Difference between active and passive filters: different principle composition, different filtering effect, different frequency changes, different costs, different applications.
1, the principle of composition is different: active filter is a kind of electronic equipment, and passive filter is mechanical. Active filter is mainly controlled by thyristor. When harmonics are generated, a current of the same size and in the opposite direction is generated to counteract the harmonic current. Passive filters produce low impedance to harmonics through a capacitor + reactance combination LC circuit, allowing harmonic currents to flow into the filtering device.
2, the filtering effect is different: active filter can realize dynamic filtering, automatic tracking compensation grid changes in the harmonic current, high controllability, fast response. Compensation performance is not affected by grid frequency fluctuations, the filtering characteristics are not affected by the system impedance, can eliminate the risk of resonance with the system impedance.
Advanced algorithms enable the device to calculate the output of the next switching frequency in 100us time, so the response speed is no more than 100us, which can quickly compensate for frequently changing harmonics. However, due to the simple structure, passive filters cannot realize the effect of real-time fast dynamics, so the filtering effect is more effective than active filters.
3, the frequency change is different: the frequency change of passive filter will lead to resonance point shift, thus affecting the filtering efficiency; but the filtering effect of active filter will not be affected by the frequency change, the stability is better.
4, the cost is different: active filters are expensive, passive filters are relatively cheap. The cost of active filters is more than three times that of passive filters, relatively immature technology, high maintenance costs; passive filters are relatively low cost, mature technology, installation of basic maintenance-free.
5, the scope of application is different: active filters are used for small current, passive filters can be used for large current. Because of the high cost, active filters are mostly used in the medical industry, precision instruments and equipment, laboratories, communications industry, shopping malls, construction and other industries with smaller capacity.
Passive filters are mostly used in industries with large capacity requirements. Such as steel mills, wind power, electrified railroads, urban rail transit industry, petrochemical and natural gas industry, iron and steel metallurgy industry, mining, shipbuilding industry and other industries.