Real-Time Implementation of an Open-Circuit Dc-Bus Capacitor Fault Diagnosis Method for a Three-Level NPC Rectifier

The main goal of this paper is to detect the opencircuit fault of the electrolytic capacitors usually used in the dcbus of a three phase/level NPC active rectifier. This phenomenon causes unavoidable overvoltage across the dc-bus leading therefore to the destruction of the converter’s power semiconductors. The real-time detection of this fault is therefore vital to avoid severe damage as well as wasted repair time. The proposed diagnosis method is based on the measurement of the voltages across the two dc-bus capacitors. Their mean values are therefore compared with the half value of the dc-bus reference voltage. If the comparison result is under a predefined threshold value, a fault alarm signal is generated in real-time by the monitoring system. The converter’s control algorithm and fault detection method are both implemented in real-time on a DSP controller. The obtained experimental results confirm the effectiveness of the proposed diagnosis technique. Indeed, a fault signal is generated at the peripheral of the DSP after 60 ms of the fault occurrence. Keywords—fault detection; capacitor failure; open-circuit fault; real-time implementation; multilevel converters