Power conversion system and method for pre-charging dc-bus capacitors therein

A medium-voltage power conversion system, comprising:

• a first power module including a first power input end, a first charging input end and a first power output end, the first power module including a first AC/DC conversion unit and a first DC/DC conversion unit, the first power module including a first DC-Bus capacitor and a second DC-Bus capacitor connected in series, the first AC/DC conversion unit being electrically connected to the first power input end and to the first and second DC-Bus capacitors, the first DC/DC conversion unit being electrically connected to the first power output end and to the first and second DC-Bus capacitors, the first power module further including a first pre-charging unit including a first primary circuit, a first isolation transformer, a first secondary circuit and a second secondary circuit, the first primary circuit being electrically connected to the first charging input end to receive a first direct current, the first secondary circuit being electrically connected in parallel to the first DC-Bus capacitor to pre-charge the first DC-Bus capacitor, and the second secondary circuit being electrically connected in parallel to the second DC-Bus capacitor to pre-charge the second DC-Bus capacitor;
• and
• a second power module including a second power input end, a second charging input end and a second power output end, the second power module including a second AC/DC conversion unit and a second DC/DC conversion unit, and the second power module including a third DC-Bus capacitor and a fourth DC-Bus capacitor connected in series, the second AC/DC conversion unit being electrically connected to the second power input end and to the third and fourth DC-Bus capacitors, the second DC/DC conversion unit being electrically connected to the second power output end and to the third and fourth DC-Bus capacitors, the second power module further including a second pre-charging unit including a second primary circuit, a second isolation transformer, a third secondary circuit and a fourth secondary circuit, the second primary circuit being electrically connected to the second charging input end to receive a second direct current, the third secondary circuit being electrically connected in parallel to the third DC-Bus capacitor to pre-charge the third DC-Bus capacitor, the fourth secondary circuit being electrically connected in parallel to the fourth DC-Bus capacitor to pre-charge the fourth DC-Bus capacitor, and the second power input end and the first power input end being connected in series and then being electrically connected to a medium-voltage alternating current power source.