| 摘要 |
PURPOSE:To effectively sense if power from a power source to an AC circuit is eliminated by providing periodic variation detecting means for detecting the periodic variation of a frequency lower than the basic frequency of an output current or voltage of an inverter for supplying power to the AC circuit having another power source from a solar cell. CONSTITUTION:Periodic variation detecting means 50 has an A/D converter 51 for converting the current Ik of an inverter 1 detected by an instrument current transformer 4 into a digital amount to output it, a microcomputer 52 for detecting its periodic variation based on the output of the converter 51, and a memory 53. When power from a power source 8 to an AC circuit is eliminated, the equivalent impedance of the AC circuit with respect to the inverter 2 is varied, and the characteristic of a control loop of the inverter 2 is varied. Accordingly, the output current Ii or output voltage of the inverter 2 is periodically varied in a frequency lower than the frequency of a basic wave, and the periodic variation is detected by the means 50. Thus, the fact that power from the power source to the AC circuit is eliminated can be known. |
