A conventional pulse frequency modulation (PFM) controlled LLC resonant converter requires a wide switching frequency operating range to regulate the output voltage. There are some disadvantages of PFM LLC resonant converters: (i) the design and optimisation of magnetic components and gate driver circuitry are challenging; (ii) due to the variable switching frequency operating range, electro-magnetic interference performance of the converter is degraded; (iii) efficiency degradation; (iv) inability to achieve independent control in multiple-output applications. To address the above-mentioned problems and achieve fixed switching frequency operation, a variable magnetising inductance control (VMIC) strategy is proposed. In the proposed VMIC control strategy, the operating switching frequency of the primary switch is fixed and the duty cycle remains constant at 0.5. At the resonant frequency operating point, the output voltage is independent of both the magnetising inductance and load. In addition, the zero current turn-off operation of the secondary rectifier requires that the switching frequency be designed below the resonant frequency. The operational principles and design considerations of the LLC resonant converter with VMIC are presented. Experimental results from a 200 W prototype are presented to validate the theoretical analysis and the effectiveness of the proposed VMIC control strategy.

中文翻译：

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具有可变励磁电感控制的LLC谐振变换器的分析与设计

传统的脉冲频率调制（PFM）控制的LLC谐振转换器需要较宽的开关频率工作范围才能调节输出电压。PFM LLC谐振转换器具有一些缺点：（i）磁性元件和栅极驱动器电路的设计和优化面临挑战；（ii）由于开关频率的工作范围可变，导致转换器的电磁干扰性能下降；（iii）效率下降；（iv）无法在多输出应用程序中实现独立控制。为了解决上述问题并实现固定的开关频率操作，提出了可变磁化电感控制（VMIC）策略。在建议的VMIC控制策略中，主开关的工作开关频率是固定的，占空比保持恒定为0.5。在谐振频率工作点，输出电压与励磁电感和负载无关。另外，次级整流器的零电流关断操作要求将开关频率设计为低于谐振频率。介绍了具有VMIC的LLC谐振转换器的工作原理和设计注意事项。给出了200 W原型的实验结果，以验证理论分析和所提出的VMIC控制策略的有效性。次级整流器的零电流关断操作要求将开关频率设计为低于谐振频率。介绍了具有VMIC的LLC谐振转换器的工作原理和设计注意事项。给出了200 W原型的实验结果，以验证理论分析和所提出的VMIC控制策略的有效性。次级整流器的零电流关断操作要求将开关频率设计为低于谐振频率。介绍了具有VMIC的LLC谐振转换器的工作原理和设计注意事项。给出了200 W原型的实验结果，以验证理论分析和所提出的VMIC控制策略的有效性。