An isolated three-phase AC-AC converter with bipolar output voltage

Hafiz Furqan Ahmed, Ashraf Ali Khan, Fazal Akbar, Shirazul Islam, Ahmad Elkhateb

Research output: Contribution to journal โ€บ Article โ€บ peer-review

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Abstract

This paper proposes a new topology of three-phase high-frequency transformer isolated bipolar ac-ac (HFTI-BP-AC) converter. It has a simple circuit topology consisting of nine active switches, three high-frequency transformers with primary and secondary series capacitors, and output LC filters. It can generate both non-inverting and inverting outputs with a symmetric bipolar voltage gain of ยฑ๐’๐’…, where n is the turns ratio of transformer and d is switch duty cycle. The proposed converter can provide step-down output by setting the turns ratio to unity, however, step-up output operation can also be achieved by increasing n beyond one when required by a particular application. The proposed converter integrates high-frequency transformer (HFT) based isolation, and therefore, can eliminate the sizeable low frequency transformer for applications requiring grid-interface. Owing to the use of series blocking capacitors, the HFT is devoid of any line-frequency component. A safe-commutation based switch modulation strategy is developed to avoid switch current and voltage overshoots. The proposed converter is well suitable for application as three-phase dynamic voltage restorer (DVR). The inverting and non-inverting operations can inject the anti-phase and same-phase series voltages to mitigate grid voltage swell and sag, respectively. Moreover, the additional line-frequency isolation and voltage injection transformers can be saved. An in-depth circuit analysis and operation is provided with proposed switch modulation strategies together with component design guidelines. Finally, the hardware measurements are taken on a laboratory build circuit to confirm the operation of the proposed converter.
Original languageEnglish
Number of pages14
JournalIEEE Transactions on Industrial Electronics
Early online date07 Dec 2023
DOIs
Publication statusEarly online date - 07 Dec 2023

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