Decentralized Control for Redundant Parallelism of Uninterruptible Power Supplies with Different Ratings Using Only Current Sensors

Authors propose a decentralized control for redundant parallel connection of multiple uninterruptible power supplies (UPS) using only current sensors. With the measurement of the output current, and following calculation of its active and reactive components, the proposed control provides suitable values of output voltage variables (phase angle and amplitude) to supply a common load without communications cabling. This paper presents design considerations of the control equations, including the development of a voltage drop compensator to attenuate the flow of reactive lateral (or circulating) current. An experimental setup with three voltage sources connected in parallel with different output power ratings verifies the feasibility and good performance of this independent control in terms of stability and load sharing. In addition, this locally-controlled parallel-connected UPS system shows promising capability to feed nonlinear loads