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:
- The rectifier that initially converts the AC voltage into DC voltage.
- The DC link in which the voltage is smoothed, and interference suppressed.
- 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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