本文借用自动控制理论中主导极点的概念，指出在静态时，谐振变量决定于代表谐振持性的主导极点，而滤波变量则由于滤波极点的作用，近似为直流（忽略纹波）；在动态时，控制频率的变化相对开关频率的变化为慢变化，慢变化仅仅引起样点的变化。在这一理论指导下，推导出混合串并联型谐振变换器小信号电路模型。 In this paper, we take the concept of the dominant pole in the theory of automatic control, and point out that in the static state, the resonant variable depends on the dominant pole representing the resonance persistence, while the filter variable approximates to the direct current (ignoring the ripple) due to the filter pole. , The change of the control frequency relative to the change of the switching frequency is a slow change, and the slow change only causes the change of the sample. Under the guidance of this theory, a small signal circuit model of hybrid series-parallel resonant converter is derived.