Eco Mode Operation and Modular UPS Systems

Several UPS manufacturers now offer an Eco-mode in their on-line uninterruptible power supplies. In Eco-mode the UPS will operate more like a line interactive UPS system.

Running in eco mode does improver operational efficiency but with a downside of lower level of power protection. Efficiency levels can typically rise from 96% in on-line mode to 99% in eco mode. In on-line mode, the UPS inverter constantly powers the load (unless the automatic bypass operates due to a system overload or inverter fault). In line interactive mode the UPS inverter may be switched into circuit to power the load during a power problem but with a 2-4ms display. Eco Mode is only ever recommended when the mains power supply is stable in terms of sags, surges and brownout voltages and free from pollution including spikes and electrical noise.

Eco Mode can also be used in parallel UPS configurations. All the UPS systems connected in parallel can be set to automatically choose between On-line or Eco Mode or be the mode itself can be actively selected. In addition to this energy saving mode, UPS systems (modules) can also be selected to switch to ‘sleep mode’ when the load on the entire system is low enough to be supported by others within the entire configuration. This ‘sleep mode’ is also referred to as ‘hibernation’. Within the UPS itself the battery charging system can also be turned off when the battery is fully charged. Any battery will self-discharge. Powering down the battery charger allows battery capacity to slowly reduce until a pre-set threshold is reached, at which point the battery charger reactivates.

Eco Mode UPS operation and hibernation also feature within modular UPS systems using slide-in modules within a total frameset. The UPS frame cabinet includes a static switch that governs the total size of load that can be supplied. Into the frame cabinet UPS modules and a control unit are placed to configure a total capacity system and N+X redundancy. From the control unit (which can be network IP accessed), the system can be put to operate in Eco Mode and to hibernate potential UPS modules. Within a slide-in modular system, hibernation also has the additional benefit of putting more load onto the active modules and potentially forcing them to operate at the peak of their energy efficiency curve.

There are many advantages to using multiple slide-in modules in a modular UPS system. Aside from parallel configuration for redundancy, ease of service and a compact footprint, the energy saving of modular UPS systems can actually be greater. The reason for this is the capability of a modular UPS system to match available module capacity to fluctuating datacentre server utilisation.