Patent ID: 8331065

Claim:
A method of controlling an inverter in an uninterruptable power supply system, the inverter being selectively coupled to a power line and comprising an input to receive an input voltage from the power line, the method comprising acts of: monitoring the input voltage; detecting based on the act of monitoring, that the input voltage exceeds a predetermined high threshold value; isolating the inverter from the power line responsive to detecting that the input voltage exceeds a predetermined high threshold value; determining whether or not a neutral lifting condition exists on the power line; indicating that the inverter is in a fault state if the neutral lifting condition exists; and reconnecting the inverter to the power line if the neutral lifting condition does not exist, wherein the act of determining whether the neutral lifting condition exists includes: determining, based on the act of monitoring the voltage, that the neutral lifting condition is suspected on the power line; and suspending state changes in the inverter responsive to the neutral lifting condition being suspected.