Power Management: Four Common UPS Technologies
When the time comes to change a UPS, managers have a number of options from which to choose, and the choice will depend on the facility's current equipment and future needs. Managers need to carefully match the UPS with emergency-power-system schemes to assure the most reliable configuration possible.
Common UPS technologies include:
Flywheel UPS. The flywheel UPS is considered new-generation technology, but it has been on the market for the better part of a decade. If managers use a UPS in conjunction with a generator system, the flywheel might be a good option. It packs enough inertia to carry the critical loads through a power outage for a short period — normally 10-20 seconds — until the generator has started, stabilized, and picked up the required loads.
Typical applications include data centers, industrial, and health care facilities with a demand for high reliability. These UPS also are lighter, have smaller footprints and require less ventilation. As a result, they pose fewer structural, architectural, and mechanical challenges than traditional battery-powered units. These systems often have a higher initial cost, but with no batteries to maintain and other advantages noted previously, the 20-year life-cycle cost is relatively low.
True online UPS. This type of UPS — sometimes referred to as double conversion or double-conversion online — provides a high level of reliability for large servers, data centers, and large, sensitive equipment. Under normal operation, it runs continually off the battery via the inverter, and the line power runs the battery charger. For a true online UPS, there is no transfer time upon the loss of utility power.
The system provides power-factor correction, frequency regulation, surge suppression, and power filtering. If the inverter fails — which is rare — the UPS will switch to power provided directly from utility power via the UPS power filter/surge suppressor.
Managers should keep several considerations in mind with this type of UPS. Because the unit converts all power from alternating current (AC) to direct current (DC) and back to AC, low efficiency and high heat output can result.
One method to reduce this inefficiency is to replace the battery charger with a delta-conversion online UPS. In this scenario, instead of providing all output from the battery under normal circumstances, some of it comes directly from the delta converter from the input-line power. In the event of a power failure, the unit operates similar to a regular, true online UPS.
Standby online hybrid. This UPS — also sometimes referred to as double conversion on demand — is similar to a true online UPS but with higher energy efficiency. The significant difference is standby online hybrid UPS loads are served directly from utility power, as long as the power is within acceptable tolerances. Once the power exceeds set tolerances, the UPS switches to standard, true online operation. Typical applications include server rooms. These units come at a higher cost than other options but offer greater energy efficiency.
Line-interactive UPS. This UPS continually conditions and regulates AC utility power to equipment via a power converter. If the utility power fails or falls outside the input range of the power converter, the UPS battery will support the loads via an inverter. The power converter filters the utility AC power, suppresses voltage spikes and regulates the voltage to provide the required power to equipment loads.
The central role of a UPS is providing power to crucial facility equipment and operations in an emergency. When a system is out of date, needs upgrading, or simply cannot perform its role properly, the best protection requires smart engineering design and appropriate equipment choices.
Michael Newbury is a principal at Sparling, an electrical engineering and technology consulting firm with offices in Seattle, Portland, San Diego, and Houston.