The Underestimated Efficiency Factor for Machines
Many drive applications could benefit from the use of supply and regeneration units, whereby kinetic energy from braking or recirculating can be reused and fed back into the DC circuit through the drive or fed back onto the mains power supply line.
Traditionally, if an application generated excess kinetic energy, it was simply dissipated electrically or mechanically – through a braking resistor or friction. By utilising regeneration drive systems, this unused, ‘lost’ energy now has valuable potential in many industrial applications by recirculating or feeding back onto the mains supply, reducing electrical running costs, as well as eliminating the heating effects from the braking resistors. The energy can also be put in ‘intermediate storage’ and harvested for use later to cope with any peak energy demands (due to heavy loads or high accelerations) from the application.
To identify suitable applications for supply and regenerative units, before system integration, a check will need to be made as to whether sufficient regenerative energy will be generated for sensible use. 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. The application itself and its utilisation must be considered to deduce the possible applications. This raises the question of where the regenerative energy is being generated. The answer lies in wherever masses are decelerated and, therefore, if kinetic energy can be converted.
STORAGE AND RETRIEVAL MACHINES
A typical storage and retrieval machine consists of running gear, a hoist unit and a load handling device. These machines typically have a high mass – the optimal application for a power supply and regen unit. When accelerating such a mass by the running gear, very high power is required. The same applies to the braking process. Here, a drive controller can electrically decelerate the masses quickly and safely. A supply and regen unit can dissipate all the regenerative energy generated in this process. Hoist applications are even greater sources of this energy, which is generated during each ‘lowering’ operation, depending on the load being handled. Even when all axes are coupled in a DC link to exchange energy, there is still a significant amount of energy left over
Potential applications for supply and regen units in other industrial sectors include woodworking, textile machines, process technology, wind turbines and generators, theatre technology, theme parks, centrifuges, cranes, conveyor systems, elevators and test benches. In this context, KEB is often asked whether plant operators are allowed to feed back into the public power grid at all. The answer is ‘yes’ because they are not classed as power generation plants.
Regeneration becomes a compelling economic choice when the value of the recovered energy is large compared to the cost of a regenerative system. So, if the system requires frequent braking and starting, or where there is speed control of overhauling loads, it would be worth considering, provided a clear understanding of the system dynamics is known.
Active or passive feed-in are possible. Passive feed-in means that the infeed and regen unit are grid-connected, and the DC link is fixed based on the infeed voltage. On the other hand, active feed-in means that the infeed and regen unit are actively controlled, for example, to regulate the DC link voltage.
Supply and regen units are an easy replacement solution for braking resistors, and they can be used for all common supply voltages of 180-528V AC, 50/60Hz. Most are compact and lightweight and often supplied with an integrated precharging circuit and optional choke or harmonic filter