| 摘要 |
PURPOSE: To surely detect the independent operating state of a distributed power source by detecting the frequency fluctuation of the voltage at a link point which occurs at the link point when the power source is independently operated within the same period as the integrated value of the fluctuation of a frequancy against a reference frequency. CONSTITUTION: A voltage detector 9 detects the voltage at a link point and a band-pass filter 21 extracts only the fundamental wave component of the voltage. Then a waveform shaping circuit 22 shapes the waveform of the fundamental wave component from a sine wave to a square wave and a frequency calculating circuit 23 calculates the frequency fN of the fundamental wave component by measuring the time from the rise point to the next rise time of the square wave, namely, the period of the component. An average frequency value calculating circuit 41 calculates the average value fO of the frequency fN by inputting the frequency fN and a frequency fluctuating value calculating circuit 42 calculates an instantaneous frequency fluctuating value ΔfN. Then a comparator 46 compares the integrated frequency fluctuating value Δf calculated by an integrated frequency fluctuating value calculating circuit 43 with the set value of a set integrated frequency fluctuating value calculating circuit 45 and identifies the independent operation of a distributed power source when the set valve is exceeded. |
