Allen Michael Ritter

A Four-Level Converter with Optimized Switching Patterns for High-Speed Electric Drives

High-speed electrical machines at multi-MW power level are being designed to drive high-speed compressor trains in oil and gas industry applications and for directly driving generators with gas turbines for shipboard and mobile power generation applications. The paper describes a converter topology to address such high power high frequency drive requirements. The proposed topology uses a three-phase bridge with series-connected single-phase bridges in each phase to obtain a four-level configuration. Optimized low pulse-count synchronous switching is used to limit the switching frequency of the individual devices; yet obtain the required power quality under all operating condition of the machine without use of external harmonic filters. Method of switching optimization and predicted performance of the drive are presented. Experimental results from a lab-scale prototype are provided to validate the concept.

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