Importance

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Abstract

A backup power system has power supply lines extending from input terminals, connectable to a main AC power system, and output terminals, connectable to a load, with a relay connected in a power supply line. The AC input power is monitored and when a fault in the power is detected, the relay is opened and an inverter is simultaneously turned on to provide backup power from a battery to the output terminals at a phase and frequency synchronized with the AC input voltage before the fault occurs. When the AC power system power is restored, the inverter power is again synchronized with the AC input power at the input terminals, the relay switch is closed and the inverter is turned off to allow the main power system to provide power to the load. The inverter may be providing power to the power lines before the relay contacts are opened to minimize the disruption of power supplied to the load during transfers. The switching of the switching devices in the inverter is cut off if the current drawn by the inverter from the battery exceeds a current limit level, but is turned on again after a short period of time less than a cycle of the AC waveform to again attempt to provide power from the inverter to the load. This process may be repeated, if necessary, to provide power to loads which require higher currents during start-up of the load than during normal operation after start-up.

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First Claim