宽范围输入三电平半桥LLC变换器混合控制

Hybrid control strategy of three-level half bridge LLC converter with wide input voltage range

针对传统变频(PFM)控制的LLC谐振变换器在宽电压输入条件下效率低的问题,提出一种三电平半桥LLC谐振变换器的变频-移相(PFM-PS)混合控制策略。首先,分析三电平半桥LLC谐振变换器的工作模态,建立其等效模型,获得了移相控制和变频控制下的电压增益曲线。其次,分析了变频控制的工作区间与软开关特性,推导得到了移相控制下实现软开关的最小占空比。通过混合控制策略,在升压时采用变频控制和在降压时采用移相控制,相较于全变频控制和全移相控制,混合控制可在较小频率变化范围内对电压进行升降压,在全增益范围内实现软开关,获得较宽的电压增益范围,提升了变换器的效率。最后,通过仿真和输入500~800 V/4.5 kW实验样机验证了所提出混合控制策略的有效性。

Aiming at the low efficiency of traditional pulse frequency modulation(PFM)method in LLC resonant converters under wide voltage input conditions,the hybrid control strategy of pulse frequency modulation-phase shifting(PFMPS)was proposed.The working modes of the three-level half-bridge LLC resonant converter were analyzed,and the model was established firstly.Voltage gain range curves of PFM and PS method were obtained.Then the working conditions and soft switching were analyzed.The minimum duty cycle of PS method was derived to achieve ZVS.The hybrid control was proposed with PFM and PS used in voltage step up and step down mode respectively.Compared with only PFM or PS method,the hybrid control has ability of voltage step-up or step-down in small frequency range.A wide voltage gain range is realized through hybrid control,which improves the overall efficiency of the converter.Finally,the feasibility of the proposed hybrid control strategy is verified by simulation and input 500-800 V/4.5 kW experimental platform.