In order to increase the reliability which is important for marine energy exploitation, five-phase PMSG diode rectifier drive is investigated in this paper. Nevertheless, the use of diode rectifier increases the difficulty of the analysis of drive's behavior, as it introduces uncertainty of harmonic components. Especially in fault mode, this irregularity greatly affects the fault detection. Harmonic components analysis can give us a better comprehension of operation modes, as well as detection methods. This paper uses simulation to make a detail harmonic study in health and fault modes; a fault detection method is thereby applied among them. Finally, detection results indicate that they can be well explained by harmonic components analysis