| 摘要 |
PURPOSE:To enable distorted current to be detected with high precision by integrating one of excited currents which runs through only a distorted current generation period and by suppressing a distorted amount according to its integral value. CONSTITUTION:Pulse signals PKP, PKN are outputted sequently from a gain adjuster 56 in response to generation of positive and negative gate pulses predicted to be influenced by generation of the DC distorsion. On the other hand, the excited current i0 of a transformer is detected by an excited current detector 52 and multiplied by multipliers 62, 64 in response to the signals PKP, PKN. Its multiplication values are integrated by integrators 66, 68, respectively, and integral values SP, SN are held until reset signal R is generated, where these integral values SP, SN are added by an adder 70 to obtain deviation DELTAS. Next, the deviation DELTAS is sample-held by a sample holder 72 at a predetermined timing to obtain differential signal DELTASh. Correction widths DELTAOP, DELTAON orresponding to polarity and level of the differential signal DELTASh are obtained by gain elements 74, 76, so that respective switching angles OP1, PN1 are corrected. |
