Series Bipolar Hybrid Voltage Optimizer Based on Switching-Cell-Inserted Direct AC-AC Converter and Multi-Windings Transformer

This paper proposes a series bipolar hybrid voltage optimizer (B-HVO), which can work at the non-inverting and inverting modes for addressing voltage sag/swell in the utility grid. The superiority of the proposed system is that the direct acac converter cell is deeply integrated with the multi-windings line frequency transformer (M-LFT), which not only effectively diminishes the switches quantities, but also avoids using of additional isolated transformers when it is applied to distribution network. The proposed B-HVO inherits the strengths of converters fast response and line frequency transformers longlife. The B-HVO has much system reliability because the direct ac-ac converter cell has no shoot-through and commutation problems. Additionally, the converter uses four switches and only two switches are switched at high frequency during each halfcycle of input voltage, which evidently reduces the total switching losses. Detailed analysis is provided with experimental results to validate the effectiveness of the proposed system. Besides, the measured data of the proposed system in the engineering demonstration application also proves its validity in handling voltage fluctuation problems