Control Architecture for Parallel-Connected Inverters in Uninterruptible Power Systems

Chi Zhang, Josep M. Guerrero, Juan Carlos Vasquez Quintero, Ernane A. A. Coelho

Research output: Contribution to journalJournal articleResearchpeer-review

55 Citations (Scopus)
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Abstract

In this paper, a control strategy for the parallel operation of three-phase inverters forming an online uninterruptible power system (UPS) is presented. The UPS system consists of a cluster of paralleled inverters with LC filters directly connected to an AC critical bus and an AC/DC forming a DC bus. The proposed control scheme comprises two layers: (i) a local layer that contains a “reactive power-to-phase droop” in order to synchronize the phase angle of each inverter and a virtual resistance loop that guarantees equal power sharing among inverters; and (ii) a central controller that guarantees synchronization with an external real/fictitious utility, and critical bus voltage amplitude restoration. Improved transient and steady-state frequency, active, reactive and harmonic power sharing, and global phase-locked loop resynchronization capability are achieved. Detailed system topology and control architecture are presented in this paper. Further, a mathematical model was derived in order to analyze critical parameters effects on system stability. The proposed control approach has been validated by means of experimental results obtained for several case-study scenarios.
Original languageEnglish
JournalI E E E Transactions on Power Electronics
Volume31
Issue number7
Pages (from-to)5176 - 5188
Number of pages13
ISSN0885-8993
DOIs
Publication statusPublished - Jul 2016

Keywords

  • UPS system
  • Virtual impedance
  • Droop control
  • Voltage restoration
  • Parallel inverters

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