Active REVCON Harmonic Filter

RHF-Active is a high efficient design used to avoid mains distortion caused by any non-linear load


Ideally all loads and sources have a pure sinusoidal current waveform. But unfortunately the true waveform of most equipment is very different. Nowadays almost every load is a non-linear load. Typical examples are the power supply of a computer or the diode input bridge of a 6 pulse drive.

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These loads are causing a distortion of the mains voltage. This distortion evaluated by the Total Harmonic distortion THD, typically evaluates frequencies from the 2nd up to the 40th or 50th harmonic. Looking at a 50Hz network this is the area between 100Hz and 2.5kHz.

he impact of harmonic distortion is diverse, but the most typical effects are:

    • Significantly reduced lifetime of electronic components
    • Transformer overload
    • Capacitor bank (PFC) overload
    • Increased energy costs
    • Decreased equipment lifetime
    • Prone to failure equipment
    • Vibration damage on rotating equipment

Find out more about the effects of harmonics in our Learning sector or visit our Webinar– Harmonic solutions for drives.

Active harmonic filters generally show significant differences in the used technology. The RHF-Active is giving up the conventional technology using IGBT Technology and relies on SiC technology (silicon carbide power modules).

This technology offers some advantages compared to the 3-level IGBT technology or even the 2-level IGBT topology.

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  • Noiseless. Due to the high clock frequency of >50kHz, the RHF-Active is operating in silence, which allows it to be used not only in industrial environment.
  • Economic. The higher efficiency (~ 98.5%) can save up to 75% energy costs compared to alternative solutions.
  • Space-saving. The high efficiency permits a unique compact design.
  • Simple. Due to the low weight of max. 18kg module, easy installation or replacement is possible without tools.
  • Accurate. Outstanding accuracy in compensating harmonics, especially the higher order.

In addition to this technological lead, the RHF-Active is delivered pre-configured for your application. This makes installation and commissioning easy.

RHF-Active – hocheffizientes
RHF Aktiv Diagramm

The working principle of the RHF-Active is completely different from any other harmonic solution. Instead of working as a line filter with tuned passive filter circuits, the active solution is connected in parallel and injects harmonics. These injected harmonics are of inversed polarity and therefore eliminate the harmonics taken from the supply.

The RHF-Active may be used for pf correction, unbalance compensation, harmonic mitigation or altogether. It reduces the harmonic current distortion of non-linear loads and sources to any required THDi. This is necessary to reach various standards and recommendations, such as IEEE 519-2014.

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The 3 advantages over a passive solution are:

1. Compensation of unknown harmonics.
A passive filter is always designed for a specific load with a specific harmonic spectrum. Our RHF-5P and RHF-8P, for example, are designed as filters for a drive. Active filters, on the other hand, can be used for many different loads. The composition of the harmonics can vary or even be dynamic. Our active harmonic filters are therefore ideal for eliminating the sum of different consumers with an unknown harmonic spectrum.

2. Decentralized compensation of harmonics
An active harmonic filter offers an enormous advantage for the compensation of a group of drives or as a retrofit installation. The filter can be installed at any point within the low voltage network and therefore the retrofit is significantly easier then adding passive filter. In addition the space requirement is usually significantly lower.

3. Avoidance of reactive power
Passive harmonic filters generally cause reactive power in the load range of 0- 30%. This is a disadvantage for systems that work permanently in this partial load range. The active harmonic filter does not cause any unwanted reactive power. And can therefore achieve a pf of almost 1, regardless of the load.

The RHF-Active is a particularly efficient harmonic filter and is based on SiC technology. We offer this technology for all service areas. Use our selection menu below and find more information about the product in the data sheet.

The RHF-Active can basically be used in any application. The filter can be used either directly on a frequency converter or as a central harmonic compensation on the feeder. Frequent applications are data-center, pumps, compressors or ventilations. These can be symmetrical 3-wire loads (3P3W) as well as 4-wire networks with single-phase loads (3P4W).

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The RHF active filter is often chosen as an alternative to a passive filter as a retro-fit, when the drive installation has already taken place. A single filter can then filter the sum current of multiple loads. But the RHF-Active can also be an interesting alternative in new designed systems due to its space and weight advantage compared to a passive solution.

Harmonics damage over time, therefore an active harmonic filter is particularly useful when the load is continuous. Especially in applications where the ratio of the non-linear load compared to connection power is high. In these situations harmonic mitigation can be essential to avoid immediate damage.

Take a look at our references for further examples where RHF filters are already being used successfully. Here you will also find our test reports which shows the Filter in combination with the corresponding VFD.


If you have any questions, don’t hesitate to contact one of our colleagues!

Rechenzentrum, Anwendungsbereiche für RHF Active
Areas of application for passive harmonic filters for frequency inverters

Active Harmonic Filters are parallel filter circuits injecting harmonics into the supply. Based on the parallel topology, the required filter current is not equal to the load current.

The first digit in the type code of the RHF-Active identifies the corresponding nominal compensation current The RHF-Active 55-400-50-20-C is therefore designed for 55A compensation current.  A de-rating of the VFD due to the voltage drop is not necessary using a REVCON RHF-5P or RHF-8P.

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The required compensation current can be calculated in many different ways, or can be taken from a power quality analysis.

Following this equation based on existing THDi and input current, an estimated required harmonic filter current IHFC can be achieved.


Formel zur Berechnung desKompensationsstrom(please click here for derivation of the equation)

When improving the line current with an active filter, the mains voltage distortion will improve, which leads to a higher distortion of the load current. Therefore its recommended to add safety factor (1.062). This factor is based on experience and may differ significant depending on mains condition. The factor is based on RHF-Active filter with SiC technology. Using the 3-Level IGBT a factor of 1,071 should be used.


In order to calculate the required harmonic current, the IRMS of  the load is required. Most frequently used non-linear-load is a VFD. The designated input current stated by the VFD supplier are typically referring to the maximum possible input current. This may differ significant mainly depending on mains voltage. Input currents found in the following RHF-Active design guide, can be used as a estimation of the input current based on motor load and corresponding voltage. The calculated values are based on  Motors with IE3 efficiency or higher. Motors with lower efficiency will likely cause higher input currents. The results shown in the tables are indicating the required compensation current. In order to calculate the required filter current the factor 1,062 (SiC) or 1,071 (3-Level IGBT) should be used.


Für die Berechnung des Filterkompensationsstromes, wird der Nennstrom der Last IRMS benötigt. Die relevanteste nichtlineare Last sind Frequenzumrichter. Hersteller von Frequenzumrichter geben typischerweise den

RHF-Active Design Guide

Input currents calculated in the RHF-Active Design Guide are All values are approximations and are not a suitable for substitute of a harmonic analysis

Further information on individual sizes are listed in the datasheets. Please select your parameter.

In our panels we combine harmonic filter up to 1500A in IP40-IP55. Specific requirement and customization can easily be added. Please contact for further information on this range.

If you can´t find your preferred filter above, please don´t hesitate to contact us. Due to our wide portfolio and long experience we are able to offer customized solutions for any application.

RHF-Active Design Guide

RHF Active Commissioning guide

User Manual – RHF-Active

Please contact our team to receive the latest version of the RHF-Active software.