In wide voltage range applications, traditional LLC converters suffer from the following issues: (i) to cover a wide voltage gain operating range, the required switching frequency range is also large, which challenges the design and optimisation of magnetic components, gate driver circuitry, and electro-magnetic interference filter; (ii) a small magnetising inductance is preferred in wide voltage gain range application, which leads to the increase of circuit circulating current and corresponding conduction loss; (iii) passive elements are determined based on the minimum switching frequency, so bulky passive elements are required to satisfy the required operation range. To solve these problems, in this study, a full-bridge LLC (FBLLC) resonant converter with two operation modes, namely full-bridge operation and frequency doubler operation, is proposed for wide voltage gain range application. The FBLLC converter discussed in this study can be designed in half of the input voltage range when compared with the conventional method, so smaller switching frequency operating range and higher efficiency operation are guaranteed. In addition, the smooth mode transition is achieved by introducing switching frequency feedforward control and small output voltage overshoot or undershoot is observed. A 150 W experimental prototype was built to validate the theoretical analysis.

中文翻译：

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具有窄开关频率范围的全桥LLC谐振转换器的宽电压增益范围应用

在宽电压范围的应用中，传统的LLC转换器存在以下问题：（i）要覆盖宽的电压增益工作范围，所需的开关频率范围也很大，这对磁性元件，栅极驱动器电路的设计和优化提出了挑战，电磁干扰滤波器；（ii）在宽电压增益范围的应用中，最好使用较小的励磁电感，这会导致电路循环电流的增加和相应的传导损耗；（iii）基于最小开关频率确定无源元件，因此需要笨重的无源元件来满足所需的工作范围。为了解决这些问题，在本研究中，采用具有两种工作模式的全桥LLC（FBLLC）谐振转换器，即全桥工作和倍频器工作，建议用于宽电压增益范围的应用。与传统方法相比，本研究中讨论的FBLLC转换器可以在输入电压范围的一半内进行设计，因此可以保证较小的开关频率工作范围和更高的效率工作。此外，通过引入开关频率前馈控制可实现平滑模式转换，并观察到较小的输出电压过冲或下冲。建立了一个150 W的实验原型以验证理论分析。通过引入开关频率前馈控制可实现平滑模式转换，并观察到较小的输出电压过冲或下冲。建立了一个150 W的实验原型以验证理论分析。通过引入开关频率前馈控制可实现平滑模式转换，并观察到较小的输出电压过冲或下冲。建立了一个150 W的实验原型以验证理论分析。