Turning waste energy into useful energy
Liam Blackshaw, ABB’s product manager for LV drives in the UK, explores how modern drives can use regenerative braking to capture wasted energy and feed it back into the network, improving efficiency and reducing the amount of additional cabinet equipment required.
Regenerative braking is a way of recovering electrical energy from a braking motor. In a conventional braking system, the motor acts as a generator and converts the surge in electrical energy created through slowing down into heat, through a braking chopper and resistor, which is essentially a waste of energy.
A regenerative drive system, on the other hand, takes the excess electrical energy and distributes it back to the supply network, resulting in energy being saved and reducing the energy wasted. This process can also help to improve the overall system energy efficiency of industrial processes.
This method is used for electric motors in cyclic or continuous braking applications – particularly in larger systems that need to stop suddenly, such as cranes, elevators, centrifuges, downhill conveyors and even test benches.
This can generate large amounts of heat, which needs additional cooling of the resistors. In a system with no means of braking (such as braking resistors or DC injection), some of this energy would go back onto the DC bus system of the drive and unfortunately create nowhere for the voltage to go. In some cases, this excess voltage can return to the motor and cause it to speed up when it should be slowing down or, in other cases, it can cause VSDs to trip.
Fortunately, regenerative drives offer an in-built solution to this which allows more energy-efficient braking with no external braking components or additional cooling. In ABB’s ACS880, for example, the drive uses software to control IGBTs on the input, which allows the drive to direct energy back onto the mains rather than onto the DC bus. In essence, it turns the system into a generator during the stopping process. As well as recovering energy which would ordinarily have been wasted, having a regenerative functionality built into the drive cuts down on the amount of cabinet apparatus required.
The amount of energy saved will vary from application to application, but the best results are found in cyclic or continuous braking applications such as those mentioned above. Indeed, energy savings for a hoist application can be up to 32%, while in applications such as offshore or marine, it can help to squeeze every drop of energy efficiency out of equipment.
For more information about ABB’s regenerative drives, visit: https://new.abb.com/drives/regenerativedrives
