Multipulse Converter - Topology and Control for Utility Power Conversion

This paper presents a novel topology highly suited for utility power conversion. The topology, referred to as the multipulse converter, uses a modular architecture, where each power module comprises a three-phase two-level bridge and a transformer. The primary windings of the transformers are wound as closed zig-zag (or polygon) and fed by a power converter, while the secondary windings of the transformers are connected in series to the utility. By selecting appropriate phase shifts between the primary and secondary sides of the transformers and synchronously switching the three-phase bridges at specified phase relations, low order harmonics can be eliminated in pairs. Thus a very high power quality voltage waveform can be synthesized using low switching frequencies. The topology supports bi-directional power flow with excellent transient control over active and reactive powers. Principle of operation, modulation strategy and control strategies are presented with validated simulation and experimental results.