Method and arrangement for detecting zero crossing of the fundamental wave of periodic AC voltages subject to frequency fluctuations

摘要

The invention relates to a method for detecting the zero crossing of the fundamental wave of periodic AC voltages subject to frequency fluctuations, in which the transmission response of filter circuits in the resonant range is employed. In order to design a method which automatically detects r.m.s. variable and frequency deviations, corrects the latter via phase relationship and thereby makes possible exact zero-crossing detection of periodic sinusoidal, rectangular or triangular quantities, even in the case of variable frequencies within defined ranges, and which furthermore works only with AC voltages between +/- 15 V maximum, it is proposed according to the invention to make use of an active band-pass filter (3) with variable resonant frequency (f0), the resonant frequency (f0) of which is matched to the frequency fluctuations or alterations of the AC voltage (UEX) to be evaluated such that the phase relation between AC voltage (UEX) to be evaluated and the output signal (NDG) of a 1st Schmitt trigger (6), with inverted output, connected downstream of the band-pass filter (3) remains constant, the resonant frequency (f0) being matched via a PLL circuit (4) outputting a control frequency (fCLK). Advantageous refinements of the method and arrangements for carrying out are described. <IMAGE>