Abstract: A power converter device including a plurality of self-commutated voltage type converter each connected to a common d.c. circuit, a plurality of transformers each having d.c. windings and a.c. windings, each of the d.c. windings being connected to an a.c. output terminal of a respective one of the converters and each of the a.c. windings being connected in series, an a.c. switch through which the serially connected a.c. windings of the transformers are adapted to be connected to a utility power system, and a d.c. overvoltage suppression device, installed in the common d.c. circuit, wherein the transformers are connected to the utility power system by synchronous making, and the d.c. overvoltage suppression device is connected to the common d.c. circuit when the converters are stopped temporarily.