Abstract: LLC resonant converter is widely used with many advantages such as high efficiency, small volume and low loss. Based on the working principle analysis of LLC resonant-based DC/DC converter, the modulation strategy of LLC resonant DC/DC converter is designed. The performance analysis including closed-loop performance, frequency domain performance, and conduction losses for the two regulation schemes (predominantly pulse-width modulation and pulse-position modulation) are carried out with PSIM 6.0 software. In these two modulation control schemes, both the two switches of half-bridge inverters are controlled by square-wave pulses with the dead-time of 250 ns, thus avoiding short-circuit of the two switches. Simulation results indicate that over a wide range of load variation, the predominantly pulse-position modulationscheme has better performance of frequency selection at high input voltage, which makes it more suitable for the design of DC/DC converter and the improvement of performance of power conversion system.

Key words: LLC resonant, DC/DC converter, closed-loop performance, frequency domain performance, conduction losses

摘要： LLC谐振变换器具有效率高、体积小、损耗低等优点。针对基于LLC谐振的DC/DC转换器，在分析其工作原理的基础上，设计LLC谐振DC/DC变换器调制策略，利用PSIM 6.0软件对脉宽调制和脉冲位置调制这两种主要调制控制方案的闭环性能、频域性能和传导损耗等性能指标进行了详细的分析。在这两种调制控制方案中，半桥逆变器的两个开关管均由死区时间为250 ns的方波脉冲进行控制，从而避免2个开关管的短路。通过仿真实验结果表明，当负荷变化范围很大时，脉冲位置调制方案在高输入电压下具有更好的频率选择性能，因此更加适用于DC/DC变化器的设计，从而提高功率转化系统的综合性能。

关键词: LLC谐振, DC/DC变换器, 闭环性能, 频域性能, 传导损耗