Condition Monitoring of a DC- Link Capacitor Used in a PWM Inverter With a Six-Pulse Diode Rectifier Without Current Sensors

Condition monitoring plays an important role in improving reliability of power electronic converters including their dc-link capacitors because it contributes to predicting converter failures. This paper proposes a current-sensor-less con-dition monitoring method of a dc-link capacitor used in a three-phase PWM inverter with a front-end six-pulse diode rectifier and a dc inductor. The method measures both the capacitance and equivalent-series resistance (ESR) of the capacitor without any current sensor. Theoretical analysis reveals that the capacitor current is calculated by the three-phase ac source voltage and the dc inductor. Experimental results obtained from a 200-V laboratory system confirmed that both the ESR and capacitance changes were observed without any current sensors.