多电飞机采用千伏级高压直流母线可有效减小电缆截面积，从而降低系统重量并提升功率传输效率，但机上关键设备（如电动液压泵、起动发电机等）仍工作于270V，仍需保留270V次级母线，故实现从1000V至270V的高效、高功率密度电能变换，对多电飞机的轻量化与性能提升至关重要。模块化多电平LLC谐振变换器凭借其软开关特性与低电压应力的优势，在高压直流供电系统应用中展现出良好潜力。然而，谐振元件参数因制造工艺限制而存在的容差，易导致并联模块间出现功率分配不均，造成部分模块空载或过载运行，进而影响系统整体稳定性与可靠性。为解决上述问题，文章提出一种面向三电平LLC拓扑的主动调相技术，以补偿由参数偏差引起的功率不均衡，并结合交错并联结构以抑制输出电流纹波。在实验环境下，所提出控制策略变换系统中实现了较高的整体效率，10%容差造成的不均衡度可从194.7%降至26.3%。研究利用主动调相技术和LLC谐振变换器的交错并联技术降低变换器输出电流纹波，在仿真环境下，纹波大小为1.8%。研究验证了模块化多电平LLC谐振变换器在多电飞机高压直流供电系统中的可行性与应用价值。
Adopting a kilovolt-level high-voltage direct current (HVDC) bus in more electric aircraft (MEA) can effectively reduce the cable cross-sectional area, thereby lowering system weight and improving power transmission efficiency. However, key onboard equipment, such as electro-hydraulic pumps (EHPs) and starter generators (SGs), still operates at 270 V, necessitating the retention of a 270 V secondary bus. Consequently, achieving efficient, high-power-density power conversion from 1000 V to 270 V is of critical importance for the weight reduction and performance enhancement of MEA. Modular multilevel LLC resonant converters, by virtue of their soft-switching characteristics and low voltage stress, demonstrate considerable potential in HVDC power supply system applications. Nevertheless, the tolerance of resonant component parameters arising from manufacturing limitations can readily lead to uneven power distribution among parallel modules, causing some modules to operate under no-load or overload conditions, which in turn compromises the overall stability and reliability of the system. To address the above issues, this paper proposes an active phase-shift technique tailored for the three-level LLC topology to compensate for the power imbalance caused by parameter deviations, combined with an interleaved parallel structure to suppress the output current ripple. Under experimental conditions, the proposed control strategy achieves high overall efficiency in a converter system, reducing the imbalance degree caused by a 10% tolerance from 194.7% to 26.3%. This paper further employs the active phase-shift technique and the interleaved parallel technique of LLC resonant converters to reduce the output current ripple, with a ripple magnitude of 1.8% observed under simulation conditions. This study validates the feasibility and application value of modular multilevel LLC resonant converters in MEA HVDC power supply systems.
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