Active Front End

AFE provides two roles:

1. Mitigates harmonics
2. Regeneration

1. To understand the benefits of AFE, it’s a good idea to have an understanding of drives that aren’t AFE. A standard AC drive uses diodes to rectify the mains. (AC to DC). What this does is cause current to be drawn in pulses. This pulsing naturally causes harmonics to be super imposed onto the incoming mains current waveform. This distorts the sinusoidal waveform pattern and causes devices connected to it to overheat which means they’ll degenerate quicker. An AFE doesn’t use diodes to convert AC to DC. It uses IGBT’s. (faster switching capacity than diodes). And by doing so, reduces the pulsing effect when reduces harmonic content. AFE technology is recognised as the best or overcoming harmonics and reducing total harmonic distortion (THD) fed back onto the mains. The main benefit of IGBT’s is that the power factor is maintained close to unity. On top of utilizing IGBT’s, AFE’s have dedicated circuitry that ‘Actively’ monitor the current waveform. Constantly reshaping it to be sinusoidal. Standard AC Drives are ‘Passive’ meaning they don’t monitor anything. They just use individual basic components to rectify the mains. 2. AFE’s are also regenerative. This means regenerated power can be fed back onto the supply. This is because IGBT rectifier design allows four quadrant operation meaning the motor can produce positive and negative torque during forward and reverse motor rotation. When torque and motor rotations are in different directions the motor acts like a generator. The power produced by the motor is fed back into the electrical supply. Benefit of this is that it eliminates the need for large resistor banks to dissipate the regenerated heat.