| 摘要 |
PURPOSE:To prevent reverse charging by promoting vertical fluctuation of the rated frequency and by stopping the operation of an inverter through the detection of an abnormal state of the frequency caused by the fluctuations. CONSTITUTION:In the case of a delay power factor, if a circuit breaker 7 is opened, then the frequency rises and the current flowing through an inductance decreases and the power factor tends to approach 1. This is detected by frequency detecting circuit 23, and an output having a polarity with phase-lead is applied to an adder 25 by a function circuit 24. Then, a PLL circuit 22 performs a control by a PPL circuit 22 so as to make the output of the adder 25 zero, and thus an inverter current supplies a leading current. Because of this, the frequency rises to balance with the current. The frequency and the rate of frequency change having rapidly risen by the positive feedback effect are detected by a frequency relay 18, a rate-of-frequency change relay 27 and an abnormality detection circuit 19, and the inverter is stopped. By doing this, the inverter is certainly stopped and the reverse charging can be prevented. |
