The Journal of Engineering (Oct 2018)
Design, analysis, and testing of PP-IGBT-based submodule stack for the MMC VSC HVDC with 3000 A DC bus current
Abstract
Voltage sourced converter (VSC) high-voltage direct current (HVDC) is moving to higher DC voltage and capacity, such as ±500 kV/3000 MW and ±800 kV/5000 MW for a single converter, which will bring tremendous challenges for converter submodule design. This work will focus on the design, analysis, and testing of press-pack insulated-gate bipolar transistor (IGBT) (PP-IGBT)-based modular multilevel converter (MMC) submodule stack that is suitable for such large converters. It starts with the introduction of internal structure and unique features of PP-IGBT and diode, which make them good choices for such projects, then followed by study of submodule topological schemes and structural design of the stack. Moreover, it presents computational fluid dynamics (CFD) simulation results on coolers, and it also provides electrothermal simulation results, for the purpose of calculating losses and junction temperature of PP-IGBT and diode. Furthermore, both device and stack level testing results will be reported, including reverse bias safe operating area, short-circuit turn-off, thermal cycling and short-circuit-failure-mode tests for device, and double-pulse commutation and frequency tests for the stack. In addition, trade-off considerations for stray inductance between normal switching and shoot-through fault will be discussed. Finally, by summarising these simulation and experimental studies, it is concluded that a PP-IGBT-based stack is proved to be a superb candidate for the coming gigawatt MMC converters.
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