Method for Detecting a Stuck AC Switch in a Converter

A method for detecting a stuck AC switch in a converter, the converter comprising:

• a plurality of converter arrangements arranged in parallel and configured for connecting to a DC source or DC load and for connecting to a plurality of AC terminals, wherein each of the plurality of converter arrangement comprises:
• a DC part comprising two capacitors arranged in parallel to the DC source or DC load and arranged in series to each other having a neutral DC point between said capacitors;
• a converter unit connected to the DC source or DC load and to an AC part;
• the AC part comprising at least one AC leg, each AC leg connected to a neutral AC point via an AC leg capacitor, and each AC leg connected to a respective leg of the AC terminal via an AC switch,
• a pre-charge unit arranged at each leg of the AC terminal, and
• a decoupling switch arranged between the neutral DC point and the neutral AC point,
• the method comprising the steps of:
• opening the second decoupling switch and all second AC switches of the second converter arrangement;
• loading the pre-charge unit;
• sequentially closing each second AC switch of the second converter arrangement;
• measuring, at each closing step, a voltage between each AC leg of the second converter arrangement;
• and
• determining the stuck AC switch of the second converter arrangement based on the measured voltage.