| 摘要 |
PURPOSE: To detect and eliminate a lower-order k-th harmonic at high speed. CONSTITUTION: A three-phase load current detected by a CT1 is converted into a biaxial current by the rotary coordinate conversion circuit 25 of a rotary coordinate system rotated at a value obtained by multiplying the order (k) of the k-th harmonic and power-supply angular frequency ω, the k-th harmonic is detected as a DC section and others as an AC section, and the DC sections of low-pass filters 261 , 262 are extracted, inverted by a reverse rotary coordinate conversion circuit 27 and the k-th harmonic of three phase is detected. Since the k-th harmonic of a lower order is sensed by the rotary coordinate system, the k-th harmonic can be detected at high speed. A higher harmonic is detected as an AC section and others as a DC section by a coordinate conversion circuit 22 in a load current, in which the k-th harmonic of the lower order from a substractor 21 is removed, the AC section is extracted by bypass filters 231 , 232 , and the higher harmonic is detected by a reverse coordinate conversion circuit 24. The detected k-th harmonic is added to the detected higher harmonic by an adder 28, and an active filter 1 is controlled through a control circuit 3 while employing the value obtained as a current command. |
