-tuning method at the drive start-up and stored in the look-up-table. The experimental results demonstrate the feasibility of proposed method especially in the low speed range.