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I know this is pure personal preference but hey let's hear opinions. It could be anything! GTO-VVVF, IGBT-VVVF, SiC-VVVF, Chopper, Rheostatic, etc...
Here's mine: Guangzhou metro Siemens Modular metro, AEG-Westinghouse GTO-VVVF propulsion system
Here's mine: Guangzhou metro Siemens Modular metro, AEG-Westinghouse GTO-VVVF propulsion system