A High-Frequency High-Power Test Bench for 11 MW/595 Hz Drives With 1.25 MW Grid Capability

This paper presents a pumpback test bench for high-frequency high-power variable-frequency drives (VFDs) with 11 MW power rating and up to 595 Hz load frequency. A voltage combiner concept is applied to allow a high-frequency output from the two three-level neutral-point-clamped integrated gate-commutated thyristor bridges with minimum switching losses. The accordingly developed pumpback test bench applies a dc power coupling concept combined with a virtual grid concept that can achieve 11 MW test capability with only a 1.25 MW facility transformer. By applying a virtual machine concept, the pumpback test can be conducted without the need of high-frequency machines, while the circulating power losses in the pumpback loop are minimized as well. The virtual grid including the concept tradeoff, filter parameters, and modulation schemes is presented in detail. Moreover, design and installation guidelines for high-frequency components, especially the cables, are presented. The high-frequency high-power VFD and its pumpback test bench are both successfully built and experimentally validated at their rated operation points.