A power conversion device (102; 1101) comprising: at least two legs (104R, 104S, 104T) connected in parallel, the at least two legs (104R, 104S, 104T) each include a first arm (105RP, 105SP, 105TP) having at least two unit converters (108, 109) connected in series, and a second arm (105RN, 105SN, 105TN) having at least two unit converters (108, 109) connected in series, wherein a connection point between the first and second arms (105RP, 105SP, 105TP, 105RN, 105SN, 105TN) is set to an AC terminal, and a parallel connection point between at least two legs (104R, 104S, 104T) connected in series is set to a DC terminal; wherein at least one of the legs (104R, 104S, 104T) is formed using at least two kinds of unit converters (108, 109) including a first type unit converter capable of outputting a unipolar voltage and a second type unit converter capable of outputting a bipolar voltage; command value generation means (412, 413) for generating an AC voltage; command value and a DC voltage; command value; and command value distribution means (504; 701) for distributing the AC voltage command value to the first type unit converter and the second type unit converter at a ratio of m:n (where m and n are any positive real numbers) and distributing the DC voltage command value to the first type unit converter and the second type unit converter at a ratio of m:n, characterised in that a sum of the maximum output voltages of the second type unit converters is equal to or larger than the sum of the maximum output voltages of the first type unit converter, the power conversion device (102; 1101) further comprises DC fault detection means for detecting a DC fault when a current of a DC system is larger than a preset value, a voltage of the DC system is smaller than a preset value, or an external signal is received, and when the DC fault detection means detects a DC fault, the command value distribution means (504; 701) has a function of: changing a distribution ratio of the AC voltage command value given to the first type unit converter and the second type unit converter from m:n to 0:(m+n) and changing the DC voltage command value given to the first type unit converter and the second type unit converter to substantially zero; or changing a distribution ratio of the DC voltage command value given to the first type unit converter and the second type unit converter from m:n to m:-m. at least two legs (104R, 104S, 104T) connected in parallel, the at least two legs (104R, 104S, 104T) each include a first arm (105RP, 105SP, 105TP) having at least two unit converters (108, 109) connected in series, and a second arm (105RN, 105SN, 105TN) having at least two unit converters (108, 109) connected in series, wherein a connection point between the first and second arms (105RP, 105SP, 105TP, 105RN, 105SN, 105TN) is set to an AC terminal, and a parallel connection point between at least two legs (104R, 104S, 104T) connected in series is set to a DC terminal; wherein at least one of the legs (104R, 104S, 104T) is formed using at least two kinds of unit converters (108, 109) including a first type unit converter capable of outputting a unipolar voltage and a second type unit converter capable of outputting a bipolar voltage; command value generation means (412, 413) for generating an AC voltage; command value and a DC voltage; command value; and command value distribution means (504; 701) for distributing the AC voltage command value to the first type unit converter and the second type unit converter at a ratio of m:n (where m and n are any positive real numbers) and distributing the DC voltage command value to the first type unit converter and the second type unit converter at a ratio of m:n, characterised in that a sum of the maximum output voltages of the second type unit converters is equal to or larger than the sum of the maximum output voltages of the first type unit converter, the power conversion device (102; 1101) further comprises DC fault detection means for detecting a DC fault when a current of a DC system is larger than a preset value, a voltage of the DC system is smaller than a preset value, or an external signal is received, and when the DC fault detection means detects a DC fault, the command value distribution means (504; 701) has a function of: changing a distribution ratio of the AC voltage command value given to the first type unit converter and the second type unit converter from m:n to 0:(m+n) and changing the DC voltage command value given to the first type unit converter and the second type unit converter to substantially zero; or changing a distribution ratio of the DC voltage command value given to the first type unit converter and the second type unit converter from m:n to m:-m. changing a distribution ratio of the AC voltage command value given to the first type unit converter and the second type unit converter from m:n to 0:(m+n) and changing the DC voltage command value given to the first type unit converter and the second type unit converter to substantially zero; or changing a distribution ratio of the DC voltage command value given to the first type unit converter and the second type unit converter from m:n to m:-m.