Hybrid 18-Pulse Rectification Scheme for Diode Front End VFDs

This paper proposes a novel hybrid 18-pulse rectification topology for Variable Frequency Drives (VFDs) that uses a phase-shifting isolation transformer to power two six-pulse rectifiers while a third is fed directly from the AC source via a matching impedance, relying on harmonic current cancellation rather than flux cancellation. The design is smaller, lighter, and lower in cost than traditional 18-pulse isolation transformer or autotransformer schemes, and experimental results validate its superior harmonic performance.