Referring to FIGS. 10A through 10C, FIG. 10A is a timing chart of the first, second and third line current command signals iTU, iTV and iTW and the first, second and third detected line currents iFU, iFV and iFW. FIG. 10B is an enlarged timing chart showing an operation of the logic circuit 10b provided with the first, second and third switching command signal delay circuits 56, 57 and 58 in the r