A power device, characterized by including: an AC input power source, which is three-phase or multi-phase AC, or three-phase or multi-phase AC of which each output terminal is connected in series with a first inductor, for generating power; a plurality of power converting units, the input terminals of which are respectively connected with two phases only of the AC input power source, for power converting the two phases of AC generated by the AC input power source respectively; an isolating transformer, the primary side of which is a three-phase winding and connected with a power network, the secondary side of which are multiple three-phase windings and connected with the output terminals of the plurality of power converting units, for feeding the AC converted by the plurality of power converting units to the power network; wherein the isolating transformer is a phase shift transformer with its secondary-side windings being formed in phase shift winding; the different secondary windings designed to have different phase shift angles wherein the power converting unit includes: a rectifier circuit, for converting the single-phase AC of the AC input power source into DC via a DC link; a three-phase thyristor controlled full bridge circuit string wherein each string consists of a plurality of three-phase thyristor controlled full-bridge circuits with its plurality of input terminals connected in series, the two free end input terminals of which are connected with the output terminals of the rectifier circuit via the DC link, for converting the DC output from the rectifier circuit into AC; wherein the different DC links are fed by different rectifiers, each DC link feeding the three-phase thyristor controlled full-bridge circuit string of one of the power converting units, each three-phase thyristor controlled full-bridge circuit output being connected to a different secondary winding of said transformer. an AC input power source, which is three-phase or multi-phase AC, or three-phase or multi-phase AC of which each output terminal is connected in series with a first inductor, for generating power; a plurality of power converting units, the input terminals of which are respectively connected with two phases only of the AC input power source, for power converting the two phases of AC generated by the AC input power source respectively; an isolating transformer, the primary side of which is a three-phase winding and connected with a power network, the secondary side of which are multiple three-phase windings and connected with the output terminals of the plurality of power converting units, for feeding the AC converted by the plurality of power converting units to the power network; wherein the isolating transformer is a phase shift transformer with its secondary-side windings being formed in phase shift winding; the different secondary windings designed to have different phase shift angles wherein the power converting unit includes: a rectifier circuit, for converting the single-phase AC of the AC input power source into DC via a DC link; a three-phase thyristor controlled full bridge circuit string wherein each string consists of a plurality of three-phase thyristor controlled full-bridge circuits with its plurality of input terminals connected in series, the two free end input terminals of which are connected with the output terminals of the rectifier circuit via the DC link, for converting the DC output from the rectifier circuit into AC; wherein the different DC links are fed by different rectifiers, each DC link feeding the three-phase thyristor controlled full-bridge circuit string of one of the power converting units, each three-phase thyristor controlled full-bridge circuit output being connected to a different secondary winding of said transformer. a rectifier circuit, for converting the single-phase AC of the AC input power source into DC via a DC link; a three-phase thyristor controlled full bridge circuit string wherein each string consists of a plurality of three-phase thyristor controlled full-bridge circuits with its plurality of input terminals connected in series, the two free end input terminals of which are connected with the output terminals of the rectifier circuit via the DC link, for converting the DC output from the rectifier circuit into AC; wherein the different DC links are fed by different rectifiers, each DC link feeding the three-phase thyristor controlled full-bridge circuit string of one of the power converting units, each three-phase thyristor controlled full-bridge circuit output being connected to a different secondary winding of said transformer.