Abstract: A power converter includes first and second power conversion units that are connected to each other by a d.c. reactor. The first power conversion unit is a converter in which arms consisting of thyristors are connected in a bridge configuration. The second power conversion unit is an inverter in which arms each of a series combination of a thyristor and a self-excited switch unit having a GTO for producing a commutation voltage for the thyristor are connected in a bridge configuration.

Abstract: A power conversion system including a plurality of converter transformers. AC side windings of the converter transformers are connected in series for connecting to an AC power system. The power conversion system further includes a plurality of series connected voltage source type self-commutated converters for converting AC power into DC power or DC power into AC power. Each of the voltage source type self-commutated converters is connected to one of DC side windings of the converter transformers, respectively. The power conversion system further includes a plurality of DC voltage sources. Each of DC output sides of the voltage source type self-commutated converters is connected to one of the DC voltage sources, respectively.

Abstract: Control units are provided associative with forward and inverse converters in a multiterminal DC power transmission system, respectively. The control units set different constant voltages in the converters. Further, the minimum value of the constant voltage set values in the forward converters is set at a value larger than the maximum value of the constant voltage set values in the inverse converters.