What is Regenerative AC Drive？

A Regenerative AC Drive (also called a regenerative variable frequency drive or regen VFD) is an advanced type of AC motor drive that can recover energy generated by the motor and feed it back into the power supply line, instead of wasting it as heat.

Basic Definition

A regenerative AC drive controls the speed and torque of an AC motor just like a standard VFD, but with one key difference:

• When the motor operates in braking or overhauling mode (for example, when lowering a load or decelerating a conveyor), the motor acts as a generator.

• Instead of dissipating this regenerative energy through braking resistors (as in conventional drives), a regenerative drive converts the energy and sends it back to the power grid.

How It Works

1. AC to DC conversion:
   The incoming AC power is converted to DC by a rectifier circuit.

2. DC to AC conversion:
   The inverter section converts the DC back to variable-frequency AC to control the motor.

3. Regeneration mode:
   When the motor generates power, the drive’s active front end (AFE) or regenerative unit converts the DC energy back into AC and synchronizes it with the grid voltage and frequency — sending energy back to the utility line.

Key Advantages

• Energy savings: Reuses braking energy instead of wasting it as heat.

• Lower heat dissipation: Reduces need for large braking resistors and cooling.

• Improved efficiency: Especially useful in applications with frequent acceleration/deceleration.

• Reduced carbon footprint: Supports sustainable, energy-efficient operations.

• Stable DC bus voltage: Improves control and reliability in multi-drive systems.

Typical Applications

• Elevators and escalators

• Cranes and hoists

• Centrifuges

• Test benches and dynamometers

• Conveyors with frequent braking cycles

• Rolling mills and winders/unwinders