Patent ID: 8606425

Claim:
An uninterruptable power supply (UPS) configured to switch power inputs between an alternating current (AC) mode and a battery mode, comprising: a DC bus having a main capacitor module for storing energy to hold up a DC bus voltage across the main capacitor module; a circuit for monitoring an amplitude and frequency of an input voltage at an input of the UPS; a DC bus voltage detection circuit for detecting the DC bus voltage across the main capacitor module; a load current sensing circuit for detecting a load current at an output of the UPS; a control circuit; and a boost-up control circuit communicating with said control circuit and said DC bus, said control circuit configured to generate an adjustment value for said DC bus based on the amplitude and frequency detected at the input of the UPS by said circuit, the load current detected at the output of the UPS by said load current sensing circuit, and the DC bus voltage across the main capacitor module detected by said DC bus voltage detection circuit, wherein said boost-up control circuit configured to provide the adjustment value generated by the control circuit to the DC bus of the UPS to modify said amplitude and/or said frequency when an unstable amplitude and/or an unstable frequency are detected at the input terminal of the input voltage.