Patent ID: 8791597

Claim:
A method of controlling an output voltage of an inverter of an uninterruptible power supply (UPS) system, the UPS system including an output transformer having a primary side coupled to an output of the inverter and a secondary side coupled to an output of the UPS system, a controller that monitors a primary side voltage and load current flowing through the output of the UPS system, the method comprising: a. decomposing with the controller the load current into active and reactive components and using them as approximations for I T — active and I T — reactive ; b. determining with the controller a voltage drop across the output transformer for a steady state mode of the UPS system (V reg2 ) and also for a continuous mode of the UPS system (V reg1 ), wherein V reg1 and V reg2 are determined by V reg1 =G active *I T — active +G reactive(low) *I T — reactive V reg2 =G active *I T — active +G reactive(high) *I T — reactive where V reg1 is the voltage drop across the output transformer for a continuous mode of the UPS system, V reg2 is the voltage drop across the output transformer for a steady state mode of the UPS system, G reactive(low) is a gain less than 300, G reactive(high) is a pain greater than 1,000, I T — active is the active component of the load current, and I T — reactive is the reactive component of the load current, and c. in each of the two modes, determining with the controller a voltage drop across the output transformer (V TVR ) to use in determining a desired inverter output voltage of the inverter by V TVR =V reg1 +ΔV T where V TVR is the voltage drop across the output transformer to use in determining a desired inverter output voltage, ΔV T is zero when the UPS system is not in the steady state mode and ΔV T =V reg2 −V reg1 when the UPS system is in the steady state mode; and d. determining with the controller a desired inverter output voltage based on a nominal output voltage of the UPS system and V TVR and controlling an actual inverter output voltage based on the desired inverter output voltage and the monitored primary side voltage.