Open-circuit fault diagnosis in three-phase power rectifier driven by a variable voltage source
University of New Brunswick
Fault diagnosis in power electronic systems is used to improve reliability and maintainability of power electronic equipment. In this research, a power conversion system which consists of an uncontrolled three-phase rectifier, a DC-DC chopper converter, and a single-phase grid-connected inverter was under study. Several types of faults can occur in the power conversion system, and the focus of this thesis is detection of open-circuit fault and isolation of faulty diodes in the three-phase rectifier. Many fault diagnosis methods have been proposed to identify open-circuit faults in a power device, but none of them are applicable in the system under study for this research due to two restrictions. The first is the number of sensors and accessible signals. There are only three sensors to capture the input voltage (one line voltage), the output voltage, and the output current of the rectifier. The second is the variability of the amplitude and frequency of the voltage source. The voltage source of the rectifier is a wind turbine generator that supplies variable voltage amplitude and frequency depending on the wind speed. The amplitude and the frequency are assumed to be constant and unknown, but limited to lie between known lower and upper bounds. In this thesis, a two-stage method is proposed which captures the input and output voltage of the rectifier to diagnose open-circuit faults and isolate faulty diodes in a three-phase rectifier driven by a three-phase voltage source with variable amplitude and frequency. In the first stage of the proposed method, different classifiers are implemented to identify the fault classes based on the various extracted feature sets, and in the second stage, the phase shift between the input voltage and the ripple of the output voltage of the rectifier is calculated to isolate the faulty diodes. For each of the proposed solutions, simulation results and experimental results are presented.