An uninterruptible power supply system comprising: an output configured to provide output AC power to a load; a DC power source coupled to a DC bus; an inverter having an input coupled to the DC bus and an output coupled to the output of the UPS system, the inverter configured to receive DC power at the input from the DC bus and provide AC power having a voltage to the output; and a controller coupled to the output of the inverter and configured to sample the voltage at the output of the inverter over a period of time, calculate an average voltage of the AC power at the output of the inverter over a period of time based on the monitored voltage at the output; compare the calculated average output voltage of the inverter to a predetermined average output threshold value; determine whether the calculated average output voltage is equal to or greater than the predetermined average output threshold value; and operate the inverter based on the average voltage of the AC power at the output of the inverter, wherein the AC power provided at the output of the inverter by the inverter includes a substantially square voltage waveform; wherein the controller is further configured to clamp the voltage at the output of the inverter to zero in response to a determination that the calculated average voltage is equal to or greater than the average output voltage threshold; and wherein the controller is further configured to: calculate, based on the monitored output voltage, an RMS voltage of the AC power at the output of the inverter; compare the RMS voltage of the AC power at the output of the inverter with a predetermined RMS output voltage threshold value; and control the AC power at the output of the inverter based on the comparison of the calculated RMS voltage to the RMS output voltage threshold. an output configured to provide output AC power to a load; a DC power source coupled to a DC bus; an inverter having an input coupled to the DC bus and an output coupled to the output of the UPS system, the inverter configured to receive DC power at the input from the DC bus and provide AC power having a voltage to the output; and a controller coupled to the output of the inverter and configured to sample the voltage at the output of the inverter over a period of time, calculate an average voltage of the AC power at the output of the inverter over a period of time based on the monitored voltage at the output; compare the calculated average output voltage of the inverter to a predetermined average output threshold value; determine whether the calculated average output voltage is equal to or greater than the predetermined average output threshold value; and operate the inverter based on the average voltage of the AC power at the output of the inverter, wherein the AC power provided at the output of the inverter by the inverter includes a substantially square voltage waveform; wherein the controller is further configured to clamp the voltage at the output of the inverter to zero in response to a determination that the calculated average voltage is equal to or greater than the average output voltage threshold; and wherein the controller is further configured to: calculate, based on the monitored output voltage, an RMS voltage of the AC power at the output of the inverter; compare the RMS voltage of the AC power at the output of the inverter with a predetermined RMS output voltage threshold value; and control the AC power at the output of the inverter based on the comparison of the calculated RMS voltage to the RMS output voltage threshold.