A power converter (3, 4, or 45) comprising: first and second DC terminals (3a, 3b) each configured to transmit and receive DC power, the first DC terminal being connected to a first DC power transmission line, the second DC terminal being connected to a second DC power transmission line; and a plurality of phase modules connected in parallel between the first and second DC terminals (3a, 3b), each of the phase modules including an AC terminal (3c, 3d, or 3e) configured to transmit and receive AC power, a first arm (A1, A2, or A3) and a circuit breaker (B11, B12, or B13) connected in series between the first DC terminal and the AC terminal (3c, 3d, or 3e), and a second arm (A4, A5, or A6) connected between the AC terminal (3c, 3d, or 3e) and the second DC terminal, the circuit breaker (B11, B12, or B13) being configured to be in a conductive state during a normal operation, the circuit breaker (B11, B12, or B13) being configured to be brought into a non-conductive state when a short circuit accident occurs between the first and second DC power transmission lines (1, 2), each of the first and second arms (A1-A6) including a plurality of unit cells connected in cascade, each of the unit cells including a voltage source, first and second switching elements (S1, S2), and first and second diodes (D1, D2), the first and second switching elements (S1, S2) being connected in series between electrodes of the voltage source, the first and second diodes (D1, D2) being respectively connected to the first and second switching elements (S1, S2) in antiparallel, each of the first and second arms (A1-A6) further including at least one bypass switch, the at least one bypass switch being configured to be brought into the conductive state when the short circuit accident occurs, so as to bypass the first or second diode (D1 or D2) of each unit cell of a corresponding arm (A1, A2, A3, A4, A5, or A6), one of the plurality of circuit breakers (B11-B13) being a DC circuit breaker configured to interrupt direct current when the short circuit accident occurs, each of the other circuit breakers (B12, B13) being an AC circuit breaker (B12 or B13) configured to interrupt alternating current when the short circuit accident occurs, wherein when the short circuit accident occurs, the each AC circuit breaker (B12, B13) is brought into the non-conductive state and the DC circuit breaker is then brought into the non-conductive state. first and second DC terminals (3a, 3b) each configured to transmit and receive DC power, the first DC terminal being connected to a first DC power transmission line, the second DC terminal being connected to a second DC power transmission line; and a plurality of phase modules connected in parallel between the first and second DC terminals (3a, 3b), each of the phase modules including an AC terminal (3c, 3d, or 3e) configured to transmit and receive AC power, a first arm (A1, A2, or A3) and a circuit breaker (B11, B12, or B13) connected in series between the first DC terminal and the AC terminal (3c, 3d, or 3e), and a second arm (A4, A5, or A6) connected between the AC terminal (3c, 3d, or 3e) and the second DC terminal, an AC terminal (3c, 3d, or 3e) configured to transmit and receive AC power, a first arm (A1, A2, or A3) and a circuit breaker (B11, B12, or B13) connected in series between the first DC terminal and the AC terminal (3c, 3d, or 3e), and a second arm (A4, A5, or A6) connected between the AC terminal (3c, 3d, or 3e) and the second DC terminal, the circuit breaker (B11, B12, or B13) being configured to be in a conductive state during a normal operation, the circuit breaker (B11, B12, or B13) being configured to be brought into a non-conductive state when a short circuit accident occurs between the first and second DC power transmission lines (1, 2), each of the first and second arms (A1-A6) including a plurality of unit cells connected in cascade, each of the unit cells including a voltage source, first and second switching elements (S1, S2), and first and second diodes (D1, D2), the first and second switching elements (S1, S2) being connected in series between electrodes of the voltage source, the first and second diodes (D1, D2) being respectively connected to the first and second switching elements (S1, S2) in antiparallel, each of the first and second arms (A1-A6) further including at least one bypass switch, the at least one bypass switch being configured to be brought into the conductive state when the short circuit accident occurs, so as to bypass the first or second diode (D1 or D2) of each unit cell of a corresponding arm (A1, A2, A3, A4, A5, or A6), one of the plurality of circuit breakers (B11-B13) being a DC circuit breaker configured to interrupt direct current when the short circuit accident occurs, each of the other circuit breakers (B12, B13) being an AC circuit breaker (B12 or B13) configured to interrupt alternating current when the short circuit accident occurs, wherein when the short circuit accident occurs, the each AC circuit breaker (B12, B13) is brought into the non-conductive state and the DC circuit breaker is then brought into the non-conductive state.