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

This article proposes a series bipolar hybrid voltage optimizer (B-HVO), which can work at the noninverting and inverting modes for addressing voltage sag/swell in the utility grid. The superiority of the proposed system is that the direct ac–ac converter cell is deeply integrated with the multiwindings line frequency transformer, which not only effectively diminishes the switches quantities, but also avoids the use 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 long-life. The B-HVO has much system reliability because the direct ac–ac converter cell has no shoot-through and commutation problems. In addition, the converter uses four switches and only two switches are switched at high frequency during each half-cycle 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.