Partial Power Processing for High Efficient Power Converters

Partial power processing technologies have emerged as a solution to the growing demand for high efficiency and power density in power electronics. By only processing a portion of the total power and regulating the voltage difference between the input and load, partial power converters can achieve higher efficiency and power density than traditional full power converters. The configuration of connecting one terminal in parallel with the power source or load and another terminal in series with the power source and load is one of the key features that allow partial power converters to achieve these improved results. Although the concept has been proposed for over a decade, many key issues still need to be addressed. For example, the power handled by the converter as a traditional evaluation metric is only a cursory evaluation of the different basic connection architectures at the system level. This does not give a clear picture of the performance of the different topologies and reflects the transformer’s role in the partial power converter. Meanwhile, the modulation strategies for step-up/down partial power converters are also rarely mentioned. This thesis investigates the four aspects of mechanism, topology, modulation strategy and electromagnetic design to design a boost partial power converter for electrolytic cells with a peak efficiency of over 99%. This Ph.D. dissertation is divided into the following three parts. In the first part, this thesis investigates the mechanism of partial power conversion and proposes an evaluation method based on inductor energy. Then, based on the mechanism research, this part summarises the construction method of partial power converters and four basic connection configurations of step-up and step-down partial power converters. Finally, the comparison between different topologies-based partial power converters has been analyzed according to the proposed evaluation method. In the second part, the step-up/down partial power converters are designed for the electrolysis systems. The uni and bidirectional step-up/down topologies are proposed. The detailed comparison analysis between the step-up/down converters and basic step-down or step-up converters is carried out based on the component stress factor. Then, the seamless modulation strategy for the step-up/down converters is proposed, achieving smooth switching between two operating modes. The proposed converter has a peak efficiency of over 99%. The final part focuses on planar transformer design. Firstly, the current distribution of parallel conductors in typical interleaved planar transformers is analyzed, and the universal formulas for leakage inductance and AC resistance are derived. Then a novel winding layout with 0.5 MMF is provided, with lower leakage inductance and AC resistance. Finally, the proposed winding structure was applied to the center-tap transformer, optimizing the switch reduction topology.