Harmonics are a problem for a wide number of business sectors. The costs are high and rising as the number of disturbances are increasing and modern production equipment becomes more sensitive to these disturbances. The use of active harmonic filters is one way to deal with these problems.

Active Harmonic Filters have been available on the market for many years but have often been given a back seat to the more common mitigation technique of Active Front End or AFE. Unlike the AFE technology, an Active Harmonic Filter is connected parallel to the load, which means that should something happen to the filter, production can continue without disturbance. Further flexibility offered by AHF in combination with variable speed drives is that they offer a wide range of harmonic cancellation, with the possibility of adding further units should the harmonic profile change in the future.

Active Harmonic Filter – A Versatile Solution

Active Harmonic Filters are also far more versatile than many of their competitors. A modern AHF does not just eliminate harmonics, but deals with other power quality problems such as:

• flicker
• voltage variations
• resonances
• reactive energy

This is achieved by using a highly dynamic, stepless digitally controlled compensation and filtering approach. By continuously monitoring the network and injecting just the right amount of compensation current – at exactly the right time – a highly efficient and accurate solution to any power quality problem can be achieved.

This approach enables the current waveform to be restored instantaneously, the current consumption to be lowered and changes in load or installation conditions to be fully compensated at all times.

For modern facilities, where load and network change constantly, the active harmonic filter may be the only adequate solution.

Common Misconceptions on AHF

A common misconception regarding Active Harmonic Filters is that they are only effective in reducing harmonic oscillations up to 2 kHz or within a specific frequency span. This however applies to just about all mitigation techniques. Active harmonic filters exist for different power levels and are adapted to fit the particular needs of the installation. Modern AHF products can operate in the range 7kHz and even some up to 17kHz. This means that it can compensate even up to the 100th harmonic.

Active Harmonic Filters are also commonly accused of causing high losses. However, as with most technology, AHF have come a long way and today exhibit very low losses. Low losses mean improved reliability and longer component life, as well a larger energy savings for the compensated load or process. Further, cooling requirements are reduced, which reduces the size and weight of the unit, positively affecting the total cost of ownership.

Many Active Harmonic Filters today are delivered with built-in automatic overload protection and extensive software controlled monitoring functions, which guarantees system safety and reliability under all operating conditions.