A General Diode Open-Circuit Fault Diagnosis Method for Autotransformer Rectifier Unit Considering Grid Voltage Disturbance

It is crucial for the reliable operation of the autotransformer rectifier unit (ATRU) to accurately diagnose diode open-circuit (OC) fault. However, grid voltage disturbance may lead to misdiagnosis by existing methods. This article takes the 18-pulse ATRU as an example and first analyzes its sag-based fault feature in the dc-link output voltage (DLOV) caused by diode OC fault under no grid voltage disturbance. Then, the reason for misdiagnosis under grid voltage disturbance is discussed. Subsequently, a general diode OC fault diagnosis method with strong immunity to grid voltage disturbance is proposed. In the proposed method, the DLOV waveform is divided equally according to the number of rectified pulses. Hausdorff distance (HD) algorithm is employed to extract the sag-based fault feature by calculating the similarity between the DLOV sampling sequence and the constructed template sequence. To be immune to grid voltage disturbance, the template sequence is adaptively generated as per the sampling sequence in each interval. Also, the generalized minimum failure mode is defined to normalize two sequences for good universality. With the help of the phase of grid single-phase voltage, OC faults can be detected and located according to the interval positions with the sag. Finally, simulation and experimental results confirm the strong immunity of the proposed method to grid voltage disturbance and its good universality to the different ATRUs.

I. Introduction

MULTIPULSE autotransformer rectifier unit (ATRU), which has the advantages of low input current harmonic, small size, less weight, and high efficiency, has been widely used in many scenarios, such as railway [1], shipboard [2], high-voltage direct-current transmission [3], aviation aircraft [4], [5], and motor drive [6], [7]. Its main idea is to use the phase-shifting transformer to generate multiple groups of balanced three-phase voltages to feed two or more three-phase rectifier bridges, which increases the number of rectified pulses, greatly reducing the total harmonic distortion (THD) of input current and the output voltage ripple [8]. In multipulse ATRUs, the use of multiple diode semiconductor devices is essential. However, these semiconductor devices are prone to failure [9], which causes the converter to work abnormally. In the standards [10] and [11], the power quality of ATRUs connected to the power grid and the aircraft is required, respectively. However, their power quality cannot meet the requirements of these standards when a diode fault occurs. Hence, it is very necessary to utilize fault diagnosis to polish the reliability of ATRUs.