Apparatus and method for an adaptive level transition of an NPC-inverter within a transformerless uniterruptible power supply

Systems and methods are provided for controlling an uninterruptible power supply (UPS) to transition between three- or higher-level operation and two-level operation in a neutral-point-clamped (NPC) inverter (22). In an example, a UPS system (10) includes an NPC inverter (22) and a controller (24). The NPC inverter (22) may supply power to a load (14). The controller (24) may control the inverter (22) to operate in a three-level mode or higher when the load (14) is substantially balanced and to operate in a two-level mode when the load (14) is substantially unbalanced.