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Governance method in the harmonic , using passive filtering device is a very common and economical method, it by adjust the capacitor and reactor parameters to showed a certain harmonic (single-tuned filter) or a certain frequency range of harmonic wave (high-pass filter, low pass filter) a very low impedance of the channel, in order to avoid their entry into the system.

According to the characteristics of harmonic frequency filtered by passive filter , it can be divided into single-tuned filter, double-tuned filter, three-tuned filters and high-pass tuned filter and detuned filter

Single-tuned filter, mainly filter a particular frequency harmonic currents, form series resonant circuit in a particular frequency , that is, XCn-XLn = 0. Double-tuned filter, has two resonant frequencies, absorbing the two frequencies harmonic ,it is equivalent of two single-tuned filter in parallel . High-pass filter, also known as damped filter , above a particular frequency it present low impedance, high impedance is presented below. High-pass filter on the structure divide into first, second, third, and C type , commonly used for the second-order high-pass tuning filter.

the resonant frequency of the detuning filter is usually lower than the lowest harmonic frequency of power grid , frequency is usually set to 3.8 to 4.2 times of fundamental frequency , can only absorb a small amount of harmonics, the main purpose is to prevent harmonic amplification, its structure and impedance characteristics similar to the single-tuned filters, but have different resonant frequencies.

Two-tuned three-tuned filter as its small footprint, low loss, commonly used in HVDC transmission systems, but the structure complex , tuning difficulties, rarely used in low pressure systems. Low-pressure systems often use a single tuning, detuning and second-order high-pass filter .

High-pass filter, also known as reduction amplitude filters, including first-order high-pass filter, second-order high-pass filter, third-order high-pass filter, and c-type filter to attenuate the harmonics whose frequency higher than a certain frequency . the frequency is called the high-pass filter cutoff frequency.