Also, the harmonic filter is a low pass filter having a frequency cut-off point that attenuates first order harmonics of the output signal.

此外，谐波滤波器是具有频率截止点的低通滤波器，该低通滤波器削弱输出信号的一次谐波。

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How to deal with three-phase unbalance compensation and how to filter the low-order harmonics, especially the2nd-order, are the two difficulties for reactive power compensation.

无功补偿的难点在于如何补偿三相不平衡以及如何有效地滤除低次谐波，尤其是2次谐波。

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