| 摘要 |
PURPOSE:To detect higher harmonic accurately even at the stationary time and the transient time by mounting pairs of band-pass filters having different Q values to a detector for higher harmonics and selectively using the band-pass filters according to the degree of the fluctuation of higher harmonics. CONSTITUTION:A band-pass filter resonating with specified high frequency is connected to a notch filter 5 removing fundamental waves in load currents as a circuit 3 detecting higher harmonics. Pairs of band-pass filters 6 and 7, 8 and 9 having different Q values are prepared as the band-pass filters. A circuit 13 detecting the degree of the fluctuation of higher harmonics and a changeover switch 10 are fitted previously, the switch 10 is changed over according to the degree of the fluctuation of higher harmonics, and an output from the switch 10 is input to a compensating circuit 4. Accordingly, the band-pass filter having an optimum Q value can be selected on the stationary time and on the transient time, thus accurately detecting higher harmonics at all times. |
