Active vs. Passive Harmonic Filters

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What are active harmonic filters?

Active harmonic filters are parallel filters (which means the current doesn’t go through the filter) that are used to reduce, or mitigate, harmonics to tolerable levels as defined by IEEE-519.  Active filters use a set of transistors and capacitors to filter (or clean) the current wave by injecting inverse currents to cancel out the undesired harmonic components.  Active filters are significantly more expensive than passive filters and take up more space.  Size is an immense factor in system design today and should be accounted for when deciding on what type of harmonic filter is right for you.

Active filters can work with multiple drives; when the active filter reaches its limit, it won’t overload. In addition, if an active filter breaks, it won’t stop the motor (since current isn’t going through the filter); it just won’t filter the current wave.