| 摘要 |
<p>PURPOSE:To detect an islanding condition surely and to stop the operation of an inverter by comparing the line voltages of a single-phase 3-line type AC system and detecting a malfunctioning condition, concerning a device having an inverter which converts DC power to AC power and interconnects to the single-phase 3-line type AC system. CONSTITUTION:A difference voltage detecting circuit 22 detects the voltage difference between the two line voltages of a single-phase 3-line type, i.e., between L1 and a midpoint and between L2 and the midpoint, and a level detector 23 performs level judgment. And if it exceeds a set value, it is judged that malfunctioning occurs, and a time function circuit 24 produces output V24. A value V25 obtained by multiplying this output V24 by the output V11 of an amplifier 11 for amplifying the voltage difference between a voltage reference 10 and a DC power source 1 through the working of a multiplier circuit 25 is inputted to a current reference circuit 12, and the magnitude of an AC current reference V12 is varied. As a result of this, the output current of an inverter 2 varies, and balance with loads 9a, 9b, and 9c is lost, and the voltage and frequency of a distribution line change swiftly. These are detected with a malfunction detecting circuit 19 through a voltage relay 17 and a frequency relay 18, and the inverter 2 is stopped.</p> |
