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%.