The open circuit fault of the Vienna rectifier of the DC charging pile in the microgrid will cause AC current distortion and then introduce harmonic current to the microgrid. Because the line impedance between the distributed power sources and the point of common coupling （PCC） is inconsistent

the harmonic power between the power sources cannot be evenly distributed

affecting the safe operation of the microgrid. It is necessary to diagnose the fault location of the power devices in time to determine the source and cause of harmonics in the microgrid

which plays an important role in reducing the maintenance time and cost of the charging pile

improving the utilization rate of the charging pile and the operation reliability of the microgrid. In this paper

aiming at the open circuit fault of single or two power devices

the frequency domain characteristic system of DC charging pile open circuit fault and its fault diagnosis method are developed. Firstly

considering the influence factors such as voltage fluctuation of microgrid

noise interference and load difference of battery packs of different types of electric vehicles

aiming at the problem that it is difficult to obtain effective fault diagnosis results by using single or a small number of frequency domain fault characteristics

the fault characteristics system of DC charging pile is constructed. Secondly

in order to realize the open circuit fault diagnosis of Vienna rectifier

RBF neural network is applied to build the fault diagnosis model of the Vienna rectifier of the DC charging pile. Finally

simulation and experimental results show that the proposed open circuit fault frequency domain characteristic system and open circuit fault diagnosis method are effective; Compared with the existing fault diagnosis methods

the proposed diagnosis method has the highest accuracy in the case of noise interference and microgrid voltage imbalance.