基于二阶拟合模型的SiC双向LLC数字同步整流控制

Two-Order Fitting Model-Based Digital Synchronous Rectifier Control for SiC Bidirectional LLC Converter

传统LLC同步整流控制采用高频信号检测的方法,易受高dv/dt影响导致占空比丢失,导通损耗增大;而直接给定占空比的方法,无法跟随负载变化,宽负载范围下导通损耗急剧上升。该文提出基于二阶拟合模型的SiC双向LLC数字同步整流控制,跟踪负载和开关频率的变化,实时计算同步整流导通时间。LLC一次侧和二次侧开关管开通时刻一致,同步整流管关断时刻由所计算的同步整流导通时间决定。在宽负载范围内实现了低导通损耗,无需检测高频信号,抗干扰性强。该文分析当谐振电感和输出等效电阻存在10%误差时,同步整流导通时间误差最大仅为2.73%。搭建6.6kWSiC双向LLC充电机实验样机,实验验证了所提同步整流控制的有效性。相比于传统LLC同步整流控制,所提控制正向满载6.6kW下效率提高了0.36%,反向满载3.3kW下效率提高了0.29%。

Conventional LLC synchronous rectifier(SR)typically senses high-frequency signals,easily affected by high dv/dt resulting in duty cycle loss and high conduction loss.The SR method with a given duty cycle cannot track load variations and causes high conduction loss in a wide load range.A two-order fitting model-based digital synchronous rectifier control is proposed for the bidirectional SiC LLC converter,which tracks load variations and switching frequency to calculate the SR on-time online.The turn-on instants between the primary and secondary switching devices are identical,while the calculated SR on-time determines the SR turn-off instants.The proposed control achieves low conduction loss and has high immunity to high switching noise without sensing high-frequency signals.When the resonant inductor and output load have 10%tolerances,the maximum tolerance for the SR on-time is only 2.73%.A prototype of a 6.6kW SiC bidirectional LLC charger was built.Compared with the conventional LLC SR control,the efficiency improvement is up to 0.36%at 6.6kW in the forward mode,and 0.29%at 3.3kW in the reverse mode.