(8th October 2010)

The latest active front-end (AFE) drive technology is fast becoming the industry standard for manufacturers, owing to its energy savings, a near unity power factor and a total harmonic distortion of current (THDi) of 5% of nominal current at full load, low-voltage components sup-
plier CHI Control Components, a division of Actom, drives product manager Derek Sleep tells Mining Weekly.

The AFE drive is a bidirectional power converter for the front end of a drive system, which provides the option of speeding up and slowing down the motor and, if the motor is not running under full load, the voltage can be limited further, which can save energy.

Unlike standard drives, an AFE drive is identified where the rectifier has been replaced by an insulated gate bipolar transistor, which is used to create the dc bus, he says.

The AFE drive can be used as a regenerative drive system so that, should braking be needed 
for the motor, when, perhaps, lowering a hoist, energy will not be released through a braking 
resistor but will regenerate back onto the system, improving the efficiency.

Sleep says that the power factor of the AFE drive is almost unity, which means that the reactive power taken from the system is almost zero, resulting in fewer power losses.

A standard drive without filters creates about 80% THDi, and drives using filtering mechanisms and other options, such as 12-pulse rectifiers, create 
between 40% to 15% THDi. 
The AFE drive creates less than 5% THDi.
Total harmonic 
distortion returned to the system can cause damage to the surrounding parts and equipment by heating up conductors and 
motors, as well as affecting bearings on the motors. 
The operation of communication devices and computers can be affected and damaged, he says.

“The key drivers for AFE drives include cost savings and the fact that you are not pushing all the harmonic distortion back onto the line, and causing interferences in computers and damaging the equipment,” says Sleep.
 “The industry is seeing the benefits and, with the cost of electricity going up in the industry, companies are looking for ways to reduce their energy use, manage bills and save costs.”

A large amount of pressure has been put on manufacturers to start using this technology throughout their range of drives. 
The cost savings, through 
energy efficiency, over a period, and the return on investment, as experienced by industry, are seen as a justification for drive manufacturers to put greater 
research and development effort into AFE drive technology.

“We are finding that the call for AFE technology is starting to gain momentum,” he says.

AFE technology has been 
developed for larger kilowatt 
motors and common dc bus systems, which are more predominant in the mining and heavy industry. “I believe that the AFE technology will be available soon for smaller motors,” he says.

“Because these AFE drives are fully imported from Europe, CHI Control is investigating the option of starting the assembly of these drives at its factory in partnership with the company’s AFE drive supplier, Vacon,” says CHI Control Component sales and marketing director Rob Hare.

“CHI aims to become the African arm for the assembly of AFE technology solutions in South Africa for European drives manufacturer Vacon – a more cost-effective solution for CHI and end-users,” says Hare.

Meanwhile, CHI Control Components has been commissioned by a mine, in Botswana, to supply AFE drives for four of the mine's crushers.

As the AFE drive manipulates the use of power, it offers greater 
efficiency control over these 1000-kW motors, ensuring that they use the correct current and voltage, says Hare.

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