| 摘要 |
<P>PROBLEM TO BE SOLVED: To solve the problem that, according to a method of detecting a zero cross point of a system voltage and detecting a frequency of the system voltage from a time change between zero cross points, a determination may be made wrong because of a harmonic distortion of a commercial system, waveform distortion caused by load insertion or noise, and since it is further determined whether the frequency of the system voltage is continuously detected, a possibility of a malfunction is reduced but a detection time may become longer. <P>SOLUTION: A frequency detection section 60 has a momentary phase detection part 30 for detecting a momentary phase θ of an AC voltage in each sampling term ts, and a phase/frequency conversion part 81 for calculating an AC frequency fac on the basis of a momentary phase change amount Δϕ that is an amount of change of the momentary phase θ in the sampling term ts. <P>COPYRIGHT: (C)2012,JPO&INPIT |
