An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide instantaneous or near-instantaneous protection from input power interruptions by means of one or more attached batteries and associated electronic circuitry for low power users, and or by means of diesel generators and flywheels for high power users.
Common power problemsThe primary role of any UPS is to provide short-term power when the input power source fails. However, most UPS units are also capable in varying degrees of correcting common utility power problems:
Power failure: defined as a total loss of input voltage.The general categories of modern UPS systems are on-line, line-interactive or standby.In a standby ("off-line") system the load is powered directly by the input power and the backup power circuitry is only invoked when the utility power fails. For large power units, dynamic uninterruptible power supplies are sometimes used. When the mains power fails, an Eddy-current regulation maintains the power on the load as long as the flywheel's energy is exhausted. A hybrid (double conversion on demand) UPS operates as an off-line/standby UPS when power conditions are within a certain preset window. This allows the UPS to achieve very high efficiency ratings.
A motor driving a mechanically connected generator,
A hybrid rotary UPS, designed similar to an online UPS, except that it uses the flywheel in place of batteries. The rectifier drives a motor to spin the flywheel, while a generator uses the flywheel to power the inverter.