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This paper deals with the modeling and analysis of a five-legged rectifier transformer that is used for parallel operation of two three-pulse rectifiers, specifically, for low-voltage high-current applications. The five-legged system is compared with the conventional rectifier system consisting of a three-legged transformer and interphase transformer (IPT). Ensuring equal current sharing between the rectifiers and obtaining output voltage with a higher pulse number are the two major requirements which are satisfied in the conventional system. A mathematical explanation for the five-legged system satisfying the mentioned requirements is given. The system is treated as a strongly coupled circuit field one, where a nonlinear finite-element model of the five-legged transformer is coupled with nonlinear circuit equations. IPT-like behavior of the five-legged rectifier transformer is also investigated. The stated theory and analytical expressions are validated experimentally on a 12-V, 5000-A rectifier system.
Date of Publication: April 2011