Current-Sensor-Less Condition Monitoring of a DC-Link Capacitor in a PWM Inverter With a Six-Pulse Diode Rectifier

Condition monitoring helps improve the reliability of power electronic converters including their dc-link capacitors because it can predict converter failure and degradation. In practice, however, condition monitoring usually utilizes current sensors to obtain health condition, which is a constraint with regard to cost. This paper proposes a current-sensor-less condition monitoring method of a dc-link capacitor in a three-phase PWM inverter with a front-end six-pulse diode rectifier and a dc inductor. The proposed method measures both the capacitance and equivalent-series resistance (ESR) of the capacitor without using current sensors. Theoretical analysis reveals that the capacitor current is calculated using 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 using current sensors.