变模态倍压型LLC谐振变换器多目标参数优化

Multi Objective Parameter Optimization of Variable Mode Voltage Doubling LLC Resonant Converter

传统LLC变换器采用基波分析法,忽略高次谐波的影响,在远离谐振频率点误差较大,宽输出电压场合下变换器精度低。对此,该文深入分析变模态倍压型LLC谐振变换器工作模式,确立PO模式是其最佳工作模式,建立PO模式下状态时域方程,求解状态方程相关系数,得到负载约束、系数约束和角度约束条件,推导谐振电容Cr、电感比系数K和P阶段导通角θ等参数。基于模式边界、谐振电容最值和ZVS多目标约束条件,提出一种多目标参数优化方法,对变换器主电路参数进行优化设计,制作504 W变模态倍压型LLC谐振变换器样机。实验结果表明,基于时域分析的多目标参数优化设计的变换器能够实现全范围内软开关,以满足增益和高效率要求。

LLC resonant converters can achieve electrical isolation and soft switching,exhibit high efficiency and power density advantages,and are widely used in new energy fields such as lithium battery charging.The traditional fundamental analysis method simplifies the analysis difficulty and calculation process.However,significant errors exist when far from the resonant frequency point,and the accuracy is low in wide output voltage scenarios.This paper focuses on the precise time-domain model analysis of a variable mode voltage doubling-type LLC resonant converter with wide output.A multi-objective parameter optimization design method is proposed.Firstly,the operating modes of LLC resonant converters and the characteristics of each operating mode are analyzed.The PO mode can achieve ZVS of the switching tube and ZCS of the rectifier tube,and the DC gain monotonically increases with the decrease of operating frequency.Accordingly,the PO mode is established as the optimal operating mode.Based on the working waveform of the PO mode and the equivalent circuit of P and O stages,a time-domain equation for the excitation current iLm,resonant current iLr,and resonant capacitor voltage uCr state variables in PO mode is established.The coefficients k1,k2,k3,and k4 in the state equation are solved to obtain the analytical formula for the PO mode state equation system.According to the coefficient analysis formula,it can be seen that k1,k2,k3,and k4 are related to the resonant capacitor Cr,inductance ratio coefficient K,and the conduction angle of the P mode sub-intervalθ.Secondly,the parameter design of the main circuit is optimized.A multi-objective parameter optimization method is proposed based on pattern boundary constraints,resonant capacitor maximum constraints,and ZVS constraints.The multi-objective parameter optimization region and the optimal solution are obtained.The gain requirements and ZVS of the switching transistor under the most stringent operating conditions are achieved with a small cyclic reactive power,thereby improving the efficiency of the converter.Finally,simulation models and experimental prototype platforms are constructed.The correctness of multi-objective parameter optimizationis verified by simulation.Simultaneously,using the traditional fundamental analysis method and the proposed parameter optimization design method,the converter parameters are designed separately,and comparative analysis is conducted from the perspectives of switch frequency variation range and resonant network current.The experimental results show that the proposed multi-objective parameter optimization design method has a narrower operating frequency range and higher operating efficiency than traditional fundamental analysis methods,which can meet the gain requirements and ZVS operating conditions of the converter over the entire load range.