| 摘要 |
<p>PURPOSE:To enable a stringing power source frequency to be detected in a short time, by providing band-pass filters in the same number as the kinds of the stringing power source frequency, and by setting the passband central frequency of these filters to coincide with each power source frequency. CONSTITUTION:The voltage Vp on the transformer primary side as a signal equivalent to stringing voltage turns into an input signal of band-pass filters 21 and 22 in a frequency detector. Output signals Vf1 and Vf2 of filters 21 and 22 respectively turn out input signals of envelope processing circuits 31 and 32 in the latter stage. Each envelope processing circuit 31 and 32 works out signals Ve1 and Ve2 proportional to the amplitude value of input signals. A comparator 40 outputs a digital signal Ps in comparison with the size of signals Ve1 and Ve2. This signal is taken into an AC/DC power converter 9, which control the firing angle of a thyrister, etc. in response to the signal Ps i.e. the frequency.</p> |
