Stator Resistance Estimation using DC Injection Robust to Inverter Nonlinearity in Induction Motors

This paper analyzes the effect of inverter nonlinearity on the stator resistance estimation using dc injection in induction motor drives. It is revealed that the performance of conventional methods can be degraded when the inverter nonlinearity compensation has errors. In this paper, 2^nd order harmonic current with varying phase according to the load is injected together with the dc current to eliminate the effect of voltage distortion caused by inaccurate inverter nonlinearity compensation. The proposed method can guarantee accurate stator resistance estimation by making the pole voltage distortions due to inverter nonlinearity cancel each other out for one electrical period. Simulations and experiments are performed to verify the proposed method.