Working principle of active harmonic filter

Active harmonic filter uses current transformer to collect current on DC line. After sampling, the obtained current signal is processed by harmonic separation algorithm, and the harmonic reference signal is obtained as a modulation signal. Compared with triangular wave, the switching signal is obtained. The switching signal is used to control the single-phase bridge. According to the principle of technology, the switching signal of the upper and lower arms is connected back, and the harmonic current equal to the harmonic signal on the line and opposite to the harmonic signal on the line can be obtained, and the harmonic current on the line can be cancelled out. This is the feedforward control part. Then the harmonic component of the line current after the access point of the active harmonic filter is fed back as the input of the regulator to adjust the error of the feedforward control.

Generally speaking, it is based on the principle of capacitance with high frequency resistance and low frequency, inductance with low frequency resistance and high frequency. For high frequencies that need to be cut off, the capacitor absorbs inductance and obstructs it. For low frequencies that need to be cut off, the capacitor has the characteristics of high resistance and low inductance to make it pass.

An ideal filter should have uniform and stable gain in the required frequency band and infinite attenuation outside the passband. However, there are some differences in the actual filter distance, so people use various functions to approximate the frequency characteristics of the ideal filter.

SOROTEC which is a professional active harmonic filter manufacturer in China can be a good choice for you, please feel free to contact us!

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