| 摘要 |
PROBLEM TO BE SOLVED: To make sampling of an AC input every constant frequency, obtain the maximum and minimum values between two time points which zero-cross in successive two sampling values, and calculate preciously the frequency change by a specific equation from these values. SOLUTION: Sampling means 301 outputs sampling values every specific frequency fs to polarity change detecting means 302. The polarity change detecting means 302 detects polarity of a sampling value x1 just before a zero- cross point t1, and in the case of a negative value, the means 302 detects positive polarity of a sampling value x2 just after it, to output a polarity change detection signal. Maximum value and minimum value measuring means 303 receives this, and monitors an increase and decrease of the sampling values, and detects the maximum value xM and outputs it to frequency change calculating means 304. The polarity change detecting means 302 obtains sampling values xn, xn+1 in a next-zero-cross point t2. The frequency change calculating means 304 obtains the changeΔu of a sampling value deviation of times t1, t2 in equation I, and obtains the changeΔf of commercial power supply frequency in equation II.
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