Current-Sensor-Less Condition Monitoring of a DC-Link Capacitor Based on Analysis of a Six-Pulse Diode Rectifier Having AC and DC Inductors

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 presents an analysis of a six-pulse diode rectifier used in the front-end of a three-phase PWM inverter intended for current-sensor-less condition monitoring of a dc-link capacitor. The analysis reveals the ripple current flowing out of a front-end six-pulse diode rectifier having ac line and dc inductors, which allows condition monitoring of both the capacitance and equivalent-series resistance (ESR) of the capacitor without using current sensors. Theoretical analysis reveals that the capacitor current is calculated by the three-phase ac source voltage, ac line inductor, dc inductor, and output power of the inverter. Experimental results obtained from a 200-V laboratory system confirmed that both the ESR and capacitance changes were observed without any current sensors.