| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem in detection, of the phase of voltage being detected with a phase detection circuit which includes a noise rejection filter, an insulation photocoupler and a comparator. SOLUTION: A phase compensation circuit 2R obtains a period Tf and a width Tdet of a pulse signal from the phase detection circuit 1R in the counters 3, 4. A calculation circuit 5 obtains a delay time TD from these periods Tf and width Tdet and the obtained constant delay time Tconst due to the filter, in order to obtain a timing signal r-s which makes zero a line-to-line voltage signal by subtracting the time TD from the phase detection signal with a subtraction circuit 6. Here, the processes for changing the phase detection period, for obtaining both the periods Tf and width Tdet with a shift average calculation of a plurality of measured values, and to obtain a phase detection signal for every phase of the voltage signal are also included. |
