正-反激组合变换器综合了正激和反激变换器的特点，不仅使变压器自然复位，还能将励磁能量传输至负载，提高了能量利用率。但变换器的效率和工作性能受到正激部分和反激部分功率传输比的影响，为此，提出一种正-反激组合变换器的优化设计方法，对于正-反激组合变换器的推广应用具有重要指导意义。

      本文对正-反激组合变换器的能量传输模式进行了分析，并推导了各模式间的临界电感解析表达式。在整个动态工作范围内，得出了工作于各模式的电感峰值电流和输出纹波电压解析表达式，通过对电感峰值电流及输出纹波电压与电感之间的关系进行分析，指出变换器工作于CCM时，正激电感峰值电流不再随变压器励磁电感和负载而变化，而输出纹波电压会随正激电感的增加先减小后增大。对变换器正激和反激部分的功率传输比进行了深入研究，得到了整个负载范围内正激和反激部分功率传输比的解析表达式，指出最大功率传输时，减小正激电感和变压器的匝比，可以减小反激部分传输功率，有助于功率的有效传输。依据电感峰值电流、输出纹波电压和功率传输比与元件参数之间的关系，综合提出了正-反激组合变换器的设计方法，同时采用状态空间平均法对变换器进行了建模，推导出了功率级的各传递函数，分析了环路补偿方法，指出采用超前-滞后补偿网络对其进行补偿，可进一步提升系统的稳定性。

       根据设计指标要求，制作了一台试验样机，并进行了仿真分析和实验验证，实验结果表明，本文所提出的设计参数可获得较好的变换效率和工作性能，从而验证了所提出设计方法的可行性和理论分析的正确性。

        The forward-flyback converter combines the characteristics of both the forward converter and the flyback converter. It can not only reset the transformer naturally, but also transfer the excitation energy to the load, which improves energy efficiency greatly. However, the efficiency and performance of the converter are affected by the power transfer ratio of the forward part and the flyback part. Therefore, an optimal design method of forward-flyback converter is proposed by this thesis, which is significant to make it used widely.

         The energy transmission modes and operation process of forward-flyback converter are analyzed, and the analytical expression of the critical inductances among various modes are derived. Then, in the whole dynamic operating range, by analyzing the inductor peak current (IPC), output ripple voltage (ORV) and the relationship between them and the inductor of the Forward-flyback converter, and the analytical expressions of the IPC and ORV among various modes are derived. It is pointed out that the forward inductor peak current is invariable when the excitation inductance and load of power transformer changed, and the ORV first decreased then increased with the increase of forward inductance when the converter is working in Continuous Conduction Mode (CCM). At the same time, the power allocation of the forward and flyback parts of the forward-flyback converter are researched in depth. It is pointed out that the smaller turns ratio of the forward inductance and transformer in the forward-flyback converter can reduce the ratio of flyback part transmission power, which helps to transfer power with higher efficiency. Based on the relationship between IPC, ORV, power transfer ratio and component parameters, a comprehensive forward-flyback combined converter design method is proposed. Meanwhile, the state space average method is used to model the converter, and the transfer functions of each power stage are derived. After that, by analyzing the loop compensation method,It is pointed out that the converter system needs to compensate by the lead-lag compensation network, in order to ensure the stability of the system.

         According to the requirements of the design indicators, an experimental prototype is designed, and then simulation analysis and experimental verification are made on it. The experimental results show that the design parameters proposed in this paper can obtain high efficiency and performance, so the effectiveness is verified.

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