Design And Stability Analysis Of Wide-Range Input Voltag Cascaded Converters

With the rapid development of power semiconductor devices,high switching frequencies have significantly increased the power density of power converters.However,for applications with a large input voltage range and high efficiency requirements,it is difficult for a traditional single-stage converter to meet the design specification.This paper adopts the cascaded converter topology of the interleaved Boost and symmetrical half-bridge dual-capacitor LLC to achieve high power density and efficiency while taking into account the wide range of input side voltage as well as good stability.In view of the wide voltage input requirements,an interleaved Boost source-converter topology is adopted.The equivalent circuit is obtained by decoupling,and circuit analysis is performed to obtain the current ripple characteristics under different coupling modes;at the same time,the circuit characteristics under different switching modes with forward coupling are analyzed in detail.To effectively enhance the efficiency of the converter,a symmetrical half-bridge dual-capacitor LLC load-converter is used.By analyzing different working modes,the working mechanism of the switch tube to achieve soft switching is obtained;the relation between voltage gain and resonant parameters of the LLC circuit is obtained by the fundamental wave analysis method.The coupling inductance used in the interleaved Boost circuit is designed.The equivalent steady-state inductance and equivalent transient inductance of the circuit are deduced,and the forward coupling mode is selected in combination with the input current index requirements;and the requirements are obtained by analyzing interleaved Boost ZVS turn-on conditions.To enhance the efficiency of the converter,a hybrid control strategy using phase-shifting control under lower input voltage and stable-shift control under higher input voltage is proposed.Through theoretical analysis,the parameters of the coupled inductor under the hybrid control strategy and the design process of the coupled inductor are obtained.The simulation verifies the accuracy of the proposed control strategy and design process.The paper studies the instability mechanism of cascaded converters.Through small-signal modeling,the output impedance of the interleaved Boost and the input impedance of the symmetrical half-bridge dual-capacitor LLC are obtained.According to the Bode diagram analysis,the factors that lead to open-loop instability are presented.The method of increasing the loop gain and increasing the capacitance of the bus capacitor is used to reduce the output impedance of the source converter and effectively improve the stability of the system.A hardware experiment platform for cascaded converters with interleaved Boost and symmetrical half-bridge double-capacitor LLC is designed and built.The input and output characteristics are verified on the platform.The experimental results meet the index requirements,which prove the correctness and feasibility of the converter design.