Bandpass allows a certain range of frequencies to pass and filters out the remaining frequencies. For example, a high-pass filter + a low-pass filter can form a band-pass filter. It is roughly divided into analog bandpass filters and digital bandpass filters. Analog bandpass filters generally use circuit components (such as resistors, capacitors, inductors) to form the frequency characteristic circuit we need. The principle of the analog bandpass filter is to configure the capacitance, resistance and inductance parameters so that the analog filter presents a small impedance to the fundamental wave and a large impedance to the harmonics. In this way, when the load current signal passes through the analog When using a bandpass filter, the fundamental signal can be extracted. At present, some active filters use analog circuits to implement band-pass filters to detect the fundamental component of the load current, and have been applied in practice. However, analog bandpass filters also have some disadvantages of their own. This is because the center frequency of the analog filter is very sensitive to the parameters of circuit components (such as capacitors, resistors, inductors), and it is difficult to design appropriate parameters. Moreover, the parameters of circuit components will change with the interference of the external environment, which will lead to The offset of the center frequency affects the accuracy of the filtering results. The digital bandpass filter uses software to implement the above filtering process, which can well overcome the shortcomings of the analog filter. Once the parameters of the digital bandpass filter are determined, they will not change. As long as the fluctuation frequency of the power grid is within our design Within the range, the fundamental wave component can be extracted relatively well. Digital filters can be divided into IIR type and FIR type according to their type. The PIR type has only zero point, so it is not easy to obtain better passband and stopband characteristics like the IIR type. Therefore, the IIR type is selected in general designs. IlR type can be divided into Butterworth type filter, Chebyshev type I filter, Chcbyshev type II filter and elliptical filter, etc.
Reference material: / dsp/ja/dspchinese/dspchinese/ ch07.pdf
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