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 language | English |
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Journal | I E E E Transactions on Power Electronics |
Volume | 31 |
Issue number | 7 |
Pages (from-to) | 5176 - 5188 |
Number of pages | 13 |
ISSN | 0885-8993 |
DOIs | |
Publication status | Published - Jul 2016 |
Keywords
- UPS system
- Virtual impedance
- Droop control
- Voltage restoration
- Parallel inverters