Line-Interactive Transformerless Uninterruptible Power Supply (UPS) with a Fuel Cell as the Primary Source

Abstract

This paper presents line-interactive transformerless Uninterruptible Power Supply (UPS) with a fuel cell as the prime energy source. The proposed UPS consists of three major parts (i.e., an output inverter, a unidirectional DC–DC converter, and a battery charger/discharger). Non-isolated topologies of both the unidirectional converter and battery charger/discharger ensure transformerless operation of the UPS system. A new topology of high gain converter is employed for boosting the low voltage of the fuel cell to a higher DC link voltage, with minimum semiconductor count, and high efficiency. A high-gain battery charger/discharger realizes the bidirectional operation between the DC link and the battery bank. Besides, it regulates the DC link voltage during the cold start of fuel cells and keeps the battery bank voltage to only 24 V. A new inverter control scheme is introduced that regulates the output voltage and minimizes the total harmonic distortion for non-linear loading condition. The proposed control scheme integrates proportional-resonant control with slide mode control, which improves the controller’s performance in transient conditions. The proposed UPS system is validated by developing a 1-kVA experimental prototype.

Key findings

• ▸The proposed UPS system achieves transformerless operation with non-isolated topologies for the unidirectional converter and battery charger/discharger.
• ▸A new topology of high-gain converter is employed to boost the low voltage of the fuel cell with minimum semiconductor count and high efficiency.
• ▸The proposed inverter control scheme integrates proportional-resonant control with slide mode control to regulate the output voltage and minimize total harmonic distortion.

Keywords

Identifiers

DOI

10.3390/en11030542

Journal

Energies

Year

2018