From the course of physics, we know that an electric motor can also work as a generator, this effect is used to regenerate electricity. If we have something massive set in motion by an electric motor, then during braking, mechanical energy can be converted back into electrical energy and sent back to the system. This approach is actively used in industry and transport: it reduces energy consumption, but is poorly compatible with uninterruptible power supplies. In a system with recuperation, they should be used with great care.
When does recovery meet UPS?
The problem arises with certain types of industrial loads, most often these are some kind of machine tools or other mechanically driven devices. They are controlled by the so-called frequency converters or servo drives, which in fact are also frequency converters with feedback. When the motor of such an installation is no longer supplied with power, it can switch to generator mode, start generating electricity during braking and supply it to the input network.
Modern industrial installations with regenerative power are often protected by a UPS against power failures. For example, consider CNC machines used for high-precision processing of expensive workpieces. The technological cycle must be completed correctly, and if the process is interrupted, it will not be possible to restore it and the workpiece will have to be disposed of. It can cost more than one million rubles, if we talk about mechanical engineering, shipbuilding and aircraft building, as well as military and space technology.
Why are UPS not compatible with recovery?
The frequency converter passes the generated electricity and outputs it to the input. In this case, the power supply management system should initially assume the possibility of returning energy to the network for beneficial use. Such a system is carefully calculated and more expensive, but it allows you to reduce energy costs and avoid accidents. If several UPS-protected installations are running at the same time, the energy generated by one of them can be consumed by neighboring ones. If there are problems with the control and load calculation, or only one unit is running in the system, the recovery will affect the UPS. Devices built according to the classical scheme are simply not designed for this: the energy passes through the inverter, which begins to play the role of a kind of booster, which leads to an increase in the voltage on the DC bus. Almost no modern UPS is able to fully cope with this problem; after the protection is triggered, it will switch to bypass mode.
Where is the way out?
To prevent the frequency converter from exploding, through which the energy generated by the unit during recuperation goes to the system, special modules with braking resistors are mounted. They are included in the circuit at the right time, dissipate excess energy in the form of heat and, in addition to industrial equipment, also protect the UPS. The task, we repeat, is solved already at the design stage of the technological complex: the load and the power management system must be correctly configured. You can also connect several UPSs in parallel to a small load - in this case, the recuperation is "crushed" by power and it will no longer be able to disable the uninterruptible power supply system.
Source: habr.com