AC induction motors are widely used in industrial applications due to their reliability and low maintenance needs. Comprised of a stator and rotor, these motors convert electrical energy into mechanical motion through electromagnetic induction.
Motor speed, influenced by the frequency of the AC power supply, can impact efficiency. When running continuously at full speed regardless of load, motors consume excess energy. Variable frequency drives (VFDs) allow motor speed to be adjusted to align with actual load requirements, thus optimizing energy use.
What is a variable frequency drive (VFD)?
A VFD regulates the frequency and voltage supplied to the motor, allowing it to operate at speeds tailored to specific load requirements. VFDs have three primary stages: a rectifier that converts AC power to DC, a DC bus that stabilizes the voltage, and an inverter that adjusts the output frequency to control motor speed. This precision in speed and torque alignment reduces energy waste and operational costs.
In addition to traditional VFDs, regenerative and modular VFDs offer enhanced efficiency and adaptability. Regenerative VFDs capture energy generated during motor deceleration, which can then be used by other systems or fed back to the power grid, making them suitable for applications with frequent braking. Modular VFDs, on the other hand, enable multiple motor control modules to share a common DC bus. This allows energy generated during deceleration in one module to be reused by another, further optimizing energy efficiency.
VFDs also offer soft-start capabilities, gradually increasing motor voltage during startup to prevent high inrush currents. This controlled acceleration reduces mechanical stress on the motor, extending its lifespan and preventing abrupt power surges.
Applications of VFDs in manufacturing
VFDs are particularly beneficial in applications with variable load requirements. Examples include:
- Pumps, fans and blowers: In fluid-based systems, power demand is proportional to the cube of the motor’s speed. Even small reductions in speed result in significant energy savings.
- Material handling: VFDs allow precise speed control, ensuring energy efficiency and synchronized production rates in material handling applications, such as with conveyors.
- Mixers/agitators: VFDs optimize energy use by adjusting motor speed to match process demands, improving product consistency.
In an automated system with payoff and tension reels, for example, modular VFDs enable efficient energy use. The payoff reel dispenses material, while the tension reel maintains the desired tightness by pulling the material forward. During deceleration the payoff reel’s motor generates energy, which is transferred back to the DC bus and used by the tension reel. This energy-sharing process reduces overall power requirements and minimizes energy waste.
Choosing the right variable frequency drive (VFD)
When selecting a VFD, consider the motor’s specifications such as type, horsepower, phase and current requirements. Compatibility with communication protocols is also important if the VFD will be integrated with a PLC. Additional factors include braking capability, which manages excess energy during deceleration, and compliance with IEEE 519 standards for total harmonic distortion (THD), ensuring safe integration with the power grid.
VFDs are invaluable in optimizing energy efficiency and supporting sustainability in manufacturing. By precisely controlling motor speed and torque, VFDs reduce excess energy use, operational costs and environmental impact. The use of regenerative and modular VFDs further enhances these benefits, offering scalable and flexible solutions to meet the demands of modern industrial processes. With VFDs, manufacturers can align operational performance with sustainability goals, paving the way for a more energy-efficient future.
Learn more from the E Tech Group about VFDs.
Ana Mircevska is engineering team lead at E Tech Group, a certified member of the Control System Integrators Association (CSIA). For more information about E Technologies Group, visit E Tech Group on the Industrial Automation Exchange.
Also, check out this podcast from Automation World on the difference between soft starters and VFDs.
