中文摘要：

为了降低三电平逆变器在高开关频率下的开关损耗，提高其效率，提出一种具有对称辅助电路的谐振直流环节三电平软开关逆变器的拓扑结构，通过在三电平硬开关逆变器的直流环节设置对称辅助谐振电路，利用辅助电路的谐振将直流母线之间谐振电容的端电压周期性下降到零，使三电平逆变器的主开关在直流母线之间的谐振电容端电压为零时完成切换，以实现零电压开关。文中依据不同工作模式下的等效电路图，详细分析该软开关逆变器的工作过程。制作3 kW 的谐振直流环节三相三电平软开关逆变器的样机，实验结果表明，逆变器的主开关和辅助开关都实现了软开关切换，效率相比于三电平硬开关逆变器有明显提高。因此所提出的拓扑结构可有效降低三电平逆变器的开关损耗，具有工程实用性。

英文摘要：

A resonant DC link three-level soft-switching inverter with symmetrical auxiliary circuits was proposed to reduce switching loss in the three-level inverter under high switching frequency. Symmetrical auxiliary circuits were arranged in the DC link of three-level inverter. The voltage across resonant capacitors between DC buses decreased to zero periodically via the resonation of auxiliary circuits. Main switching devices in the three-level inverter were operated when the voltage across resonant capacitors between DC buses was zero to realize zero-voltage switching. The operation principle of the soft-switching inverter was analyzed in detail on the basis of equivalent circuits at different operation modes. A 3 kW laboratory prototype of resonant DC link three-phase three-level soft-switching inverter had been built. Experimental results were demonstrated to confirm validity of soft-switching and improve efficiency compared with hard-switching inverters. Therefore, the proposed topology with engineering practicability in the paper can effectively reduce switching loss.