Steady-state invariant-frequency control of parallel redundant uninterruptible power supplies

In this paper, a new approach for the wireless control of parallel-connected Uninterruptible Power Supplies is proposed. This method can perform the output-voltage frequency accuracy of the paralleled system, by using a transient droop characteristic. In this manner, the controller endows to the system absence of frequency-deviation in steady state conditions. This fact contrasts with conventional P-ω droop schemes, in which the trade-off between active power sharing and frequency variation limits strongly the performances. The proposed control is particularly suitable since both steady-state invariant frequency and good current balance are achieved. In addition, the transient response can be easily modified by means of controller parameters. Simulation results are reported to prove the feasibility of the approach for this kind of systems.