Patent ID: 9214874
Filing Date: 2015-12-15
Classification: H02J,H02M

Abstract:
1. An uninterruptible power supply (UPS) system comprising: a neutral-point-clamped inverter to supply power to a load; and a controller configured to control the inverter to operate in a three-level mode of operation or higher when the power to the load is substantially balanced and to operate in a two-level mode of operation when the power to the load is substantially unbalanced, wherein the controller is configured to determine when the load is substantially balanced and substantially unbalanced based at least in part on a difference between voltage differences of capacitors, wherein the controller is configured to control the inverter to operate in a normal three-level mode when the difference between the voltage differences of the capacitors exceeds a first threshold and to operate in a modified three-level mode when the difference between the voltage differences of the capacitors exceeds the first threshold but not a second threshold.