Effects of firing angle imbalance on 12-pulse rectifiers with interphase transformers

Firing angle imbalance between six-pulse groups of a 12-pulse rectifier leads to current imbalance, due to the finite magnetizing inductance of the interphase transformer. The amount of current imbalance is limited by the load regulation of the six-pulse groups. This paper presents a quantitative analysis of this effect and others, based on appropriate models of the system. Equations are developed which predict steady-state current shifts and transient behavior using an averaged model. A piecewise-linear model of the system is used to verify and extend the results via computer simulation. Results are normalized, making them useful for design purposes.<>