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 (Nu, Nv, Nw) connectable to the AC circuit and a positive-side DC terminal (Np) connectable to the DC circuit; and - a second arm circuit provided between the AC connection portion (Nu, Nv, Nw) and a negative-side DC terminal (Nn) 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 (40p, 40n), each converter cell containing an energy storage and a plurality of switching elements, each switching element having a diode being connected in anti-parallel, - the plurality of converter cells included in each of the plurality of cell blocks including: - at least one first converter cell (21F, 21HYB) of a full-bridge or hybrid configuration, wherein the hybrid configuration is a converter cell configuration with any one of the switching elements (22a, 22b, 22c, and 22d) having been removed from a full-bridge converter cell; and - at least one second converter cell of a half-bridge configuration, - the power conversion device further comprising a control device, the control device being configured to detect a short-circuiting failure in the DC circuit, and then to turn off the plurality of switching elements contained in each converter cell, and wherein when a voltage of the energy storage in the at least one first converter cell exceeds a threshold voltage in an event of the short-circuiting failure, the plurality of bypass circuits are configured to become conductive, thereby the short-circuiting current to flow through the plurality of bypass circuits instead of the plurality of cascaded cell blocks. - a first arm circuit provided between an AC connection portion (Nu, Nv, Nw) connectable to the AC circuit and a positive-side DC terminal (Np) connectable to the DC circuit; and - a second arm circuit provided between the AC connection portion (Nu, Nv, Nw) and a negative-side DC terminal (Nn) 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 (40p, 40n), each converter cell containing an energy storage and a plurality of switching elements, each switching element having a diode being connected in anti-parallel, - the plurality of converter cells included in each of the plurality of cell blocks including: - at least one first converter cell (21F, 21HYB) of a full-bridge or hybrid configuration, wherein the hybrid configuration is a converter cell configuration with any one of the switching elements (22a, 22b, 22c, and 22d) having been removed from a full-bridge converter cell; and - at least one second converter cell of a half-bridge configuration, - the power conversion device further comprising a control device, - the plurality of converter cells included in each of the plurality of cell blocks including: - at least one first converter cell (21F, 21HYB) of a full-bridge or hybrid configuration, wherein the hybrid configuration is a converter cell configuration with any one of the switching elements (22a, 22b, 22c, and 22d) having been removed from a full-bridge converter cell; and - at least one second converter cell of a half-bridge configuration, - the power conversion device further comprising a control device, the control device being configured to detect a short-circuiting failure in the DC circuit, and then to turn off the plurality of switching elements contained in each converter cell, and wherein when a voltage of the energy storage in the at least one first converter cell exceeds a threshold voltage in an event of the short-circuiting failure, the plurality of bypass circuits are configured to become conductive, thereby the short-circuiting current to flow through the plurality of bypass circuits instead of the plurality of cascaded cell blocks.