Low-harmonic drives span the spectrum

Vacon has developed has developed an active front-end (AFE) technology for AC drives which, it says, will reduce dramatically the harmonic content in the power supply. The company claims that it is the world`s first drive supplier to offer AFE regenerative AC drives in ratings from 2.2kW-3MW, and from 380-690V AC.

With a conventional AC drive using a six-pulse diode bridge rectifier, the total harmonic distortion (THD) to the supply current can reach more than 70%. With a correctly-sized AC choke, this can be reduced to around 30%. Vacon claims that its new AFE technology cuts current distortion to less than 4%, and harmonic voltage distortion to less than 3%. The most stringent standards and regulations allow a THD of up to 5%.

The low harmonic distortion helps to reduce the supply current, allowing smaller fuses, cables and transformers to be used. Vacon`s AFE technology uses an intermediate DC voltage that is above the supply voltage, allowing the voltage fed to the motor to be higher than the supply. For instance, 500V can be fed to the motor from a 400V mains supply, resulting in lower output currents and voltage losses - or 20-25% more motor power.

Vacon expects the AFE drives to be particularly useful on weak networks, such as on board ships. When stopping winches and cranes, the drives` regenerative capabilities could be used to save energy that would otherwise be lost in braking resistors.