Patent ID: 6891413

Claim:
A periodic signal controller for generating a periodic AC output signal synchronized with a periodic AC input signal, comprising: a first sine-wave signal generation circuit for outputting a first sine-wave signal with a frequency varied according to a first command signal; a first phase difference detection circuit for detecting a phase difference between the AC input signal and the first sine-wave signal output from said first sine-wave signal detection circuit and then outputting the first command signal indicating the phase difference; a second sine-wave signal generation circuit for outputting a second sine-wave signal as the AC output signal, the second sine-wave signal having a frequency varied according to a second command signal; a second phase difference detection circuit for detecting a phase difference between the first sine-wave signal output from said first sine-wave signal generation circuit and the second sine-wave signal output from said second sine-wave signal generation circuit and then outputting a phase difference detection signal indicating the phase difference; a frequency difference detection circuit for detecting a frequency difference between the first sine-wave signal output from said first sine-wave signal generation circuit and the second sine-wave signal output from said second sine-wave signal generation circuit and then outputting a frequency difference detection signal indicating the frequency difference; an adder circuit for adding the phase difference detection signal output from said second phase difference detection circuit to the frequency difference detection signal output from said frequency difference detection circuit; and a frequency variation rate limiter circuit for receiving an output of said adder circuit and outputting to said second sine-wave signal generation circuit the second command signal for limiting a frequency variation rate of the second sine-wave signal to a fixed value or less and synchronizing the second sine-wave signal with the AC input signal; wherein said first phase difference detection circuit and said first sine-wave signal generation circuit constitute a phase-locked loop.