An Instantaneous Average Current Sharing Scheme for Parallel UPS Modules

The instantaneous average current sharing (IACS) control strategy ensures accurate transient and steady-state current sharing among uninterruptible power supply (UPS) modules connected in parallel, but is dependent on a communication backbone. This paper proposes a new IACS scheme that is more reliable and economically efficient. In the process of deriving this control scheme, two existing IACS schemes are examined in detail. It is shown that both the schemes offer distinct structural and performance related advantages and disadvantages. The proposed scheme is shown to provide more reliable operation without sacrificing the system performance and incurring extra control cost. Performance of the proposed approach is analytically predicted and validated through experimental results with a 22.5-kW system supported by three parallel-connected three-phase UPS modules.