The PWM signals PWM1 for the first step-up/step-down circuit CNV1 (PWM1 and its inversion signal /PWM1) and the PWM signal PWM2 for the second step-up/step-down circuit CNV2 (PWM2 and its inversion signal /PWM2) are assigned to the switching elements S1 to S3 on the basis of the above-described distribution of functions of the upper and lower arms. The CNV controller 13 executes the above-described phase shift over the PWM signals PWM1, PWM2.

Second Alternative Embodiment of Electric Power Converter

FIG. 16 shows a further alternative embodiment of the electric power converter 11. The electric power converter 11, as in the case of FIG. 15, includes three series-connected arms from the high-voltage line 26 toward the reference line 28.

The electric power converter 11 shown in FIG. 16 differs from the electric power converter 11 shown in FIG. 15 in arrangement of the first step-up/step-down circuit CNV1. That is, the first battery B1, the first reactor L1 and the first capacitor C1 are connected between the connection point 42 and the connection point 40. The connection point 42 is provided between the first arm and the second arm from the high-voltage line 26 side. The connection point 40 is provided between the second arm and the third arm from the high-voltage line 26 side.