Analysis of a Shunt Wye–Delta Transformer for Multi-Generator Harmonic Elimination Under Non-Ideal Phase-Shift Conditions

摘要

A 12-pulse converter has been commonly used for a large-scale power generating system. The arrangement of a delta-delta (Delta-Delta) and a delta-wye (Delta-Y) phase-shift transformer pair in series with the voltage source eliminates undesirable harmonics from nonlinear loads. Recently, a novel front-end for a multi-generator power system was proposed, which utilizes a single Y-Delta transformer to shunt between the two 30 degrees phase-shifted generator outputs and results in the comparable harmonic elimination performance to the conventional 12-pulse rectifier. The shunt-type Y-Delta transformer front-end achieves more than 75% transformer size reduction, making it extremely attractive to large-scale industrial and shipboard applications. However, the exact 30 degrees phase shift between the two rotating generators can drift in a practical system, especially under dynamic conditions. The harmonic performance under the non-ideal 30 degrees phase-shift condition can deteriorate with the Y-Delta shunt-type front-end. To understand the impact of non-ideal phase-shifted generator sources, this paper derives the mathematical models through the use of an equivalent circuit, a square-wave analysis, and the phasor representation to show the harmonic cancellation principle and verifies the results with the computer simulation.