What The Tech: The impor­tance of frequen­cies for high-perfor­mance fans and motors

Why does a fan need a frequency converter? Why is it impor­tant? And how does it work?

Frequen­cies are impor­tant not only in sound studios, but also for fans. A so-called vari­able frequency drive increases the energy effi­ciency of high-perfor­mance fans and reduces the mechan­ical load, which extends the service life of the motors and fans to a maximum. But how does a frequency drive work?

Every fan with a three-phase motor oper­ates under different condi­tions. Logi­cally, then, a supply of uniform AC voltage is suit­able for one device, but less good for another. In order to always obtain the best perfor­mance with minimal wear from all devices, a so-called vari­able frequency drive is often connected upstream of large fans with AC motors. They convert the uniform AC voltage provided by the local power grid into an AC voltage, the ampli­tude and frequency of which can be changed. Without this, the fan would only run according to its constant speed – depending on the local power grid. In Europe, for example, the frequency is 50; in the USA, 60 hertz. A change in speed would there­fore not be possible. By contrast, the speed of the motor can be adjusted contin­u­ously from almost zero to the maximum.

A vari­able frequency drive is installed upstream from the motor and consists of several compo­nents:

  1. The recti­fier that initially converts the AC voltage into DC voltage.
  2. The DC link in which the voltage is smoothed, and inter­fer­ence suppressed.
  3. The inverter, which usually switches the voltage on and off quickly in a fast sequence using pulse width modu­la­tion.

The frequency of switching on and off produces the new frequency. The vari­able frequency drive there­fore not only changes the frequency but also the ampli­tude. This enables the voltage level to be regu­lated higher or lower in volts. Since the speed is now only as high as required, the motor’s energy consump­tion also reduces the mechan­ical load, which extends the service life of the motors and fans to a maximum.

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