不对称控制方式三相三电平直流变换器

Three-phase Three-level DC/DC Converters With an Asymmetrical Control Strategy

三相三电平直流变换器中开关管具有低电压、电流应力,适用于高压大功率场合。采用对称控制方式,可提高输入输出电流脉动频率,从而减小滤波器,但开关管为硬开关,存在较大开关损耗。为解决该问题,提出一种适用于该变换器的不对称控制策略,在保留变换器原有优点基础上,可利现开关管的零电压开关,从而提高变换器效率。简要分析采用输出滤波电感和变压器漏感（或外加谐振电感）的能量实用不对称控制方式后变换器的工作原理,重点讨论其基本特性及软开关实现条件,完成一台540~660V输入、48V/20A输出的原理样机,实验结果验证了理论分析的有效性和正确性。

Three-phase three-level （TL） dc/dc converters have the advantages of low voltage and current stress on switches, which is suitable for high＇ power and high input voltage applications. Adopting a symmetrical control strategy, the ripple frequency of the input and output current can be increased significantly, resulting in a reduced filter requirement. However, all the switches are hardware, leading to a considerable switching loss. In this paper, an asymmetrical control strategy was proposed to the three-phase TL dc/dc converter. The converter can keep all the advantages compared with the original control strategy; meanwhile, soft-switching can be achieved using the energy stored in the output filter inductance and leakage inductances of transformers （or resonant inductances）. In this paper, the operation principle with asymmetrical control was analyzed, along with the characteristics and soft-switching conditions of the converter. Experimental results from a prototype of 540-660V input and 48V/20A output are presented to verify the theoretical analysis and the performance of the proposed converter.