用于快速充电站的高频高效模块化固态变压器

High-frequency High-efficiency Modular Solid State Transformer for Quick Charging Stations

随着碳化硅器件的发展,基于固态变压器SST(solid state transformer)的充电站供电架构相比传统基于工频变压器的方案在效率、功率密度及扩展性等方面已展现出优势。为此,提出一种基于三电平功率单元输入串联输出并联的模块化SST。其中,隔离DC-DC级采用串联半桥LLC变换器,分析其软开关实现条件和参数设计表明,与中点箝位型三电平LLC相比更易实现ZVS,更适合高频高效运行。为实现单元间均压均流,基于后级均压前级均功率的协调控制思想,提出一种基于直流链电压反下垂的分布式控制方法,可同时实现均压、均功率和输出电压二次调节等多个目标。所提方法在一台电压10 kV、功率360 kW的SST样机上得到了实验验证。

With the advancements in silicon carbide power devices,the solid state transformer(SST)-based power de-livery architecture for charging stations shows advantages over the traditional line-frequency transformer-based solution in terms of efficiency,power density,and scalability.In this paper,a modular SST is proposed based on input-series output-parallel three-level power cells,in which a series-half-bridge(SHB)LLC converter is adopted at the DC-DC stage.Com-pared with the neutral-point-clamped three-level LLC converter in terms of soft-switching condition and parameter design,the SHB LLC converter is easier to achieve zero voltage switching(ZVS),which is more suitable for high-frequency high-efficiency operation.To achieve voltage and current sharing among cells,a distributed DC-link voltage inverse-droop control method is proposed on the basis of the coordinated control strategy,where the front stage is responsible for power sharing while the back stage is responsible for voltage balancing.Meanwhile,multiple objectives are realized,in-cluding voltage balancing,power sharing,and the secondary regulation of output voltage.The proposed method was ex-perimentally verified on a 360 kW SST prototype with 10 kV input.