四开关Buck-Boost(Four Switch Buck-Boost—FSBB)变换器具有升降压功能，被广泛应用于宽输入电压范围场合，如煤矿、通信、分布式发电、电动汽车及无人驾驶飞机等领域，但FSBB变换器在输入与输出电压接近时存在模式频繁切换引起输出电压不稳定的问题，因此，本文研究FSBB变换器工作方式及控制策略，实现其增益连续变化，确保输出电压在宽输入电压范围内维持稳定，具有重要的现实意义与工程应用价值。

通过对FSBB变换器工作状态进行分析，按照不同数量和不同状态的组合推导出变换器存在13种工作模式，对比发现三模态-Case3在能量传输和开关噪声抑制方面具有较好的工作特性，确定其为最佳工作模式并对该模式下变换器功率传输特性进行深入研究，依据能量是否反向传递确定临界模式并推导临界电感表达式。分析变换器增益与占空比控制变量d₁和d₂之间的数学关系，研究得出三种占空比调节曲线，分别从控制过程和控制变量对切换策略进行优化，提出一种基于单变量且控制过程可回溯的FSBB变换器运行模式切换控制策略，对FSBB变换器增益和电感电流纹波进行稳定性分析，指出在临界区间增益和电感电流纹波连续变化。建立了FSBB变换器最佳工作模式下的小信号模型，并推导出各参变量之间的传递函数，得到适应变换器工作于混合Buck和混合Boost两种运行模式的电压环补偿网络设计方法；为提高变换器对输入电压扰动的抑制能力，增加电压前馈支路并推导出前馈补偿网络传递函数表达式，基于误差信号的连续性对混合Buck模式的电压前馈传递函数进行修正，得到适用于FSBB变换器的前馈补偿网络模型。

根据技术指标完成FSBB变换器主电路及控制器设计，搭建测试平台并完成实验验证，结果表明，在输入电压与输出电压接近的临界区间，变换器增益连续变化且电感电流纹波不突变，对输入扰动具有明显的抑制能力，效率可达95%，适用于宽输入电压范围场合，验证了理论分析的正确性和控制策略的有效性。

Four-Switch Buck-Boost (FSBB) converter has boost and buck functions, and is widely used in wide input voltage range occasions, such as coal mine, communications, distributed generation, electric vehicles and unmanned aircraft, etc. But FSBB exists output voltage instability problems caused by frequent mode switching in the input voltage and output voltage is close. Therefore, this paper studies FSBB converter working mode and control strategy to realize gain continuous change and ensure that the output voltage to maintain stability within the wide input voltage range, which has important practical significance and engineering application value.

The working status of the FSBB converter is analyzed. According to the combination of different numbers of states, it is derived that there are 13 working modes of the converter. Comparative analysis shows that the three modes-Case3 has a better working characteristic in energy transmission and suppression of switching noise. It is determined as the best working mode and the power transmission characteristics of the converter are deeply studied in this mode, determine the critical mode and derive the critical inductance expression according to whether the energy is reversely transferred. Analyze the mathematical relationship between the converter gain and the duty cycle control variables d₁ and d₂, and study three kinds of duty cycle adjustment curves. Optimize the control process and the number of control variables, propose a single-variable control and traceable FSBB converter mode switching control strategy. The stability analysis of the FSBB converter gain and inductor current ripple is carried out. It is pointed out that the gain and inductor current ripple can be continuously changed in the critical interval. The small-signal model of FSBB converter operating in the best mode is established, and the transfer function between the parameters is deduced. The design method of voltage loop compensation network is obtained, which is suitable for the converter operating in the two modes of hybrid Buck and hybrid Boost; In order to improve the converter’s ability to suppress input voltage disturbances, the voltage feedforward branch is added and the feedforward compensation network transfer function expression is derived. Based on the continuity of the error signal, the hybrid Buck voltage feedforward transfer function is corrected, and it is applicable the feedforward compensation network model of the FSBB converter.

According to the technical indicators, the design of the main circuit and controller of the FSBB converter were completed, a test platform was built and experimental verification was completed. The results show that in the critical interval where the input voltage is equal to the output voltage, the converter gain continuously changes and the inductor current ripple does not change suddenly. The converter has obvious suppression ability to input voltage disturbance, and the efficiency can reach up to 95%. It is suitable for wide input voltage range occasions, which verifies the correctness of the theoretical analysis and the effectiveness of the control strategy.

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