宽输出LLC谐振变换器的定频PWM控制策略

传统频率控制的LLC谐振变换器不适用于宽电压范围的应用场合，且存在较大的循环电流而难以实现高转换效率。为了解决这些问题，提出一种简单的定频PWM控制策略，谐振变换器的后桥臂通过固定的开关频率控制，开关频率等于谐振频率；前桥臂采用PWM控制，将谐振网络的输入电压转换成多电平电压，谐振变换器实现2倍的电压增益调节范围。在这种控制方式中，增益范围独立于负载和励磁电感，可以简化谐振参数设计，通过设计较大的励磁电感减小电路的传导损耗和开关关断损耗，提升转换效率。仿真结果表明：谐振变换器可以实现宽输出电压，该控制策略降低了循环电流和关断电流。最后，通过实验验证了所提控制策略的可行性。

Fixed-frequency PWM Control Strategy of LLC Resonant Converter for Wide Output Range

The conventional frequency-controlled LLC resonant converter is unsuitable for wide voltage range applications, and it suffers from a large circulating current, which makes it difficult to achieve a high conversion efficiency. To cope with these issues, a simple fixed-frequency PWM control strategy is proposed. The rear arm of the resonant converter is controlled by a fixed switching frequency, and the switching frequency is equal to the resonant frequency. Then, the front arm adopts PWM control to convert the input voltage of the resonant network into a multi-level voltage, so that the voltage gain adjustment range of the resonant converter is doubled. Under this control strategy, the gain range is independent of load and magnetizing inductance, which can simplify the design of resonant parameters. By designing a larger magnetizing inductance, the conduction loss of circuit and turn-off loss are reduced to improve the conversion efficiency. Simulation results show that the resonant converter can achieve a wide output voltage range. In addition, the circulating current and turn-off current are reduced. Finally, the feasibility of the proposed control strategy was verified by experimental results.