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.