Cyclically occurring processes in particular usually have a high potential of regenerative energy that could be used easily and efficiently. "However, these aspects for economy and efficiency still do not find the place they should have in the technical solution and implementation of the machines," says Ethem Demirkol, application engineer at KEB Automation. The energy is often burned up in braking resistors, which is not only a waste of energy but also a fire hazard. Feed-in and regenerative units offer a practical alternative.
"Before system integration, it must be checked whether sufficient regenerative energy is generated for sensible use," explains Demirkol. In addition to transporting this energy away, feed-in and regenerative units also serve as "feeders". This reduces the number of feed-in points and simplifies the planning of the control cabinet considerably. In order to weigh up the possible uses, the application and its utilisation must be considered. This raises the question: Where does the regenerative energy actually come from? The answer: wherever masses are decelerated and thus potential as well as kinetic energy is converted. "Of course, that leaves a lot of room for manoeuver," Demirkol says. What does 'slowing down masses' or 'converting potential and kinetic energy' actually mean?
Storage and retrieval machine as an application example
As a rule, a storage and retrieval machine consists of a running gear, lifting gear and the load handling attachment. Storage and retrieval machines usually have a high weight - the optimal application for a power supply and regenerative unit. "When such a mass is accelerated by the running gear, very high power is required. The same applies to the braking process," says Demirkol. Here, a drive controller can be used to brake the masses quickly and safely electrically. All the regenerative energy generated in this process can be dissipated by a power feed and recovery unit. Hoist applications are even greater sources of this energy, which is generated during each lowering process depending on the load carried. "Even if all axes are coupled in a DC network to exchange energy, there is still a considerable amount left over," explains the application engineer.
In other areas of application, such as woodworking, textile machines, process technology, wind turbines or test benches, there are also possible applications. "In this context, we are often asked whether plant operators are allowed to feed back into the public grid at all. The answer is: yes, because they are not energy generation plants. All valid guidelines for electrical machines and systems are complied with," says Demirkol.
The use cases offer two technologically different solutions: active or passive feed-in and feedback units. "Passive means that the feed-in and regenerative unit is mains-controlled and the DC link is fixed based on the feed-in voltage. Active, on the other hand, means that the feed-in and feedback unit is actively controlled, for example to regulate the DC link voltage," Demirkol explains. Both systems bring different advantages:
COMBIVERT R6 power feed and regenerative system (KEB Automation)
Suitable for industrial applications with regenerative energy
Cost effective application
Compact and lightweight solutions
Active Infeed Converter COMBIVERT AIC (KEB Automation)
Sinusoidal currents to reduce harmonics → Reactive power reduction for large outputs
Power factor correction (PFC) with cos ϕ = 1
Stabilised DC voltage and step-up converter → Extended speed range and more torque in the field weakening range