High Reliability and High Performance Parallel-Connected UPS System with Independent Control

This paper presents an independent control for multiple parallel-connected uninterruptible power supplies (UPSs) system, in which it only requires current sensors. With the calculation of the active and reactive currents, the controllers provide suitable values of the phase angle and amplitude variation of the output voltage reference signal to meet the load demand. A consistent choice of the control parameters results in a stable controller with higher performance, and consequently, higher reliability. Experimental results using three UPSs connected in parallel with different output power ratings feeding a rectifier load exhibit stability and good sharing of active and reactive current components