Redundant uninterruptible power supply systems

A system (100) is provided. The system includes a utility (122), a plurality of uninterruptible power supplies (UPSs) (104,106,108,110), a ring bus (132), at least one load (124,126,128,130) electrically coupled to the plurality of UPSs and the ring bus, and a controller (200) communicatively coupled to the plurality of UPSs, the controller configured to determine a common reference angle while the utility is disconnected from at least one UPS (104) of the plurality of UPSs, calculate a phase angle for each UPS of the plurality of UPSs, wherein the phase angle for each UPS is calculated relative to the common reference angle, and control operation of each UPS based on the respective calculated phase angles.