Thermal Monitoring of Induction Motors with DC Injection Considering Inverter Nonlinearity Compensation Error

This paper analyzes the effect of inverter nonlinearity compensation error on the stator resistance estimation using DC injection in induction motor drives. Although inverter nonlinearity compensation schemes have been improved, it is still challenging to ensure high accuracy in some applications such as general-purpose induction motor drives. This paper reveals that the performance of conventional DC injection methods can be degraded when the inverter nonlinearity compensation has errors. Based on the analysis, an injection method that is robust against the voltage distortion caused by inverter nonlinearity is proposed. The proposed method injects 2nd order harmonic current with varying phase together with the DC. Simulations and experiments are performed to verify the effectiveness of the proposed method.