Modular DIN-rail UPS uses LiFePO4 or supercap power

Modular DIN-rail UPS uses LiFePO4 or supercap power

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By Nick Flaherty

The UPSI system provides effective protection against power outages, flicker, fluctuations or voltage dips in the DC power supply, eliminating costly plant or system downtime. The compact DIN rail version UPSI-XXXXD with robust aluminum housing is equipped with an universal DIN rail mounting system for quick and flexible installation in control cabinets. Separate DIN rail energy storage units with particularly long-lasting and safe LiFePO4 battery cells (lithium iron phosphate) as well as maintenance-free ultracapacitors are available.

It is aimed at a wide range of applications, such as monitoring and controls technology, automation, Industry 4.0 / IIoT, motor drives, sensors, camera and security systems, industrial PCs, gateways and more.

Into the compact control and charging modules Bicker UPSI-1208D (12VDC) and Bicker UPSI-2406D(24VDC), a bidirectional buck-boost converter was implemented as a central element for the charging and discharging process of the connected energy packs to ensure a very efficient and safe operation. In order to use the UPSI system with different battery chemistries, three charging methods with individual end-of-charge voltage adjustments are implemented: Constant Current, Constant Voltage and Constant Power.

The charging and control module is connected to the respective energy storage via two lines. In addition to the energy transmission line (BAT PWR), all relevant operating data of the energy storage device are continuously monitored and controlled on the data line (BAT DATA) via I2C interface. When changing the energy storage, which is possible even during operation (hot-swapping), a battery type ID authentication is performed so that the appropriate charging and discharging parameters can be automatically set on the DC-UPS. The intelligent PowerSharing function on the input side ensures that the upstream AC/DC power supply does not have to be oversized, but the input power is kept constant and distributed accordingly to load and charger. In other words, with low load at the output, more energy flows into the charger and vice versa.

For short and medium bridging, ultracapacitors provide over 500,000 charging and discharging cycles. Unlike batteries, which store energy by the detour of a chemical reaction, Supercaps are based on electrophysical principles and are loaded and ready for use within a very short time. Energy storage with supercapacitors convince with high current carrying capacity, power density and reliability. The Bicker BP-SUC-D energy storage units have an integrated control and protection circuit as well as a Connect / Disconnect Power function and work in the extended temperature range.

For longer bridging times,it is advisable to take a closer look at the cathode material used. Especially in cells with chemically and thermally unstable cathode material such as lithium-cobalt-oxide (LCO) or lithium-nickel-manganese-cobalt-oxide (NMC), in-cell exothermic chemical reactions can occur under certain conditions which ultimately result in an uncontrollable “thermal runaway”. For this reason, Bicker Elektronik decided to use lithium iron phosphate (LiFePO4) for the cathode material which, compared to LCO / NMC, has a much more stable chemical compound with increased safety and around ten times higher cycle stability (6,000 charging and discharging cycles). The BP-LFP-D battery packs also have an integrated high-performance battery management system (BMS) to optimize lifetime and safety. The BMS monitors and controls the complete charging and discharging process of each battery cell of the energy storage. The integrated cell balancing ensures a balanced and uniform charge of all cells, so that the full capacity of the lithium-ion battery pack remains permanently usable.

With the Battery Relax mode, Bicker Elektronik addresses the problem that in many DC UPS systems the battery pack is often operated for a very long time (possibly for months) to end-of-charge voltage on the charger, in order to guarantee full UPS readiness at any time. However, when lithium-ion cells remain in the end-of-charge state for such a long period of time, the lifetime of cells decreases sharply after a few months.
To protect the cells, it is therefore necessary that after a defined time the charging MOSFET is deactivated at end-of-charge. The discharge MOSFET remains active, so that a discharge is possible at any time. When discharge is detected (UPS operation after power failure), the previously deactivated charge MOSFET is immediately reconnected, so that the current flow through the body diode lasts only a few microseconds and the charger returns to the regular operating mode. Protecting the battery pack by the Relax Mode results in a significantly longer lifetime and thus an increased system availability.

The minimum load detection of the UPSI control unit monitors in backup mode (battery mode) the output load supplied from the energy storage system. If the load at the output falls below a certain threshold, the energy storage is automatically disconnected from the UPSI charging and control unit, so that the energy storage is not unnecessarily emptied by the DC UPS electronics. For PC-based controllers and computer systems, the integrated reboot function automatically restarts the PC system after a shutdown and a recurring supply voltage without the intervention of a service employee being necessary. In addition, a battery start function allows to manually activate the (separated) energy storage and thus initially start the system out of the battery, for example to carry out a diagnosis.

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