基于最小二乘法的开环LLC电路优化控制

Optimal Control of Open-loop LLC Circuits Based on Least Square Method

研究一种改善宽电压输入范围DC/DC变换器输出动态电压纹波的控制策略,该变换器采用两级级联结构,前级为定频/开环工作的变压器初级串联结构半桥LLC电路,后级为闭环工作的交错并联Buck电路。为提升变换器性能,减小变换器输出动态电压纹波,该控制策略将前级LLC启动过程分为两段,在第2段软启过程中记录LLC的开关频率与电压增益,提出运用最小二乘法进行电压增益曲线拟合,根据拟合的曲线得到LLC最大电压增益对应的谐振频率,将其作为开环工作的恒定开关频率。最后,通过仿真与搭建实验样机,验证了该控制策略具有较好的抑制输出动态电压纹波的性能,并且不影响变换器的其他性能。

A DC/DC converter control strategy that improves the output dynamic voltage ripple of wide voltage input range has been studied.The converter adopts a two-stage structure.The front stage is a fixed-frequency/open-loop transformer primary-side series half bridge LLC structure.The second stage is an closed-loop interleaved parallel closed-loop Buck circuit.In order to improve the performance of the converter and reduce the dynamic voltage ripple of the coverter,the control strategy divides the LLC startup process into two soft-starts,and records the switching frequency and voltage gain of the LLC during the second process.The voltage gain curve is fitted by the least square method,and the resonant frequency corresponding to the maximum voltage gain of the LLC is obtained according to the fitted curve,which is used as the constant switching frequency of the open loop operation.Finally,it is verified that the control strategy has a good performance of suppressing the output dynamic voltage ripple,and does not affect the other performance of the converter by simulation and experimental prototype.