DISCHARGING DC LINK CAPACITORS IN AN NPC CONVERTER

摘要

An electrical converter (10) comprises at least two converter units (16), each converter unit (16) comprising a neutral point clamped half-bridge (32, 34) with a neutral point (30), an AC output (38, 40), a positive DC output (26) and a negative DC output (28) and each converter unit (16) comprising a DC link (20) with two DC link capacitors (31), which are interconnecting the positive DC output (26) and the negative DC output (28) with the neutral point (30). The half-bridges (32, 34) of the converter units (16) are interconnected via its neutral points (30) via a first connection and via its AC outputs via a second connection and at least one of the first connection and the second connection comprises an electrical filter (52, 54). A method for discharging the DC link capacitors (31) comprises: switching a first half bridge (32, 34) of a first converter unit (16) to a positive state, in which its AC output (38, 40) is connected with its positive DC output (26), and simultaneously switching a second half bridge (32, 34) of a second converter unit (16) to a negative state, in which its AC output (38, 40) is connected with its negative DC output (28), such that a DC link capacitor (31) of the first converter unit and a DC link capacitor (31) of the second converter unit (16) are interconnected oppositely to each other and discharged via the electrical filter (52, 54).