LLC谐振变换器作为一种高效率、高功率密度的开关变换器，在现代电力电子技术中具有广泛的应用场合。但在服务器电源等特殊场合，对系统的动态响应提出了更高的要求，而目前常用的单电压环控制方法存在闭环动态响应差等问题，为此，本文对LLC变换器的电流控制方法及其数字实现方式进行研究，对于提高LLC变换器的动态响应性能具有重要意义。

首先，对全桥LLC谐振变换器的工作原理和特性进行了分析，使用基波近似法搭建近似等效模型，对谐振腔参数和开关频率归一化处理后，利用Maple绘制的变换器增益曲线研究品质因数Q和电感比L_n对电路的影响，并对电压控制策略进行了分析。然后对电流控制策略的工作原理进行了详细的研究，并对该种控制方法下电路稳态特性和动态特性进行分析。随后利用拓展描述函数法建立了变换器的小信号模型，将得到的高阶模型在谐振点处中低频段等效简化，推导了二阶小信号模型，利用扫频法对简化后的模型精确度检验，验证了简化模型的实用性和可靠性。接着对电流控制环路进行分析，得到了相应的控制-输出电压传递函数和环路增益表达式，分析了关键参数积分电容的大小对电路性能影响的趋势，通过对两种控制手段的环路增益Bode图比较，证明了电流控制策略的动态性能优于单电压控制方法。

最后，搭建了变换器的闭环仿真模型和实验样机，两种控制方式稳态响应证明参数设计的合理性和理论分析的正确性，动态响应表明：当负载跳变时，电流控制的负载瞬态响应速度比单电压控制提升了一个数量级，输出电压在数个开关周期左右便能稳定，大大降低了后级变换器因前级动态性能差而损坏的风险。

The LLC resonant converter, as a high efficiency, high power density switching converter, has a wide range of applications in modern power electronics.. However, special occasions such as server power supplies have put forward higher requirements for the dynamic response of the system, and the currently commonly used voltage-type control has problems such as poor closed-loop dynamic response. For this reason, this article discusses the current control method of LLC converter and its digital implementation. Research in this way is of great significance for improving the dynamic response performance of LLC converter.

First, the operating principle and characteristics of the full-bridge LLC resonant converter are analyzed, an approximate equivalent model is constructed using the fundamental wave approximation method, and after normalizing the resonant cavity parameters and the switching frequency, the Maple-drawn gain curves of the converter are used to study the effects of the quality factor Q and the inductance ratio Ln on the circuit. Then the working principle and control flow of the current-type control method are studied in detail, and the dynamic characteristics of this control method are analyzed when the input voltage and load are perturbed. Subsequently, a small-signal model of the converter was developed using the expanded describing function method, and the obtained high-order model is simplified equivalently in the middle and low frequency bands at the resonance point to derive a second-order small-signal model, and the accuracy of the simplified model is examined by using the frequency sweep method, which verifies the practicability and reliability of the model. Then the current control loop is analysed, the corresponding control-output voltage transfer function and loop gain expression are obtained, the trend of the effect of the size of the key parameter integrating capacitance on the circuit performance is analysed, and by comparing the loop gain Bode plots of the two control means, it is demonstrated that the dynamic performance of the current control strategy is superior to that of the single-voltage control method.

Finally, the simulation model and experimental prototype of the converter are built. The simulation and experimental results of the dynamic response of the two control modes show that when the load jumps, the current-type control improves the load transient response speed by an order of magnitude compared with the voltage-type control, and the output voltage can be stabilized in a few switching cycles, which greatly reduces the risk of the damage of the back-end converter due to the poor dynamic performance of the front-end.

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