基于LLC谐振变换器的电力电子变压器

Power Electronic Transformer Based on LLC Resonant Converter

提出了一种基于LLC谐振变换器的三级型降压式电力电子变压器(PET)拓扑结构。所述结构的输入侧高压级为二极管钳位三电平整流电路,以降低开关器件耐压等级;隔离级采用了三电平LLC串联谐振型DC/DC变换器,其每个主开关电压应力是输入电压的一半,并且在全负载范围内工作在软开关状态,可降低PET的损耗,提高其效率;输出侧低压级为两电平三相四桥臂逆变电路,以应对大量存在的不平衡和非线性负载。对所述的PET结构进行了控制方案设计,并做了仿真研究。仿真结果表明:该PET结构在实现了传统变压器隔离、变压和能量传递等功能的基础上,还具备电能质量调节功能,可有效避免系统与负载之间因不平衡或畸变而对彼此产生的影响。

A three-stage buck power electronic transformer（PET）topology based on the LLC resonant converter is proposed. In the proposed PET,the high voltage stage on the input side is a diode-clamped three-level rectifier for use in reducing the voltage withstanding grade of switching devices.The isolation stage adopts a three-level LLC series resonant DC-DC converter, the voltage stress of each of whose main switches is half the input voltage.It can realize soft-switching from no-load to full load,which will reduce losses and improve efficiency.The low voltage stage on the output side is a two-level three-phase four- leg inverter to cope with the huge imbalance and nonlinear loads.A control scheme is designed and simulation is performed to verify the performance of the proposed PET.Simulation results show that the proposed PET not only has the basic features of isolation,voltage transformation and energy transmission as does the traditional transformer,but also carries out the power quality regulating function,which can avoid the mutual influence between system and load due to imbalance and distortion.