OFFLINE UNINTERRUPTIBLE POWER SUPPLIES (UPSs) AND RELATED DESIGN OF ENERGY (DOE) MODE FAILURE DETECTION METHODS

An offline uninterruptible power supply (UPS) is provided, including: a transformer, configured to output a utility power voltage to a load; a bidirectional converter, configured to convert alternating current from the transformer into direct current to charge a rechargeable battery, and convert direct current from the rechargeable battery into alternating current to be outputted to the transformer; and a control unit, configured to control operation of the offline UPS, where when the utility power voltage is within a normal range and the rechargeable battery is fully charged, the offline UPS enters a design of energy (DOE) mode, in the DOE mode, the transformer and the bidirectional converter are turned off, and in the DOE mode, the control unit is configured to detect a voltage of the rechargeable battery, and calculate a slope of decrease in the voltage of the rechargeable battery, and when the slope of decrease in the voltage is greater than a preset first threshold, the control unit controls the offline UPS to delete the DOE mode.