Initial charging system for medium-voltage inverter and method for controlling the system

An initial charging system for a medium-voltage inverter, wherein the medium-voltage inverter includes a phase-shift transformer and a plurality of power cells, wherein each power cell includes a rectifier for rectifying power input from the transformer, and a direct current link capacitor for smoothing a voltage received from the rectifier, wherein the initial charging system comprises:

• a first switch for switching between the medium-voltage inverter and a power supply thereto;
• a second switch for switching between an output stage of the medium-voltage inverter and an electric motor;
• a first initial charging unit disposed between and connected to the first switch and the medium-voltage inverter for limiting an initial excitation current to be applied to the phase-shift transformer;
• and
• a second initial charging unit disposed between and connected to an input stage of each power cell and the direct current link capacitor for limiting an initial charging current in the direct current link capacitor.