18-pulse Autotransformer Rectifier Unit Research Articles

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.

Open-Circuit Fault Research on Asymmetric Delta-Polygon 18-Pulse Autotransformer Rectifier Unit for More Electric Aircraft

In aviation aircraft, autotransformer rectifier units (ATRUs) have been widely used as front-end rectifiers. The comprehensive analysis of its operating characteristics under the fault is beneficial to assessing the hazards of the faults and developing a fault diagnosis scheme. This article investigates two types of open-circuit (OC) faults in delta-polygon 18-pulse ATRU, namely, diode OC fault and input OC fault. First, the effects of the diode OC fault on five aspects are quantitatively analyzed: diode conduction angle, output voltage ripple, winding current, input current harmonics, and diode and transformer winding losses. Next, the operating characteristics of ATRU are investigated under input OC fault, and the quantitative effects of the five aspects above are also calculated. Then, based on the affected intervals of dc output voltage, a fault diagnosis idea dealing with two types of OC faults is discussed. Meanwhile, the predictive maintenance objects after the fault location are also summarized. Finally, the simulation and experimental results validate the theoretical analysis and discussion. This work is very significant for guiding the fault detection, fault location, and predictive maintenance of ATRUs.

Investigation on Design of Novel Step-Up 18-Pulse Auto-Transformer Rectifier

The multi-pulse rectifier has gained a wide range of applications in the high-power rectification system due to the advantages like simple structure, high efficiency, and high reliability. In this paper, an 18-pulse auto-transformer rectifier unit (ATRU) with adjustable output DC voltage was studied, to meet the requirements of high efficiency and low harmonic pollution of ATRU. Firstly, the basic operating principle of the proposed ATRU was analyzed in detail. The essential relationship between the step-up ratio factor and the output DC voltage, the total harmonic distortion (THD) of the input line current, and the equivalent kVA rating of the transformer was deduced considerately, which provides a theoretical basis for the optimization design of the system. Finally, the correctness of the theoretical analysis was verified by simulation and experiment. The experimental results show that under the 6kVA rating condition when the step-up ratio is 1.137, the transformer equivalent kVA rating is only 27.8% of the load output power, the input line current THD of ATRU is 6.58%, and the efficiency is 98.5%.

Dynamic Phasor Modeling of Various Multipulse Rectifiers and a VSI Fed by 18-Pulse Asymmetrical Autotransformer Rectifier Unit for Fast Transient Analysis

To study the fast modelling of dynamic characteristics caused by power electronic switching, the dynamic phasor (DP) theory based on the time-varying Fourier decomposition and frequency shifting is firstly applied to the modelling of various multipulse rectifiers. The DP model for symmetrical 12-pulse phase-shifting reactor rectifier unit (PSR-RU) is derived with model order reduction, relations between ac and dc terminals, and Taylor series expansion. The DP model of asymmetrical 18-pulse autotransformer rectifier unit (AT-RU) is proposed based on the switching functions expressed in the DP domain. Meanwhile, the DP model of voltage source inverter (VSI) fed by asymmetrical 18-pulse AT-RU is built with the harmonic state-space (HSS) equations. Under both balanced and unbalanced conditions, the good calculation accuracy and rapid simulation speed of the developed DP models are validated by the detailed time-domain (TD) simulation.

Investigation on the Selection and Design of Step-Up/Down 18-Pulse ATRUs for More Electric Aircrafts

Multi-pulse autotransformer rectifier units (ATRUs) have been widely used in aviation applications due to their rugged structure, cost-effectiveness, and high-reliability features. In this paper, up to six types of autotransformers for an 18-pulse ATRU are investigated, aiming to provide an optimal selection guideline for a proper structure. By conducting a thorough comparative study on the kilovoltampere (kVA) rating of the autotransformers and the current harmonic characteristics over a wide voltage step-up or step-down range, the asymmetric delta–polygon (DP) structure is considered as the most promising choice. Subsequently, an example 18-pulse ATRU with such structure is adopted as the front end of an alternative current (ac)/ac converter powering an onboard hydraulic pump. After analyzing the operational principle, accurate mathematical expressions among the overall voltage gain $K$ , the total harmonic distortion (THD) of the line current, and the kVA rating of the autotransformer were carefully deduced. Before conclusions, the theoretical analyses were verified by simulations and experiments. It is shown that the THD of the input line current of the designed 10-kW ATRU is 6.74%, the rated efficiency reaches 98.5%, and the autotransformer’s weight is merely 3.3 kg.

Average modeling and evaluation of 18-pulse autotransformer rectifier unit without interphase transformers

This paper presents an improved average model and evaluation of an 18-pulse autotransformer rectifier unit (ATRU) in differential delta configuration. Average models remove the switching behavior of diode rectifiers and high bandwidth transients, which not only facilitates simulation of power systems by reducing computational cost but also enables impedance-based stability analysis for large complex power systems. To experimentally validate the proposed average model, a 2-kW, 18-pulse ATRU has been tested and the results of the derived model are compared with those of the switching model and experimental prototype. Computed transfer function of load impedance from the proposed average model closely resembles those of the switching model and the experimentally measured results validate the modeling procedure. Furthermore, stability analysis of the 18-pulse ATRU may be executed based on the return ratio of source and load impedance.

Comparative Analysis of 18-Pulse Autotransformer Rectifier Unit Topologies with Intrinsic Harmonic Current Cancellation

With the evolution of the More Electric Aircraft (MEA) concept, high pulse converters have gained the attention of researchers due to their higher power quality. Among the high pulse converters, 18-pulse autotransformer rectifier unit (ATRU) offers better power quality level with small size, weight and medium complexity. The conventional topologies of autotransformers that require the use of extra elements such as Inter Phase Transformers (IPT) or Zero Sequence Blocking Transformers (ZSBT), adding to the complexity, weight and size of the overall system, are not considered in the analysis. For 18-pulse rectification, only those topologies of autotransformers which have the intrinsic current harmonic cancellation capabilities are presented here for comparison. These topologies offer current harmonic levels within limits specified by IEEE 519 with reduced weight and size as compared to the conventional multi-pulse converters. A comparison of different differential delta/fork configured 18-pulse autotransformer rectifier units is presented so as to come up with the best among available topologies with respect to weight, size and power quality. Experimental prototypes of each topology were designed and their results are displayed along with the simulation results for comparison.

Modeling and stability analysis of hybrid power systems for the more electric aircraft

This paper presents a detailed modeling and a comprehensive assessment of small-signal stability for a “more-electric” vehicular power system consisting of a synchronous variable-frequency generator which supplies power electronic controlled loads via an 18-pulse autotransformer rectifier unit for AC-DC conversion. Functional models for key power system components and loads are derived. Analytical derivations employed for small signal stability analysis based on linearized equations are described, and the influence of leading design parameters on system stability is evaluated.