Journal
IEEE TRANSACTIONS ON POWER ELECTRONICS
Volume 36, Issue 12, Pages 13968-13984Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TPEL.2021.3089079
Keywords
Uninterruptible power systems; Topology; Switches; Voltage control; Batteries; Prototypes; Power system measurements; AC-DC power converter; ac-dc-ac power conversion; battery; boundary conduction mode (BCM); bridgeless PFC; common-neutral; dc-ac power converter; digital control; electrolytic-free; inverter; online UPS; power factor correction (PFC); rectifier; single dc-bus; transformerless; uninterruptible power supply (UPS); voltage-mode control
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Funding
- Schneider Electric, Andover, MA
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This article introduces a new transformerless ac-dc-ac converter topology suitable for a high-power-density high-frequency single-phase online UPS, achieving high efficiency and performance through optimized rectification and inversion stages, while reducing capacitance requirements and increasing power density.
This article introduces a new transformerless ac-dc-ac converter topology suitable for a high-power-density high-frequency single-phase online uninterruptible power supply (UPS) with a common neutral between the input and output ac ports. The proposed converter comprises an input power factor correction rectification (ac-dc) stage which is followed by an inversion (dc-ac) stage. The rectification stage operates in boost mode during the input positive half line cycle and buck-boost mode during the input negative half line cycle, while the inversion stage operates in buck and buck-boost modes in the output positive and negative half line cycles, respectively. The rectification stage utilizes boundary conduction mode control enabling soft-switching and allowing high-frequency operation. The inversion stage is operated in continuous conduction mode, wherein a digital controller regulates the output voltage of the converter across both resistive and reactive loads. The proposed online UPS utilizes a single (nonsplit) dc-bus between the rectification and inversion stages, resulting in a 50% reduction in dc-bus capacitance requirement compared to conventional split-bus online UPS topologies. Additionally, two battery interface solutions are also investigated which provide a trade-off between passive volume and additional switch-count. To verify the performance and control of the proposed online UPS, a GaN-based electrolytic-free 1-kVA prototype online UPS is designed, built, and tested. The prototype ac-dc-ac converter achieves a peak efficiency of 95.2% and maintains a high efficiency of above 92.3% across the full output power range. The electrolytic-free prototype ac-dc-ac converter for the online UPS achieves a power density of 26.4 W/in(3).
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