Power conversion device having bypass circuit protection

A power conversion device which converts power between an AC circuit and a DC circuit, the power conversion device comprising:

• a first arm circuit provided between an AC connection portion connected to the AC circuit and a positive-side DC terminal connected to the DC circuit;
• and
• a second arm circuit provided between the AC connection portion and a negative-side DC terminal connected to the DC circuit,
• each of the first and second arm circuits including:
• a plurality of cascaded cell blocks;
• and
• a plurality of bypass circuits connected to the respective cell blocks in parallel, each of the plurality of cell blocks including:
• a first connection node on a high potential side and a second connection node on a low potential side for connection to another cell block;
• and
• a plurality of converter cells cascaded between the first and second connection nodes, each converter cell containing an energy storage and semiconductor switching elements,
• all of the semiconductor switching elements contained in each converter cell being controlled to turn off when a short-circuiting failure occurs in the DC circuit,
• the plurality of converter cells included in each of the plurality of cell blocks including:
• at least one first converter cell of a full-bridge or hybrid configuration;
• and
• at least one second converter cell of a half-bridge configuration,
• each of the plurality of bypass circuits including:
• a plurality of diode elements connected in series such that a direction from the negative-side DC terminal to the positive-side DC terminal is defined as a forward direction;
• a dual-terminal element connected in series to the plurality of diode elements, wherein
• a discharge gap is adopted as the dual-terminal element, and
• when a short-circuiting failure occurs in the DC circuit, a DC short-circuiting current flows through the discharge gap and the plurality of diode elements in each of the plurality of bypass circuits.