DC offset reference correction in PWM voltage source inverters

Sensorless winding temperature monitoring of PWM inverter-fed electrical machines may be made by a superposition method. A small dc offset current superimposed on the AC current may be used to measure winding resistances during machine operation. To obtain acceptable results, the dc voltage component in the inverter output must be measured with sufficient accuracy. Previous investigations showed that the referenced DC voltage offset is distorted by parasitic effects. A deeper knowledge of these parasitic effects is necessary. The paper describes a suitable correction method. Experimental results verify the proposed method.