采用模块化结构的多相多电平LLC谐振变换器

Multi-phase Multi-level LLC Resonant Converter With Modular Structure

在电动汽车和轨道交通辅助电源等高压大功率场合，开关管电压电流应力较高，功率器件选择困难。为此，该文提出了一种适用于高压大功率场合的模块化多相多电平LLC 谐振变换器。其中，多电平结构使得原边开关管的电压应力仅为输入电压的1/n，多相结构可有效降低开关管电流定额。采用变频控制策略，在宽电压和宽负载范围内，所有原边开关管均可实现零电压开关，所有副边整流管均可实现零电流开关。以3个模块结构为例，分析了变频控制策略下多相多电平LLC谐振变换器的工作原理，通过基波分析法得到变换器的等效电路模型和输入输出电压增益。分别对开关频率低于谐振频率和高于谐振频率两个工作区域进行参数设计，完成一台540~660 V输入、400 V/5 A输出的原理样机，实验结果验证了理论分析的正确性。

In some applications with high voltage and high power, such as electrical vehicles and auxiliary power supplies in traction system, the voltage and current stress of power devices are relatively high, which is difficult to select the power devices. To satisfy the requirement for above applications, a multi-phase multi-level LLC resonant converter with modular structure was proposed. The voltage stress on the primary switch is only one-nth of the input voltage due to its multi-level structure, the current rating of power devices can be reduced by introducing the proposed multi-phase structure. By using the variable frequency control strategy, the primary switches can operate with zero-voltage- switching （ZVS） and the rectifier diodes can operate with zero-current-switching （ZCS） in a wide voltage and wide load range. Taken the topology with three modules for example, the operation principle of the converter under variable frequency control method was analyzed, the equivalent model and voltage gain of the converter were derived according to fundamental harmonic analysis. The parameters are designed under the condition that the switching frequency is higher or lower than the resonant frequency. To validate the feasibility of the proposed converter, a prototype with 540~660V input and 400V/5A output has been built and tested in the lab and the experimental results can agree with the theoretical analysis.