具有宽范围输出电压的三电平半桥LLC谐振变换器控制策略

Research on Control Strategy of Three-Level Half-Bridge LLC Resonant Converter with Wide Output Voltage Range

由于三电平变换器的开关管电压应力仅为输入电压的一半,在大功率DC-DC电源、电动汽车充电等应用领域得到广泛的关注和研究。为了实现宽范围输出电压调节控制,克服三电平半桥LLC谐振变换器采用变频调制时电压调节范围小的缺点,将移相调制策略引入三电平半桥LLC谐振变换器控制,分析了其工作过程、电压调节范围及软开关条件,导出了实现软开关的工作状态分界点,由此提出一种三电平半桥LLC谐振变换器移相和变频相结合的混合式调制策略。该策略根据软开关工作状态,切换移相调制和变频调制,以实现全程软开关和宽范围输出电压控制。实验验证了理论分析结果的正确性以及所提调制策略的可行性和有效性。

Three-level( TL) converter is received extensive attention and research in some applications with high voltage and high power,such as DC-DC supplies and electrical vehicles,because voltage stress of each switch in TL converter is half of input voltage. In order to achieve a wide range of output voltage,and to overcome the shortcoming of variable frequency( VF) modulation that the voltage range is small, this paper introduces phase-shift( PS) modulation to Three-level Half-bridge( TL HB) LLC converter. It analyzes the working process,voltage adjustment range and soft switching condition of PS modulation. Besides,it deduces the demarcation point at working state of soft switching,thus proposes a hybrid modulation strategy of TL HB LLC converter. According to the soft switching state, this strategy can achieve soft-switching during the whole control process and wide range of output voltage from switching PS mode and VF mode. The experiment can verify the correctness of theoretical analysis results,the feasibility and effectiveness of the proposed modulation strategy.