PURPOSE: To reduce a current ripple by constituting a power inverter for regeneration of a transistor while regulating the switching frequency of the power inverter.

CONSTITUTION: A DC power device is constituted in such a manner that a diode rectifier 11, a smoothing capacitor 12 and a voltage detector 18 are mounted, a transistor power inverter 31 is used in place of a thyristor power inverter and the DC power source device is connected directly to an AC power supply 10 through an AC reactor 32. A level detector 20A outputs 21 a data when both the triangular-wave output voltage level of a carrier frequency generator 19 and the output level of the voltage detector 18 reach a detecting level. The regenerative currents of the power inverter 31 are detected by a current transformer 33 and a current detector 36, and a base drive signal is distributed to each transistor for the power inverter 31 through a comparator 35 and a distributor 38 and by said output 21 by the level detector 20A from the voltage detector 18. Accordingly, when load voltage ed is higher than a reference value, DC power is regenerated directly to the AG power supply 10.