To reduce the harmonic noise with no energy losses. More over, it is dynamic system can adapt and work with any frequency contamination form.

Active filter uses operational amplifier for gain boosting and control and moreover for amplification. So an Active Filter is the best.

Dear Saurav Chanda , I do not think the answer is so obvious. It is conditioned by a lot of circumstances. It is also about what the questioner meant by the term "power filter".

Interesting query@ Ravikumar Srinivasa

Low pass filters considred as passive filters which are used to suppress current harmonics and to mitigate the power pollution in grid. Although, this kind of filters offer numerous shortcomings such as huge size, resonance problems, and sensitivity to parameters variation. The abovementioned problems are effectually relieved by using shunt active filters....many paper are published on this topic..

You can have a look on the following paper:

1.Article Simulation and real time implementation of three phase four ...

2. Article Review of active filters for power quality improvement

3. Article Fuzzy logic controller for three-level shunt active filter c...

As name indicate active filter acts according to the noise and not tuned at particular frequency like passive filter. Normally passive filters are RLC based but active filters are designed using opamp and active devices like transistor diodes etc.

Conventionally, passive filters consisting of tuned L-C filters have been used to suppress harmonics because of their low initial cost. However, passive filters suffer with drawbacks such as large size, parallel and series resonance that could be created with both load and utility impedances. These drawbacks of passive filters, active power filters (APF) were developed. APF are power electronic converter based devices that are used for power quality improvement. APF have many advantages compared to passive filter such as, they are less bulky, superior filtering characteristics as well as dynamic performance, flexible operation etc. APF are classified into three types:- shunt active power filter; series active power filter and hybrid active power filter.

Dear Ravikumar Srinivasa

I think the comparison should be between active and passive filters. Each of them has advantages and disadvantages and both of them could be low, high, bandpass or bandreject filter. There are some highlighted points of comparison as follow:

· Active filter amplifies signal, whereas passive does not.

· Active filter is less reliable than the passive one due to the failure of its electronic component (operational amplifier).

· Passive filter is more bulky than the active one especially in case of using inductor (no inductors in active filter).

· The cut off frequency of active filter is not affected by load, whereas it is affected in case of passive filter, as the load becomes part of its transfer function.

· Active filter could be used as buffer circuit due the huge difference between its input and output impedance.

· Active filter has a drawback in very high frequency of operation, whereas passive one is more suited.

Good luck

Active filters come into their own in power filtering applications at lower frequencies where passive network components are necessarily large to provide suppression at lower frequencies. Active filters are smaller than passive filters. Generally, these will be embedded with HF passives which suppress noise beyond a few tens of kHz.

An active filter is a type of analog circuit implementing an electronic filter using active components, typically an amplifier. Amplifiers included in a filter design can be used to improve the cost, performance and predictability of a filter.

An amplifier prevents the load impedance of the following stage from affecting the characteristics of the filter. An active filter can have complex poles and zeros without using a bulky or expensive inductor. The shape of the response, the Q (quality factor), and the tuned frequency can often be set with inexpensive variable resistors. In some active filter circuits, one parameter can be adjusted without affecting the others.

an active filter is a type of analog circuit implementing an electronic filter using active components typically an amplifier,amplifiers included in a predictabikity of filter.

an active filter can have complex poles and zeros without using a bulky or expensive inductor.the shape of the response the Q quality factor and the tuned frequency can often be set with inexpensive,resistors;in some active filter circuits,one parameter can be adjusted without affecting others.

low pass filter blocks frequencies above cut-off frequency, whereas active filter eliminates sub harmonics also

low pass filter blocks frequencies above cut-off frequency, whereas active filter eliminates sub harmonics also.

Both are used to eliminate Voltage and current Harmonics which are harmful for loads or power transfer they could do cutoffs and transformer saturation. Passive filters could do the same functionalities as Active power filters with their different types (series and parallel), essentially 4 types.advantages of passive filters are:

• Reduced cost compared to active filters.
• Simple design, algorithm control and implementation.

disadvantages of passive filters are:

• Big size.
• .Big problem of resonance(that's why we migrate from passive to active).
• Many topologies for the Harmonic elimination(depends from the frequency numbers which they will be eliminated).

Active Power Filter usually noted as APFs: there are two types series for voltage harmonics elimination and parallel for current harmonic elimination.

Advantages of Active filters are:

• Reduced Size.
• One topology for Harmonic elimination type(voltage or current).

Disadvantages of Active filters are:

• Expensive components.
• More complex in control point of view.

power factor improvement to unity power factor, harmonic elimination and voltage regulation are main advantages of active power factor than passive filter

The main motive is to suppress harmonics and reactive power compensation. Both active power filters and passive filters have their own advantages. The best way is to use both in a grid connected system at point of common coupling. So hybrid filter is best choice for power quality improvement.

I think the preference depends on usage

It's not what is better. It's what gets the job done that is needed. The difference between an active filter and a passive filter is an active filter requires power in order to operate. Power is used if amplification is needed for a circuit. If a signal is small and needs to be larger, then an active filter is more appropriate. If no amplification is needed, a passive filter is better because it requires less energy requirement for a circuit.