Regenerative energy – the underestimated efficiency factor for machines
Especially processes that occur cyclically 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. Energy is often burned up in braking resistors, which is not only a waste of energy but also a fire hazard. Supply 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, the infeed and regenerative unit also serve as “feeders”. This allows the number of feed points to be reduced and significantly simplifies the planning of the control cabinet. In order to weigh up the possible applications, the application and its utilization must be considered. This raises the question: Where is the regenerative energy actually generated? The answer: wherever masses are decelerated and thus potential as well as kinetic energy is converted. “Of course, this leaves a lot of room for maneuver,” says Demirkol. 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, hoist unit and the load handling device. Storage and retrieval machines usually have a high weight – the optimal application for a power supply and regenerative unit. “When accelerating such a mass 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 electrically decelerate the masses quickly and safely. All the regenerative energy generated in this process can be dissipated by a supply and regenerative units. Hoist applications are even greater sources of this energy, which is generated during each lowering operation depending on the load being carried. “Even when all axes are coupled in a DC link to exchange energy, there is still a significant amount left over,” explains the applications 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 power 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 regenerative units. “Passive means that the infeed and regenerative unit is grid-connected and the DC link is fixed based on the infeed voltage. Active, on the other hand, means that the infeed and regenerative unit is actively controlled, for example to regulate the DC link voltage,” explains Demirkol. Both systems bring different advantages:
- Suitable for industrial applications with regenerative energy
- Cost effective application
- Compact and lightweight solutions
- Easy installation
- 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
- For highly dynamic applications
In addition to the technical and ecological advantages, a regenerative unit also brings economic benefits. Often, the acquisition costs have already paid for themselves after less than two years. “So, from this point on, you also earn money with the expanded system. The payback period is quickly determined by the utilization of the system, the number of motion cycles and the price of electricity,” says Demirkol.