Leakage Flux Modeling of Medium-Voltage Phase-Shift Transformers for System-Level Simulations

Cascaded H-Bridge converters in medium-voltage (MV) applications have all the dc link capacitors supplied from external source through a multiwinding phase-shift transformer. This type of transformers has a complex winding geometry, which leads to unbalanced leakage flux paths. The unbalance affects the dynamic behavior of the converters. This work proposes a modeling approach, which realistically captures the unbalance in the leakage flux path of phase-shift transformers, using permeance magnetic circuit. The model can be seamlessly integrated into system-level simulation of power electronic circuits. Taking advantage of the repetitive structure of the windings, the model requires very limited number of parameters, which can be easily obtained from the geometry data together with only a few experimental tests. The fidelity of the model is experimentally confirmed on a phase-shift transformer from a commercial MV drive system.