As motors and drives become more efficient powering loads, it's shameful to throw away energy when bringing them to a stop. Yet that is exactly what dynamic braking does. Spinning motors become generators. Power created by their inertia dissipates in large resistive load banks as waste heat. With energy costs rising to all-time highs, engineers and designers look to conserve every joule they can.

Regenerative motor drives answer the conservation call by returning this previously wasted power back to the electrical grid. Also known as fourquadrant drives, ac regenerative drives incorporate an active supply circuit rather than the passive diodes used in conventional ac drives.

Regenerative drives supply other benefits besides saving energy. One area in which they excel is in reducing electrical harmonics. Plant engineers and utilities are increasingly concerned about the harmful effects of harmonics and low power factor. Many have tightened power quality requirements. Regenerative ac drives' superior harmonic performance make them favorable alternatives to other, more expensive harmonic-mitigation methods. Most drives already have built-in LCL filters that eliminate high-frequency harmonics. So not only do regenerative ac drives recover previously wasted energy, but they also help maintain electric-supply quality.

A final benefit of regenerative ac drives is their ability to compensate for network fluctuations. They maintain fullmotor voltage even when network voltage is low, reducing damage from recurring under-voltage situations.

Applications for regenerative ac drives include industrial centrifuges, test stands for vehicle engines and transmission, sheet-metal presses, cranes and lifting equipment, conveyors, escalators, and even ski lifts and cable cars. In short, any application that has residual momentum when coming to a stop.

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